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SETJMP(3)		 BSD Library Functions Manual		     SETJMP(3)

NAME
     sigsetjmp,	siglongjmp, setjmp, longjmp, _setjmp, _longjmp,	longjmperror
     --	non-local jumps

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <setjmp.h>

     int
     sigsetjmp(sigjmp_buf env, int savemask);

     void
     siglongjmp(sigjmp_buf env,	int val);

     int
     setjmp(jmp_buf env);

     void
     longjmp(jmp_buf env, int val);

     int
     _setjmp(jmp_buf env);

     void
     _longjmp(jmp_buf env, int val);

     void
     longjmperror(void);

DESCRIPTION
     The sigsetjmp(), setjmp(),	and _setjmp() functions	save their calling en-
     vironment 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 invocation
     duration that do not have the volatile type and have been changed between
     the setjmp() invocation and longjmp() call	are indeterminate.

     The setjmp()/longjmp() function pairs save	and restore the	signal mask
     while _setjmp()/_longjmp()	function pairs save and	restore	only the reg-
     ister 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 register
     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 porta-
     bility.

ERRORS
     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 longjmperror().

SEE ALSO
     sigaction(2), sigaltstack(2), sigprocmask(2), pthread_sigmask(3),
     signal(3)

STANDARDS
     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").

CAVEATS
     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 de-
     sired.

     Use of longjmp() or siglongjmp() from inside a signal handler is not as
     easy as it	might seem.  Generally speaking, all possible code paths be-
     tween 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 previ-
     ously thought.

BSD				 June 1, 2008				   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | ERRORS | SEE ALSO | STANDARDS | CAVEATS

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