模板继承内部类访问问题 [英] Template inheritance inner class access problem

问题描述

我不敢相信 gcc 不会接受以下代码...请告诉我，如果从基本模板访问内部类是真的不可能，或者我丢失了一些东西？ p>

I can't believe gcc won't accept the following code... Please tell me if accessing an inner class from a base template is really not possible or am i missing something?

template <class T> class BaseClass
{
public:
    struct MyStruct
    {
        T *data;
    };
};

template <class T> class ChildClass : public BaseClass <T>
{
    public:

    void problem()
    {
        MyStruct ms1; //error: 'MyStruct' was not declared in this scope
        ::MyStruct ms2; //error: '::MyStruct' has not been declared
        BaseClass<T>::MyStruct ms3; //error: expected `;' before 'ms3'
    }
};

推荐答案

问题是 MyStruct 是一个依赖的名称，所以你必须告诉编译器延迟名称查找，直到模板被实例化，通过限定它的基类名：

The problem is that MyStruct is a dependent name, so you have to tell the compiler to defer name lookup until the template is instantiated by qualifying it with the base class name:

typename BaseClass<T>::MyStruct ms1;

更多信息，我将阅读Parashift C ++ FAQ条目，当我的模板派生类使用嵌套类型时，为什么我会收到错误，它继承自它的template-base-class？

For more information, I'd read the Parashift C++ FAQ entry, "Why am I getting errors when my template-derived-class uses a nested type it inherits from its template-base-class?"

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