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diff --git a/src/cJSON.readme b/src/cJSON.readme new file mode 100644 index 00000000..61623b4f --- /dev/null +++ b/src/cJSON.readme @@ -0,0 +1,270 @@ +/* + 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 -lm +./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 |