longjmp, siglongjmp - non-local jump to a saved stack con-
void longjmp(jmp_buf env, int val));
void siglongjmp(sigjmp_buf env, int val));
longjmp() and setjmp() are useful for dealing with errors
and interrupts encountered in a low-level subroutine of a
program. longjmp() restores the environment saved by the
last call of setjmp() with the corresponding env argument.
After longjmp() is completed, program execution continues as
if the corresponding call of setjmp() 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
siglongjmp() is similar to longjmp() except for the type of
its env argument. If the sigsetjmp() call that set this env
used a nonzero savesigs flag, siglongjmp() also restores the
set of blocked signals.
These functions never return.
POSIX does not specify whether longjmp will restore the sig-
nal context. If you want to save and restore signal masks,
longjmp() and siglongjmp() make programs hard to understand
and maintain. If possible an alternative should be used.