Chapter 5 · perform special operations relative to classes that you ... Suppose we want to find...

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Chapter 5Chapter 5

Sahaj Computer Solutions 1OOPS WITH C++

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Contents� Overloading

� Function Overloading

� Operator overloading

Rules for Operator Overloading� Rules for Operator Overloading

� Overloading of Unary Operators

� Overloading of Binary Operators

� Manipulation on strings

� Type Conversion


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Function Overloading� Function overloading is the process of using the same

name for two or more functions.

� The secret to overloading is that each redefinition of the function must use either different types of the function must use either different types of parameters or a different number of parameters.

� It is only through these differences that the compiler knows which function to call in any given situation.

� For example, CH5PG1.CPP program overloads myfunc() by using different types of parameters.

� Next example: CH5PG2.CPP


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Operator Overloading� Closely related to function overloading is operator

overloading.

� In C++, you can overload most operators so that they perform special operations relative to classes that you perform special operations relative to classes that you create.

� For example, a class that maintains a stack might overload + to perform a push operation and – – to perform a pop.


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Operator Overloading� When an operator is overloaded, none of its original

meanings are lost.

� Instead, the type of objects it can be applied to is expanded.expanded.

� DEFINITION: The mechanism of giving special meanings to an operator is known as operator overloading.


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Do all Operators overload?� We can overload all the operators except the following:

� Class member access Operator (. ,.*)

� Scope resolution Operator(::)

� Size of Operator (sizeof)� Size of Operator (sizeof)

� Conditional Operator(?:)


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Rules for Operator Overloading� Only existing operators can be overloaded. New

operators cannot be created.

� The overloaded operator must have at least one operand that is of user-defined type.operand that is of user-defined type.

� We cannot change the meaning of an operator. That is say, we cannot define + plus operator to subtract one value from the other.

� Overloaded operators follow the syntax rules of the original operators. They cannot be overridden.


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Rules for Operator Overloading� There are some operators that cannot be overloaded.

� We can make use of friend function to overload certain operators shown in below table:

Operators Description

= Assignment Operator

( ) Function Operator

[ ] Subscripting Operator

-> Class member access operators


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Defining Operator Overloading� To define an additional operator, we must specify what

it means in relation to the class to which the operator is applied. This is done with a special function , called operator function, which describes the task.operator function, which describes the task.

� The general form of an operator function is:

return-type operator op(arg-list){

function body //task defined

}


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Defining Operator Overloading� The process of overloading involves the following

steps:

� Create a class that defines the data type that is to be used in the overloading operation.used in the overloading operation.

� Declare the operator function operator op() in the public part of the class. It may be either member function or friend function.

� Define the operator function to implement the required operations.


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Overloading Unary Operators� Let us consider the unary minus operator.

� A minus operator is used as a unary operator and takes only one operand.

� This operator changes the sign of an operand.This operator changes the sign of an operand.

� However we can apply it to user-defined types by overloading it as follows:

void operator –()

{

x=-x;

y=-y;

z=-z;

}


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Overloading Unary Operators� Here void is the return type of the function.

� The keyword operator tells the compiler that an operator is getting overloaded.

� - tells the compiler that the operator – (unary minus is � - tells the compiler that the operator – (unary minus is getting overloaded.

� ()does not take any arguments. Since the function is the member of the class , it can directly access the members of the object which activated it.


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Overloading Unary Operators� If friend function is used then the following code had

to be written.

friend void operator –(test &t)

� Note that the argument is passed by reference. � Note that the argument is passed by reference.

� It will not work if we pass argument by value because only copy of the object that activated the call is passed to operator-().

� Therefore changes made are not reflected in the called object.


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Creating Prefix and Postfix Forms of the

Increment and Decrement Operators� C++ allows you to explicitly create separate prefix and

postfix versions of increment or decrement operators.

� To accomplish this, you must define two versions of theoperator++() function.

One is defined as shown as shown above and the other is� One is defined as shown as shown above and the other isdeclared like this:

loc operator++(int x);

� If the ++ precedes its operand, the operator++() function iscalled.

� If the ++ follows its operand, the operator++(int x) iscalled and x has the value zero.


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Overloading Binary Operators� Like unary operators binary operators can be

overloaded with same mechanism.

� Suppose we want to find sum of two complex numbers then a statement like C= sum(A,B);then a statement like C= sum(A,B);

� Would be replaced by C=A+B; by overloading the operator +.

� The following program shows overloading of binary addition operator (+).

