Template inheritance inner class access problem
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>
{
开发者_C百科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'
}
};
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;
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?"
BaseClass<T>::MyStruct ms3;
Should be
typename BaseClass<T>::MyStruct ms3;
Since the MyStruct
is a dependent name, i.e., it depends on the template argument.
Relevant: Where and why do I have to put “template” and “typename” on dependent names?
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