What is the difference between default and copy constructor

Sign in Join Now. New Post. Jeevang 1. Hi, We need copy constructor when we are passing the object to a function or if the function returns any object. Suppose if we haven't defined the user defined copy constructor, it will give a call to default copy constructor. Won't it solve our purpose?

Why we have to define the default copy constructor explicitely?? Thanks, Jeevan. Follow Post Reply. Meetee Expert Mod MB. So there is no need to define it explicitly. Default is default and not made defined by user.

Regards Whether or not there's a need for a user supplied copy ctor is entirely up on the application. The default copy ctor builds a shallow copy of the original which may not be what you want, i. Banfa 9, Expert Mod 8TB. The default copy constructor does a 'shallow' copy, that is it copies the values of the members from 1 object to the other. In the above example 1 calls copy constructor and 2 calls assignment operator.

See this for more details. Write an example class where copy constructor is needed? In the following String class, we must write copy constructor.

The changes made to str2 reflect in str1 as well which is never expected. Yes, a copy constructor can be made private. When we make a copy constructor private in a class, objects of that class become non-copyable. This is particularly useful when our class has pointers or dynamically allocated resources.

In such situations, we can either write our own copy constructor like above String example or make a private copy constructor so that users get compiler errors rather than surprises at runtime. Why argument to a copy constructor must be passed as a reference?

A copy constructor is called when an object is passed by value. Copy constructor itself is a function. So if we pass an argument by value in a copy constructor, a call to copy constructor would be made to call copy constructor which becomes a non-terminating chain of calls.

Why argument to a copy constructor should be const? If you like GeeksforGeeks and would like to contribute, you can also mail your article to review-team geeksforgeeks. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. Both the target object and the initializing object shares same allocated memory. A copy constructor is only called or invoked for initialization purpose.

A copy constructor initializes the newly created object by another existing object. When a copy constructor is used to initialize the newly created target object, then both the target object and the source object shares a different memory location. Changes done to the source object do not reflect in the target object. The general form of the copy constructor is. An implicit copy constructor provided by the compiler does the member-wise copy of the source object.

But, sometimes the member-wise copy is not sufficient, as the object may contain a pointer variable. Copying a pointer variable means, we copy the address stored in the pointer variable, but we do not want to copy address stored in the pointer variable, instead, we want to copy what pointer points to. This copy constructor is being called when object B is initialized using object A. Second time it is called when object C is being initialized using object A.

When object D is initialized using object A the copy constructor is not called because when D is being initialized it is already in the existence, not the newly created one. Hence, here the assignment operator is invoked. It copies the data in one object identically to another object.