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

This is a simple counter I use each so often for debugging:

// counter.hpp
#ifndef COUNTER_HPP
#define COUNTER_HPP

template 
class Counter
{
public:
    Counter( bool do_count = true ) : counted(do_count) 
    { if ( counted ) get_count()++; }
    ~Counter() { if (counted) --count_; }

    static unsigned long count() { return count_; }
    static unsigned long& get_count() { 
       static unsigned long count=0;
       return count;
    }
private:
    bool do_count;
};
#endif 

The usage is simple, just inherit from it:

class BaseClass : public Counter
{
public:
   explicit BaseClass( bool do_count = true ) 
      : Counter( do_count )
   {}
};
class DerivedClass : public BaseClass, Counter
{
public:
   explicit DerivedClass( bool do_count = true )
      : BaseClass(false), Counter(do_count)
   {}
};

User code will call a parameterless constructor:

int main() {
   BaseClass b; // will call Counter(true)
   DerivedClass d; // will call Counter(false), Counter(true)
}