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

[Duncan Roe <duncan_roe at acslink dot net dot au>]

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:

20:45:23$ uname -a
Linux dimstar 3.19.0-k8 #1 SMP Mon Mar 2 21:58:02 EST 2015 i686 AMD Athlon(tm) 64 X2 Dual Core Processor 6000+ AuthenticAMD GNU/Linux
20:45:44$ g++ --version
g++ (GCC) 4.8.2
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

20:47:26$ g++ -std=c++11 cygwin.cpp -o cygwin
20:50:25$ ./cygwin
3.32193
20:50:36$ cat cygwin.cpp
#include <cmath>
#include <iostream>
int main()
{
  auto x = std::log2(10);
  std::cout << x << std::endl;
}                                  /* int main() */

Cheers ... Duncan.

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