SETJMP

 

NAME

setjmp, sigsetjmp – save stack context for nonlocal goto  

SYNOPSIS

#include <setjmp.h>

int setjmp(jmp_buf env);

int sigsetjmp(sigjmp_buf env, int savesigs);

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

setjmp(): see NOTES.
sigsetjmp(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_C_SOURCE  

DESCRIPTION

setjmp() and longjmp(3) are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program. setjmp() saves the stack context/environment in env for later use by longjmp(3). The stack context will be invalidated if the function which called setjmp() returns.

sigsetjmp() is similar to setjmp(). If, and only if, savesigs is nonzero, the process’s current signal mask is saved in env and will be restored if a siglongjmp(3) is later performed with this env.  

RETURN VALUE

setjmp() and sigsetjmp() return 0 if returning directly, and nonzero when returning from longjmp(3) or siglongjmp(3) using the saved context.  

CONFORMING TO

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

NOTES

POSIX does not specify whether setjmp() will save the signal mask (to be later restored during longjmp(3)). In System V it will not. In 4.3BSD it will, and there is a function _setjmp that will not. On Linux with glibc versions before 2.19, setjmp() follows the System V behavior by default, but the BSD behavior is provided if the _BSD_SOURCE feature test macro is defined and none of _POSIX_SOURCE, _POSIX_C_SOURCE, _XOPEN_SOURCE, _XOPEN_SOURCE_EXTENDED, _GNU_SOURCE, or _SVID_SOURCE is defined. Since glibc 2.19, <setjmp.h> exposes only the System V version of setjmp(). Programs that need the BSD semantics should replace calls to setjmp() with calls to sigsetjmp() with a nonzero savesigs argument.

If you want to portably save and restore signal masks, use sigsetjmp() and siglongjmp(3).

setjmp() and sigsetjmp() make programs hard to understand and maintain. If possible, an alternative should be used.  

COLOPHON

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