A better way to define class id

[fmad]

Hello.
Currently I define class ids as follows:

class Base {
public:
    static unsigned typeId() { return s_typeId; }

protected:
    static unsigned s_typeCounter;
    static unsigned s_typeId;
}

unsigned Base::s_typeCounter{0};
unsigned Base::s_typeId{s_typeCounter++};

class A : public Base {
public:
    static unsigned typeId() { return s_typeId; }

private:
    static unsigned s_typeId;
}

unsigned A::s_typeId{s_typeCounter++};

But defining class ids in such a way is a bother. So maybe there's a better way to define class ids considering that ids must be unique among multiple translation units (__COUNTER__ won't do)?

Update:
RTTI is not available.

[JLBorges]

Use std::type_index perhaps? http://en.cppreference.com/w/cpp/types/type_index

[fmad]

JLBorges
Oh, forgot to mention. RTTI is not available.

[mbozzi]

CRTP?

# include <iostream>

struct counter { 
  static int c;
};

int counter::c = 0;

template <typename Derived>
struct has_counter: counter {
    static int id()
    { static int c = counter::c++; return c; }    
};

class A: public has_counter<A> {};
class B: public has_counter<B> {};

int main() { 
    std::cout << A::id() << '\n' << B::id() << '\n';    
}

[fmad]

mbozzi
This looks good. Thanks.