The <signal.h> include file defines the values for signals and declares the signal and raise functions.
<signal.h> also defines the following macros:
| SIGABRT | SIG_ERR | SIGILL | SIGSEGV |
| SIGALL | SIGFPE | SIGINT | SIGUSR1 |
| SIGSEGV | SIGUSR2 | SIGBREAK | SIG_DFL |
| SIGUSR3 | SIG_IGN |