Question

The code:

int main(void) 
{
    printf("pid: %d\n", getpid());
    pid = fork();


    if (pid < 0) {
        fprintf(stderr, "Fork Failed!");
        exit(-1);
    } else if (pid == 0) {
        execv("sum", argv);
    } else {
        printf("  pid: %d\n", pid);
        wait(NULL);
    }
}

The output:

pid: 280
   pid: 281

The question:

Why are the two pid’s different. I thought they should be the same because the parent is what is executing in the else block and the parent is what is executing before the fork so they should be the same, no?

Answer 1

RETURN VALUE
       On success, the PID of the child process is returned in the parent, 
       and 0 is returned in the child.  On failure, -1 is returned in the parent,
       no child process  is  created,  and  errno  is  set appropriately.

So, in the parent process, fork() returns the pid of the child process that was created.