error: cannot declare member function ‘static void C::f()’ to have static linkage

You have put static not only on the member function declaration, but on the definition too. Remove static from the definition.

class C
{
    static void f();
};

void C::f() // ← there should be no static here
{
    // ...
}

error: static member function ‘static void C::f()’ cannot have cv-qualifier

You can’t have a const static member function. Remove the const qualifier from the static member function.

The const qualifier means that the implicit this* will not be modified by the member function. However, this* is not passed to static member functions—only non-static member functions. Therefore, there is no this* to be declared const.

undefined reference to vtable for C::f()

Check for the following:

• You declared a virtual method in a base class but did not implement it. Also, make sure your build system is including the .o or .cpp file that defines the method.
• If you have a static member variable, you must define it in your .cpp file too:

  // c.h
  
  class C
  {
      static std::vector<std::string> databases;
  };
  
  // c.cpp
  
  #include "c.h"
  std::vector<std::string> C::databases; // ← define it in your .cpp file as well!
  

B is an inaccessible base of C

B is a base class for C. In class A, you’re trying to access B but you’ve likely forgotten to mark the inheritance public:

// c.h

class B { }; // a base class

class C : B // ← forgot to specify public B!
{
    public:
        static B* create(); // trying to return the parent class type,
                            // but it can't be accessed (it's private by default)
};

Also, the public qualifier isn’t distributive. So:

class C : public B1, B2 { }; // B2 is private here

is not the same as:

class C : public B1, public B2 { };