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- Lua 5.4 Reference Manual
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- by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
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- <!-- ====================================================================== -->
- <p>
- <!-- $Id: manual.of $ -->
- <h1>1 – <a name="1">Introduction</a></h1>
- <p>
- Lua is a powerful, efficient, lightweight, embeddable scripting language.
- It supports procedural programming,
- object-oriented programming, functional programming,
- data-driven programming, and data description.
- <p>
- Lua combines simple procedural syntax with powerful data description
- constructs based on associative arrays and extensible semantics.
- Lua is dynamically typed,
- runs by interpreting bytecode with a register-based
- virtual machine,
- and has automatic memory management with
- a generational garbage collection,
- making it ideal for configuration, scripting,
- and rapid prototyping.
- <p>
- Lua is implemented as a library, written in <em>clean C</em>,
- the common subset of Standard C and C++.
- The Lua distribution includes a host program called <code>lua</code>,
- which uses the Lua library to offer a complete,
- standalone Lua interpreter,
- for interactive or batch use.
- Lua is intended to be used both as a powerful, lightweight,
- embeddable scripting language for any program that needs one,
- and as a powerful but lightweight and efficient stand-alone language.
- <p>
- As an extension language, Lua has no notion of a "main" program:
- it works <em>embedded</em> in a host client,
- called the <em>embedding program</em> or simply the <em>host</em>.
- (Frequently, this host is the stand-alone <code>lua</code> program.)
- The host program can invoke functions to execute a piece of Lua code,
- can write and read Lua variables,
- and can register C functions to be called by Lua code.
- Through the use of C functions, Lua can be augmented to cope with
- a wide range of different domains,
- thus creating customized programming languages sharing a syntactical framework.
- <p>
- Lua is free software,
- and is provided as usual with no guarantees,
- as stated in its license.
- The implementation described in this manual is available
- at Lua's official web site, <code>www.lua.org</code>.
- <p>
- Like any other reference manual,
- this document is dry in places.
- For a discussion of the decisions behind the design of Lua,
- see the technical papers available at Lua's web site.
- For a detailed introduction to programming in Lua,
- see Roberto's book, <em>Programming in Lua</em>.
- <h1>2 – <a name="2">Basic Concepts</a></h1>
- <p>
- This section describes the basic concepts of the language.
- <h2>2.1 – <a name="2.1">Values and Types</a></h2>
- <p>
- Lua is a dynamically typed language.
- This means that
- variables do not have types; only values do.
- There are no type definitions in the language.
- All values carry their own type.
- <p>
- All values in Lua are first-class values.
- This means that all values can be stored in variables,
- passed as arguments to other functions, and returned as results.
- <p>
- There are eight basic types in Lua:
- <em>nil</em>, <em>boolean</em>, <em>number</em>,
- <em>string</em>, <em>function</em>, <em>userdata</em>,
- <em>thread</em>, and <em>table</em>.
- The type <em>nil</em> has one single value, <b>nil</b>,
- whose main property is to be different from any other value;
- it often represents the absence of a useful value.
- The type <em>boolean</em> has two values, <b>false</b> and <b>true</b>.
- Both <b>nil</b> and <b>false</b> make a condition false;
- they are collectively called <em>false values</em>.
- Any other value makes a condition true.
- <p>
- The type <em>number</em> represents both
- integer numbers and real (floating-point) numbers,
- using two subtypes: <em>integer</em> and <em>float</em>.
- Standard Lua uses 64-bit integers and double-precision (64-bit) floats,
- but you can also compile Lua so that it
- uses 32-bit integers and/or single-precision (32-bit) floats.
- The option with 32 bits for both integers and floats
- is particularly attractive
- for small machines and embedded systems.
- (See macro <code>LUA_32BITS</code> in file <code>luaconf.h</code>.)
- <p>
- Unless stated otherwise,
- any overflow when manipulating integer values <em>wrap around</em>,
- according to the usual rules of two-complement arithmetic.
- (In other words,
- the actual result is the unique representable integer
- that is equal modulo <em>2<sup>n</sup></em> to the mathematical result,
- where <em>n</em> is the number of bits of the integer type.)
- <p>
- Lua has explicit rules about when each subtype is used,
- but it also converts between them automatically as needed (see <a href="#3.4.3">§3.4.3</a>).
- Therefore,
- the programmer may choose to mostly ignore the difference
- between integers and floats
- or to assume complete control over the representation of each number.
- <p>
- The type <em>string</em> represents immutable sequences of bytes.
- Lua is 8-bit clean:
- strings can contain any 8-bit value,
- including embedded zeros ('<code>\0</code>').
- Lua is also encoding-agnostic;
- it makes no assumptions about the contents of a string.
- The length of any string in Lua must fit in a Lua integer.
- <p>
- Lua can call (and manipulate) functions written in Lua and
- functions written in C (see <a href="#3.4.10">§3.4.10</a>).
- Both are represented by the type <em>function</em>.
- <p>
- The type <em>userdata</em> is provided to allow arbitrary C data to
- be stored in Lua variables.
- A userdata value represents a block of raw memory.
- There are two kinds of userdata:
- <em>full userdata</em>,
- which is an object with a block of memory managed by Lua,
- and <em>light userdata</em>,
- which is simply a C pointer value.
- Userdata has no predefined operations in Lua,
- except assignment and identity test.
- By using <em>metatables</em>,
- the programmer can define operations for full userdata values
- (see <a href="#2.4">§2.4</a>).
- Userdata values cannot be created or modified in Lua,
- only through the C API.
- This guarantees the integrity of data owned by
- the host program and C libraries.
- <p>
- The type <em>thread</em> represents independent threads of execution
- and it is used to implement coroutines (see <a href="#2.6">§2.6</a>).
- Lua threads are not related to operating-system threads.
- Lua supports coroutines on all systems,
- even those that do not support threads natively.
- <p>
- The type <em>table</em> implements associative arrays,
- that is, arrays that can have as indices not only numbers,
- but any Lua value except <b>nil</b> and NaN.
- (<em>Not a Number</em> is a special floating-point value
- used by the IEEE 754 standard to represent
- undefined numerical results, such as <code>0/0</code>.)
- Tables can be <em>heterogeneous</em>;
- that is, they can contain values of all types (except <b>nil</b>).
- Any key associated to the value <b>nil</b> is not considered part of the table.
- Conversely, any key that is not part of a table has
- an associated value <b>nil</b>.
- <p>
- Tables are the sole data-structuring mechanism in Lua;
- they can be used to represent ordinary arrays, lists,
- symbol tables, sets, records, graphs, trees, etc.
- To represent records, Lua uses the field name as an index.
- The language supports this representation by
- providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
- There are several convenient ways to create tables in Lua
- (see <a href="#3.4.9">§3.4.9</a>).
- <p>
- Like indices,
- the values of table fields can be of any type.
- In particular,
- because functions are first-class values,
- table fields can contain functions.
- Thus tables can also carry <em>methods</em> (see <a href="#3.4.11">§3.4.11</a>).
- <p>
- The indexing of tables follows
- the definition of raw equality in the language.
- The expressions <code>a[i]</code> and <code>a[j]</code>
- denote the same table element
- if and only if <code>i</code> and <code>j</code> are raw equal
- (that is, equal without metamethods).
- In particular, floats with integral values
- are equal to their respective integers
- (e.g., <code>1.0 == 1</code>).
- To avoid ambiguities,
- any float used as a key that is equal to an integer
- is converted to that integer.
- For instance, if you write <code>a[2.0] = true</code>,
- the actual key inserted into the table will be the integer <code>2</code>.
- <p>
- Tables, functions, threads, and (full) userdata values are <em>objects</em>:
- variables do not actually <em>contain</em> these values,
- only <em>references</em> to them.
- Assignment, parameter passing, and function returns
- always manipulate references to such values;
- these operations do not imply any kind of copy.
- <p>
- The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
- of a given value (see <a href="#pdf-type"><code>type</code></a>).
- <h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2>
- <p>
- As we will discuss further in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>,
- any reference to a free name
- (that is, a name not bound to any declaration) <code>var</code>
- is syntactically translated to <code>_ENV.var</code>.
- Moreover, every chunk is compiled in the scope of
- an external local variable named <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>),
- so <code>_ENV</code> itself is never a free name in a chunk.
- <p>
- Despite the existence of this external <code>_ENV</code> variable and
- the translation of free names,
- <code>_ENV</code> is a completely regular name.
- In particular,
- you can define new variables and parameters with that name.
- Each reference to a free name uses the <code>_ENV</code> that is
- visible at that point in the program,
- following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>).
- <p>
- Any table used as the value of <code>_ENV</code> is called an <em>environment</em>.
- <p>
- Lua keeps a distinguished environment called the <em>global environment</em>.
- This value is kept at a special index in the C registry (see <a href="#4.3">§4.3</a>).
- In Lua, the global variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value.
- (<a href="#pdf-_G"><code>_G</code></a> is never used internally,
- so changing its value will affect only your own code.)
- <p>
- When Lua loads a chunk,
- the default value for its <code>_ENV</code> variable
- is the global environment (see <a href="#pdf-load"><code>load</code></a>).
- Therefore, by default,
- free names in Lua code refer to entries in the global environment
- and, therefore, they are also called <em>global variables</em>.
- Moreover, all standard libraries are loaded in the global environment
- and some functions there operate on that environment.
- You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>)
- to load a chunk with a different environment.
- (In C, you have to load the chunk and then change the value
- of its first upvalue; see <a href="#lua_setupvalue"><code>lua_setupvalue</code></a>.)
- <h2>2.3 – <a name="2.3">Error Handling</a></h2>
- <p>
- Several operations in Lua can <em>raise</em> an error.
- An error interrupts the normal flow of the program,
- which can continue by <em>catching</em> the error.
- <p>
- Lua code can explicitly raise an error by calling the
- <a href="#pdf-error"><code>error</code></a> function.
- (This function never returns.)
- <p>
- To catch errors in Lua,
- you can do a <em>protected call</em>,
- using <a href="#pdf-pcall"><code>pcall</code></a> (or <a href="#pdf-xpcall"><code>xpcall</code></a>).
- The function <a href="#pdf-pcall"><code>pcall</code></a> calls a given function in <em>protected mode</em>.
- Any error while running the function stops its execution,
- and control returns immediately to <code>pcall</code>,
- which returns a status code.
- <p>
- Because Lua is an embedded extension language,
- Lua code starts running by a call
- from C code in the host program.
- (When you use Lua standalone,
- the <code>lua</code> application is the host program.)
- Usually, this call is protected;
- so, when an otherwise unprotected error occurs during
- the compilation or execution of a Lua chunk,
- control returns to the host,
- which can take appropriate measures,
- such as printing an error message.
- <p>
- Whenever there is an error,
- an <em>error object</em>
- is propagated with information about the error.
- Lua itself only generates errors whose error object is a string,
- but programs may generate errors with
- any value as the error object.
- It is up to the Lua program or its host to handle such error objects.
- For historical reasons,
- an error object is often called an <em>error message</em>,
- even though it does not have to be a string.
- <p>
- When you use <a href="#pdf-xpcall"><code>xpcall</code></a> (or <a href="#lua_pcall"><code>lua_pcall</code></a>, in C)
- you may give a <em>message handler</em>
- to be called in case of errors.
- This function is called with the original error object
- and returns a new error object.
- It is called before the error unwinds the stack,
- so that it can gather more information about the error,
- for instance by inspecting the stack and creating a stack traceback.
- This message handler is still protected by the protected call;
- so, an error inside the message handler
- will call the message handler again.
- If this loop goes on for too long,
- Lua breaks it and returns an appropriate message.
- The message handler is called only for regular runtime errors.
- It is not called for memory-allocation errors
- nor for errors while running finalizers or other message handlers.
- <p>
- Lua also offers a system of <em>warnings</em> (see <a href="#pdf-warn"><code>warn</code></a>).
- Unlike errors, warnings do not interfere
- in any way with program execution.
- They typically only generate a message to the user,
- although this behavior can be adapted from C (see <a href="#lua_setwarnf"><code>lua_setwarnf</code></a>).
- <h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2>
- <p>
- Every value in Lua can have a <em>metatable</em>.
- This <em>metatable</em> is an ordinary Lua table
- that defines the behavior of the original value
- under certain events.
- You can change several aspects of the behavior
- of a value by setting specific fields in its metatable.
- For instance, when a non-numeric value is the operand of an addition,
- Lua checks for a function in the field "<code>__add</code>" of the value's metatable.
- If it finds one,
- Lua calls this function to perform the addition.
- <p>
- The key for each event in a metatable is a string
- with the event name prefixed by two underscores;
- the corresponding value is called a <em>metavalue</em>.
- For most events, the metavalue must be a function,
- which is then called a <em>metamethod</em>.
- In the previous example, the key is the string "<code>__add</code>"
- and the metamethod is the function that performs the addition.
- Unless stated otherwise,
- a metamethod may in fact be any callable value,
- which is either a function or a value with a <code>__call</code> metamethod.
- <p>
- You can query the metatable of any value
- using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
- Lua queries metamethods in metatables using a raw access (see <a href="#pdf-rawget"><code>rawget</code></a>).
- <p>
- You can replace the metatable of tables
- using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function.
- You cannot change the metatable of other types from Lua code,
- except by using the debug library (<a href="#6.10">§6.10</a>).
- <p>
- Tables and full userdata have individual metatables,
- although multiple tables and userdata can share their metatables.
- Values of all other types share one single metatable per type;
- that is, there is one single metatable for all numbers,
- one for all strings, etc.
- By default, a value has no metatable,
- but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>).
- <p>
- A detailed list of operations controlled by metatables is given next.
- Each event is identified by its corresponding key.
- By convention, all metatable keys used by Lua are composed by
- two underscores followed by lowercase Latin letters.
- <ul>
- <li><b><code>__add</code>: </b>
- the addition (<code>+</code>) operation.
- If any operand for an addition is not a number,
- Lua will try to call a metamethod.
- It starts by checking the first operand (even if it is a number);
- if that operand does not define a metamethod for <code>__add</code>,
- then Lua will check the second operand.
- If Lua can find a metamethod,
- it calls the metamethod with the two operands as arguments,
- and the result of the call
- (adjusted to one value)
- is the result of the operation.
- Otherwise, if no metamethod is found,
- Lua raises an error.
- </li>
- <li><b><code>__sub</code>: </b>
- the subtraction (<code>-</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__mul</code>: </b>
- the multiplication (<code>*</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__div</code>: </b>
- the division (<code>/</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__mod</code>: </b>
- the modulo (<code>%</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__pow</code>: </b>
- the exponentiation (<code>^</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__unm</code>: </b>
- the negation (unary <code>-</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__idiv</code>: </b>
- the floor division (<code>//</code>) operation.
- Behavior similar to the addition operation.
- </li>
- <li><b><code>__band</code>: </b>
- the bitwise AND (<code>&</code>) operation.
- Behavior similar to the addition operation,
- except that Lua will try a metamethod
- if any operand is neither an integer
- nor a float coercible to an integer (see <a href="#3.4.3">§3.4.3</a>).
- </li>
- <li><b><code>__bor</code>: </b>
- the bitwise OR (<code>|</code>) operation.
- Behavior similar to the bitwise AND operation.
- </li>
- <li><b><code>__bxor</code>: </b>
- the bitwise exclusive OR (binary <code>~</code>) operation.
- Behavior similar to the bitwise AND operation.
- </li>
- <li><b><code>__bnot</code>: </b>
- the bitwise NOT (unary <code>~</code>) operation.
- Behavior similar to the bitwise AND operation.
- </li>
- <li><b><code>__shl</code>: </b>
- the bitwise left shift (<code><<</code>) operation.
- Behavior similar to the bitwise AND operation.
- </li>
- <li><b><code>__shr</code>: </b>
- the bitwise right shift (<code>>></code>) operation.
- Behavior similar to the bitwise AND operation.
- </li>
- <li><b><code>__concat</code>: </b>
- the concatenation (<code>..</code>) operation.
- Behavior similar to the addition operation,
- except that Lua will try a metamethod
- if any operand is neither a string nor a number
- (which is always coercible to a string).
- </li>
- <li><b><code>__len</code>: </b>
- the length (<code>#</code>) operation.
- If the object is not a string,
- Lua will try its metamethod.
- If there is a metamethod,
- Lua calls it with the object as argument,
- and the result of the call
- (always adjusted to one value)
- is the result of the operation.
- If there is no metamethod but the object is a table,
- then Lua uses the table length operation (see <a href="#3.4.7">§3.4.7</a>).
- Otherwise, Lua raises an error.
- </li>
- <li><b><code>__eq</code>: </b>
- the equal (<code>==</code>) operation.
- Behavior similar to the addition operation,
- except that Lua will try a metamethod only when the values
- being compared are either both tables or both full userdata
- and they are not primitively equal.
- The result of the call is always converted to a boolean.
- </li>
- <li><b><code>__lt</code>: </b>
- the less than (<code><</code>) operation.
- Behavior similar to the addition operation,
- except that Lua will try a metamethod only when the values
- being compared are neither both numbers nor both strings.
- Moreover, the result of the call is always converted to a boolean.
- </li>
- <li><b><code>__le</code>: </b>
- the less equal (<code><=</code>) operation.
- Behavior similar to the less than operation.
- </li>
- <li><b><code>__index</code>: </b>
- The indexing access operation <code>table[key]</code>.
- This event happens when <code>table</code> is not a table or
- when <code>key</code> is not present in <code>table</code>.
- The metavalue is looked up in the metatable of <code>table</code>.
- <p>
- The metavalue for this event can be either a function, a table,
- or any value with an <code>__index</code> metavalue.
- If it is a function,
- it is called with <code>table</code> and <code>key</code> as arguments,
- and the result of the call
- (adjusted to one value)
- is the result of the operation.
- Otherwise,
- the final result is the result of indexing this metavalue with <code>key</code>.
- This indexing is regular, not raw,
- and therefore can trigger another <code>__index</code> metavalue.
- </li>
- <li><b><code>__newindex</code>: </b>
- The indexing assignment <code>table[key] = value</code>.
- Like the index event,
- this event happens when <code>table</code> is not a table or
- when <code>key</code> is not present in <code>table</code>.
- The metavalue is looked up in the metatable of <code>table</code>.
- <p>
- Like with indexing,
- the metavalue for this event can be either a function, a table,
- or any value with an <code>__newindex</code> metavalue.
- If it is a function,
- it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments.
- Otherwise,
- Lua repeats the indexing assignment over this metavalue
- with the same key and value.
- This assignment is regular, not raw,
- and therefore can trigger another <code>__newindex</code> metavalue.
- <p>
- Whenever a <code>__newindex</code> metavalue is invoked,
- Lua does not perform the primitive assignment.
- If needed,
- the metamethod itself can call <a href="#pdf-rawset"><code>rawset</code></a>
- to do the assignment.
- </li>
- <li><b><code>__call</code>: </b>
- The call operation <code>func(args)</code>.
- This event happens when Lua tries to call a non-function value
- (that is, <code>func</code> is not a function).
- The metamethod is looked up in <code>func</code>.
- If present,
- the metamethod is called with <code>func</code> as its first argument,
- followed by the arguments of the original call (<code>args</code>).
- All results of the call
- are the results of the operation.
- This is the only metamethod that allows multiple results.
- </li>
- </ul>
- <p>
- In addition to the previous list,
- the interpreter also respects the following keys in metatables:
- <code>__gc</code> (see <a href="#2.5.3">§2.5.3</a>),
- <code>__close</code> (see <a href="#3.3.8">§3.3.8</a>),
- <code>__mode</code> (see <a href="#2.5.4">§2.5.4</a>),
- and <code>__name</code>.
- (The entry <code>__name</code>,
- when it contains a string,
- may be used by <a href="#pdf-tostring"><code>tostring</code></a> and in error messages.)
- <p>
- For the unary operators (negation, length, and bitwise NOT),
- the metamethod is computed and called with a dummy second operand,
- equal to the first one.
- This extra operand is only to simplify Lua's internals
- (by making these operators behave like a binary operation)
- and may be removed in future versions.
- For most uses this extra operand is irrelevant.
- <p>
- Because metatables are regular tables,
- they can contain arbitrary fields,
- not only the event names defined above.
- Some functions in the standard library
- (e.g., <a href="#pdf-tostring"><code>tostring</code></a>)
- use other fields in metatables for their own purposes.
- <p>
- It is a good practice to add all needed metamethods to a table
- before setting it as a metatable of some object.
- In particular, the <code>__gc</code> metamethod works only when this order
- is followed (see <a href="#2.5.3">§2.5.3</a>).
- It is also a good practice to set the metatable of an object
- right after its creation.
- <h2>2.5 – <a name="2.5">Garbage Collection</a></h2>
- <p>
- Lua performs automatic memory management.
- This means that
- you do not have to worry about allocating memory for new objects
- or freeing it when the objects are no longer needed.
- Lua manages memory automatically by running
- a <em>garbage collector</em> to collect all <em>dead</em> objects.
- All memory used by Lua is subject to automatic management:
- strings, tables, userdata, functions, threads, internal structures, etc.
- <p>
- An object is considered <em>dead</em>
- as soon as the collector can be sure the object
- will not be accessed again in the normal execution of the program.
- ("Normal execution" here excludes finalizers,
- which can resurrect dead objects (see <a href="#2.5.3">§2.5.3</a>),
- and excludes also operations using the debug library.)
- Note that the time when the collector can be sure that an object
- is dead may not coincide with the programmer's expectations.
- The only guarantees are that Lua will not collect an object
- that may still be accessed in the normal execution of the program,
- and it will eventually collect an object
- that is inaccessible from Lua.
- (Here,
- <em>inaccessible from Lua</em> means that neither a variable nor
- another live object refer to the object.)
- Because Lua has no knowledge about C code,
- it never collects objects accessible through the registry (see <a href="#4.3">§4.3</a>),
- which includes the global environment (see <a href="#2.2">§2.2</a>).
- <p>
- The garbage collector (GC) in Lua can work in two modes:
- incremental and generational.
- <p>
- The default GC mode with the default parameters
- are adequate for most uses.
- However, programs that waste a large proportion of their time
- allocating and freeing memory can benefit from other settings.
- Keep in mind that the GC behavior is non-portable
- both across platforms and across different Lua releases;
- therefore, optimal settings are also non-portable.
- <p>
- You can change the GC mode and parameters by calling
- <a href="#lua_gc"><code>lua_gc</code></a> in C
- or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
- You can also use these functions to control
- the collector directly (e.g., to stop and restart it).
- <h3>2.5.1 – <a name="2.5.1">Incremental Garbage Collection</a></h3>
- <p>
- In incremental mode,
- each GC cycle performs a mark-and-sweep collection in small steps
- interleaved with the program's execution.
- In this mode,
- the collector uses three numbers to control its garbage-collection cycles:
- the <em>garbage-collector pause</em>,
- the <em>garbage-collector step multiplier</em>,
- and the <em>garbage-collector step size</em>.
- <p>
- The garbage-collector pause
- controls how long the collector waits before starting a new cycle.
- The collector starts a new cycle when the use of memory
- hits <em>n%</em> of the use after the previous collection.
- Larger values make the collector less aggressive.
- Values equal to or less than 100 mean the collector will not wait to
- start a new cycle.
- A value of 200 means that the collector waits for the total memory in use
- to double before starting a new cycle.
- The default value is 200; the maximum value is 1000.
- <p>
- The garbage-collector step multiplier
- controls the speed of the collector relative to
- memory allocation,
- that is,
- how many elements it marks or sweeps for each
- kilobyte of memory allocated.
- Larger values make the collector more aggressive but also increase
- the size of each incremental step.
- You should not use values less than 100,
- because they make the collector too slow and
- can result in the collector never finishing a cycle.
- The default value is 100; the maximum value is 1000.
- <p>
- The garbage-collector step size controls the
- size of each incremental step,
- specifically how many bytes the interpreter allocates
- before performing a step.
- This parameter is logarithmic:
- A value of <em>n</em> means the interpreter will allocate <em>2<sup>n</sup></em>
- bytes between steps and perform equivalent work during the step.
- A large value (e.g., 60) makes the collector a stop-the-world
- (non-incremental) collector.
- The default value is 13,
- which means steps of approximately 8 Kbytes.
- <h3>2.5.2 – <a name="2.5.2">Generational Garbage Collection</a></h3>
- <p>
- In generational mode,
- the collector does frequent <em>minor</em> collections,
- which traverses only objects recently created.
- If after a minor collection the use of memory is still above a limit,
- the collector does a stop-the-world <em>major</em> collection,
- which traverses all objects.
- The generational mode uses two parameters:
- the <em>minor multiplier</em> and the <em>the major multiplier</em>.
- <p>
- The minor multiplier controls the frequency of minor collections.
- For a minor multiplier <em>x</em>,
- a new minor collection will be done when memory
- grows <em>x%</em> larger than the memory in use after the previous major
- collection.
- For instance, for a multiplier of 20,
- the collector will do a minor collection when the use of memory
- gets 20% larger than the use after the previous major collection.
- The default value is 20; the maximum value is 200.
- <p>
- The major multiplier controls the frequency of major collections.
- For a major multiplier <em>x</em>,
- a new major collection will be done when memory
- grows <em>x%</em> larger than the memory in use after the previous major
- collection.
- For instance, for a multiplier of 100,
- the collector will do a major collection when the use of memory
- gets larger than twice the use after the previous collection.
- The default value is 100; the maximum value is 1000.
- <h3>2.5.3 – <a name="2.5.3">Garbage-Collection Metamethods</a></h3>
- <p>
- You can set garbage-collector metamethods for tables
- and, using the C API,
- for full userdata (see <a href="#2.4">§2.4</a>).
- These metamethods, called <em>finalizers</em>,
- are called when the garbage collector detects that the
- corresponding table or userdata is dead.
- Finalizers allow you to coordinate Lua's garbage collection
- with external resource management such as closing files,
- network or database connections,
- or freeing your own memory.
- <p>
- For an object (table or userdata) to be finalized when collected,
- you must <em>mark</em> it for finalization.
- You mark an object for finalization when you set its metatable
- and the metatable has a field indexed by the string "<code>__gc</code>".
- Note that if you set a metatable without a <code>__gc</code> field
- and later create that field in the metatable,
- the object will not be marked for finalization.
- <p>
- When a marked object becomes dead,
- it is not collected immediately by the garbage collector.
- Instead, Lua puts it in a list.
- After the collection,
- Lua goes through that list.
- For each object in the list,
- it checks the object's <code>__gc</code> metamethod:
- If it is present,
- Lua calls it with the object as its single argument.
- <p>
- At the end of each garbage-collection cycle,
- the finalizers are called in
- the reverse order that the objects were marked for finalization,
- among those collected in that cycle;
- that is, the first finalizer to be called is the one associated
- with the object marked last in the program.
- The execution of each finalizer may occur at any point during
- the execution of the regular code.
- <p>
- Because the object being collected must still be used by the finalizer,
- that object (and other objects accessible only through it)
- must be <em>resurrected</em> by Lua.
- Usually, this resurrection is transient,
- and the object memory is freed in the next garbage-collection cycle.
- However, if the finalizer stores the object in some global place
- (e.g., a global variable),
- then the resurrection is permanent.
- Moreover, if the finalizer marks a finalizing object for finalization again,
- its finalizer will be called again in the next cycle where the
- object is dead.
- In any case,
- the object memory is freed only in a GC cycle where
- the object is dead and not marked for finalization.
- <p>
- When you close a state (see <a href="#lua_close"><code>lua_close</code></a>),
- Lua calls the finalizers of all objects marked for finalization,
- following the reverse order that they were marked.
- If any finalizer marks objects for collection during that phase,
- these marks have no effect.
- <p>
- Finalizers cannot yield.
- Except for that, they can do anything,
- such as raise errors, create new objects,
- or even run the garbage collector.
- However, because they can run in unpredictable times,
- it is good practice to restrict each finalizer
- to the minimum necessary to properly release
- its associated resource.
- <p>
- Any error while running a finalizer generates a warning;
- the error is not propagated.
- <h3>2.5.4 – <a name="2.5.4">Weak Tables</a></h3>
- <p>
- A <em>weak table</em> is a table whose elements are
- <em>weak references</em>.
- A weak reference is ignored by the garbage collector.
- In other words,
- if the only references to an object are weak references,
- then the garbage collector will collect that object.
- <p>
- A weak table can have weak keys, weak values, or both.
- A table with weak values allows the collection of its values,
- but prevents the collection of its keys.
- A table with both weak keys and weak values allows the collection of
- both keys and values.
- In any case, if either the key or the value is collected,
- the whole pair is removed from the table.
- The weakness of a table is controlled by the
- <code>__mode</code> field of its metatable.
- This metavalue, if present, must be one of the following strings:
- "<code>k</code>", for a table with weak keys;
- "<code>v</code>", for a table with weak values;
- or "<code>kv</code>", for a table with both weak keys and values.
- <p>
- A table with weak keys and strong values
- is also called an <em>ephemeron table</em>.
- In an ephemeron table,
- a value is considered reachable only if its key is reachable.
- In particular,
- if the only reference to a key comes through its value,
- the pair is removed.
- <p>
- Any change in the weakness of a table may take effect only
- at the next collect cycle.
- In particular, if you change the weakness to a stronger mode,
- Lua may still collect some items from that table
- before the change takes effect.
- <p>
- Only objects that have an explicit construction
- are removed from weak tables.
- Values, such as numbers and light C functions,
- are not subject to garbage collection,
- and therefore are not removed from weak tables
- (unless their associated values are collected).
- Although strings are subject to garbage collection,
- they do not have an explicit construction and
- their equality is by value;
- they behave more like values than like objects.
- Therefore, they are not removed from weak tables.
- <p>
- Resurrected objects
- (that is, objects being finalized
- and objects accessible only through objects being finalized)
- have a special behavior in weak tables.
- They are removed from weak values before running their finalizers,
- but are removed from weak keys only in the next collection
- after running their finalizers, when such objects are actually freed.
- This behavior allows the finalizer to access properties
- associated with the object through weak tables.
- <p>
- If a weak table is among the resurrected objects in a collection cycle,
- it may not be properly cleared until the next cycle.
- <h2>2.6 – <a name="2.6">Coroutines</a></h2>
- <p>
- Lua supports coroutines,
- also called <em>collaborative multithreading</em>.
- A coroutine in Lua represents an independent thread of execution.
- Unlike threads in multithread systems, however,
- a coroutine only suspends its execution by explicitly calling
- a yield function.
- <p>
- You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
- Its sole argument is a function
- that is the main function of the coroutine.
- The <code>create</code> function only creates a new coroutine and
- returns a handle to it (an object of type <em>thread</em>);
- it does not start the coroutine.
- <p>
- You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- passing as its first argument
- a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
- the coroutine starts its execution by
- calling its main function.
- Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed
- as arguments to that function.
- After the coroutine starts running,
- it runs until it terminates or <em>yields</em>.
- <p>
- A coroutine can terminate its execution in two ways:
- normally, when its main function returns
- (explicitly or implicitly, after the last instruction);
- and abnormally, if there is an unprotected error.
- In case of normal termination,
- <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
- plus any values returned by the coroutine main function.
- In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
- plus the error object.
- In this case, the coroutine does not unwind its stack,
- so that it is possible to inspect it after the error
- with the debug API.
- <p>
- A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
- When a coroutine yields,
- the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
- even if the yield happens inside nested function calls
- (that is, not in the main function,
- but in a function directly or indirectly called by the main function).
- In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
- plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
- The next time you resume the same coroutine,
- it continues its execution from the point where it yielded,
- with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
- arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- <p>
- Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
- the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
- but instead of returning the coroutine itself,
- it returns a function that, when called, resumes the coroutine.
- Any arguments passed to this function
- go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
- <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- except the first one (the boolean error code).
- Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
- the function created by <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a>
- propagates any error to the caller.
- In this case,
- the function also closes the coroutine (see <a href="#pdf-coroutine.close"><code>coroutine.close</code></a>).
- <p>
- As an example of how coroutines work,
- consider the following code:
- <pre>
- function foo (a)
- print("foo", a)
- return coroutine.yield(2*a)
- end
-
- co = coroutine.create(function (a,b)
- print("co-body", a, b)
- local r = foo(a+1)
- print("co-body", r)
- local r, s = coroutine.yield(a+b, a-b)
- print("co-body", r, s)
- return b, "end"
- end)
-
- print("main", coroutine.resume(co, 1, 10))
- print("main", coroutine.resume(co, "r"))
- print("main", coroutine.resume(co, "x", "y"))
- print("main", coroutine.resume(co, "x", "y"))
- </pre><p>
- When you run it, it produces the following output:
- <pre>
- co-body 1 10
- foo 2
- main true 4
- co-body r
- main true 11 -9
- co-body x y
- main true 10 end
- main false cannot resume dead coroutine
- </pre>
- <p>
- You can also create and manipulate coroutines through the C API:
- see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>,
- and <a href="#lua_yield"><code>lua_yield</code></a>.
- <h1>3 – <a name="3">The Language</a></h1>
- <p>
- This section describes the lexis, the syntax, and the semantics of Lua.
- In other words,
- this section describes
- which tokens are valid,
- how they can be combined,
- and what their combinations mean.
- <p>
- Language constructs will be explained using the usual extended BNF notation,
- in which
- {<em>a</em>} means 0 or more <em>a</em>'s, and
- [<em>a</em>] means an optional <em>a</em>.
- Non-terminals are shown like non-terminal,
- keywords are shown like <b>kword</b>,
- and other terminal symbols are shown like ‘<b>=</b>’.
- The complete syntax of Lua can be found in <a href="#9">§9</a>
- at the end of this manual.
- <h2>3.1 – <a name="3.1">Lexical Conventions</a></h2>
- <p>
- Lua is a free-form language.
- It ignores spaces and comments between lexical elements (tokens),
- except as delimiters between two tokens.
