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



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

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
       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 POSIX.1-2017. Although it is outside the scope of this volume of
       POSIX.1-2017 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
       Section 2.4, Signal Concepts, pthread__sigmask(), sigaction(),
       sigaddset(), sigdelset(), sigfillset(), sigismember(), sigpending(),
       sigsuspend()

       The Base Definitions volume of POSIX.1-2017, <signal.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                       SIGEMPTYSET(3)
