Mastering Operator Overloading in C++...

Overloading Unary Operators
// countpp1.cpp
// increment counter variable with ++ operator
#include <iostream>
using namespace std;
/////////////////////////////////////////////////////////////
///
class Counter
{
private:
unsigned int count; //count
public:
Counter() : count(0) //constructor
{ }
unsigned int get_count() //return count
{ return count; }
void operator ++ () //increment (prefix)
{
++count;
}
};
Keyword

Overloading Unary Operators
int main()
{
Counter c1, c2; //define and initialize
cout << “nc1=” << c1.get_count(); //display
cout << “nc2=” << c2.get_count();
++c1; //increment c1
cout << “nc1=” << c1.get_count(); //display again
cout << “nc2=” << c2.get_count() << endl;
return 0;
}
Output
c1=0 ← counts are initially 0
c2=0
c1=1 ← incremented once
c2=2 ←incremented twice

Operator Return Values
void operator ++ () //increment (prefix)
{
++count;
}
Counter c1, c2;
c1 = ++c2; //
Error

class Counter
{
private:
public:
Counter() : count(0) //constructor
{ }
{ return count; }
Counter operator ++ () //increment count
{
++count; //increment count
Counter temp; //make a temporary Counter
temp.count = count; //give it same value as this obj
return temp; //return the copy
}
};

int main()
{
Counter c1, c2; //c1=0, c2=0
++c1; //c1=1
c2 = ++c1; //c1=2, c2=2
return 0;
}
Output
c1=0
c2=0
c1=2
c2=2

Nameless Temporary Objects
class Counter
{
private:
public:
Counter() : count(0) //constructor no args
{ }
Counter(int c) : count(c) //constructor, one arg
{ }
{ return count; }
Counter operator ++ () //increment count
{
++count; // increment count, then return
return Counter(count); // an unnamed temporary object
} // initialized to this count
};

int main()
{
Counter c1, c2; //c1=0, c2=0
++c1; //c1=1
c2 = ++c1; //c1=2, c2=2
return 0;
}
Output
c1=0
c2=0
c1=2
c2=2
Nameless Temporary Objects

class Counter
{
private:
public:
Counter() : count(0) //constructor no args
{ }
Counter(int c) : count(c) //constructor, one arg
{ }
unsigned int get_count() const //return count
{ return count; }
Counter operator ++ () //increment count (prefix)
{ //increment count, then return
return Counter(++count); //an unnamed temporary object
} //initialized to this count
Counter operator ++ (int) //increment count (postfix)
{ //return an unnamed temporary
return Counter(count++); //object initialized to this
} //count, then increment count
};
Postfix Notation

int main()
{
Counter c1, c2; //c1=0, c2=0
++c1; //c1=1
c2 = ++c1; //c1=2, c2=2 (prefix)
c2 = c1++; //c1=3, c2=2 (postfix)
return 0;
}
Postfix Notation
Output
c1=0
c2=0
c1=2
c2=2
c1=3
c2=2

Arithmetic Operators
class Distance //English Distance class
{
private: int feet; float inches;
public: //constructor (no args)
Distance() : feet(0), inches(0.0)
{ } //constructor (two args)
Distance(int ft, float in) : feet(ft), inches(in)
{ }
void getdist() //get length from user
{
cout << “nEnter feet: “; cin >> feet;
cout << “Enter inches: “; cin >> inches;
}
void showdist() const //display distance
{ cout << feet << “’-” << inches << ‘”’; }
Distance operator + ( Distance ); //add 2 distances
};
Overloading Binary Operators

Distance Distance::operator + (Distance d2) //return sum
{
int f = feet + d2.feet; //add the feet
float i = inches + d2.inches; //add the inches
if(i >= 12.0) //if total exceeds 12.0,
{ //then decrease inches
i -= 12.0; //by 12.0 and
f++; //increase feet by 1
} //return a temporary Distance
return Distance(f,i); //initialized to sum
}

int main()
{
Distance dist1, dist3; //define distances
dist1.getdist(); //get dist1 from user
Distance dist2(11, 6.25); //define, initialize dist2
dist3 = dist1 + dist2; //single ‘+’ operator
//display all lengths
cout << “dist1 = “; dist1.showdist(); cout << endl;
return 0;
}
Output
Enter feet: 10
Enter inches: 6.5
dist1 = 10’-6.5” ← from user
dist2 = 11’-6.25” ← initialized in program
dist3 = 22’-0.75” ← dist1+dist2

dist3 = dist1 + dist2;

Comparison Operators
bool operator < (Distance d2)
{
float bf1 = feet + inches/12;
float bf2 = d2.feet + d2.inches/12;
return (bf1 < bf2) ? true : false;
}

Operator overloading restrictions
• The following operators cannot be overloaded
– the member access or dot operator (.)
– the scope resolution operator (::)
– the conditional operator (?:)
– the pointer-to-member operator (->)
• One can’t create new operators ,only existing
operators can be overloaded

Mastering Operator Overloading in C++...

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