setjmp(3) [ultrix man page]

setjmp(3)						     Library Functions Manual							 setjmp(3)

Name
       setjmp, longjmp - non-local goto

Syntax
       #include <setjmp.h>

       int setjmp (env)
       jmp_buf env;

       void longjmp (env, val)
       jmp_buf env;
       int val;

Description
       The and functions help deal with errors and interrupts encountered in a low-level subroutine of a program.

       The function saves its stack environment in env (whose type, jmp_buf, is defined in the <setjmp.h> header file) for later use by It returns
       the value 0.

       The function restores the environment saved by the last call of with the corresponding env argument.   After  finishes,	program  execution
       continues  as if the corresponding call of (which must not itself have returned in the interim) had just returned the value val.  The func-
       tion cannot cause to return the value 0.  If is invoked with a second argument of 0, returns 1.	At the time of the second return from  all
       accessible  data  have  values as of the time is called.  However, global variables have the expected values.  For example, those as of the
       time of the

Examples
       #include <setjmp.h>

       jmp_buf env;
       int i = 0;
       main ()
       {
	    void exit();

	    if(setjmp(env) != 0) {
		 (void) printf("value of i on 2nd return from setjmp: %d0, i);
		 exit(0);
	    }
	    (void) printf("value of i on 1st return from setjmp: %d0, i);
	    i = 1;
	    g();
	    /*NOTREACHED*/
       }

       g()
       {
	    longjmp(env, 1);
	    /*NOTREACHED*/
       }

       If the a.out resulting from this C language code is run, the output is as follows:
       value of i on 1st return from setjmp:0

       value of i on 2nd return from setjmp:1
       Unexpected behavior occurs if is called without a previous call to or when the last such call was in a function which has since returned.

Restrictions
       The values of the registers on the second return from are register values at the time of the first call to not those of the Thus, variables
       in a given function can produce unexpected results in the presence of depending on whether they are register or stack variables.

See Also
       signal(2).

								       RISC								 setjmp(3)

SETJMP(3)						     Library Functions 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 interrupts 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 continues 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 sigmask(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 longjm-
       perror.	If longjmperror returns the program is aborted.  The default version of longjmperror prints the message ``longjmp botch'' to stan-
       dard 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 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 variables.  The bug some-
       times 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.

4th Berkeley Distribution					  January 9, 1986							 SETJMP(3)