Question

I’m trying to replicate a template I’ve used before with a member function, and it isn’t going very well. The basic form of the function is

template<class T>
T Convert( HRESULT (*Foo)(T*))
{
    T temp;
    Foo(&temp); //Throw if HRESULT is a failure
    return temp;
}

HRESULT Converter(UINT* val)
{
    *val = 1;
    return S_OK;
}


int _tmain(int argc, _TCHAR* argv[])
{
    std::cout << Convert<UINT>(Converter) << std::endl;
    return 0;
}

For the life of me, I can’t get this to work with a member variable. I’ve read up on their syntax, and I can’t seem to figure out how to make it work with templates.

The class would be something similar to

class TestClass
{ 
    HRESULT Converter(UINT* val)
    {
      *val = 1;
      return S_OK;
    }

}

Answer 1

TestClass is stateless. So why do you want to pass a non-static member function? If in the real code you need access to non-static members, you also need to pass the object along

template<class T, class C>
T Convert( HRESULT (C::*Foo)(T*), C c)
{
    T temp;
    (c.*Foo)(&temp); //Throw if HRESULT is a failure
    return temp;
}

You can then call it like the following, assuming the member function is made public

TestClass c;
Convert(&TestClass::Converter, c);

If the class is heavy-weight or if the function changes its object during execution, you may decide to pass the object to Convert by reference.