C++ template errors with implementation in CPP file (Visual Studio)

Question

I have a C++ class definition declared in a header file as follows:

template <class T>
class MyClass : public T
{

public:

    STDMETHODIMP myMethod();

};

The implementation in a .cpp is this:

template <class T>
STDMETHODIMP MyClass<T>::myMethod() {
// Implementation...
}

The compiler (Visual Studio) is complaining about the method implementation, saying that "anachronism used : modifiers on data ignored" and also "unrecognizable template declaration / definition".

Any ideas what's going wrong?

EDIT:

Might the error be here?

I am trying to extend MyClass, so I declare

class ChildClass : MyClass<SomeConcreteClass>
{
// Stuff...
};

If you want to keep your headers clean, you can write it into a .inl file and simply include "<implementation>.inl" at the end of your header — smoothware
– smoothware, Commented Dec 5, 2014 at 15:16

Bathsheba · Accepted Answer · 2014-12-05 14:44:18Z

0

The definition of the template function has to be in the header file too. (The only exception to this rule is if the template is only instantiated in one compilation unit; in which case you can put the definitions in the same source.). So move the implementation out of the .cpp and into the header.
Your writing STDMETHODIMP in the class declaration looks suspect as well (and is probably the source of the immediate error). Are you sure there's not another macro like STDMETHOD that you should be using there?

answered Dec 5, 2014 at 14:44

Bathsheba

235k35 gold badges376 silver badges504 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

IdeaHat Over a year ago

that isn't the only exception, you can also explicitly instantiate in the header and then define the implementation in the cpp file. But that's like, a super edge case that no one ever uses.

Boon Over a year ago

STDMETHOD includes "virtual", the only difference with STDMETHODIMP so should I be using it? This is a COM class by the way. Even having moved the impl into the header I'm still getting "unnamed class template"

Bathsheba Over a year ago

For now, use STDMETHOD in the class declaration and include the definition of the function there too. Fix the compile errors, verify the runtime, then separate out the implementation.

Boon Over a year ago

Might the issue be somewhere else? If I am extending MyClass, is this ok: class My2ndClass : public MyClass<AnotherClass>

Collectives™ on Stack Overflow

C++ template errors with implementation in CPP file (Visual Studio)

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related