Copy Constructor in C++
A copy constructor is a member function that initializes an object using another object of the same class.
Syntax of Copy Constructor
Copy constructor takes a reference to an object of the same class as an argument.
ClassName (ClassName &obj)
{
// body_containing_logic
}
Just like the default constructor, the C++ compiler also provides an implicit copy constructor if the explicit copy constructor definition is not present. Here, it is to be noted that, unlike the default constructor where the presence of any type of explicit constructor results in the deletion of the implicit default constructor, the implicit copy constructor will always be created by the compiler if there is no explicit copy constructor or explicit move constructor is present.
Examples of Copy Constructor
The below examples demonstrate how to use the copy constructors in C++.
Example 1: Illustration of Implicit Copy Constructor
C++
// C++ program to illustrate the use of Implicit copy// constructor#include <iostream>using namespace std;class Sample { int id;public: // parameterized constructor Sample(int x) { id = x; } void display() { cout << "ID=" << id; }};int main(){ Sample obj1(10); obj1.display(); cout << endl; // creating an object of type Sample from the obj Sample obj2(obj1); // or obj2=obj1; obj2.display(); return 0;} |
ID=10 ID=10
Example 2: Defining of Explicit Copy Constructor
C++
// C++ Program to demonstrate how to define the explicit// copy constructor#include <iostream>using namespace std;class Sample { int id;public: // default constructor with empty body Sample() {} // parameterized constructor Sample(int x) { id = x; } // copy constructor Sample(Sample& t) { id = t.id; } void display() { cout << "ID=" << id; }};// driver codeint main(){ Sample obj1(10); obj1.display(); cout << endl; // copy constructor called Sample obj2(obj1); // or obj2=obj1; obj2.display(); return 0;} |
ID=10 ID=10
Example 3: Defining of Explicit Copy Constructor with Parameterized Constructor
C++
// C++ program to demonstrate copy construction along with// parameterized constructor#include <iostream>#include <string.h>using namespace std;// class definitionclass student { int rno; char name[50]; double fee;public: student(int, char[], double); student(student& t) // copy constructor { rno = t.rno; strcpy(name, t.name); fee = t.fee; } void display();};student::student(int no, char n[], double f){ rno = no; strcpy(name, n); fee = f;}void student::display(){ cout << endl << rno << "\t" << name << "\t" << fee;}int main(){ student s(1001, "Manjeet", 10000); s.display(); student manjeet(s); // copy constructor called manjeet.display(); return 0;} |
1001 Manjeet 10000 1001 Manjeet 10000
Uses of Copy Constructor
- Constructs a new object by copying values from an existing object.
- Can be used to perform deep copy.
- Modify specific attributes during the copy process if needed.
Constructors in C++
Constructor in C++ is a special method that is invoked automatically at the time of object creation. It is used to initialize the data members of new objects generally. The constructor in C++ has the same name as the class or structure. It constructs the values i.e. provides data for the object which is why it is known as a constructor.
- Constructor is a member function of a class, whose name is the same as the class name.
- Constructor is a special type of member function that is used to initialize the data members for an object of a class automatically when an object of the same class is created.
- Constructor is invoked at the time of object creation. It constructs the values i.e. provides data for the object that is why it is known as a constructor.
- Constructors do not return value, hence they do not have a return type.
- A constructor gets called automatically when we create the object of the class.
- Constructors can be overloaded.
- A constructor can not be declared virtual.