a readme of documentation.

git-svn-id: http://svn.code.sf.net/p/cjson/code@4 e3330c51-1366-4df0-8b21-3ccf24e3d50e

README

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+/*
+  Copyright (c) 2009 Dave Gamble
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+  THE SOFTWARE.
+*/
+
+Welcome to cJSON.
+
+cJSON aims to be the dumbest possible parser that you can get your job done with.
+It's a single file of C, and a single header file.
+
+JSON is described best here: http://www.json.org/
+It's like XML, but fat-free. You use it to move data around, store things, or just
+generally represent your program's state.
+
+
+First up, how do I build?
+Add cJSON.c to your project, and put cJSON.h somewhere in the header search path.
+For example, to build the test app:
+
+gcc cJSON.c test.c -o test
+./test
+
+
+As a library, cJSON exists to take away as much legwork as it can, but not get in your way.
+As a point of pragmatism (i.e. ignoring the truth), I'm going to say that you can use it
+in one of two modes: Auto and Manual. Let's have a quick run-through.
+
+
+I lifted some JSON from this page: http://www.json.org/fatfree.html
+That page inspired me to write cJSON, which is a parser that tries to share the same
+philosophy as JSON itself. Simple, dumb, out of the way.
+
+Some JSON:
+{
+    "name": "Jack (\"Bee\") Nimble", 
+    "format": {
+        "type":       "rect", 
+        "width":      1920, 
+        "height":     1080, 
+        "interlace":  false, 
+        "frame rate": 24
+    }
+}
+
+Assume that you got this from a file, a webserver, or magic JSON elves, whatever,
+you have a char * to it. Everything is a cJSON struct.
+Get it parsed:
+	cJSON *root = cJSON_Parse(my_json_string);
+
+This is an object. We're in C. We don't have objects. But we do have structs.
+What's the framerate?
+
+	cJSON *format = cJSON_GetObjectItem(root,"format");
+	int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;
+
+
+Want to change the framerate?
+	cJSON_GetObjectItem(format,"frame rate")->valueint=25;
+	
+Back to disk?
+	char *rendered=cJSON_Print(root);
+
+Finished? Delete the root (this takes care of everything else).
+	cJSON_Delete(root);
+
+That's AUTO mode. If you're going to use Auto mode, you really ought to check pointers
+before you dereference them. If you want to see how you'd build this struct in code?
+	cJSON *root,*fmt;
+	root=cJSON_CreateObject();	
+	cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));
+	cJSON_AddItemToObject(root, "format", fmt=cJSON_CreateObject());
+	cJSON_AddStringToObject(fmt,"type",		"rect");
+	cJSON_AddNumberToObject(fmt,"width",		1920);
+	cJSON_AddNumberToObject(fmt,"height",		1080);
+	cJSON_AddFalseToObject (fmt,"interlace");
+	cJSON_AddNumberToObject(fmt,"frame rate",	24);
+
+Hopefully we can agree that's not a lot of code? There's no overhead, no unnecessary setup.
+Look at test.c for a bunch of nice examples, mostly all ripped off the json.org site, and
+a few from elsewhere.
+
+What about manual mode? First up you need some detail.
+Let's cover how the cJSON objects represent the JSON data.
+cJSON doesn't distinguish arrays from objects in handling; just type.
+Each cJSON has, potentially, a child, siblings, value, a name.
+
+The root object has: Object Type and a Child
+The Child has name "name", with value "Jack ("Bee") Nimble", and a sibling:
+Sibling has type Object, name "format", and a child.
+That child has type String, name "type", value "rect", and a sibling:
+Sibling has type Number, name "width", value 1920, and a sibling:
+Sibling has type Number, name "height", value 1080, and a sibling:
+Sibling hs type False, name "interlace", and a sibling:
+Sibling has type Number, name "frame rate", value 24
+
+Here's the structure:
+typedef struct cJSON {
+	struct cJSON *next,*prev;
+	struct cJSON *child;
+
+	int type;
+
+	char *valuestring;
+	int valueint;
+	double valuedouble;
+
+	char *string;
+} cJSON;
+
+By default all values are 0 unless set by virtue of being meaningful.
+
+next/prev is a doubly linked list of siblings. next takes you to your sibling,
