operator overloading & type conversion in cpp

Chap 7
Operator Overloading & Type
Conversion
1 By:-Gourav Kottawar

Contents
7.1 Defining operator Overloading
7.2 Overloading Unary Operator
7.3 Overloading Binary Operator
7.4 Overloading Binary Operator Using
Friend function
7.5 Manipulating of String Using
Operators
7.6 Type Conversion
7.7 Rules for Overloading Operators

Introduction
 Important technique allows C++ user
defined data types behave in much the
same way as built in types.
 C++ has ability to provide the operators
with a special meanings for a data type.
 The mechanism of giving such special
meaning to an operator is known as
operator overloading.

By:-Gourav Kottawar4
Why Operator Overloading?
 Readable code
 Extension of language to include user-defined
types
 I.e., classes
 Make operators sensitive to context
 Generalization of function overloading

Simple Example
class complex {
double real, imag;
public:
complex(double r, double i) :
real(r), imag(i) {}
}
 Would like to be able to write:–
complex a = complex(1, 3.0);
complex b = complex(1.2, 2);
complex c = b;
a = b + c;
b = b+c*a;
c = a*b + complex(1,2);
I.e., would like to write
ordinary arithmetic expressions
on this user-defined class.

With Operator Overloading, We
Can
class complex {
double real, imag;
public:
complex(double r, double i) :
real(r), imag(i) {}
complex operator+(complex a, complex b);
complex operator*(complex a, complex b);
complex& operator=(complex a, complex b);
...
}

General Format
returnType operator*(parameters);
  
any type keyword operator symbol
 Return type may be whatever the operator
returns
 Including a reference to the object of the operand
 Operator symbol may be any overloadable
operator from the list.

C++ Philosophy
 All operators have context
 Even the simple “built-in” operators of basic types
 E.g., '+', '-', '*', '/' for numerical types
 Compiler generators different code depending upon type of
operands
 Operator overloading is a generalization of this
feature to non-built-in types
 E.g., '<<', '>>' for bit-shift operations and also for
stream operations

C++ Philosophy (continued)
 Operators retain their precedence and
associativity, even when overloaded
 Operators retain their number of operands
 Cannot redefine operators on built-in types
 Not possible to define new operators
 Only (a subset of) the built-in C++ operators can be
overloaded

Restrictions on Operator Overloading
 C++ operators that can be overloaded
 C++ Operators that cannot be overloaded
Operators that cannot be overloaded
. .* :: ?: sizeof
Operators that can be overloaded
+ - * / % ^ & |
~ ! = < > += -= *=
/= %= ^= &= |= << >> >>=
<<= == != <= >= && || ++
-- ->* , -> [] () new delete
new[] delete[]

7.2 Overloading Unary Operator

#include <iostream>
using namespace std;
class temp
{
private:
int count;
public:
temp():count(5)
{ }
void operator ++()
{
count=count+1;
}
void Display()
{
cout<<"Count:
"<<count;
}
};
int main()
{
temp t;
++t;
/* operator function void
operator ++() is called */
t.Display();
return 0;
}

#include <iostream>
class temp
{
private:
int count;
public:
temp():count(5)
{ }
void operator ++()
{
count=count+1;
}
void Display()
{
cout<<"Count:
"<<count;
}
};
int main()
{
temp t;
++t;
/* operator function void
operator ++() is called */
t.Display();
return 0;
}
Output
Count: 6

Note
 Operator overloading cannot be used to change the
way operator works on built-in types. Operator
overloading only allows to redefine the meaning of
operator for user-defined types.
 There are two operators assignment operator(=) and
address operator(&) which does not need to be
overloaded. Because these two operators are already
overloaded in C++ library. For example: If obj1 and
obj2 are two objects of same class then, you can use
code obj1=obj2; without overloading = operator. This
code will copy the contents object of obj2 to obj1.
Similarly, you can use address operator directly
without overloading which will return the address of
object in memory.
 Operator overloading cannot change the precedence

