How to serialize the data in Binary I/O? - c++

Question

Here is my C++ class and code snip. Data does not gets properly loaded in objects which gives me memory access error. What can i do?
Base Class
using namespace std;
class Person;
class Person
{protected:
int ID;
string name;
string address;
long int phone;
string dob;
//char pass[25];
std::string pass;
public:
Person();
Person(int ID,string name, string address, long int phone, string dob, string pass) :
ID(ID),name(name), phone(phone),address(address),dob(dob),pass(pass)
{};
//COPY CONSTRUCTOR MUST BE CREATED INORDER TO MAKE VECTOR WORK
Person(const Person&);
virtual void showDetails() const = 0;
//MAKING THIS CLASS AN ABSTRACT CLASS
//BUNCH OF GETTERS
int getID() const;
string getName() const;
string getAddress() const;
long int getPhone() const;
string getDob() const;
string getPass() const;
void setPass(string a);
};
Here is the derived class from it :
#include<iostream>
#include"Person.h"
#ifndef CUSTOMER_H
#define CUSTOMER_H
class Customer :public Person {
private:
float balance;
protected:
public:
Customer() :Person(), balance(0) {}
Customer(int ID,std::string name,std::string address,long int phone, string dob,std::string
pass,float balance):
Person(ID,name,address,phone,dob,pass),balance(balance){};
//Customer(int ID, const char* name, const char* address, long int phone, string dob, const
char* pass, float balance) :
// Person(ID, name, address, phone, dob, pass), balance(balance) {};
//COPY CONSTRUCTOR MUST BE PROVIDED, ELSE VECTOR WONT WORK
Customer(const Customer& other) :Person(other) {
this->balance = other.balance;
}
float getBalance() const;
void showDetails() const;
// void setValues();
void deposit(float);
void withdraw(float);
};
#endif
Im having issues that data is not copied from file into vector properly : Here is the implementation of file handling:
void Controller::displayCustomers()
{
vector<Customer> custVector;
Customer cust;
fstream fin("customer.txt", ios::binary | ios::in);
while (fin.read(reinterpret_cast<char*>(&cust), sizeof(cust)));
{
custVector.push_back(cust);
}
fin.close();
cout << "ID\tNAME\tADDRESS\tPHONE\t\tDOB\tPASSWORD\tBALANCE" << endl;
for (vector<Customer>::iterator itr = custVector.begin();
itr != custVector.end(); ++itr)
{
cout << itr->getID() << "\t" << itr->getName() << "\t" << itr->getAddress() << "\t"
<< itr->getPhone() << "\t" << itr->getDob() << "\t" << itr->getPass() <<
"\t" << itr->getBalance() << endl;
}
cout << endl;
}
The constuctors runs more than data members and gives a memory access error when vector members are accessed. What should be the best practice.?

Answer 1

You cannot use binary I/O to directly read or write objects containing std::string. So this code is wrong.
fin.read(reinterpret_cast<char*>(&cust), sizeof(cust))
Best practise depends entirely on what you are trying to achieve. Must you use binary I/O? Can you change the class? Are you trying to get indexed access on your file?
For better advice you need to state what you are actually trying to achieve. At the moment all anyone can say it that this code is wrong.
It's possible that you just chose binary I/O because you throught it would be easiest. If that's the case then you should probably abandon it and switch to text I/O. But I'm not going to give advice based on speculation. You need to say what you are trying to do here.
ADDENDUM
I noticed this is your code
//char pass[25];
std::string pass;
If you followed through with that, and replaced all the strings in your classes then you might find that your reading and writing code started working. This is what's known as a plain old data (POD) class. POD classes can be read and written in the way you are trying to.
Note you would also have to remove any virtual functions as well, so maybe a POD class isn't such a good idea.