- In source code,
- Lua recognizes as spaces the standard ASCII whitespace
- characters space, form feed, newline,
- carriage return, horizontal tab, and vertical tab.
- <p>
- <em>Names</em>
- (also called <em>identifiers</em>)
- in Lua can be any string of Latin letters,
- Arabic-Indic digits, and underscores,
- not beginning with a digit and
- not being a reserved word.
- Identifiers are used to name variables, table fields, and labels.
- <p>
- The following <em>keywords</em> are reserved
- and cannot be used as names:
- <pre>
- and break do else elseif end
- false for function goto if in
- local nil not or repeat return
- then true until while
- </pre>
- <p>
- Lua is a case-sensitive language:
- <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
- are two different, valid names.
- As a convention,
- programs should avoid creating
- names that start with an underscore followed by
- one or more uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>).
- <p>
- The following strings denote other tokens:
- <pre>
- + - * / % ^ #
- & ~ | << >> //
- == ~= <= >= < > =
- ( ) { } [ ] ::
- ; : , . .. ...
- </pre>
- <p>
- A <em>short literal string</em>
- can be delimited by matching single or double quotes,
- and can contain the following C-like escape sequences:
- '<code>\a</code>' (bell),
- '<code>\b</code>' (backspace),
- '<code>\f</code>' (form feed),
- '<code>\n</code>' (newline),
- '<code>\r</code>' (carriage return),
- '<code>\t</code>' (horizontal tab),
- '<code>\v</code>' (vertical tab),
- '<code>\\</code>' (backslash),
- '<code>\"</code>' (quotation mark [double quote]),
- and '<code>\'</code>' (apostrophe [single quote]).
- A backslash followed by a line break
- results in a newline in the string.
- The escape sequence '<code>\z</code>' skips the following span
- of whitespace characters,
- including line breaks;
- it is particularly useful to break and indent a long literal string
- into multiple lines without adding the newlines and spaces
- into the string contents.
- A short literal string cannot contain unescaped line breaks
- nor escapes not forming a valid escape sequence.
- <p>
- We can specify any byte in a short literal string,
- including embedded zeros,
- by its numeric value.
- This can be done
- with the escape sequence <code>\x<em>XX</em></code>,
- where <em>XX</em> is a sequence of exactly two hexadecimal digits,
- or with the escape sequence <code>\<em>ddd</em></code>,
- where <em>ddd</em> is a sequence of up to three decimal digits.
- (Note that if a decimal escape sequence is to be followed by a digit,
- it must be expressed using exactly three digits.)
- <p>
- The UTF-8 encoding of a Unicode character
- can be inserted in a literal string with
- the escape sequence <code>\u{<em>XXX</em>}</code>
- (with mandatory enclosing braces),
- where <em>XXX</em> is a sequence of one or more hexadecimal digits
- representing the character code point.
- This code point can be any value less than <em>2<sup>31</sup></em>.
- (Lua uses the original UTF-8 specification here,
- which is not restricted to valid Unicode code points.)
- <p>
- Literal strings can also be defined using a long format
- enclosed by <em>long brackets</em>.
- We define an <em>opening long bracket of level <em>n</em></em> as an opening
- square bracket followed by <em>n</em> equal signs followed by another
- opening square bracket.
- So, an opening long bracket of level 0 is written as <code>[[</code>,
- an opening long bracket of level 1 is written as <code>[=[</code>,
- and so on.
- A <em>closing long bracket</em> is defined similarly;
- for instance,
- a closing long bracket of level 4 is written as <code>]====]</code>.
- A <em>long literal</em> starts with an opening long bracket of any level and
- ends at the first closing long bracket of the same level.
- It can contain any text except a closing bracket of the same level.
- Literals in this bracketed form can run for several lines,
- do not interpret any escape sequences,
- and ignore long brackets of any other level.
- Any kind of end-of-line sequence
- (carriage return, newline, carriage return followed by newline,
- or newline followed by carriage return)
- is converted to a simple newline.
- When the opening long bracket is immediately followed by a newline,
- the newline is not included in the string.
- <p>
- As an example, in a system using ASCII
- (in which '<code>a</code>' is coded as 97,
- newline is coded as 10, and '<code>1</code>' is coded as 49),
- the five literal strings below denote the same string:
- <pre>
- a = 'alo\n123"'
- a = "alo\n123\""
- a = '\97lo\10\04923"'
- a = [[alo
- 123"]]
- a = [==[
- alo
- 123"]==]
- </pre>
- <p>
- Any byte in a literal string not
- explicitly affected by the previous rules represents itself.
- However, Lua opens files for parsing in text mode,
- and the system's file functions may have problems with
- some control characters.
- So, it is safer to represent
- binary data as a quoted literal with
- explicit escape sequences for the non-text characters.
- <p>
- A <em>numeric constant</em> (or <em>numeral</em>)
- can be written with an optional fractional part
- and an optional decimal exponent,
- marked by a letter '<code>e</code>' or '<code>E</code>'.
- Lua also accepts hexadecimal constants,
- which start with <code>0x</code> or <code>0X</code>.
- Hexadecimal constants also accept an optional fractional part
- plus an optional binary exponent,
- marked by a letter '<code>p</code>' or '<code>P</code>'.
- <p>
- A numeric constant with a radix point or an exponent
- denotes a float;
- otherwise,
- if its value fits in an integer or it is a hexadecimal constant,
- it denotes an integer;
- otherwise (that is, a decimal integer numeral that overflows),
- it denotes a float.
- Hexadecimal numerals with neither a radix point nor an exponent
- always denote an integer value;
- if the value overflows, it <em>wraps around</em>
- to fit into a valid integer.
- <p>
- Examples of valid integer constants are
- <pre>
- 3 345 0xff 0xBEBADA
- </pre><p>
- Examples of valid float constants are
- <pre>
- 3.0 3.1416 314.16e-2 0.31416E1 34e1
- 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
- </pre>
- <p>
- A <em>comment</em> starts with a double hyphen (<code>--</code>)
- anywhere outside a string.
- If the text immediately after <code>--</code> is not an opening long bracket,
- the comment is a <em>short comment</em>,
- which runs until the end of the line.
- Otherwise, it is a <em>long comment</em>,
- which runs until the corresponding closing long bracket.
- <h2>3.2 – <a name="3.2">Variables</a></h2>
- <p>
- Variables are places that store values.
- There are three kinds of variables in Lua:
- global variables, local variables, and table fields.
- <p>
- A single name can denote a global variable or a local variable
- (or a function's formal parameter,
- which is a particular kind of local variable):
- <pre>
- var ::= Name
- </pre><p>
- Name denotes identifiers (see <a href="#3.1">§3.1</a>).
- <p>
- Any variable name is assumed to be global unless explicitly declared
- as a local (see <a href="#3.3.7">§3.3.7</a>).
- Local variables are <em>lexically scoped</em>:
- local variables can be freely accessed by functions
- defined inside their scope (see <a href="#3.5">§3.5</a>).
- <p>
- Before the first assignment to a variable, its value is <b>nil</b>.
- <p>
- Square brackets are used to index a table:
- <pre>
- var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’
- </pre><p>
- The meaning of accesses to table fields can be changed via metatables
- (see <a href="#2.4">§2.4</a>).
- <p>
- The syntax <code>var.Name</code> is just syntactic sugar for
- <code>var["Name"]</code>:
- <pre>
- var ::= prefixexp ‘<b>.</b>’ Name
- </pre>
- <p>
- An access to a global variable <code>x</code>
- is equivalent to <code>_ENV.x</code>.
- Due to the way that chunks are compiled,
- the variable <code>_ENV</code> itself is never global (see <a href="#2.2">§2.2</a>).
- <h2>3.3 – <a name="3.3">Statements</a></h2>
- <p>
- Lua supports an almost conventional set of statements,
- similar to those in other conventional languages.
- This set includes
- blocks, assignments, control structures, function calls,
- and variable declarations.
- <h3>3.3.1 – <a name="3.3.1">Blocks</a></h3>
- <p>
- A block is a list of statements,
- which are executed sequentially:
- <pre>
- block ::= {stat}
- </pre><p>
- Lua has <em>empty statements</em>
- that allow you to separate statements with semicolons,
- start a block with a semicolon
- or write two semicolons in sequence:
- <pre>
- stat ::= ‘<b>;</b>’
- </pre>
- <p>
- Both function calls and assignments
- can start with an open parenthesis.
- This possibility leads to an ambiguity in Lua's grammar.
- Consider the following fragment:
- <pre>
- a = b + c
- (print or io.write)('done')
- </pre><p>
- The grammar could see this fragment in two ways:
- <pre>
- a = b + c(print or io.write)('done')
-
- a = b + c; (print or io.write)('done')
- </pre><p>
- The current parser always sees such constructions
- in the first way,
- interpreting the open parenthesis
- as the start of the arguments to a call.
- To avoid this ambiguity,
- it is a good practice to always precede with a semicolon
- statements that start with a parenthesis:
- <pre>
- ;(print or io.write)('done')
- </pre>
- <p>
- A block can be explicitly delimited to produce a single statement:
- <pre>
- stat ::= <b>do</b> block <b>end</b>
- </pre><p>
- Explicit blocks are useful
- to control the scope of variable declarations.
- Explicit blocks are also sometimes used to
- add a <b>return</b> statement in the middle
- of another block (see <a href="#3.3.4">§3.3.4</a>).
- <h3>3.3.2 – <a name="3.3.2">Chunks</a></h3>
- <p>
- The unit of compilation of Lua is called a <em>chunk</em>.
- Syntactically,
- a chunk is simply a block:
- <pre>
- chunk ::= block
- </pre>
- <p>
- Lua handles a chunk as the body of an anonymous function
- with a variable number of arguments
- (see <a href="#3.4.11">§3.4.11</a>).
- As such, chunks can define local variables,
- receive arguments, and return values.
- Moreover, such anonymous function is compiled as in the
- scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>).
- The resulting function always has <code>_ENV</code> as its only external variable,
- even if it does not use that variable.
- <p>
- A chunk can be stored in a file or in a string inside the host program.
- To execute a chunk,
- Lua first <em>loads</em> it,
- precompiling the chunk's code into instructions for a virtual machine,
- and then Lua executes the compiled code
- with an interpreter for the virtual machine.
- <p>
- Chunks can also be precompiled into binary form;
- see the program <code>luac</code> and the function <a href="#pdf-string.dump"><code>string.dump</code></a> for details.
- Programs in source and compiled forms are interchangeable;
- Lua automatically detects the file type and acts accordingly (see <a href="#pdf-load"><code>load</code></a>).
- <h3>3.3.3 – <a name="3.3.3">Assignment</a></h3>
- <p>
- Lua allows multiple assignments.
- Therefore, the syntax for assignment
- defines a list of variables on the left side
- and a list of expressions on the right side.
- The elements in both lists are separated by commas:
- <pre>
- stat ::= varlist ‘<b>=</b>’ explist
- varlist ::= var {‘<b>,</b>’ var}
- explist ::= exp {‘<b>,</b>’ exp}
- </pre><p>
- Expressions are discussed in <a href="#3.4">§3.4</a>.
- <p>
- Before the assignment,
- the list of values is <em>adjusted</em> to the length of
- the list of variables.
- If there are more values than needed,
- the excess values are thrown away.
- If there are fewer values than needed,
- the list is extended with <b>nil</b>'s.
- If the list of expressions ends with a function call,
- then all values returned by that call enter the list of values,
- before the adjustment
- (except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>).
- <p>
- The assignment statement first evaluates all its expressions
- and only then the assignments are performed.
- Thus the code
- <pre>
- i = 3
- i, a[i] = i+1, 20
- </pre><p>
- sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
- because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
- before it is assigned 4.
- Similarly, the line
- <pre>
- x, y = y, x
- </pre><p>
- exchanges the values of <code>x</code> and <code>y</code>,
- and
- <pre>
- x, y, z = y, z, x
- </pre><p>
- cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
- <p>
- An assignment to a global name <code>x = val</code>
- is equivalent to the assignment
- <code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>).
- <p>
- The meaning of assignments to table fields and
- global variables (which are actually table fields, too)
- can be changed via metatables (see <a href="#2.4">§2.4</a>).
- <h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p>
- The control structures
- <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
- familiar syntax:
- <pre>
- stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
- stat ::= <b>repeat</b> block <b>until</b> exp
- stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
- </pre><p>
- Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>).
- <p>
- The condition expression of a
- control structure can return any value.
- Both <b>false</b> and <b>nil</b> test false.
- All values different from <b>nil</b> and <b>false</b> test true.
- In particular, the number 0 and the empty string also test true.
- <p>
- In the <b>repeat</b>–<b>until</b> loop,
- the inner block does not end at the <b>until</b> keyword,
- but only after the condition.
- So, the condition can refer to local variables
- declared inside the loop block.
- <p>
- The <b>goto</b> statement transfers the program control to a label.
- For syntactical reasons,
- labels in Lua are considered statements too:
- <pre>
- stat ::= <b>goto</b> Name
- stat ::= label
- label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
- </pre>
- <p>
- A label is visible in the entire block where it is defined,
- except inside nested functions.
- A goto may jump to any visible label as long as it does not
- enter into the scope of a local variable.
- A label should not be declared
- where a label with the same name is visible,
- even if this other label has been declared in an enclosing block.
- <p>
- Labels and empty statements are called <em>void statements</em>,
- as they perform no actions.
- <p>
- The <b>break</b> statement terminates the execution of a
- <b>while</b>, <b>repeat</b>, or <b>for</b> loop,
- skipping to the next statement after the loop:
- <pre>
- stat ::= <b>break</b>
- </pre><p>
- A <b>break</b> ends the innermost enclosing loop.
- <p>
- The <b>return</b> statement is used to return values
- from a function or a chunk
- (which is handled as an anonymous function).
- Functions can return more than one value,
- so the syntax for the <b>return</b> statement is
- <pre>
- stat ::= <b>return</b> [explist] [‘<b>;</b>’]
- </pre>
- <p>
- The <b>return</b> statement can only be written
- as the last statement of a block.
- If it is necessary to <b>return</b> in the middle of a block,
- then an explicit inner block can be used,
- as in the idiom <code>do return end</code>,
- because now <b>return</b> is the last statement in its (inner) block.
- <h3>3.3.5 – <a name="3.3.5">For Statement</a></h3>
- <p>
- The <b>for</b> statement has two forms:
- one numerical and one generic.
- <h4>The numerical <b>for</b> loop</h4>
- <p>
- The numerical <b>for</b> loop repeats a block of code while a
- control variable goes through an arithmetic progression.
- It has the following syntax:
- <pre>
- stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b>
- </pre><p>
- The given identifier (Name) defines the control variable,
- which is a new variable local to the loop body (<em>block</em>).
- <p>
- The loop starts by evaluating once the three control expressions.
- Their values are called respectively
- the <em>initial value</em>, the <em>limit</em>, and the <em>step</em>.
- If the step is absent, it defaults to 1.
- <p>
- If both the initial value and the step are integers,
- the loop is done with integers;
- note that the limit may not be an integer.
- Otherwise, the three values are converted to
- floats and the loop is done with floats.
- Beware of floating-point accuracy in this case.
- <p>
- After that initialization,
- the loop body is repeated with the value of the control variable
- going through an arithmetic progression,
- starting at the initial value,
- with a common difference given by the step.
- A negative step makes a decreasing sequence;
- a step equal to zero raises an error.
- The loop continues while the value is less than
- or equal to the limit
- (greater than or equal to for a negative step).
- If the initial value is already greater than the limit
- (or less than, if the step is negative),
- the body is not executed.
- <p>
- For integer loops,
- the control variable never wraps around;
- instead, the loop ends in case of an overflow.
- <p>
- You should not change the value of the control variable
- during the loop.
- If you need its value after the loop,
- assign it to another variable before exiting the loop.
- <h4>The generic <b>for</b> loop</h4>
- <p>
- The generic <b>for</b> statement works over functions,
- called <em>iterators</em>.
- On each iteration, the iterator function is called to produce a new value,
- stopping when this new value is <b>nil</b>.
- The generic <b>for</b> loop has the following syntax:
- <pre>
- stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
- namelist ::= Name {‘<b>,</b>’ Name}
- </pre><p>
- A <b>for</b> statement like
- <pre>
- for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>body</em> end
- </pre><p>
- works as follows.
- <p>
- The names <em>var_i</em> declare loop variables local to the loop body.
- The first of these variables is the <em>control variable</em>.
- <p>
- The loop starts by evaluating <em>explist</em>
- to produce four values:
- an <em>iterator function</em>,
- a <em>state</em>,
- an initial value for the control variable,
- and a <em>closing value</em>.
- <p>
- Then, at each iteration,
- Lua calls the iterator function with two arguments:
- the state and the control variable.
- The results from this call are then assigned to the loop variables,
- following the rules of multiple assignments (see <a href="#3.3.3">§3.3.3</a>).
- If the control variable becomes <b>nil</b>,
- the loop terminates.
- Otherwise, the body is executed and the loop goes
- to the next iteration.
- <p>
- The closing value behaves like a
- to-be-closed variable (see <a href="#3.3.8">§3.3.8</a>),
- which can be used to release resources when the loop ends.
- Otherwise, it does not interfere with the loop.
- <p>
- You should not change the value of the control variable
- during the loop.
- <h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p>
- To allow possible side-effects,
- function calls can be executed as statements:
- <pre>
- stat ::= functioncall
- </pre><p>
- In this case, all returned values are thrown away.
- Function calls are explained in <a href="#3.4.10">§3.4.10</a>.
- <h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p>
- Local variables can be declared anywhere inside a block.
- The declaration can include an initialization:
- <pre>
- stat ::= <b>local</b> attnamelist [‘<b>=</b>’ explist]
- attnamelist ::= Name attrib {‘<b>,</b>’ Name attrib}
- </pre><p>
- If present, an initial assignment has the same semantics
- of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>).
- Otherwise, all variables are initialized with <b>nil</b>.
- <p>
- Each variable name may be postfixed by an attribute
- (a name between angle brackets):
- <pre>
- attrib ::= [‘<b><</b>’ Name ‘<b>></b>’]
- </pre><p>
- There are two possible attributes:
- <code>const</code>, which declares a constant variable,
- that is, a variable that cannot be assigned to
- after its initialization;
- and <code>close</code>, which declares a to-be-closed variable (see <a href="#3.3.8">§3.3.8</a>).
- A list of variables can contain at most one to-be-closed variable.
- <p>
- A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>),
- and so local variables can be declared in a chunk outside any explicit block.
- <p>
- The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>.
- <h3>3.3.8 – <a name="3.3.8">To-be-closed Variables</a></h3>
- <p>
- A to-be-closed variable behaves like a constant local variable,
- except that its value is <em>closed</em> whenever the variable
- goes out of scope, including normal block termination,
- exiting its block by <b>break</b>/<b>goto</b>/<b>return</b>,
- or exiting by an error.
- <p>
- Here, to <em>close</em> a value means
- to call its <code>__close</code> metamethod.
- When calling the metamethod,
- the value itself is passed as the first argument
- and the error object that caused the exit (if any)
- is passed as a second argument;
- if there was no error, the second argument is <b>nil</b>.
- <p>
- The value assigned to a to-be-closed variable
- must have a <code>__close</code> metamethod
- or be a false value.
- (<b>nil</b> and <b>false</b> are ignored as to-be-closed values.)
- <p>
- If several to-be-closed variables go out of scope at the same event,
- they are closed in the reverse order that they were declared.
- <p>
- If there is any error while running a closing method,
- that error is handled like an error in the regular code
- where the variable was defined.
- However, Lua may call the method one more time.
- <p>
- After an error,
- the other pending closing methods will still be called.
- Errors in these methods
- interrupt the respective method and generate a warning,
- but are otherwise ignored;
- the error reported is only the original one.
- <p>
- If a coroutine yields and is never resumed again,
- some variables may never go out of scope,
- and therefore they will never be closed.
- (These variables are the ones created inside the coroutine
- and in scope at the point where the coroutine yielded.)
- Similarly, if a coroutine ends with an error,
- it does not unwind its stack,
- so it does not close any variable.
- In both cases,
- you can either use finalizers
- or call <a href="#pdf-coroutine.close"><code>coroutine.close</code></a> to close the variables.
- However, if the coroutine was created
- through <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a>,
- then its corresponding function will close the coroutine
- in case of errors.
- <h2>3.4 – <a name="3.4">Expressions</a></h2>
- <p>
- The basic expressions in Lua are the following:
- <pre>
- exp ::= prefixexp
- exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
- exp ::= Numeral
- exp ::= LiteralString
- exp ::= functiondef
- exp ::= tableconstructor
- exp ::= ‘<b>...</b>’
- exp ::= exp binop exp
- exp ::= unop exp
- prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
- </pre>
- <p>
- Numerals and literal strings are explained in <a href="#3.1">§3.1</a>;
- variables are explained in <a href="#3.2">§3.2</a>;
- function definitions are explained in <a href="#3.4.11">§3.4.11</a>;
- function calls are explained in <a href="#3.4.10">§3.4.10</a>;
- table constructors are explained in <a href="#3.4.9">§3.4.9</a>.
- Vararg expressions,
- denoted by three dots ('<code>...</code>'), can only be used when
- directly inside a vararg function;
- they are explained in <a href="#3.4.11">§3.4.11</a>.
- <p>
- Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>),
- bitwise operators (see <a href="#3.4.2">§3.4.2</a>),
- relational operators (see <a href="#3.4.4">§3.4.4</a>), logical operators (see <a href="#3.4.5">§3.4.5</a>),
- and the concatenation operator (see <a href="#3.4.6">§3.4.6</a>).
- Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>),
- the unary bitwise NOT (see <a href="#3.4.2">§3.4.2</a>),
- the unary logical <b>not</b> (see <a href="#3.4.5">§3.4.5</a>),
- and the unary <em>length operator</em> (see <a href="#3.4.7">§3.4.7</a>).
- <p>
- Both function calls and vararg expressions can result in multiple values.
- If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>),
- then its return list is adjusted to zero elements,
- thus discarding all returned values.
- If an expression is used as the last (or the only) element
- of a list of expressions,
- then no adjustment is made
- (unless the expression is enclosed in parentheses).
- In all other contexts,
- Lua adjusts the result list to one element,
- either discarding all values except the first one
- or adding a single <b>nil</b> if there are no values.
- <p>
- Here are some examples:
- <pre>
- f() -- adjusted to 0 results
- g(f(), x) -- f() is adjusted to 1 result
- g(x, f()) -- g gets x plus all results from f()
- a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
- a,b = ... -- a gets the first vararg argument, b gets
- -- the second (both a and b can get nil if there
- -- is no corresponding vararg argument)
-
- a,b,c = x, f() -- f() is adjusted to 2 results
- a,b,c = f() -- f() is adjusted to 3 results
- return f() -- returns all results from f()
- return ... -- returns all received vararg arguments
- return x,y,f() -- returns x, y, and all results from f()
- {f()} -- creates a list with all results from f()
- {...} -- creates a list with all vararg arguments
- {f(), nil} -- f() is adjusted to 1 result
- </pre>
- <p>
- Any expression enclosed in parentheses always results in only one value.
- Thus,
- <code>(f(x,y,z))</code> is always a single value,
- even if <code>f</code> returns several values.
- (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
- or <b>nil</b> if <code>f</code> does not return any values.)
- <h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p>
- Lua supports the following arithmetic operators:
- <ul>
- <li><b><code>+</code>: </b>addition</li>
- <li><b><code>-</code>: </b>subtraction</li>
- <li><b><code>*</code>: </b>multiplication</li>
- <li><b><code>/</code>: </b>float division</li>
- <li><b><code>//</code>: </b>floor division</li>
- <li><b><code>%</code>: </b>modulo</li>
- <li><b><code>^</code>: </b>exponentiation</li>
- <li><b><code>-</code>: </b>unary minus</li>
- </ul>
- <p>
- With the exception of exponentiation and float division,
- the arithmetic operators work as follows:
- If both operands are integers,
- the operation is performed over integers and the result is an integer.
- Otherwise, if both operands are numbers,
- then they are converted to floats,
- the operation is performed following the machine's rules
- for floating-point arithmetic
- (usually the IEEE 754 standard),
- and the result is a float.
- (The string library coerces strings to numbers in
- arithmetic operations; see <a href="#3.4.3">§3.4.3</a> for details.)
- <p>
- Exponentiation and float division (<code>/</code>)
- always convert their operands to floats
- and the result is always a float.
- Exponentiation uses the ISO C function <code>pow</code>,
- so that it works for non-integer exponents too.
- <p>
- Floor division (<code>//</code>) is a division
- that rounds the quotient towards minus infinity,
- resulting in the floor of the division of its operands.
- <p>
- Modulo is defined as the remainder of a division
- that rounds the quotient towards minus infinity (floor division).
- <p>
- In case of overflows in integer arithmetic,
- all operations <em>wrap around</em>.
- <h3>3.4.2 – <a name="3.4.2">Bitwise Operators</a></h3><p>
- Lua supports the following bitwise operators:
- <ul>
- <li><b><code>&</code>: </b>bitwise AND</li>
- <li><b><code>|</code>: </b>bitwise OR</li>
- <li><b><code>~</code>: </b>bitwise exclusive OR</li>
- <li><b><code>>></code>: </b>right shift</li>
- <li><b><code><<</code>: </b>left shift</li>
- <li><b><code>~</code>: </b>unary bitwise NOT</li>
- </ul>
- <p>
- All bitwise operations convert its operands to integers
- (see <a href="#3.4.3">§3.4.3</a>),
- operate on all bits of those integers,
- and result in an integer.
- <p>
- Both right and left shifts fill the vacant bits with zeros.
- Negative displacements shift to the other direction;
- displacements with absolute values equal to or higher than
- the number of bits in an integer
- result in zero (as all bits are shifted out).
- <h3>3.4.3 – <a name="3.4.3">Coercions and Conversions</a></h3><p>
- Lua provides some automatic conversions between some
- types and representations at run time.
- Bitwise operators always convert float operands to integers.
- Exponentiation and float division
- always convert integer operands to floats.
- All other arithmetic operations applied to mixed numbers
- (integers and floats) convert the integer operand to a float.
- The C API also converts both integers to floats and
- floats to integers, as needed.
- Moreover, string concatenation accepts numbers as arguments,
- besides strings.
- <p>
- In a conversion from integer to float,
- if the integer value has an exact representation as a float,
- that is the result.
- Otherwise,
- the conversion gets the nearest higher or
- the nearest lower representable value.
- This kind of conversion never fails.
- <p>
- The conversion from float to integer
- checks whether the float has an exact representation as an integer
- (that is, the float has an integral value and
- it is in the range of integer representation).
- If it does, that representation is the result.
- Otherwise, the conversion fails.
- <p>
- Several places in Lua coerce strings to numbers when necessary.
- In particular,
- the string library sets metamethods that try to coerce
- strings to numbers in all arithmetic operations.
- If the conversion fails,
- the library calls the metamethod of the other operand
- (if present) or it raises an error.
- Note that bitwise operators do not do this coercion.
- <p>
- Nonetheless, it is always a good practice not to rely on these
- implicit coercions, as they are not always applied;
- in particular, <code>"1"==1</code> is false and <code>"1"<1</code> raises an error
- (see <a href="#3.4.4">§3.4.4</a>).
- These coercions exist mainly for compatibility and may be removed
- in future versions of the language.
- <p>
- A string is converted to an integer or a float
- following its syntax and the rules of the Lua lexer.
- The string may have also leading and trailing whitespaces and a sign.
- All conversions from strings to numbers
- accept both a dot and the current locale mark
- as the radix character.
- (The Lua lexer, however, accepts only a dot.)
- If the string is not a valid numeral,
- the conversion fails.
- If necessary, the result of this first step is then converted
- to a specific number subtype following the previous rules
- for conversions between floats and integers.
- <p>
- The conversion from numbers to strings uses a
- non-specified human-readable format.
- To convert numbers to strings in any specific way,
- use the function <a href="#pdf-string.format"><code>string.format</code></a>.
- <h3>3.4.4 – <a name="3.4.4">Relational Operators</a></h3><p>
- Lua supports the following relational operators:
- <ul>
- <li><b><code>==</code>: </b>equality</li>
- <li><b><code>~=</code>: </b>inequality</li>
- <li><b><code><</code>: </b>less than</li>
- <li><b><code>></code>: </b>greater than</li>
- <li><b><code><=</code>: </b>less or equal</li>
- <li><b><code>>=</code>: </b>greater or equal</li>
- </ul><p>
- These operators always result in <b>false</b> or <b>true</b>.
- <p>
- Equality (<code>==</code>) first compares the type of its operands.
- If the types are different, then the result is <b>false</b>.
- Otherwise, the values of the operands are compared.
- Strings are equal if they have the same byte content.
- Numbers are equal if they denote the same mathematical value.
- <p>
- Tables, userdata, and threads
- are compared by reference:
- two objects are considered equal only if they are the same object.
- Every time you create a new object
- (a table, a userdata, or a thread),
- this new object is different from any previously existing object.
- A function is always equal to itself.
- Functions with any detectable difference
- (different behavior, different definition) are always different.
- Functions created at different times but with no detectable differences
- may be classified as equal or not
- (depending on internal caching details).
- <p>
- You can change the way that Lua compares tables and userdata
- by using the <code>__eq</code> metamethod (see <a href="#2.4">§2.4</a>).
- <p>
- Equality comparisons do not convert strings to numbers
- or vice versa.
- Thus, <code>"0"==0</code> evaluates to <b>false</b>,
- and <code>t[0]</code> and <code>t["0"]</code> denote different
- entries in a table.
- <p>
- The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
- <p>
- The order operators work as follows.
- If both arguments are numbers,
- then they are compared according to their mathematical values,
- regardless of their subtypes.
- Otherwise, if both arguments are strings,
- then their values are compared according to the current locale.
- Otherwise, Lua tries to call the <code>__lt</code> or the <code>__le</code>
- metamethod (see <a href="#2.4">§2.4</a>).
- A comparison <code>a > b</code> is translated to <code>b < a</code>
- and <code>a >= b</code> is translated to <code>b <= a</code>.
- <p>
- Following the IEEE 754 standard,
- the special value NaN is considered neither less than,
- nor equal to, nor greater than any value, including itself.
- <h3>3.4.5 – <a name="3.4.5">Logical Operators</a></h3><p>
- The logical operators in Lua are
- <b>and</b>, <b>or</b>, and <b>not</b>.
- Like the control structures (see <a href="#3.3.4">§3.3.4</a>),
- all logical operators consider both <b>false</b> and <b>nil</b> as false
- and anything else as true.
- <p>
- The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
- The conjunction operator <b>and</b> returns its first argument
- if this value is <b>false</b> or <b>nil</b>;
- otherwise, <b>and</b> returns its second argument.
- The disjunction operator <b>or</b> returns its first argument
- if this value is different from <b>nil</b> and <b>false</b>;
- otherwise, <b>or</b> returns its second argument.
- Both <b>and</b> and <b>or</b> use short-circuit evaluation;
- that is,
- the second operand is evaluated only if necessary.
- Here are some examples:
- <pre>
- 10 or 20 --> 10
- 10 or error() --> 10
- nil or "a" --> "a"
- nil and 10 --> nil
- false and error() --> false
- false and nil --> false
- false or nil --> nil
- 10 and 20 --> 20
- </pre>
- <h3>3.4.6 – <a name="3.4.6">Concatenation</a></h3><p>
- The string concatenation operator in Lua is
- denoted by two dots ('<code>..</code>').
- If both operands are strings or numbers,
- then the numbers are converted to strings
- in a non-specified format (see <a href="#3.4.3">§3.4.3</a>).
- Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>).
- <h3>3.4.7 – <a name="3.4.7">The Length Operator</a></h3>
- <p>
- The length operator is denoted by the unary prefix operator <code>#</code>.
- <p>
- The length of a string is its number of bytes.
- (That is the usual meaning of string length when each
- character is one byte.)
- <p>
- The length operator applied on a table
- returns a border in that table.
- A <em>border</em> in a table <code>t</code> is any natural number
- that satisfies the following condition:
- <pre>
- (border == 0 or t[border] ~= nil) and t[border + 1] == nil
- </pre><p>
- In words,
- a border is any (natural) index present in the table
- that is followed by an absent index
- (or zero, when index 1 is absent).
- <p>
- A table with exactly one border is called a <em>sequence</em>.
- For instance, the table <code>{10, 20, 30, 40, 50}</code> is a sequence,
- as it has only one border (5).
- The table <code>{10, 20, 30, nil, 50}</code> has two borders (3 and 5),
- and therefore it is not a sequence.
- (The <b>nil</b> at index 4 is called a <em>hole</em>.)
- The table <code>{nil, 20, 30, nil, nil, 60, nil}</code>
- has three borders (0, 3, and 6) and three holes
- (at indices 1, 4, and 5),
- so it is not a sequence, too.
- The table <code>{}</code> is a sequence with border 0.
- Note that non-natural keys do not interfere
- with whether a table is a sequence.
- <p>
- When <code>t</code> is a sequence,
- <code>#t</code> returns its only border,
- which corresponds to the intuitive notion of the length of the sequence.
- When <code>t</code> is not a sequence,
- <code>#t</code> can return any of its borders.
- (The exact one depends on details of
- the internal representation of the table,
- which in turn can depend on how the table was populated and
- the memory addresses of its non-numeric keys.)
- <p>
- The computation of the length of a table
- has a guaranteed worst time of <em>O(log n)</em>,
- where <em>n</em> is the largest natural key in the table.
- <p>
- A program can modify the behavior of the length operator for
- any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>).
- <h3>3.4.8 – <a name="3.4.8">Precedence</a></h3><p>
- Operator precedence in Lua follows the table below,
- from lower to higher priority:
- <pre>
- or
- and
- < > <= >= ~= ==
- |
- ~
- &
- << >>
- ..
