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：
11012121aaa
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);