Question

I have some code that has to compile for multiple platforms. The following will make the code compile but I want to know where the SIGUNUSED symbol is actually defined:

Working Code

#ifdef LINUX
#define SIGEMT SIGUNUSED
#endif

…

void set_sig_trap()
{
   signal( SIGHUP, Signal );       /* floating point exception            */
   signal( SIGINT , Signal );      /* Interrupt                           */
   signal( SIGQUIT, Signal );      /* quit                                */
   signal( SIGILL, Signal );       /* Illegal instruction                 */
   signal( SIGTRAP, Signal );      /* trace trap                          */
   signal( SIGABRT, Signal );      /* Process abort signal                */
   signal( SIGEMT, Signal );       /* EMT instruction                     */
   signal( SIGFPE, Signal );       /* Floating point exception            */
   signal( SIGBUS, Signal );       /* bus error                           */
   signal( SIGSEGV, Signal );      /* Segmentation violation              */
   signal( SIGSYS, Signal );       /* bad argument to system call         */
   signal( SIGPIPE, Signal );      /* write on a pipe - no one to read it */
   signal( SIGTERM, Signal );      /* Software termination sig. from kill */
   signal( SIGALRM, Signal );      /* alarm clock                         */
   return;
}

…

I have looked for SIGUNUSED in /usr/include with no hits. It is not in signal.h. Where is it coming from?

Update:

I did not think the signal definition would be outside of signal.h as the response indicated a recursive search did find the definition:

me@mymachine.:/usr/include $ grep -d recurse SIGUNUSED *
asm/signal.h:#define    SIGUNUSED       31
asm-arm/signal.h:#define        SIGUNUSED       31
asm-ia64/signal.h:/* signal 31 is no longer "unused", but the SIGUNUSED macro remains for backwards compatibility */
asm-ia64/signal.h:#define       SIGUNUSED       31
asm-parisc/signal.h:#define     SIGUNUSED       31
asm-parisc/signal.h:#define SIGRESERVE  SIGUNUSED
asm-powerpc/signal.h:#define    SIGUNUSED       31
asm-s390/signal.h:#define SIGUNUSED       31
asm-x86/signal.h:#define        SIGUNUSED       31
bits/signum.h:#define SIGUNUSED 31

Thanks!

Answer 1

I see it defined in bits/signum.h, which is included from signal.h:

#define SIGUNUSED 31

Maybe you forgot to grep recursively?