Re: CURRENT: CLANG 3.3 and -stad=c++11 and -stdlib=libc++: isnan()/isninf() oddity

On 2013-07-10 20:32, O. Hartmann wrote:
> On Wed, 10 Jul 2013 18:04:16 +0100
> David Chisnall <theraven_at_FreeBSD.org> wrote:
> 
>> On 10 Jul 2013, at 17:33, "O. Hartmann" <ohartman_at_zedat.fu-berlin.de>
>> wrote:
>>
>>> Hi David,
>>>
>>> thanks for the fast response.
>>>
>>> The code I was told to check with is this:
>>>
>>> #include <iostream>
>>> #include <typeinfo>
>>> #include <cmath>
>>>
>>> int
>>> main(void)
>>> {
>>>
>>>        std::cout << typeid(isnan(1.0)).name() << "\n";
>>>
>>> }
>>>
>>>
>>> If I compile it with 
>>>
>>> c++ -o testme -std=c++11 -stdlib=libc++ source.cc
>>>
>>> and run the binary, the result is "i" which I interpret as "INT".
>>
>> I believe there is a bug, which is that the math.h things are being
>> exposed but shouldn't be, however it is not the bug that you think it
>> is.  Try this line instead:
>>
>>        std::cout << typeid(std::isnan(1.0)).name() << "\n";
>>
>> We have a libm function, isnan(), and a libc++ function,
>> std::isnan().  The former is detected if you do not specify a
>> namespace.  I am not sure what will happen if you do:
>>
>> #include <iostream>
>> #include <typeinfo>
>> #include <cmath>
>> using namespace std;
>>
>> int
>> main(void)
>> {
>>
>>        cout << typeid(isnan(1.0)).name() << "\n";
>>
>> }
>>
>> This is considered bad form, but does happen in some code.  I am not
>> certain what the precedence rules are in this case and so I don't
>> know what happens.
>>
>> To properly fix this, we'd need to namespace the libm functions when
>> including math.h in C++.  This would also include fixing tweaking the
>> macros.  
>>
>> A fix for your code is to ensure isnan() and isinf() are explicitly
>> namespaced.  Potentially, this may also work:
>>
>> using std::isinf;
>> using std::isnan;
>>
>> David
>>
> 
> I tried in the test code I provided using 
> 
> 
> #include <iostream>
> #include <typeinfo>
> #include <cmath>
> 
> int
> main(void)
> {
> 
>         std::cout << typeid(std::isnan(1.0)).name() << "\n";
> 
> }
> 
> now std::isnan().
> 
> The result is the same, it flags "INT".
> 
> Using 
> 
> #include <iostream>
> #include <typeinfo>
> #include <cmath>
> 
> using namespace std;
> 
> int
> main(void)
> {
> 
>         std::cout << typeid(std::isnan(1.0)).name() << "\n";
> 
> }
> 
> which is considered "bad coding" also results in "INT" (it gives "i").
> 
> So, is this woth a PR?

isnan is overloaded. There's "int isnan(double)" in math.h and
"bool isnan(arithmetic)" in cmath. When you call isnan(1.0),
isnan(double) is selected.

I think isnan(double) and isinf(double) in math.h should only be
visible if (_BSD_VISIBLE || _XSI_VISIBLE) && __ISO_C_VISIBLE < 1999.
For C99 and higher there should only be the isnan/isinf macros.

CCed standards_at_.