On Fri, Feb 19, 2016 at 01:04:04PM +0100, Petr Spacek wrote:
> On 19.2.2016 08:50, Jakub Jelinek wrote:
> > On Fri, Feb 19, 2016 at 03:12:29AM +0100, Kevin Kofler wrote:
> >> Jakub Jelinek wrote:
> >>> ASSERT(this) is pointless, it is testing if undefined behavior didn't
> >>> happen after the fact, that is just too late. As I said, use
> >>> -fsanitize=undefined to make sure you don't call methods on nullptr.
> >>
> >> Doesn't -fno-delete-null-pointer-checks make such ASSERTs work (and also
> >> explicit "if (this)" type checks)? I read that that flag fixes programs
> >> which rely on "if (this)" checks.
> >
> > That switch allows to work around buggy programs, at the cost of optimizing
> > them less, yes. In any case, such programs should be fixed, this must be
> > always non-NULL, methods can't be called on NULL pointers.
>
> Could you elaborate on this, please?
>
> What is wrong with
> if (ptr != NULL)
> ?
>
> What standard says that it is wrong?
It's about checking whether "this", in C++, is NULL. Since any call on a null
pointer is undefined behavior, any code relying on such checks is non-standard.
Marek
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