Where do I put perror("wait") with fork code - c

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>
int main(int argc, char **argv) {
for(int i = 0; i < 10; i++) {
pid_t pid = fork();
if(pid == 0) {
while(1) {
pid_t pid2 = fork();
wait(NULL);
}
}
}
wait(NULL);
return(0);
}
Basically the program runs several hello world processes and closes with ctrl+C. How would I do the wait error? Like perror(wait). I think I have to use int status instead of NULL but unsure how to go about it when theres orphan processes involved.
The given code is
$ gcc -Wall above.c
$ ./a.out
hello world
hello world
hello world
hello world
hello world
hello world
hello world
hello world
hello world
hello world
hello world
hello world
^C (until ctrl C is hit)
$

Answer 1

The function perror is only useful when you know that a function failed and
errno is set, so you want to print an error message. You usually write
perror("something failed") right after the function that could fail and
sets errno (the documentation of the function will tell you whether the
function set errno on failure).
man perror
SYNOPSIS
#include <stdio.h>
void perror(const char *s);
#include <errno.h>
DESCRIPTION
The perror() function produces a message on standard error describing the last error encountered during a call to a system or library
function....
This has nothing to do with wait and it's parameter, it's only useful if
wait fails and you want to print an error message about wait failing.
man wait
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(int *wstatus);
pid_t waitpid(pid_t pid, int *wstatus, int options);
DESCRIPTION
All of these system calls are used to wait for state changes in a child of the calling process...
...
wait() and waitpid()
The wait() system call suspends execution of the calling process until one of its children terminates. The call wait(&wstatus) is
equivalent to:
waitpid(-1, &wstatus, 0);
...
RETURN VALUE
wait(): on success, returns the process ID of the terminated child; on error, -1 is returned.
...
Each of these calls sets errno to an appropriate value in the case of an error.
If you just want to wait for a child to exit, you can do just wait(NULL).
However if you want to know the status of the child that exited, then you have
to pass a pointer to int.
int wstatus;
pid_t wp = wait(&wstatus);
if(wp == -1)
{
// here I use perror because if wait returns -1 then there
// was an error and errno is set
perror("could not wait for child\n");
exit(1);
}
if(WIFEXITED(wstatus))
printf("Child with pid %d exited normally with status %d\n", wp, WEXITSTATUS(wstatus));
else
printf("Child with pid %d exited abnormally\n", wp);
I personally prefer waitpid over wait, it gives you more control over the
child you are waiting.
See man wait