12438_13 Type Conversion

7/29/2019 12438_13 Type Conversion

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Type Conversion


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Introduction

It is the process of converting incompatible

values from one type to another type.

Forbuilt-in typesit happens automatically

(implicitly), but foruser - defined types, wehave to define them.

Types :

Conversion from basic type to class type Conversion from class type to basic type

Conversion from one class type to another class

type


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Example:

int m;

float x = 3.145;m = x;

convert x to an integer before its value isassigned to m.


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Conversion from Basic Type to

Class Type

It takes place automatically using one

argument constructor of the destination class.

Example:

string :: string (char *a)

{ length = strlen (a);

P = new char [length + 1];

strcpy (P, a); }

This constructor builds a string type object from achar* type variable a. The variables length and Pare the data members of the class string.


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string s1, s2;

char* name1 = IBM PC;

char* name2 = Apple Computers;s1 = string (name1);

s2 = name2;

The statement s1 = string (name1); firstconverts name1 from char* type to string type

& then assigns the string type values to the

object s1. The statement s2 = name2; alsodoes the same job by invoking the constructor

implicitly.


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Note: -

The constructor used for type conversion

from basic type to class type takes a single

argument.

The left hand operand of assignment

operator = is always a class object.

Therefore, this type of conversion can be

performed by overloading assignmentoperator.


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Conversion from Class Type to

Basic Type

It can be performed by defining conversion

function in the source class.

Casting Operator or conversion function.

Syntax:

operator typename ()

{ :::::::::

::::::::: //function statement

}


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Example:

vector :: operator double ()

{ double sum = 0;

for (int i = 0; i < size; i++)

sum = sum + v [i] * v [i];

return sqrt (sum);

}

The operator double () converts a class object to typedouble, the operator int () converts a class type objectto type int, so on


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Conversion from Class Type to

Another Class Type

It can be performed by defining conversion

function in the source class or through one

argument constructor, that takes an object of

the source class, in the destination class.

It depends upon where you want to

conversion facility to be located.


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If you want to place the conversion facility in

the source class, then use conversion function

with name of the destination class as

typename.

class x; //forward declaration

class y //source class{ ::::::::

operator x() //conversion function

{ ::::::: }

::::::::::}

class x //destination class

{ :::::::::: }


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If you want to place the conversion facility in

the destination class, then use constructor that

takes object of source class as its only

argument.

class y; //forward declaration

class x //destination class{ ::::::::

x ( y obj ) //constructor for conversion

{ ::::::: }

::::::::::

}

class y //source class

{ :::::::::: }


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Summary of Type Conversion

Types Source Class Destination Class

Basic Type to Class Type Not applicable Constructor

Class Type to Basic Type Conversion Function Not applicable

Class Type to Class Type Conversion Function Constructor

Casting Operator function : - Conditions

It must be a class member.

It must not specify a return value.

It must not have any arguments.


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Thank You!!!

12438_13 Type Conversion

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