dev-cpp-users

[Dev-C++] object evaluation

[<or...@vp...>]

Hi!

I'm just courious about how can I "evaluate" an object, like fstream=20
does it:

ifstream infile( "C:/file.txt" );
if ( !infile ) { /*...*/ }

Is it done with the type conversion operator (converting to bool)?

--
Greetings,
   Bal=E1zs

Re: [Dev-C++] object evaluation

[Tim S. <ti...@we...>]

Hi Oroszi,

you wrote:

> I'm just courious about how can I "evaluate" an object, like fstream=20
> does it:
>=20
> ifstream infile( "C:/file.txt" );
> if ( !infile ) { /*...*/ }
>=20
> Is it done with the type conversion operator (converting to bool)?

!object you can do with overloading operators, for just checking object
I didnt figured out yet. This is a small Program which I tried and
seemed to work:

<<<<<<<<<<<<<< Schnip <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
#include <iostream>
                                                                           =
                                                 =20
using namespace std;
                                                                           =
                                                 =20
class test
{
        private:
                bool bimbes;
        public:
                bool operator!()
                {
                        return bimbes;
                }
                test(bool a)
                {
                        bimbes =3D a;
                }
                                                                           =
                                                 =20
};
                                                                           =
                                                 =20
int main()
{
        test blub =3D test(true);
        if (!blub)
        {
                cout << "Cool!" << endl;
        }
        return 0;
}

>>>>>>>>>>>> Schnapp >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

but if you want to know how it works exactly, just look at the source of
fstream.

so long

Tim

--=20
http://we-are-teh-b.org/~tim/borg.key
http://learn.to/quote

Re: [Dev-C++] object evaluation

[<or...@vp...>]

Tim Schumacher wrote:
> !object you can do with overloading operators, for just checking object
> I didnt figured out yet. This is a small Program which I tried and
> seemed to work:

I think I found it :)

----

       /**
        *  @brief  The quick-and-easy status check.
        *
        *  This allows you to write constructs such as
        *  "if (!a_stream) ..." and "while (a_stream) ..."
       */
       operator void*() const
       { return this->fail() ? 0 : const_cast<basic_ios*>(this); }

       bool
       operator!() const
       { return this->fail(); }

----

Seems I was right about the conversion, but they simplified the whole=20
thing with converting it to void*, as it will also be used in a bool=20
context (one less operator overload to write).

I still wonder, what if I write a bool conversion operator only. Then I=20
wouldn't even need operator!, because bool conversion is made first, and=20
"not" (operator!) is used afterwards for the converted bool value.

It's late now. I'll write some test-progs tomorrow.

--
Greetings,
   Bal=E1zs