+prev takes you back from your sibling to you.
+Only objects and arrays have a "child", and it's the head of the doubly linked list.
+A "child" entry will have prev==0, but next potentially points on. The last sibling has next=0.
+The type expresses Null/True/False/Number/String/Array/Object, all of which are #defined in
+cJSON.h
+
+A Number has valueint and valuedouble. If you're expecting an int, read valueint, if not read
+valuedouble.
+
+Any entry which is in the linked list which is the child of an object will have a "string"
+which is the "name" of the entry. When I said "name" in the above example, that's "string".
+"string" is the JSON name for the 'variable name' if you will.
+
+Now you can trivially walk the lists, recursively, and parse as you please.
+You can invoke cJSON_Parse to get cJSON to parse for you, and then you can take
+the root object, and traverse the structure (which is, formally, an N-tree),
+and tokenise as you please. If you wanted to build a callback style parser, this is how
+you'd do it (just an example, since these things are very specific):
+
+void parse_and_callback(cJSON *item,const char *prefix)
+{
+	while (item)
+	{
+		char *newprefix=malloc(strlen(prefix)+strlen(item->name)+2);
+		sprintf(newprefix,"%s/%s",prefix,item->name);
+		int dorecurse=callback(newprefix, item->type, item);
+		if (item->child && dorecurse) parse_and_callback(item->child,newprefix);
+		item=item->next;
+		free(newprefix);
+	}
+}
+
+The prefix process will build you a separated list, to simplify your callback handling.
+The 'dorecurse' flag would let the callback decide to handle sub-arrays on it's own, or
+let you invoke it per-item. For the item above, your callback might look like this:
+
+int callback(const char *name,int type,cJSON *item)
+{
+	if (!strcmp(name,"name"))	{ /* populate name */ }
+	else if (!strcmp(name,"format/type")	{ /* handle "rect" */ }
+	else if (!strcmp(name,"format/width")	{ /* 800 */ }
+	else if (!strcmp(name,"format/height")	{ /* 600 */ }
+	else if (!strcmp(name,"format/interlace")	{ /* false */ }
+	else if (!strcmp(name,"format/frame rate")	{ /* 24 */ }
+	return 1;
+}
+
+Alternatively, you might like to parse iteratively.
+You'd use:
+
+void parse_object(cJSON *item)
+{
+	int i; for (i=0;i<cJSON_GetArraySize(item);i++)
+	{
+		cJSON *subitem=cJSON_GetArrayItem(item,i);
+		// handle subitem.	
+	}
+}
+
+Or, for PROPER manual mode:
+
+void parse_object(cJSON *item)
+{
+	cJSON *subitem=item->child;
+	while (subitem)
+	{
+		// handle subitem
+		if (subitem->child) parse_object(subitem->child);
+		
+		subitem=subitem->next;
+	}
+}
+
+Of course, this should look familiar, since this is just a stripped-down version
+of the callback-parser.
+
+This should cover most uses you'll find for parsing. The rest should be possible
+to infer.. and if in doubt, read the source! There's not a lot of it! ;)
+
+
+In terms of constructing JSON data, the example code above is the right way to do it.
+You can, of course, hand your sub-objects to other functions to populate.
+Also, if you find a use for it, you can manually build the objects.
+For instance, suppose you wanted to build an array of objects?
+
+cJSON *objects[24];
+
+cJSON *Create_array_of_anything(cJSON **items,int num)
+{
+	int i;cJSON *prev, *root=cJSON_CreateArray();
+	for (i=0;i<24;i++)
+	{
+		if (!i)	root->child=objects[i];
+		else	prev->next=objects[i], objects[i]->prev=prev;
+		prev=objects[i];
+	}
+	return root;
+}
+	
+and simply: Create_array_of_anything(objects,24);
+
+cJSON doesn't make any assumptions about what order you create things in.
+You can attach the objects, as above, and later add children to each
+of those objects.
+
+As soon as you call cJSON_Print, it renders the structure to text.
+
+
+
+The test.c code shows how to handle a bunch of typical cases. If you uncomment
+the code, it'll load, parse and print a bunch of test files, also from json.org,
+which are more complex than I'd care to try and stash into a const char array[].
+
+
+Enjoy cJSON!
+
+
+- Dave Gamble, Aug 2009