Re: KNF and the C preprocessor

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> I would like to propose an additional, perhaps controversial, use.

> 5 Breaking the flow of control:

> #ifdef K5BAIL(x) do {
>               ret = x;
>               if (ret) {
>                       /* format error message and whatnot
>                        * in terms of #x.
>                        */
> 
>                       goto bail;
>               }
>       } while (0)

> You can't do this with an inline function, because it can't use goto
> or return.

If you're willing to commit to gcc - which I gather is the case, if
we're even discussing gccisms like __attribute__((__always_inline__)) -
then you can do it really easily and relatively elegantly (relative to
the other ways, that is) with a nested function and a nonlocal goto:

void something_hairy(...)
{
 __label__ bail_to;

 ...variable declarations...

 auto void bail(const char *, ...) 
__attribute__((__format__(__printf__,1,2),__noreturn__));
 auto void bail(const char *fmt, ...)
  { va_list ap;
    va_start(ap,fmt);
    ...
    va_end(ap);
    goto bail_to;
  }

 if (0)
  {
bail_to:;
    if (thing1) cleanup_thing1();
    if (thing2) cleanup_thing2();
    ...
    return;
  }
 thing1 = 0;
 thing2 = 0;
 ...
 thing1 = new_thing1();
 if (...failure...) bail("can't do it: %d < %d (from %s)",...);
 ...
}

(Okay, that's not quite true.  Using always_inline doesn't necessarily
mean committing to gcc.  But _depending on_ always_inline does, ISTM.)

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