[Python-Dev] if/else and macros (was: CVS: python/dist/src/Objects unicodeobject.c,2.48,2.49)

Thomas Wouters thomas@xs4all.net
Mon, 17 Jul 2000 11:17:41 +0200

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");

It's very clearly defined what happens, here, but gcc can't see the macro as
is, and mis-placing 'else's is a very common error. Especially combined with
macros :) In absense of a standard-defined error-reporting tool, gcc -Wall
does a very good job. And don't start about lint, the versions of lint I've
seen were much more picky ;)

> > The goto solution is much cleaner and also easier to understand.
> Arguable.

Even more arguable is the coding style issue ;) I haven't seen this 'if (1)
{} else' trick used in macros elsewhere, not in Python and not in other
code. Granted, those pieces of code didn't need to call continue, but I
personally prefer the goto over the weird macro.

Thomas Wouters <thomas@xs4all.net>

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