mirror of
https://github.com/DaveGamble/cJSON
synced 2024-12-24 23:52:07 +00:00
247 lines
8.5 KiB
Plaintext
247 lines
8.5 KiB
Plaintext
|
/*
|
||
|
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
|