Skip to main content

Overloading Increment/Decrement Operators

In this article we are going to overload the increment (++) and decrement (--) operators by using operator overloading.

As increment (++) and decrement (--) are unary operators, therefore the operator functions that we need to define won’t take any arguments.

These operators are overloaded as usual so further discussion is not required and we straightaway look at the example program:


  // overloading the increment 
  // and decrement operators
  #include <iostream.h>

  // class
  class myclass
  {
    int a;

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

    void operator ++();
    void operator --();
  };

  myclass::myclass(int x)
  {
    a=x;
  };

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

  void myclass::operator ++()
  {
    // increment a
    a++;
  }

  void myclass::operator --()
  {
    // decrement a
    a--;
  }

  // main
  void main()
  {
    myclass ob(10);

    ob.show();

    ++ob;
    ob.show();

    --ob;
    ob.show();
  }

The overloaded (++ and --) operators in the above program has some problems however. As operator functions are not returning anything therefore a statement like the one below is not legal.

  ob2 = ++ob;

Although pretty much used the above statement is not possible, of course unless we return the object that generated the call from the overloaded operator function. As in the line:

  ob2 = ++ob;

If we return the object ‘ob’ from the overloaded operator function then the above statement would be perfectly legal.

To do this the ‘this’ pointer is used. The program with slight modification is below:


  // overloading the increment 
  // and decrement operators
  //  -- corrected version --
  #include <iostream.h>

  // class
  class myclass
  {
    int a;

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

    myclass operator ++();
    myclass operator --();
  };

  myclass::myclass(int x)
  {
    a=x;
  };

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

  myclass myclass::operator ++()
  {
    // increment a
    a++;

    // return the object
    // that generated call
    return *this;
  }

  myclass myclass::operator --()
  {
    // decrement a
    a--;

    // return the object
    // that generated call
    return *this;
  }

  // main
  void main()
  {
    myclass ob(10);
    myclass ob2(100);

    ob.show();

    ++ob;
    ob.show();

    // now this is legal
    // as the incremented
    // value of ob may be
    // assigned to other
    // objects
    ob2=++ob;
    ob2.show();

    --ob2;
    ob2.show();
  }

This is one of the situations when you can’t live without using the ‘this’ pointer!

NOTE: This way we can overload prefix form of the increment and decrement operators, we'll be discussing postfix form in the coming articles.

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