cJson的学习与总结

场景：需要进行大量数据解析，存储，传输

1.数据结构

typedef struct cJSON {    
 struct cJSON *next,*prev;     
 struct cJSON *child;     
 int type;     
 char *valuestring;     
 int valueint;    
 double valuedouble;     
 char *string;     
} cJSON;  

每个json对象都有一个type，对象的值可以是字符串(valuestring),整形(valueint)，浮点型(valuedouble)

2.创建json对象

cJSON_CreateObject//创建一个json对象-- {对象}

cJSON_AddStringToObject//向json对象中添加一个元素，元素的值是字符串-- {"type":""}

cJSON_AddNumberToObject//向json对象中添加一个对象，该对象的值是整形-- {"type":int}

cJSON_CreateArray();//创建json对象数组-- [{ : } ,{ : }]

cJSON_CreateString//具体解释可参考下面例子

cJSON_CreateNumber//具体解释可参考下面例子

cJSON_Delete//释放内存

cJSON_PrintUnformatted(root)  cJSON_Print(root)//将json数据转换成字符串，然后将字符串打印，第二个是含有换行符等格式的

举例：

2.1.创建 {"name": "fengxin", "passwd":   "123",  "num":  1  } 

#include<stdio.h>  
#include<stdlib.h>  
#include<string.h>  
#include"cJSON.h"  
  
int main()  
{  
        cJSON * usr;  
        cJSON *arry;  
  
        usr=cJSON_CreateObject();   //创建根数据对象  
        cJSON_AddStringToObject(usr,"name","fengxin");  //加入键值，加字符串  
        cJSON_AddStringToObject(usr,"passwd","123");  
        cJSON_AddNumberToObject(usr,"num",1);  //加整数  
          
        char *out = cJSON_Print(usr);   //将json形式打印成正常字符串形式  
        printf("%s\n",out);  
         
        // 释放内存    
        cJSON_Delete(usr);    
        free(out);   
  
          
} 

2.2 创建一个json数组，["Hello world",10] 

int create_js(void)  
{  
    cJSON *root, *js_body;  
    root = cJSON_CreateArray();  
    cJSON_AddItemToArray(root, cJSON_CreateString("Hello world"));  
    cJSON_AddItemToArray(root, cJSON_CreateNumber(10));   
    {  
//      char *s = cJSON_Print(root);  
        char *s = cJSON_PrintUnformatted(root);  
        if(s){  
           printf(" %s \n",s);  
            free(s);  
        }  
    }  
    if(root)  
    cJSON_Delete(root);  
  
    return 0;  
  
}  
  
int main(int argc, char **argv)  
{  
    create_js();  
    return 0;  
}

2.3  创建json  {"body":[{"name":"fengxin","status":100}]}  元素值是一个json数组，数组里面又含有两个json对象

int create_js(void)  
{  
    cJSON *root, *js_body, *js_list;  
    root = cJSON_CreateObject();  
    cJSON_AddItemToObject(root,"body", js_body = cJSON_CreateArray());  
    cJSON_AddItemToArray(js_body, js_list = cJSON_CreateObject());  
    cJSON_AddStringToObject(js_list,"name","fengxin");  
    cJSON_AddNumberToObject(js_list,"status",100);  
  
    {  
        //        char *s = cJSON_Print(root);  
        char *s = cJSON_PrintUnformatted(root);  
        if(s){  
            printf(" %s \n",s);  
            free(s);  
        }  
    }  
    if(root)  
        cJSON_Delete(root);  
  
    return 0;  
}  
  
int main(int argc, char **argv)  
{  
    create_js();  
    return 0;  
}  

3. 解析json字符串

cJSON_Parse//将字符串转换成json对象

cJSON_GetObjectItem//从json元素中获取一个元素

cJSON_GetArraySize//获取json数组的长度

cJSON_GetArrayItem//从json数组中获取一个对象

3.1解析字符串--{\"list\":{\"name\":\"xiao hong\",\"age\":10},\"other\":{\"name\":\"hua hua\"}} 

