use of operator() in a class or struct

[pmanjrekar]

Hi All,

in some of the code that i am reusing. i was surprise to see

operator()

operator used in a struct.

dose any one knows what this operator is and how it works?
searched around the internet but could not found any answer

struct EventSetter
{
	void operator()()
	{
		SetEvent(BackgroundTask, event_writer);
	}
};

[Peter87]

It's the function call operator. Calling it will look like a function call

EventSetter es;
es(); // this calls operator() 

[zb0S216C]

I'm not too sure of the name, but the operator can be used for anything; functional notation, accessing something within an array, return a piece of data, et cetera. There's no defined suggestion as to what each overloaded operator should do. For instance:

struct Structure
{
    // To return something:
    int operator () ()
    {
        int MyInt(0);
        
        // Do something with "MyInt"...

        return(MyInt);
    }

    // To access an array:
    int MyArray[3];
    int &operator () (int Index = 0) const
    {
        return(this->MyArray[Index]);
    }
 
    // As a function:
    void operator () ()
    {
        // Do something a function would do...
    }
};

_Wazzak

[webJose]

The most typical of uses for this operator is functors and the STL, I would say.

[therockon7throw]

The operator() is wildly used in STL, mostly as a function object. It is also used in expression template in the same way, as function object

e.g.

template<class T, class Op>
ResultObj< ResultObj< T, T , Op > , OtherObj< T, T , Op >,OperationObj< typename ResultObj< T, T , Op >::value_type> >

operator + (const ResultObj< T, T , Op >& a, const OtherObj< T, T , Op >& b)
{
	return ResultObj< ResultObj< T, T , Op > , OtherObj< T, T , Op >,OperationObj< typename ResultObj< T, T , Op >::value_type> > (a,b, OperationObj< typename ResultObj< T, T , Op >::value_type>() ) ;
}