[置顶] cJSON库(构建json与解析json字符串)-c语言

 一、c语言获取json中的数据。

1、先要有cJOSN库，两个文件分别是cJSON.c和cJSON.h。

2、感性认识

char * json = "{ \"json\" : { \"id\":1, \"nodeId\":11, \"deviceId\":111, \"deviceName\":\"aaa\", \"ieee\":\"01212\", \"ep\":\"1111\", \"type\":\"bbb\" }}";
char * json1 = "{\"id\":1, \"nodeId\":11, \"deviceId\":111, \"deviceName\":\"aaa\"}";
cJSON * root;
cJSON * format;
int value_int;
char * value_string;

root = cJSON_Parse(json);
format = cJSON_GetObjectItem(root,"json");
value_int = cJSON_GetObjectItem(format,"nodeId")->valueint;
value_string = cJSON_GetObjectItem(format,"ieee")->valuestring;
printf( "%d\n", value_int );
printf( "%s\n", value_string );
cJSON_Delete(root);

root = cJSON_Parse(json1);
value_int = cJSON_GetObjectItem(root,"id")->valueint;
value_string = cJSON_GetObjectItem(root,"deviceName")->valuestring;
printf( "%d\n", value_int );
printf( "%s\n", value_string );
cJSON_Delete(root);

结果：

11
01212
1
aaa

二、cJSON库

1、json的数据结构 

c语言中json数据是采用链表存储的

typedef struct cJSON {

struct cJSON *next,*prev;// 数组 对象数据中用到

struct cJSON *child;// 数组 和对象中指向子数组对象或值

int type;// 元素的类型，如是对象还是数组

char *valuestring;// 如果是字符串

int valueint; // 如果是数值

double valuedouble;// 如果类型是cJSON_Number

char *string;// The item's name string, if this item is the child of, or is in the list of subitems of an object.

} cJSON;

三、cJSON使用

{

"name": "Jack (\"Bee\") Nimble",

"format": {

"type":       "rect",

"width":      1920,

"height":     1080,

"interlace":  false,

"frame rate": 24

}

}

"name": "Jack (\"Bee\") Nimble",

"format": {

"type":       "rect",

"width":      1920,

"height":     1080,

"interlace":  false,

"frame rate": 24

}

}

1、字符串解析成json结构体

1)：讲字符串解析成json结构体。

cJSON *root = cJSON_Parse(my_json_string);

2):获取某个元素

cJSON *format = cJSON_GetObjectItem(root,"format");

int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;

int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;

3）:讲json结构体转换成字符串

char *rendered=cJSON_Print(root);

4）：删除

cJSON_Delete(root);

2：构建一个json结构体 

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)

out =cJSON_Print(root);

printf("%s\n",out);

cJSON_Delete(root);

free(out);