/*
 Creating a shared memory segment and attaching it 
 to the logical address space.  sharedMem1.c++       
 $ g++ -Wall sharedMem1.c++              
 $ ./a.out w                                  
 $ ./a.out r                                    
*/
#include <iostream>
using namespace std;
#include <cstdlib>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#define SIZE 4

int main(int count, char *vect[]) {
	int shmID, *p ;

	if(count < 2) {
           cerr << "No 2nd argument\n";
           exit(1) ;
	}		
	shmID = shmget(ftok("/home/goutam", 1234), SIZE, IPC_CREAT | 0777);
	if(shmID == -1) {
           cerr << "Error in shmget" ;
           exit(1) ;
	}
	p = (int *) shmat(shmID, 0, 0777) ;
        cout << "Attached at VA: " << p << endl;
	if(vect[1][0] == 'w') {  
           cout << "Enter an integer: ";
           cin >> *p ;  // Write data
	   shmdt(p) ;
	}
        else if(vect[1][0] == 'r'){
                cout << "The data is:" << *p << "\n";
	        shmdt(p) ;
             }    
// The shared memory segment remains in the system
// $ ipcs
// $ ipcrm -m<number>	
	return 0 ;
}