c++ - 返回子类型的成员模板函数

Question

是否有正确的方法为模板类定义成员函数，返回子类的实例？

这是一个无法在 VC++ 2010 中编译的示例:

template<class T> class A {
public:
    class B {
    public:
        T i;
    };

    A();
    B* foo();
};

/////////////////////////////////////////////

template<class T> A<T>::A() {}

template<class T> A<T>::B* A<T>::foo() {
    cout << "foo" << endl;
    return new B();
}

我明白了

Error   8   error C1903: unable to recover from previous error(s); stopping compilation 

在 foo 的定义开始的行。

我对 iostream 等有正确的包含和命名空间声明。

谢谢大家!

编辑:

根据要求，这是完整的错误列表，全部在同一行:

Warning 1   warning C4346: 'A<T>::B' : dependent name is not a type
Error   2   error C2143: syntax error : missing ';' before '*'
Error   3   error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error   4   error C1903: unable to recover from previous error(s); stopping compilation
Warning 5   warning C4346: 'A<T>::B' : dependent name is not a type
Error   6   error C2143: syntax error : missing ';' before '*'
Error   7   error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
Error   8   error C1903: unable to recover from previous error(s); stopping compilation

Answer 1

姓名A<T>::B是相关的，您需要提示编译器相关名称是类型

template<class T> typename A<T>::B* A<T>::foo() {...}

此行相同:return new B(); -> return new typename A<T>::B();

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