7.3 Overloading Binary Operator
#include<iostream.h>
#include<conio.h>
class complex
{
int a,b;
public:
void getvalue()
{
cout<<"Enter the
value of Complex Numbers
a,b:";
cin>>a>>b;
}
complex
operator+(complex ob)
{ complex t;
t.a=ob.a +a;
t.b=ob.b+b;
return(t);
}
complex operator-(complex ob)
{
complex t;
t.a=ob.a - a;
t.b=ob.b -b;
return(t);
}
void display()
{
cout<<a<<"+"<<b<<"i"
<<"n";
}
};

void main()
{
clrscr();
complex
obj1,obj2,result,result1;
obj1.getvalue();
obj2.getvalue();
result = obj1+obj2;
result1=obj1-obj2;
cout<<"Input Values:n";
obj1.display();
obj2.display();
cout<<"Result:";
result.display();
result1.display();
getch();
}

void main()
{
clrscr();
complex
obj1,obj2,result,result1;
obj1.getvalue();
obj2.getvalue();
result = obj1+obj2;
result1=obj1-obj2;
cout<<"Input Values:n";
obj1.display();
obj2.display();
cout<<"Result:";
result.display();
result1.display();
getch();
}
In overloading of binary operators the left hand operand
is used to invoke the operator function and the right hand
operand is passed as an argument.17 By:-Gourav Kottawar

7.5 Overloading Binary operators using
Friend
 Friend function can be used to overload binary
operator.
 Required two arguments to be passed explicitly.#include <iostream>
#include <conio.h>
class s
{
public:
int i,j;
s()
{ i=j=0;}
void disp(){cout << i <<" " <<
j;}
void getdata(){cin>>i>>j;}
friend s operator+(int,s);
};
s operator+(int a, s s1)
{ s k;
k.i = a+s1.i;
k.j = a+s1.j;
return k;
}
int main()
{ s s2;
s2.getdata();
s s3 = 10+s2;
s3.disp();
getch();
return 0;
}18 By:-Gourav Kottawar

class stud
{
int rno;
char *name;
int marks;
public:
friend istream &operator>>(istream
&,stud &);
friend void operator<<(ostream
&,stud &);
};
istream &operator>>(istream
&tin,stud &s)
{
cout<<"n Enter the no";
tin>>s.rno;
cout<<"n Enter the name";
tin>>s.name;
cout<<"n Enter Marks";
tin>>s.marks;
return tin;
void operator<<(ostream &tout,stud &s)
{
tout<<”n”<<s.rno;
tout<<”n”<<s.name;
tout<<”n”<<s.marks;
}
void main()
{
cout<<"ttBinaryOperator Overloading
Using FriendFunction";
stud s[3];
for(int i=0;i<3;i++)
{
cin>>s[i];
}
for( i=0;i<3;i++)
{
cout<<s[i];
}
getch();
}19 By:-Gourav Kottawar

Manipulation of Strings using Operators
 There are lot of limitations in string manipulation in C
as well as in C++.
 Implementation of strings require character arrays,
pointers and string functions.
 C++ permits us to create our own definitions of
operators that can be used to manipulate the strings
very much similar to other built-in data types.
 ANSI C++ committee has added a new class called
string to the C++ class library that supports all kinds of
string manipulations.20 By:-Gourav Kottawar

 Strings can be defined as class objects which can be
then manipulated like the built-in types.
 Since the strings vary in size, we use new to allocate
memory for each string and a pointer variable to point
to the string array.
continue…

 We must create string objects that can hold two pieces
of information:
 Length
 Location
class string
{
char *p; // pointer to string
int len; // length of string
public :
------
------
};
continue…

// string manipulation
#include<string.h>
class string
{
char str[25];
public:
void getstring();
void putstring(string&);
void display();
string operator+(string&);
int operator==(string&);
void operator=(string&);
void operator+=(string&);
};
void string::getstring()
{
cout<<"Enter string:";
gets(str);
}
void string::putstring(string &s)
{
int len=strlen(s.str);
cout<<len;
}

string string::operator+(string
&s)
{
string temp;
if((strlen(str)+strlen(s.str))<25)
{
strcpy(temp.str,s.str);
strcat(temp.str,s.str);
}
else
{
cout<<endl<<"nconcatenation
is not possible";
}
return temp;
}
int string::operator==(string &s)
{
return(strcmp(str,s.str)==0?1:0)
;
}
void string::operator=(string
&s)
{
strcpy(str,s.str);
}
void string::operator+=(string
&s)
{
strcat(str,s.str);
}
void string::display()
{
cout<<str;

void main()
{
string s1,s2,s3,s4;
clrscr();
s1.getstring();
s2.getstring();
s3=s1+s2;
cout<<"nFirst string length=";
s1.putstring(s1);
cout<<"nSecond string
length=";
s2.putstring(s2);
cout<<endl<<"nConcatenate
d string:";
s3.display();
if(s1==s2)
cout<<endl<<"nComparison:
Equal";
else
cout<<endl<<"nComparison:
Not equaln";
cout<<endl<<"nafter
addition:n";
s1+=s2;
s1.display();
s4=s3;
cout<<endl<<"copy:";
s4.display();
s1=s2;
getch();

Rules For Overloading
Operators
 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.
 We cannot change the basic meaning of an operator.
 Overloaded operators follow the syntax rules of the
original operators.

