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Re: Strange C++ function pointer test

On 31 December 2015 at 18:49, James Dennett <> wrote:
> On Thu, Dec 31, 2015 at 4:42 AM, Jonathan Wakely <>
> wrote:
>> On 31 December 2015 at 11:54, Dominik Vogt wrote:
>> > Is there a requirement for a certain minimum Glibc version for
>> > this to work?
>> It doesn't work with any glibc, because it doesn't declare the C++
>> overloads.
>> Libstdc++ has an include/c_compatibility/math.h header that would
>> include <cmath> (which declares the C++ overloads) and then pull them
>> into the global namespace, but that isn't used on GNU/Linux, and would
>> create other problems.
> What other problems?
> It's something of an assumption of the C++ Standard that it's practical for
> C++ implementations to provide such wrappers to add overloads for C++.  If
> that's causing some fundamental problem then we should document it (and
> ideally address it).

Not fundamental problems in the standard, just with the implementation
of that header. It won't work as is and would need changes, but I
don't think doing it that way is the right fix for GNU/Linux anyway.
If we fix it in glibc we don't need that header.

>> This is already in Bugzilla:
> I don't see much information on that bug, beyond an assertion that this
> needs coordination with the underlying C library.  There's a reference to an
> e-mail thread, but there's little more information in the thread.

Is that a question? :-)

The point is just it's a known bug, not that Bugzilla contains all the

> p.s. a tentatively ready DR indicates that the C++ headers should stop
> splitting the overloads for std::abs/::abs up, so that if you include either
> cmath or cstdlib (or the deprecated/C compatibility headers) you get the
> full overload set.  That seems the only way, short of a warning like
> Clang's, to ensure that people write correct code when they use abs().


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