Simplest way to count instances of an object

Have a "counted object" class that does the proper reference counting in its constructor(s) and destructor, then derive your objects that you want to track from it. You can then use the curiously recurring template pattern to get distinct counts for any object types you wish to track.

// warning: pseudo code

template <class Obj>
class CountedObj
{
public:
   CountedObj() {++total_;}
   CountedObj(const CountedObj& obj) {if(this != &obj) ++total_;}
   ~CountedObj() {--total_;}

   static size_t OustandingObjects() {return total_;}

private:
   static size_t total_;
};

class MyClass : private CountedObj<MyClass>
{};

you can apply this approach

#ifdef DEBUG

class ObjectCount {
    static int count;
  protected:
    ObjectCount() {
        count++;
    }
  public:
    void static showCount() {
        cout << count;
    }
};

int ObjectCount::count = 0;


class Employee : public ObjectCount {
#else
class Employee {
#endif
  public:
    Employee(){}
    Employee(const Employee & emp) {

    }
};

at DEBUG mode, invoking of ObjectCount::showCount() method will return count of object(s) created.

Better off to use memory profiling & leak detection tools like Valgrind or Rational Purify.

If you can't and want to implement your own mechanism then,

You should overload the new and delete operators for your class and then implement the memory diagnostic in them.

Have a look at this C++ FAQ answer to know how to do that and what precautions you should take.