How To declare a variable in a class that will track the count of objects Created c++

Question

How to declare a variable in a class that will track the count of objects created? example Object obj; obj.object_count();

Answer 1

You can store the object count using a static class member. And increase its value in class constructors, decrease its value in destructor.

Please find comments inline:

#include <iostream>
#include <atomic>

class Object
{
public:
    Object()    // Constructor
    {
        // initialize the object
        // ...

        m_objCount++;   // Increase object count when creating object (In constructor)
    }

    Object(const Object& obj)   // Copy constructor
    {
        m_objCount++;
    }

    Object(Object&&) // Move constructor
    {
        m_objCount++;
    }

    ~Object()
    {
        m_objCount--;   // Decrease object count when destroying object
    }

    static int object_count()   // Define a static member function to retrive the count
    {
        return m_objCount;
    }

private:
    static std::atomic_int m_objCount;  // Use static member to store object count, 
                                        // use std::atomic_int to make sure it is thread safe
};

std::atomic_int Object::m_objCount; // Initialize static member

int main()
{
    Object obj;

    // prints "obj count: 1"
    std::cout << "obj count: " << obj.object_count() << std::endl;          // call object_count() with object
    std::cout << "obj count: " << Object::object_count() << std::endl;      // call object_count() with class name
}