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