C++ 使用nlohmann/json.hpp库读写json字符串

1. json库

我个人比较喜欢 nlohmann/json.hpp 这个库，因为它只需要一个hpp文件即可，足够轻量！

这是它的github地址。

2. 简单实例代码

#include <iostream>
#include <json.hpp>
#include <fstream>
#include <string>using namespace nlohmann;
using namespace std;string GenerateJsonStr()
{/** 生成json格式字符串** 预计的json格式文本为：* {*   "name": "ashui",*   "school": ["A school", "B school", "C school"],*   "money": [124.5, 345.3, 457.4],**   physic*   {*       "height": 180,*       "weight": 68.5*   }* }*/json json_data;json_data["name"] = "ashui";json_data["school"] = { "A school", "B school", "C school" };json_data["money"] = { 124.5, 345.3, 457.4 };json physic_data;physic_data["height"] = 180;physic_data["weight"] = 68.5;json_data["physic"] = physic_data;return json_data.dump();
}bool SaveJsonStr()
{string jsonStr = GenerateJsonStr();// Save to filestd::ofstream file("output.json");if (file.is_open()){file << jsonStr;file.close();std::cout << "dump string:" << std::endl;std::cout << jsonStr << std::endl;return true;}return false;
}bool ReadJsonObj()
{std:ifstream jsonFile("D:\\Project\\C++\\json_example\\x64\\Debug\\output.json");if (!jsonFile.is_open()){std::cout << "Open json file error" << std::endl;return false;}json jsonData;try{jsonData = json::parse(jsonFile);if (jsonData.is_null()){std::cout << "The json object is null" << std::endl;return false;}std::string name = jsonData["name"];std::vector<std::string> school = jsonData["school"];std::vector<float> money = jsonData["money"];int height = jsonData["physic"]["height"];float weigjt = jsonData["physic"]["weight"];std::cout << std::endl;std::cout << "parse string:" << std::endl;std::cout << "name: " << name << std::endl;std::cout << "height: " << height << std::endl;std::cout << "weigjt: " << weigjt << std::endl;std::cout << "school: ";for (auto s : school){std::cout << s << ", ";}std::cout << std::endl;std::cout << "money: ";for (auto m : money){std::cout << m << ", ";;}std::cout << std::endl;}catch (const std::exception& e){std::cout << "json error: "<< e.what() << std::endl;return false;}return true;
}int main()
{SaveJsonStr();ReadJsonObj();
}

值得注意的是，在使用[]读取json内容时，最外层一定要套一个try-catch用以补获异常，这样比起一个一个元素去判断是否为空、是否为数组等要方便且安全！