SETJMP(3) BSD Library Functions Manual SETJMP(3)
sigsetjmp, siglongjmp, setjmp, longjmp, _setjmp, _longjmp, longjmperror -- non-local jumps
Standard C Library (libc, -lc)
sigsetjmp(sigjmp_buf env, int savemask);
siglongjmp(sigjmp_buf env, int val);
longjmp(jmp_buf env, int val);
_longjmp(jmp_buf env, int val);
The sigsetjmp(), setjmp(), and _setjmp() functions save their calling environment in env. Each of these functions returns 0.
The corresponding longjmp() functions restore the environment saved by the most recent invocation of the respective setjmp() function. They
then return so that program execution continues as if the corresponding invocation of the setjmp() call had just returned the value specified
by val, instead of 0.
Pairs of calls may be intermixed, i.e., both sigsetjmp() and siglongjmp() as well as setjmp() and longjmp() combinations may be used in the
same program. However, individual calls may not, e.g., the env argument to setjmp() may not be passed to siglongjmp().
The longjmp() routines may not be called after the routine which called the setjmp() routines returns.
All accessible objects have values as of the time longjmp() routine was called, except that the values of objects of automatic storage invo-
cation duration that do not have the volatile type and have been changed between the setjmp() invocation and longjmp() call are indetermi-
The setjmp()/longjmp() function pairs save and restore the signal mask while _setjmp()/_longjmp() function pairs save and restore only the
register set and the stack. (See sigprocmask(2).)
The sigsetjmp()/siglongjmp() function pairs save and restore the signal mask if the argument savemask is non-zero. Otherwise, only the reg-
ister set and the stack are saved.
In other words, setjmp()/longjmp() are functionally equivalent to sigsetjmp()/siglongjmp() when sigsetjmp() is called with a non-zero
savemask argument. Conversely, _setjmp()/_longjmp() are functionally equivalent to sigsetjmp()/siglongjmp() when sigsetjmp() is called with
a zero-value savemask.
The sigsetjmp()/siglongjmp() interfaces are preferred for maximum portability.
If the contents of the env are corrupted or correspond to an environment that has already returned, the longjmp() routine calls the routine
longjmperror(3). If longjmperror() returns, the program is aborted (see abort(3)). The default version of longjmperror() prints the message
``longjmp botch'' to standard error and returns. User programs wishing to exit more gracefully should write their own versions of
sigaction(2), sigaltstack(2), sigprocmask(2), pthread_sigmask(3), signal(3)
The setjmp() and longjmp() functions conform to ANSI X3.159-1989 (``ANSI C89''). The sigsetjmp() and siglongjmp() functions conform to
ISO/IEC 9945-1:1990 (``POSIX.1'').
Historically, on AT&T System V UNIX, the setjmp()/longjmp() functions have been equivalent to the BSD _setjmp()/_longjmp() functions and do
not restore the signal mask. Because of this discrepancy, the sigsetjmp()/siglongjmp() interfaces should be used if portability is desired.
Use of longjmp() or siglongjmp() from inside a signal handler is not as easy as it might seem. Generally speaking, all possible code paths
between the setjmp() and longjmp() must be signal race safe. Furthermore, the code paths must not do resource management (such as open(2) or
close(2)) without blocking the signal in question, or resources might be mismanaged. Obviously this makes longjmp() much less useful than
June 1, 2008 BSD