Why do we use write function twice ?

[daksh717]

Why do we need to use read function in while loop when already used once before starting the loop ? And whats the exact use of getting the size of class ?

#include <fstream>
#include "stdafx.h"
#include <iostream>

using namespace std;
class student
{
private:
	int reg;
	char name[20];
public:
	void setreg()
	{
	cout<<"enter reg";
	cin>>reg;
	}

	void setname()
	{
	cout<<"eneter name";
	cin>>name;
	}

	int getreg()
	{
	return reg;
	}
	char *getname()
	{
	return name;
	}
};

void main()
{
ofstream Sfil("stud.dat");
	char ch;
student Svar;
while(1)
{
cout<<"want to enter more records";
cin>>ch;
if (ch=='n')
	break;
Svar.setreg();
Svar.setname();
Sfil.write((char*)&Svar,sizeof(student));
}
Sfil.close();
cout<<"do u wanna cont ?";
cin>>ch;
if (ch=='y')
{
ifstream Sfil("stud.dat")
	Sfil.read((char*)&Svar, sizeof(student));
while(Sfil)
{
cout<<"reg no. is"<<Svar.getnum();
cout<<"name is"<<Svar.getname();
Sfil.read((char*)&Svar, sizeof(student));
}
}
}

[Computergeek01]

Why do we need to use read function in while loop when already used once before starting the loop ?

Because you didn't use do ... while.

And whats the exact use of getting the size of class ?

Because "std::ofstream.write()" requires it as a parameter: http://www.cplusplus.com/reference/ostream/ostream/write/

[dhayden]

You could just do

while (Sfil.read((char*)&Svar, sizeof(student))) {
    cout<<"reg no. is"<<Svar.getnum();
    cout<<"name is"<<Svar.getname();
}

Sfil.read() returns a reference to Sfil