ATEXIT(3POSIX)

💖 ATEXIT(3POSIX) — bestie's guide to registering cleanup functions 💖

okay so first things first: this page lives in the POSIX Programmer's Manual, and its whole name-and-number situation is ATEXIT(3POSIX). 🎀

Real talk before we dive in: the Linux implementation of this interface may differ, so if you're on Linux, go check the corresponding Linux manual page for the deets on Linux behavior. Or — plot twist — the interface might not be implemented on Linux at all. 🙈

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✨ 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.

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🌸 NAME 🌸

atexit — register a function to run at process termination

like, you're literally telling the system "bestie, when I go, run this for me" 💅

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🦋 SYNOPSIS 🦋

#include <stdlib.h>

int atexit(void (*func)(void));

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💜 DESCRIPTION 💜

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

The atexit() function shall register the function pointed to by func, to be called without arguments at normal program termination. At normal program termination, all functions registered by the atexit() function shall be called, in the reverse order of their registration, except that a function is called after any previously registered functions that had already been called at the time it was registered. (iykyk — it's giving last-in-first-out but with ✨nested chaos✨)

Normal termination occurs either by a call to exit() or a return from main(). 🫶

At least 32 functions can be registered with atexit(). no cap.

After a successful call to any of the exec functions, any functions previously registered by atexit() shall no longer be registered. gone. vanished. blocked. 💀

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👑 RETURN VALUE 👑

Upon successful completion, atexit() shall return 0; otherwise, it shall return a non-zero value.

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💅 ERRORS 💅

No errors are defined. icon behavior honestly. ✨

The following sections are informative.

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🍓 EXAMPLES 🍓

None. (the audacity 😭 but okay, nothing here!)

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🌈 APPLICATION USAGE 🌈

The functions registered by a call to atexit() must return to ensure that all registered functions are called. if your function doesn't come back, the whole chain stalls out, bestie. 😭

The application should call sysconf() to obtain the value of {ATEXIT_MAX}, the number of functions that can be registered. There is no way for an application to tell how many functions have already been registered with atexit(). literally zero. it's a mystery box. 🎁

Since the behavior is undefined if the exit() function is called more than once, portable applications calling atexit() must ensure that the exit() function is not called at normal process termination when all functions registered by the atexit() function are called. do not do the thing. 🙈

All functions registered by the atexit() function are called at normal process termination, which occurs by a call to the exit() function or a return from main() or on the last thread termination, when the behavior is as if the implementation called exit() with a zero argument at thread termination time.

If, at normal process termination, a function registered by the atexit() function is called and a portable application needs to stop further exit() processing, it must call the _exit() function or the _Exit() function or one of the functions which cause abnormal process termination. that's the emergency exit (pun fully intended) 🚪💨

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🧚 RATIONALE 🧚

None. (we love a low-effort queen 💅)

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⭐ FUTURE DIRECTIONS ⭐

None. the future is bright and unchanged ✨

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🔥 SEE ALSO 🔥

• exec
• exit()
• sysconf()

The Base Definitions volume of POSIX.1‐2017, <stdlib.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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okay that's the whole thing, and for the cute sign-off: this was brought to you by IEEE/The Open Group, dated 2017, and the page is ATEXIT(3POSIX). slay, go register your cleanup functions responsibly bestie 🫶💖✨