Example of waitpid() in use?

Question

I know that waitpid() is used to wait for a process to finish, but how would one use it exactly?

Here what I want to do is, create two children and wait for the first child to finish, then kill the second child before exiting.

//Create two children
pid_t child1;
pid_t child2;
child1 = fork();

//wait for child1 to finish, then kill child2
waitpid() ... child1 {
kill(child2) }

Answer 1

Syntax of waitpid():

pid_t waitpid(pid_t pid, int *status, int options);

The value of pid can be:

• < -1: Wait for any child process whose process group ID is equal to the absolute value of pid.
• -1: Wait for any child process.
• 0: Wait for any child process whose process group ID is equal to that of the calling process.
• > 0: Wait for the child whose process ID is equal to the value of pid.

The value of options is an OR of zero or more of the following constants:

• WNOHANG: Return immediately if no child has exited.
• WUNTRACED: Also return if a child has stopped. Status for traced children which have stopped is provided even if this option is not specified.
• WCONTINUED: Also return if a stopped child has been resumed by delivery of SIGCONT.

For more help, use man waitpid.