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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 (consult 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 POSIX.1-2008 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  struc-
       ture,  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 argu-
       ment to sigpending()).  This function is not intended for dynamic allo-
       cation.
       The sigfillset() and sigemptyset() functions require that the resulting
       signal  set include (or exclude) all the signals defined in this volume
       of POSIX.1-2008. Although it is outside the scope  of  this  volume  of
       POSIX.1-2008  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 rea-
       son 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  unsup-
       ported  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 sig-
       nals. With that distinction, it is not necessary to require implementa-
       tions  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 sig-
       nals and optional for unsupported signals, but this seemed  unnecessar-
       ily complex. Thus, the error is optional in both cases.
FUTURE DIRECTIONS
       None.
SEE ALSO
       Section 2.4, Signal Concepts, pthread_sigmask(), sigaction(),
       sigaddset(), sigdelset(), sigfillset(), sigismember(), sigpending(),
       sigsuspend()
       The Base Definitions volume of POSIX.1-2008, <signal.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/online.html .
       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,  see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                      SIGEMPTYSET(3P)