[C++ practice road] IO stream architecture and use

foreword

Long time no see, let's learn the IO stream in C++ together today.

I/O library

These two architecture diagrams are slightly complicated. Here is a clearer IO flow architecture diagram:

In other words, the things we usually use such as cin, cout, cerr, and clog all come from the <iostream> header file, and they are the instance objects of istream and ostream under the
<istream> header file respectively.

The iostream in the <istream> header file inherits the two classes istream and ostream, so the fstream and sstream in the <fstream> and <sstream> classes both have corresponding io functions.

file read and write

Let me explain here by the way: the implementation of friends is authorized by the compiler through a special mechanism so that this function can get the members of the class, not through the this pointer, and istream is actually basic_istream<char, char_traits<char>> an alias.

class Date
{
    
    	
	//友元关系不会被继承
	friend istream& operator >>(istream& in, Date& date);
	friend ostream& operator <<(ostream& out, const Date& date);
public:


	Date(int year = 1, int month = 1, int day = 1)
		:_year(year)
		, _month(month)
		, _day(day)
	{
    
    }

	operator bool()
	{
    
    
		if (_year == 0)
			return false;

		return true;
	}

private:
	int _year;
	int _month;
	int _day;
};

//输入重定向
//
//decltype(cin)& operator >>(decltype(cin)& no,const Date& date)
//basic_istream<char, struct std::char_traits<char>>& operator >>(decltype(cin)& no, const Date& date)
//basic_istream<char>& operator >>(decltype(cin)& no, const Date& date)
istream& operator >>(istream& in, Date& date)
{
    
    
	//cout << ">> ok" << endl;
	//cout << typeid(cin).name() << endl;

	in >> date._year >> date._month >> date._day;
	return in;
}

//输出重定向
ostream& operator <<(ostream& out, const Date& date)
{
    
    
	out << date._year << " " << date._month << " " << date._day;
	return out;
}


#include <fstream>
struct ServerInfo
{
    
    

	//string _address;
	char _address[32];
	int _port;
	Date _date;
};

class ConfigManager
{
    
    
public:
	ConfigManager(string filename) : _filename(filename)
	{
    
    

	}

	//二进制读写
	void ReadBin(ServerInfo& info)
	{
    
    
		ifstream ifs(_filename, istream::in | istream::binary);
		ifs.read((char*)&info, sizeof(info));
	}

	void WriteBin(const ServerInfo& info)
	{
    
    
		ofstream ofs(_filename, ofstream::out | ofstream::binary);
		ofs.write((char*)&info, sizeof(info));
		//必然不能写入string，string的内容是new出来的，这里只把指针存好了
	}


	//文本读写
	void ReadText(ServerInfo& info)
	{
    
    
		ifstream ifs(_filename);
		ifs >> info._address;
		ifs >> info._port;
		ifs >> info._date;
	}

	void WriteText(const ServerInfo& info)
	{
    
    
		ofstream ofs(_filename);
		ofs << info._address << endl;
		ofs << info._port << endl;
		ofs << info._date << endl;
	}

private:
	string _filename;
};

Serialization and deserialization

// 序列化和反序列化
#include <sstream>

struct ChatInfo
{
    
    
	string _name; // 名字
	int _id;      // id
	Date _date;   // 时间
	string _msg;  // 聊天信息
};

ostream& operator<<(ostream& out, ChatInfo& info)
{
    
    
	cout << info._name << info._id << info._date << info._msg << endl;
	return out;
}


int main()
{
    
    
	ChatInfo winfo = {
    
     "丁真", 135246, {
    
     2022, 7, 14 }, "你好我是雪豹" };
	stringstream oss;
	oss << winfo._name << " ";
	oss << winfo._id << " ";
	oss << winfo._date << " ";
	oss << winfo._msg;

	string str = oss.str();

	stringstream iss(str);
	ChatInfo rinfo;
	iss >> rinfo._name;
	iss >> rinfo._id;
	iss >> rinfo._date;
	iss >> rinfo._msg;

	cout << rinfo << endl;

	return 0;
}

epilogue

This is the whole content of the IO stream, thank you for watching, and see you next time~