- + -
- * / // %
- unary operators (not # - ~)
- ^
- </pre><p>
- As usual,
- you can use parentheses to change the precedences of an expression.
- The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
- operators are right associative.
- All other binary operators are left associative.
- <h3>3.4.9 – <a name="3.4.9">Table Constructors</a></h3><p>
- Table constructors are expressions that create tables.
- Every time a constructor is evaluated, a new table is created.
- A constructor can be used to create an empty table
- or to create a table and initialize some of its fields.
- The general syntax for constructors is
- <pre>
- tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
- fieldlist ::= field {fieldsep field} [fieldsep]
- field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
- fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
- </pre>
- <p>
- Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
- with key <code>exp1</code> and value <code>exp2</code>.
- A field of the form <code>name = exp</code> is equivalent to
- <code>["name"] = exp</code>.
- Fields of the form <code>exp</code> are equivalent to
- <code>[i] = exp</code>, where <code>i</code> are consecutive integers
- starting with 1;
- fields in the other formats do not affect this counting.
- For example,
- <pre>
- a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
- </pre><p>
- is equivalent to
- <pre>
- do
- local t = {}
- t[f(1)] = g
- t[1] = "x" -- 1st exp
- t[2] = "y" -- 2nd exp
- t.x = 1 -- t["x"] = 1
- t[3] = f(x) -- 3rd exp
- t[30] = 23
- t[4] = 45 -- 4th exp
- a = t
- end
- </pre>
- <p>
- The order of the assignments in a constructor is undefined.
- (This order would be relevant only when there are repeated keys.)
- <p>
- If the last field in the list has the form <code>exp</code>
- and the expression is a function call or a vararg expression,
- then all values returned by this expression enter the list consecutively
- (see <a href="#3.4.10">§3.4.10</a>).
- <p>
- The field list can have an optional trailing separator,
- as a convenience for machine-generated code.
- <h3>3.4.10 – <a name="3.4.10">Function Calls</a></h3><p>
- A function call in Lua has the following syntax:
- <pre>
- functioncall ::= prefixexp args
- </pre><p>
- In a function call,
- first prefixexp and args are evaluated.
- If the value of prefixexp has type <em>function</em>,
- then this function is called
- with the given arguments.
- Otherwise, if present,
- the prefixexp <code>__call</code> metamethod is called:
- its first argument is the value of prefixexp,
- followed by the original call arguments
- (see <a href="#2.4">§2.4</a>).
- <p>
- The form
- <pre>
- functioncall ::= prefixexp ‘<b>:</b>’ Name args
- </pre><p>
- can be used to emulate methods.
- A call <code>v:name(<em>args</em>)</code>
- is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
- except that <code>v</code> is evaluated only once.
- <p>
- Arguments have the following syntax:
- <pre>
- args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’
- args ::= tableconstructor
- args ::= LiteralString
- </pre><p>
- All argument expressions are evaluated before the call.
- A call of the form <code>f{<em>fields</em>}</code> is
- syntactic sugar for <code>f({<em>fields</em>})</code>;
- that is, the argument list is a single new table.
- A call of the form <code>f'<em>string</em>'</code>
- (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
- is syntactic sugar for <code>f('<em>string</em>')</code>;
- that is, the argument list is a single literal string.
- <p>
- A call of the form <code>return <em>functioncall</em></code> not in the
- scope of a to-be-closed variable is called a <em>tail call</em>.
- Lua implements <em>proper tail calls</em>
- (or <em>proper tail recursion</em>):
- in a tail call,
- the called function reuses the stack entry of the calling function.
- Therefore, there is no limit on the number of nested tail calls that
- a program can execute.
- However, a tail call erases any debug information about the
- calling function.
- Note that a tail call only happens with a particular syntax,
- where the <b>return</b> has one single function call as argument,
- and it is outside the scope of any to-be-closed variable.
- This syntax makes the calling function return exactly
- the returns of the called function,
- without any intervening action.
- So, none of the following examples are tail calls:
- <pre>
- return (f(x)) -- results adjusted to 1
- return 2 * f(x) -- result multiplied by 2
- return x, f(x) -- additional results
- f(x); return -- results discarded
- return x or f(x) -- results adjusted to 1
- </pre>
- <h3>3.4.11 – <a name="3.4.11">Function Definitions</a></h3>
- <p>
- The syntax for function definition is
- <pre>
- functiondef ::= <b>function</b> funcbody
- funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
- </pre>
- <p>
- The following syntactic sugar simplifies function definitions:
- <pre>
- stat ::= <b>function</b> funcname funcbody
- stat ::= <b>local</b> <b>function</b> Name funcbody
- funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
- </pre><p>
- The statement
- <pre>
- function f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- f = function () <em>body</em> end
- </pre><p>
- The statement
- <pre>
- function t.a.b.c.f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- t.a.b.c.f = function () <em>body</em> end
- </pre><p>
- The statement
- <pre>
- local function f () <em>body</em> end
- </pre><p>
- translates to
- <pre>
- local f; f = function () <em>body</em> end
- </pre><p>
- not to
- <pre>
- local f = function () <em>body</em> end
- </pre><p>
- (This only makes a difference when the body of the function
- contains references to <code>f</code>.)
- <p>
- A function definition is an executable expression,
- whose value has type <em>function</em>.
- When Lua precompiles a chunk,
- all its function bodies are precompiled too,
- but they are not created yet.
- Then, whenever Lua executes the function definition,
- the function is <em>instantiated</em> (or <em>closed</em>).
- This function instance, or <em>closure</em>,
- is the final value of the expression.
- <p>
- Parameters act as local variables that are
- initialized with the argument values:
- <pre>
- parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
- </pre><p>
- When a Lua function is called,
- it adjusts its list of arguments to
- the length of its list of parameters,
- unless the function is a <em>vararg function</em>,
- which is indicated by three dots ('<code>...</code>')
- at the end of its parameter list.
- A vararg function does not adjust its argument list;
- instead, it collects all extra arguments and supplies them
- to the function through a <em>vararg expression</em>,
- which is also written as three dots.
- The value of this expression is a list of all actual extra arguments,
- similar to a function with multiple results.
- If a vararg expression is used inside another expression
- or in the middle of a list of expressions,
- then its return list is adjusted to one element.
- If the expression is used as the last element of a list of expressions,
- then no adjustment is made
- (unless that last expression is enclosed in parentheses).
- <p>
- As an example, consider the following definitions:
- <pre>
- function f(a, b) end
- function g(a, b, ...) end
- function r() return 1,2,3 end
- </pre><p>
- Then, we have the following mapping from arguments to parameters and
- to the vararg expression:
- <pre>
- CALL PARAMETERS
-
- f(3) a=3, b=nil
- f(3, 4) a=3, b=4
- f(3, 4, 5) a=3, b=4
- f(r(), 10) a=1, b=10
- f(r()) a=1, b=2
-
- g(3) a=3, b=nil, ... --> (nothing)
- g(3, 4) a=3, b=4, ... --> (nothing)
- g(3, 4, 5, 8) a=3, b=4, ... --> 5 8
- g(5, r()) a=5, b=1, ... --> 2 3
- </pre>
- <p>
- Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>).
- If control reaches the end of a function
- without encountering a <b>return</b> statement,
- then the function returns with no results.
- <p>
- There is a system-dependent limit on the number of values
- that a function may return.
- This limit is guaranteed to be greater than 1000.
- <p>
- The <em>colon</em> syntax
- is used to emulate <em>methods</em>,
- adding an implicit extra parameter <code>self</code> to the function.
- Thus, the statement
- <pre>
- function t.a.b.c:f (<em>params</em>) <em>body</em> end
- </pre><p>
- is syntactic sugar for
- <pre>
- t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
- </pre>
- <h2>3.5 – <a name="3.5">Visibility Rules</a></h2>
- <p>
- Lua is a lexically scoped language.
- The scope of a local variable begins at the first statement after
- its declaration and lasts until the last non-void statement
- of the innermost block that includes the declaration.
- Consider the following example:
- <pre>
- x = 10 -- global variable
- do -- new block
- local x = x -- new 'x', with value 10
- print(x) --> 10
- x = x+1
- do -- another block
- local x = x+1 -- another 'x'
- print(x) --> 12
- end
- print(x) --> 11
- end
- print(x) --> 10 (the global one)
- </pre>
- <p>
- Notice that, in a declaration like <code>local x = x</code>,
- the new <code>x</code> being declared is not in scope yet,
- and so the second <code>x</code> refers to the outside variable.
- <p>
- Because of the lexical scoping rules,
- local variables can be freely accessed by functions
- defined inside their scope.
- A local variable used by an inner function is called an <em>upvalue</em>
- (or <em>external local variable</em>, or simply <em>external variable</em>)
- inside the inner function.
- <p>
- Notice that each execution of a <b>local</b> statement
- defines new local variables.
- Consider the following example:
- <pre>
- a = {}
- local x = 20
- for i = 1, 10 do
- local y = 0
- a[i] = function () y = y + 1; return x + y end
- end
- </pre><p>
- The loop creates ten closures
- (that is, ten instances of the anonymous function).
- Each of these closures uses a different <code>y</code> variable,
- while all of them share the same <code>x</code>.
- <h1>4 – <a name="4">The Application Program Interface</a></h1>
- <p>
- This section describes the C API for Lua, that is,
- the set of C functions available to the host program to communicate
- with Lua.
- All API functions and related types and constants
- are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
- <p>
- Even when we use the term "function",
- any facility in the API may be provided as a macro instead.
- Except where stated otherwise,
- all such macros use each of their arguments exactly once
- (except for the first argument, which is always a Lua state),
- and so do not generate any hidden side-effects.
- <p>
- As in most C libraries,
- the Lua API functions do not check their arguments
- for validity or consistency.
- However, you can change this behavior by compiling Lua
- with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined.
- <p>
- The Lua library is fully reentrant:
- it has no global variables.
- It keeps all information it needs in a dynamic structure,
- called the <em>Lua state</em>.
- <p>
- Each Lua state has one or more threads,
- which correspond to independent, cooperative lines of execution.
- The type <a href="#lua_State"><code>lua_State</code></a> (despite its name) refers to a thread.
- (Indirectly, through the thread, it also refers to the
- Lua state associated to the thread.)
- <p>
- A pointer to a thread must be passed as the first argument to
- every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
- which creates a Lua state from scratch and returns a pointer
- to the <em>main thread</em> in the new state.
- <h2>4.1 – <a name="4.1">The Stack</a></h2>
- <p>
- Lua uses a <em>virtual stack</em> to pass values to and from C.
- Each element in this stack represents a Lua value
- (<b>nil</b>, number, string, etc.).
- Functions in the API can access this stack through the
- Lua state parameter that they receive.
- <p>
- Whenever Lua calls C, the called function gets a new stack,
- which is independent of previous stacks and of stacks of
- C functions that are still active.
- This stack initially contains any arguments to the C function
- and it is where the C function can store temporary
- Lua values and must push its results
- to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- For convenience,
- most query operations in the API do not follow a strict stack discipline.
- Instead, they can refer to any element in the stack
- by using an <em>index</em>:
- A positive index represents an absolute stack position,
- starting at 1 as the bottom of the stack;
- a negative index represents an offset relative to the top of the stack.
- More specifically, if the stack has <em>n</em> elements,
- then index 1 represents the first element
- (that is, the element that was pushed onto the stack first)
- and
- index <em>n</em> represents the last element;
- index -1 also represents the last element
- (that is, the element at the top)
- and index <em>-n</em> represents the first element.
- <h3>4.1.1 – <a name="4.1.1">Stack Size</a></h3>
- <p>
- When you interact with the Lua API,
- you are responsible for ensuring consistency.
- In particular,
- <em>you are responsible for controlling stack overflow</em>.
- You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
- to ensure that the stack has enough space for pushing new elements.
- <p>
- Whenever Lua calls C,
- it ensures that the stack has space for
- at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots.
- <code>LUA_MINSTACK</code> is defined as 20,
- so that usually you do not have to worry about stack space
- unless your code has loops pushing elements onto the stack.
- <p>
- When you call a Lua function
- without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>),
- Lua ensures that the stack has enough space for all results,
- but it does not ensure any extra space.
- So, before pushing anything in the stack after such a call
- you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
- <h3>4.1.2 – <a name="4.1.2">Valid and Acceptable Indices</a></h3>
- <p>
- Any function in the API that receives stack indices
- works only with <em>valid indices</em> or <em>acceptable indices</em>.
- <p>
- A <em>valid index</em> is an index that refers to a
- position that stores a modifiable Lua value.
- It comprises stack indices between 1 and the stack top
- (<code>1 ≤ abs(index) ≤ top</code>)
- plus <em>pseudo-indices</em>,
- which represent some positions that are accessible to C code
- but that are not in the stack.
- Pseudo-indices are used to access the registry (see <a href="#4.3">§4.3</a>)
- and the upvalues of a C function (see <a href="#4.2">§4.2</a>).
- <p>
- Functions that do not need a specific mutable position,
- but only a value (e.g., query functions),
- can be called with acceptable indices.
- An <em>acceptable index</em> can be any valid index,
- but it also can be any positive index after the stack top
- within the space allocated for the stack,
- that is, indices up to the stack size.
- (Note that 0 is never an acceptable index.)
- Indices to upvalues (see <a href="#4.2">§4.2</a>) greater than the real number
- of upvalues in the current C function are also acceptable (but invalid).
- Except when noted otherwise,
- functions in the API work with acceptable indices.
- <p>
- Acceptable indices serve to avoid extra tests
- against the stack top when querying the stack.
- For instance, a C function can query its third argument
- without the need to check whether there is a third argument,
- that is, without the need to check whether 3 is a valid index.
- <p>
- For functions that can be called with acceptable indices,
- any non-valid index is treated as if it
- contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>,
- which behaves like a nil value.
- <h2>4.2 – <a name="4.2">C Closures</a></h2>
- <p>
- When a C function is created,
- it is possible to associate some values with it,
- thus creating a <em>C closure</em>
- (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>);
- these values are called <em>upvalues</em> and are
- accessible to the function whenever it is called.
- <p>
- Whenever a C function is called,
- its upvalues are located at specific pseudo-indices.
- These pseudo-indices are produced by the macro
- <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>.
- The first upvalue associated with a function is at index
- <code>lua_upvalueindex(1)</code>, and so on.
- Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
- where <em>n</em> is greater than the number of upvalues of the
- current function
- (but not greater than 256,
- which is one plus the maximum number of upvalues in a closure),
- produces an acceptable but invalid index.
- <p>
- A C closure can also change the values
- of its corresponding upvalues.
- <h2>4.3 – <a name="4.3">Registry</a></h2>
- <p>
- Lua provides a <em>registry</em>,
- a predefined table that can be used by any C code to
- store whatever Lua values it needs to store.
- The registry table is always accessible at pseudo-index
- <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>.
- Any C library can store data into this table,
- but it must take care to choose keys
- that are different from those used
- by other libraries, to avoid collisions.
- Typically, you should use as key a string containing your library name,
- or a light userdata with the address of a C object in your code,
- or any Lua object created by your code.
- As with variable names,
- string keys starting with an underscore followed by
- uppercase letters are reserved for Lua.
- <p>
- The integer keys in the registry are used
- by the reference mechanism (see <a href="#luaL_ref"><code>luaL_ref</code></a>)
- and by some predefined values.
- Therefore, integer keys in the registry
- must not be used for other purposes.
- <p>
- When you create a new Lua state,
- its registry comes with some predefined values.
- These predefined values are indexed with integer keys
- defined as constants in <code>lua.h</code>.
- The following constants are defined:
- <ul>
- <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has
- the main thread of the state.
- (The main thread is the one created together with the state.)
- </li>
- <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has
- the global environment.
- </li>
- </ul>
- <h2>4.4 – <a name="4.4">Error Handling in C</a></h2>
- <p>
- Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
- (Lua will use exceptions if you compile it as C++;
- search for <code>LUAI_THROW</code> in the source code for details.)
- When Lua faces any error,
- such as a memory allocation error or a type error,
- it <em>raises</em> an error;
- that is, it does a long jump.
- A <em>protected environment</em> uses <code>setjmp</code>
- to set a recovery point;
- any error jumps to the most recent active recovery point.
- <p>
- Inside a C function you can raise an error explicitly
- by calling <a href="#lua_error"><code>lua_error</code></a>.
- <p>
- Most functions in the API can raise an error,
- for instance due to a memory allocation error.
- The documentation for each function indicates whether
- it can raise errors.
- <p>
- If an error happens outside any protected environment,
- Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>)
- and then calls <code>abort</code>,
- thus exiting the host application.
- Your panic function can avoid this exit by
- never returning
- (e.g., doing a long jump to your own recovery point outside Lua).
- <p>
- The panic function,
- as its name implies,
- is a mechanism of last resort.
- Programs should avoid it.
- As a general rule,
- when a C function is called by Lua with a Lua state,
- it can do whatever it wants on that Lua state,
- as it should be already protected.
- However,
- when C code operates on other Lua states
- (e.g., a Lua-state argument to the function,
- a Lua state stored in the registry, or
- the result of <a href="#lua_newthread"><code>lua_newthread</code></a>),
- it should use them only in API calls that cannot raise errors.
- <p>
- The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>);
- in particular, the error object is on the top of the stack.
- However, there is no guarantee about stack space.
- To push anything on the stack,
- the panic function must first check the available space (see <a href="#4.1.1">§4.1.1</a>).
- <h3>4.4.1 – <a name="4.4.1">Status Codes</a></h3>
- <p>
- Several functions that report errors in the API use the following
- status codes to indicate different kinds of errors or other conditions:
- <ul>
- <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b> no errors.</li>
- <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b> a runtime error.</li>
- <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
- memory allocation error.
- For such errors, Lua does not call the message handler.
- </li>
- <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b> error while running the message handler.</li>
- <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b> syntax error during precompilation.</li>
- <li><b><a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a>: </b> the thread (coroutine) yields.</li>
- <li><b><a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>: </b> a file-related error;
- e.g., it cannot open or read the file.</li>
- </ul><p>
- These constants are defined in the header file <code>lua.h</code>.
- <h2>4.5 – <a name="4.5">Handling Yields in C</a></h2>
- <p>
- Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine.
- Therefore, if a C function <code>foo</code> calls an API function
- and this API function yields
- (directly or indirectly by calling another function that yields),
- Lua cannot return to <code>foo</code> any more,
- because the <code>longjmp</code> removes its frame from the C stack.
- <p>
- To avoid this kind of problem,
- Lua raises an error whenever it tries to yield across an API call,
- except for three functions:
- <a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>.
- All those functions receive a <em>continuation function</em>
- (as a parameter named <code>k</code>) to continue execution after a yield.
- <p>
- We need to set some terminology to explain continuations.
- We have a C function called from Lua which we will call
- the <em>original function</em>.
- This original function then calls one of those three functions in the C API,
- which we will call the <em>callee function</em>,
- that then yields the current thread.
- This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a>
- and the function called by them yields.
- <p>
- Suppose the running thread yields while executing the callee function.
- After the thread resumes,
- it eventually will finish running the callee function.
- However,
- the callee function cannot return to the original function,
- because its frame in the C stack was destroyed by the yield.
- Instead, Lua calls a <em>continuation function</em>,
- which was given as an argument to the callee function.
- As the name implies,
- the continuation function should continue the task
- of the original function.
- <p>
- As an illustration, consider the following function:
- <pre>
- int original_function (lua_State *L) {
- ... /* code 1 */
- status = lua_pcall(L, n, m, h); /* calls Lua */
- ... /* code 2 */
- }
- </pre><p>
- Now we want to allow
- the Lua code being run by <a href="#lua_pcall"><code>lua_pcall</code></a> to yield.
- First, we can rewrite our function like here:
- <pre>
- int k (lua_State *L, int status, lua_KContext ctx) {
- ... /* code 2 */
- }
-
- int original_function (lua_State *L) {
- ... /* code 1 */
- return k(L, lua_pcall(L, n, m, h), ctx);
- }
- </pre><p>
- In the above code,
- the new function <code>k</code> is a
- <em>continuation function</em> (with type <a href="#lua_KFunction"><code>lua_KFunction</code></a>),
- which should do all the work that the original function
- was doing after calling <a href="#lua_pcall"><code>lua_pcall</code></a>.
- Now, we must inform Lua that it must call <code>k</code> if the Lua code
- being executed by <a href="#lua_pcall"><code>lua_pcall</code></a> gets interrupted in some way
- (errors or yielding),
- so we rewrite the code as here,
- replacing <a href="#lua_pcall"><code>lua_pcall</code></a> by <a href="#lua_pcallk"><code>lua_pcallk</code></a>:
- <pre>
- int original_function (lua_State *L) {
- ... /* code 1 */
- return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
- }
- </pre><p>
- Note the external, explicit call to the continuation:
- Lua will call the continuation only if needed, that is,
- in case of errors or resuming after a yield.
- If the called function returns normally without ever yielding,
- <a href="#lua_pcallk"><code>lua_pcallk</code></a> (and <a href="#lua_callk"><code>lua_callk</code></a>) will also return normally.
- (Of course, instead of calling the continuation in that case,
- you can do the equivalent work directly inside the original function.)
- <p>
- Besides the Lua state,
- the continuation function has two other parameters:
- the final status of the call and the context value (<code>ctx</code>) that
- was passed originally to <a href="#lua_pcallk"><code>lua_pcallk</code></a>.
- Lua does not use this context value;
- it only passes this value from the original function to the
- continuation function.
- For <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
- the status is the same value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
- except that it is <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when being executed after a yield
- (instead of <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>).
- For <a href="#lua_yieldk"><code>lua_yieldk</code></a> and <a href="#lua_callk"><code>lua_callk</code></a>,
- the status is always <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when Lua calls the continuation.
- (For these two functions,
- Lua will not call the continuation in case of errors,
- because they do not handle errors.)
- Similarly, when using <a href="#lua_callk"><code>lua_callk</code></a>,
- you should call the continuation function
- with <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> as the status.
- (For <a href="#lua_yieldk"><code>lua_yieldk</code></a>, there is not much point in calling
- directly the continuation function,
- because <a href="#lua_yieldk"><code>lua_yieldk</code></a> usually does not return.)
- <p>
- Lua treats the continuation function as if it were the original function.
- The continuation function receives the same Lua stack
- from the original function,
- in the same state it would be if the callee function had returned.
- (For instance,
- after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are
- removed from the stack and replaced by the results from the call.)
- It also has the same upvalues.
- Whatever it returns is handled by Lua as if it were the return
- of the original function.
- <h2>4.6 – <a name="4.6">Functions and Types</a></h2>
- <p>
- Here we list all functions and types from the C API in
- alphabetical order.
- Each function has an indicator like this:
- <span class="apii">[-o, +p, <em>x</em>]</span>
- <p>
- The first field, <code>o</code>,
- is how many elements the function pops from the stack.
- The second field, <code>p</code>,
- is how many elements the function pushes onto the stack.
- (Any function always pushes its results after popping its arguments.)
- A field in the form <code>x|y</code> means the function can push (or pop)
- <code>x</code> or <code>y</code> elements,
- depending on the situation;
- an interrogation mark '<code>?</code>' means that
- we cannot know how many elements the function pops/pushes
- by looking only at its arguments.
- (For instance, they may depend on what is on the stack.)
- The third field, <code>x</code>,
- tells whether the function may raise errors:
- '<code>-</code>' means the function never raises any error;
- '<code>m</code>' means the function may raise only out-of-memory errors;
- '<code>v</code>' means the function may raise the errors explained in the text;
- '<code>e</code>' means the function can run arbitrary Lua code,
- either directly or through metamethods,
- and therefore may raise any errors.
- <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_absindex (lua_State *L, int idx);</pre>
- <p>
- Converts the acceptable index <code>idx</code>
- into an equivalent absolute index
- (that is, one that does not depend on the stack top).
- <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
- <pre>typedef void * (*lua_Alloc) (void *ud,
- void *ptr,
- size_t osize,
- size_t nsize);</pre>
- <p>
- The type of the memory-allocation function used by Lua states.
- The allocator function must provide a
- functionality similar to <code>realloc</code>,
- but not exactly the same.
- Its arguments are
- <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
- <code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
- <code>osize</code>, the original size of the block or some code about what
- is being allocated;
- and <code>nsize</code>, the new size of the block.
- <p>
- When <code>ptr</code> is not <code>NULL</code>,
- <code>osize</code> is the size of the block pointed by <code>ptr</code>,
- that is, the size given when it was allocated or reallocated.
- <p>
- When <code>ptr</code> is <code>NULL</code>,
- <code>osize</code> encodes the kind of object that Lua is allocating.
- <code>osize</code> is any of
- <a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
- <a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when)
- Lua is creating a new object of that type.
- When <code>osize</code> is some other value,
- Lua is allocating memory for something else.
- <p>
- Lua assumes the following behavior from the allocator function:
- <p>
- When <code>nsize</code> is zero,
- the allocator must behave like <code>free</code>
- and then return <code>NULL</code>.
- <p>
- When <code>nsize</code> is not zero,
- the allocator must behave like <code>realloc</code>.
- In particular, the allocator returns <code>NULL</code>
- if and only if it cannot fulfill the request.
- <p>
- Here is a simple implementation for the allocator function.
- It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
- <pre>
- static void *l_alloc (void *ud, void *ptr, size_t osize,
- size_t nsize) {
- (void)ud; (void)osize; /* not used */
- if (nsize == 0) {
- free(ptr);
- return NULL;
- }
- else
- return realloc(ptr, nsize);
- }
- </pre><p>
- Note that Standard C ensures
- that <code>free(NULL)</code> has no effect and that
- <code>realloc(NULL,size)</code> is equivalent to <code>malloc(size)</code>.
- <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p>
- <span class="apii">[-(2|1), +1, <em>e</em>]</span>
- <pre>void lua_arith (lua_State *L, int op);</pre>
- <p>
- Performs an arithmetic or bitwise operation over the two values
- (or one, in the case of negations)
- at the top of the stack,
- with the value on the top being the second operand,
- pops these values, and pushes the result of the operation.
- The function follows the semantics of the corresponding Lua operator
- (that is, it may call metamethods).
- <p>
- The value of <code>op</code> must be one of the following constants:
- <ul>
- <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li>
- <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li>
- <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li>
- <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs float division (<code>/</code>)</li>
- <li><b><a name="pdf-LUA_OPIDIV"><code>LUA_OPIDIV</code></a>: </b> performs floor division (<code>//</code>)</li>
- <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li>
- <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li>
- <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li>
- <li><b><a name="pdf-LUA_OPBNOT"><code>LUA_OPBNOT</code></a>: </b> performs bitwise NOT (<code>~</code>)</li>
- <li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise AND (<code>&</code>)</li>
- <li><b><a name="pdf-LUA_OPBOR"><code>LUA_OPBOR</code></a>: </b> performs bitwise OR (<code>|</code>)</li>
- <li><b><a name="pdf-LUA_OPBXOR"><code>LUA_OPBXOR</code></a>: </b> performs bitwise exclusive OR (<code>~</code>)</li>
- <li><b><a name="pdf-LUA_OPSHL"><code>LUA_OPSHL</code></a>: </b> performs left shift (<code><<</code>)</li>
- <li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>>></code>)</li>
- </ul>
- <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
- <p>
- Sets a new panic function and returns the old one (see <a href="#4.4">§4.4</a>).
- <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
- <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span>
- <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
- <p>
- Calls a function.
- Like regular Lua calls,
- <code>lua_call</code> respects the <code>__call</code> metamethod.
- So, here the word "function"
- means any callable value.
- <p>
- To do a call you must use the following protocol:
- first, the function to be called is pushed onto the stack;
- then, the arguments to the call are pushed
- in direct order;
- that is, the first argument is pushed first.
- Finally you call <a href="#lua_call"><code>lua_call</code></a>;
- <code>nargs</code> is the number of arguments that you pushed onto the stack.
- When the function returns,
- all arguments and the function value are popped
- and the call results are pushed onto the stack.
- The number of results is adjusted to <code>nresults</code>,
- unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
- In this case, all results from the function are pushed;
- Lua takes care that the returned values fit into the stack space,
- but it does not ensure any extra space in the stack.
- The function results are pushed onto the stack in direct order
- (the first result is pushed first),
- so that after the call the last result is on the top of the stack.
- <p>
- Any error while calling and running the function is propagated upwards
- (with a <code>longjmp</code>).
- <p>
- The following example shows how the host program can do the
- equivalent to this Lua code:
- <pre>
- a = f("how", t.x, 14)
- </pre><p>
- Here it is in C:
- <pre>
- lua_getglobal(L, "f"); /* function to be called */
- lua_pushliteral(L, "how"); /* 1st argument */
- lua_getglobal(L, "t"); /* table to be indexed */
- lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */
- lua_remove(L, -2); /* remove 't' from the stack */
- lua_pushinteger(L, 14); /* 3rd argument */
- lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */
- lua_setglobal(L, "a"); /* set global 'a' */
- </pre><p>
- Note that the code above is <em>balanced</em>:
- at its end, the stack is back to its original configuration.
- This is considered good programming practice.
- <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
- <pre>void lua_callk (lua_State *L,
- int nargs,
- int nresults,
- lua_KContext ctx,
- lua_KFunction k);</pre>
- <p>
- This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>,
- but allows the called function to yield (see <a href="#4.5">§4.5</a>).
- <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
- <pre>typedef int (*lua_CFunction) (lua_State *L);</pre>
- <p>
- Type for C functions.
- <p>
- In order to communicate properly with Lua,
- a C function must use the following protocol,
- which defines the way parameters and results are passed:
- a C function receives its arguments from Lua in its stack
- in direct order (the first argument is pushed first).
- So, when the function starts,
- <code>lua_gettop(L)</code> returns the number of arguments received by the function.
- The first argument (if any) is at index 1
- and its last argument is at index <code>lua_gettop(L)</code>.
- To return values to Lua, a C function just pushes them onto the stack,
- in direct order (the first result is pushed first),
- and returns in C the number of results.
- Any other value in the stack below the results will be properly
- discarded by Lua.
- Like a Lua function, a C function called by Lua can also return
- many results.
- <p>
- As an example, the following function receives a variable number
- of numeric arguments and returns their average and their sum:
- <pre>
- static int foo (lua_State *L) {
- int n = lua_gettop(L); /* number of arguments */
- lua_Number sum = 0.0;
- int i;
- for (i = 1; i <= n; i++) {
- if (!lua_isnumber(L, i)) {
- lua_pushliteral(L, "incorrect argument");
- lua_error(L);
- }
- sum += lua_tonumber(L, i);
- }
- lua_pushnumber(L, sum/n); /* first result */
- lua_pushnumber(L, sum); /* second result */
- return 2; /* number of results */
- }
- </pre>
- <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_checkstack (lua_State *L, int n);</pre>
- <p>
- Ensures that the stack has space for at least <code>n</code> extra slots,
- that is, that you can safely push up to <code>n</code> values into it.
- It returns false if it cannot fulfill the request,
- either because it would cause the stack
- to be greater than a fixed maximum size
- (typically at least several thousand elements) or
- because it cannot allocate memory for the extra space.
- This function never shrinks the stack;
- if the stack already has space for the extra slots,
- it is left unchanged.
- <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_close (lua_State *L);</pre>
- <p>
- Close all active to-be-closed variables in the main thread,
- release all objects in the given Lua state
- (calling the corresponding garbage-collection metamethods, if any),
- and frees all dynamic memory used by this state.
- <p>
- On several platforms, you may not need to call this function,
- because all resources are naturally released when the host program ends.
- On the other hand, long-running programs that create multiple states,
- such as daemons or web servers,
- will probably need to close states as soon as they are not needed.
- <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre>
- <p>
- Compares two Lua values.
- Returns 1 if the value at index <code>index1</code> satisfies <code>op</code>
- when compared with the value at index <code>index2</code>,
- following the semantics of the corresponding Lua operator
- (that is, it may call metamethods).
- Otherwise returns 0.
- Also returns 0 if any of the indices is not valid.
- <p>
- The value of <code>op</code> must be one of the following constants:
- <ul>
- <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li>
- <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li>
- <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li>
- </ul>
- <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
- <span class="apii">[-n, +1, <em>e</em>]</span>
- <pre>void lua_concat (lua_State *L, int n);</pre>
- <p>
- Concatenates the <code>n</code> values at the top of the stack,
- pops them, and leaves the result on the top.
- If <code>n</code> is 1, the result is the single value on the stack
- (that is, the function does nothing);
- if <code>n</code> is 0, the result is the empty string.
- Concatenation is performed following the usual semantics of Lua
- (see <a href="#3.4.6">§3.4.6</a>).
- <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre>
- <p>
- Copies the element at index <code>fromidx</code>
- into the valid index <code>toidx</code>,
- replacing the value at that position.
- Values at other positions are not affected.
- <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
- <p>
- Creates a new empty table and pushes it onto the stack.
- Parameter <code>narr</code> is a hint for how many elements the table
- will have as a sequence;
- parameter <code>nrec</code> is a hint for how many other elements
- the table will have.
- Lua may use these hints to preallocate memory for the new table.
- This preallocation may help performance when you know in advance
- how many elements the table will have.
- Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
- <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_dump (lua_State *L,
- lua_Writer writer,
- void *data,
- int strip);</pre>
- <p>
- Dumps a function as a binary chunk.
- Receives a Lua function on the top of the stack
- and produces a binary chunk that,
- if loaded again,
- results in a function equivalent to the one dumped.
- As it produces parts of the chunk,
- <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
- with the given <code>data</code>
- to write them.
- <p>
- If <code>strip</code> is true,
- the binary representation may not include all debug information
- about the function,
- to save space.
- <p>
- The value returned is the error code returned by the last
- call to the writer;
- 0 means no errors.
- <p>
- This function does not pop the Lua function from the stack.
