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 .

IEEE/The Open Group                                   2017                                       LONGJMP(3POSIX)