Fork - unpredictable?

Hi,

I am trying to learn the concept of fork, thus I wrote a program to test my knowledge, I will appreicate if anyone can point out what am I doing wrong with this codes. Thank you !

Freddie

Code:

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


// fork() -1 no process is created, original goes on running
// fork(), The child returns 0
// fork(), parent returns positive PID of the child

int main(int argc,char **argv) {

pid_t child, parent, old_ppid, new_ppid;
    
 printf(" Current PID is %d\n", parent = getpid());
 printf(" Current process PPID %d\n ", old_ppid = getppid()); 

 if ((  child =  fork() ) < 0 ) 
     /* handle error */
     fprintf(stderr, " %s Fork failed! %s", argv[0], strerror(errno));
     exit(1);

   else if (child == 0 ) {  //fork succesful
     {
           sleep(3); //if it is a process , sleep for one second
           printf("This is the new process\n");
           printf("It PID as %d \n",getpid());
           printf("Parent PID as %d\n", getppid() );
           exit(0);
 } else{

           sleep(1); //if it is a parent , sleep for 2 seconds
           printf("This is the parent process\n");
           printf("Parent PID as %d \n", getppid( ));
           exit(0);}
 return 0;
}

Seems OK to me, apart from your comments

sleep(3); //if it is a process , sleep for one second
sleep(1); //if it is a parent , sleep for 2 seconds

"Fork - unpredictable?"
But what is your question?
What are you seeing, and what is it that you don't understand about what you're seeing?

You also don't seem to be waiting for the child, look up the wait and wait_pid manpages.
I don't exactly know what your having trouble understanding either, since you haven't told us what you mean by unpredictable.

If I don't get it wrong, you're asking about whether the child or the parent will execute first, right?

Yes, it is unpredictable whether the child or the parent execute first. It all depends on the os to determine who runs first. Even you call some functions such as sleep, also it isn't guaranteed who will run first. But you can call the wait funtion family to wait for the child to execute.

Code:

if ((  child =  fork() ) < 0 ) 
     /* handle error */
     fprintf(stderr, " %s Fork failed! %s", argv[0], strerror(errno));
     exit(1);

you are missing { and } for that if.