Question

I’m trying to understand operator overloading in C++, and can see the usefulness when used carefully on operators like + and []. I’m interested now in the overloading of (). Boost seems to use it with its statistical classes, and I can use them, but don’t really understand what I’m doing.

Can anyone provide a simple example of when overloading the () operator would be useful?
Thanks guys
Pete

Answer 1

A common use of overloading the operator() is for function objects or functors. You can use objects of a class that defines the operator() and use as if it is a function as shown in example below:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class multiply
{
private:
    int x;
public:
    multiply(int value):x(value) { }
    int operator()(int y) { return x * y; }
    int getValue() { return x; }
};

int main()
{
    multiply m(10); //create an object
    cout << "old value is " << m.getValue() << endl;
    int newValue = m(2); //this will call the overloaded () 
    cout << "new value is " << newValue << endl;
}