cJSON用法总结

cJSON是一个很好用的轻量级JSON解析器，也可以用于创建JSON，用C语言写的，最新的代码约700多行。

下载地址

https://github.com/DaveGamble/cJSON
https://sourceforge.net/projects/cjson/

编译方式（cJSON库，一共两个文件：cJSON.c、cJSON.h）

gcc cJSON.c main.c -o main -lm

基本接口说明

创建的JSON格式说明：{}表示一个Object，[]表示一个Array

cJSON_CreateObject：创建一个JSON结构体
cJSON_AddItemToObject：把一个item添加到JSON结构体里
cJSON_Print：将JSON格式的字符串转成普通字符串
cJSON_Parse：将普通字符串转成JSON格式的字符串
cJSON_Delete：释放JSON结构体

下面这些宏定义可以更快捷地帮助你创建JSON节点

 #define cJSON_AddNullToObject(object,name)     cJSON_AddItemToObject(object, name, cJSON_CreateNull())
 #define cJSON_AddTrueToObject(object,name)     cJSON_AddItemToObject(object, name, cJSON_CreateTrue())
 #define cJSON_AddFalseToObject(object,name)        cJSON_AddItemToObject(object, name, cJSON_CreateFalse())
 #define cJSON_AddBoolToObject(object,name,b)   cJSON_AddItemToObject(object, name, cJSON_CreateBool(b))
 #define cJSON_AddNumberToObject(object,name,n) cJSON_AddItemToObject(object, name, cJSON_CreateNumber(n))
 #define cJSON_AddStringToObject(object,name,s) cJSON_AddItemToObject(object, name, cJSON_CreateString(s))

比如如果要添加一个“name”：“Tom”的节点，下面两行代码都是相等的

cJSON_AddStringToObject(root, "name", "Tom")
cJSON_AddItemToObject(root, "name", cJSON_CreateString("Tom"))

下面介绍JSON创建和解析的demo

---

创建JSON的方法

demo1

    {
        "name": "Tom",
        "age":  25,
        "marry":        true,
        "child":        null
    }

创建demo1的代码实现

char * cjson_create_test1(void)
{
   char * out;
   cJSON *root;

   root = cJSON_CreateObject();
   if(!root)
   {
       printf("cJSON create error!!\n");
       return NULL;
   }

   cJSON_AddItemToObject(root, "name", cJSON_CreateString("Tom"));
   cJSON_AddItemToObject(root, "age", cJSON_CreateNumber(25));
   cJSON_AddItemToObject(root, "marry", cJSON_CreateBool(1));
   cJSON_AddItemToObject(root, "child", cJSON_CreateNull());

   out=cJSON_Print(root);
   cJSON_Delete(root);    

   if(out)
   {
       printf("%s\n", out);
       return out;
   }

   return NULL;
}

demo2

{
    "name": "Tom",
    "age":  25,
    "marry":        true,
    "children":     [{
                    "name": "May",
                    "age":  2
            }, {
                    "name": "Kendy",
                    "age":  3
            }, {
                    "name": "Mark",
                    "age":  1
            }]
}

创建demo2的实现方法

char * cjson_create_test2(void)
{
    char * out;
    cJSON *root;
    cJSON *child, *child1, *child2, *child3;

    root = cJSON_CreateObject();
    if(!root)
    {
        printf("cJSON create error!!\n");
        return NULL;
    }

    cJSON_AddItemToObject(root, "name", cJSON_CreateString("Tom"));
    cJSON_AddItemToObject(root, "age", cJSON_CreateNumber(25));
    cJSON_AddItemToObject(root, "marry", cJSON_CreateBool(1));

    child = cJSON_CreateArray();    
    CJSON_CHK_FAIL(child, NULL);
    cJSON_AddItemToObject(root, "children", child);

    child1 = cJSON_CreateObject();    
    CJSON_CHK_FAIL(child1, NULL);
    cJSON_AddItemToObject(child1, "name", cJSON_CreateString("May"));
    cJSON_AddItemToObject(child1, "age", cJSON_CreateNumber(2));

    child2 = cJSON_CreateObject();    
    CJSON_CHK_FAIL(child2, NULL);
    cJSON_AddItemToObject(child2, "name", cJSON_CreateString("Kendy"));
    cJSON_AddItemToObject(child2, "age", cJSON_CreateNumber(3));

    child3 = cJSON_CreateObject();    
    CJSON_CHK_FAIL(child3, NULL);
    cJSON_AddItemToObject(child3, "name", cJSON_CreateString("Mark"));
    cJSON_AddItemToObject(child3, "age", cJSON_CreateNumber(1));

    cJSON_AddItemToArray(child, child1);
    cJSON_AddItemToArray(child, child2);
    cJSON_AddItemToArray(child, child3);

    out=cJSON_Print(root);
    cJSON_Delete(root);    

    if(out)
    {
        printf("%s\n", out);      
        return out;
    }

    return NULL;
}

解析JSON的方法

解析上面的demo1

void cjson_parse_test1(void)
{
    cJSON * root;
    cJSON *name, *age, *marry, *child;

    root = cJSON_Parse(cjson_create_test1());   
    if(!root)
    {
        printf("cJSON_Parse error!!\n");
        return;
    }

    name = cJSON_GetObjectItem(root, "name");
    if(name)
    {
        printf("Get name value : %s\n", name->valuestring);
    }

    age = cJSON_GetObjectItem(root, "age");
    if(age)
    {
        printf("Get age value : %d\n", age->valueint);
    }

    marry = cJSON_GetObjectItem(root, "marry");
    if(marry)
    {
        printf("Get marry value : %d\n", marry->valueint);
    }

    child = cJSON_GetObjectItem(root, "child");
    if(child)
    {
        printf("Get child value : %s\n", marry->valuestring);
    }

    cJSON_Delete(root);    
}

解析上面的demo2

void cjson_parse_test2(void)
{
    cJSON * root;
    cJSON *name, *age, *marry, *children;
    cJSON *childNode, *childName, *childAge;

    root = cJSON_Parse(cjson_create_test2());   
    if(!root)
    {
        printf("cJSON_Parse error!!\n");
        return;
    }

    name = cJSON_GetObjectItem(root, "name");
    if(name)
    {
        printf("Get name value : %s\n", name->valuestring);
    }

    age = cJSON_GetObjectItem(root, "age");
    if(age)
    {
        printf("Get age value : %d\n", age->valueint);
    }

    marry = cJSON_GetObjectItem(root, "marry");
    if(marry)
    {
        printf("Get marry value : %d\n", marry->valueint);
    }

    children = cJSON_GetObjectItem(root, "children");
    if(children)
    {
        int size = cJSON_GetArraySize(children);
        printf("Get children size : %d\n", size);

        int i = 0;
        for(i=0; iif(childNode)
            {                
                childName = cJSON_GetObjectItem(childNode,"name");
                if(childName)
                {            
                    printf("Get child name : %s\n", childName->valuestring);
                }

                childAge = cJSON_GetObjectItem(childNode,"age");
                if(childAge)
                {            
                    printf("Get child age : %d\n", childAge->valueint);
                }
            }

        }
    }

    cJSON_Delete(root);    
}

PS：这里介绍一个很方便的在线JSON格式校验以及格式化的网站
http://pro.jsonlint.com/