- <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
- <span class="apii">[-1, +0, <em>v</em>]</span>
- <pre>int lua_error (lua_State *L);</pre>
- <p>
- Raises a Lua error,
- using the value on the top of the stack as the error object.
- This function does a long jump,
- and therefore never returns
- (see <a href="#luaL_error"><code>luaL_error</code></a>).
- <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gc (lua_State *L, int what, ...);</pre>
- <p>
- Controls the garbage collector.
- <p>
- This function performs several tasks,
- according to the value of the parameter <code>what</code>.
- For options that need extra arguments,
- they are listed after the option.
- <ul>
- <li><b><code>LUA_GCCOLLECT</code>: </b>
- Performs a full garbage-collection cycle.
- </li>
- <li><b><code>LUA_GCSTOP</code>: </b>
- Stops the garbage collector.
- </li>
- <li><b><code>LUA_GCRESTART</code>: </b>
- Restarts the garbage collector.
- </li>
- <li><b><code>LUA_GCCOUNT</code>: </b>
- Returns the current amount of memory (in Kbytes) in use by Lua.
- </li>
- <li><b><code>LUA_GCCOUNTB</code>: </b>
- Returns the remainder of dividing the current amount of bytes of
- memory in use by Lua by 1024.
- </li>
- <li><b><code>LUA_GCSTEP</code> <code>(int stepsize)</code>: </b>
- Performs an incremental step of garbage collection,
- corresponding to the allocation of <code>stepsize</code> Kbytes.
- </li>
- <li><b><code>LUA_GCISRUNNING</code>: </b>
- Returns a boolean that tells whether the collector is running
- (i.e., not stopped).
- </li>
- <li><b><code>LUA_GCINC</code> (int pause, int stepmul, stepsize): </b>
- Changes the collector to incremental mode
- with the given parameters (see <a href="#2.5.1">§2.5.1</a>).
- Returns the previous mode (<code>LUA_GCGEN</code> or <code>LUA_GCINC</code>).
- </li>
- <li><b><code>LUA_GCGEN</code> (int minormul, int majormul): </b>
- Changes the collector to generational mode
- with the given parameters (see <a href="#2.5.2">§2.5.2</a>).
- Returns the previous mode (<code>LUA_GCGEN</code> or <code>LUA_GCINC</code>).
- </li>
- </ul><p>
- For more details about these options,
- see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>.
- <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre>
- <p>
- Returns the memory-allocation function of a given state.
- If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
- opaque pointer given when the memory-allocator function was set.
- <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int lua_getfield (lua_State *L, int index, const char *k);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the value at the given index.
- As in Lua, this function may trigger a metamethod
- for the "index" event (see <a href="#2.4">§2.4</a>).
- <p>
- Returns the type of the pushed value.
- <hr><h3><a name="lua_getextraspace"><code>lua_getextraspace</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void *lua_getextraspace (lua_State *L);</pre>
- <p>
- Returns a pointer to a raw memory area associated with the
- given Lua state.
- The application can use this area for any purpose;
- Lua does not use it for anything.
- <p>
- Each new thread has this area initialized with a copy
- of the area of the main thread.
- <p>
- By default, this area has the size of a pointer to void,
- but you can recompile Lua with a different size for this area.
- (See <code>LUA_EXTRASPACE</code> in <code>luaconf.h</code>.)
- <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int lua_getglobal (lua_State *L, const char *name);</pre>
- <p>
- Pushes onto the stack the value of the global <code>name</code>.
- Returns the type of that value.
- <hr><h3><a name="lua_geti"><code>lua_geti</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int lua_geti (lua_State *L, int index, lua_Integer i);</pre>
- <p>
- Pushes onto the stack the value <code>t[i]</code>,
- where <code>t</code> is the value at the given index.
- As in Lua, this function may trigger a metamethod
- for the "index" event (see <a href="#2.4">§2.4</a>).
- <p>
- Returns the type of the pushed value.
- <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>int lua_getmetatable (lua_State *L, int index);</pre>
- <p>
- If the value at the given index has a metatable,
- the function pushes that metatable onto the stack and returns 1.
- Otherwise,
- the function returns 0 and pushes nothing on the stack.
- <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
- <span class="apii">[-1, +1, <em>e</em>]</span>
- <pre>int lua_gettable (lua_State *L, int index);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the value at the given index
- and <code>k</code> is the value on the top of the stack.
- <p>
- This function pops the key from the stack,
- pushing the resulting value in its place.
- As in Lua, this function may trigger a metamethod
- for the "index" event (see <a href="#2.4">§2.4</a>).
- <p>
- Returns the type of the pushed value.
- <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gettop (lua_State *L);</pre>
- <p>
- Returns the index of the top element in the stack.
- Because indices start at 1,
- this result is equal to the number of elements in the stack;
- in particular, 0 means an empty stack.
- <hr><h3><a name="lua_getiuservalue"><code>lua_getiuservalue</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_getiuservalue (lua_State *L, int index, int n);</pre>
- <p>
- Pushes onto the stack the <code>n</code>-th user value associated with the
- full userdata at the given index and
- returns the type of the pushed value.
- <p>
- If the userdata does not have that value,
- pushes <b>nil</b> and returns <a href="#pdf-LUA_TNONE"><code>LUA_TNONE</code></a>.
- <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
- <span class="apii">[-1, +1, –]</span>
- <pre>void lua_insert (lua_State *L, int index);</pre>
- <p>
- Moves the top element into the given valid index,
- shifting up the elements above this index to open space.
- This function cannot be called with a pseudo-index,
- because a pseudo-index is not an actual stack position.
- <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
- <pre>typedef ... lua_Integer;</pre>
- <p>
- The type of integers in Lua.
- <p>
- By default this type is <code>long long</code>,
- (usually a 64-bit two-complement integer),
- but that can be changed to <code>long</code> or <code>int</code>
- (usually a 32-bit two-complement integer).
- (See <code>LUA_INT_TYPE</code> in <code>luaconf.h</code>.)
- <p>
- Lua also defines the constants
- <a name="pdf-LUA_MININTEGER"><code>LUA_MININTEGER</code></a> and <a name="pdf-LUA_MAXINTEGER"><code>LUA_MAXINTEGER</code></a>,
- with the minimum and the maximum values that fit in this type.
- <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isboolean (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a boolean,
- and 0 otherwise.
- <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_iscfunction (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a C function,
- and 0 otherwise.
- <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isfunction (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a function
- (either C or Lua), and 0 otherwise.
- <hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isinteger (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is an integer
- (that is, the value is a number and is represented as an integer),
- and 0 otherwise.
- <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_islightuserdata (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a light userdata,
- and 0 otherwise.
- <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnil (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is <b>nil</b>,
- and 0 otherwise.
- <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnone (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the given index is not valid,
- and 0 otherwise.
- <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnoneornil (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the given index is not valid
- or if the value at this index is <b>nil</b>,
- and 0 otherwise.
- <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isnumber (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a number
- or a string convertible to a number,
- and 0 otherwise.
- <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isstring (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a string
- or a number (which is always convertible to a string),
- and 0 otherwise.
- <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_istable (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a table,
- and 0 otherwise.
- <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isthread (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a thread,
- and 0 otherwise.
- <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isuserdata (lua_State *L, int index);</pre>
- <p>
- Returns 1 if the value at the given index is a userdata
- (either full or light), and 0 otherwise.
- <hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_isyieldable (lua_State *L);</pre>
- <p>
- Returns 1 if the given coroutine can yield,
- and 0 otherwise.
- <hr><h3><a name="lua_KContext"><code>lua_KContext</code></a></h3>
- <pre>typedef ... lua_KContext;</pre>
- <p>
- The type for continuation-function contexts.
- It must be a numeric type.
- This type is defined as <code>intptr_t</code>
- when <code>intptr_t</code> is available,
- so that it can store pointers too.
- Otherwise, it is defined as <code>ptrdiff_t</code>.
- <hr><h3><a name="lua_KFunction"><code>lua_KFunction</code></a></h3>
- <pre>typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);</pre>
- <p>
- Type for continuation functions (see <a href="#4.5">§4.5</a>).
- <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void lua_len (lua_State *L, int index);</pre>
- <p>
- Returns the length of the value at the given index.
- It is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>) and
- may trigger a metamethod for the "length" event (see <a href="#2.4">§2.4</a>).
- The result is pushed on the stack.
- <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_load (lua_State *L,
- lua_Reader reader,
- void *data,
- const char *chunkname,
- const char *mode);</pre>
- <p>
- Loads a Lua chunk without running it.
- If there are no errors,
- <code>lua_load</code> pushes the compiled chunk as a Lua
- function on top of the stack.
- Otherwise, it pushes an error message.
- <p>
- The <code>lua_load</code> function uses a user-supplied <code>reader</code> function
- to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
- The <code>data</code> argument is an opaque value passed to the reader function.
- <p>
- The <code>chunkname</code> argument gives a name to the chunk,
- which is used for error messages and in debug information (see <a href="#4.7">§4.7</a>).
- <p>
- <code>lua_load</code> automatically detects whether the chunk is text or binary
- and loads it accordingly (see program <code>luac</code>).
- The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>,
- with the addition that
- a <code>NULL</code> value is equivalent to the string "<code>bt</code>".
- <p>
- <code>lua_load</code> uses the stack internally,
- so the reader function must always leave the stack
- unmodified when returning.
- <p>
- <code>lua_load</code> can return
- <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>, <a href="#pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>, or <a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>.
- The function may also return other values corresponding to
- errors raised by the read function (see <a href="#4.4.1">§4.4.1</a>).
- <p>
- If the resulting function has upvalues,
- its first upvalue is set to the value of the global environment
- stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.3">§4.3</a>).
- When loading main chunks,
- this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
- Other upvalues are initialized with <b>nil</b>.
- <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre>
- <p>
- Creates a new independent state and returns its main thread.
- Returns <code>NULL</code> if it cannot create the state
- (due to lack of memory).
- The argument <code>f</code> is the allocator function;
- Lua will do all memory allocation for this state
- through this function (see <a href="#lua_Alloc"><code>lua_Alloc</code></a>).
- The second argument, <code>ud</code>, is an opaque pointer that Lua
- passes to the allocator in every call.
- <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void lua_newtable (lua_State *L);</pre>
- <p>
- Creates a new empty table and pushes it onto the stack.
- It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
- <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>lua_State *lua_newthread (lua_State *L);</pre>
- <p>
- Creates a new thread, pushes it on the stack,
- and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
- The new thread returned by this function shares with the original thread
- its global environment,
- but has an independent execution stack.
- <p>
- Threads are subject to garbage collection,
- like any Lua object.
- <hr><h3><a name="lua_newuserdatauv"><code>lua_newuserdatauv</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void *lua_newuserdatauv (lua_State *L, size_t size, int nuvalue);</pre>
- <p>
- This function creates and pushes on the stack a new full userdata,
- with <code>nuvalue</code> associated Lua values, called <code>user values</code>,
- plus an associated block of raw memory with <code>size</code> bytes.
- (The user values can be set and read with the functions
- <a href="#lua_setiuservalue"><code>lua_setiuservalue</code></a> and <a href="#lua_getiuservalue"><code>lua_getiuservalue</code></a>.)
- <p>
- The function returns the address of the block of memory.
- <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
- <span class="apii">[-1, +(2|0), <em>v</em>]</span>
- <pre>int lua_next (lua_State *L, int index);</pre>
- <p>
- Pops a key from the stack,
- and pushes a key–value pair from the table at the given index,
- the "next" pair after the given key.
- If there are no more elements in the table,
- then <a href="#lua_next"><code>lua_next</code></a> returns 0 and pushes nothing.
- <p>
- A typical table traversal looks like this:
- <pre>
- /* table is in the stack at index 't' */
- lua_pushnil(L); /* first key */
- while (lua_next(L, t) != 0) {
- /* uses 'key' (at index -2) and 'value' (at index -1) */
- printf("%s - %s\n",
- lua_typename(L, lua_type(L, -2)),
- lua_typename(L, lua_type(L, -1)));
- /* removes 'value'; keeps 'key' for next iteration */
- lua_pop(L, 1);
- }
- </pre>
- <p>
- While traversing a table,
- avoid calling <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
- unless you know that the key is actually a string.
- Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change
- the value at the given index;
- this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
- <p>
- This function may raise an error if the given key
- is neither <b>nil</b> nor present in the table.
- See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
- the table during its traversal.
- <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
- <pre>typedef ... lua_Number;</pre>
- <p>
- The type of floats in Lua.
- <p>
- By default this type is double,
- but that can be changed to a single float or a long double.
- (See <code>LUA_FLOAT_TYPE</code> in <code>luaconf.h</code>.)
- <hr><h3><a name="lua_numbertointeger"><code>lua_numbertointeger</code></a></h3>
- <pre>int lua_numbertointeger (lua_Number n, lua_Integer *p);</pre>
- <p>
- Tries to convert a Lua float to a Lua integer;
- the float <code>n</code> must have an integral value.
- If that value is within the range of Lua integers,
- it is converted to an integer and assigned to <code>*p</code>.
- The macro results in a boolean indicating whether the
- conversion was successful.
- (Note that this range test can be tricky to do
- correctly without this macro, due to rounding.)
- <p>
- This macro may evaluate its arguments more than once.
- <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
- <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre>
- <p>
- Calls a function (or a callable object) in protected mode.
- <p>
- Both <code>nargs</code> and <code>nresults</code> have the same meaning as
- in <a href="#lua_call"><code>lua_call</code></a>.
- If there are no errors during the call,
- <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
- However, if there is any error,
- <a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
- pushes a single value on the stack (the error object),
- and returns an error code.
- Like <a href="#lua_call"><code>lua_call</code></a>,
- <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
- and its arguments from the stack.
- <p>
- If <code>msgh</code> is 0,
- then the error object returned on the stack
- is exactly the original error object.
- Otherwise, <code>msgh</code> is the stack index of a
- <em>message handler</em>.
- (This index cannot be a pseudo-index.)
- In case of runtime errors,
- this handler will be called with the error object
- and its return value will be the object
- returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
- <p>
- Typically, the message handler is used to add more debug
- information to the error object, such as a stack traceback.
- Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
- since by then the stack has unwound.
- <p>
- The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following status codes:
- <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>, <a href="#pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>, <a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>, or <a href="#pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>.
- <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p>
- <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
- <pre>int lua_pcallk (lua_State *L,
- int nargs,
- int nresults,
- int msgh,
- lua_KContext ctx,
- lua_KFunction k);</pre>
- <p>
- This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>,
- except that it allows the called function to yield (see <a href="#4.5">§4.5</a>).
- <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
- <span class="apii">[-n, +0, –]</span>
- <pre>void lua_pop (lua_State *L, int n);</pre>
- <p>
- Pops <code>n</code> elements from the stack.
- <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushboolean (lua_State *L, int b);</pre>
- <p>
- Pushes a boolean value with value <code>b</code> onto the stack.
- <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
- <span class="apii">[-n, +1, <em>m</em>]</span>
- <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
- <p>
- Pushes a new C closure onto the stack.
- This function receives a pointer to a C function
- and pushes onto the stack a Lua value of type <code>function</code> that,
- when called, invokes the corresponding C function.
- The parameter <code>n</code> tells how many upvalues this function will have
- (see <a href="#4.2">§4.2</a>).
- <p>
- Any function to be callable by Lua must
- follow the correct protocol to receive its parameters
- and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- When a C function is created,
- it is possible to associate some values with it,
- the so called upvalues;
- these upvalues are then accessible to the function whenever it is called.
- This association is called a C closure (see <a href="#4.2">§4.2</a>).
- To create a C closure,
- first the initial values for its upvalues must be pushed onto the stack.
- (When there are multiple upvalues, the first value is pushed first.)
- Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
- is called to create and push the C function onto the stack,
- with the argument <code>n</code> telling how many values will be
- associated with the function.
- <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
- <p>
- The maximum value for <code>n</code> is 255.
- <p>
- When <code>n</code> is zero,
- this function creates a <em>light C function</em>,
- which is just a pointer to the C function.
- In that case, it never raises a memory error.
- <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
- <p>
- Pushes a C function onto the stack.
- This function is equivalent to <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> with no upvalues.
- <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>v</em>]</span>
- <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre>
- <p>
- Pushes onto the stack a formatted string
- and returns a pointer to this string.
- It is similar to the ISO C function <code>sprintf</code>,
- but has two important differences.
- First,
- you do not have to allocate space for the result;
- the result is a Lua string and Lua takes care of memory allocation
- (and deallocation, through garbage collection).
- Second,
- the conversion specifiers are quite restricted.
- There are no flags, widths, or precisions.
- The conversion specifiers can only be
- '<code>%%</code>' (inserts the character '<code>%</code>'),
- '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
- '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
- '<code>%I</code>' (inserts a <a href="#lua_Integer"><code>lua_Integer</code></a>),
- '<code>%p</code>' (inserts a pointer),
- '<code>%d</code>' (inserts an <code>int</code>),
- '<code>%c</code>' (inserts an <code>int</code> as a one-byte character), and
- '<code>%U</code>' (inserts a <code>long int</code> as a UTF-8 byte sequence).
- <p>
- This function may raise errors due to memory overflow
- or an invalid conversion specifier.
- <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushglobaltable (lua_State *L);</pre>
- <p>
- Pushes the global environment onto the stack.
- <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
- <p>
- Pushes an integer with value <code>n</code> onto the stack.
- <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
- <p>
- Pushes a light userdata onto the stack.
- <p>
- Userdata represent C values in Lua.
- A <em>light userdata</em> represents a pointer, a <code>void*</code>.
- It is a value (like a number):
- you do not create it, it has no individual metatable,
- and it is not collected (as it was never created).
- A light userdata is equal to "any"
- light userdata with the same C address.
- <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre>
- <p>
- This macro is equivalent to <a href="#lua_pushstring"><code>lua_pushstring</code></a>,
- but should be used only when <code>s</code> is a literal string.
- (Lua may optimize this case.)
- <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre>
- <p>
- Pushes the string pointed to by <code>s</code> with size <code>len</code>
- onto the stack.
- Lua will make or reuse an internal copy of the given string,
- so the memory at <code>s</code> can be freed or reused immediately after
- the function returns.
- The string can contain any binary data,
- including embedded zeros.
- <p>
- Returns a pointer to the internal copy of the string.
- <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushnil (lua_State *L);</pre>
- <p>
- Pushes a nil value onto the stack.
- <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
- <p>
- Pushes a float with value <code>n</code> onto the stack.
- <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre>
- <p>
- Pushes the zero-terminated string pointed to by <code>s</code>
- onto the stack.
- Lua will make or reuse an internal copy of the given string,
- so the memory at <code>s</code> can be freed or reused immediately after
- the function returns.
- <p>
- Returns a pointer to the internal copy of the string.
- <p>
- If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>.
- <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_pushthread (lua_State *L);</pre>
- <p>
- Pushes the thread represented by <code>L</code> onto the stack.
- Returns 1 if this thread is the main thread of its state.
- <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void lua_pushvalue (lua_State *L, int index);</pre>
- <p>
- Pushes a copy of the element at the given index
- onto the stack.
- <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>v</em>]</span>
- <pre>const char *lua_pushvfstring (lua_State *L,
- const char *fmt,
- va_list argp);</pre>
- <p>
- Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
- instead of a variable number of arguments.
- <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
- <p>
- Returns 1 if the two values in indices <code>index1</code> and
- <code>index2</code> are primitively equal
- (that is, equal without calling the <code>__eq</code> metamethod).
- Otherwise returns 0.
- Also returns 0 if any of the indices are not valid.
- <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
- <span class="apii">[-1, +1, –]</span>
- <pre>int lua_rawget (lua_State *L, int index);</pre>
- <p>
- Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
- (i.e., without metamethods).
- <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_rawgeti (lua_State *L, int index, lua_Integer n);</pre>
- <p>
- Pushes onto the stack the value <code>t[n]</code>,
- where <code>t</code> is the table at the given index.
- The access is raw,
- that is, it does not use the <code>__index</code> metavalue.
- <p>
- Returns the type of the pushed value.
- <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int lua_rawgetp (lua_State *L, int index, const void *p);</pre>
- <p>
- Pushes onto the stack the value <code>t[k]</code>,
- where <code>t</code> is the table at the given index and
- <code>k</code> is the pointer <code>p</code> represented as a light userdata.
- The access is raw;
- that is, it does not use the <code>__index</code> metavalue.
- <p>
- Returns the type of the pushed value.
- <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Unsigned lua_rawlen (lua_State *L, int index);</pre>
- <p>
- Returns the raw "length" of the value at the given index:
- for strings, this is the string length;
- for tables, this is the result of the length operator ('<code>#</code>')
- with no metamethods;
- for userdata, this is the size of the block of memory allocated
- for the userdata.
- For other values, this call returns 0.
- <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
- <span class="apii">[-2, +0, <em>m</em>]</span>
- <pre>void lua_rawset (lua_State *L, int index);</pre>
- <p>
- Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
- (i.e., without metamethods).
- <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
- <span class="apii">[-1, +0, <em>m</em>]</span>
- <pre>void lua_rawseti (lua_State *L, int index, lua_Integer i);</pre>
- <p>
- Does the equivalent of <code>t[i] = v</code>,
- where <code>t</code> is the table at the given index
- and <code>v</code> is the value on the top of the stack.
- <p>
- This function pops the value from the stack.
- The assignment is raw,
- that is, it does not use the <code>__newindex</code> metavalue.
- <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
- <span class="apii">[-1, +0, <em>m</em>]</span>
- <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre>
- <p>
- Does the equivalent of <code>t[p] = v</code>,
- where <code>t</code> is the table at the given index,
- <code>p</code> is encoded as a light userdata,
- and <code>v</code> is the value on the top of the stack.
- <p>
- This function pops the value from the stack.
- The assignment is raw,
- that is, it does not use the <code>__newindex</code> metavalue.
- <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
- <pre>typedef const char * (*lua_Reader) (lua_State *L,
- void *data,
- size_t *size);</pre>
- <p>
- The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
- Every time <a href="#lua_load"><code>lua_load</code></a> needs another piece of the chunk,
- it calls the reader,
- passing along its <code>data</code> parameter.
- The reader must return a pointer to a block of memory
- with a new piece of the chunk
- and set <code>size</code> to the block size.
- The block must exist until the reader function is called again.
- To signal the end of the chunk,
- the reader must return <code>NULL</code> or set <code>size</code> to zero.
- The reader function may return pieces of any size greater than zero.
- <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre>
- <p>
- Sets the C function <code>f</code> as the new value of global <code>name</code>.
- It is defined as a macro:
- <pre>
- #define lua_register(L,n,f) \
- (lua_pushcfunction(L, f), lua_setglobal(L, n))
- </pre>
- <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_remove (lua_State *L, int index);</pre>
- <p>
- Removes the element at the given valid index,
- shifting down the elements above this index to fill the gap.
- This function cannot be called with a pseudo-index,
- because a pseudo-index is not an actual stack position.
- <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>void lua_replace (lua_State *L, int index);</pre>
- <p>
- Moves the top element into the given valid index
- without shifting any element
- (therefore replacing the value at that given index),
- and then pops the top element.
- <hr><h3><a name="lua_resetthread"><code>lua_resetthread</code></a></h3><p>
- <span class="apii">[-0, +?, –]</span>
- <pre>int lua_resetthread (lua_State *L);</pre>
- <p>
- Resets a thread, cleaning its call stack and closing all pending
- to-be-closed variables.
- Returns a status code:
- <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> for no errors in closing methods,
- or an error status otherwise.
- In case of error,
- leaves the error object on the top of the stack,
- <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>int lua_resume (lua_State *L, lua_State *from, int nargs,
- int *nresults);</pre>
- <p>
- Starts and resumes a coroutine in the given thread <code>L</code>.
- <p>
- To start a coroutine,
- you push the main function plus any arguments
- onto the empty stack of the thread.
- then you call <a href="#lua_resume"><code>lua_resume</code></a>,
- with <code>nargs</code> being the number of arguments.
- This call returns when the coroutine suspends or finishes its execution.
- When it returns,
- <code>*nresults</code> is updated and
- the top of the stack contains
- the <code>*nresults</code> values passed to <a href="#lua_yield"><code>lua_yield</code></a>
- or returned by the body function.
- <a href="#lua_resume"><code>lua_resume</code></a> returns
- <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
- <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution
- without errors,
- or an error code in case of errors (see <a href="#4.4.1">§4.4.1</a>).
- In case of errors,
- the error object is on the top of the stack.
- <p>
- To resume a coroutine,
- you remove the <code>*nresults</code> yielded values from its stack,
- push the values to be passed as results from <code>yield</code>,
- and then call <a href="#lua_resume"><code>lua_resume</code></a>.
- <p>
- The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>.
- If there is no such coroutine,
- this parameter can be <code>NULL</code>.
- <hr><h3><a name="lua_rotate"><code>lua_rotate</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_rotate (lua_State *L, int idx, int n);</pre>
- <p>
- Rotates the stack elements between the valid index <code>idx</code>
- and the top of the stack.
- The elements are rotated <code>n</code> positions in the direction of the top,
- for a positive <code>n</code>,
- or <code>-n</code> positions in the direction of the bottom,
- for a negative <code>n</code>.
- The absolute value of <code>n</code> must not be greater than the size
- of the slice being rotated.
- This function cannot be called with a pseudo-index,
- because a pseudo-index is not an actual stack position.
- <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre>
- <p>
- Changes the allocator function of a given state to <code>f</code>
- with user data <code>ud</code>.
- <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
- <p>
- Does the equivalent to <code>t[k] = v</code>,
- where <code>t</code> is the value at the given index
- and <code>v</code> is the value on the top of the stack.
- <p>
- This function pops the value from the stack.
- As in Lua, this function may trigger a metamethod
- for the "newindex" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_setglobal (lua_State *L, const char *name);</pre>
- <p>
- Pops a value from the stack and
- sets it as the new value of global <code>name</code>.
- <hr><h3><a name="lua_seti"><code>lua_seti</code></a></h3><p>
- <span class="apii">[-1, +0, <em>e</em>]</span>
- <pre>void lua_seti (lua_State *L, int index, lua_Integer n);</pre>
- <p>
- Does the equivalent to <code>t[n] = v</code>,
- where <code>t</code> is the value at the given index
- and <code>v</code> is the value on the top of the stack.
- <p>
- This function pops the value from the stack.
- As in Lua, this function may trigger a metamethod
- for the "newindex" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_setiuservalue"><code>lua_setiuservalue</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>int lua_setiuservalue (lua_State *L, int index, int n);</pre>
- <p>
- Pops a value from the stack and sets it as
- the new <code>n</code>-th user value associated to the
- full userdata at the given index.
- Returns 0 if the userdata does not have that value.
- <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
- <span class="apii">[-1, +0, –]</span>
- <pre>int lua_setmetatable (lua_State *L, int index);</pre>
- <p>
- Pops a table or <b>nil</b> from the stack and
- sets that value as the new metatable for the value at the given index.
- (<b>nil</b> means no metatable.)
- <p>
- (For historical reasons, this function returns an <code>int</code>,
- which now is always 1.)
- <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
- <span class="apii">[-2, +0, <em>e</em>]</span>
- <pre>void lua_settable (lua_State *L, int index);</pre>
- <p>
- Does the equivalent to <code>t[k] = v</code>,
- where <code>t</code> is the value at the given index,
- <code>v</code> is the value on the top of the stack,
- and <code>k</code> is the value just below the top.
- <p>
- This function pops both the key and the value from the stack.
- As in Lua, this function may trigger a metamethod
- for the "newindex" event (see <a href="#2.4">§2.4</a>).
- <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>void lua_settop (lua_State *L, int index);</pre>
- <p>
- Accepts any index, or 0,
- and sets the stack top to this index.
- If the new top is greater than the old one,
- then the new elements are filled with <b>nil</b>.
- If <code>index</code> is 0, then all stack elements are removed.
- <hr><h3><a name="lua_setwarnf"><code>lua_setwarnf</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_setwarnf (lua_State *L, lua_WarnFunction f, void *ud);</pre>
- <p>
- Sets the warning function to be used by Lua to emit warnings
- (see <a href="#lua_WarnFunction"><code>lua_WarnFunction</code></a>).
- The <code>ud</code> parameter sets the value <code>ud</code> passed to
- the warning function.
- <hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
- <pre>typedef struct lua_State lua_State;</pre>
- <p>
- An opaque structure that points to a thread and indirectly
- (through the thread) to the whole state of a Lua interpreter.
- The Lua library is fully reentrant:
- it has no global variables.
- All information about a state is accessible through this structure.
- <p>
- A pointer to this structure must be passed as the first argument to
- every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
- which creates a Lua state from scratch.
- <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_status (lua_State *L);</pre>
- <p>
- Returns the status of the thread <code>L</code>.
- <p>
- The status can be <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> for a normal thread,
- an error code if the thread finished the execution
- of a <a href="#lua_resume"><code>lua_resume</code></a> with an error,
- or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
- <p>
- You can call functions only in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>.
- You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
- (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a>
- (to resume a coroutine).
- <hr><h3><a name="lua_stringtonumber"><code>lua_stringtonumber</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>size_t lua_stringtonumber (lua_State *L, const char *s);</pre>
- <p>
- Converts the zero-terminated string <code>s</code> to a number,
- pushes that number into the stack,
- and returns the total size of the string,
- that is, its length plus one.
- The conversion can result in an integer or a float,
- according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>).
- The string may have leading and trailing whitespaces and a sign.
- If the string is not a valid numeral,
- returns 0 and pushes nothing.
- (Note that the result can be used as a boolean,
- true if the conversion succeeds.)
- <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_toboolean (lua_State *L, int index);</pre>
- <p>
- Converts the Lua value at the given index to a C boolean
- value (0 or 1).
- Like all tests in Lua,
- <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value
- different from <b>false</b> and <b>nil</b>;
- otherwise it returns false.
- (If you want to accept only actual boolean values,
- use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
- <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
- <p>
- Converts a value at the given index to a C function.
- That value must be a C function;
- otherwise, returns <code>NULL</code>.
- <hr><h3><a name="lua_toclose"><code>lua_toclose</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void lua_toclose (lua_State *L, int index);</pre>
- <p>
- Marks the given index in the stack as a
- to-be-closed "variable" (see <a href="#3.3.8">§3.3.8</a>).
- Like a to-be-closed variable in Lua,
- the value at that index in the stack will be closed
- when it goes out of scope.
- Here, in the context of a C function,
- to go out of scope means that the running function returns to Lua,
- there is an error,
- or the index is removed from the stack through
- <a href="#lua_settop"><code>lua_settop</code></a> or <a href="#lua_pop"><code>lua_pop</code></a>.
- An index marked as to-be-closed should not be removed from the stack
- by any other function in the API except <a href="#lua_settop"><code>lua_settop</code></a> or <a href="#lua_pop"><code>lua_pop</code></a>.
- <p>
- This function should not be called for an index
- that is equal to or below an active to-be-closed index.
- <p>
- This function can raise an out-of-memory error.
- In that case, the value in the given index is immediately closed,
- as if it was already marked.
- <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre>
- <p>
- Converts the Lua value at the given index
- to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
- The Lua value must be an integer,
- or a number or string convertible to an integer (see <a href="#3.4.3">§3.4.3</a>);
- otherwise, <code>lua_tointegerx</code> returns 0.
- <p>
- If <code>isnum</code> is not <code>NULL</code>,
- its referent is assigned a boolean value that
- indicates whether the operation succeeded.
- <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>m</em>]</span>
- <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre>
- <p>
- Converts the Lua value at the given index to a C string.
- If <code>len</code> is not <code>NULL</code>,
- it sets <code>*len</code> with the string length.
- The Lua value must be a string or a number;
- otherwise, the function returns <code>NULL</code>.
- If the value is a number,
- then <code>lua_tolstring</code> also
- <em>changes the actual value in the stack to a string</em>.
- (This change confuses <a href="#lua_next"><code>lua_next</code></a>
- when <code>lua_tolstring</code> is applied to keys during a table traversal.)
- <p>
- <code>lua_tolstring</code> returns a pointer
- to a string inside the Lua state.
- This string always has a zero ('<code>\0</code>')
- after its last character (as in C),
- but can contain other zeros in its body.
- <p>
- Because Lua has garbage collection,
- there is no guarantee that the pointer returned by <code>lua_tolstring</code>
- will be valid after the corresponding Lua value is removed from the stack.
- <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre>
- <p>
- Converts the Lua value at the given index
- to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
- The Lua value must be a number or a string convertible to a number
- (see <a href="#3.4.3">§3.4.3</a>);
- otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0.
- <p>
- If <code>isnum</code> is not <code>NULL</code>,
- its referent is assigned a boolean value that
- indicates whether the operation succeeded.
- <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const void *lua_topointer (lua_State *L, int index);</pre>
- <p>
- Converts the value at the given index to a generic
- C pointer (<code>void*</code>).
- The value can be a userdata, a table, a thread, a string, or a function;
- otherwise, <code>lua_topointer</code> returns <code>NULL</code>.
- Different objects will give different pointers.
- There is no way to convert the pointer back to its original value.
- <p>
- Typically this function is used only for hashing and debug information.
- <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>m</em>]</span>
- <pre>const char *lua_tostring (lua_State *L, int index);</pre>
- <p>
- Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
- <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *lua_tothread (lua_State *L, int index);</pre>
- <p>
- Converts the value at the given index to a Lua thread
- (represented as <code>lua_State*</code>).
- This value must be a thread;
- otherwise, the function returns <code>NULL</code>.
- <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void *lua_touserdata (lua_State *L, int index);</pre>
- <p>
- If the value at the given index is a full userdata,
- returns its memory-block address.
- If the value is a light userdata,
- returns its value (a pointer).
- Otherwise, returns <code>NULL</code>.
