SIGEMPTYSET(3P)                                     POSIX Programmer's Manual                                    SIGEMPTYSET(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       sigemptyset - initialize and empty a signal set

SYNOPSIS
       #include <signal.h>

       int sigemptyset(sigset_t *set);


DESCRIPTION
       The  sigemptyset()  function  initializes  the  signal  set  pointed  to  by  set,  such  that  all  signals  defined  in
       IEEE Std 1003.1-2001 are excluded.

RETURN VALUE
       Upon successful completion, sigemptyset() shall return 0; otherwise, it shall return -1 and set  errno  to  indicate  the
       error.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The  implementation  of the sigemptyset() (or sigfillset()) function could quite trivially clear (or set) all the bits in
       the signal set.  Alternatively, it would be reasonable to initialize part of the structure, such as a version  field,  to
       permit  binary-compatibility between releases where the size of the set varies. For such reasons, either sigemptyset() or
       sigfillset() must be called prior to any other use of the signal set, even if such use is read-only (for example,  as  an
       argument to sigpending()). This function is not intended for dynamic allocation.

       The  sigfillset()  and sigemptyset() functions require that the resulting signal set include (or exclude) all the signals
       defined in this volume of IEEE Std 1003.1-2001. Although it is outside the scope of this volume  of  IEEE Std 1003.1-2001
       to  place  this  requirement on signals that are implemented as extensions, it is recommended that implementation-defined
       signals also be affected by these functions. However, there may be a good reason  for  a  particular  signal  not  to  be
       affected.  For  example, blocking or ignoring an implementation-defined signal may have undesirable side effects, whereas
       the default action for that signal is harmless.  In such a case, it would be preferable for such a signal to be  excluded
       from the signal set returned by sigfillset().

       In  early  proposals there was no distinction between invalid and unsupported signals (the names of optional signals that
       were not supported by an implementation were not defined by that implementation).  The [EINVAL] error was thus  specified
       as  a  required error for invalid signals. With that distinction, it is not necessary to require implementations of these
       functions to determine whether an optional signal is actually supported, as that could  have  a  significant  performance
       impact for little value. The error could have been required for invalid signals and optional for unsupported signals, but
       this seemed unnecessarily complex. Thus, the error is optional in both cases.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Signal Concepts, sigaction(), sigaddset(), sigdelset(), sigfillset(), sigismember(), sigpending(), sigprocmask(), sigsus-
       pend(), the Base Definitions volume of IEEE Std 1003.1-2001, <signal.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                               SIGEMPTYSET(3P)