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 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-
     nate.

     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.

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 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
     previously thought.

BSD
								   June 1, 2008 							       BSD