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);