Question

我无法相信 gcc 不接受以下代码...请告诉我，如果从基本模板访问内部类是不可能的，或者我错过了什么？

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'
    }
};

Answer 1

问题是MyStruct是一个依赖名称，所以你必须告诉编译器推迟名称查找，直到模板通过用基类名称限定来实例化：

typename BaseClass<T>::MyStruct ms1;

有关详细信息，请阅读Parashift C ++ FAQ条目"Why am I getting errors when my template-derived-class uses a nested type it inherits from its template-base-class?"

Answer 2

BaseClass<T>::MyStruct ms3;

应该是

typename BaseClass<T>::MyStruct ms3;

由于MyStruct是一个从属名称，即它取决于模板参数相关：Where and why do I have to put “template” and “typename” on dependent names?

模板继承内部类访问问题

2 个答案: