why are copy constructors needed and what are the cases where they are very helpful

Question

Why do we require copy constructors?

 

I'm learning C++ and I'm not sure why copy constructors are necessary, because I was getting correct results without them as well.

I went through a few examples, but it seemed to me that having copy constructors, such as to initialise variables, is just good practise.

Could someone please explain the concept of copy constructors to me?

Any assistance will be greatly appreciated.

Thank you very much.

Answer 1

A copy constructor is a member function that uses another object of the same class to initialize an object.

When is it appropriate to write our own copy constructor?

The C++ compiler includes a copy constructor (and assignment operator) by default with each class.

When we don't provide an implementation of the copy constructor (and assignment operator) and attempt to initialize an object with an already initialized object of the same class, the copy constructor is called and copies class members one by one in the target object.

However, the default copy constructor (and assignment operator) has the following flaw:

When we have members that are dynamically initialized at run time, the default copy constructor copies this member with the address of dynamically allocated memory rather than making a true copy of this memory.

Both objects now point to the same memory, and changes in one are mirrored in the other.