C++: CRTP: How to know all objects count?

Question

I need you guys help in (may be basic question, sorry for that) in CRTP. This is based on following posts: C++ object lifetime profiling How to count the number of CRTP subclasses of a template class?

Using CRTP, we can able to count the number of objects created for each class type. But, using this approach I can't find the total number of objects created in the system.

Is there any way to achieve this?

Thanks in advance.

Regards, SNR

Answer 1

This solution contains code for both (per-class and global) counters.

extern size_t Global_counter; //In .cpp file define it: size_t Global_counter = 0;

template <class T>
class CountedClass
{
protected:
  static size_t this_class_counter;

public:
  static size_t GetThisClassCounter()
  {
    return this_class_counter;
  }

  static size_t GetGlobalCounter()
  {
    return Global_counter;
  }

  CountedClass()
  {
    ++this_class_counter;
    ++Global_counter;
  }
};

template <class T>
size_t CountedClass<T>::this_class_counter = 0;

Sample usage:

class A : public CountedClass<A>
{
public:
  A() : CountedClass<A>()
  {
  }
};

class B : public CountedClass<B>
{
public:
  B() : CountedClass<B>()
  {
  }
};

A a1;
A a2;
B b2;

std::cout<<A::GetThisClassCounter(); //prints 2
std::cout<<A::GetGlobalCounter(); //prints 3

std::cout<<B::GetThisClassCounter(); //prints 1
std::cout<<B::GetGlobalCounter(); //prints 3

Answer 2

Have all classes inherit from a common base class which keeps a counter, something like

class Counter {
  static int count = 0;

protected:
  Counter() { count++; }

public:
  int getCount() { return count; }
};

As you want to count all the instances you don't need to distinguish different derived classes, so you don't need CRTP.

If you want both counts you can use a class like the one above as a base class for your CRTP class.