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# cJSON
Copyright (c) 2009 Dave Gamble Ultralightweight JSON parser in ANSI C.
Permission is hereby granted, free of charge, to any person obtaining a copy ## Table of contents
of this software and associated documentation files (the "Software"), to deal * [License](#license)
in the Software without restriction, including without limitation the rights * [Usage](#usage)
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * [Welcome to cJSON](#welcome-to-cjson)
copies of the Software, and to permit persons to whom the Software is * [Some JSON](#some-json)
furnished to do so, subject to the following conditions: * [Here's the structure](#heres-the-structure)
* [Enjoy cJSON!](#enjoy-cjson)
The above copyright notice and this permission notice shall be included in ## License
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR > Copyright (c) 2009-2016 Dave Gamble
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, >
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE > Permission is hereby granted, free of charge, to any person obtaining a copy
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER > of this software and associated documentation files (the "Software"), to deal
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, > in the Software without restriction, including without limitation the rights
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN > to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
THE SOFTWARE. > 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.
## Usage
Welcome to cJSON. ### Welcome to cJSON.
-----------------
cJSON aims to be the dumbest possible parser that you can get your job done with. 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. It's a single file of C, and a single header file.
@@ -34,8 +47,10 @@ First up, how do I build?
Add cJSON.c to your project, and put cJSON.h somewhere in the header search path. Add cJSON.c to your project, and put cJSON.h somewhere in the header search path.
For example, to build the test app: For example, to build the test app:
gcc cJSON.c test.c -o test -lm ```
./test 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 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 As a point of pragmatism (i.e. ignoring the truth), I'm going to say that you can use it
@@ -45,56 +60,69 @@ 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 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. philosophy as JSON itself. Simple, dumb, out of the way.
Some JSON: ### Some JSON:
----------
{ ```json
"name": "Jack (\"Bee\") Nimble", {
"format": { "name": "Jack (\"Bee\") Nimble",
"type": "rect", "format": {
"width": 1920, "type": "rect",
"height": 1080, "width": 1920,
"interlace": false, "height": 1080,
"frame rate": 24 "interlace": false,
} "frame rate": 24
} }
}
```
Assume that you got this from a file, a webserver, or magic JSON elves, whatever, 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. you have a char * to it. Everything is a cJSON struct.
Get it parsed: Get it parsed:
cJSON * root = cJSON_Parse(my_json_string); ```c
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. This is an object. We're in C. We don't have objects. But we do have structs.
What's the framerate? What's the framerate?
cJSON * format = cJSON_GetObjectItem(root,"format"); ```c
int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint; cJSON * format = cJSON_GetObjectItem(root,"format");
int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;
```
Want to change the framerate? Want to change the framerate?
cJSON_GetObjectItem(format,"frame rate")->valueint = 25; ```c
cJSON_GetObjectItem(format,"frame rate")->valueint = 25;
```
Back to disk? Back to disk?
char * rendered = cJSON_Print(root); ```c
char * rendered = cJSON_Print(root);
```
Finished? Delete the root (this takes care of everything else). Finished? Delete the root (this takes care of everything else).
cJSON_Delete(root); ```c
cJSON_Delete(root);
```
That's AUTO mode. If you're going to use Auto mode, you really ought to check pointers 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? before you dereference them. If you want to see how you'd build this struct in code?
cJSON *root,*fmt; ```c
root = cJSON_CreateObject(); cJSON *root,*fmt;
cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble")); root = cJSON_CreateObject();
cJSON_AddItemToObject(root, "format", fmt = cJSON_CreateObject()); cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));
cJSON_AddStringToObject(fmt, "type", "rect"); cJSON_AddItemToObject(root, "format", fmt = cJSON_CreateObject());
cJSON_AddNumberToObject(fmt, "width", 1920); cJSON_AddStringToObject(fmt, "type", "rect");
cJSON_AddNumberToObject(fmt, "height", 1080); cJSON_AddNumberToObject(fmt, "width", 1920);
cJSON_AddFalseToObject (fmt, "interlace"); cJSON_AddNumberToObject(fmt, "height", 1080);
cJSON_AddNumberToObject(fmt, "frame rate", 24); 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. 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 Look at test.c for a bunch of nice examples, mostly all ripped off the json.org site, and
@@ -114,21 +142,22 @@ Sibling has type Number, name "height", value 1080, and a sibling:
Sibling has type False, name "interlace", and a sibling: Sibling has type False, name "interlace", and a sibling:
Sibling has type Number, name "frame rate", value 24 Sibling has type Number, name "frame rate", value 24
Here's the structure: # Here's the structure:
---------------------
typedef struct cJSON { ```c
struct cJSON *next,*prev; typedef struct cJSON {
struct cJSON *child; struct cJSON *next,*prev;
struct cJSON *child;
int type; int type;
char *valuestring; char *valuestring;
int valueint; int valueint;
double valuedouble; double valuedouble;
char *string; char *string;
} cJSON; } cJSON;
```
By default all values are 0 unless set by virtue of being meaningful. By default all values are 0 unless set by virtue of being meaningful.
