'log2' is not a member of 'std'

Ryan Schmidt ryandesign at macports.org
Sun Jul 2 18:02:44 UTC 2017

On Jul 2, 2017, at 12:28, Joshua Root wrote:

>> This is MacOSX 10.6.8 running various compilers provided by MacPorts.
>> Compiling the following C++ source
>> 	#include <cmath>
>> 	int main(void)
>> 	{
>> 		double d = std::log2(2.3456789f);
>> 		return 0;
>> 	}
>> results in
>> 	'log2' is not a member of 'std'.
>> This happens with the system g++, which is i686-apple-darwin10-g++-4.2.1,
>> each of g++-4.0 g++-4.2 g++-mp-5 g++-mp-6, and with clang++-mp-3.4;
>> in each case, I am compiling as $CXX -std=c++11 prog.c
>> Apparently, there is some relatively recent turmoil about the C++ libs;
>> I don't know much c++ but find myself compiling some third party C++ code.
>> Am I missing something obvious?
> Well the Xcode-supplied g++s and clang would be using the system libstdc++, which doesn't support C++11, and std::log2 is a C++11 feature.
> The g++-mp variants should support it, but seemingly don't because of the bug that Ken mentioned, which should be fixed in GCC 7.
> Clang can support C++11 if you use -stdlib=libc++.

But on Snow Leopard, since it does not include libc++, you'd have to install it first (the libcxx port).

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