Chapter 6. Overloading Operator

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Chapter 5. OVERLOADING OPERATOR

Object-oriented programs use polymorphism to carry out the sameoperation in a manner customized to the object. Withoutpolymorphism, you would have to use a separate module or

method name for a method that multiplies two numbers and onethat multiplies three numbers. Just as your blender can produce juice regardless of whether you insert two fruits or three vegetables,using a polymorphic, object-oriented multiplication function callwill produce a correct product whether you send it two integers or

three floatingpoint numbers. This is how the English languageworks; you understand words based on their context.

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Minh Quang NGUYEN

Hanoi National University of Education

September 2015



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Understanding polymorphism

What is polymophism?

Polymorphism is the object-oriented program feature thatallows the same operation to be carried out differentlydepending on the object.

When you write C++ (and other object-oriented) programs,you can send the same message to different objects anddifferent types of objects.

Example: there are two members of the Employee class, clerk

and driver. You can display the ID number of each memberwith the following statements:

cout


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cout


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cout


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cout


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Ad hoc polymorphysm: overloading functions

Why overloading functions? In many computer programming languages, each function

used in a program must have a unique name. For example, if you want a function to display a value’s square,

you could create a function that squares integers, a function

that squares floats, and a function that squares doubles.void squareInteger(int x)

{

cout


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{

cout


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{

cout


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What is polymorphism?

C++ allows you to reuse, or overload, function names.

When you overload a function, you create multiple functionswith the same name but with different parameter lists.

For example, each function that squares a value can bear thename square(). If you want three versions of the function, youmust still write three versions of square() - one that accepts anint, one that accepts a double, and one that accepts a float.


Ch te 5 OVERLOADING OPERATOR


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Chapter 5 OVERLOADING OPERATOR


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Example

Three functions do the same works.

void squareInteger(int x)

{

cout


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Example

Three functions do the same works.

void square(int x)

{

cout


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p


Overloading: avoiding ambiguity

It must be ensured that the compiler can tell which functionto call by making sure each overloaded function has adifferent parameter list.void someFunction(int a) and someFunction(int b)Which version of a function is used?




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Overloading an operator

When two objects are added using the + operator, the objects donot have to be the same type on both sides of the operator. Forexample, you can add an integer and a double with an expressionsuch as 5 + 7.84.Structure:

class class_name{

return_type operator symbol (parameter);

};

//implementation

return_type class_name::operator symbol (parameter){

return_type x;

//...

return x;

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Example

class complex{

private:

int i, r;

public:complex operator+(int);

};

//implementation

complex complex::operator+(int p)

{

complex x;

x.i = i;

x.r = r + p;

return x;

}

You do itWrite operator + to add 2complex numbers.




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Example

class complex{

private:

int i, r;

public:complex operator+(int);

};

//implementation

complex complex::operator+(int p)

{

complex x;

x.i = i;

x.r = r + p;

return x;

}

You do itWrite operator + to add 2complex numbers.



Ad h l h l d f


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Overloading output

The


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Overloading output

The


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Overloading output

The


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Example (cont.)

Derive class 1: Triangle

class Triangle: public Shape{

public:

float area ()

{

return width * height / 2;}

};

main() function

int main (){

Rectangle rect;

Triangle tri;

rect.set_data (5,3);

tri.set_data (2,5);cout

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Chapter 6. Overloading Operator