Operators
 The following operators that cannot be overloaded:
 Size of Size of operator
 . Membership operator
 .* Pointer-to-member operator
 : : Scope resolution operator
 ? ; Conditional operator
continue…

Operators
 The following operators can be over loaded with the
use of member functions and not by the use of friend
functions:
 Assignment operator =
 Function call operator( )
 Subscripting operator [ ]
 Class member access operator ->
 Unary operators, overloaded by means of a member
function, take no explicit arguments and return no
explicit values, but, those overloaded by means of a
friend function, take one reference argument.
continue…

Operators
 Binary operators overloaded through a member
function take one explicit argument and those which
are overloaded through a friend function take two
explicit arguments.
 When using binary operators overloaded through a
member function, the left hand operand must be an
object of the relevant class.
 Binary arithmetic operators such as +, -, * and / must
explicitly return a value. They must not attempt to
change their own arguments.
continue…

Type Conversions
 The type conversions are automatic only when the
data types involved are built-in types.
int m;
float x = 3.14159;
m = x; // convert x to integer before its value is assigned
// to m.
 For user defined data types, the compiler does not
support automatic type conversions.
 We must design the conversion routines by
ourselves.

Type Conversions
Different situations of data conversion between
incompatible types.
 Conversion from basic type to class type.
 Conversion from class type to basic type.
 Conversion from one class type to another
class type.
continue…

Basic to Class Type
A constructor to build a string type object from a
char * type variable.
string : : string(char *a)
{
length = strlen(a);
P = new char[length+1];
strcpy(P,a);
}
The variables length and p are data members of
the class string.

Basic to Class Type
string s1, s2;
string name1 = “IBM PC”;
string name2 = “Apple Computers”;
s1 = string(name1);
s2 = name2;
continue…
First converts name1 from char*
type to string type and then
assigns the string type value to
the object s1.
First converts name2 from char*
type to string type and then
assigns the string type value to
the object s2.

Basic to Class Type
class time
{ int hrs ;
int mins ;
public :
…
time (int t)
{
hrs = t / 60 ;
mins = t % 60;
}
} ;
time T1;
int duration = 85;
T1 = duration;
continue…

Class To Basic Type
A constructor function do not support type conversion
from a class type to a basic type.
An overloaded casting operator is used to convert a
class type data to a basic type.
It is also referred to as conversion function.
operator typename( )
{
…
… ( function statements )
…
}
This function converts a calss type data to typename.

Class To Basic Type
vector : : operator double( )
{
double sum = 0;
for (int i=0; i < size ; i++)
sum = sum + v[i] * v[i];
return sqrt (sum);
}
This function converts a vector to the square root of the
sum of squares of its components.
continue…

Class To Basic Type
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.
vector : : operator double( )
{
double sum = 0;
for (int i=0; i < size ; i++)
sum = sum + v[i] * v[i];
return sqrt (sum);
}
continue…

Class To Basic Type
 Conversion functions are member functions and
it is invoked with objects.
 Therefore the values used for conversion inside
the function belong to the object that invoked
the function.
 This means that the function does not need an
argument.
continue…

One Class To Another Class
Type
objX = objY ; // objects of different types
 objX is an object of class X and objY is an object of
class Y.
 The class Y type data is converted to the class X type
data and the converted value is assigned to the objX.
 Conversion is takes place from class Y to class X.
 Y is known as source class.
 X is known as destination class.

Type
Conversion between objects of different classes can be
carried out by either a constructor or a conversion
function.
Choosing of constructor or the conversion function
depends upon where we want the type-conversion
function to be located in the source class or in the
destination class.
continue…

Type
operator typename( )
 Converts the class object of which it is a member to
typename.
 The typename may be a built-in type or a user-defined
one.
 In the case of conversions between objects, typename
refers to the destination class.
 When a class needs to be converted, a casting
operator function can be used at the source class.
 The conversion takes place in the source class and
the result is given to the destination class object.
continue…

Type
Consider a constructor function with a single
argument
 Construction function will be a member of the
destination class.
 The argument belongs to the source class and is
passed to the destination class for conversion.
 The conversion constructor be placed in the
destination class.
continue…

operator overloading & type conversion in cpp

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