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.

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 .