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longjmp, siglongjmp - non-local jump to a saved stack context
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 || _XOPEN_SOURCE
longjmp() and setjmp(3) 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(3)
with the corresponding env argument. After longjmp() is completed,
program execution 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 instead.
siglongjmp() is similar to longjmp() except for the type of its env
argument. If the sigsetjmp(3) call that set this env used a non-zero
savesigs flag, siglongjmp() also restores the set of blocked signals.
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
context. If you want to save and restore signal masks, use
The values of automatic variables are unspecified after a call to
longjmp() if they meet all the following criteria:
· they are local to the function that made the corresponding setjmp(3)
· their values are changed between the calls to setjmp(3) and
· they are not declared as volatile.
Analogous remarks apply for siglongjmp().
longjmp() and siglongjmp() make programs hard to understand and
maintain. If possible an alternative should be used.
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