@@ -152,23 +181,26 @@ 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 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): you'd do it (just an example, since these things are very specific):
void parse_and_callback(cJSON *item,const char *prefix) ```c
{ void parse_and_callback(cJSON *item,const char *prefix)
while (item) {
{ while (item)
char *newprefix = malloc(strlen(prefix) + strlen(item->name) + 2); {
sprintf(newprefix,"%s/%s",prefix,item->name); char *newprefix = malloc(strlen(prefix) + strlen(item->name) + 2);
int dorecurse = callback(newprefix, item->type, item); sprintf(newprefix,"%s/%s",prefix,item->name);
if (item->child && dorecurse) parse_and_callback(item->child, newprefix); int dorecurse = callback(newprefix, item->type, item);
item = item->next; if (item->child && dorecurse) parse_and_callback(item->child, newprefix);
free(newprefix); item = item->next;
} free(newprefix);
} }
}
```
The prefix process will build you a separated list, to simplify your callback handling. 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 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: let you invoke it per-item. For the item above, your callback might look like this:
```c
int callback(const char *name,int type,cJSON *item) int callback(const char *name,int type,cJSON *item)
{ {
if (!strcmp(name,"name")) { /* populate name */ } if (!strcmp(name,"name")) { /* populate name */ }
@@ -179,33 +211,38 @@ let you invoke it per-item. For the item above, your callback might look like th
else if (!strcmp(name,"format/frame rate") { /* 24 */ } else if (!strcmp(name,"format/frame rate") { /* 24 */ }
return 1; return 1;
} }
```
Alternatively, you might like to parse iteratively. Alternatively, you might like to parse iteratively.
You'd use: You'd use:
void parse_object(cJSON *item) ```c
{ void parse_object(cJSON *item)
int i; {
for (i = 0 ; i < cJSON_GetArraySize(item) ; i++) int i;
{ for (i = 0 ; i < cJSON_GetArraySize(item) ; i++)
cJSON * subitem = cJSON_GetArrayItem(item, i); {
// handle subitem. cJSON * subitem = cJSON_GetArrayItem(item, i);
} // handle subitem
} }
}
```
Or, for PROPER manual mode: Or, for PROPER manual mode:
void parse_object(cJSON * item) ```c
{ void parse_object(cJSON * item)
cJSON *subitem = item->child; {
while (subitem) cJSON *subitem = item->child;
{ while (subitem)
// handle subitem {
if (subitem->child) parse_object(subitem->child); // handle subitem
if (subitem->child) parse_object(subitem->child);
subitem = subitem->next;
} subitem = subitem->next;
} }
}
```
Of course, this should look familiar, since this is just a stripped-down version Of course, this should look familiar, since this is just a stripped-down version
of the callback-parser. of the callback-parser.
@@ -218,22 +255,24 @@ 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. 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? For instance, suppose you wanted to build an array of objects?
cJSON * objects[24]; ```c
cJSON * objects[24];
cJSON * Create_array_of_anything(cJSON ** items, int num) cJSON * Create_array_of_anything(cJSON ** items, int num)
{ {
int i; int i;
cJSON * prev, * root = cJSON_CreateArray(); cJSON * prev, * root = cJSON_CreateArray();
for (i = 0 ; i < 24 ; i++) for (i = 0 ; i < 24 ; i++)
{ {
if (!i) root->child = objects[i]; if (!i) root->child = objects[i];
else prev->next = objects[i], objects[i]->prev = prev; else prev->next = objects[i], objects[i]->prev = prev;
prev = objects[i]; prev = objects[i];
} }
return root; return root;
} }
```
and simply: Create_array_of_anything(objects, 24);
and simply: `Create_array_of_anything(objects, 24);`
cJSON doesn't make any assumptions about what order you create things in. 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 You can attach the objects, as above, and later add children to each
@@ -245,7 +284,6 @@ 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, 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[]. which are more complex than I'd care to try and stash into a const char array[].
Enjoy cJSON! # Enjoy cJSON!
-----------------------
- Dave Gamble, Aug 2009 - Dave Gamble, Aug 2009