C++ allows you to specify more than one definition for a
function name or an
operator in the same scope, which is called
function overloading and
operator overloading respectively.
An overloaded declaration is a declaration that had been declared
with the same name as a previously declared declaration in the same
scope, except that both declarations have different arguments and
obviously different definition (implementation).
When you call an overloaded
function or
operator, the
compiler determines the most appropriate definition to use by comparing
the argument types you used to call the function or operator with the
parameter types specified in the definitions. The process of selecting
the most appropriate overloaded function or operator is called
overload resolution.
Function overloading in C++:
You can have multiple definitions for the same function name in the
same scope. The definition of the function must differ from each other
by the types and/or the number of arguments in the argument list. You
can not overload function declarations that differ only by return type.
Following is the example where same function
print() is being used to print different data types:
#include <iostream>
using namespace std;
class printData
{
public:
void print(int i) {
cout << "Printing int: " << i << endl;
}
void print(double f) {
cout << "Printing float: " << f << endl;
}
void print(char* c) {
cout << "Printing character: " << c << endl;
}
};
int main(void)
{
printData pd;
// Call print to print integer
pd.print(5);
// Call print to print float
pd.print(500.263);
// Call print to print character
pd.print("Hello C++");
return 0;
}
When the above code is compiled and executed, it produces following result:
Printing int: 5
Printing float: 500.263
Printing character: Hello C++
Operators overloading in C++:
You can redefine or overload most of the built-in operators available
in C++. Thus a programmer can use operators with user-defined types as
well.
Overloaded operators are functions with special names the keyword
operator followed by the symbol for the operator being defined. Like any
other function, an overloaded operator has a return type and a
parameter list.
Box operator+(const Box&);
declares the addition operator that can be used to
add two Box
objects and returns final Box object. Most overloaded operators may be
defined as ordinary non-member functions or as class member functions.
In case we define above function as non-member function of a class then
we would have to pass two arguments for each operand as follows:
Box operator+(const Box&, const Box&);
Following is the example to show the concept of operator over loading
using a member function. Here an object is passed as an argument whose
properties will be accessed using this object, the object which will
call this operator can be accessed using
this operator as explained below:
#include <iostream>
using namespace std;
class Box
{
public:
double getVolume(void)
{
return length * breadth * height;
}
void setLength( double len )
{
length = len;
}
void setBreadth( double bre )
{
breadth = bre;
}
void setHeight( double hei )
{
height = hei;
}
// Overload + operator to add two Box objects.
Box operator+(const Box& b)
{
Box box;
box.length = this->length + b.length;
box.breadth = this->breadth + b.breadth;
box.height = this->height + b.height;
return box;
}
private:
double length; // Length of a box
double breadth; // Breadth of a box
double height; // Height of a box
};
// Main function for the program
int main( )
{
Box Box1; // Declare Box1 of type Box
Box Box2; // Declare Box2 of type Box
Box Box3; // Declare Box3 of type Box
double volume = 0.0; // Store the volume of a box here
// box 1 specification
Box1.setLength(6.0);
Box1.setBreadth(7.0);
Box1.setHeight(5.0);
// box 2 specification
Box2.setLength(12.0);
Box2.setBreadth(13.0);
Box2.setHeight(10.0);
// volume of box 1
volume = Box1.getVolume();
cout << "Volume of Box1 : " << volume <<endl;
// volume of box 2
volume = Box2.getVolume();
cout << "Volume of Box2 : " << volume <<endl;
// Add two object as follows:
Box3 = Box1 + Box2;
// volume of box 3
volume = Box3.getVolume();
cout << "Volume of Box3 : " << volume <<endl;
return 0;
}
When the above code is compiled and executed, it produces following result:
Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400
Overloadable/Non-overloadableOperators:
Following is the list of operators which can be overloaded:
+ | - | * | / | % | ^ |
& | | | ~ | ! | , | = |
< | > | <= | >= | ++ | -- |
<< | >> | == | != | && | || |
+= | -= | /= | %= | ^= | &= |
|= | *= | <<= | >>= | [] | () |
-> | ->* | new | new [] | delete | delete [] |
Following is the list of operators which can not be overloaded:
Operator Overloading Examples:
Here are various operator overloading examples to help you in understanding the concept.
S.N. | Operators and Example |
1 | Unary operators overloading |
2 | Binary operators overloading |
3 | Relational operators overloading |
4 | Input/Output operators overloading |
5 | ++ and -- operators overloading |
6 | Assignment operators overloading |
7 | Function call () operator overloading |
8 | Subscripting [] operator overloading |
9 | Class member access operator -> overloading |