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这个问题与这个线程有关：cygwin support for C++11 in g++4.9.2

我遇到过同样的问题：

error: ‘log2’ is not a member of ‘std’

我应用了建议的补丁，只是得到另一个错误。包括 cmath 这里

#include <cmath>
#include <iostream>
int main()
{
        std::cout << "hello" << std::endl;
}

返回此错误

$ g++ -std=c++11 test.cpp
In file included from test.cpp:1:0:
/usr/lib/gcc/x86_64-pc-cygwin/4.9.2/include/c++/cmath:1107:11: error: '::lrintl' has not been declared
   using ::lrintl;
           ^
/usr/lib/gcc/x86_64-pc-cygwin/4.9.2/include/c++/cmath:1129:11: error: '::rintl' has not been declared
   using ::rintl;

我在 cygwin IRC 频道上寻求帮助：

[23:02] <XXX> hi, has anyone had problems with gcc 4.9.2 in cygwin? i encountered the problem discussed here : https://cygwin.com/ml/cygwin/2015-03/msg00247.html
[23:03] <XXX> yet, if i apply the patch, i get another error: /usr/lib/gcc/x86_64-pc-cygwin/4.9.2/include/c++/cmath:1107:11: error: '::lrintl' has not been declared
[23:28] <YYY> long double functions are still missing on cygwin
[23:30] <XXX> so is there no way to make it work then?
[23:31] <YYY> sure, help add the missing functions to newlib/cygwin
[23:34] <XXX> i am not using any long double functions in my code -- so i assume including cmath does not work for anybody?
[23:35] <YYY> just drop the std:: instead
[23:37] <XXX> sorry, i'm not sure what you mean. remove 'std::' where ?

遗憾的是，谈话就这样结束了。我不知道应该在哪里“删除 std::”，也不知道这是否可以解决问题。有人能帮忙吗？

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1 回答 1

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<cmath>如果我这样做，未修补的工作正常：

auto x = log2(10);

代替：

auto x = std::log2(10);

也许这就是 YYY 所说的 'drop std::' 的意思。

如果您必须使用 patched <cmath>，您可以注释掉两个违规行，或者如果您不想修改已经拥有的标题，请在包含它之前添加一些rintland的虚拟定义。lrintl例如：

#include <stdexcept>
long double rintl(long double arg) { throw std::runtime_error("rintl not implemented"); }
long lrintl(long double arg) { throw std::runtime_error("lrintl not implemented"); }

#include <cmath>
于 2015-04-24T22:51:27.433 回答