cJSON库(构建json与解析json字符串)-c语言

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,"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( "%dn",value_int );
printf( "%sn",value_string );
cJSON_Delete(root);
	
root = cJSON_Parse(json1); 
value_int = cJSON_GetObjectItem(root,"id")->valueint; 
value_string = cJSON_GetObjectItem(root,"deviceName")->valuestring; 
printf( "%dn",value_string );
cJSON_Delete(root);

结果：

11
01212
1
aaa

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;

{

"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("%sn",out);

cJSON_Delete(root);

free(out);

（编辑：李大同）

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