cstdlib declarations of ::abs

[Jonathan Wakely]

On 5 March 2017 at 23:36, Dave Gittins wrote:
> Yes, the same logic would apply to all of them. I agree that the best
> solution is to include what you use - but in the wild, on large
> projects that use various libraries, it seems easy to overlook this
> unless you have tools enforcing it. (I am of course saying that partly
> to make myself feel better after I overlooked it...) I don't think
> it's such a bad idea to put all the overloads into the global
> namespace personally - given that *most* of them are there it is
> unfortunately a common assumption that *all* of them are there.

It's not the case that most are there, for <cmath> it's around a third
of them (e.g. it declares three overloads of std::sin but only one of
the three is also in the global namespace).

> Alternatively, I wonder if gcc could warn for this? Presumably the
> compiler will be aware that I am calling a function that was
> "indirectly" declared in a C-library header, and therefore outside the
> realm of standard-controlled behaviour? I don't know how hard that
> would be to achieve, just wonder if it's a possibility.

I think the compiler would have to have special cases for every
function. I don't think your heuristic would work, because if you
#include <stdlib.h> and call ::abs then it's still declared in a
C-library header but there's no problem and no need to warn in that
case.