Counting instances of individual derived classes

Question

I\'d like to be able to count instances of classes that belong in the same class hierarchy.

For example, let\'s say I have this:

class A;
class B: pu         


        

Answer 1

There is a problem with proposed solutions: when you create B you A constructor will be called automatically and thus increment count of A.

class A
{
public:
    A(bool doCount = true)
    {
        if (doCount)
            ++instanceCount_;
    }

    static std::size_t GetInstanceCount()
    {
        return instanceCount_;
    }

    virtual ~A(){}
private:
    static std::size_t instanceCount_;
};

class B: public A
{
public:
    B(bool doCount = true):A(false)
    {
        if (doCount)
            ++instanceCount_;
    }

    static std::size_t GetInstanceCount()
    {
        return instanceCount_;
    }
private:
    static std::size_t instanceCount_;
};

std::size_t A::instanceCount_ = 0;
std::size_t B::instanceCount_ = 0;