On Mon, 22 Jan 2007, Yitzchak Scott-Thoennes wrote:
> Dave Korn writes:
> > On 21 January 2007 14:38, Christopher Layne wrote:
> > > I notice in some places, there are double-negates, like:
> > >
> > > me->read_ready |= ret || !!(events & (FD_READ | FD_ACCEPT | FD_CLOSE));
> > >
> > > What's the rationale for these? To enforce either a 0 or 1, to be
> > > directly in line with boolean, rather than a zero or non-zero
> > > result?
> >
> > It's a standard C idiom for that, yeh, it normalizes zero/non-zero
> > into 0/1.
>
> Also protects against accidentally truncating true values to false (e.g.
> if events is an int and events |(FD_READ...) is 0x80000000 and
> me->read_ready is a short, the implicit cast to short in the assignment
> turns 0x80000000 into 0).
>
> This is also a Perl idiom (though Perl doesn't suffer the above
> problem).
>
> Some people prefer (expr) ? 1 : 0, which looks a lot worse to me than
> !!(expr).
It seems that (expr) != 0 should do the same (and is a bit more readable
than the ternary ?: operator).
Igor
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