template function

[D_Drmmr]

I declared a template function in my .h file, but it doesn't seem to be able to take virtual.

It's not clear from your code what you are actually trying to show.
Non-member functions cannot be virtual.
Template member functions also cannot be virtual. This is because a template (member) function actually defines a "family" of functions. Virtual functions work (in all known C++ compilers AFAIK) by storing a so-called vtable that stores pointers to the member functions that are resolved at run-time when a virtual function is called. When you instantiate a derived class, it will set the function pointer in the vtable to the overridden member function. That's a concept that cannot be scaled to a (possibly infinite) family of functions. Thus, template member functions cannot be virtual. For the same reason you also cannot take a pointer to a template function.

What is possible is what monarch_dodra mentioned, i.e. a template class can have a virtual (non-template) member function. Something like this

template <class T>
struct Base
{
    virtual ~Base() {}
    virtual T Foo() { return T(); }
};

struct Derived : public Base<int>
{
    virtual int Foo() { return 1; }
};