[json] JSON for Modern C++

古城微笑少年丶 2022-03-18 04:25 197阅读 0赞

有幸能接触到这个，这是我遇到的使用最方便的json了，效率没研究过！

简单了使用了下，感觉非常好用，记录下：

要使用这个json，只需要使用json.hpp就行，放入自己的工程里，但是我这里是安装过的，为了其他项目也能使用！

环境: Mac OS X 10.12.6, Xcode(Version 8.3.3 (8E3004b))

安装：

brew tap nlohmann/json
    brew search nlohmann
    brew info nlohmann/json/nlohmann_json
    brew install nlohmann/json/nlohmann_json

安装就是第1，4两句, 等待安装完成就行！

开发: 新建一个c++控制台程序，添加以下代码：

//
    //  main.cpp
    //  hello
    //
    //  Created by zcm on 2019/2/18.
    //  Copyright © 2019年 zcm. All rights reserved.
    //
    
    #include <iostream>
    #include <vector>
    #include "nlohmann/json.hpp"
    
    using namespace std;
    using json = nlohmann::json;
    
    int main(int argc, const char * argv[]) {
    	json j2 = {
    		{"pi", 3.141},
    		{"happy", true},
    		{"name", "Niels"},
    		{"nothing", nullptr},
    		{"answer", {
    			{"everything", 42}
    		}},
    		{"list", {1, 0, 2}},
    		{"object", {
    			{"currency", "USD"},
    			{"value", 42.99}
    		}}
    	};
    	cout << j2.dump() << endl;
    	
    	// this writing looks good
    	auto j = R"(
    	{
    		"happy": true,
    		"pi": 3.141,
    		"arr": [1, 4, 6]
    	})"_json;
    	cout << j << endl;
    	
    	j = json::parse("{ \"happy\": false, \"pi\": 3.141 }");
    	j["pi"] = 3.666;				// 修改键值
    	j.emplace("pi2", 3.5);			// 如果键不存在, 则添加
    	j["add"] = {
       {"pi", 4.5}, {"p", 6}};
    	cout << j << endl;
    	
    	for(auto& i : j.items())		// 遍历键值对
    	{
    		cout << i.key() << " : " << i.value() << endl;
    	}
    	
    	if(j.find("pi") != j.end())		// 键存在
    	   cout << j["pi"] << endl;
    	cout << j.count("add") << endl;	// count()返回1表示键存在, 否则不存在
    	
    	vector<int> v {1, 5, 7};
    	json j3(v);						// 通过vector初始化json
    	cout << j3 << endl;
    
    	return 0;
    }

项目配置，增加:

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pvZUJsYWNrenFx_size_16_color_FFFFFF_t_70][]

运行结果:

{"answer":{"everything":42},"happy":true,"list":[1,0,2],"name":"Niels","nothing":null,"object":{"currency":"USD","value":42.99},"pi":3.141}
    {"arr":[1,4,6],"happy":true,"pi":3.141}
    {"add":{"p":6,"pi":4.5},"happy":false,"pi":3.666,"pi2":3.5}
    add : {"p":6,"pi":4.5}
    happy : false
    pi : 3.666
    pi2 : 3.5
    3.666
    1
    [1,5,7]
    Program ended with exit code: 0

## 注意: **必须开启c++11** 编译选项 ##

======================================

再补充说明下，上图:

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pvZUJsYWNrenFx_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pvZUJsYWNrenFx_size_16_color_FFFFFF_t_70]: /images/20220318/2e377e7a06ee4299993d6440161eb93c.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0pvZUJsYWNrenFx_size_16_color_FFFFFF_t_70 1]: /images/20220318/01159fe098334ba9ae0c7729093064e3.png