Please consider the following ill-formed program:
struct S {
template<class T> struct J { };
};
template<>
struct S::J<void> {
void f();
};
template<>
void S::J<void>::f() {} // ERROR
$ clang++ -std=c++11 test.cpp
no function template matches function template specialization 'f'
$ g++ -std=c++11 test.cpp
template-id ‘f<>’ for ‘void S::J<void>::f()’ does not match any template declaration
Why doesn't the definition of f compile? How do I define the function f correctly in the above?
The clang error is very helpful here:
no function template matches function template specialization 'f'
// ^^^^^^^^^^^^^^^^^
The syntax you're using is for a function template. But f isn't a function template, it's just a function. To define it, we don't need the template keyword:
void S::J<void>::f() {}
At this point, S::J<void> is just another class, so this is no different than your standard:
void Class::method() { }
You'd only need template if you were defining a member function of a template, for instance:
template <typename T>
void S::J<T>::g() { }
or a member function template:
template <typename T>
void S::J<void>::h<T>() { }
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