char *s = "{\"list\":{\"name\":\"xiao hong\",\"age\":10},\"other\":{\"name\":\"hua hua\"}}";  
cJSON *root = cJSON_Parse(s);  
if(!root) {  
    printf("get root faild !\n");  
    return -1;  
}  
  
cJSON *js_list = cJSON_GetObjectItem(root, "list");  
if(!js_list) {  
    printf("no list!\n");  
    return -1;  
}  
printf("list type is %d\n",js_list->type);  
  
cJSON *name = cJSON_GetObjectItem(js_list, "name");  
if(!name) {  
    printf("No name !\n");  
    return -1;  
}  
printf("name type is %d\n",name->type);  
printf("name is %s\n",name->valuestring);  
  
cJSON *age = cJSON_GetObjectItem(js_list, "age");  
if(!age) {  
    printf("no age!\n");  
    return -1;  
}  
printf("age type is %d\n", age->type);  
printf("age is %d\n",age->valueint);  
  
cJSON *js_other = cJSON_GetObjectItem(root, "other");  
if(!js_other) {  
    printf("no list!\n");  
    return -1;  
}  
printf("list type is %d\n",js_other->type);  
  
cJSON *js_name = cJSON_GetObjectItem(js_other, "name");  
if(!js_name) {  
    printf("No name !\n");  
    return -1;  
}  
printf("name type is %d\n",js_name->type);  
printf("name is %s\n",js_name->valuestring);  
  
if(root)  
    cJSON_Delete(root);  
    return 0;  

3.2.解析字符串;{\"list\":[\"name1\",\"name2\"]}

int main(int argc, char **argv)  
{  
char *s = "{\"list\":[\"name1\",\"name2\"]}";  
cJSON *root = cJSON_Parse(s);  
if(!root) {  
    printf("get root faild !\n");  
    return -1;  
}  
cJSON *js_list = cJSON_GetObjectItem(root, "list");  
if(!js_list){  
    printf("no list!\n");  
    return -1;  
}  
int array_size = cJSON_GetArraySize(js_list);  
printf("array size is %d\n",array_size);  
int i = 0;  
cJSON *item;  
for(i=0; i< array_size; i++) {  
    item = cJSON_GetArrayItem(js_list, i);  
    printf("item type is %d\n",item->type);  
    printf("%s\n",item->valuestring);  
}  
  
if(root)  
    cJSON_Delete(root);  
    return 0;  
} 

3.3 解析字符串：{ \"list\":[{\"name\":\"xiao hong\",\"age\":10},{\"name\":\"hua hua\",\"age\":11}]}  ，注意下面示例中函数

cJSON_PrintUnformatted的使用

int main(int argc, char **argv)  
{  
char *s = "{\"list\":[{\"name\":\"xiao hong\",\"age\":10},{\"name\":\"hua hua\",\"age\":11}]}";  
cJSON *root = cJSON_Parse(s);  
if(!root) {  
    printf("get root faild !\n");  
    return -1;  
}  
cJSON *js_list = cJSON_GetObjectItem(root, "list");  
if(!js_list){  
    printf("no list!\n");  
    return -1;  
}  
int array_size = cJSON_GetArraySize(js_list);  
printf("array size is %d\n",array_size);  
int i = 0;  
cJSON *item,*it, *js_name, *js_age;  
char *p  = NULL;  
for(i=0; i< array_size; i++) {  
    item = cJSON_GetArrayItem(js_list, i);  
    if(!item) {  
        //TODO...  
    }  
    p = cJSON_PrintUnformatted(item);  
    it = cJSON_Parse(p);  
    if(!it)  
        continue ;  
    js_name = cJSON_GetObjectItem(it, "name");  
    printf("name is %s\n",js_name->valuestring);  
    js_age = cJSON_GetObjectItem(it, "age");  
    printf("age is %d\n",js_age->valueint);  
  
}  
  
if(root)  
    cJSON_Delete(root);  
    return 0;  
}