#include <iostream>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
using namespace std;

static int *nptr;
int main()
{
	nptr = (int*)mmap(NULL, sizeof *nptr, PROT_READ | PROT_WRITE, 
                    MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (nptr != NULL) {
    	int& n = *nptr = 0;

		for (int i = 1; i < 4; i++)
		{
			n++;
			fork();
			cout << "Process pid=" << getpid() << " has n=" << n << endl;
		}
	}
	munmap(nptr, sizeof *nptr);
	return 0;
}