- <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_type (lua_State *L, int index);</pre>
- <p>
- Returns the type of the value in the given valid index,
- or <code>LUA_TNONE</code> for a non-valid but acceptable index.
- The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
- defined in <code>lua.h</code>:
- <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>,
- <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>,
- <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>,
- <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>,
- <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>,
- <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
- <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>,
- <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>,
- and
- <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>.
- <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const char *lua_typename (lua_State *L, int tp);</pre>
- <p>
- Returns the name of the type encoded by the value <code>tp</code>,
- which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
- <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3>
- <pre>typedef ... lua_Unsigned;</pre>
- <p>
- The unsigned version of <a href="#lua_Integer"><code>lua_Integer</code></a>.
- <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_upvalueindex (int i);</pre>
- <p>
- Returns the pseudo-index that represents the <code>i</code>-th upvalue of
- the running function (see <a href="#4.2">§4.2</a>).
- <code>i</code> must be in the range <em>[1,256]</em>.
- <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Number lua_version (lua_State *L);</pre>
- <p>
- Returns the version number of this core.
- <hr><h3><a name="lua_WarnFunction"><code>lua_WarnFunction</code></a></h3>
- <pre>typedef void (*lua_WarnFunction) (void *ud, const char *msg, int tocont);</pre>
- <p>
- The type of warning functions, called by Lua to emit warnings.
- The first parameter is an opaque pointer
- set by <a href="#lua_setwarnf"><code>lua_setwarnf</code></a>.
- The second parameter is the warning message.
- The third parameter is a boolean that
- indicates whether the message is
- to be continued by the message in the next call.
- <p>
- See <a href="#pdf-warn"><code>warn</code></a> for more details about warnings.
- <hr><h3><a name="lua_warning"><code>lua_warning</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_warning (lua_State *L, const char *msg, int tocont);</pre>
- <p>
- Emits a warning with the given message.
- A message in a call with <code>tocont</code> true should be
- continued in another call to this function.
- <p>
- See <a href="#pdf-warn"><code>warn</code></a> for more details about warnings.
- <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
- <pre>typedef int (*lua_Writer) (lua_State *L,
- const void* p,
- size_t sz,
- void* ud);</pre>
- <p>
- The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
- Every time <a href="#lua_dump"><code>lua_dump</code></a> produces another piece of chunk,
- it calls the writer,
- passing along the buffer to be written (<code>p</code>),
- its size (<code>sz</code>),
- and the <code>ud</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
- <p>
- The writer returns an error code:
- 0 means no errors;
- any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
- calling the writer again.
- <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre>
- <p>
- Exchange values between different threads of the same state.
- <p>
- This function pops <code>n</code> values from the stack <code>from</code>,
- and pushes them onto the stack <code>to</code>.
- <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
- <span class="apii">[-?, +?, <em>v</em>]</span>
- <pre>int lua_yield (lua_State *L, int nresults);</pre>
- <p>
- This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- but it has no continuation (see <a href="#4.5">§4.5</a>).
- Therefore, when the thread resumes,
- it continues the function that called
- the function calling <code>lua_yield</code>.
- To avoid surprises,
- this function should be called only in a tail call.
- <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p>
- <span class="apii">[-?, +?, <em>v</em>]</span>
- <pre>int lua_yieldk (lua_State *L,
- int nresults,
- lua_KContext ctx,
- lua_KFunction k);</pre>
- <p>
- Yields a coroutine (thread).
- <p>
- When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- the running coroutine suspends its execution,
- and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
- The parameter <code>nresults</code> is the number of values from the stack
- that will be passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
- <p>
- When the coroutine is resumed again,
- Lua calls the given continuation function <code>k</code> to continue
- the execution of the C function that yielded (see <a href="#4.5">§4.5</a>).
- This continuation function receives the same stack
- from the previous function,
- with the <code>n</code> results removed and
- replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>.
- Moreover,
- the continuation function receives the value <code>ctx</code>
- that was passed to <a href="#lua_yieldk"><code>lua_yieldk</code></a>.
- <p>
- Usually, this function does not return;
- when the coroutine eventually resumes,
- it continues executing the continuation function.
- However, there is one special case,
- which is when this function is called
- from inside a line or a count hook (see <a href="#4.7">§4.7</a>).
- In that case, <code>lua_yieldk</code> should be called with no continuation
- (probably in the form of <a href="#lua_yield"><code>lua_yield</code></a>) and no results,
- and the hook should return immediately after the call.
- Lua will yield and,
- when the coroutine resumes again,
- it will continue the normal execution
- of the (Lua) function that triggered the hook.
- <p>
- This function can raise an error if it is called from a thread
- with a pending C call with no continuation function
- (what is called a <em>C-call boundary</em>),
- or it is called from a thread that is not running inside a resume
- (typically the main thread).
- <h2>4.7 – <a name="4.7">The Debug Interface</a></h2>
- <p>
- Lua has no built-in debugging facilities.
- Instead, it offers a special interface
- by means of functions and <em>hooks</em>.
- This interface allows the construction of different
- kinds of debuggers, profilers, and other tools
- that need "inside information" from the interpreter.
- <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
- <pre>typedef struct lua_Debug {
- int event;
- const char *name; /* (n) */
- const char *namewhat; /* (n) */
- const char *what; /* (S) */
- const char *source; /* (S) */
- size_t srclen; /* (S) */
- int currentline; /* (l) */
- int linedefined; /* (S) */
- int lastlinedefined; /* (S) */
- unsigned char nups; /* (u) number of upvalues */
- unsigned char nparams; /* (u) number of parameters */
- char isvararg; /* (u) */
- char istailcall; /* (t) */
- unsigned short ftransfer; /* (r) index of first value transferred */
- unsigned short ntransfer; /* (r) number of transferred values */
- char short_src[LUA_IDSIZE]; /* (S) */
- /* private part */
- <em>other fields</em>
- } lua_Debug;</pre>
- <p>
- A structure used to carry different pieces of
- information about a function or an activation record.
- <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
- of this structure, for later use.
- To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
- you must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
- <p>
- The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
- <ul>
- <li><b><code>source</code>: </b>
- the source of the chunk that created the function.
- If <code>source</code> starts with a '<code>@</code>',
- it means that the function was defined in a file where
- the file name follows the '<code>@</code>'.
- If <code>source</code> starts with a '<code>=</code>',
- the remainder of its contents describes the source in a user-dependent manner.
- Otherwise,
- the function was defined in a string where
- <code>source</code> is that string.
- </li>
- <li><b><code>srclen</code>: </b>
- The length of the string <code>source</code>.
- </li>
- <li><b><code>short_src</code>: </b>
- a "printable" version of <code>source</code>, to be used in error messages.
- </li>
- <li><b><code>linedefined</code>: </b>
- the line number where the definition of the function starts.
- </li>
- <li><b><code>lastlinedefined</code>: </b>
- the line number where the definition of the function ends.
- </li>
- <li><b><code>what</code>: </b>
- the string <code>"Lua"</code> if the function is a Lua function,
- <code>"C"</code> if it is a C function,
- <code>"main"</code> if it is the main part of a chunk.
- </li>
- <li><b><code>currentline</code>: </b>
- the current line where the given function is executing.
- When no line information is available,
- <code>currentline</code> is set to -1.
- </li>
- <li><b><code>name</code>: </b>
- a reasonable name for the given function.
- Because functions in Lua are first-class values,
- they do not have a fixed name:
- some functions can be the value of multiple global variables,
- while others can be stored only in a table field.
- The <code>lua_getinfo</code> function checks how the function was
- called to find a suitable name.
- If it cannot find a name,
- then <code>name</code> is set to <code>NULL</code>.
- </li>
- <li><b><code>namewhat</code>: </b>
- explains the <code>name</code> field.
- The value of <code>namewhat</code> can be
- <code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
- <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
- according to how the function was called.
- (Lua uses the empty string when no other option seems to apply.)
- </li>
- <li><b><code>istailcall</code>: </b>
- true if this function invocation was called by a tail call.
- In this case, the caller of this level is not in the stack.
- </li>
- <li><b><code>nups</code>: </b>
- the number of upvalues of the function.
- </li>
- <li><b><code>nparams</code>: </b>
- the number of parameters of the function
- (always 0 for C functions).
- </li>
- <li><b><code>isvararg</code>: </b>
- true if the function is a vararg function
- (always true for C functions).
- </li>
- <li><b><code>ftransfer</code>: </b>
- the index on the stack of the first value being "transferred",
- that is, parameters in a call or return values in a return.
- (The other values are in consecutive indices.)
- Using this index, you can access and modify these values
- through <a href="#lua_getlocal"><code>lua_getlocal</code></a> and <a href="#lua_setlocal"><code>lua_setlocal</code></a>.
- This field is only meaningful during a
- call hook, denoting the first parameter,
- or a return hook, denoting the first value being returned.
- (For call hooks, this value is always 1.)
- </li>
- <li><b><code>ntransfer</code>: </b>
- The number of values being transferred (see previous item).
- (For calls of Lua functions,
- this value is always equal to <code>nparams</code>.)
- </li>
- </ul>
- <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_Hook lua_gethook (lua_State *L);</pre>
- <p>
- Returns the current hook function.
- <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gethookcount (lua_State *L);</pre>
- <p>
- Returns the current hook count.
- <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_gethookmask (lua_State *L);</pre>
- <p>
- Returns the current hook mask.
- <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
- <span class="apii">[-(0|1), +(0|1|2), <em>m</em>]</span>
- <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre>
- <p>
- Gets information about a specific function or function invocation.
- <p>
- To get information about a function invocation,
- the parameter <code>ar</code> must be a valid activation record that was
- filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
- given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
- <p>
- To get information about a function, you push it onto the stack
- and start the <code>what</code> string with the character '<code>></code>'.
- (In that case,
- <code>lua_getinfo</code> pops the function from the top of the stack.)
- For instance, to know in which line a function <code>f</code> was defined,
- you can write the following code:
- <pre>
- lua_Debug ar;
- lua_getglobal(L, "f"); /* get global 'f' */
- lua_getinfo(L, ">S", &ar);
- printf("%d\n", ar.linedefined);
- </pre>
- <p>
- Each character in the string <code>what</code>
- selects some fields of the structure <code>ar</code> to be filled or
- a value to be pushed on the stack:
- <ul>
- <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>;
- </li>
- <li><b>'<code>S</code>': </b>
- fills in the fields <code>source</code>, <code>short_src</code>,
- <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
- </li>
- <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>;
- </li>
- <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>;
- </li>
- <li><b>'<code>u</code>': </b> fills in the fields
- <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>;
- </li>
- <li><b>'<code>f</code>': </b>
- pushes onto the stack the function that is
- running at the given level;
- </li>
- <li><b>'<code>L</code>': </b>
- pushes onto the stack a table whose indices are the
- numbers of the lines that are valid on the function.
- (A <em>valid line</em> is a line with some associated code,
- that is, a line where you can put a break point.
- Non-valid lines include empty lines and comments.)
- <p>
- If this option is given together with option '<code>f</code>',
- its table is pushed after the function.
- <p>
- This is the only option that can raise a memory error.
- </li>
- </ul>
- <p>
- This function returns 0 to signal an invalid option in <code>what</code>;
- even then the valid options are handled correctly.
- <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);</pre>
- <p>
- Gets information about a local variable or a temporary value
- of a given activation record or a given function.
- <p>
- In the first case,
- the parameter <code>ar</code> must be a valid activation record that was
- filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
- given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
- The index <code>n</code> selects which local variable to inspect;
- see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices
- and names.
- <p>
- <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
- and returns its name.
- <p>
- In the second case, <code>ar</code> must be <code>NULL</code> and the function
- to be inspected must be on the top of the stack.
- In this case, only parameters of Lua functions are visible
- (as there is no information about what variables are active)
- and no values are pushed onto the stack.
- <p>
- Returns <code>NULL</code> (and pushes nothing)
- when the index is greater than
- the number of active local variables.
- <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre>
- <p>
- Gets information about the interpreter runtime stack.
- <p>
- This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
- an identification of the <em>activation record</em>
- of the function executing at a given level.
- Level 0 is the current running function,
- whereas level <em>n+1</em> is the function that has called level <em>n</em>
- (except for tail calls, which do not count on the stack).
- When called with a level greater than the stack depth,
- <a href="#lua_getstack"><code>lua_getstack</code></a> returns 0;
- otherwise it returns 1.
- <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
- <span class="apii">[-0, +(0|1), –]</span>
- <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
- <p>
- Gets information about the <code>n</code>-th upvalue
- of the closure at index <code>funcindex</code>.
- It pushes the upvalue's value onto the stack
- and returns its name.
- Returns <code>NULL</code> (and pushes nothing)
- when the index <code>n</code> is greater than the number of upvalues.
- <p>
- See <a href="#pdf-debug.getupvalue"><code>debug.getupvalue</code></a> for more information about upvalues.
- <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
- <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
- <p>
- Type for debugging hook functions.
- <p>
- Whenever a hook is called, its <code>ar</code> argument has its field
- <code>event</code> set to the specific event that triggered the hook.
- Lua identifies these events with the following constants:
- <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
- <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
- and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
- Moreover, for line events, the field <code>currentline</code> is also set.
- To get the value of any other field in <code>ar</code>,
- the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
- <p>
- For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>,
- the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call;
- in this case, there will be no corresponding return event.
- <p>
- While Lua is running a hook, it disables other calls to hooks.
- Therefore, if a hook calls back Lua to execute a function or a chunk,
- this execution occurs without any calls to hooks.
- <p>
- Hook functions cannot have continuations,
- that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
- <a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>.
- <p>
- Hook functions can yield under the following conditions:
- Only count and line events can yield;
- to yield, a hook function must finish its execution
- calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero
- (that is, with no values).
- <hr><h3><a name="lua_setcstacklimit"><code>lua_setcstacklimit</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>int (lua_setcstacklimit) (lua_State *L, unsigned int limit);</pre>
- <p>
- Sets a new limit for the C stack.
- This limit controls how deeply nested calls can go in Lua,
- with the intent of avoiding a stack overflow.
- Returns the old limit in case of success,
- or zero in case of error.
- For more details about this function,
- see <a href="#pdf-debug.setcstacklimit"><code>debug.setcstacklimit</code></a>,
- its equivalent in the standard library.
- <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
- <p>
- Sets the debugging hook function.
- <p>
- Argument <code>f</code> is the hook function.
- <code>mask</code> specifies on which events the hook will be called:
- it is formed by a bitwise OR of the constants
- <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
- <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
- <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
- and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
- The <code>count</code> argument is only meaningful when the mask
- includes <code>LUA_MASKCOUNT</code>.
- For each event, the hook is called as explained below:
- <ul>
- <li><b>The call hook: </b> is called when the interpreter calls a function.
- The hook is called just after Lua enters the new function,
- before the function gets its arguments.
- </li>
- <li><b>The return hook: </b> is called when the interpreter returns from a function.
- The hook is called just before Lua leaves the function.
- </li>
- <li><b>The line hook: </b> is called when the interpreter is about to
- start the execution of a new line of code,
- or when it jumps back in the code (even to the same line).
- This event only happens while Lua is executing a Lua function.
- </li>
- <li><b>The count hook: </b> is called after the interpreter executes every
- <code>count</code> instructions.
- This event only happens while Lua is executing a Lua function.
- </li>
- </ul>
- <p>
- Hooks are disabled by setting <code>mask</code> to zero.
- <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
- <span class="apii">[-(0|1), +0, –]</span>
- <pre>const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);</pre>
- <p>
- Sets the value of a local variable of a given activation record.
- It assigns the value on the top of the stack
- to the variable and returns its name.
- It also pops the value from the stack.
- <p>
- Returns <code>NULL</code> (and pops nothing)
- when the index is greater than
- the number of active local variables.
- <p>
- Parameters <code>ar</code> and <code>n</code> are as in the function <a href="#lua_getlocal"><code>lua_getlocal</code></a>.
- <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
- <span class="apii">[-(0|1), +0, –]</span>
- <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
- <p>
- Sets the value of a closure's upvalue.
- It assigns the value on the top of the stack
- to the upvalue and returns its name.
- It also pops the value from the stack.
- <p>
- Returns <code>NULL</code> (and pops nothing)
- when the index <code>n</code> is greater than the number of upvalues.
- <p>
- Parameters <code>funcindex</code> and <code>n</code> are as in
- the function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>.
- <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre>
- <p>
- Returns a unique identifier for the upvalue numbered <code>n</code>
- from the closure at index <code>funcindex</code>.
- <p>
- These unique identifiers allow a program to check whether different
- closures share upvalues.
- Lua closures that share an upvalue
- (that is, that access a same external local variable)
- will return identical ids for those upvalue indices.
- <p>
- Parameters <code>funcindex</code> and <code>n</code> are as in
- the function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>,
- but <code>n</code> cannot be greater than the number of upvalues.
- <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
- int funcindex2, int n2);</pre>
- <p>
- Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code>
- refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>.
- <h1>5 – <a name="5">The Auxiliary Library</a></h1>
- <p>
- The <em>auxiliary library</em> provides several convenient functions
- to interface C with Lua.
- While the basic API provides the primitive functions for all
- interactions between C and Lua,
- the auxiliary library provides higher-level functions for some
- common tasks.
- <p>
- All functions and types from the auxiliary library
- are defined in header file <code>lauxlib.h</code> and
- have a prefix <code>luaL_</code>.
- <p>
- All functions in the auxiliary library are built on
- top of the basic API,
- and so they provide nothing that cannot be done with that API.
- Nevertheless, the use of the auxiliary library ensures
- more consistency to your code.
- <p>
- Several functions in the auxiliary library use internally some
- extra stack slots.
- When a function in the auxiliary library uses less than five slots,
- it does not check the stack size;
- it simply assumes that there are enough slots.
- <p>
- Several functions in the auxiliary library are used to
- check C function arguments.
- Because the error message is formatted for arguments
- (e.g., "<code>bad argument #1</code>"),
- you should not use these functions for other stack values.
- <p>
- Functions called <code>luaL_check*</code>
- always raise an error if the check is not satisfied.
- <h2>5.1 – <a name="5.1">Functions and Types</a></h2>
- <p>
- Here we list all functions and types from the auxiliary library
- in alphabetical order.
- <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
- <p>
- Adds the byte <code>c</code> to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- <hr><h3><a name="luaL_addgsub"><code>luaL_addgsub</code></a></h3><p>
- <span class="apii">[-0, +0, <em>m</em>]</span>
- <pre>const void luaL_addgsub (luaL_Buffer *B, const char *s,
- const char *p, const char *r);</pre>
- <p>
- Adds a copy of the string <code>s</code> to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>),
- replacing any occurrence of the string <code>p</code>
- with the string <code>r</code>.
- <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre>
- <p>
- Adds the string pointed to by <code>s</code> with length <code>l</code> to
- the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- The string can contain embedded zeros.
- <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
- <span class="apii">[-?, +?, –]</span>
- <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
- <p>
- Adds to the buffer <code>B</code>
- a string of length <code>n</code> previously copied to the
- buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
- <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre>
- <p>
- Adds the zero-terminated string pointed to by <code>s</code>
- to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
- <span class="apii">[-1, +?, <em>m</em>]</span>
- <pre>void luaL_addvalue (luaL_Buffer *B);</pre>
- <p>
- Adds the value on the top of the stack
- to the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- Pops the value.
- <p>
- This is the only function on string buffers that can (and must)
- be called with an extra element on the stack,
- which is the value to be added to the buffer.
- <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_argcheck (lua_State *L,
- int cond,
- int arg,
- const char *extramsg);</pre>
- <p>
- Checks whether <code>cond</code> is true.
- If it is not, raises an error with a standard message (see <a href="#luaL_argerror"><code>luaL_argerror</code></a>).
- <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre>
- <p>
- Raises an error reporting a problem with argument <code>arg</code>
- of the C function that called it,
- using a standard message
- that includes <code>extramsg</code> as a comment:
- <pre>
- bad argument #<em>arg</em> to '<em>funcname</em>' (<em>extramsg</em>)
- </pre><p>
- This function never returns.
- <hr><h3><a name="luaL_argexpected"><code>luaL_argexpected</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_argexpected (lua_State *L,
- int cond,
- int arg,
- const char *tname);</pre>
- <p>
- Checks whether <code>cond</code> is true.
- If it is not, raises an error about the type of the argument <code>arg</code>
- with a standard message (see <a href="#luaL_typeerror"><code>luaL_typeerror</code></a>).
- <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
- <pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
- <p>
- Type for a <em>string buffer</em>.
- <p>
- A string buffer allows C code to build Lua strings piecemeal.
- Its pattern of use is as follows:
- <ul>
- <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
- <li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li>
- <li>
- Then add string pieces to the buffer calling any of
- the <code>luaL_add*</code> functions.
- </li>
- <li>
- Finish by calling <code>luaL_pushresult(&b)</code>.
- This call leaves the final string on the top of the stack.
- </li>
- </ul>
- <p>
- If you know beforehand the maximum size of the resulting string,
- you can use the buffer like this:
- <ul>
- <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
- <li>Then initialize it and preallocate a space of
- size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li>
- <li>Then produce the string into that space.</li>
- <li>
- Finish by calling <code>luaL_pushresultsize(&b, sz)</code>,
- where <code>sz</code> is the total size of the resulting string
- copied into that space (which may be less than or
- equal to the preallocated size).
- </li>
- </ul>
- <p>
- During its normal operation,
- a string buffer uses a variable number of stack slots.
- So, while using a buffer, you cannot assume that you know where
- the top of the stack is.
- You can use the stack between successive calls to buffer operations
- as long as that use is balanced;
- that is,
- when you call a buffer operation,
- the stack is at the same level
- it was immediately after the previous buffer operation.
- (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
- After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>,
- the stack is back to its level when the buffer was initialized,
- plus the final string on its top.
- <hr><h3><a name="luaL_buffaddr"><code>luaL_buffaddr</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>char *luaL_buffaddr (luaL_Buffer *B);</pre>
- <p>
- Returns the address of the current content of buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- Note that any addition to the buffer may invalidate this address.
- <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre>
- <p>
- Initializes a buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- This function does not allocate any space;
- the buffer must be declared as a variable.
- <hr><h3><a name="luaL_bufflen"><code>luaL_bufflen</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>size_t luaL_bufflen (luaL_Buffer *B);</pre>
- <p>
- Returns the length of the current content of buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre>
- <p>
- Equivalent to the sequence
- <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>.
- <hr><h3><a name="luaL_buffsub"><code>luaL_buffsub</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_buffsub (luaL_Buffer *B, int n);</pre>
- <p>
- Removes <code>n</code> bytes from the the buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- The buffer must have at least that many bytes.
- <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
- <span class="apii">[-0, +(0|1), <em>e</em>]</span>
- <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre>
- <p>
- Calls a metamethod.
- <p>
- If the object at index <code>obj</code> has a metatable and this
- metatable has a field <code>e</code>,
- this function calls this field passing the object as its only argument.
- In this case this function returns true and pushes onto the
- stack the value returned by the call.
- If there is no metatable or no metamethod,
- this function returns false without pushing any value on the stack.
- <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checkany (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function has an argument
- of any type (including <b>nil</b>) at position <code>arg</code>.
- <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is an integer
- (or can be converted to an integer)
- and returns this integer.
- <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string
- and returns this string;
- if <code>l</code> is not <code>NULL</code> fills its referent
- with the string's length.
- <p>
- This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
- so all conversions and caveats of that function apply here.
- <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a number
- and returns this number converted to a <code>lua_Number</code>.
- <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_checkoption (lua_State *L,
- int arg,
- const char *def,
- const char *const lst[]);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string and
- searches for this string in the array <code>lst</code>
- (which must be NULL-terminated).
- Returns the index in the array where the string was found.
- Raises an error if the argument is not a string or
- if the string cannot be found.
- <p>
- If <code>def</code> is not <code>NULL</code>,
- the function uses <code>def</code> as a default value when
- there is no argument <code>arg</code> or when this argument is <b>nil</b>.
- <p>
- This is a useful function for mapping strings to C enums.
- (The usual convention in Lua libraries is
- to use strings instead of numbers to select options.)
- <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre>
- <p>
- Grows the stack size to <code>top + sz</code> elements,
- raising an error if the stack cannot grow to that size.
- <code>msg</code> is an additional text to go into the error message
- (or <code>NULL</code> for no additional text).
- <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a string
- and returns this string.
- <p>
- This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
- so all conversions and caveats of that function apply here.
- <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre>
- <p>
- Checks whether the function argument <code>arg</code> has type <code>t</code>.
- See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
- <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre>
- <p>
- Checks whether the function argument <code>arg</code> is a userdata
- of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and
- returns the userdata's memory-block address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>).
- <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>void luaL_checkversion (lua_State *L);</pre>
- <p>
- Checks whether the code making the call and the Lua library being called
- are using the same version of Lua and the same numeric types.
- <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
- <span class="apii">[-0, +?, <em>m</em>]</span>
- <pre>int luaL_dofile (lua_State *L, const char *filename);</pre>
- <p>
- Loads and runs the given file.
- It is defined as the following macro:
- <pre>
- (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
- </pre><p>
- It returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if there are no errors,
- or an error code in case of errors (see <a href="#4.4.1">§4.4.1</a>).
- <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
- <span class="apii">[-0, +?, –]</span>
- <pre>int luaL_dostring (lua_State *L, const char *str);</pre>
- <p>
- Loads and runs the given string.
- It is defined as the following macro:
- <pre>
- (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
- </pre><p>
- It returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if there are no errors,
- or an error code in case of errors (see <a href="#4.4.1">§4.4.1</a>).
- <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre>
- <p>
- Raises an error.
- The error message format is given by <code>fmt</code>
- plus any extra arguments,
- following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
- It also adds at the beginning of the message the file name and
- the line number where the error occurred,
- if this information is available.
- <p>
- This function never returns,
- but it is an idiom to use it in C functions
- as <code>return luaL_error(<em>args</em>)</code>.
- <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p>
- <span class="apii">[-0, +3, <em>m</em>]</span>
- <pre>int luaL_execresult (lua_State *L, int stat);</pre>
- <p>
- This function produces the return values for
- process-related functions in the standard library
- (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>).
- <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p>
- <span class="apii">[-0, +(1|3), <em>m</em>]</span>
- <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre>
- <p>
- This function produces the return values for
- file-related functions in the standard library
- (<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.).
- <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
- <span class="apii">[-0, +(0|1), <em>m</em>]</span>
- <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre>
- <p>
- Pushes onto the stack the field <code>e</code> from the metatable
- of the object at index <code>obj</code> and returns the type of the pushed value.
- If the object does not have a metatable,
- or if the metatable does not have this field,
- pushes nothing and returns <code>LUA_TNIL</code>.
- <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>int luaL_getmetatable (lua_State *L, const char *tname);</pre>
- <p>
- Pushes onto the stack the metatable associated with the name <code>tname</code>
- in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>),
- or <b>nil</b> if there is no metatable associated with that name.
- Returns the type of the pushed value.
- <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre>
- <p>
- Ensures that the value <code>t[fname]</code>,
- where <code>t</code> is the value at index <code>idx</code>,
- is a table,
- and pushes that table onto the stack.
- Returns true if it finds a previous table there
- and false if it creates a new table.
- <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>const char *luaL_gsub (lua_State *L,
- const char *s,
- const char *p,
- const char *r);</pre>
- <p>
- Creates a copy of string <code>s</code>,
- replacing any occurrence of the string <code>p</code>
- with the string <code>r</code>.
- Pushes the resulting string on the stack and returns it.
- <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>lua_Integer luaL_len (lua_State *L, int index);</pre>
- <p>
- Returns the "length" of the value at the given index
- as a number;
- it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>).
- Raises an error if the result of the operation is not an integer.
- (This case can only happen through metamethods.)
- <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadbuffer (lua_State *L,
- const char *buff,
- size_t sz,
- const char *name);</pre>
- <p>
- Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>.
- <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadbufferx (lua_State *L,
- const char *buff,
- size_t sz,
- const char *name,
- const char *mode);</pre>
- <p>
- Loads a buffer as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
- buffer pointed to by <code>buff</code> with size <code>sz</code>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
- <code>name</code> is the chunk name,
- used for debug information and error messages.
- The string <code>mode</code> works as in the function <a href="#lua_load"><code>lua_load</code></a>.
- <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre>
- <p>
- Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>.
- <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>int luaL_loadfilex (lua_State *L, const char *filename,
- const char *mode);</pre>
- <p>
- Loads a file as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
- named <code>filename</code>.
- If <code>filename</code> is <code>NULL</code>,
- then it loads from the standard input.
- The first line in the file is ignored if it starts with a <code>#</code>.
- <p>
- The string <code>mode</code> works as in the function <a href="#lua_load"><code>lua_load</code></a>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>
- or <a href="#pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> for file-related errors.
- <p>
- As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
- it does not run it.
- <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>int luaL_loadstring (lua_State *L, const char *s);</pre>
- <p>
- Loads a string as a Lua chunk.
- This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
- the zero-terminated string <code>s</code>.
- <p>
- This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
- <p>
- Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
- it does not run it.
- <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void luaL_newlib (lua_State *L, const luaL_Reg l[]);</pre>
- <p>
- Creates a new table and registers there
- the functions in the list <code>l</code>.
- <p>
- It is implemented as the following macro:
- <pre>
- (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
- </pre><p>
- The array <code>l</code> must be the actual array,
- not a pointer to it.
- <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre>
- <p>
- Creates a new table with a size optimized
- to store all entries in the array <code>l</code>
- (but does not actually store them).
- It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>
- (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>).
- <p>
- It is implemented as a macro.
- The array <code>l</code> must be the actual array,
- not a pointer to it.
- <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre>
- <p>
- If the registry already has the key <code>tname</code>,
- returns 0.
- Otherwise,
- creates a new table to be used as a metatable for userdata,
- adds to this new table the pair <code>__name = tname</code>,
- adds to the registry the pair <code>[tname] = new table</code>,
- and returns 1.
- <p>
- In both cases,
- the function pushes onto the stack the final value associated
- with <code>tname</code> in the registry.
- <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>lua_State *luaL_newstate (void);</pre>
- <p>
- Creates a new Lua state.
- It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
- allocator based on the standard C allocation functions
- and then sets a warning function and a panic function (see <a href="#4.4">§4.4</a>)
- that print messages to the standard error output.
- <p>
- Returns the new state,
- or <code>NULL</code> if there is a memory allocation error.
- <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
- <span class="apii">[-0, +0, <em>e</em>]</span>
- <pre>void luaL_openlibs (lua_State *L);</pre>
- <p>
- Opens all standard Lua libraries into the given state.
- <hr><h3><a name="luaL_opt"><code>luaL_opt</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>T luaL_opt (L, func, arg, dflt);</pre>
- <p>
- This macro is defined as follows:
- <pre>
- (lua_isnoneornil(L,(arg)) ? (dflt) : func(L,(arg)))
- </pre><p>
- In words, if the argument <code>arg</code> is nil or absent,
- the macro results in the default <code>dflt</code>.
- Otherwise, it results in the result of calling <code>func</code>
- with the state <code>L</code> and the argument index <code>arg</code> as
- arguments.
- Note that it evaluates the expression <code>dflt</code> only if needed.
- <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Integer luaL_optinteger (lua_State *L,
- int arg,
- lua_Integer d);</pre>
- <p>
- If the function argument <code>arg</code> is an integer
- (or it is convertible to an integer),
- returns this integer.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_optlstring (lua_State *L,
- int arg,
- const char *d,
- size_t *l);</pre>
- <p>
- If the function argument <code>arg</code> is a string,
- returns this string.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <p>
- If <code>l</code> is not <code>NULL</code>,
- fills its referent with the result's length.
- If the result is <code>NULL</code>
- (only possible when returning <code>d</code> and <code>d == NULL</code>),
- its length is considered zero.
- <p>
- This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
- so all conversions and caveats of that function apply here.
- <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre>
- <p>
- If the function argument <code>arg</code> is a number,
- returns this number as a <code>lua_Number</code>.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_optstring (lua_State *L,
- int arg,
- const char *d);</pre>
- <p>
- If the function argument <code>arg</code> is a string,
- returns this string.
- If this argument is absent or is <b>nil</b>,
- returns <code>d</code>.
- Otherwise, raises an error.
- <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre>
- <p>
- Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>
- with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>.
- <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p>
- <span class="apii">[-?, +?, <em>m</em>]</span>
- <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre>
- <p>
- Returns an address to a space of size <code>sz</code>
- where you can copy a string to be added to buffer <code>B</code>
- (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
- After copying the string into this space you must call
- <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
- it to the buffer.
- <hr><h3><a name="luaL_pushfail"><code>luaL_pushfail</code></a></h3><p>
- <span class="apii">[-0, +1, –]</span>
- <pre>void luaL_pushfail (lua_State *L);</pre>
- <p>
- Pushes the <b>fail</b> value onto the stack (see <a href="#6">§6</a>).
- <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
- <span class="apii">[-?, +1, <em>m</em>]</span>
- <pre>void luaL_pushresult (luaL_Buffer *B);</pre>
- <p>
- Finishes the use of buffer <code>B</code> leaving the final string on
- the top of the stack.
- <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p>
- <span class="apii">[-?, +1, <em>m</em>]</span>
- <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre>
- <p>
- Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>.
- <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
- <span class="apii">[-1, +0, <em>m</em>]</span>
- <pre>int luaL_ref (lua_State *L, int t);</pre>
- <p>
- Creates and returns a <em>reference</em>,
- in the table at index <code>t</code>,
- for the object on the top of the stack (and pops the object).
- <p>
- A reference is a unique integer key.
- As long as you do not manually add integer keys into the table <code>t</code>,
- <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
- You can retrieve an object referred by the reference <code>r</code>
- by calling <code>lua_rawgeti(L, t, r)</code>.
- The function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference.
