Using JSON in C language projects

With the development of Internet of things , More and more things need to connect to the network to upload data , The server needs to connect to many types of terminals at the same time , The diversity of protocols is an important aspect of increasing the complexity of the server , At the same time, it also increases the complexity of maintenance , After weighing, the terminal finally adopts json data format .

Reason for use ：

1、 standard   Mainstream languages support json, convenient Terminal and server resolution

2、 Good scalability

3、 Easy to maintain

shortcoming ：

It takes more bandwidth than binary data types

Usage method ：

1、 download

https://sourceforge.net/projects/cjson/

There is a test package in the official project And use the tutorial

2、 take cjson package Included in the project    #include "cJSON.h"

3、 Be careful cjson In the source file malloc  and free Method replacement

void cJSON_InitHooks(cJSON_Hooks* hooks)
{
    if (!hooks) { /* Reset hooks */
        cJSON_malloc = vm_malloc;
        cJSON_free = vm_free;
        return;
    }


cJSON_malloc = (hooks->malloc_fn)?hooks->malloc_fn:vm_malloc;
cJSON_free = (hooks->free_fn)?hooks->free_fn:vm_free;

}

I'm using vm_malloc  and vm_free  So I replaced it with my own method

4、json After converting to string , Release after the string is used   because char* It's using malloc Created memory space

out = cJSON_Print(root);  or    out = cJSON_PrintUnformatted(root);    stay out After use To manually release   Otherwise, it will cause memory leakage

5、 Empathy , String rotation json after stay json After use, you should call   cJSON_Delete（） Release json object , because json Number is using malloc Created memory space Such as ：

json = cJSON_Parse((char*)readBuf);      After use   cJSON_Delete（json ）;

6、 Common functions can be found on the Internet   

establish and Value