Sword nlohmann::json的使用

#include <iostream>
#include <string>
#include<sstream>
#include "json.hpp"

// C++ 之 nlohmann::json 的使用

/*
知识补充:
    1. nlohmann::json编译依赖于-std=c++11
*/

// 初始化
void test1()
{
    nlohmann::json obj1, obj2, obj3, obj4;
    const char* p = "{\"age\":22,\"gender\":true,\"name\":\"jack\",\"pet\":{\"name\":\"wang\",\"type\":\"dog\"}}";
    std::istringstream ostr("{\"age\":45,\"gender\":true,\"name\":\"skipper\",\"pet\":{\"name\":\"wang\",\"type\":\"dog\"}}");
    
    // 示例json
    // {"age":22,"family":[{"call":"father","name":"adam"},{"call":"mother","name":"eve"},
              {"call":"wife","name":"shine"}],"gender":true,"name":"jack","pet":{"name":"wang","type":"dog"}}

    // a.赋值构造
    
    obj1["name"] = "jack";                                            //字符串  
    obj1["age"] = 22;                                                 //整数
    obj1["gender"] = true;                                            //布尔值
    obj1["pet"] = { {"type","dog"}, {"name" , "wang" } };             //对象
    /*
    知识补充:
        nlohmann::json 中的数组是用{}，而不是[]
    */
    obj1["family"] = { {{"call","father"}, {"name" , "adam" }},{{"call","mother"}, {"name" , "eve" }} };     //数组
    obj1["family"][2] = { {"call","wife"}, {"name" , "shine" } };     // 元素赋值

    // b.直接构造
    obj2 = { {"type","dog"}, {"name" , "wang" } };

    // c.字符串构造
    /*
    知识补充:
        注意nlohmann::json::parse()函数签名
        nlohmann::json::parse(const char*, const char*)
    */
    obj3 = nlohmann::json::parse(p, p + strlen(p));

    // d.字符流构造(也可以使用std::ifstream之类替换)
    ostr >> obj4;
}

// 属性提取
void test2()
{
    nlohmann::json tmp;
    const char* p = "{\"age\":22,\"gender\":true,\"name\":\"jack\",\"pet\":{\"name\":\"wang\",\"type\":\"dog\"}}";
    nlohmann::json obj = nlohmann::json::parse(p, p + strlen(p));
    
    // nlohmann::json为空判断(不可以使用NULL)
    if (nullptr == tmp)
    {
        std::cout << "empty" << std::endl;
    }

    // 提取字符串
    std::string name = obj["name"].get<std::string>();
    // 提取整型
    int age = obj["age"].get<int>();
    // 提取布尔值
    bool gender = obj["gender"].get<bool>();
    // 提取对象
    nlohmann::json pet = obj["pet"];

    std::cout << name << ":" << age << ":" << gender << std::endl;
}

// 数组遍历
void test3()
{
    const char* p = "[{\"name\":\"1\",\"type\":\"a\"},{\"name\":\"2\",\"type\":\"b\"},
          {\"name\":\"c\",\"type\":\"a\"},{\"name\":\"4\",\"type\":\"d\"}]";
    nlohmann::json obj;

    obj = nlohmann::json::parse(p, p + strlen(p));

    if (obj.empty())
    {
        // 数组为空
        std::cout << "The array is empty" << std::endl;
        return;
    }

    // 遍历数组
    for (auto& item : obj.items())
    {
        // item.value() = {"name":"1","type":"a"}
        std::cout << item.value() << std::endl;
    }

}

int main()
{
    //test1();
    //test2();
    test3();
    return 0;
}