Re: Simple functor

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Tue, 21 Aug 2007 08:08:28 -0400

Message-ID:

<faekjr$q5q$1@news.datemas.de>

Neelesh Bodas wrote:

On Aug 21, 4:59 pm, CodeGrommet <rick.sof...@gmail.com> wrote:

Hi. Please excuse this post. I searched functor in this group and
had around 1600 hits. The first page couldn't help me. Would
someone be so kind as to look at this code and tell me why it won't
compile? I'm using a mingW compiler.

******************************code*****************************************?***
#include <iostream>
using namespace std;

class mySquare
{
public:
int operator()(int x) const { return x * x; }

}

missing semicolon

int main(){
cout<<mySquare(2)<<endl;

non-static function should only be called on object. Here you are
trying to invoke a non-existant unary constructor of mySquare class.

Do this:

    mySquare m;
    cout<< m(2) <<endl;

Or this:

   cout<< mySquare()(2) <<endl;

There is another possibility. Redefine your class to have a c-tor
and a conversion function:

    class mySquare {
        int x;
    public:
        mySquare(int x) : x(x) {}
        operator int() const { return x*x; }
    };

and you should be able to use the syntax you had:

    cout << mySquare(2) << endl;

V
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