_LONGJMP(3POSIX)

💫 PROLOG 💫

okay bestie, real talk before we even start: this page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so pls go read the corresponding Linux manual page for the actual deets), or — and this is the part nobody likes — the interface might just not be implemented on Linux at all. 🫠

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✨ NAME ✨

_longjmp, _setjmp — non-local goto 💅

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🌸 SYNOPSIS 🌸

#include <setjmp.h>

void _longjmp(jmp_buf env, int val);
int _setjmp(jmp_buf env);

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🦋 DESCRIPTION 🦋

so _longjmp() and _setjmp() are equivalent to longjmp() and setjmp() respectively, except — and this is the whole personality of these two — they have one extra restriction: they shall not manipulate the signal mask. That's it, that's the vibe. ✨

now the scary part 😭 if you call _longjmp() even though env was never initialized by a call to _setjmp(), or when the last such call was in a function that has since returned? yeah. the results are undefined. no cap, do not do this.

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💖 RETURN VALUE 💖

go read longjmp() and setjmp(), bestie — they're the main characters here and they've got the answer. 🫶

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🎀 ERRORS 🎀

No errors are defined. literally none. icon behaviour, honestly. ✨

The following sections are informative. (translation: they're the bonus content, not the rules 🍓)

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🌈 EXAMPLES 🌈

None. 💀 (we move.)

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👑 APPLICATION USAGE 👑

okay so this is the part where I hold your hand. 🫶

If _longjmp() is executed and the environment in which _setjmp() was executed no longer exists, errors can occur. The conditions under which the environment of the _setjmp() no longer exists include:

• exiting the function that contains the _setjmp() call
• exiting an inner block with temporary storage

This condition might not be detectable, in which case the _longjmp() occurs and — if the environment no longer exists — the contents of the temporary storage of an inner block are unpredictable. 😭 This condition might also cause unexpected process termination. And if the function has returned? the results are undefined. periodt.

Now the chaotic part, and I need you to pay attention:

• passing longjmp() a pointer to a buffer not created by setjmp()
• passing _longjmp() a pointer to a buffer not created by _setjmp()
• passing siglongjmp() a pointer to a buffer not created by sigsetjmp()
• or passing any of these three functions a buffer that has been modified by the user 👀

…can cause all the problems listed above, and more. not "and more" like a fun surprise. like a bad surprise. 💀

the tea ☕ _longjmp() and _setjmp() are included to support programs written to historical system interfaces. New applications should use siglongjmp() and sigsetjmp() respectively. yes queen, upgrade. 💅

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🧚 RATIONALE 🧚

None. 🎀

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⭐ FUTURE DIRECTIONS ⭐

heads up bestie: _longjmp() and _setjmp() may be removed in a future version. 👀

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🔥 SEE ALSO 🔥

• longjmp()
• setjmp()
• siglongjmp()
• sigsetjmp()

And from the Base Definitions volume of POSIX.1‐2017: <setjmp.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 💖 this was brought to you by IEEE/The Open Group, 2017 — the _LONGJMP(3POSIX) era, iconic, no notes 🎀✨💅