mirror of https://github.com/DaveGamble/cJSON
README: new doc: Remove old explanation.
This commit is contained in:
Max Bruckner
parent
cdcd553769
commit
5605fa4ad5
271
README.md
271
README.md
|
|
@ -13,8 +13,6 @@ Ultralightweight JSON parser in ANSI C.
|
|||
* [Parsing JSON](#parsing-json)
|
||||
* [Printing JSON](#printing-json)
|
||||
* [Example](#example)
|
||||
* [Some JSON](#some-json)
|
||||
* [Here's the structure](#heres-the-structure)
|
||||
* [Caveats](#caveats)
|
||||
* [Enjoy cJSON!](#enjoy-cjson)
|
||||
|
||||
|
|
@ -463,270 +461,6 @@ end:
|
|||
|
||||
Note that there are no NULL checks except for the result of `cJSON_Parse` because `cJSON_GetObjectItemCaseSensitive` checks for `NULL` inputs already, so a `NULL` value is just propagated and `cJSON_IsNumber` and `cJSON_IsString` return `0` if the input is `NULL`.
|
||||
|
||||
### Some JSON:
|
||||
|
||||
```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:
|
||||
|
||||
```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.
|
||||
What's the framerate?
|
||||
|
||||
```c
|
||||
cJSON *format = cJSON_GetObjectItemCaseSensitive(root, "format");
|
||||
cJSON *framerate_item = cJSON_GetObjectItemCaseSensitive(format, "frame rate");
|
||||
double framerate = 0;
|
||||
if (cJSON_IsNumber(framerate_item))
|
||||
{
|
||||
framerate = framerate_item->valuedouble;
|
||||
}
|
||||
```
|
||||
|
||||
Want to change the framerate?
|
||||
|
||||
```c
|
||||
cJSON *framerate_item = cJSON_GetObjectItemCaseSensitive(format, "frame rate");
|
||||
cJSON_SetNumberValue(framerate_item, 25);
|
||||
```
|
||||
|
||||
Back to disk?
|
||||
|
||||
```c
|
||||
char *rendered = cJSON_Print(root);
|
||||
```
|
||||
|
||||
Finished? Delete the root (this takes care of everything else).
|
||||
|
||||
```c
|
||||
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?
|
||||
|
||||
```c
|
||||
cJSON *root;
|
||||
cJSON *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](http://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 has type *False*, name "interlace", and a sibling:
|
||||
* Sibling has type *Number*, name "frame rate", value 24
|
||||
|
||||
### Here's the structure:
|
||||
|
||||
```c
|
||||
typedef struct cJSON {
|
||||
struct cJSON *next,*prev;
|
||||
struct cJSON *child;
|
||||
|
||||
int type;
|
||||
|
||||
char *valuestring;
|
||||
int valueint; /* writing to valueint is DEPRECATED, please use cJSON_SetNumberValue instead */
|
||||
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`. `valueint` is a relict of the past, so always use `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):
|
||||
|
||||
```c
|
||||
void parse_and_callback(cJSON *item, const char *prefix)
|
||||
{
|
||||
while (item)
|
||||
{
|
||||
char *newprefix = malloc(strlen(prefix) + strlen(item->string) + 2);
|
||||
sprintf(newprefix, "%s/%s", prefix, item->string);
|
||||
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:
|
||||
|
||||
```c
|
||||
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:
|
||||
|
||||
```c
|
||||
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:
|
||||
|
||||
```c
|
||||
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?
|
||||
|
||||
```c
|
||||
cJSON *objects[24];
|
||||
|
||||
cJSON *Create_array_of_anything(cJSON **items, int num)
|
||||
{
|
||||
int i;
|
||||
cJSON *prev;
|
||||
cJSON *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](http://json.org),
|
||||
which are more complex than I'd care to try and stash into a `const char array[]`.
|
||||
|
||||
### Caveats
|
||||
|
||||
#### Zero Character
|
||||
|
|
@ -768,5 +502,6 @@ When cJSON was originally created, it didn't follow the JSON standard and didn't
|
|||
|
||||
# Enjoy cJSON!
|
||||
|
||||
- Dave Gamble, Aug 2009
|
||||
- [cJSON contributors](CONTRIBUTORS.md)
|
||||
- Dave Gamble (original author)
|
||||
- Max Bruckner (current maintainer)
|
||||
- and the other [cJSON contributors](CONTRIBUTORS.md)
|
||||
|
|
|
|||
Loading…
Reference in New Issue