Copy Constructor

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 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. Therefore compiler doesn’t allow parameters to be pass by value.


When is user defined copy constructor needed?If we don’t define our own copy constructor, the C++ compiler creates a default copy constructor for each class which does a member wise copy between objects. The compiler created copy constructor works fine in general. We need to define our own copy constructor only if an object has pointers or any run time allocation of resource like file handle, a network connection..etc.


Deep copy is possible only with user defined copy constructor. In user defined copy constructor, we make sure that pointers (or references) of copied object point to new memory locations.

Default constructor does only shallow copy.

Deep copy is possible only with user defined copy constructor. In user defined copy constructor, we make sure that pointers (or references) of copied object point to new memory locations.

class String

{

private:

    char *s;

    int size;

public:

    String(const char *str = NULL); // default constructor

    ~String() { delete [] s;  }// destructor

    String(const String&); // copy constructor

    void print() { cout << s << endl; } // Function to print string

    void change(const char *);  // Function to change

};

//Copy constructor

String::String(const String& old_str)

{

    size = old_str.size;

    s = new char[size+1];

    strcpy(s, old_str.s);

}

Point(int x1, int y1) { x = x1; y = y1; }

// Copy constructor

Point(const Point &p2) {x = p2.x; y = p2.y; }

When is copy constructor called?

In C++, a Copy Constructor may be called in following cases:

1. When an object of the class is returned by value.
2. When an object of the class is passed (to a function) by value as an argument.
3. When an object is constructed based on another object of the same class.
4. When compiler generates a temporary object.

Can we make copy constructor private?

Yes, a copy constructor can be made private