C ++ 11编译器错误，当使用decltype（var）后跟内部类型“var” [英] C++11 compiler error when using decltype(var) followed by internal type of "var"

问题描述

我使用Visual C ++ 2010，这里是我的代码片段：

  std :: set< int& s; 
 decltype（s）:: value_type param = 0; 
  

我收到以下错误讯息，任何人都可以帮助我？

 >错误C2039：'value_type'：不是`全局命名空间''的成员
>错误C2146：语法错误：缺少';'标识符'param'之前
  

解决方案>

这是去年在Connect上提出的Visual Studio错误。这是问题757545（无法使用decltype

这个问题有一个与@ iammillind's实际上相同的解决方法，除了它使用无论什么原因，在C ++ 11发布之前不久从< functional> 中删除​​的std :: identity （ std :: common_type 与一个模板参数等效; std :: remove_reference 在某些情况下是相同的。）

I'm using Visual C++ 2010, and here's my code snippet:

std::set<int> s;
decltype(s)::value_type param = 0;

I got the following error message, anyone can help me?

> error C2039: 'value_type' : is not a member of '`global namespace''
> error C2146: syntax error : missing ';' before identifier 'param'

解决方案

This is a Visual Studio bug that was raised last year on Connect. It is issue 757545 ("Cannot use decltype before scope operator").

The issue has a workaround listed alongside it that is effectively the same as @iammillind's, except it uses std::identity that was removed from <functional> shortly prior to the publication of C++11, for whatever reason. (std::common_type with one template parameter is equivalent; std::remove_reference is the same in some cases.)

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