File I/O (Reading from a Random-Access File)

#ifndef CIRCLE_H
#define CIRCLE_H

#include <iostream>
#include <fstream>
using namespace std;

class Circle
{
	friend ostream& operator <<(ostream& output, const Circle& aCircle);
	friend istream& operator >>(istream& input, Circle& aCircle);

public:
	Circle();
	Circle(double radius, int id);
	Circle(const Circle& aCircle);

	void SetCircleRadius(double radius) { _circleRadius = radius; }
	void SetCircleId(int id)   { _circleId = id; }

	double GetCircleRadius() const   { return _circleRadius; }
	int GetCircleId() const { return _circleId; }

private:
	double  _circleRadius;
	int     _circleId;
};

#endif

#include "Circle.h"

Circle::Circle()
{
	_circleId = 0;
	_circleRadius = 0.0;
}

Circle::Circle(double radius, int id)
{
	_circleId = id;
	_circleRadius = radius;
}

Circle::Circle(const Circle& aCircle)
{
	_circleId = aCircle._circleId;
	_circleRadius = aCircle._circleRadius;
}

ostream& operator <<(ostream& output, const Circle& aCircle)
{
	output << "\n          ------------" << endl;
	output << "          Id    radius" << endl;
	output << "          ------------" << endl;
	output << "          " << aCircle._circleId << "     " << aCircle._circleRadius << endl;
	output << "          ------------" << "\n\n";

	return (output);
}

istream& operator >>(istream& input, Circle& aCircle)
{
	int quantity;
	cout << "\nHow many circles do you want to add ";
	input >> quantity;

	for (int i = 0; i < quantity; ++i)
	{
		cout << "\n\nEnter the ID of Circle #" << (i + 1) << " : ";
		input >> aCircle._circleId;

		cout << "Enter Radius of Circle #" << (i + 1) << " : ";
		input >> aCircle._circleRadius;

		cout << endl;
	}

	return (input);
}

#include <iostream>
#include <conio.h>
#include <fstream>
using namespace std;

#include "Circle.h"

int main ()
{
	Circle aCircle;
	fstream file;
	int option;

	do
	{
		cout << "Menu \n"
			 << " (1) Add Circle(s) \n"
			 << " (2) Find a Circle by ID \n"
			 << " (3) Exit \n"
			 << "Your Selection -> ";
		cin >> option;

		switch (option)
		{
		case 1:
			file.close();
			file.clear();

			file.open("Circle.dat", ios::out | ios::app | ios::binary);
			
			if (!file)
			{
				cerr << "\n\nFailed to open file.\n\n";
				system("PAUSE");
				exit(1);
			}
			else
			{
				cin >> aCircle;
				file.write(reinterpret_cast<char*> (&aCircle), sizeof(Circle));
			}
			break;

		case 2:
			file.close();
			file.clear();


			cout << "Enter id: ";
			int id;
			cin >> id;
			aCircle.SetCircleId(id);

			file.open("Circle.dat", ios::in | ios::app | ios::binary);

			if (!file)
			{
				cerr << "\n\nFailed to open file.\n\n";
				system("PAUSE");
				exit(1);
			}
			else
			{
				file.seekg(id * sizeof(Circle), ios::beg);
				file.read(reinterpret_cast<char *> (&aCircle), sizeof(Circle));

				cout << aCircle;
			}	
			break;


		case 3:
			file.close();
			cout << "\n\nG   o    o    D    B    y    E\n\n";
			exit(0);
			break;


		default:
			cerr << "\nERROR: Wrong Option menu. Please try again.\n\n";

		}

	} while (option != 3);

	return EXIT_SUCCESS;
}