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 returned instead.
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.
POSIX does not specify whether longjmp will restore the signal context.
If you want to save and restore signal masks, use siglongjmp.
longjmp() and siglongjmp() make programs hard to understand and
maintain. If possible an alternative should be used.