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() , sigsuspend() , 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, Copyright (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.opengroup.org/unix/online.html .