c 使用cJSON生成及解析json类型数据

一、概述

　　cJSON官网

　　作用：可以在c程序中方便的进行json字符串的解析及生成

二、代码示例

//组装一个json串
void CJsonTest::valueToJsonObject() {
    cJSON* root, * fmt;
    char* out;
    root = cJSON_CreateObject();//创建一个obj（申请了堆内存记得释放）
    cJSON_AddItemToObject(root, "name", cJSON_CreateString("luoluoyang"));
    cJSON_AddNumberToObject(root, "age", 6);
    cJSON_AddItemToObject(root, "address", fmt = cJSON_CreateObject());//创建一个新的Object放入到root中
    //给新的对象增加属性
    cJSON_AddStringToObject(fmt, "addr", "he nan");
    cJSON_AddNumberToObject(fmt, "width", 10);
    cJSON_AddNumberToObject(fmt, "height", 10);
    cJSON_AddFalseToObject(fmt, "interlace");
    cJSON_AddTrueToObject(fmt, "isOpen");
    cJSON_AddNumberToObject(fmt, "frame_rate", 24);
    //将cJSON转为json字符串输出
    out = cJSON_Print(root);
    cout << out << endl;
    //释放申请的内存空间
    cJSON_Delete(root);
    free(out);
}

//解析json串
void CJsonTest::parseJsonObject() {
    //组装json字符串(用于最后的测试)
    char* jsonStr;
    cJSON* root;
    root = cJSON_CreateObject();//初始化cJSON，这一步需要申请内存，记得清理
    cJSON_AddStringToObject(root, "name", "LOL");//添加一个name属性，value是LOL
    cJSON* heros, * countrys;
    heros = cJSON_AddArrayToObject(root, "heros");//向root中添加一个heros数组
    //向数组中添加元素
    cJSON_AddItemToArray(heros, cJSON_CreateString("Tom"));
    cJSON_AddItemToArray(heros, cJSON_CreateString("Jack"));
    countrys = cJSON_AddArrayToObject(root, "countrys");//再创一个数组
    cJSON* obj = cJSON_CreateObject();//创建一个object
    cJSON_AddStringToObject(obj, "name", "xiao ming");
    cJSON_AddNumberToObject(obj, "age", 10);
    cJSON_AddItemToArray(countrys, obj);//将obj添加进数组
    jsonStr = cJSON_Print(root);
    cout << jsonStr << endl;
    cJSON_Delete(root);

    //解析json字符串
    cJSON* parseObj = cJSON_Parse(jsonStr);
    char* rootName = cJSON_GetObjectItem(parseObj, "name")->valuestring;
    cout << "rootName:" << rootName << endl;
    //从根节点中拿到数组
    cJSON* arrStr = cJSON_GetObjectItem(parseObj, "heros");
    //拿到json数组的长度
    int arrLen = cJSON_GetArraySize(arrStr);
    //循环从数组中取出item
    for (int i = 0;i < arrLen;i++) {
        char* nameStr = cJSON_GetArrayItem(arrStr, i)->valuestring;
        cout << "nameStr:" << nameStr << endl;
    }
    //从object中取出对象数组
    cJSON* myCountrys = cJSON_GetObjectItem(parseObj, "countrys");
    cout << "myCountrys:" << cJSON_Print(myCountrys) << endl;
    cout << "------------解析jsonObject----------" << endl;
    //获取对象数组的长度
    int countryLen = cJSON_GetArraySize(myCountrys);
    //循环遍历对象数组，并解析里面对象的value值
    for (int i = 0;i < countryLen;i++) {
        cJSON* myObj = cJSON_GetArrayItem(myCountrys, i);
        char* itemName = cJSON_GetObjectItem(myObj, "name")->valuestring;
        cout << "itemName:" << itemName << endl;
        int myAge = cJSON_GetObjectItem(myObj, "age")->valueint;
        cout << "myAge:" << myAge << endl;
    }

    //释放开辟的内存
    if (parseObj) {
        cJSON_Delete(parseObj);
    }
    free(jsonStr);
}