Computer Notes - Destruct Or

8/3/2019 Computer Notes - Destruct Or

1/28

DestructorDestructor

http://ecomputernotes.com


2/28

ReviewReview

Copy constructorsCopy constructorsDestructorDestructor

Accessor FunctionsAccessor Functionsthis Pointerthis Pointer



3/28

this Pointerthis PointerThere are situations whereThere are situations where

designer wants to returndesigner wants to returnreference to current object fromreference to current object from

a functiona functionIn such cases reference is takenIn such cases reference is taken

from this pointer like (*this)from this pointer like (*this)



4/28

ExampleExampleStudentStudent Student::setRollNo(intStudent::setRollNo(int aNoaNo))

{{

return *this;return *this;

}}StudentStudent Student::setName(charStudent::setName(char **aNameaName))

{{

return *this;return *this;

}}



5/28

ExampleExampleintintmain()main()

{{

StudentStudent aStudentaStudent;;

StudentStudentbStudentbStudent;;

bStudentbStudent == aStudent.setName(aStudent.setName(AhmadAhmad););

bStudentbStudent = aStudent.setName(= aStudent.setName(AliAli).setRollNo(2);).setRollNo(2);

return 0;return 0;

}}



6/28

Separation of interface andSeparation of interface and

implementationimplementation

Public member function exposed by aPublic member function exposed by aclass is called interfaceclass is called interface

Separation of implementation from theSeparation of implementation from the

interface is good software engineeringinterface is good software engineering



7/28

Complex NumberComplex Number

There are two representations ofThere are two representations ofcomplex numbercomplex number Euler formEuler form

z = x +z = x + ii yy PhasorPhasor formform

z = |z| (z = |z| (coscos

++ii

sinsin

))z is known as the complex modulus andz is known as the complex modulus and is known as the complex argument oris known as the complex argument or

phasephase


8/28

ExampleExample

floatfloat getXgetX()()

floatfloat getYgetY()()

voidvoid setNumbersetNumber

(float i, float j)(float i, float j)

float xfloat x

float yfloat y

ComplexComplex

Old implementationOld implementation

floatfloat getXgetX()()

floatfloat getYgetY()()

voidvoid setNumbersetNumber

(float i, float j)(float i, float j)

float zfloat z

float thetafloat theta

ComplexComplex

New implementationNew implementation


9/28

ExampleExampleclass Complex{ //oldclass Complex{ //old

float x;float x;

float y;float y;

public:public:

voidvoidsetNumber(floatsetNumber(float i, float j){i, float j){

x = i;x = i;

y = j;y = j;

}}

};};



10/28

ExampleExampleclass Complex{ //newclass Complex{ //new

float z;float z;

float theta;float theta;

public:public:

voidvoidsetNumber(floatsetNumber(float i, float j){i, float j){

theta =theta = arctan(j/iarctan(j/i););

}}

};};



11/28

AdvantagesAdvantages

User is only concerned about ways ofUser is only concerned about ways of

accessing data (interface)accessing data (interface)

User has no concern about theUser has no concern about the

internal representation andinternal representation and

implementation of the classimplementation of the class



12/28

Separation of interface andSeparation of interface and

implementationimplementation

Usually functions are defined inUsually functions are defined in

implementation files (.implementation files (.cppcpp) while the) while the

class definition is given in header fileclass definition is given in header file

(.h)(.h)

Some authors also consider this asSome authors also consider this as

separation of interface andseparation of interface andimplementationimplementation



13/28

Student.hStudent.hclass Student{class Student{

intint rollNorollNo;;public:public:

voidvoidsetRollNo(intsetRollNo(int aRollNoaRollNo););

intint getRollNogetRollNo();();

};};



14/28

Student.cppStudent.cpp#include#include student.hstudent.h

voidvoidStudent::setRollNo(intStudent::setRollNo(int aNoaNo){){

}}intint Student::getRollNoStudent::getRollNo(){(){

}}



15/28

Driver.cppDriver.cpp#include#include student.hstudent.h

intintmain(){main(){

StudentStudent aStudentaStudent;;

}}



16/28

There are functions that areThere are functions that are

meant to be read onlymeant to be read only

There must exist a mechanism toThere must exist a mechanism todetect error if such functionsdetect error if such functions

accidentally change the dataaccidentally change the datamembermember

constconst Member FunctionsMember Functions



17/28

KeywordKeyword constconst is placed at theis placed at the

end of the parameter listend of the parameter list




18/28


Declaration:Declaration:

classclass ClassNameClassName{{ReturnValReturnVal Function() const;Function() const;

};};

Definition:Definition:

ReturnValReturnVal ClassName::FunctionClassName::Function() const{() const{

}}



19/28

ExampleExampleclass Student{class Student{

public:public:

intint getRollNogetRollNo()() constconst{{

returnreturn rollNorollNo;;}}

};};



20/28

constconst FunctionsFunctions

Constant member functions cannotConstant member functions cannot

modify the state of any objectmodify the state of any object

They are justThey are just readread--onlyonly

Errors due to typing are also caught atErrors due to typing are also caught at

compile timecompile time



21/28

ExampleExampleboolbool Student::isRollNo(intStudent::isRollNo(int aNoaNo){){

if(rollNoif(rollNo == == aNoaNo){){

return true;return true;

}}return false;return false;

}}



22/28

ExampleExampleboolbool Student::isRollNo(intStudent::isRollNo(int aNoaNo){){

/*undetected typing mistake*//*undetected typing mistake*/

if(rollNoif(rollNo == aNoaNo){){

return true;return true;}}

return false;return false;

}}



23/28

ExampleExampleboolbool Student::isRollNoStudent::isRollNo

(int(int aNo)constaNo)const{{/*compiler error*//*compiler error*/

if(rollNoif(rollNo == aNoaNo){){

return true;return true;

}}

return false;return false;}}



24/28

constconst FunctionsFunctions

Constructors and Destructors cannotConstructors and Destructors cannotbebe constconst

Constructor and destructor are usedConstructor and destructor are used

to modify the object to a well definedto modify the object to a well defined

statestate



25/28

ExampleExampleclass Time{class Time{

public:public:

Time() const {}Time() const {} //error//error

~Time() const {}~Time() const {} //error//error

};};



26/28

constconst FunctionFunction

Constant member function cannotConstant member function cannot

change data memberchange data member

Constant member function cannotConstant member function cannotaccess nonaccess non--constant memberconstant member

functionsfunctions



27/28

ExampleExampleclass Student{class Student{

char * name;char * name;public:public:

char *char *getNamegetName();();

voidvoidsetName(charsetName(char ** aNameaName););intint ConstFuncConstFunc() const{() const{

name =name = getNamegetName();();//error//error

setName(setName(

AhmadAhmad

);//error);//error

}}

};};



28/28

this Pointer and const Member Functionthis Pointer and const Member Function

this pointer is passed as constantthis pointer is passed as constant

pointer to const data in case ofpointer to const data in case of

constant member functionsconstant member functions

const Student *const this;const Student *const this;

instead ofinstead of

Student * const this;Student * const this;


Documents

Computer Notes - Destruct Or