Waiting for all child processes to be created - C - c

Question

Let's suppose I have a code like the following
switch (fork()) {
case -1:
//error checking
break;
case 0:
//child code
break;
default:
int i;
for (i = 0; i < n; i++) {
switch (fork()) {
case -1:
//error checking
break;
case 0:
//exec
break;
default:
//parent that waits for all childs to be created
break;
}
}
}
How do I make the second parent process wait for all the other processes to be created exactly ...
I was told I had to make a loop but I don't know how to implement it exactly. Supposing there are n child processes.

Answer 1

I think you may have misunderstood the requirement slightly. The term 'second parent' doesn't make a lot of sense to me.
What makes most sense as a requirement is:
Parent process launches N children.
Each child does its appropriate stuff.
The parent process must then wait for all N children to complete.
Then it can report its own completion (or get on with other work, or ...).
In outline, you would then have:
int pid;
for (int i = 0; i < N; i++)
{
switch (pid = fork())
{
case 0:
be_childish(i);
/*NOTREACHED*/
break;
case -1:
// Print error report
break;
default:
printf("Started PID %d\n", pid);
break;
}
}
int status;
while ((pid = wait(&status)) > 0)
{
printf("PID %d exited (status 0x%.4X)\n", pid, status);
}
printf("All done!\n");
Note the /*NOTREACHED*/ comment. I assume that the child process exits from within the be_childish() function. The code could ensure no damage by including an exit(1); or perhaps _exit(1); or _Exit(1);. It is rather important that a child process does not continue the loop.