- <p>
- If the object on the top of the stack is <b>nil</b>,
- <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
- The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
- from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
- <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
- <pre>typedef struct luaL_Reg {
- const char *name;
- lua_CFunction func;
- } luaL_Reg;</pre>
- <p>
- Type for arrays of functions to be registered by
- <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>.
- <code>name</code> is the function name and <code>func</code> is a pointer to
- the function.
- Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with a sentinel entry
- in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
- <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>void luaL_requiref (lua_State *L, const char *modname,
- lua_CFunction openf, int glb);</pre>
- <p>
- If <code>package.loaded[modname]</code> is not true,
- calls the function <code>openf</code> with the string <code>modname</code> as an argument
- and sets the call result to <code>package.loaded[modname]</code>,
- as if that function has been called through <a href="#pdf-require"><code>require</code></a>.
- <p>
- If <code>glb</code> is true,
- also stores the module into the global <code>modname</code>.
- <p>
- Leaves a copy of the module on the stack.
- <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p>
- <span class="apii">[-nup, +0, <em>m</em>]</span>
- <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre>
- <p>
- Registers all functions in the array <code>l</code>
- (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack
- (below optional upvalues, see next).
- <p>
- When <code>nup</code> is not zero,
- all functions are created with <code>nup</code> upvalues,
- initialized with copies of the <code>nup</code> values
- previously pushed on the stack
- on top of the library table.
- These values are popped from the stack after the registration.
- <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre>
- <p>
- Sets the metatable of the object on the top of the stack
- as the metatable associated with name <code>tname</code>
- in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
- <hr><h3><a name="luaL_Stream"><code>luaL_Stream</code></a></h3>
- <pre>typedef struct luaL_Stream {
- FILE *f;
- lua_CFunction closef;
- } luaL_Stream;</pre>
- <p>
- The standard representation for file handles
- used by the standard I/O library.
- <p>
- A file handle is implemented as a full userdata,
- with a metatable called <code>LUA_FILEHANDLE</code>
- (where <code>LUA_FILEHANDLE</code> is a macro with the actual metatable's name).
- The metatable is created by the I/O library
- (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
- <p>
- This userdata must start with the structure <code>luaL_Stream</code>;
- it can contain other data after this initial structure.
- The field <code>f</code> points to the corresponding C stream
- (or it can be <code>NULL</code> to indicate an incompletely created handle).
- The field <code>closef</code> points to a Lua function
- that will be called to close the stream
- when the handle is closed or collected;
- this function receives the file handle as its sole argument and
- must return either a true value, in case of success,
- or a false value plus an error message, in case of error.
- Once Lua calls this field,
- it changes the field value to <code>NULL</code>
- to signal that the handle is closed.
- <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p>
- <span class="apii">[-0, +0, <em>m</em>]</span>
- <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre>
- <p>
- This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>,
- except that, when the test fails,
- it returns <code>NULL</code> instead of raising an error.
- <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p>
- <span class="apii">[-0, +1, <em>e</em>]</span>
- <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre>
- <p>
- Converts any Lua value at the given index to a C string
- in a reasonable format.
- The resulting string is pushed onto the stack and also
- returned by the function.
- If <code>len</code> is not <code>NULL</code>,
- the function also sets <code>*len</code> with the string length.
- <p>
- If the value has a metatable with a <code>__tostring</code> field,
- then <code>luaL_tolstring</code> calls the corresponding metamethod
- with the value as argument,
- and uses the result of the call as its result.
- <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
- int level);</pre>
- <p>
- Creates and pushes a traceback of the stack <code>L1</code>.
- If <code>msg</code> is not <code>NULL</code>, it is appended
- at the beginning of the traceback.
- The <code>level</code> parameter tells at which level
- to start the traceback.
- <hr><h3><a name="luaL_typeerror"><code>luaL_typeerror</code></a></h3><p>
- <span class="apii">[-0, +0, <em>v</em>]</span>
- <pre>const char *luaL_typeerror (lua_State *L,
- int arg,
- const char *tname);</pre>
- <p>
- Raises a type error for the argument <code>arg</code>
- of the C function that called it,
- using a standard message;
- <code>tname</code> is a "name" for the expected type.
- This function never returns.
- <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>const char *luaL_typename (lua_State *L, int index);</pre>
- <p>
- Returns the name of the type of the value at the given index.
- <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
- <span class="apii">[-0, +0, –]</span>
- <pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
- <p>
- Releases the reference <code>ref</code> from the table at index <code>t</code>
- (see <a href="#luaL_ref"><code>luaL_ref</code></a>).
- The entry is removed from the table,
- so that the referred object can be collected.
- The reference <code>ref</code> is also freed to be used again.
- <p>
- If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>,
- <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
- <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
- <span class="apii">[-0, +1, <em>m</em>]</span>
- <pre>void luaL_where (lua_State *L, int lvl);</pre>
- <p>
- Pushes onto the stack a string identifying the current position
- of the control at level <code>lvl</code> in the call stack.
- Typically this string has the following format:
- <pre>
- <em>chunkname</em>:<em>currentline</em>:
- </pre><p>
- Level 0 is the running function,
- level 1 is the function that called the running function,
- etc.
- <p>
- This function is used to build a prefix for error messages.
- <h1>6 – <a name="6">The Standard Libraries</a></h1>
- <p>
- The standard Lua libraries provide useful functions
- that are implemented in C through the C API.
- Some of these functions provide essential services to the language
- (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
- others provide access to outside services (e.g., I/O);
- and others could be implemented in Lua itself,
- but that for different reasons
- deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
- <p>
- All libraries are implemented through the official C API
- and are provided as separate C modules.
- Unless otherwise noted,
- these library functions do not adjust its number of arguments
- to its expected parameters.
- For instance, a function documented as <code>foo(arg)</code>
- should not be called without an argument.
- <p>
- The notation <b>fail</b> means a false value representing
- some kind of failure.
- (Currently, <b>fail</b> is equal to <b>nil</b>,
- but that may change in future versions.
- The recommendation is to always test the success of these functions
- with <code>(not status)</code>, instead of <code>(status == nil)</code>.)
- <p>
- Currently, Lua has the following standard libraries:
- <ul>
- <li>basic library (<a href="#6.1">§6.1</a>);</li>
- <li>coroutine library (<a href="#6.2">§6.2</a>);</li>
- <li>package library (<a href="#6.3">§6.3</a>);</li>
- <li>string manipulation (<a href="#6.4">§6.4</a>);</li>
- <li>basic UTF-8 support (<a href="#6.5">§6.5</a>);</li>
- <li>table manipulation (<a href="#6.6">§6.6</a>);</li>
- <li>mathematical functions (<a href="#6.7">§6.7</a>) (sin, log, etc.);</li>
- <li>input and output (<a href="#6.8">§6.8</a>);</li>
- <li>operating system facilities (<a href="#6.9">§6.9</a>);</li>
- <li>debug facilities (<a href="#6.10">§6.10</a>).</li>
- </ul><p>
- Except for the basic and the package libraries,
- each library provides all its functions as fields of a global table
- or as methods of its objects.
- <p>
- To have access to these libraries,
- the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
- which opens all standard libraries.
- Alternatively,
- the host program can open them individually by using
- <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call
- <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
- <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
- <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library),
- <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
- <a name="pdf-luaopen_utf8"><code>luaopen_utf8</code></a> (for the UTF-8 library),
- <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
- <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
- <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
- <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the operating system library),
- and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
- These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>.
- <h2>6.1 – <a name="6.1">Basic Functions</a></h2>
- <p>
- The basic library provides core functions to Lua.
- If you do not include this library in your application,
- you should check carefully whether you need to provide
- implementations for some of its facilities.
- <p>
- <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
- <p>
- Raises an error if
- the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
- otherwise, returns all its arguments.
- In case of error,
- <code>message</code> is the error object;
- when absent, it defaults to "<code>assertion failed!</code>"
- <p>
- <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3>
- <p>
- This function is a generic interface to the garbage collector.
- It performs different functions according to its first argument, <code>opt</code>:
- <ul>
- <li><b>"<code>collect</code>": </b>
- Performs a full garbage-collection cycle.
- This is the default option.
- </li>
- <li><b>"<code>stop</code>": </b>
- Stops automatic execution of the garbage collector.
- The collector will run only when explicitly invoked,
- until a call to restart it.
- </li>
- <li><b>"<code>restart</code>": </b>
- Restarts automatic execution of the garbage collector.
- </li>
- <li><b>"<code>count</code>": </b>
- Returns the total memory in use by Lua in Kbytes.
- The value has a fractional part,
- so that it multiplied by 1024
- gives the exact number of bytes in use by Lua.
- </li>
- <li><b>"<code>step</code>": </b>
- Performs a garbage-collection step.
- The step "size" is controlled by <code>arg</code>.
- With a zero value,
- the collector will perform one basic (indivisible) step.
- For non-zero values,
- the collector will perform as if that amount of memory
- (in Kbytes) had been allocated by Lua.
- Returns <b>true</b> if the step finished a collection cycle.
- </li>
- <li><b>"<code>isrunning</code>": </b>
- Returns a boolean that tells whether the collector is running
- (i.e., not stopped).
- </li>
- <li><b>"<code>incremental</code>": </b>
- Change the collector mode to incremental.
- This option can be followed by three numbers:
- the garbage-collector pause,
- the step multiplier,
- and the step size (see <a href="#2.5.1">§2.5.1</a>).
- A zero means to not change that value.
- </li>
- <li><b>"<code>generational</code>": </b>
- Change the collector mode to generational.
- This option can be followed by two numbers:
- the garbage-collector minor multiplier
- and the major multiplier (see <a href="#2.5.2">§2.5.2</a>).
- A zero means to not change that value.
- </li>
- </ul><p>
- See <a href="#2.5">§2.5</a> for more details about garbage collection
- and some of these options.
- <p>
- <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3>
- Opens the named file and executes its content as a Lua chunk.
- When called without arguments,
- <code>dofile</code> executes the content of the standard input (<code>stdin</code>).
- Returns all values returned by the chunk.
- In case of errors, <code>dofile</code> propagates the error
- to its caller.
- (That is, <code>dofile</code> does not run in protected mode.)
- <p>
- <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
- Raises an error (see <a href="#2.3">§2.3</a>) with @{message} as the error object.
- This function never returns.
- <p>
- Usually, <code>error</code> adds some information about the error position
- at the beginning of the message, if the message is a string.
- The <code>level</code> argument specifies how to get the error position.
- With level 1 (the default), the error position is where the
- <code>error</code> function was called.
- Level 2 points the error to where the function
- that called <code>error</code> was called; and so on.
- Passing a level 0 avoids the addition of error position information
- to the message.
- <p>
- <hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
- A global variable (not a function) that
- holds the global environment (see <a href="#2.2">§2.2</a>).
- Lua itself does not use this variable;
- changing its value does not affect any environment,
- nor vice versa.
- <p>
- <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
- <p>
- If <code>object</code> does not have a metatable, returns <b>nil</b>.
- Otherwise,
- if the object's metatable has a <code>__metatable</code> field,
- returns the associated value.
- Otherwise, returns the metatable of the given object.
- <p>
- <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
- <p>
- Returns three values (an iterator function, the table <code>t</code>, and 0)
- so that the construction
- <pre>
- for i,v in ipairs(t) do <em>body</em> end
- </pre><p>
- will iterate over the key–value pairs
- (<code>1,t[1]</code>), (<code>2,t[2]</code>), ...,
- up to the first absent index.
- <p>
- <hr><h3><a name="pdf-load"><code>load (chunk [, chunkname [, mode [, env]]])</code></a></h3>
- <p>
- Loads a chunk.
- <p>
- If <code>chunk</code> is a string, the chunk is this string.
- If <code>chunk</code> is a function,
- <code>load</code> calls it repeatedly to get the chunk pieces.
- Each call to <code>chunk</code> must return a string that concatenates
- with previous results.
- A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
- <p>
- If there are no syntactic errors,
- <code>load</code> returns the compiled chunk as a function;
- otherwise, it returns <b>fail</b> plus the error message.
- <p>
- When you load a main chunk,
- the resulting function will always have exactly one upvalue,
- the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
- However,
- when you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>),
- the resulting function can have an arbitrary number of upvalues,
- and there is no guarantee that its first upvalue will be
- the <code>_ENV</code> variable.
- (A non-main function may not even have an <code>_ENV</code> upvalue.)
- <p>
- Regardless, if the resulting function has any upvalues,
- its first upvalue is set to the value of <code>env</code>,
- if that parameter is given,
- or to the value of the global environment.
- Other upvalues are initialized with <b>nil</b>.
- All upvalues are fresh, that is,
- they are not shared with any other function.
- <p>
- <code>chunkname</code> is used as the name of the chunk for error messages
- and debug information (see <a href="#4.7">§4.7</a>).
- When absent,
- it defaults to <code>chunk</code>, if <code>chunk</code> is a string,
- or to "<code>=(load)</code>" otherwise.
- <p>
- The string <code>mode</code> controls whether the chunk can be text or binary
- (that is, a precompiled chunk).
- It may be the string "<code>b</code>" (only binary chunks),
- "<code>t</code>" (only text chunks),
- or "<code>bt</code>" (both binary and text).
- The default is "<code>bt</code>".
- <p>
- Lua does not check the consistency of binary chunks.
- Maliciously crafted binary chunks can crash
- the interpreter.
- <p>
- <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3>
- <p>
- Similar to <a href="#pdf-load"><code>load</code></a>,
- but gets the chunk from file <code>filename</code>
- or from the standard input,
- if no file name is given.
- <p>
- <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
- <p>
- Allows a program to traverse all fields of a table.
- Its first argument is a table and its second argument
- is an index in this table.
- A call to <code>next</code> returns the next index of the table
- and its associated value.
- When called with <b>nil</b> as its second argument,
- <code>next</code> returns an initial index
- and its associated value.
- When called with the last index,
- or with <b>nil</b> in an empty table,
- <code>next</code> returns <b>nil</b>.
- If the second argument is absent, then it is interpreted as <b>nil</b>.
- In particular,
- you can use <code>next(t)</code> to check whether a table is empty.
- <p>
- The order in which the indices are enumerated is not specified,
- <em>even for numeric indices</em>.
- (To traverse a table in numerical order,
- use a numerical <b>for</b>.)
- <p>
- The behavior of <code>next</code> is undefined if,
- during the traversal,
- you assign any value to a non-existent field in the table.
- You may however modify existing fields.
- In particular, you may set existing fields to nil.
- <p>
- <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
- <p>
- If <code>t</code> has a metamethod <code>__pairs</code>,
- calls it with <code>t</code> as argument and returns the first three
- results from the call.
- <p>
- Otherwise,
- returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
- so that the construction
- <pre>
- for k,v in pairs(t) do <em>body</em> end
- </pre><p>
- will iterate over all key–value pairs of table <code>t</code>.
- <p>
- See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
- the table during its traversal.
- <p>
- <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3>
- <p>
- Calls the function <code>f</code> with
- the given arguments in <em>protected mode</em>.
- This means that any error inside <code>f</code> is not propagated;
- instead, <code>pcall</code> catches the error
- and returns a status code.
- Its first result is the status code (a boolean),
- which is true if the call succeeds without errors.
- In such case, <code>pcall</code> also returns all results from the call,
- after this first result.
- In case of any error, <code>pcall</code> returns <b>false</b> plus the error object.
- Note that errors caught by <code>pcall</code> do not call a message handler.
- <p>
- <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3>
- Receives any number of arguments
- and prints their values to <code>stdout</code>,
- converting each argument to a string
- following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
- <p>
- The function <code>print</code> is not intended for formatted output,
- but only as a quick way to show a value,
- for instance for debugging.
- For complete control over the output,
- use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>.
- <p>
- <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
- Checks whether <code>v1</code> is equal to <code>v2</code>,
- without invoking the <code>__eq</code> metamethod.
- Returns a boolean.
- <p>
- <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
- Gets the real value of <code>table[index]</code>,
- without using the <code>__index</code> metavalue.
- <code>table</code> must be a table;
- <code>index</code> may be any value.
- <p>
- <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3>
- Returns the length of the object <code>v</code>,
- which must be a table or a string,
- without invoking the <code>__len</code> metamethod.
- Returns an integer.
- <p>
- <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
- Sets the real value of <code>table[index]</code> to <code>value</code>,
- without using the <code>__newindex</code> metavalue.
- <code>table</code> must be a table,
- <code>index</code> any value different from <b>nil</b> and NaN,
- and <code>value</code> any Lua value.
- <p>
- This function returns <code>table</code>.
- <p>
- <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3>
- <p>
- If <code>index</code> is a number,
- returns all arguments after argument number <code>index</code>;
- a negative number indexes from the end (-1 is the last argument).
- Otherwise, <code>index</code> must be the string <code>"#"</code>,
- and <code>select</code> returns the total number of extra arguments it received.
- <p>
- <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
- <p>
- Sets the metatable for the given table.
- If <code>metatable</code> is <b>nil</b>,
- removes the metatable of the given table.
- If the original metatable has a <code>__metatable</code> field,
- raises an error.
- <p>
- This function returns <code>table</code>.
- <p>
- To change the metatable of other types from Lua code,
- you must use the debug library (<a href="#6.10">§6.10</a>).
- <p>
- <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
- <p>
- When called with no <code>base</code>,
- <code>tonumber</code> tries to convert its argument to a number.
- If the argument is already a number or
- a string convertible to a number,
- then <code>tonumber</code> returns this number;
- otherwise, it returns <b>fail</b>.
- <p>
- The conversion of strings can result in integers or floats,
- according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>).
- The string may have leading and trailing spaces and a sign.
- <p>
- When called with <code>base</code>,
- then <code>e</code> must be a string to be interpreted as
- an integer numeral in that base.
- The base may be any integer between 2 and 36, inclusive.
- In bases above 10, the letter '<code>A</code>' (in either upper or lower case)
- represents 10, '<code>B</code>' represents 11, and so forth,
- with '<code>Z</code>' representing 35.
- If the string <code>e</code> is not a valid numeral in the given base,
- the function returns <b>fail</b>.
- <p>
- <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3>
- <p>
- Receives a value of any type and
- converts it to a string in a human-readable format.
- <p>
- If the metatable of <code>v</code> has a <code>__tostring</code> field,
- then <code>tostring</code> calls the corresponding value
- with <code>v</code> as argument,
- and uses the result of the call as its result.
- Otherwise, if the metatable of <code>v</code> has a <code>__name</code> field
- with a string value,
- <code>tostring</code> may use that string in its final result.
- <p>
- For complete control of how numbers are converted,
- use <a href="#pdf-string.format"><code>string.format</code></a>.
- <p>
- <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
- <p>
- Returns the type of its only argument, coded as a string.
- The possible results of this function are
- "<code>nil</code>" (a string, not the value <b>nil</b>),
- "<code>number</code>",
- "<code>string</code>",
- "<code>boolean</code>",
- "<code>table</code>",
- "<code>function</code>",
- "<code>thread</code>",
- and "<code>userdata</code>".
- <p>
- <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
- <p>
- A global variable (not a function) that
- holds a string containing the running Lua version.
- The current value of this variable is "<code>Lua 5.4</code>".
- <p>
- <hr><h3><a name="pdf-warn"><code>warn (msg1, ···)</code></a></h3>
- <p>
- Emits a warning with a message composed by the concatenation
- of all its arguments (which should be strings).
- <p>
- By convention,
- a one-piece message starting with '<code>@</code>'
- is intended to be a <em>control message</em>,
- which is a message to the warning system itself.
- In particular, the standard warning function in Lua
- recognizes the control messages "<code>@off</code>",
- to stop the emission of warnings,
- and "<code>@on</code>", to (re)start the emission;
- it ignores unknown control messages.
- <p>
- <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3>
- <p>
- This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
- except that it sets a new message handler <code>msgh</code>.
- <h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2>
- <p>
- This library comprises the operations to manipulate coroutines,
- which come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
- See <a href="#2.6">§2.6</a> for a general description of coroutines.
- <p>
- <hr><h3><a name="pdf-coroutine.close"><code>coroutine.close (co)</code></a></h3>
- <p>
- Closes coroutine <code>co</code>,
- that is,
- closes all its pending to-be-closed variables
- and puts the coroutine in a dead state.
- The given coroutine must be dead or suspended.
- In case of error closing some variable,
- returns <b>false</b> plus the error object;
- otherwise returns <b>true</b>.
- <p>
- <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
- <p>
- Creates a new coroutine, with body <code>f</code>.
- <code>f</code> must be a function.
- Returns this new coroutine,
- an object with type <code>"thread"</code>.
- <p>
- <hr><h3><a name="pdf-coroutine.isyieldable"><code>coroutine.isyieldable ([co])</code></a></h3>
- <p>
- Returns true when the coroutine <code>co</code> can yield.
- The default for <code>co</code> is the running coroutine.
- <p>
- A coroutine is yieldable if it is not the main thread and
- it is not inside a non-yieldable C function.
- <p>
- <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3>
- <p>
- Starts or continues the execution of coroutine <code>co</code>.
- The first time you resume a coroutine,
- it starts running its body.
- The values <code>val1</code>, ... are passed
- as the arguments to the body function.
- If the coroutine has yielded,
- <code>resume</code> restarts it;
- the values <code>val1</code>, ... are passed
- as the results from the yield.
- <p>
- If the coroutine runs without any errors,
- <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
- (when the coroutine yields) or any values returned by the body function
- (when the coroutine terminates).
- If there is any error,
- <code>resume</code> returns <b>false</b> plus the error message.
- <p>
- <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
- <p>
- Returns the running coroutine plus a boolean,
- true when the running coroutine is the main one.
- <p>
- <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
- <p>
- Returns the status of the coroutine <code>co</code>, as a string:
- <code>"running"</code>,
- if the coroutine is running
- (that is, it is the one that called <code>status</code>);
- <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
- or if it has not started running yet;
- <code>"normal"</code> if the coroutine is active but not running
- (that is, it has resumed another coroutine);
- and <code>"dead"</code> if the coroutine has finished its body function,
- or if it has stopped with an error.
- <p>
- <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
- <p>
- Creates a new coroutine, with body <code>f</code>;
- <code>f</code> must be a function.
- Returns a function that resumes the coroutine each time it is called.
- Any arguments passed to this function behave as the
- extra arguments to <code>resume</code>.
- The function returns the same values returned by <code>resume</code>,
- except the first boolean.
- In case of error,
- the function closes the coroutine and propagates the error.
- <p>
- <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3>
- <p>
- Suspends the execution of the calling coroutine.
- Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
- <h2>6.3 – <a name="6.3">Modules</a></h2>
- <p>
- The package library provides basic
- facilities for loading modules in Lua.
- It exports one function directly in the global environment:
- <a href="#pdf-require"><code>require</code></a>.
- Everything else is exported in the table <a name="pdf-package"><code>package</code></a>.
- <p>
- <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
- <p>
- Loads the given module.
- The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
- to determine whether <code>modname</code> is already loaded.
- If it is, then <code>require</code> returns the value stored
- at <code>package.loaded[modname]</code>.
- (The absence of a second result in this case
- signals that this call did not have to load the module.)
- Otherwise, it tries to find a <em>loader</em> for the module.
- <p>
- To find a loader,
- <code>require</code> is guided by the table <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
- Each item in this table is a search function,
- that searches for the module in a particular way.
- By changing this table,
- we can change how <code>require</code> looks for a module.
- The following explanation is based on the default configuration
- for <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
- <p>
- First <code>require</code> queries <code>package.preload[modname]</code>.
- If it has a value,
- this value (which must be a function) is the loader.
- Otherwise <code>require</code> searches for a Lua loader using the
- path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
- If that also fails, it searches for a C loader using the
- path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
- If that also fails,
- it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>).
- <p>
- Once a loader is found,
- <code>require</code> calls the loader with two arguments:
- <code>modname</code> and an extra value,
- a <em>loader data</em>,
- also returned by the searcher.
- The loader data can be any value useful to the module;
- for the default searchers,
- it indicates where the loader was found.
- (For instance, if the loader came from a file,
- this extra value is the file path.)
- If the loader returns any non-nil value,
- <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
- If the loader does not return a non-nil value and
- has not assigned any value to <code>package.loaded[modname]</code>,
- then <code>require</code> assigns <b>true</b> to this entry.
- In any case, <code>require</code> returns the
- final value of <code>package.loaded[modname]</code>.
- Besides that value, <code>require</code> also returns as a second result
- the loader data returned by the searcher,
- which indicates how <code>require</code> found the module.
- <p>
- If there is any error loading or running the module,
- or if it cannot find any loader for the module,
- then <code>require</code> raises an error.
- <p>
- <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3>
- <p>
- A string describing some compile-time configurations for packages.
- This string is a sequence of lines:
- <ul>
- <li>The first line is the directory separator string.
- Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li>
- <li>The second line is the character that separates templates in a path.
- Default is '<code>;</code>'.</li>
- <li>The third line is the string that marks the
- substitution points in a template.
- Default is '<code>?</code>'.</li>
- <li>The fourth line is a string that, in a path in Windows,
- is replaced by the executable's directory.
- Default is '<code>!</code>'.</li>
- <li>The fifth line is a mark to ignore all text after it
- when building the <code>luaopen_</code> function name.
- Default is '<code>-</code>'.</li>
- </ul>
- <p>
- <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
- <p>
- A string with the path used by <a href="#pdf-require"><code>require</code></a>
- to search for a C loader.
- <p>
- Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
- it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
- using the environment variable <a name="pdf-LUA_CPATH_5_4"><code>LUA_CPATH_5_4</code></a>,
- or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>,
- or a default path defined in <code>luaconf.h</code>.
- <p>
- <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
- <p>
- A table used by <a href="#pdf-require"><code>require</code></a> to control which
- modules are already loaded.
- When you require a module <code>modname</code> and
- <code>package.loaded[modname]</code> is not false,
- <a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
- <p>
- This variable is only a reference to the real table;
- assignments to this variable do not change the
- table used by <a href="#pdf-require"><code>require</code></a>.
- <p>
- <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
- <p>
- Dynamically links the host program with the C library <code>libname</code>.
- <p>
- If <code>funcname</code> is "<code>*</code>",
- then it only links with the library,
- making the symbols exported by the library
- available to other dynamically linked libraries.
- Otherwise,
- it looks for a function <code>funcname</code> inside the library
- and returns this function as a C function.
- So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype
- (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
- <p>
- This is a low-level function.
- It completely bypasses the package and module system.
- Unlike <a href="#pdf-require"><code>require</code></a>,
- it does not perform any path searching and
- does not automatically adds extensions.
- <code>libname</code> must be the complete file name of the C library,
- including if necessary a path and an extension.
- <code>funcname</code> must be the exact name exported by the C library
- (which may depend on the C compiler and linker used).
- <p>
- This function is not supported by Standard C.
- As such, it is only available on some platforms
- (Windows, Linux, Mac OS X, Solaris, BSD,
- plus other Unix systems that support the <code>dlfcn</code> standard).
- <p>
- <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
- <p>
- A string with the path used by <a href="#pdf-require"><code>require</code></a>
- to search for a Lua loader.
- <p>
- At start-up, Lua initializes this variable with
- the value of the environment variable <a name="pdf-LUA_PATH_5_4"><code>LUA_PATH_5_4</code></a> or
- the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
- with a default path defined in <code>luaconf.h</code>,
- if those environment variables are not defined.
- A "<code>;;</code>" in the value of the environment variable
- is replaced by the default path.
- <p>
- <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
- <p>
- A table to store loaders for specific modules
- (see <a href="#pdf-require"><code>require</code></a>).
- <p>
- This variable is only a reference to the real table;
- assignments to this variable do not change the
- table used by <a href="#pdf-require"><code>require</code></a>.
- <p>
- <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3>
- <p>
- A table used by <a href="#pdf-require"><code>require</code></a> to control how to find modules.
- <p>
- Each entry in this table is a <em>searcher function</em>.
- When looking for a module,
- <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
- with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
- sole argument.
- If the searcher finds the module,
- it returns another function, the module <em>loader</em>,
- plus an extra value, a <em>loader data</em>,
- that will be passed to that loader and
- returned as a second result by <a href="#pdf-require"><code>require</code></a>.
- If it cannot find the module,
- it returns a string explaining why
- (or <b>nil</b> if it has nothing to say).
- <p>
- Lua initializes this table with four searcher functions.
- <p>
- The first searcher simply looks for a loader in the
- <a href="#pdf-package.preload"><code>package.preload</code></a> table.
- <p>
- The second searcher looks for a loader as a Lua library,
- using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
- The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- <p>
- The third searcher looks for a loader as a C library,
- using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
- Again,
- the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- For instance,
- if the C path is the string
- <pre>
- "./?.so;./?.dll;/usr/local/?/init.so"
- </pre><p>
- the searcher for module <code>foo</code>
- will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
- and <code>/usr/local/foo/init.so</code>, in that order.
- Once it finds a C library,
- this searcher first uses a dynamic link facility to link the
- application with the library.
- Then it tries to find a C function inside the library to
- be used as the loader.
- The name of this C function is the string "<code>luaopen_</code>"
- concatenated with a copy of the module name where each dot
- is replaced by an underscore.
- Moreover, if the module name has a hyphen,
- its suffix after (and including) the first hyphen is removed.
- For instance, if the module name is <code>a.b.c-v2.1</code>,
- the function name will be <code>luaopen_a_b_c</code>.
- <p>
- The fourth searcher tries an <em>all-in-one loader</em>.
- It searches the C path for a library for
- the root name of the given module.
- For instance, when requiring <code>a.b.c</code>,
- it will search for a C library for <code>a</code>.
- If found, it looks into it for an open function for
- the submodule;
- in our example, that would be <code>luaopen_a_b_c</code>.
- With this facility, a package can pack several C submodules
- into one single library,
- with each submodule keeping its original open function.
- <p>
- All searchers except the first one (preload) return as the extra value
- the file path where the module was found,
- as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
- The first searcher always returns the string "<code>:preload:</code>".
- <p>
- Searchers should raise no errors and have no side effects in Lua.
- (They may have side effects in C,
- for instance by linking the application with a library.)
- <p>
- <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3>
- <p>
- Searches for the given <code>name</code> in the given <code>path</code>.
- <p>
- A path is a string containing a sequence of
- <em>templates</em> separated by semicolons.
- For each template,
- the function replaces each interrogation mark (if any)
- in the template with a copy of <code>name</code>
- wherein all occurrences of <code>sep</code>
- (a dot, by default)
- were replaced by <code>rep</code>
- (the system's directory separator, by default),
- and then tries to open the resulting file name.
- <p>
- For instance, if the path is the string
- <pre>
- "./?.lua;./?.lc;/usr/local/?/init.lua"
- </pre><p>
- the search for the name <code>foo.a</code>
- will try to open the files
- <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and
- <code>/usr/local/foo/a/init.lua</code>, in that order.
- <p>
- Returns the resulting name of the first file that it can
- open in read mode (after closing the file),
- or <b>fail</b> plus an error message if none succeeds.
- (This error message lists all file names it tried to open.)
- <h2>6.4 – <a name="6.4">String Manipulation</a></h2>
- <p>
- This library provides generic functions for string manipulation,
- such as finding and extracting substrings, and pattern matching.
- When indexing a string in Lua, the first character is at position 1
- (not at 0, as in C).
- Indices are allowed to be negative and are interpreted as indexing backwards,
- from the end of the string.
- Thus, the last character is at position -1, and so on.
- <p>
- The string library provides all its functions inside the table
- <a name="pdf-string"><code>string</code></a>.
- It also sets a metatable for strings
- where the <code>__index</code> field points to the <code>string</code> table.
- Therefore, you can use the string functions in object-oriented style.
- For instance, <code>string.byte(s,i)</code>
- can be written as <code>s:byte(i)</code>.
- <p>
- The string library assumes one-byte character encodings.
- <p>
- <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
- Returns the internal numeric codes of the characters <code>s[i]</code>,
- <code>s[i+1]</code>, ..., <code>s[j]</code>.
- The default value for <code>i</code> is 1;
- the default value for <code>j</code> is <code>i</code>.
- These indices are corrected
- following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
- <p>
- Numeric codes are not necessarily portable across platforms.
- <p>
- <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3>
- Receives zero or more integers.
- Returns a string with length equal to the number of arguments,
- in which each character has the internal numeric code equal
- to its corresponding argument.
- <p>
- Numeric codes are not necessarily portable across platforms.
- <p>
- <hr><h3><a name="pdf-string.dump"><code>string.dump (function [, strip])</code></a></h3>
- <p>
- Returns a string containing a binary representation
- (a <em>binary chunk</em>)
- of the given function,
- so that a later <a href="#pdf-load"><code>load</code></a> on this string returns
- a copy of the function (but with new upvalues).
- If <code>strip</code> is a true value,
- the binary representation may not include all debug information
- about the function,
- to save space.
- <p>
- Functions with upvalues have only their number of upvalues saved.
- When (re)loaded,
- those upvalues receive fresh instances.
- (See the <a href="#pdf-load"><code>load</code></a> function for details about
- how these upvalues are initialized.
- You can use the debug library to serialize
- and reload the upvalues of a function
- in a way adequate to your needs.)
- <p>
- <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
- <p>
- Looks for the first match of
- <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>.
- If it finds a match, then <code>find</code> returns the indices of <code>s</code>
- where this occurrence starts and ends;
- otherwise, it returns <b>fail</b>.
- A third, optional numeric argument <code>init</code> specifies
- where to start the search;
- its default value is 1 and can be negative.
- A value of <b>true</b> as a fourth, optional argument <code>plain</code>
- turns off the pattern matching facilities,
- so the function does a plain "find substring" operation,
- with no characters in <code>pattern</code> being considered magic.
- <p>
- If the pattern has captures,
- then in a successful match
- the captured values are also returned,
- after the two indices.
- <p>
- <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3>
- <p>
- Returns a formatted version of its variable number of arguments
- following the description given in its first argument,
- which must be a string.
