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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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LONGJMP(3P) POSIX Programmer's Manual LONGJMP(3P)
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.
longjmp — non-local goto
#include <setjmp.h>
void longjmp(jmp_buf env, int val);
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.
The longjmp() function shall restore the environment saved by the
most recent invocation of setjmp() in the same process, with the
corresponding jmp_buf argument. If the most recent invocation of
setjmp() with the corresponding jmp_buf occurred in another
thread, or if there is no such invocation, or if the function
containing the invocation of setjmp() has terminated execution in
the interim, or if the invocation of setjmp() was within the scope
of an identifier with variably modified type and execution has
left that scope in the interim, the behavior is undefined. It is
unspecified whether longjmp() restores the signal mask, leaves the
signal mask unchanged, or restores it to its value at the time
setjmp() was called.
All accessible objects have values, and all other components of
the abstract machine have state (for example, floating-point
status flags and open files), as of the time longjmp() was called,
except that the values of objects of automatic storage duration
are unspecified if they meet all the following conditions:
* They are local to the function containing the corresponding
setjmp() invocation.
* They do not have volatile-qualified type.
* They are changed between the setjmp() invocation and longjmp()
call.
Although longjmp() is an async-signal-safe function, if it is
invoked from a signal handler which interrupted a non-async-
signal-safe function or equivalent (such as the processing
equivalent to exit() performed after a return from the initial
call to main()), the behavior of any subsequent call to a non-
async-signal-safe function or equivalent is undefined.
The effect of a call to longjmp() where initialization of the
jmp_buf structure was not performed in the calling thread is
undefined.
After longjmp() is completed, program execution continues as if
the corresponding invocation of setjmp() had just returned the
value specified by val. The longjmp() function shall not cause
setjmp() to return 0; if val is 0, setjmp() shall return 1.
No errors are defined.
The following sections are informative.
None.
Applications whose behavior depends on the value of the signal
mask should not use longjmp() and setjmp(), since their effect on
the signal mask is unspecified, but should instead use the
siglongjmp() and sigsetjmp() functions (which can save and restore
the signal mask under application control).
It is recommended that applications do not call longjmp() or
siglongjmp() from signal handlers. To avoid undefined behavior
when calling these functions from a signal handler, the
application needs to ensure one of the following two things:
1. After the call to longjmp() or siglongjmp() the process only
calls async-signal-safe functions and does not return from the
initial call to main().
2. Any signal whose handler calls longjmp() or siglongjmp() is
blocked during every call to a non-async-signal-safe function,
and no such calls are made after returning from the initial
call to main().
None.
None.
setjmp(3p), sigaction(3p), siglongjmp(3p), sigsetjmp(3p)
The Base Definitions volume of POSIX.1‐2017, setjmp.h(0p)
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 LONGJMP(3P)
Pages that refer to this page: setjmp.h(0p), exit(3p), ftw(3p), _longjmp(3p), setjmp(3p), sigaction(3p), siglongjmp(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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