C++ 使用jsoncpp解析json文件

今天复习一下jsoncpp解析库的用法

1.Github搜jsoncpp下载工程源码

Github传送门
下载工程源码：

2.解压得到需要使用的两个目录include和src

3. 创建新测试工程：

4.解决方案目录下创建新目录json，存储上文拿到的json文件：

5.测试工程添加筛选器，并且添加进去得到的jsoncpp文件：

6.工程属性，附加包含两个目录:

7.添加解析类 JsoncppAssistant

#pragma once
#include "json.h"
#include 
#include 
using namespace std;


struct Score
{
	string subject;
	float score;
	bool bChecked;
	Score(const string& nm, float fS,bool bV = true)
		:subject(nm),
		score(fS),
		bChecked(bV)
	{
		bChecked = true;
	}
};
struct Student
{
	string name;
	vector<Score> arr;
};

//两个全局互斥锁保证多线程调用Read()、Write()方法线程安全
extern std::mutex g_read_mutex;
extern std::mutex g_write_mutex;
class JsoncppAssistant
{
private:
	JsoncppAssistant() = default;
	~JsoncppAssistant() = default;
	JsoncppAssistant(const JsoncppAssistant& src) = delete;
	JsoncppAssistant& operator=(const JsoncppAssistant& src) = delete;
	static JsoncppAssistant* instance;
	static std::mutex m_mutex;
public:
	/*
	双重检查锁定（double-checked locking）模式和互斥锁 m_mutex
	确保在多线程环境下只创建一个 JsoncppAssistant 
	*/
	static JsoncppAssistant* GetInstance()
	{
		if (instance == nullptr)
		{
			//锁定互斥量
			std::lock_guard<std::mutex> lock(m_mutex);
			if (instance == nullptr)
			{
				instance = new JsoncppAssistant();
			}
		}
		return instance;
	}
	bool Read(vector<Student>& arr, string path = "");
	bool Write(const vector<Student>& arr);
};

extern JsoncppAssistant* GetJscppMgr();

#include "JsoncppAssistant.h"
#include 
#include 


std::mutex g_read_mutex;
std::mutex g_write_mutex;
JsoncppAssistant* JsoncppAssistant::instance = nullptr;
std::mutex JsoncppAssistant::m_mutex;


JsoncppAssistant* GetJscppMgr()
{
	return JsoncppAssistant::GetInstance();
}

bool JsoncppAssistant::Read(vector<Student>& arr, string path)
{
	std::lock_guard<std::mutex> lock(g_read_mutex);
	arr.clear();

	Json::Reader reader;
	Json::Value root;

	ifstream ifs;
	ifs.open("test.json");
	if (!ifs.is_open())
	{
		return false;
	}

	if (!reader.parse(ifs, root))
	{
		return false;
	}
	if (root["data"].isNull()) return false;

	int nSize = root["data"].size();
	for (int i = 0; i < nSize; i++)
	{
		Student stu;
		stu.name = root["data"][i]["name"].asString();
		if (!root["data"][i]["Score"].isNull())
		{
			int nSz2 = root["data"][i]["Score"].size();
			stu.arr.reserve(nSz2);
			for (int j = 0; j < nSz2; j++)
			{
				stu.arr.emplace_back(Score(root["data"][i]["Score"][j]["subject"].asString(),
					root["data"][i]["Score"][j]["score"].asFloat(),
					root["data"][i]["Score"][j]["bChecked"].asBool()));
			}
		}
		arr.push_back(stu);
	}
	return true;
}


bool JsoncppAssistant::Write(const vector<Student>& arr)
{
	std::lock_guard<std::mutex> lock(g_write_mutex);
	if (arr.empty()) return false;

	Json::Value root;

	for (const auto& it : arr)
	{
		Json::Value JsStu;
		JsStu["name"] = it.name;
		for (const auto& it2 : it.arr)
		{
			Json::Value JsScore;
			JsScore["subject"] = it2.subject;
			JsScore["score"] = it2.score;
			JsScore["bChecked"] = it2.bChecked;
			JsStu["Score"].append(JsScore);
		}
		root["data"].append(JsStu);
	}

	Json::StreamWriterBuilder writerBuilder;
	std::string json_file = Json::writeString(writerBuilder, root);
	ofstream ofs("test.json", std::ios::out | std::ios::trunc);
	if (!ofs.is_open())
	{
		return false;
	}
	ofs << json_file;
	ofs.close();
	return true;
}

8.测试看看：

8.1写文件

void Write()
{
    vector<Student> arr;

    Student aaa;
    aaa.name = "aaa";
    aaa.arr.push_back(Score("c", 60.5));
    aaa.arr.push_back(Score("cpp", 88.5));
    aaa.arr.push_back(Score("python", 99.5));
    arr.push_back(aaa);
    Student bbb;
    bbb.name = "bbb";
    bbb.arr.push_back(Score("c", 77.5));
    bbb.arr.push_back(Score("cpp", 67));
    bbb.arr.push_back(Score("python", 95));
    arr.push_back(bbb);
    Student ccc;
    ccc.name = "ccc";
    ccc.arr.push_back(Score("c", 85));
    ccc.arr.push_back(Score("cpp", 76.5));
    ccc.arr.push_back(Score("python", 69.5));
    arr.push_back(ccc);

    GetJscppMgr()->Write(arr);
}

8.2读文件：

bool JsoncppAssistant::Read(vector<Student>& arr, string path)
{
	arr.clear();

	Json::Reader reader;
	Json::Value root;

	ifstream ifs;
	ifs.open("test.json");
	if (!ifs.is_open())
	{
		return false;
	}

	if (!reader.parse(ifs, root))
	{
		return false;
	}
	if (root["data"].isNull()) return false;

	int nSize = root["data"].size();
	for (int i = 0; i < nSize; i++)
	{
		Student stu;
		stu.name = root["data"][i]["name"].asString();
		if (!root["data"][i]["Score"].isNull())
		{
			int nSz2 = root["data"][i]["Score"].size();
			stu.arr.reserve(nSz2);
			for (int j = 0; j < nSz2; j++)
			{
				stu.arr.push_back(Score(root["data"][i]["Score"][j]["subject"].asString(),
					root["data"][i]["Score"][j]["score"].asFloat(),
					root["data"][i]["Score"][j]["bChecked"].asBool()));
			}
		}
		arr.push_back(stu);
	}
	return true;
}