#include <iostream>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

void parent();
void child ();

#define SHMKEY	859047             /* Parent and child agree on common key.*/
#define BUFF_SZ	sizeof ( int )

using namespace std;

int main()
{
    switch ( fork() )
    {
	case -1:
	    cerr << "Failed to fork" << endl;
	    return ( 1 );

	case 0:
	    child();
	    break;

	default:
	    parent();
	    break;
    }

    return ( 0 );
}

void parent()
{
    // Get shared memory segment identifier

    int shmid = shmget ( SHMKEY, BUFF_SZ, 0777 | IPC_CREAT );
    if ( shmid == -1 )
    {
	cerr << "Parent: ... Error in shmget ..." << endl;
	exit (1);
    }

    // Get the pointer to shared block

    char * paddr = ( char * )( shmat ( shmid, 0, 0 ) );
    int * pint = ( int * )( paddr );

    for ( int i ( 0 ); i < 10; i++ )
    {
	sleep ( 2 );

	*pint = 10 *i ;             /* Write into the shared area. */

	cout << "Parent: Written Val.: = " << *pint << endl;
    }
}

void child()
{
    sleep ( 5 );
    int shmid = shmget ( SHMKEY, BUFF_SZ, 0777 );

    if ( shmid == -1 )
    {
	cerr << "Child: ... Error in shmget ..." << endl;
	exit ( 1 );
    }

    int * cint = ( int * )( shmat ( shmid, 0, 0 ) );

    for ( int i ( 0 ); i < 10; i++ )
    {
	sleep ( 1 );
	cout << "Child: Read Val. = " << *cint << endl;
    }
}