- The format string follows the same rules as the ISO C function <code>sprintf</code>.
- The only differences are that the conversion specifiers and modifiers
- <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, and <code>n</code> are not supported
- and that there is an extra specifier, <code>q</code>.
- <p>
- The specifier <code>q</code> formats booleans, nil, numbers, and strings
- in a way that the result is a valid constant in Lua source code.
- Booleans and nil are written in the obvious way
- (<code>true</code>, <code>false</code>, <code>nil</code>).
- Floats are written in hexadecimal,
- to preserve full precision.
- A string is written between double quotes,
- using escape sequences when necessary to ensure that
- it can safely be read back by the Lua interpreter.
- For instance, the call
- <pre>
- string.format('%q', 'a string with "quotes" and \n new line')
- </pre><p>
- may produce the string:
- <pre>
- "a string with \"quotes\" and \
- new line"
- </pre><p>
- This specifier does not support modifiers (flags, width, length).
- <p>
- The conversion specifiers
- <code>A</code>, <code>a</code>, <code>E</code>, <code>e</code>, <code>f</code>,
- <code>G</code>, and <code>g</code> all expect a number as argument.
- The specifiers <code>c</code>, <code>d</code>,
- <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>
- expect an integer.
- When Lua is compiled with a C89 compiler,
- the specifiers <code>A</code> and <code>a</code> (hexadecimal floats)
- do not support modifiers.
- <p>
- The specifier <code>s</code> expects a string;
- if its argument is not a string,
- it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
- If the specifier has any modifier,
- the corresponding string argument should not contain embedded zeros.
- <p>
- The specifier <code>p</code> formats the pointer
- returned by <a href="#lua_topointer"><code>lua_topointer</code></a>.
- That gives a unique string identifier for tables, userdata,
- threads, strings, and functions.
- For other values (numbers, nil, booleans),
- this specifier results in a string representing
- the pointer <code>NULL</code>.
- <p>
- <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern [, init])</code></a></h3>
- Returns an iterator function that,
- each time it is called,
- returns the next captures from <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>)
- over the string <code>s</code>.
- If <code>pattern</code> specifies no captures,
- then the whole match is produced in each call.
- A third, optional numeric argument <code>init</code> specifies
- where to start the search;
- its default value is 1 and can be negative.
- <p>
- As an example, the following loop
- will iterate over all the words from string <code>s</code>,
- printing one per line:
- <pre>
- s = "hello world from Lua"
- for w in string.gmatch(s, "%a+") do
- print(w)
- end
- </pre><p>
- The next example collects all pairs <code>key=value</code> from the
- given string into a table:
- <pre>
- t = {}
- s = "from=world, to=Lua"
- for k, v in string.gmatch(s, "(%w+)=(%w+)") do
- t[k] = v
- end
- </pre>
- <p>
- For this function, a caret '<code>^</code>' at the start of a pattern does not
- work as an anchor, as this would prevent the iteration.
- <p>
- <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
- Returns a copy of <code>s</code>
- in which all (or the first <code>n</code>, if given)
- occurrences of the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) have been
- replaced by a replacement string specified by <code>repl</code>,
- which can be a string, a table, or a function.
- <code>gsub</code> also returns, as its second value,
- the total number of matches that occurred.
- The name <code>gsub</code> comes from <em>Global SUBstitution</em>.
- <p>
- If <code>repl</code> is a string, then its value is used for replacement.
- The character <code>%</code> works as an escape character:
- any sequence in <code>repl</code> of the form <code>%<em>d</em></code>,
- with <em>d</em> between 1 and 9,
- stands for the value of the <em>d</em>-th captured substring;
- the sequence <code>%0</code> stands for the whole match;
- the sequence <code>%%</code> stands for a single <code>%</code>.
- <p>
- If <code>repl</code> is a table, then the table is queried for every match,
- using the first capture as the key.
- <p>
- If <code>repl</code> is a function, then this function is called every time a
- match occurs, with all captured substrings passed as arguments,
- in order.
- <p>
- In any case,
- if the pattern specifies no captures,
- then it behaves as if the whole pattern was inside a capture.
- <p>
- If the value returned by the table query or by the function call
- is a string or a number,
- then it is used as the replacement string;
- otherwise, if it is <b>false</b> or <b>nil</b>,
- then there is no replacement
- (that is, the original match is kept in the string).
- <p>
- Here are some examples:
- <pre>
- x = string.gsub("hello world", "(%w+)", "%1 %1")
- --> x="hello hello world world"
-
- x = string.gsub("hello world", "%w+", "%0 %0", 1)
- --> x="hello hello world"
-
- x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
- --> x="world hello Lua from"
-
- x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
- --> x="home = /home/roberto, user = roberto"
-
- x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
- return load(s)()
- end)
- --> x="4+5 = 9"
-
- local t = {name="lua", version="5.4"}
- x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
- --> x="lua-5.4.tar.gz"
- </pre>
- <p>
- <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
- <p>
- Receives a string and returns its length.
- The empty string <code>""</code> has length 0.
- Embedded zeros are counted,
- so <code>"a\000bc\000"</code> has length 5.
- <p>
- <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
- <p>
- Receives a string and returns a copy of this string with all
- uppercase letters changed to lowercase.
- All other characters are left unchanged.
- The definition of what an uppercase letter is depends on the current locale.
- <p>
- <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
- <p>
- Looks for the first <em>match</em> of
- the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>.
- If it finds one, then <code>match</code> returns
- the captures from the pattern;
- otherwise it returns <b>fail</b>.
- If <code>pattern</code> specifies no captures,
- then the whole match is returned.
- A third, optional numeric argument <code>init</code> specifies
- where to start the search;
- its default value is 1 and can be negative.
- <p>
- <hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, ···)</code></a></h3>
- <p>
- Returns a binary string containing the values <code>v1</code>, <code>v2</code>, etc.
- serialized in binary form (packed)
- according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>).
- <p>
- <hr><h3><a name="pdf-string.packsize"><code>string.packsize (fmt)</code></a></h3>
- <p>
- Returns the size of a string resulting from <a href="#pdf-string.pack"><code>string.pack</code></a>
- with the given format.
- The format string cannot have the variable-length options
- '<code>s</code>' or '<code>z</code>' (see <a href="#6.4.2">§6.4.2</a>).
- <p>
- <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3>
- <p>
- Returns a string that is the concatenation of <code>n</code> copies of
- the string <code>s</code> separated by the string <code>sep</code>.
- The default value for <code>sep</code> is the empty string
- (that is, no separator).
- Returns the empty string if <code>n</code> is not positive.
- <p>
- (Note that it is very easy to exhaust the memory of your machine
- with a single call to this function.)
- <p>
- <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
- <p>
- Returns a string that is the string <code>s</code> reversed.
- <p>
- <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
- <p>
- Returns the substring of <code>s</code> that
- starts at <code>i</code> and continues until <code>j</code>;
- <code>i</code> and <code>j</code> can be negative.
- If <code>j</code> is absent, then it is assumed to be equal to -1
- (which is the same as the string length).
- In particular,
- the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
- with length <code>j</code>,
- and <code>string.sub(s, -i)</code> (for a positive <code>i</code>)
- returns a suffix of <code>s</code>
- with length <code>i</code>.
- <p>
- If, after the translation of negative indices,
- <code>i</code> is less than 1,
- it is corrected to 1.
- If <code>j</code> is greater than the string length,
- it is corrected to that length.
- If, after these corrections,
- <code>i</code> is greater than <code>j</code>,
- the function returns the empty string.
- <p>
- <hr><h3><a name="pdf-string.unpack"><code>string.unpack (fmt, s [, pos])</code></a></h3>
- <p>
- Returns the values packed in string <code>s</code> (see <a href="#pdf-string.pack"><code>string.pack</code></a>)
- according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>).
- An optional <code>pos</code> marks where
- to start reading in <code>s</code> (default is 1).
- After the read values,
- this function also returns the index of the first unread byte in <code>s</code>.
- <p>
- <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
- <p>
- Receives a string and returns a copy of this string with all
- lowercase letters changed to uppercase.
- All other characters are left unchanged.
- The definition of what a lowercase letter is depends on the current locale.
- <h3>6.4.1 – <a name="6.4.1">Patterns</a></h3>
- <p>
- Patterns in Lua are described by regular strings,
- which are interpreted as patterns by the pattern-matching functions
- <a href="#pdf-string.find"><code>string.find</code></a>,
- <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>,
- <a href="#pdf-string.gsub"><code>string.gsub</code></a>,
- and <a href="#pdf-string.match"><code>string.match</code></a>.
- This section describes the syntax and the meaning
- (that is, what they match) of these strings.
- <h4>Character Class:</h4><p>
- A <em>character class</em> is used to represent a set of characters.
- The following combinations are allowed in describing a character class:
- <ul>
- <li><b><em>x</em>: </b>
- (where <em>x</em> is not one of the <em>magic characters</em>
- <code>^$()%.[]*+-?</code>)
- represents the character <em>x</em> itself.
- </li>
- <li><b><code>.</code>: </b> (a dot) represents all characters.</li>
- <li><b><code>%a</code>: </b> represents all letters.</li>
- <li><b><code>%c</code>: </b> represents all control characters.</li>
- <li><b><code>%d</code>: </b> represents all digits.</li>
- <li><b><code>%g</code>: </b> represents all printable characters except space.</li>
- <li><b><code>%l</code>: </b> represents all lowercase letters.</li>
- <li><b><code>%p</code>: </b> represents all punctuation characters.</li>
- <li><b><code>%s</code>: </b> represents all space characters.</li>
- <li><b><code>%u</code>: </b> represents all uppercase letters.</li>
- <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li>
- <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li>
- <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character)
- represents the character <em>x</em>.
- This is the standard way to escape the magic characters.
- Any non-alphanumeric character
- (including all punctuation characters, even the non-magical)
- can be preceded by a '<code>%</code>' to represent itself in a pattern.
- </li>
- <li><b><code>[<em>set</em>]</code>: </b>
- represents the class which is the union of all
- characters in <em>set</em>.
- A range of characters can be specified by
- separating the end characters of the range,
- in ascending order, with a '<code>-</code>'.
- All classes <code>%</code><em>x</em> described above can also be used as
- components in <em>set</em>.
- All other characters in <em>set</em> represent themselves.
- For example, <code>[%w_]</code> (or <code>[_%w]</code>)
- represents all alphanumeric characters plus the underscore,
- <code>[0-7]</code> represents the octal digits,
- and <code>[0-7%l%-]</code> represents the octal digits plus
- the lowercase letters plus the '<code>-</code>' character.
- <p>
- You can put a closing square bracket in a set
- by positioning it as the first character in the set.
- You can put a hyphen in a set
- by positioning it as the first or the last character in the set.
- (You can also use an escape for both cases.)
- <p>
- The interaction between ranges and classes is not defined.
- Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
- have no meaning.
- </li>
- <li><b><code>[^<em>set</em>]</code>: </b>
- represents the complement of <em>set</em>,
- where <em>set</em> is interpreted as above.
- </li>
- </ul><p>
- For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
- the corresponding uppercase letter represents the complement of the class.
- For instance, <code>%S</code> represents all non-space characters.
- <p>
- The definitions of letter, space, and other character groups
- depend on the current locale.
- In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
- <h4>Pattern Item:</h4><p>
- A <em>pattern item</em> can be
- <ul>
- <li>
- a single character class,
- which matches any single character in the class;
- </li>
- <li>
- a single character class followed by '<code>*</code>',
- which matches sequences of zero or more characters in the class.
- These repetition items will always match the longest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>+</code>',
- which matches sequences of one or more characters in the class.
- These repetition items will always match the longest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>-</code>',
- which also matches sequences of zero or more characters in the class.
- Unlike '<code>*</code>',
- these repetition items will always match the shortest possible sequence;
- </li>
- <li>
- a single character class followed by '<code>?</code>',
- which matches zero or one occurrence of a character in the class.
- It always matches one occurrence if possible;
- </li>
- <li>
- <code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
- such item matches a substring equal to the <em>n</em>-th captured string
- (see below);
- </li>
- <li>
- <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
- such item matches strings that start with <em>x</em>, end with <em>y</em>,
- and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
- This means that, if one reads the string from left to right,
- counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
- the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
- For instance, the item <code>%b()</code> matches expressions with
- balanced parentheses.
- </li>
- <li>
- <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>;
- such item matches an empty string at any position such that
- the next character belongs to <em>set</em>
- and the previous character does not belong to <em>set</em>.
- The set <em>set</em> is interpreted as previously described.
- The beginning and the end of the subject are handled as if
- they were the character '<code>\0</code>'.
- </li>
- </ul>
- <h4>Pattern:</h4><p>
- A <em>pattern</em> is a sequence of pattern items.
- A caret '<code>^</code>' at the beginning of a pattern anchors the match at the
- beginning of the subject string.
- A '<code>$</code>' at the end of a pattern anchors the match at the
- end of the subject string.
- At other positions,
- '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
- <h4>Captures:</h4><p>
- A pattern can contain sub-patterns enclosed in parentheses;
- they describe <em>captures</em>.
- When a match succeeds, the substrings of the subject string
- that match captures are stored (<em>captured</em>) for future use.
- Captures are numbered according to their left parentheses.
- For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
- the part of the string matching <code>"a*(.)%w(%s*)"</code> is
- stored as the first capture, and therefore has number 1;
- the character matching "<code>.</code>" is captured with number 2,
- and the part matching "<code>%s*</code>" has number 3.
- <p>
- As a special case, the capture <code>()</code> captures
- the current string position (a number).
- For instance, if we apply the pattern <code>"()aa()"</code> on the
- string <code>"flaaap"</code>, there will be two captures: 3 and 5.
- <h4>Multiple matches:</h4><p>
- The function <a href="#pdf-string.gsub"><code>string.gsub</code></a> and the iterator <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>
- match multiple occurrences of the given pattern in the subject.
- For these functions,
- a new match is considered valid only
- if it ends at least one byte after the end of the previous match.
- In other words, the pattern machine never accepts the
- empty string as a match immediately after another match.
- As an example,
- consider the results of the following code:
- <pre>
- > string.gsub("abc", "()a*()", print);
- --> 1 2
- --> 3 3
- --> 4 4
- </pre><p>
- The second and third results come from Lua matching an empty
- string after '<code>b</code>' and another one after '<code>c</code>'.
- Lua does not match an empty string after '<code>a</code>',
- because it would end at the same position of the previous match.
- <h3>6.4.2 – <a name="6.4.2">Format Strings for Pack and Unpack</a></h3>
- <p>
- The first argument to <a href="#pdf-string.pack"><code>string.pack</code></a>,
- <a href="#pdf-string.packsize"><code>string.packsize</code></a>, and <a href="#pdf-string.unpack"><code>string.unpack</code></a>
- is a format string,
- which describes the layout of the structure being created or read.
- <p>
- A format string is a sequence of conversion options.
- The conversion options are as follows:
- <ul>
- <li><b><code><</code>: </b>sets little endian</li>
- <li><b><code>></code>: </b>sets big endian</li>
- <li><b><code>=</code>: </b>sets native endian</li>
- <li><b><code>![<em>n</em>]</code>: </b>sets maximum alignment to <code>n</code>
- (default is native alignment)</li>
- <li><b><code>b</code>: </b>a signed byte (<code>char</code>)</li>
- <li><b><code>B</code>: </b>an unsigned byte (<code>char</code>)</li>
- <li><b><code>h</code>: </b>a signed <code>short</code> (native size)</li>
- <li><b><code>H</code>: </b>an unsigned <code>short</code> (native size)</li>
- <li><b><code>l</code>: </b>a signed <code>long</code> (native size)</li>
- <li><b><code>L</code>: </b>an unsigned <code>long</code> (native size)</li>
- <li><b><code>j</code>: </b>a <code>lua_Integer</code></li>
- <li><b><code>J</code>: </b>a <code>lua_Unsigned</code></li>
- <li><b><code>T</code>: </b>a <code>size_t</code> (native size)</li>
- <li><b><code>i[<em>n</em>]</code>: </b>a signed <code>int</code> with <code>n</code> bytes
- (default is native size)</li>
- <li><b><code>I[<em>n</em>]</code>: </b>an unsigned <code>int</code> with <code>n</code> bytes
- (default is native size)</li>
- <li><b><code>f</code>: </b>a <code>float</code> (native size)</li>
- <li><b><code>d</code>: </b>a <code>double</code> (native size)</li>
- <li><b><code>n</code>: </b>a <code>lua_Number</code></li>
- <li><b><code>c<em>n</em></code>: </b>a fixed-sized string with <code>n</code> bytes</li>
- <li><b><code>z</code>: </b>a zero-terminated string</li>
- <li><b><code>s[<em>n</em>]</code>: </b>a string preceded by its length
- coded as an unsigned integer with <code>n</code> bytes
- (default is a <code>size_t</code>)</li>
- <li><b><code>x</code>: </b>one byte of padding</li>
- <li><b><code>X<em>op</em></code>: </b>an empty item that aligns
- according to option <code>op</code>
- (which is otherwise ignored)</li>
- <li><b>'<code> </code>': </b>(space) ignored</li>
- </ul><p>
- (A "<code>[<em>n</em>]</code>" means an optional integral numeral.)
- Except for padding, spaces, and configurations
- (options "<code>xX <=>!</code>"),
- each option corresponds to an argument in <a href="#pdf-string.pack"><code>string.pack</code></a>
- or a result in <a href="#pdf-string.unpack"><code>string.unpack</code></a>.
- <p>
- For options "<code>!<em>n</em></code>", "<code>s<em>n</em></code>", "<code>i<em>n</em></code>", and "<code>I<em>n</em></code>",
- <code>n</code> can be any integer between 1 and 16.
- All integral options check overflows;
- <a href="#pdf-string.pack"><code>string.pack</code></a> checks whether the given value fits in the given size;
- <a href="#pdf-string.unpack"><code>string.unpack</code></a> checks whether the read value fits in a Lua integer.
- For the unsigned options,
- Lua integers are treated as unsigned values too.
- <p>
- Any format string starts as if prefixed by "<code>!1=</code>",
- that is,
- with maximum alignment of 1 (no alignment)
- and native endianness.
- <p>
- Native endianness assumes that the whole system is
- either big or little endian.
- The packing functions will not emulate correctly the behavior
- of mixed-endian formats.
- <p>
- Alignment works as follows:
- For each option,
- the format gets extra padding until the data starts
- at an offset that is a multiple of the minimum between the
- option size and the maximum alignment;
- this minimum must be a power of 2.
- Options "<code>c</code>" and "<code>z</code>" are not aligned;
- option "<code>s</code>" follows the alignment of its starting integer.
- <p>
- All padding is filled with zeros by <a href="#pdf-string.pack"><code>string.pack</code></a>
- and ignored by <a href="#pdf-string.unpack"><code>string.unpack</code></a>.
- <h2>6.5 – <a name="6.5">UTF-8 Support</a></h2>
- <p>
- This library provides basic support for UTF-8 encoding.
- It provides all its functions inside the table <a name="pdf-utf8"><code>utf8</code></a>.
- This library does not provide any support for Unicode other
- than the handling of the encoding.
- Any operation that needs the meaning of a character,
- such as character classification, is outside its scope.
- <p>
- Unless stated otherwise,
- all functions that expect a byte position as a parameter
- assume that the given position is either the start of a byte sequence
- or one plus the length of the subject string.
- As in the string library,
- negative indices count from the end of the string.
- <p>
- Functions that create byte sequences
- accept all values up to <code>0x7FFFFFFF</code>,
- as defined in the original UTF-8 specification;
- that implies byte sequences of up to six bytes.
- <p>
- Functions that interpret byte sequences only accept
- valid sequences (well formed and not overlong).
- By default, they only accept byte sequences
- that result in valid Unicode code points,
- rejecting values greater than <code>10FFFF</code> and surrogates.
- A boolean argument <code>lax</code>, when available,
- lifts these checks,
- so that all values up to <code>0x7FFFFFFF</code> are accepted.
- (Not well formed and overlong sequences are still rejected.)
- <p>
- <hr><h3><a name="pdf-utf8.char"><code>utf8.char (···)</code></a></h3>
- <p>
- Receives zero or more integers,
- converts each one to its corresponding UTF-8 byte sequence
- and returns a string with the concatenation of all these sequences.
- <p>
- <hr><h3><a name="pdf-utf8.charpattern"><code>utf8.charpattern</code></a></h3>
- <p>
- The pattern (a string, not a function) "<code>[\0-\x7F\xC2-\xFD][\x80-\xBF]*</code>"
- (see <a href="#6.4.1">§6.4.1</a>),
- which matches exactly one UTF-8 byte sequence,
- assuming that the subject is a valid UTF-8 string.
- <p>
- <hr><h3><a name="pdf-utf8.codes"><code>utf8.codes (s [, lax])</code></a></h3>
- <p>
- Returns values so that the construction
- <pre>
- for p, c in utf8.codes(s) do <em>body</em> end
- </pre><p>
- will iterate over all UTF-8 characters in string <code>s</code>,
- with <code>p</code> being the position (in bytes) and <code>c</code> the code point
- of each character.
- It raises an error if it meets any invalid byte sequence.
- <p>
- <hr><h3><a name="pdf-utf8.codepoint"><code>utf8.codepoint (s [, i [, j [, lax]]])</code></a></h3>
- <p>
- Returns the code points (as integers) from all characters in <code>s</code>
- that start between byte position <code>i</code> and <code>j</code> (both included).
- The default for <code>i</code> is 1 and for <code>j</code> is <code>i</code>.
- It raises an error if it meets any invalid byte sequence.
- <p>
- <hr><h3><a name="pdf-utf8.len"><code>utf8.len (s [, i [, j [, lax]]])</code></a></h3>
- <p>
- Returns the number of UTF-8 characters in string <code>s</code>
- that start between positions <code>i</code> and <code>j</code> (both inclusive).
- The default for <code>i</code> is 1 and for <code>j</code> is -1.
- If it finds any invalid byte sequence,
- returns <b>fail</b> plus the position of the first invalid byte.
- <p>
- <hr><h3><a name="pdf-utf8.offset"><code>utf8.offset (s, n [, i])</code></a></h3>
- <p>
- Returns the position (in bytes) where the encoding of the
- <code>n</code>-th character of <code>s</code>
- (counting from position <code>i</code>) starts.
- A negative <code>n</code> gets characters before position <code>i</code>.
- The default for <code>i</code> is 1 when <code>n</code> is non-negative
- and <code>#s + 1</code> otherwise,
- so that <code>utf8.offset(s, -n)</code> gets the offset of the
- <code>n</code>-th character from the end of the string.
- If the specified character is neither in the subject
- nor right after its end,
- the function returns <b>fail</b>.
- <p>
- As a special case,
- when <code>n</code> is 0 the function returns the start of the encoding
- of the character that contains the <code>i</code>-th byte of <code>s</code>.
- <p>
- This function assumes that <code>s</code> is a valid UTF-8 string.
- <h2>6.6 – <a name="6.6">Table Manipulation</a></h2>
- <p>
- This library provides generic functions for table manipulation.
- It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
- <p>
- Remember that, whenever an operation needs the length of a table,
- all caveats about the length operator apply (see <a href="#3.4.7">§3.4.7</a>).
- All functions ignore non-numeric keys
- in the tables given as arguments.
- <p>
- <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3>
- <p>
- Given a list where all elements are strings or numbers,
- returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>.
- The default value for <code>sep</code> is the empty string,
- the default for <code>i</code> is 1,
- and the default for <code>j</code> is <code>#list</code>.
- If <code>i</code> is greater than <code>j</code>, returns the empty string.
- <p>
- <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3>
- <p>
- Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>,
- shifting up the elements
- <code>list[pos], list[pos+1], ···, list[#list]</code>.
- The default value for <code>pos</code> is <code>#list+1</code>,
- so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
- of the list <code>t</code>.
- <p>
- <hr><h3><a name="pdf-table.move"><code>table.move (a1, f, e, t [,a2])</code></a></h3>
- <p>
- Moves elements from the table <code>a1</code> to the table <code>a2</code>,
- performing the equivalent to the following
- multiple assignment:
- <code>a2[t],··· = a1[f],···,a1[e]</code>.
- The default for <code>a2</code> is <code>a1</code>.
- The destination range can overlap with the source range.
- The number of elements to be moved must fit in a Lua integer.
- <p>
- Returns the destination table <code>a2</code>.
- <p>
- <hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3>
- <p>
- Returns a new table with all arguments stored into keys 1, 2, etc.
- and with a field "<code>n</code>" with the total number of arguments.
- Note that the resulting table may not be a sequence,
- if some arguments are <b>nil</b>.
- <p>
- <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3>
- <p>
- Removes from <code>list</code> the element at position <code>pos</code>,
- returning the value of the removed element.
- When <code>pos</code> is an integer between 1 and <code>#list</code>,
- it shifts down the elements
- <code>list[pos+1], list[pos+2], ···, list[#list]</code>
- and erases element <code>list[#list]</code>;
- The index <code>pos</code> can also be 0 when <code>#list</code> is 0,
- or <code>#list + 1</code>.
- <p>
- The default value for <code>pos</code> is <code>#list</code>,
- so that a call <code>table.remove(l)</code> removes the last element
- of the list <code>l</code>.
- <p>
- <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3>
- <p>
- Sorts the list elements in a given order, <em>in-place</em>,
- from <code>list[1]</code> to <code>list[#list]</code>.
- If <code>comp</code> is given,
- then it must be a function that receives two list elements
- and returns true when the first element must come
- before the second in the final order
- (so that, after the sort,
- <code>i < j</code> implies <code>not comp(list[j],list[i])</code>).
- If <code>comp</code> is not given,
- then the standard Lua operator <code><</code> is used instead.
- <p>
- Note that the <code>comp</code> function must define
- a strict partial order over the elements in the list;
- that is, it must be asymmetric and transitive.
- Otherwise, no valid sort may be possible.
- <p>
- The sort algorithm is not stable:
- elements considered equal by the given order
- may have their relative positions changed by the sort.
- <p>
- <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3>
- <p>
- Returns the elements from the given list.
- This function is equivalent to
- <pre>
- return list[i], list[i+1], ···, list[j]
- </pre><p>
- By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>.
- <h2>6.7 – <a name="6.7">Mathematical Functions</a></h2>
- <p>
- This library provides basic mathematical functions.
- It provides all its functions and constants inside the table <a name="pdf-math"><code>math</code></a>.
- Functions with the annotation "<code>integer/float</code>" give
- integer results for integer arguments
- and float results for non-integer arguments.
- The rounding functions
- <a href="#pdf-math.ceil"><code>math.ceil</code></a>, <a href="#pdf-math.floor"><code>math.floor</code></a>, and <a href="#pdf-math.modf"><code>math.modf</code></a>
- return an integer when the result fits in the range of an integer,
- or a float otherwise.
- <p>
- <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
- <p>
- Returns the maximum value between <code>x</code> and <code>-x</code>. (integer/float)
- <p>
- <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
- <p>
- Returns the arc cosine of <code>x</code> (in radians).
- <p>
- <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
- <p>
- Returns the arc sine of <code>x</code> (in radians).
- <p>
- <hr><h3><a name="pdf-math.atan"><code>math.atan (y [, x])</code></a></h3>
- <p>
- Returns the arc tangent of <code>y/x</code> (in radians),
- but uses the signs of both arguments to find the
- quadrant of the result.
- It also handles correctly the case of <code>x</code> being zero.
- <p>
- The default value for <code>x</code> is 1,
- so that the call <code>math.atan(y)</code>
- returns the arc tangent of <code>y</code>.
- <p>
- <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
- <p>
- Returns the smallest integral value greater than or equal to <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
- <p>
- Returns the cosine of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
- <p>
- Converts the angle <code>x</code> from radians to degrees.
- <p>
- <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
- <p>
- Returns the value <em>e<sup>x</sup></em>
- (where <code>e</code> is the base of natural logarithms).
- <p>
- <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
- <p>
- Returns the largest integral value less than or equal to <code>x</code>.
- <p>
- <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
- <p>
- Returns the remainder of the division of <code>x</code> by <code>y</code>
- that rounds the quotient towards zero. (integer/float)
- <p>
- <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
- <p>
- The float value <code>HUGE_VAL</code>,
- a value greater than any other numeric value.
- <p>
- <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3>
- <p>
- Returns the logarithm of <code>x</code> in the given base.
- The default for <code>base</code> is <em>e</em>
- (so that the function returns the natural logarithm of <code>x</code>).
- <p>
- <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3>
- <p>
- Returns the argument with the maximum value,
- according to the Lua operator <code><</code>.
- <p>
- <hr><h3><a name="pdf-math.maxinteger"><code>math.maxinteger</code></a></h3>
- An integer with the maximum value for an integer.
- <p>
- <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3>
- <p>
- Returns the argument with the minimum value,
- according to the Lua operator <code><</code>.
- <p>
- <hr><h3><a name="pdf-math.mininteger"><code>math.mininteger</code></a></h3>
- An integer with the minimum value for an integer.
- <p>
- <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
- <p>
- Returns the integral part of <code>x</code> and the fractional part of <code>x</code>.
- Its second result is always a float.
- <p>
- <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
- <p>
- The value of <em>π</em>.
- <p>
- <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
- <p>
- Converts the angle <code>x</code> from degrees to radians.
- <p>
- <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
- <p>
- When called without arguments,
- returns a pseudo-random float with uniform distribution
- in the range <em>[0,1)</em>.
- When called with two integers <code>m</code> and <code>n</code>,
- <code>math.random</code> returns a pseudo-random integer
- with uniform distribution in the range <em>[m, n]</em>.
- The call <code>math.random(n)</code>, for a positive <code>n</code>,
- is equivalent to <code>math.random(1,n)</code>.
- The call <code>math.random(0)</code> produces an integer with
- all bits (pseudo)random.
- <p>
- This function uses the <code>xoshiro256**</code> algorithm to produce
- pseudo-random 64-bit integers,
- which are the results of calls with argument 0.
- Other results (ranges and floats)
- are unbiased extracted from these integers.
- <p>
- Lua initializes its pseudo-random generator with the equivalent of
- a call to <a href="#pdf-math.randomseed"><code>math.randomseed</code></a> with no arguments,
- so that <code>math.random</code> should generate
- different sequences of results each time the program runs.
- <p>
- <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed ([x [, y]])</code></a></h3>
- <p>
- When called with at least one argument,
- the integer parameters <code>x</code> and <code>y</code> are
- joined into a 128-bit <em>seed</em> that
- is used to reinitialize the pseudo-random generator;
- equal seeds produce equal sequences of numbers.
- The default for <code>y</code> is zero.
- <p>
- When called with no arguments,
- Lua generates a seed with
- a weak attempt for randomness.
- <p>
- This function returns the two seed components
- that were effectively used,
- so that setting them again repeats the sequence.
- <p>
- To ensure a required level of randomness to the initial state
- (or contrarily, to have a deterministic sequence,
- for instance when debugging a program),
- you should call <a href="#pdf-math.randomseed"><code>math.randomseed</code></a> with explicit arguments.
- <p>
- <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
- <p>
- Returns the sine of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
- <p>
- Returns the square root of <code>x</code>.
- (You can also use the expression <code>x^0.5</code> to compute this value.)
- <p>
- <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
- <p>
- Returns the tangent of <code>x</code> (assumed to be in radians).
- <p>
- <hr><h3><a name="pdf-math.tointeger"><code>math.tointeger (x)</code></a></h3>
- <p>
- If the value <code>x</code> is convertible to an integer,
- returns that integer.
- Otherwise, returns <b>fail</b>.
- <p>
- <hr><h3><a name="pdf-math.type"><code>math.type (x)</code></a></h3>
- <p>
- Returns "<code>integer</code>" if <code>x</code> is an integer,
- "<code>float</code>" if it is a float,
- or <b>fail</b> if <code>x</code> is not a number.
- <p>
- <hr><h3><a name="pdf-math.ult"><code>math.ult (m, n)</code></a></h3>
- <p>
- Returns a boolean,
- true if and only if integer <code>m</code> is below integer <code>n</code> when
- they are compared as unsigned integers.
- <h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2>
- <p>
- The I/O library provides two different styles for file manipulation.
- The first one uses implicit file handles;
- that is, there are operations to set a default input file and a
- default output file,
- and all input/output operations are done over these default files.
- The second style uses explicit file handles.
- <p>
- When using implicit file handles,
- all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
- When using explicit file handles,
- the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file handle
- and then all operations are supplied as methods of the file handle.
- <p>
- The metatable for file handles provides metamethods
- for <code>__gc</code> and <code>__close</code> that try
- to close the file when called.
- <p>
- The table <code>io</code> also provides
- three predefined file handles with their usual meanings from C:
- <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>.
- The I/O library never closes these files.
- <p>
- Unless otherwise stated,
- all I/O functions return <b>fail</b> on failure,
- plus an error message as a second result and
- a system-dependent error code as a third result,
- and some non-false value on success.
- On non-POSIX systems,
- the computation of the error message and error code
- in case of errors
- may be not thread safe,
- because they rely on the global C variable <code>errno</code>.
- <p>
- <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
- <p>
- Equivalent to <code>file:close()</code>.
- Without a <code>file</code>, closes the default output file.
- <p>
- <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
- <p>
- Equivalent to <code>io.output():flush()</code>.
- <p>
- <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
- <p>
- When called with a file name, it opens the named file (in text mode),
- and sets its handle as the default input file.
- When called with a file handle,
- it simply sets this file handle as the default input file.
- When called without arguments,
- it returns the current default input file.
- <p>
- In case of errors this function raises the error,
- instead of returning an error code.
- <p>
- <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename, ···])</code></a></h3>
- <p>
- Opens the given file name in read mode
- and returns an iterator function that
- works like <code>file:lines(···)</code> over the opened file.
- When the iterator function fails to read any value,
- it automatically closes the file.
