Tuesday, June 17, 2008

What is copy assignment operator in C++?

  • The copy assignment operator allows to assign objects of same class to each other by overloading '=' operator.
  • The compiler automatically generates this member function if is not defined explicitly.
  • The generated copy assignment funcion does a bit wise copy or in other words shallow copy.
  • If our class has dynamically allocated members then it becomes necessary to write our own implementation of copy assignment function to perform a deep copy.

Demonstrate the usage of copy assignment operator

#include <iostream>
using namespace std;

class MyClass {  
    private:      
        char* str;  
    public:      
        MyClass();
        MyClass(char* aStr);      
        MyClass& operator=(const MyClass& obj);      
        void Print();      
        ~MyClass();
};

MyClass::MyClass() {
}

MyClass::MyClass(char* aStr) {  
    cout << "In constructor ..." << endl;  
    str = strdup(aStr);
}

// Copy assignment
MyClass& MyClass::operator=(const MyClass& other) {
    cout << "In copy assignment ..." << endl;
    str = strdup(other.str);
    return *this;
}

void MyClass::Print() {  
    cout << str << endl;
}

MyClass::~MyClass() {  
    cout << "In destructor ..." << endl;  
    delete str;
}

void main()
{  
    // Create obj1
    MyClass* obj1 = new MyClass("Hello World");
    obj1->Print();

    // Assignment. obj1 to obj2
    MyClass obj2;
    obj2 = *obj1;

    // Cleanup obj1
    delete obj1;

    obj2.Print();
}
OUTPUT:-
In constructor ...
Hello World
In copy assignment ...
In destructor ...
Hello World
In destructor ...

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