The type sigset_t represents a set of signals.

To create a set with the single signal, SIGCHLD:

1. declare a sigset_t variable and initialize it (to be the empty set of signals)
2. add the SIGCHLD signal to the sigset_t

Example:

  sigset_t sset;
  
  sigemtpyset(&sset);
  sigaddset(&sset, SIGCHLD);