c++ - 在模板类中使用嵌套嵌套类时“依赖名称不是类型”

Question

这个问题在这里已经有了答案:





Where and why do I have to put the "template" and "typename" keywords?

(8 个回答)


4年前关闭。




有谁知道为什么以下编译失败(在 MSVC2015 中测试)？

template<int N> // when this line is removed it compiles successfully
class A {
    class B {
    public:
        class C {
        };
    };
    void func(B b){} // compiles fine
    void func(B::C c){} // generates warning C4346 and error C2061
};

它在标有注释的行上生成以下内容:

warning C4346: 'A<N>::B::C': dependent name is not a type

error C2061: syntax error: identifier 'C'

Answer 1

让我们为你谷歌它。

The typename keyword is requiretd if a dependent name is to be treated as a type.

C++ 规则。

14.6 Name resolution

A name used in a template declaration or definition and that is dependent on a template-parameter is assumed not to name a type unless the applicable name lookup finds a type name or the name is qualified by the keyword typename.