Function Overloading

Overview

Teaching: 15 min
Exercises: 15 min

Questions

Objectives

In C++, two different functions can have the same name provided their parameters are different. This can be either because they have a different number of parameters, or because any of their parameters are of a different type.

For example:

// overloading functions
#include <iostream>
using namespace std;

int operate(int a, int b)
{
  return (a * b);
}

double operate(double a, double b)
{
  return (a / b);
}

int main ()
{
  int x=5,y=2;
  double n=5.0,m=2.0;
  cout << operate(x, y) << endl;
  cout << operate(n, m) << endl;
  return 0;
}

Running this program produces:

10
2.5

In this example, there are two functions called operate, but one of them has two parameters of type int, while the other has prameters of type double. The compiler knows which one to use in each case by examining the types passed as arguments when the function is called.

We’ve defined both functions have quite different behaviors, the int version multiplies its arguments, while the double version divides them. This is generally not a good idea. Two functions with the same name are generally expected to have -at least- a similar behavior, but this example demonstrates that is entirely possible for them to do completely different things.

Note that a function cannot be overloaded only by its return type. At least one of its parameters must have a different type.

Key Points