Question

My professor shows the following example in C:

#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>

int main() {
   pid_t pid;

   /* fork another process */
   pid = fork();
   if (pid < 0) { /* error occurred */
         fprintf(stderr, "Fork Failed");
         return 1;
   }
   else if (pid == 0) { /* child process */
         execlp("/bin/ls", "ls", NULL);
   }
   else { /* parent process */
        /* parent will wait for the child */
        wait (NULL);
        printf("Child Completed its execution\n");
   }

return 0;
}

I compiled it and ran it. I saw a strange behavior in this code:

The result of ‘ls’ program/command is printed which is in the else if condition but also the string “Child Completed its execution\n” printed too which is in else.

Isn’t this a strange behavior?

Answer 1

No, you forked it. There are two processes running. One reported the ls and the other reported the printf().

Specifically, the child/forked process executed /bin/ls and the parent called printf(), the output you see.