Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 18

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 18

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Object-Oriented Programming

(OOP)Lecture No. 18


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ssignment operatorModifying:

class String{

public:

void operator =(const String &);

};


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ssignment operatorvoid String::operator = (const String & rhs){

size = rhs.size;

delete [] bufferPtr;if(rhs.size != 0){

bufferPtr = new char[rhs.size+1];

strcpy(bufferPtr,rhs.bufferPtr);

}else

bufferPtr = NULL;

}


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ssignment operatorint main(){

String str1(ABC");

String str2(DE), str3(FG);

str1 = str2; // Valid

str1 = str2 = str3; // Errorreturn 0;

}


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ssignment operatorstr1=str2=str3is resolved as:

str1.operator=(str2.operator=

(str3))

Return type isvoid. Parameter

cant be void


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ssignment operatorSolution: modify the operator=function as follows:

class String{

public:

String & operator = (constString &);

};


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ssignment operatorString & String :: operator = (const String &

rhs){

size = rhs.size;

delete [] bufferPtr;

if(rhs.size != 0){


strcpy(bufferPtr,rhs.bufferPtr);

}

else bufferPtr = NULL;

return *this;

}


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ssignment operatorvoid main(){

String str1(AB");

String str2(CD), str3(EF);

str1 = str2;

str1 = str2 = str3; // Now valid

}


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ssignment operator

Return type isString .

str1=str2=str3is resolved as:

str1.operator=(str2.operator=

(str3))


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ssignment operator

int main(){String str1("Fakhir");

// Self Assignment problem

str1 = str1;

return 0;

}


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// size = rhs.size;

// delete [] bufferPtr;

???

ssignment operatorResult of str1 = str1

str1

Fakhir


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ssignment operatorString & String :: operator = (const

String & rhs){

if(this != &rhs){

size = rhs.size;delete [] bufferPtr;

if(rhs.bufferPtr != NULL){


strcpy(bufferPtr,rhs.bufferPtr);}

else bufferPtr = NULL;

}

return *this; }


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ssignment operatorNow self-assignment is properly handled:

int main(){

String str1("Fakhir");

str1 = str1;return 0;

}


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ssignment operatorSolution: modify the operator=function as follows:

class String{

public:

constString & operator=

(const String &);

};


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ssignment operatorint main(){

String s1(ABC),

s2(DEF),

s3(GHI);

// Error

(s1 = s2) = s3;return 0;

}


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ssignment operatorBut we can do the following withprimitive types:

int main(){

int a, b, c;

(a = b) = c;

return 0;

}


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Other Binary operatorsOverloading +=operator:

class Complex{

double real, img;

public:

Complex & operator+=(const Complex &rhs);

Complex & operator+=(count double &

rhs);

...

};


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Other Binary operatorsComplex & Complex::operator +=

(const Complex & rhs){

real = real + rhs.real;

img = img + rhs.img;

return * this;

}


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Other Binary operatorsint main(){

Complex c1, c2, c3;

c1 += c2;

c3 += 0.087;

return 0;

}


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Operator overloadingFriend functions minimizeencapsulation

This can result in:Data vulnerability

Programming bugs

Tough debugging

Hence, use of friend functions mustbe limited


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Operator overloadingThe + operator can be defined as anon-member, non-friend function:

Complex operator + (const Complex &

a, const Complex & b){

Complex t = a;

return t += b

}


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Operator overloadingComplex operator + (const double &

a, const Complex & b){Complex t = b;

return t += a;

}


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Operator overloadingComplex operator + (const Complex &

a, const double & b){Complex t = a;

return t += b;

}


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Other Binary operatorsThe operators

-=, /=, *=, |=, %=, &=, ^=,

=, !=

can be overloaded in a very

similar fashion

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Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 18