SIGEMPTYSET(3POSIX)

💖 SIGEMPTYSET(3POSIX) 💖

okay bestie, so this one is from the POSIX Programmer's Manual (yes, the Programmer's one, not the Linux one, iykyk) and it's genuinely one of the cutest little functions in the whole signal family. let's get into it 🫶

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✨ PROLOG ✨

so like, heads up before we even start: this manual page is part of the POSIX Programmer's Manual. the Linux implementation of this interface may differ — so if you're on Linux, go peek at the corresponding Linux manual page for the deets on actual Linux behavior. OR, plot twist, the interface might not be implemented on Linux at all. 🙈

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🌸 NAME 🌸

sigemptyset — initialize and empty a signal set

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🎀 SYNOPSIS 🎀

#include <signal.h>

int sigemptyset(sigset_t *set);

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🦋 DESCRIPTION 🦋

okay so the sigemptyset() function initializes the signal set pointed to by set, in a way that all signals defined in POSIX.1‐2008 are excluded. that's it. that's the whole job. it hands you a clean, empty little signal set. brand new. no signals in it. a fresh start. ✨

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⭐ RETURN VALUE ⭐

if it goes well, sigemptyset() shall return 0. if it doesn't, it shall return -1 and set errno to indicate the error. classic. no notes.

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💅 ERRORS 💅

No errors are defined.

The following sections are informative. (translation: they're the vibe, not the rules 💜)

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🌈 EXAMPLES 🌈

None.

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💜 APPLICATION USAGE 💜

None.

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👑 RATIONALE 👑

okay so the tea: the implementation of sigemptyset() (or sigfillset()) could quite trivially clear (or set) all the bits in the signal set. like, super easy. but alternatively — and honestly this is the more iconic choice — 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. so for those reasons, either sigemptyset() or sigfillset() must be called prior to any other use of the signal set, even if that use is read-only (for example, as an argument to sigpending()). periodt. and just so we're clear: 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. now, it's outside the scope of this volume of POSIX.1‐2017 to place this requirement on signals that are implemented as extensions, but 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().

and now some history, because we love a lore drop: 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.

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🧚 FUTURE DIRECTIONS 🧚

None.

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🔥 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>

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📜 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 .

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and that's the whole page, bestie — shoutout to IEEE/The Open Group, 2017, the icons who brought us SIGEMPTYSET(3POSIX). go forth and empty those signal sets responsibly 💖✨🎀