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SETJMP(3)                  Library Functions Manual                  SETJMP(3)

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

     Standard C Library (libc, -lc)

     #include <setjmp.h>

     sigsetjmp(sigjmp_buf env, int savemask);

     siglongjmp(sigjmp_buf env, int val);

     setjmp(jmp_buf env);

     longjmp(jmp_buf env, int val);

     _setjmp(jmp_buf env);

     _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.  The longjmp() functions cannot cause setjmp() to
     return 0; if val is 0, setjmp() returns 1 instead.

     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
     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 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

     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().

     sigaction(2), sigaltstack(2), sigprocmask(2), pthread_sigmask(3),

     The setjmp() and longjmp() functions conform to ANSI X3.159-1989
     ("ANSI C89").  The sigsetjmp() and siglongjmp() functions conform to IEEE
     Std 1003.1-1990 ("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

     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.

NetBSD 10.99                     June 1, 2008                     NetBSD 10.99