g++4.9.2 fails to compile standard C++11 code

[Christian Franke]

Corinna Vinschen wrote:
> On Mar 13 09:13, Csaba Raduly wrote:
>> Hi
>>
>> On Thu, Mar 12, 2015 at 10:55 AM, Duncan Roe  wrote:
>>> On Wed, Mar 11, 2015 at 06:55:16PM -0400, Vlad Gheorghiu wrote:
>>>> The following code fails to compile under latest cygwin, Windows 7,
>>>> g++4.9.2. Compiled with g++ -std=c++11 test.cpp. The compiler
>>>> complains that std::log2 is not a member of std.
>>>>
>>>>      #include <cmath>
>>>>      #include <iostream>
>>>>
>>>>      int main()
>>>>      {
>>>>              auto x = std::log2(10);
>>>>              std::cout << x << std::endl;
>>>>      }
>>>>
>>>>
>>>> Verbatim error:
>>>>
>>>>      g++ -std=c++11 test.cpp
>>>>      test.cpp: In function 'int main()':
>>>>      test.cpp:5:11: error: 'log2' is not a member of 'std'
>>>>        auto x = std::log2(10);
>>>>                 ^
>>>>      test.cpp:5:11: note: suggested alternative:
>>>>      In file included from
>>>> /usr/lib/gcc/i686-pc-cygwin/4.9.2/include/c++/cmath:44:0,
>>>>                       from test.cpp:1:
>>>>      /usr/include/math.h:305:15: note:   ???log2???
>>>>       extern double log2 _PARAMS((double));
>>>>
>>> FWIW, this program works fine under Linux / gcc4.8.2:
>> ISTR a discussion about some C++11 features being configured away due
>> to Cygwin's lack of some C library functions ("to_string not a member
>> of std"): https://sourceware.org/ml/cygwin/2015-01/msg00245.html
>>
>> Your issue may be related (I'm guessing here because I don't have
>> Cygwin at hand right now).
> I guess the same.  The problem is probably related to the fact that
> newlib is still missing most of the long double functions (cosl, sinl,
> etc).  The libstdc++ configury seems to activate the related std methods
> only if *all* related C library functions for double, float and long
> double (e.g. cos, cosf, cosl) are implemented by the platform.

Yes. The attached patch for cmath include file would fix this.

Christian

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