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Re: Template linking problem

On Nov 7, 2007, at 7:44 AM, John Love-Jensen wrote:

Your Singleton class forward declares a "static Type* ptr", but doesn't
actually allocate the space anywhere. (Unless you have it in a different
.cc file.)

Add this to your source file:

template <typename Type>
Type* Singleton<Type>::ptr;

That worked. Thank you.

Now, why did I have to do that? The static functions that I wrote inside the class definition were allocated without issue. The code you had me add just looks like defining a function outside of a class header except in this case nothing new was added. Is there something I could have added to the class header that would have avoided that piece of code you gave me? If I had a non-template class with a static data member, gcc doesn't complain if I don't redefine it outside of the header. In other words, why does a template require the code you gave me and why doesn't a regular class then require something like the following:

class A
  static int number;

int A::number;

I hope I'm conveying the question clearly. I'm trying to gain a better understanding to avoid future problems and it will help me remember all of this if I know why I'm doing it.

Thanks again,


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