This is signals/intquit.c (Listing 20-2, page 401), an example from the book, The Linux Programming Interface.

The source code file is copyright 2010, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* intquit.c
+   Catch the SIGINT and SIGQUIT signals, which are normally generated
+   by the control-C (^C) and control-\ (^\) keys respectively.
+   Note that although we use signal() to establish signal handlers in this
+   program, the use of sigaction() is always preferable for this task.
 #include <signal.h>
 #include "tlpi_hdr.h"
 static void
 sigHandler(int sig)
     static int count = 0;
     /* UNSAFE: This handler uses non-async-signal-safe functions
        (printf(), exit(); see Section 21.1.2) */
     if (sig == SIGINT) {
         printf("Caught SIGINT (%d)\n", count);
         return;                 /* Resume execution at point of interruption */
     /* Must be SIGQUIT - print a message and terminate the process */
     printf("Caught SIGQUIT - that's all folks!\n");
 main(int argc, char *argv[])
-    /* Establish same handler for SIGINT and SIGQUIT */
+    /* Establish same handler for SIGINT and SIGQUIT. Here we use the
+       simpler signal() API to establish a signal handler, but for the
+       reasons described in Section 22.7 of TLPI, sigaction() is the
+       (strongly) preferred API for this task. */
     if (signal(SIGINT, sigHandler) == SIG_ERR)
     if (signal(SIGQUIT, sigHandler) == SIG_ERR)
     for (;;)                    /* Loop forever, waiting for signals */
         pause();                /* Block until a signal is caught */

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