cJSON库(构建json与解析json字符串)-c语言

工程中要先要有cJSONN库，两个文件分别是cJSON.c和cJSON.h。

下载地址：http://sourceforge.net/projects/cjson/

例子1、解析JSON

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);

例子二：生成JSON数据

 cJSON* pRoot = cJSON_CreateObject();
 cJSON* pArray = cJSON_CreateArray();
 cJSON_AddItemToObject(pRoot, "students_info", pArray);
 char* szOut = cJSON_Print(pRoot);

 cJSON* pItem = cJSON_CreateObject();
 cJSON_AddStringToObject(pItem, "name", "chenzhongjing");
 cJSON_AddStringToObject(pItem, "sex", "male");
 cJSON_AddNumberToObject(pItem, "age", 28);
 cJSON_AddItemToArray(pArray, pItem);

 pItem = cJSON_CreateObject();
 cJSON_AddStringToObject(pItem, "name", "fengxuan");
 cJSON_AddStringToObject(pItem, "sex", "male");
 cJSON_AddNumberToObject(pItem, "age", 24);
 cJSON_AddItemToArray(pArray, pItem);

 pItem = cJSON_CreateObject();
 cJSON_AddStringToObject(pItem, "name", "tuhui");
 cJSON_AddStringToObject(pItem, "sex", "male");
 cJSON_AddNumberToObject(pItem, "age", 22);
 cJSON_AddItemToArray(pArray, pItem);

 char* szJSON = cJSON_Print(pRoot);
 cJSON_Delete(pRoot);
 //free(szJSON);

 pRoot = cJSON_Parse(szJSON);
 pArray = cJSON_GetObjectItem(pRoot, "students_info");
 if (NULL == pArray)
 {
     return -1;
 }
 
 int iCount = cJSON_GetArraySize(pArray);
 for (int i = 0; i < iCount; ++i)
 {
     cJSON* pItem = cJSON_GetArrayItem(pArray, i);
     if (NULL == pItem)
     {
         continue;
     }

     string strName = cJSON_GetObjectItem(pItem, "name")->valuestring;
     string strSex = cJSON_GetObjectItem(pItem, "sex")->valuestring;
     int iAge = cJSON_GetObjectItem(pItem, "age")->valueint;
 }

 cJSON_Delete(pRoot);
 free(szJSON);

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);