� Example: CH5PG5.CPP


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Overloading Binary Operators� Let us take a close look at the function operator+()

and see how the operator overloading is implemented.

complex operator+(complex c)

{{

complex temp;

temp.real=real+c.real;

temp.img=img+c.img;

return(temp);

}


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Overloading Binary Operators� Note the following:

� It receives only one complex type argument explicitly

� It returns a complex type argument.

� It is a member function of complex.� It is a member function of complex.

� The statement C3= C1+C2; that invokes the operator+() function.

� Here the object C1 invokes the operator+() function and passes c2 as its parameter.

� The above invocation is equivalent to c3=c1.operator+(c2);


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Overloading Binary Operators� Therefore the data members of C1 are accessed directly

and the data members of C2 are accessed using the dot operator.

� As a rule in overloading of binary operators, the left � As a rule in overloading of binary operators, the left hand operand is used to implement the operator function and the right hand operand is passed as an argument.


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Implementation of the Overload +

Operator

Complex operator +(complex c){

complex temp;

temp.real c.real real;+=

temp

return temp;}

temp.real

temp.img

c.real

c.img

real;

img;+

+=

=

4.1

6.2

1.6

2.7

2.5

3.5

4.1

6.2

C3 = C1 + C2

return


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Overloading Comparison Operator� Let’s see how to overload different type of operator :

Comparison operators.

� The next program overloads the comparison operator < to compare two distance objects.< to compare two distance objects.

� PROGRAM: CH5PG7.CPP


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Overloading Arithmetic

Assignment Operators� The arithmetic assignment operator (+=) operator

combines assignment and addition operation into one step.

� The following program uses this operator to add one � The following program uses this operator to add one distance to another leaving the result in the first.

� PROGRAM : CH5PG8.CPP


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Type Conversion� When an a program uses constants and variables of

different types then the compiler automatically performs type conversion to the operands as per the rules.

� The type of data to the right of an assignment operator is automatically converted to the type of the variable on the left.

� For example:int m;

float x=3.14215;

m=x;


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Type Conversion� Converts x to an integer before its value is assigned to

m.

� When user-defined data types are considered for exampleexample

v3=cv+v2; //v1,v2,v3 are class type variables

� When the objects are of the same type, the operations of addition and assignment are carried out smoothly and the compiler does not make any complaints.

� The values of right hand side class are simply copied to the left hand side class variables.


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Type Conversion� What if one of the operands is an object and the other

is built in type variables?

� Since user defined data types are designed by us to suit our requirements, the compiler does not support our requirements, the compiler does not support automatic conversions for such types.

� We must therefore, design the conversion routines by ourselves, if such operations are required.


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Type Conversion� There are three type of data conversions:

� Conversion from basic type to class type

� Conversion from class type to basic type

� Conversion from one class type to another class type� Conversion from one class type to another class type


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Basic to Class type� The conversion from basic to class type is easy to

accomplish

� It may be recalled that the use of constructors was explained earlier to initilize objects.explained earlier to initilize objects.

� For example , a constructor can be used to built a vector type from an integer type array.

� Similarly it can convert a *char data to String class type data.

� In all the above examples constructors perform a defacto type conversion from the argument’s type to the constructor’s class type.


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Class type to Basic type� The Constructors did a fine job in type conversion

from basic type to class type.

� When we convert class type data to basic type constructor will not support this operation.constructor will not support this operation.

� C++ allows to define an overloaded casting operatorthat could be used to convert a class type data to a basic type.

� The general form of an overloaded casting operator function (usually referred to conversion function) is:


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Class type to basic typeSyntax:

operator typename()

{

function statements

Example:String :: operator char*(){

return( p );}function statements

}

� The casting operator function should satisfy the following conditions� It must be a class member.

� It must not specify a return type

� It must not have any arguments.

}


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One Class to Another Class Type� We have seen data conversion technique from a basic

type to class type and a class type to basic type.

� But there are situations where we want to convert one class type data to another class type data.class type data to another class type data.

� Example;

obj1=obj2; //objects of different types

� Such conversions between objects can be carried out by either a constructor or a conversion function.

� The compiler treats them the same way.


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Type conversions

Conversion required Conversion takes place in

Source Class Destination Class

The table below provides the summary of all the three conversions.

Basic � Class Not Applicable Constructor

Class �Basic Casting Operator Not Applicable

Class �Class Casting Operator Constructor

Example: ch5pg12.cpp


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