Re: function returning reference to empty object

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 16 May 2007 20:30:22 -0700

Message-ID:

<L%P2i.477$Oo7.136@newsfe02.lga>

"Dejfson" <dejfson@dejfson.org> wrote in message
news:464b9951$0$146$fb624d75@newsspool.solnet.ch...

Dear All,
can someone clarify me how to return the reference to the empty object in
case of error?

_not working_ Example of what i'd like to do:

const MyClassData& MyClass ()
{
QListIterator<MyClassData> it(fancylist)

while (it.hasNext())
{
const MyClassData &data = it.next();

if (data are ok)
return data;
}

return MyClassData();
}

This compiles, but of course it returns invalid reference in the case when
I don't find any suitable data. It there a way how to use the reference in
such case??

I have just one solution in my mind: if I create class variable:

class MyClass {
public:
MyClass () : errorVariable() {};

private:
MyClassData errorVariable;
}

and then I modify function:

const MyClassData& MyClass ()
{
QListIterator<MyClassData> it(fancylist)

while (it.hasNext())
{
const MyClassData &data = it.next();

if (data are ok)
return data;
}

return errorVariable;
}

But I'm not sure whether I like the idea of creating additional variable
just as placeholder for something which doesn't really exist..

Is there another way?

I used throw as thus:

CPlayer& FindPlayer( const SOCKET Socket )
{
    // Get a reference in the map for this player
    map_player::iterator it = World.ConnectedPlayers.find( Socket );
    if ( it != World.ConnectedPlayers.end() )
        return (*it).second;
    else
        throw 0;
}

which I use a number of ways (is a client logged in, get a reference,
etc...) A few examples of usage:

            // Get a reference in the map for this player
            try
            {
                // Just do it to see if it throws
                FindPlayer( Socket );
            }
            catch ( int )
            {
                SendMessageToPlayer( Socket, MSG_SERVER_MESSAGE, "<Message
not sent, please relog - Error has been logged>" );
                World.MessageBuffer.push_back( LogError( "Unlogged in client
attempting to send message on socket " + jml::StrmConvert( Socket ) + " on
IP " + IP ) );
                return 0;
            }

===================

            case MSG_REQUEST_PLAYER_INFO: // "PlayerID"
                {
                    SOCKET PlayerID = jml::StrmConvert<SOCKET>(
StrMessage );

                    try
                    {
                        CPlayer& TargetPlayer = FindPlayer( PlayerID );
                        if ( ThisPlayer.Character.Map ==
TargetPlayer.Character.Map ) // Make sure on same map
                        {
                            SendMessageToPlayer( Socket,
MSG_CREATE_PLAYER_OBJECT, CreateCharMessage( TargetPlayer.Socket,
TargetPlayer.Character ) );
                        }
                    }
                    catch ( int )
                    {
                    }
                }

                break;

======================

    case MSG_DESTROY_CLIENT:
        {
            try
            {
                CPlayer& ThisPlayer = FindPlayer( