How to write/read classes within classes to binary file C++

问题

I'm working on a project where I have to write a class that contains three other classes as private member variables to a binary file, where it can then be read back into variables to be used in the code. The code writes to the file, but I don't know if it is writing the correct info as when I try to read the file it reads in junk. I have included my current setup, does this look correct? If so, what could be going wrong, and if not, how can I fix this?

If you need me to add any extra code, please ask. Another consideration is that two of the classes being used as member functions for the players objects inherit from other classes.

    if (cFile.is_open())
    {
        cFile.seekp(ios::beg);
        for (int i = 0; i < 3; i++)
        {
            cFile.write(reinterpret_cast<char *>(&players[i]), sizeof(Character));
        }

        cFile.seekg(ios::beg);
        for (int i = 0; i < 3; i++)
        {
            cFile.read(reinterpret_cast<char *>(&playersRead[i]), sizeof(Character));
            playersRead[i].display();
        }

        cFile.close();
    }
    else
    {
        cout << "Error opening file." << endl;
    }

I've been working on this code for a few days and am really having trouble. I appreciate any help I can get, thanks in advance.

#pragma once
#include <iostream>
using std::ostream;
#include "string.h"
#include "coinPouch.h"
#include "backpack.h"

class Character
{
public:
	Character();
	Character(String name);
	Character(String name, CoinPouch wallet, Backpack storage);
	Character(const Character & copy);
	~Character();
	Character & operator =(const Character & rhs);

	friend ostream & operator << (ostream & out, const Character & c);

	void purchase(int p, int g, int s, int c);
	void income(int p, int g, int s, int c);
	void addPotion(const Potion & toAdd);
	void checkBalance();
	void checkBackpack();
	void changeName(const String & newN);
	void display();

	String getName();
	CoinPouch getWallet();
	Backpack getStorage();
	void setName(String name);
	void setWallet(CoinPouch wallet);
	void setStorage(Backpack storage);

private:
	String m_name;
	CoinPouch m_wallet;
	Backpack m_storage;

};

#include "character.h"
using std::endl;
using std::cout;

Character::Character() : m_name("Player")
{
	CoinPouch initialW;
	Backpack initialS;
	m_wallet = initialW;
	m_storage = initialS;
}

Character::Character(String name) : m_name(name)
{
	CoinPouch initialW;
	Backpack initialS;
	m_wallet = initialW;
	m_storage = initialS;
}

Character::Character(String name, CoinPouch wallet, Backpack storage) : m_name(name), m_wallet(wallet), m_storage(storage)
{

}

Character::Character(const Character & copy) : m_name(copy.m_name), m_wallet(copy.m_wallet), m_storage(copy.m_storage)
{

}

Character::~Character()
{

}

Character & Character::operator =(const Character & rhs)
{
	if (this != &rhs)
	{
		m_name = rhs.m_name;
		m_wallet = rhs.m_wallet;
		m_storage = rhs.m_storage;
	}

	return *this;
}

ostream & operator << (ostream & out, const Character & c)
{
	out << c.m_name << ": " << endl;
	out << c.m_wallet << endl;
	out << c.m_storage << endl;
	
	return out;
}

void Character::purchase(int p, int g, int s, int c)
{
	m_wallet.buy(p, g, s, c);
}

void Character::income(int p, int g, int s, int c)
{
	m_wallet.add(p, g, s, c);
}

void Character::addPotion(const Potion & toAdd)
{
	m_storage.addPotion(toAdd);
}

void Character::checkBalance()
{
	m_wallet.display();
}

void Character::checkBackpack()
{
	m_storage.displayContents();
}

void Character::changeName(const String & newN)
{
	m_name = newN;
}

void Character::display()
{
	cout << m_name << ": " << endl;
	m_wallet.display();
	m_storage.displayContents();
}

String Character::getName()
{
	return m_name;
}

CoinPouch Character::getWallet()
{
	return m_wallet;
}

Backpack Character::getStorage()
{
	return m_storage;
}

void Character::setName(String name)
{
	m_name = name;
}

void Character::setWallet(CoinPouch wallet)
{
	m_wallet = wallet;
}

void Character::setStorage(Backpack storage)
{
	m_storage = storage;
}

#pragma once
#include <iostream>
using std::ostream;
#include "string.h"

class CoinPouch
{
public:
	CoinPouch();
	CoinPouch(String init);
	CoinPouch(int p, int g, int s, int c);
	CoinPouch(const CoinPouch & copy);
	~CoinPouch();
	CoinPouch & operator = (const CoinPouch & rhs);
	friend ostream & operator << (ostream & out, const CoinPouch & c);
	
	void add(int p, int g, int s, int c);
	bool checkCost(int p, int g, int s, int c);
	void buy(int p, int g, int s, int c);
	void convertCost();
	void roundUp();
	void display();

	int getP();
	int getG();
	int getS();
	int getC();

private:
	String m_amount;

	int m_platinum;
	int m_gold;
	int m_silver;
	int m_copper;
};

