Re: do { } while (0) question

[Jiri Slaby <jirislaby@gmail.com>]

Peter Zijlstra wrote:
> On Tue, 2006-08-01 at 11:45 +0159, Jiri Slaby wrote:
> > Peter Zijlstra wrote:
> > > On Tue, 2006-08-01 at 02:03 -0700, Hua Zhong wrote:
> > > > > #if KILLER == 1
> > > > > #define MACRO
> > > > > #else
> > > > > #define MACRO do { } while (0)
> > > > > #endif
> > > > >
> > > > > {
> > > > > 	if (some_condition)
> > > > > 		MACRO
> > > > >
> > > > > 	if_this_is_not_called_you_loose_your_data();
> > > > > }
> > > > >
> > > > > How do you want to define KILLER, 0 or 1? I personally choose 0.
> > > > Really? Does it compile?
> > > No, and that is the whole point.
> > >
> > > The empty 'do {} while (0)' makes the missing semicolon a syntax error.
> > Bulls^WNope, it was a bad example (we don't want to break the compilation, just 
> > not want to emit a warn or an err).
>
> It was a perfectly good example why 'do {} while (0)' is useful. The
> perhaps mistakenly forgotten ';' after MACRO will not stop your example
> from compiling if KILLER == 1. Even worse, it will compile and do
> something totally unexpected.
>
> If however you use KILLER != 1, the while(0) will require a ';' and this
> example will fail to compile.

That's what I'm trying to say. It was a _bad_ piece of code. It doesn't 
demonstrate I want it to demonstrate.

> Not compiling when you made a coding error (forgetting ';' is one of the
> most common) is a great help.

regards,
--
<a href="http://www.fi.muni.cz/~xslaby/";>Jiri Slaby</a>
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E
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