// CS 450: Process example 3: Address space of child processes
// version 2014-01-21 7:13 PM
//
#include <stdio.h>
#include <unistd.h>    // fork
#include <stdlib.h>    // exit
#include <sys/wait.h>  // wait

// Child will get duplicate of parent's address
// space, so its global variable will be at the
// same location, but in its own space, not the
// parent's
//
int glovar = 1;

int main(int argc, char *argv[]) {
	pid_t pid = fork();

	// Parent prints global var,
	// waits for child to finish,
	// then reprints global var
	//
	if (pid > 0) {
		fprintf(stderr, "Parent: &glovar: %p, glovar: %d\n",
		    &glovar, glovar );
		fprintf(stderr, "Wait for child with pid %d\n", pid);

		wait(NULL);
		fprintf(stderr, "Parent: glovar: %d\n", glovar);
		return pid;
	}

	// Child changes global variable
	// then returns
	//
	else if (pid == 0) {
		glovar = 1234;
		fprintf(stderr, "Child:  &glovar: %p, glovar: %d\n",
		    &glovar, glovar );
		exit(0);
	}
	
	// Complain if fork failed
	//
	else if (pid == -1) {
		fprintf(stderr, "Fork failed\n");
		exit(1);
	}
}

// Sample output
//
// Parent: &glovar: 0x10b681068, glovar: 1
// Wait for child with pid 2457
// Child:  &glovar: 0x10b681068, glovar: 1234
// Parent: glovar: 1