fork.c

//
// Created by Robert Li on 14/3/21.
//
/*
 * Write a program that calls fork(). Before calling fork(), have the main process access a variable (e.g., x) and
 * set its value to something (e.g., 100). What value is the variable in the child process? What happens to the
 * variable when both the child and parent change the value of x?
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main(int argc, char *argv[])
{
    int x = 9;
    printf("Address of X initially: %p\n", &x);
    printf("hello world (pid:%d), (value of X: %d)\n", (int) getpid(), x);
    int rc = fork();
    if (rc < 0) {
        // fork failed; exit
        fprintf(stderr, "fork failed\n");
        exit(1);
    } else if (rc == 0) {
        // child (new process)
        printf("hello, I am child (pid:%d) (value of X: %d)\n", (int) getpid(), x);
        printf("Address of X in Child: %p\n", &x);
        x = 10;
        printf("In Child X is now %d\n", x);
        printf("Address of X in Child is now: %p\n", &x);
        sleep(1);
    } else {
        printf("Address of X in Parent after fork: %p\n", &x);
        // parent goes down this path (original process)
        int wc = wait(NULL);
        printf("hello, I am parent of %d (wc:%d) (pid:%d) (value of X: %d)\n",
               rc, wc, (int) getpid(), x);
    }
    return 0;
}

/usr/bin/make -f /Users/robertli/Documents/Workspace_Coding/ostep/ostep-homework/cpu-api/Makefile run-fork
gcc -o fork fork.c -Wall
./fork
Address of X initially: 0x7ffee05f0abc
hello world (pid:74633), (value of X: 9)
Address of X in Parent after fork: 0x7ffee05f0abc
hello, I am child (pid:74634) (value of X: 9)
Address of X in Child: 0x7ffee05f0abc
In Child X is now 10
Address of X in Child is now: 0x7ffee05f0abc
hello, I am parent of 74634 (wc:74634) (pid:74633) (value of X: 9)

Process finished with exit code 0

How is X different but the address of X is the same?