# 2.11BSD#431 - /usr/man/cat3/_setjmp.0

    SETJMP(3)	    UNIX Programmer's Manual		SETJMP(3)

    NAME
         setjmp, longjmp - non-local goto

    SYNOPSIS
         #include <setjmp.h>

         setjmp(env)
         jmp_buf env;

         longjmp(env, val)
         jmp_buf env;

         _setjmp(env)
         jmp_buf env;

         _longjmp(env, val)
         jmp_buf env;

    DESCRIPTION
         These routines are useful for dealing with errors and inter-
         rupts encountered in a low-level subroutine of a program.

         Setjmp saves its stack environment in env for later use by
         longjmp. It returns value 0.

         Longjmp restores the environment saved by the last call of
         setjmp.  It then returns in such a way that execution con-
         tinues as if the call of setjmp had just returned the value
         val to the function that invoked setjmp, which must not
         itself have returned in the interim.  All accessible data
         have values as of the time longjmp was called.

         Setjmp and longjmp save and restore the signal mask sig-
         mask(2), while _setjmp and _longjmp manipulate only the C
         stack and registers.

    ERRORS
         If the contents of the jmp_buf are corrupted, or correspond
         to an environment that has already returned, longjmp calls
         the routine longjmperror.	If longjmperror returns the pro-
         gram is aborted.  The default version of longjmperror prints
         the message ``longjmp botch'' to standard error and returns.
         User programs wishing to exit more gracefully can write
         their own versions of longjmperror.

    SEE ALSO
         sigvec(2), sigstack(2), signal(3)

    NOTES  (PDP-11)
         On the PDP-11, longjmperror is called as _ljerr.  This
         difference stems from the limited name size of the PDP-11
         that requires all external names to be unique within the

    Printed 11/26/99	 January 9, 1986			1

    SETJMP(3)	    UNIX Programmer's Manual		SETJMP(3)

         first seven characters.  However, <setjmp.h> automatically
         translates longjmperror to ljerror and should be included
         before any definition longjmperror.

         The PDP-11 implementation also contains a subtle bug that
         occurs when a routine containing a setjmp has register vari-
         ables.  The bug sometimes causes those variables to be given
         invalid values when a longjmp is made back to the routine.
         Register variables should therefore be avoided in routines
         containing setjmps.

         And finally, _longjmp may sometimes die fatally.  Sorry.

    Printed 11/26/99	 January 9, 1986			2

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