025Overload_new_delete_operators_in_a_class.cpp

#include<iostream>
#include<string.h>
#include<new>
#include<stdlib.h>

using namespace std;
const int MAX = 5;
const int FREE = 0;
const int OCCUPIED = 1;

void memwarning( )
{
	cout << endl <<"Free store has now gone empty";
	exit( 1 );
}

class employee
{
	private:
		char name[20];
		int age;
		float sal;
	public:
		void *operator new(size_t bytes);
		void operator delete( void * q );
		void setdata( char * n, int a, float s );
		void showdata();
			~employee();
};

struct pool
{
	employee obj;
	int status;
};

int flag=0;
struct pool *p = NULL;

void * employee::operator new( size_t sz )
{
	int i;
	if( flag == 0 )
	{
		p = ( pool * )malloc( sz * MAX );
		if( p == NULL )
			memwarning( );
		for( i = 0; i < MAX; i++ )
			p[ i ].status = FREE;
		flag = 1;
		p[ 0 ].status = OCCUPIED;
		return &p[ 0 ].obj;
	}
	else
	{
		for( i = 0; i < MAX; i++ )
		{
			if( p[ i ].status = FREE )
			{
				p[ i ].status = OCCUPIED;
				return &p[ i ].obj;
			}
		}
		memwarning( );
	}
}

void employee::operator delete( void * q )
{
	if(q == NULL)
		return;
	for(int i = 0; i < MAX; i++)
	{
		if(q == &p[ i ].obj)
		{
			p[i].status = FREE;
			strcpy(p[i].obj.name, "" );
			p[i].obj.age = 0;
			p[i].obj.sal = 0.0;
		}
	}
}

void employee::setdata( char * n, int a, float s )
{
	strcpy(name, n);
	age = a;
	sal = s;
}

void employee::showdata()
{
	cout << endl << name << "\t" << age << "\t" << sal;
}

employee::~employee()
{
	cout << endl << "reached destructor";
	free(p);
}

int main()
{
	void memwarning();
	set_new_handler(memwarning);
	employee * e1,*e2,*e3,*e4,*e5,*e6;
	e1 = new employee;
	e1->setdata("ajay", 23, 4500.50 );
	e2 = new employee;
	e2->setdata("amol", 25, 5500.50 );
	e3 = new employee;
	e3->setdata("anil", 26, 3500.50 );
	e4 = new employee;
	e4->setdata("anuj", 30, 6500.50 );
	e5 = new employee;
	e5->setdata("atul", 23, 4200.50 );
	e1->showdata();
	e2->showdata();
	e3->showdata();
	e4->showdata();
	e5->showdata();

	delete e4;
	delete e5;
	
	e4->showdata( );
	e5->showdata( );
	
	e4 = new employee;
	e5 = new employee;
	e6 = new employee;
	
	cout << endl << "Done!!";
	return 0;
}