- Besides the iterator function,
- <code>io.lines</code> returns three other values:
- two <b>nil</b> values as placeholders,
- plus the created file handle.
- Therefore, when used in a generic <b>for</b> loop,
- the file is closed also if the loop is interrupted by an
- error or a <b>break</b>.
- <p>
- The call <code>io.lines()</code> (with no file name) is equivalent
- to <code>io.input():lines("l")</code>;
- that is, it iterates over the lines of the default input file.
- In this case, the iterator does not close the file when the loop ends.
- <p>
- In case of errors opening the file,
- this function raises the error,
- instead of returning an error code.
- <p>
- <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
- <p>
- This function opens a file,
- in the mode specified in the string <code>mode</code>.
- In case of success,
- it returns a new file handle.
- <p>
- The <code>mode</code> string can be any of the following:
- <ul>
- <li><b>"<code>r</code>": </b> read mode (the default);</li>
- <li><b>"<code>w</code>": </b> write mode;</li>
- <li><b>"<code>a</code>": </b> append mode;</li>
- <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li>
- <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li>
- <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved,
- writing is only allowed at the end of file.</li>
- </ul><p>
- The <code>mode</code> string can also have a '<code>b</code>' at the end,
- which is needed in some systems to open the file in binary mode.
- <p>
- <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
- <p>
- Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
- <p>
- <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
- <p>
- This function is system dependent and is not available
- on all platforms.
- <p>
- Starts the program <code>prog</code> in a separated process and returns
- a file handle that you can use to read data from this program
- (if <code>mode</code> is <code>"r"</code>, the default)
- or to write data to this program
- (if <code>mode</code> is <code>"w"</code>).
- <p>
- <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3>
- <p>
- Equivalent to <code>io.input():read(···)</code>.
- <p>
- <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
- <p>
- In case of success,
- returns a handle for a temporary file.
- This file is opened in update mode
- and it is automatically removed when the program ends.
- <p>
- <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
- <p>
- Checks whether <code>obj</code> is a valid file handle.
- Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
- <code>"closed file"</code> if <code>obj</code> is a closed file handle,
- or <b>fail</b> if <code>obj</code> is not a file handle.
- <p>
- <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3>
- <p>
- Equivalent to <code>io.output():write(···)</code>.
- <p>
- <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
- <p>
- Closes <code>file</code>.
- Note that files are automatically closed when
- their handles are garbage collected,
- but that takes an unpredictable amount of time to happen.
- <p>
- When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>,
- <a href="#pdf-file:close"><code>file:close</code></a> returns the same values
- returned by <a href="#pdf-os.execute"><code>os.execute</code></a>.
- <p>
- <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
- <p>
- Saves any written data to <code>file</code>.
- <p>
- <hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3>
- <p>
- Returns an iterator function that,
- each time it is called,
- reads the file according to the given formats.
- When no format is given,
- uses "<code>l</code>" as a default.
- As an example, the construction
- <pre>
- for c in file:lines(1) do <em>body</em> end
- </pre><p>
- will iterate over all characters of the file,
- starting at the current position.
- Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
- when the loop ends.
- <p>
- <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3>
- <p>
- Reads the file <code>file</code>,
- according to the given formats, which specify what to read.
- For each format,
- the function returns a string or a number with the characters read,
- or <b>fail</b> if it cannot read data with the specified format.
- (In this latter case,
- the function does not read subsequent formats.)
- When called without arguments,
- it uses a default format that reads the next line
- (see below).
- <p>
- The available formats are
- <ul>
- <li><b>"<code>n</code>": </b>
- reads a numeral and returns it as a float or an integer,
- following the lexical conventions of Lua.
- (The numeral may have leading whitespaces and a sign.)
- This format always reads the longest input sequence that
- is a valid prefix for a numeral;
- if that prefix does not form a valid numeral
- (e.g., an empty string, "<code>0x</code>", or "<code>3.4e-</code>")
- or it is too long (more than 200 characters),
- it is discarded and the format returns <b>fail</b>.
- </li>
- <li><b>"<code>a</code>": </b>
- reads the whole file, starting at the current position.
- On end of file, it returns the empty string;
- this format never fails.
- </li>
- <li><b>"<code>l</code>": </b>
- reads the next line skipping the end of line,
- returning <b>fail</b> on end of file.
- This is the default format.
- </li>
- <li><b>"<code>L</code>": </b>
- reads the next line keeping the end-of-line character (if present),
- returning <b>fail</b> on end of file.
- </li>
- <li><b><em>number</em>: </b>
- reads a string with up to this number of bytes,
- returning <b>fail</b> on end of file.
- If <code>number</code> is zero,
- it reads nothing and returns an empty string,
- or <b>fail</b> on end of file.
- </li>
- </ul><p>
- The formats "<code>l</code>" and "<code>L</code>" should be used only for text files.
- <p>
- <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3>
- <p>
- Sets and gets the file position,
- measured from the beginning of the file,
- to the position given by <code>offset</code> plus a base
- specified by the string <code>whence</code>, as follows:
- <ul>
- <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li>
- <li><b>"<code>cur</code>": </b> base is current position;</li>
- <li><b>"<code>end</code>": </b> base is end of file;</li>
- </ul><p>
- In case of success, <code>seek</code> returns the final file position,
- measured in bytes from the beginning of the file.
- If <code>seek</code> fails, it returns <b>fail</b>,
- plus a string describing the error.
- <p>
- The default value for <code>whence</code> is <code>"cur"</code>,
- and for <code>offset</code> is 0.
- Therefore, the call <code>file:seek()</code> returns the current
- file position, without changing it;
- the call <code>file:seek("set")</code> sets the position to the
- beginning of the file (and returns 0);
- and the call <code>file:seek("end")</code> sets the position to the
- end of the file, and returns its size.
- <p>
- <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
- <p>
- Sets the buffering mode for a file.
- There are three available modes:
- <ul>
- <li><b>"<code>no</code>": </b> no buffering.</li>
- <li><b>"<code>full</code>": </b> full buffering.</li>
- <li><b>"<code>line</code>": </b> line buffering.</li>
- </ul>
- <p>
- For the last two cases,
- <code>size</code> is a hint for the size of the buffer, in bytes.
- The default is an appropriate size.
- <p>
- The specific behavior of each mode is non portable;
- check the underlying ISO C function <code>setvbuf</code> in your platform for
- more details.
- <p>
- <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3>
- <p>
- Writes the value of each of its arguments to <code>file</code>.
- The arguments must be strings or numbers.
- <p>
- In case of success, this function returns <code>file</code>.
- <h2>6.9 – <a name="6.9">Operating System Facilities</a></h2>
- <p>
- This library is implemented through table <a name="pdf-os"><code>os</code></a>.
- <p>
- <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
- <p>
- Returns an approximation of the amount in seconds of CPU time
- used by the program,
- as returned by the underlying ISO C function <code>clock</code>.
- <p>
- <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
- <p>
- Returns a string or a table containing date and time,
- formatted according to the given string <code>format</code>.
- <p>
- If the <code>time</code> argument is present,
- this is the time to be formatted
- (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
- Otherwise, <code>date</code> formats the current time.
- <p>
- If <code>format</code> starts with '<code>!</code>',
- then the date is formatted in Coordinated Universal Time.
- After this optional character,
- if <code>format</code> is the string "<code>*t</code>",
- then <code>date</code> returns a table with the following fields:
- <code>year</code>, <code>month</code> (1–12), <code>day</code> (1–31),
- <code>hour</code> (0–23), <code>min</code> (0–59),
- <code>sec</code> (0–61, due to leap seconds),
- <code>wday</code> (weekday, 1–7, Sunday is 1),
- <code>yday</code> (day of the year, 1–366),
- and <code>isdst</code> (daylight saving flag, a boolean).
- This last field may be absent
- if the information is not available.
- <p>
- If <code>format</code> is not "<code>*t</code>",
- then <code>date</code> returns the date as a string,
- formatted according to the same rules as the ISO C function <code>strftime</code>.
- <p>
- If <code>format</code> is absent, it defaults to "<code>%c</code>",
- which gives a human-readable date and time representation
- using the current locale.
- <p>
- On non-POSIX systems,
- this function may be not thread safe
- because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>.
- <p>
- <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
- <p>
- Returns the difference, in seconds,
- from time <code>t1</code> to time <code>t2</code>
- (where the times are values returned by <a href="#pdf-os.time"><code>os.time</code></a>).
- In POSIX, Windows, and some other systems,
- this value is exactly <code>t2</code><em>-</em><code>t1</code>.
- <p>
- <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
- <p>
- This function is equivalent to the ISO C function <code>system</code>.
- It passes <code>command</code> to be executed by an operating system shell.
- Its first result is <b>true</b>
- if the command terminated successfully,
- or <b>fail</b> otherwise.
- After this first result
- the function returns a string plus a number,
- as follows:
- <ul>
- <li><b>"<code>exit</code>": </b>
- the command terminated normally;
- the following number is the exit status of the command.
- </li>
- <li><b>"<code>signal</code>": </b>
- the command was terminated by a signal;
- the following number is the signal that terminated the command.
- </li>
- </ul>
- <p>
- When called without a <code>command</code>,
- <code>os.execute</code> returns a boolean that is true if a shell is available.
- <p>
- <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close]])</code></a></h3>
- <p>
- Calls the ISO C function <code>exit</code> to terminate the host program.
- If <code>code</code> is <b>true</b>,
- the returned status is <code>EXIT_SUCCESS</code>;
- if <code>code</code> is <b>false</b>,
- the returned status is <code>EXIT_FAILURE</code>;
- if <code>code</code> is a number,
- the returned status is this number.
- The default value for <code>code</code> is <b>true</b>.
- <p>
- If the optional second argument <code>close</code> is true,
- closes the Lua state before exiting.
- <p>
- <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
- <p>
- Returns the value of the process environment variable <code>varname</code>
- or <b>fail</b> if the variable is not defined.
- <p>
- <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
- <p>
- Deletes the file (or empty directory, on POSIX systems)
- with the given name.
- If this function fails, it returns <b>fail</b>
- plus a string describing the error and the error code.
- Otherwise, it returns true.
- <p>
- <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
- <p>
- Renames the file or directory named <code>oldname</code> to <code>newname</code>.
- If this function fails, it returns <b>fail</b>,
- plus a string describing the error and the error code.
- Otherwise, it returns true.
- <p>
- <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
- <p>
- Sets the current locale of the program.
- <code>locale</code> is a system-dependent string specifying a locale;
- <code>category</code> is an optional string describing which category to change:
- <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
- <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
- the default category is <code>"all"</code>.
- The function returns the name of the new locale,
- or <b>fail</b> if the request cannot be honored.
- <p>
- If <code>locale</code> is the empty string,
- the current locale is set to an implementation-defined native locale.
- If <code>locale</code> is the string "<code>C</code>",
- the current locale is set to the standard C locale.
- <p>
- When called with <b>nil</b> as the first argument,
- this function only returns the name of the current locale
- for the given category.
- <p>
- This function may be not thread safe
- because of its reliance on C function <code>setlocale</code>.
- <p>
- <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
- <p>
- Returns the current time when called without arguments,
- or a time representing the local date and time specified by the given table.
- This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
- and may have fields
- <code>hour</code> (default is 12),
- <code>min</code> (default is 0),
- <code>sec</code> (default is 0),
- and <code>isdst</code> (default is <b>nil</b>).
- Other fields are ignored.
- For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
- <p>
- When the function is called,
- the values in these fields do not need to be inside their valid ranges.
- For instance, if <code>sec</code> is -10,
- it means 10 seconds before the time specified by the other fields;
- if <code>hour</code> is 1000,
- it means 1000 hours after the time specified by the other fields.
- <p>
- The returned value is a number, whose meaning depends on your system.
- In POSIX, Windows, and some other systems,
- this number counts the number
- of seconds since some given start time (the "epoch").
- In other systems, the meaning is not specified,
- and the number returned by <code>time</code> can be used only as an argument to
- <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>.
- <p>
- When called with a table,
- <code>os.time</code> also normalizes all the fields
- documented in the <a href="#pdf-os.date"><code>os.date</code></a> function,
- so that they represent the same time as before the call
- but with values inside their valid ranges.
- <p>
- <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
- <p>
- Returns a string with a file name that can
- be used for a temporary file.
- The file must be explicitly opened before its use
- and explicitly removed when no longer needed.
- <p>
- In POSIX systems,
- this function also creates a file with that name,
- to avoid security risks.
- (Someone else might create the file with wrong permissions
- in the time between getting the name and creating the file.)
- You still have to open the file to use it
- and to remove it (even if you do not use it).
- <p>
- When possible,
- you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
- which automatically removes the file when the program ends.
- <h2>6.10 – <a name="6.10">The Debug Library</a></h2>
- <p>
- This library provides
- the functionality of the debug interface (<a href="#4.7">§4.7</a>) to Lua programs.
- You should exert care when using this library.
- Several of its functions
- violate basic assumptions about Lua code
- (e.g., that variables local to a function
- cannot be accessed from outside;
- that userdata metatables cannot be changed by Lua code;
- that Lua programs do not crash)
- and therefore can compromise otherwise secure code.
- Moreover, some functions in this library may be slow.
- <p>
- All functions in this library are provided
- inside the <a name="pdf-debug"><code>debug</code></a> table.
- All functions that operate over a thread
- have an optional first argument which is the
- thread to operate over.
- The default is always the current thread.
- <p>
- <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
- <p>
- Enters an interactive mode with the user,
- running each string that the user enters.
- Using simple commands and other debug facilities,
- the user can inspect global and local variables,
- change their values, evaluate expressions, and so on.
- A line containing only the word <code>cont</code> finishes this function,
- so that the caller continues its execution.
- <p>
- Note that commands for <code>debug.debug</code> are not lexically nested
- within any function and so have no direct access to local variables.
- <p>
- <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
- <p>
- Returns the current hook settings of the thread, as three values:
- the current hook function, the current hook mask,
- and the current hook count,
- as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function.
- <p>
- Returns <b>fail</b> if there is no active hook.
- <p>
- <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3>
- <p>
- Returns a table with information about a function.
- You can give the function directly
- or you can give a number as the value of <code>f</code>,
- which means the function running at level <code>f</code> of the call stack
- of the given thread:
- level 0 is the current function (<code>getinfo</code> itself);
- level 1 is the function that called <code>getinfo</code>
- (except for tail calls, which do not count on the stack);
- and so on.
- If <code>f</code> is a number greater than the number of active functions,
- then <code>getinfo</code> returns <b>fail</b>.
- <p>
- The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
- with the string <code>what</code> describing which fields to fill in.
- The default for <code>what</code> is to get all information available,
- except the table of valid lines.
- If present,
- the option '<code>f</code>'
- adds a field named <code>func</code> with the function itself.
- If present,
- the option '<code>L</code>'
- adds a field named <code>activelines</code> with the table of
- valid lines.
- <p>
- For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
- a name for the current function,
- if a reasonable name can be found,
- and the expression <code>debug.getinfo(print)</code>
- returns a table with all available information
- about the <a href="#pdf-print"><code>print</code></a> function.
- <p>
- <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3>
- <p>
- This function returns the name and the value of the local variable
- with index <code>local</code> of the function at level <code>f</code> of the stack.
- This function accesses not only explicit local variables,
- but also parameters and temporary values.
- <p>
- The first parameter or local variable has index 1, and so on,
- following the order that they are declared in the code,
- counting only the variables that are active
- in the current scope of the function.
- Compile-time constants may not appear in this listing,
- if they were optimized away by the compiler.
- Negative indices refer to vararg arguments;
- -1 is the first vararg argument.
- The function returns <b>fail</b>
- if there is no variable with the given index,
- and raises an error when called with a level out of range.
- (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
- <p>
- Variable names starting with '<code>(</code>' (open parenthesis)
- represent variables with no known names
- (internal variables such as loop control variables,
- and variables from chunks saved without debug information).
- <p>
- The parameter <code>f</code> may also be a function.
- In that case, <code>getlocal</code> returns only the name of function parameters.
- <p>
- <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3>
- <p>
- Returns the metatable of the given <code>value</code>
- or <b>nil</b> if it does not have a metatable.
- <p>
- <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
- <p>
- Returns the registry table (see <a href="#4.3">§4.3</a>).
- <p>
- <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3>
- <p>
- This function returns the name and the value of the upvalue
- with index <code>up</code> of the function <code>f</code>.
- The function returns <b>fail</b>
- if there is no upvalue with the given index.
- <p>
- (For Lua functions,
- upvalues are the external local variables that the function uses,
- and that are consequently included in its closure.)
- <p>
- For C functions, this function uses the empty string <code>""</code>
- as a name for all upvalues.
- <p>
- Variable name '<code>?</code>' (interrogation mark)
- represents variables with no known names
- (variables from chunks saved without debug information).
- <p>
- <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u, n)</code></a></h3>
- <p>
- Returns the <code>n</code>-th user value associated
- to the userdata <code>u</code> plus a boolean,
- <b>false</b> if the userdata does not have that value.
- <p>
- <hr><h3><a name="pdf-debug.setcstacklimit"><code>debug.setcstacklimit (limit)</code></a></h3>
- <p>
- Sets a new limit for the C stack.
- This limit controls how deeply nested calls can go in Lua,
- with the intent of avoiding a stack overflow.
- A limit too small restricts recursive calls pointlessly;
- a limit too large exposes the interpreter to stack-overflow crashes.
- Unfortunately, there is no way to know a priori
- the maximum safe limit for a platform.
- <p>
- Each call made from Lua code counts one unit.
- Other operations (e.g., calls made from C to Lua or resuming a coroutine)
- may have a higher cost.
- <p>
- This function has the following restrictions:
- <ul>
- <li>It can only be called from the main coroutine (thread);</li>
- <li>It cannot be called while handling a stack-overflow error;</li>
- <li><code>limit</code> must be less than 40000;</li>
- <li><code>limit</code> cannot be less than the amount of C stack in use.</li>
- </ul><p>
- If a call does not respect some restriction,
- it returns a false value.
- Otherwise,
- the call returns the old limit.
- <p>
- <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
- <p>
- Sets the given function as the debug hook.
- The string <code>mask</code> and the number <code>count</code> describe
- when the hook will be called.
- The string mask may have any combination of the following characters,
- with the given meaning:
- <ul>
- <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li>
- <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li>
- <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li>
- </ul><p>
- Moreover,
- with a <code>count</code> different from zero,
- the hook is called also after every <code>count</code> instructions.
- <p>
- When called without arguments,
- <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
- <p>
- When the hook is called, its first parameter is a string
- describing the event that has triggered its call:
- <code>"call"</code>, <code>"tail call"</code>, <code>"return"</code>,
- <code>"line"</code>, and <code>"count"</code>.
- For line events,
- the hook also gets the new line number as its second parameter.
- Inside a hook,
- you can call <code>getinfo</code> with level 2 to get more information about
- the running function.
- (Level 0 is the <code>getinfo</code> function,
- and level 1 is the hook function.)
- <p>
- <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
- <p>
- This function assigns the value <code>value</code> to the local variable
- with index <code>local</code> of the function at level <code>level</code> of the stack.
- The function returns <b>fail</b> if there is no local
- variable with the given index,
- and raises an error when called with a <code>level</code> out of range.
- (You can call <code>getinfo</code> to check whether the level is valid.)
- Otherwise, it returns the name of the local variable.
- <p>
- See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about
- variable indices and names.
- <p>
- <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3>
- <p>
- Sets the metatable for the given <code>value</code> to the given <code>table</code>
- (which can be <b>nil</b>).
- Returns <code>value</code>.
- <p>
- <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3>
- <p>
- This function assigns the value <code>value</code> to the upvalue
- with index <code>up</code> of the function <code>f</code>.
- The function returns <b>fail</b> if there is no upvalue
- with the given index.
- Otherwise, it returns the name of the upvalue.
- <p>
- See <a href="#pdf-debug.getupvalue"><code>debug.getupvalue</code></a> for more information about upvalues.
- <p>
- <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value, n)</code></a></h3>
- <p>
- Sets the given <code>value</code> as
- the <code>n</code>-th user value associated to the given <code>udata</code>.
- <code>udata</code> must be a full userdata.
- <p>
- Returns <code>udata</code>,
- or <b>fail</b> if the userdata does not have that value.
- <p>
- <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
- <p>
- If <code>message</code> is present but is neither a string nor <b>nil</b>,
- this function returns <code>message</code> without further processing.
- Otherwise,
- it returns a string with a traceback of the call stack.
- The optional <code>message</code> string is appended
- at the beginning of the traceback.
- An optional <code>level</code> number tells at which level
- to start the traceback
- (default is 1, the function calling <code>traceback</code>).
- <p>
- <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3>
- <p>
- Returns a unique identifier (as a light userdata)
- for the upvalue numbered <code>n</code>
- from the given function.
- <p>
- These unique identifiers allow a program to check whether different
- closures share upvalues.
- Lua closures that share an upvalue
- (that is, that access a same external local variable)
- will return identical ids for those upvalue indices.
- <p>
- <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3>
- <p>
- Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code>
- refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>.
- <h1>7 – <a name="7">Lua Standalone</a></h1>
- <p>
- Although Lua has been designed as an extension language,
- to be embedded in a host C program,
- it is also frequently used as a standalone language.
- An interpreter for Lua as a standalone language,
- called simply <code>lua</code>,
- is provided with the standard distribution.
- The standalone interpreter includes
- all standard libraries.
- Its usage is:
- <pre>
- lua [options] [script [args]]
- </pre><p>
- The options are:
- <ul>
- <li><b><code>-e <em>stat</em></code>: </b> execute string <em>stat</em>;</li>
- <li><b><code>-i</code>: </b> enter interactive mode after running <em>script</em>;</li>
- <li><b><code>-l <em>mod</em></code>: </b> "require" <em>mod</em> and assign the
- result to global <em>mod</em>;</li>
- <li><b><code>-v</code>: </b> print version information;</li>
- <li><b><code>-E</code>: </b> ignore environment variables;</li>
- <li><b><code>-W</code>: </b> turn warnings on;</li>
- <li><b><code>--</code>: </b> stop handling options;</li>
- <li><b><code>-</code>: </b> execute <code>stdin</code> as a file and stop handling options.</li>
- </ul><p>
- After handling its options, <code>lua</code> runs the given <em>script</em>.
- When called without arguments,
- <code>lua</code> behaves as <code>lua -v -i</code>
- when the standard input (<code>stdin</code>) is a terminal,
- and as <code>lua -</code> otherwise.
- <p>
- When called without the option <code>-E</code>,
- the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_4"><code>LUA_INIT_5_4</code></a>
- (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if the versioned name is not defined)
- before running any argument.
- If the variable content has the format <code>@<em>filename</em></code>,
- then <code>lua</code> executes the file.
- Otherwise, <code>lua</code> executes the string itself.
- <p>
- When called with the option <code>-E</code>,
- Lua does not consult any environment variables.
- In particular,
- the values of <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a>
- are set with the default paths defined in <code>luaconf.h</code>.
- <p>
- The options <code>-e</code>, <code>-l</code>, and <code>-W</code> are handled in
- the order they appear.
- For instance, an invocation like
- <pre>
- $ lua -e 'a=1' -llib1 script.lua
- </pre><p>
- will first set <code>a</code> to 1, then require the library <code>lib1</code>,
- and finally run the file <code>script.lua</code> with no arguments.
- (Here <code>$</code> is the shell prompt. Your prompt may be different.)
- <p>
- Before running any code,
- <code>lua</code> collects all command-line arguments
- in a global table called <code>arg</code>.
- The script name goes to index 0,
- the first argument after the script name goes to index 1,
- and so on.
- Any arguments before the script name
- (that is, the interpreter name plus its options)
- go to negative indices.
- For instance, in the call
- <pre>
- $ lua -la b.lua t1 t2
- </pre><p>
- the table is like this:
- <pre>
- arg = { [-2] = "lua", [-1] = "-la",
- [0] = "b.lua",
- [1] = "t1", [2] = "t2" }
- </pre><p>
- If there is no script in the call,
- the interpreter name goes to index 0,
- followed by the other arguments.
- For instance, the call
- <pre>
- $ lua -e "print(arg[1])"
- </pre><p>
- will print "<code>-e</code>".
- If there is a script,
- the script is called with arguments
- <code>arg[1]</code>, ···, <code>arg[#arg]</code>.
- Like all chunks in Lua,
- the script is compiled as a vararg function.
- <p>
- In interactive mode,
- Lua repeatedly prompts and waits for a line.
- After reading a line,
- Lua first try to interpret the line as an expression.
- If it succeeds, it prints its value.
- Otherwise, it interprets the line as a statement.
- If you write an incomplete statement,
- the interpreter waits for its completion
- by issuing a different prompt.
- <p>
- If the global variable <a name="pdf-_PROMPT"><code>_PROMPT</code></a> contains a string,
- then its value is used as the prompt.
- Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> contains a string,
- its value is used as the secondary prompt
- (issued during incomplete statements).
- <p>
- In case of unprotected errors in the script,
- the interpreter reports the error to the standard error stream.
- If the error object is not a string but
- has a metamethod <code>__tostring</code>,
- the interpreter calls this metamethod to produce the final message.
- Otherwise, the interpreter converts the error object to a string
- and adds a stack traceback to it.
- When warnings are on,
- they are simply printed in the standard error output.
- <p>
- When finishing normally,
- the interpreter closes its main Lua state
- (see <a href="#lua_close"><code>lua_close</code></a>).
- The script can avoid this step by
- calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate.
- <p>
- To allow the use of Lua as a
- script interpreter in Unix systems,
- Lua skips the first line of a file chunk if it starts with <code>#</code>.
- Therefore, Lua scripts can be made into executable programs
- by using <code>chmod +x</code> and the <code>#!</code> form,
- as in
- <pre>
- #!/usr/local/bin/lua
- </pre><p>
- Of course,
- the location of the Lua interpreter may be different in your machine.
- If <code>lua</code> is in your <code>PATH</code>,
- then
- <pre>
- #!/usr/bin/env lua
- </pre><p>
- is a more portable solution.
- <h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1>
- <p>
- Here we list the incompatibilities that you may find when moving a program
- from Lua 5.3 to Lua 5.4.
- <p>
- You can avoid some incompatibilities by compiling Lua with
- appropriate options (see file <code>luaconf.h</code>).
- However,
- all these compatibility options will be removed in the future.
- More often than not,
- compatibility issues arise when these compatibility options
- are removed.
- So, whenever you have the chance,
- you should try to test your code with a version of Lua compiled
- with all compatibility options turned off.
- That will ease transitions to newer versions of Lua.
- <p>
- Lua versions can always change the C API in ways that
- do not imply source-code changes in a program,
- such as the numeric values for constants
- or the implementation of functions as macros.
- Therefore,
- you should never assume that binaries are compatible between
- different Lua versions.
- Always recompile clients of the Lua API when
- using a new version.
- <p>
- Similarly, Lua versions can always change the internal representation
- of precompiled chunks;
- precompiled chunks are not compatible between different Lua versions.
- <p>
- The standard paths in the official distribution may
- change between versions.
- <h2>8.1 – <a name="8.1">Incompatibilities in the Language</a></h2>
- <ul>
- <li>
- The coercion of strings to numbers in
- arithmetic and bitwise operations
- has been removed from the core language.
- The string library does a similar job
- for arithmetic (but not for bitwise) operations
- using the string metamethods.
- However, unlike in previous versions,
- the new implementation preserves the implicit type of the numeral
- in the string.
- For instance, the result of <code>"1" + "2"</code> now is an integer,
- not a float.
- </li>
- <li>
- Literal decimal integer constants that overflow are read as floats,
- instead of wrapping around.
- You can use hexadecimal notation for such constants if you
- want the old behavior
- (reading them as integers with wrap around).
- </li>
- <li>
- The use of the <code>__lt</code> metamethod to emulate <code>__le</code>
- has been removed.
- When needed, this metamethod must be explicitly defined.
- </li>
- <li>
- The semantics of the numerical <b>for</b> loop
- over integers changed in some details.
- In particular, the control variable never wraps around.
- </li>
- <li>
- A label for a <b>goto</b> cannot be declared where a label with the same
- name is visible, even if this other label is declared in an enclosing
- block.
- </li>
- <li>
- When finalizing an object,
- Lua does not ignore <code>__gc</code> metamethods that are not functions.
- Any value will be called, if present.
- (Non-callable values will generate a warning,
- like any other error when calling a finalizer.)
- </li>
- </ul>
- <h2>8.2 – <a name="8.2">Incompatibilities in the Libraries</a></h2>
- <ul>
- <li>
- The function <a href="#pdf-print"><code>print</code></a> does not call <a href="#pdf-tostring"><code>tostring</code></a>
- to format its arguments;
- instead, it has this functionality hardwired.
- You should use <code>__tostring</code> to modify how values are printed.
- </li>
- <li>
- The pseudo-random number generator used by the function <a href="#pdf-math.random"><code>math.random</code></a>
- now starts with a somewhat random seed.
- Moreover, it uses a different algorithm.
- </li>
- <li>
- By default, the decoding functions in the <a href="#pdf-utf8"><code>utf8</code></a> library
- do not accept surrogates as valid code points.
- An extra parameter in these functions makes them more permissive.
- </li>
- <li>
- The options "<code>setpause</code>" and "<code>setstepmul</code>"
- of the function <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> are deprecated.
- You should use the new option "<code>incremental</code>" to set them.
- </li>
- <li>
- The function <a href="#pdf-io.lines"><code>io.lines</code></a> now returns four values,
- instead of just one.
- That can be a problem when it is used as the sole
- argument to another function that has optional parameters,
- such as in <code>load(io.lines(filename, "L"))</code>.
- To fix that issue,
- you can wrap the call into parentheses,
- to adjust its number of results to one.
- </li>
- </ul>
- <h2>8.3 – <a name="8.3">Incompatibilities in the API</a></h2>
- <ul>
- <li>
- Full userdata now has an arbitrary number of associated user values.
- Therefore, the functions <code>lua_newuserdata</code>,
- <code>lua_setuservalue</code>, and <code>lua_getuservalue</code> were
- replaced by <a href="#lua_newuserdatauv"><code>lua_newuserdatauv</code></a>,
- <a href="#lua_setiuservalue"><code>lua_setiuservalue</code></a>, and <a href="#lua_getiuservalue"><code>lua_getiuservalue</code></a>,
- which have an extra argument.
- <p>
- For compatibility, the old names still work as macros assuming
- one single user value.
- Note, however, that userdata with zero user values
- are more efficient memory-wise.
- </li>
- <li>
- The function <a href="#lua_resume"><code>lua_resume</code></a> has an extra parameter.
- This out parameter returns the number of values on
- the top of the stack that were yielded or returned by the coroutine.
- (In previous versions,
- those values were the entire stack.)
- </li>
- <li>
- The function <a href="#lua_version"><code>lua_version</code></a> returns the version number,
- instead of an address of the version number.
- The Lua core should work correctly with libraries using their
- own static copies of the same core,
- so there is no need to check whether they are using the same
- address space.
- </li>
- <li>
- The constant <code>LUA_ERRGCMM</code> was removed.
- Errors in finalizers are never propagated;
- instead, they generate a warning.
- </li>
- <li>
- The options <code>LUA_GCSETPAUSE</code> and <code>LUA_GCSETSTEPMUL</code>
- of the function <a href="#lua_gc"><code>lua_gc</code></a> are deprecated.
- You should use the new option <code>LUA_GCINC</code> to set them.
- </li>
- </ul>
- <h1>9 – <a name="9">The Complete Syntax of Lua</a></h1>
- <p>
- Here is the complete syntax of Lua in extended BNF.
- As usual in extended BNF,
- {A} means 0 or more As,
- and [A] means an optional A.
- (For operator precedences, see <a href="#3.4.8">§3.4.8</a>;
- for a description of the terminals
- Name, Numeral,
- and LiteralString, see <a href="#3.1">§3.1</a>.)
- <pre>
- chunk ::= block
- block ::= {stat} [retstat]
- stat ::= ‘<b>;</b>’ |
- varlist ‘<b>=</b>’ explist |
- functioncall |
- label |
- <b>break</b> |
- <b>goto</b> Name |
- <b>do</b> block <b>end</b> |
- <b>while</b> exp <b>do</b> block <b>end</b> |
- <b>repeat</b> block <b>until</b> exp |
- <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
- <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> |
- <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> |
- <b>function</b> funcname funcbody |
- <b>local</b> <b>function</b> Name funcbody |
- <b>local</b> attnamelist [‘<b>=</b>’ explist]
- attnamelist ::= Name attrib {‘<b>,</b>’ Name attrib}
- attrib ::= [‘<b><</b>’ Name ‘<b>></b>’]
- retstat ::= <b>return</b> [explist] [‘<b>;</b>’]
- label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
- funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
- varlist ::= var {‘<b>,</b>’ var}
- var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name
- namelist ::= Name {‘<b>,</b>’ Name}
- explist ::= exp {‘<b>,</b>’ exp}
- exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | ‘<b>...</b>’ | functiondef |
- prefixexp | tableconstructor | exp binop exp | unop exp
- prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
- functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args
- args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | LiteralString
- functiondef ::= <b>function</b> funcbody
- funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
- parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
- tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
- fieldlist ::= field {fieldsep field} [fieldsep]
- field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
- fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
- binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>//</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ |
- ‘<b>&</b>’ | ‘<b>~</b>’ | ‘<b>|</b>’ | ‘<b>>></b>’ | ‘<b><<</b>’ | ‘<b>..</b>’ |
- ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ |
- <b>and</b> | <b>or</b>
- unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’ | ‘<b>~</b>’
- </pre>
- <p>
- <P CLASS="footer">
- Last update:
- Thu Jun 18 16:10:16 UTC 2020
- </P>
- <!--
- Last change: revised for Lua 5.4.0 (final)
- -->
- </body></html>
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