[Python-Dev] if/else and macros

[Greg Stein]

On Mon, Jul 17, 2000 at 11:17:41AM +0200, Thomas Wouters wrote:
> On Mon, Jul 17, 2000 at 02:05:32AM -0700, Greg Stein wrote:
> > On Mon, Jul 17, 2000 at 09:55:02AM +0200, M.-A. Lemburg wrote:
> 
> > > and it produces warnings which relate to the fact that the "else"
> > > part is ambiguous:
> > > 
> > > if (condition) UTF8_ERROR();
> > > else {...}
> > > 
> > > expands to:
> > > 
> > > if (condition)
> > > if (1) {...}
> > > else ;
> > > else {...}
> > 
> > That is not ambiguous.
> 
> Nope. The example was flawed. *this* is ambiguous:
> 
> if (condition) UTF8_ERROR();
> 
> And that's exactly what gcc is whining about:
> 
>         if (s + n > e)
>             UTF8_ERROR("unexpected end of data");

Oh come on. This is getting silly.

Neither of those examples are ambiguous. C has a very strict definition of
what happens. In your examples, it expands to:

    if (condition)
        if (1) {
	    ...
	} else
	    ;

GCC spits out a warning to tell the person "oh hey... I'm associating that
else with the second 'if' command... but I'm going to spit out a warning
just in case that isn't want you really meant."

There is no ambiguity. Zero. I repeat: none.

GCC is simply *assuming* that you may have messed up, so it spits out a
warning.

But ambiguity? Not at all.

Cheers,
-g

-- 
Greg Stein, http://www.lyra.org/