c++ - 如何重载 << 运算符以便将对象的数据写入文件？

Question

我有一个 piggyBank 类型的对象，我需要将这个对象的数据写入一个文件，然后读取它。我知道如何写入/读取文本文件，但如何重载 << 运算符以便将有关对象的数据写入文件？

我在这里类的代码:

piggyBank.h

#include <string>
#ifndef PIGGYBANK_H
#define PIGGYBANK_H

class PiggyBank
{
 private:
        std::string owner; 
        int balance; 
        bool broken; 
        int id;
        static int nrOfObjects;
    public:
        PiggyBank(void);
        PiggyBank(std::string name);
        std::string getOwnerName() const;
        void setOwnerName(std::string name);
        bool isBroken() ;
        int getBalance(int & amount) ;


};



#endif /* PIGGYBANK_H */

piggyBank.cpp

#include "PiggyBank.h"
#include "readWrite.h"
#include <string>
#include <iostream>
using namespace std;

int PiggyBank::nrOfObjects = 0; // outside constructor


PiggyBank::getNrOfObjects(){

    return nrOfObjects;

}

PiggyBank::PiggyBank(void){
    {this->owner="";this->balance=0;this->broken=false;}
     id = ++nrOfObjects;

}


PiggyBank::PiggyBank(std::string name, int startBalance){
     {this->owner=name;this->balance=startBalance;this->broken=false;}
     id = ++nrOfObjects;
}

string PiggyBank::getOwnerName() const{
    return this->owner;
}
void PiggyBank::setOwnerName(string name){
    this->owner = name;
}
bool PiggyBank::isBroken() {
    return this->broken;
}

int PiggyBank::getBalance(int & amount) {
    if(!broken){
        amount = balance;
        return 0;
    }else{
        return -1;
    }
}

Answer 1

你想要 << operator成为friend上课和return ostream& .这是一个简单的示例，可以了解它的工作原理。

friend ostream& operator << (ostream& os, const PiggyBank& obj)
{
   // For example something like this
   os << "Information that you want to output to the file:\n";
   os << "Owner: " << obj.owner << "\n";
   return os;
}

然后你可以像这样使用它:

PiggyBack obj;
ofstream fout("file.txt");

// also check to see if the file opened correctly
if(fout.fail())
{
   cout << "File failed to open\n";
   return 0;
}
fout << obj;
// now you have written the owner information onto the file as well as the message before it
// inside the  operator<< overload

// close the resource at the end
fout.close();

很酷的部分是您也可以使用它通过更改 fout 来打印到控制台成为cout .例如:

cout << obj; // will print to the console