On Tue, 19 May 2020 at 12:07, Florian Weimer <fweimer@xxxxxxxxxx> wrote:
>
> * Jonathan Wakely via Gcc-help:
>
> > And G++ does allow arithmetic involving a void* and an integer, e.g.
> > p1 - 32 or p2 + 64, it doesn't allow subtracting one void* from the
> > other. So the extension is only partially supported for C++. We should
> > probably document that.
>
> And it's a regression, GCC 2.7.2.3 can compile it, but GCC 2.95.2
> cannot. (Of course, I'm only half-serious here.)
>
> The problem I see with such extensions in C++ is that they could alter
> SFINAE outcomes. But maybe that's less important these days because
> people don't write custom type traits anymore.
Most such extensions are disabled in SFINAE contexts:
template<typename T>
auto f(T* p) -> decltype(p+1) { return p + 1; }
int main()
{
void* p = nullptr;
p = p + 1; // warning
f(p); // error
}
