用C++处理JSON的库有很多,JSONCPP,json-parser,Jansson…太多了
不过我们搞程序开发，不一定需要一个库有多么强大的功能，但是这个库一定要能满足我们的要求，同时，开发起来要简单，最好不要增加我们的开发负担和学习负担。
我在开发menthol语言的JSON模块处理时，发现了一个简单、易用的JSON处理库-CJSON
看它的官方介绍
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.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.
就像上面说的，它的使用相对很简单，就两个文件cJSON.c，cJSON.h，开发的时候，引入你的项目中一起编译就可以了。
先要了解一下cjson几个基本类型：cJSON_False，cJSON_True，cJSON_NULL，cJSON_Number，cJSON_String，cJSON_Array，cJSON_Object
1.使用Cjson分析json各时时，要首先使用cJSON_Parse，来返回JSON结构
cJSON *json = cJSON_Parse(string);
Cjson结构如下
typedef struct cJSON
{
struct cJSON *next;
struct cJSON *prev;
struct cJSON *child;
int type;
char *valuestring;
/* writing to valueint is DEPRECATED, use cJSON_SetNumberValue instead */
int valueint;
double valuedouble;
char *string;
} cJSON;
2.用cJSON_GetObjectItem来获取你要的key所对应的value
cJSON *json = cJSON_Parse(string);
v = cJSON_GetObjectItemCaseSensitive(json, "key");
3.用type属性来判断返回的数据类型，根据不同的数据类型，取不同的值
v->type
如果type是cJSON_Number，则用v->valuedouble来取数值
如果type是cJSON_String，则用v->valuestring来取数值
4.如果是array,需要用cJSON_GetArrayItem(json,index)来获取一个cJSON*类型，然后在用第3步的方式来获取数据
5.cJSON_GetArraySize可以获取到数组的大小
6.解析完成后需要调用cJSON_Delete删除,第一步返回的指针
cJSON_Delete（json）
看一个官方实例
JSON实例
{
"name": "Awesome 4K",
"resolutions": [
{
"width": 1280,
"height": 720
},
{
"width": 1920,
"height": 1080
},
{
"width": 3840,
"height": 2160
}
]
}
Cjson解析程序
int supports_full_hd(const char * const monitor)
{
const cJSON *resolution = NULL;
const cJSON *resolutions = NULL;
const cJSON *name = NULL;
int status = 0;
cJSON *monitor_json = cJSON_Parse(monitor);
if (monitor_json == NULL)
{
const char *error_ptr = cJSON_GetErrorPtr();
if (error_ptr != NULL)
{
fprintf(stderr, "Error before: %s\n", error_ptr);
}
status = 0;
goto end;
}
name = cJSON_GetObjectItemCaseSensitive(monitor_json, "name");
if (cJSON_IsString(name) && (name->valuestring != NULL))
{
printf("Checking monitor \"%s\"\n", name->valuestring);
}
resolutions = cJSON_GetObjectItemCaseSensitive(monitor_json, "resolutions");
cJSON_ArrayForEach(resolution, resolutions)
{
cJSON *width = cJSON_GetObjectItemCaseSensitive(resolution, "width");
cJSON *height = cJSON_GetObjectItemCaseSensitive(resolution, "height");
if (!cJSON_IsNumber(width) || !cJSON_IsNumber(height))
{
status = 0;
goto end;
}
if ((width->valuedouble == 1920) && (height->valuedouble == 1080))
{
status = 1;
goto end;
}
}
end:
cJSON_Delete(monitor_json);
return status;
}
总体来说，Cjson使用简单、简便、无学习成本，可以说是分析JSON的一个很好的工具