LONGJMP(3)                 POSIX Programmer's Manual                LONGJMP(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       longjmp -- non-local goto

SYNOPSIS
       #include <setjmp.h>

       void longjmp(jmp_buf env, int val);

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.

       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.

RETURN VALUE
       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.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       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().

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       setjmp(), sigaction(), siglongjmp(), sigsetjmp()

       The Base Definitions volume of POSIX.1-2017, <setjmp.h>

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 .



IEEE/The Open Group                  2017                           LONGJMP(3)