#pragma once
#include "potions.h"

class DynamicArray
{
public:
	// Constructors
	DynamicArray();
	~DynamicArray();
	DynamicArray(const DynamicArray & copy);

	// Op Equals
	DynamicArray & operator =(const DynamicArray & rhs);

	// Insert, delete, and get elements functions
	int getElements();
	void Insert(const Potion & add);
	void Delete(const Potion & rmv);
	void display();

	// Overloaded operators
	Potion & operator [](int index);
	friend ostream & operator << (ostream & out, const DynamicArray & d);

private:
	// Member variables
	Potion * m_array;
	int m_elements;

	// Find function
	int Find(const Potion & target);
};

#pragma once
#include "string.h"
#include <iostream>
using std::ostream;

class Potion
{
public:
	// Constructors
	Potion();
	Potion(String name, String description, String potency, String cost);
	Potion & operator = (const Potion & rhs);
	Potion(const Potion & copy);

	// Desctructor
	~Potion();

	// Overloaded operators
	bool operator == (const Potion & rhs) const;
	friend ostream & operator << (ostream & out, const Potion & p);

	// Getter functions
	String getName();
	String getDesc();
	String getPotency();
	String getCost();
	int getP();
	int getG();
	int getS(); 
	int getC();

	// Setter functions
	void setName(String name);
	void setDesc(String desc);
	void setPotency(String potency);
	void setCost(String cost);

	// Convert and display functions
	void convertCost();
	void display();

private:
	// Strings to hold item information
	String m_name;
	String m_description;
	String m_potency;
	String m_cost;

	// Ints to hold cost information
	int m_platinum;
	int m_gold;
	int m_silver;
	int m_copper;

	// Logical test
	bool m_isnull = false;
};

#pragma once
#include <iostream>
using std::ostream;

class String
{
public:
	// Constructors
	String();
	String(char ch);
	String(const char * str);

	// Destructor
	~String();

	// Copy Constructor and Copy Assignment Constructor
	String(const String & copy);
	String & operator=(const String & rhs);
	friend ostream & operator << (ostream & out, const String & s);

	// Added Functionality
	void display();
	void upper();
	void lower();

	// Operator Conversion
	operator char *();
	operator const char *();

	// Overloaded operator
	bool operator == (const String & rhs) const;

private:
	// Member variables
	char * m_str;
	int m_ischar;

};

#pragma once
#include "dynamicarray.h"
#include "coinPouch.h"
#include "string.h"

class Backpack
{
public:
	Backpack();
	Backpack(DynamicArray potions);
	Backpack(const Backpack & copy);
	~Backpack();
	Backpack & operator = (const Backpack & rhs);
	friend ostream & operator << (ostream & out, const Backpack & c);

	void addPotion(const Potion & add);
	void usePotion(const Potion & rm);
	void displayContents();

private:
	DynamicArray m_potions;

	int m_number;
};

This is a school project, and I am supposed to write the Character class to a binary file in order to save the characters so I can load them in on the program start. Right now I'm just trying to make sure that they can be successfully written to and read from the binary file and I have had no luck.

My bad, didn't know what to post and I didn't want to post everything in my file. Here is the character class. Let me know what else is needed, if anything.

回答1:

It should be immediately obvious that this code can't possibly work.

        cFile.write(reinterpret_cast<char *>(&players[i]), sizeof(Character));

However big sizeof(Character) is, we could have a Character with an m_name that takes up more bytes than that. So this code can't possibly be writing the character's name, and it clearly needs to do that.

Before you write anything to a file, decide on (and ideally, document) a file format at the byte level. Make sure your code writes in the format you documented and also can read in the format you documented. Skipping this step leads to pain and it also makes debugging impossible because you can't look at the file and compare it to a specification to see whether the writer or the reader is at fault.

Had you documented what bytes the player's name will occupy in the file, you'd immediately realize that you either need to have a variable-length object and encode the length somehow or pick a largest size name and allocate those many bytes. But because you skipped that vital step, you never actually worked out how to write a Character to a file.

来源：https://stackoverflow.com/questions/53454617/how-to-write-read-classes-within-classes-to-binary-file-c