Skip to main content

Overloading the Assignment Operator (=)

We know that if we want objects of a class to be operated by common operators then we need to overload them. But there is one operator whose operation is automatically crested by C++ for every class we define, it is the assignment operator ‘=’.

Actually we have been using similar statements like the one below previously

  ob1=ob2;

where ob1 and ob2 are objects of a class.

This is because even if we don’t overload the ‘=’ operator, the above statement is valid.

As I said C++ automatically creates a default assignment operator. The default operator created, does a member-by-member copy, but if we want to do something specific we may overload it.

The simple program below illustrates how it can be done. Here we are defining two similar classes, one with the default assignment operator (created automatically) and the other with the overloaded one. Notice how we could control the way assignments are done in that case.


  // Program to illustrate the
  // overloading of assignment
  // operator '='
  #include <iostream.h>

  // class not overloading the
  // assignment operator
  class myclass
  {
    int a;
    int b;

  public:
    myclass(int, int);
    void show();
  };

  myclass::myclass(int x,int y)
  {
    a=x;
    b=y;
  }

  void myclass::show()
  {
    cout<<a<<endl<<b<<endl;
  }

  // class having overloaded
  // assignment operator
  class myclass2
  {
    int a;
    int b;

  public:
    myclass2(int, int);
    void show();

    myclass2 operator=(myclass2);
  };

  myclass2 myclass2::operator=(myclass2 ob)
  {
    // -- do something specific --
    // this is just to illustrate
    // that when overloading '='
    // we can define our own way
    // of assignment
    b=ob.b;

    return *this;
  };

  myclass2::myclass2(int x,int y)
  {
    a=x;
    b=y;
  }

  void myclass2::show()
  {
    cout<<a<<endl<<b<<endl;
  }

  // main
  void main()
  {
    myclass ob(10,11);
    myclass ob2(20,21);

    myclass2 ob3(100,110);
    myclass2 ob4(200,210);

    // does a member-by-member copy
    // '=' operator is not overloaded
    ob=ob2;
    ob.show();


    // does specific assignment as 
    // defined in the overloaded
    // operator definition
    ob3=ob4;
    ob3.show();
  }

Related Articles:

Popular posts from this blog

Fix For Toshiba Satellite "RTC Battery is Low" Error (with Pictures)

RTC Battery is Low Error on a Toshiba Satellite laptop "RTC Battery is Low..." An error message flashing while you try to boot your laptop is enough to panic many people. But worry not! "RTC Battery" stands for Real-Time Clock battery which almost all laptops and PCs have on their motherboard to power the clock and sometimes to also keep the CMOS settings from getting erased while the system is switched off.  It is not uncommon for these batteries to last for years before requiring a replacement as the clock consumes very less power. And contrary to what some people tell you - they are not rechargeable or getting charged while your computer or laptop is running. In this article, we'll learn everything about RTC batteries and how to fix the error on your Toshiba Satellite laptop. What is an RTC Battery? RTC or CMOS batteries are small coin-shaped lithium batteries with a 3-volts output. Most laptops use

The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example: <?php // Single line comment code (); # Single line Comment code2 (); /* Multi Line comment code(); The code inside doesn't run */ // /* This doesn NOT start a multi-line comment block /* Multi line comment block The following line still ends the multi-line comment block //*/ The " # " comment style, though, is rarely used. Do note, in the example, that anything (even a multi-block comment /* ) after a " // " or " # " is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next. Comment out PHP Code Blocks Check the following code <?php //* Toggle line if ( 1 ) {      // } else {      // } //*/ //* Toggle line if ( 2 ) {      // } else {      // } //*/ Now see how easy it is to toggle a part of PHP code by just removing or adding a single " / " from th

Introduction to Operator Overloading in C++

a1 = a2 + a3; The above operation is valid, as you know if a1, a2 and a3 are instances of in-built Data Types . But what if those are, say objects of a Class ; is the operation valid? Yes, it is, if you overload the ‘+’ Operator in the class, to which a1, a2 and a3 belong. Operator overloading is used to give special meaning to the commonly used operators (such as +, -, * etc.) with respect to a class. By overloading operators, we can control or define how an operator should operate on data with respect to a class. Operators are overloaded in C++ by creating operator functions either as a member or a s a Friend Function of a class. Since creating member operator functions are easier, we’ll be using that method in this article. As I said operator functions are declared using the following general form: ret-type operator#(arg-list); and then defining it as a normal member function. Here, ret-type is commonly the name of the class itself as the ope