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 .