#include <setjmp.h>

       void longjmp(jmp_buf env, int val);

       void siglongjmp(sigjmp_buf env, int val);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       siglongjmp(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_C_SOURCE

       longjmp()  and  setjmp(3) are useful for dealing with errors and inter-
       rupts encountered in a low-level subroutine of  a  program.   longjmp()
       restores  the  environment saved by the last call of setjmp(3) with the
       corresponding env argument.  After longjmp() is completed, program exe-
       cution  continues  as  if  the corresponding call of setjmp(3) had just
       returned the value val.  longjmp() cannot cause 0 to be  returned.   If
       longjmp()  is  invoked  with a second argument of 0, 1 will be returned

       siglongjmp() is similar to longjmp() except for the  type  of  its  env
       argument.   If,  and  only  if, the sigsetjmp(3) call that set this env
       used a nonzero savesigs flag, siglongjmp()  also  restores  the  signal
       mask that was saved by sigsetjmp(3).

       These functions never return.

       C89,  C99,  and POSIX.1-2001 specify longjmp().  POSIX.1-2001 specifies

       POSIX does not specify whether longjmp() will restore the  signal  con-
       text  (see  setjmp(3)  for some more details).  If you want to portably
       save and restore signal masks, use sigsetjmp(3) and siglongjmp().

       The values of automatic variables  are  unspecified  after  a  call  to
       longjmp() if they meet all the following criteria:

       o  they are local to the function that made the corresponding setjmp(3)

       o  their  values  are  changed  between  the  calls  to  setjmp(3)  and
          longjmp(); and

       o  they are not declared as volatile.

       Analogous remarks apply for siglongjmp().

       longjmp()  and  siglongjmp() make programs hard to understand and main-
       tain.  If possible an alternative should be used.
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