Mire jó az operator=?

A 24 órás könyvből tanulok és nincs nagyon részletezve ezen kívül a felfogásom nem túl jó.

Nehezen értek meg dolgokat.

De ezt nem értem:

.....

const CAT CAT::operator= (const CAT &rhs)

{

cout <<"operator= \n";

if(this == &rhs)

return *this;

delete itsAge;

delete itsWeight;

itsAge = new ushort;

itsWeight = new ushort;

*itsAge = rhs.GetAge();

*itsWeight = rhs.GetWeight();

return *this;

}

Minek kell az összehasonlítás?

if(this == &rhs)

És mi az istennek törölni,benne a tagváltozókat ha úgyis újból lefoglalunk nekik területet.

//main.cpp

# include <iostream> //std::cin;std::cout;std::endl;std::string;

# include <string> //std::string;

# include <windows.h> //Sleep(500);exit(0);

# include <stdlib.h> //EXIT_SUCCESS;

typedef unsigned short ushort;

typedef unsigned int uint;

using std::cout;

using std::cin;

using std::endl;

using std::string;

//create CAT

class CAT

{

public:

CAT(); //konstruktor

CAT(ushort age,ushort weight); //konstruktor2

CAT(const CAT &rhs); //copy konstruktor

~CAT(); //destruktor

const CAT operator= (const CAT &rhs); //operator=

const CAT& operator++ (); //operator++ prefix

const CAT operator++ (int); //operator++ postfix

const CAT operator+ (const CAT &rhs); //operator+

ushort GetAge()const;

void SetAge(ushort age);

ushort GetWeight()const;

void SetWeight(ushort weight);

private:

ushort *itsAge;

ushort *itsWeight;

};

//konst,konst2,copy konst,dest,operator=

CAT::CAT():

itsAge(new ushort(0)),

itsWeight(new ushort(0))

{cout <<"Konstruktor \n";}

CAT::CAT(ushort age,ushort weight):

itsAge(new ushort(age)),

itsWeight(new ushort(weight))

{cout <<"Konstruktor2 \n";}

CAT::CAT(const CAT &rhs)

{

cout <<"Copy konstruktor \n";

itsAge = new ushort;

itsWeight = new ushort;

*itsAge = rhs.GetAge();

*itsWeight = rhs.GetWeight();

}

CAT::~CAT()

{

cout <<"Destruktor \n";

delete itsAge;

delete itsWeight;

itsAge = NULL;

itsWeight = NULL;

}

const CAT CAT::operator= (const CAT &rhs)

{

cout <<"operator= \n";

if(this == &rhs)

return *this;

delete itsAge;

delete itsWeight;

itsAge = new ushort;

itsWeight = new ushort;

*itsAge = rhs.GetAge();

*itsWeight = rhs.GetWeight();

return *this;

}

//operator++ pre,operator++ post,operator+

const CAT& CAT::operator++ ()

{

cout <<"opeator++ prefix \n";

++*itsAge;

++*itsWeight;

return *this;

}

const CAT CAT::operator++ (int)

{

cout <<"operator++ postfix \n";

++*itsAge;

++*itsWeight;

return *this;

}

const CAT CAT::operator+ (const CAT &rhs)

{

cout <<"operator+ \n";

return CAT(*itsAge+rhs.GetAge(),*itsWeight+rhs.GetWeight());

}

//metódus

ushort CAT::GetAge()const

{return *itsAge;}

void CAT::SetAge(ushort age)

{*itsAge = age;}

ushort CAT::GetWeight()const

{return *itsWeight;}

void CAT::SetWeight(ushort weight)

{*itsWeight = weight;}

//main start.

int main()

{

CAT CatOne(2,3),CatTwo(4,6),CatThree;

cout <<"\nCatOne age: "<< CatOne.GetAge() << endl

<<"CatOne weight: "<< CatOne.GetWeight() << endl

<<"CatTwo age: "<< CatTwo.GetAge() << endl

<<"CatTwo weight: "<< CatTwo.GetWeight() << endl

<<"CatThree age: "<< CatThree.GetAge() << endl

<<"CatThree weight: "<< CatThree.GetWeight() << endl << endl;

CatThree = CatOne + CatTwo;

cout <<"\nCatOne age: "<< CatOne.GetAge() << endl

<<"CatOne weight: "<< CatOne.GetWeight() << endl

<<"CatTwo age: "<< CatTwo.GetAge() << endl

<<"CatTwo weight: "<< CatTwo.GetWeight() << endl

<<"CatThree age: "<< CatThree.GetAge() << endl

<<"CatThree weight: "<< CatThree.GetWeight() << endl << endl;

return EXIT_SUCCESS;

}

//Kimenet:

Konstruktor2

Konstruktor2

konstruktor

CatOne age: 2

CatOne weight: 3

CatTwo age: 4

CatTwo weight: 6

CatThree age: 0

CatThree weight: 0

operator+

Konstruktor2

operator=

Copy konstruktor /*Ezt nem értem,hogy itt miért hívódik meg a másoló konstruktor */

Destruktor

Destruktor

CatOne age: 2

CatOne weight: 3

CatTwo age: 4

CatTwo weight: 6

CatThree age: 6

CatThree weight: 9

Destruktor

Destruktor

Destruktor

Részletesebben valaki.

Mert így nem értem.