signals/signal.c

This is signals/signal.c (Listing 22-1, page 455), an example from the book, The Linux Programming Interface.

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Cover of The Linux Programming Interface

+/* signal.c
+
+   An implementation of signal() using sigaction().
+
+   Compiling with "-DOLD_SIGS" provides the older, unreliable signal handler
+   semantics (which are still the default on some System V derivatives).
+*/
+/* Some UNIX implementations follow the BSD signal() semantics, including
+   Linux, Tru64, and of course the BSD derivatives. Others, such as Solaris,
+   follow the System V semantics. We'll conditionally override signal() on
+   platforms following the System V semantics. For the other implementations,
+   we'll provide a dummy source file that doesn't implement signal().
+*/
+#if defined(__sun) || defined(__sgi)
 #include <signal.h>
 
 typedef void (*sighandler_t)(int);
 
 sighandler_t
 signal(int sig, sighandler_t handler)
 {
     struct sigaction newDisp, prevDisp;
 
     newDisp.sa_handler = handler;
     sigemptyset(&newDisp.sa_mask);
 #ifdef OLD_SIGNAL
     newDisp.sa_flags = SA_RESETHAND | SA_NODEFER;
 #else
     newDisp.sa_flags = SA_RESTART;
 #endif
 
     if (sigaction(sig, &newDisp, &prevDisp) == -1)
         return SIG_ERR;
     else
         return prevDisp.sa_handler;
 }
+
+#else
+/* The following declaration is provided purely to avoid gcc's
+   "warning: ISO C forbids an empty source file" warnings. */
+
+extern int signalDummyVar;
+
+#endif

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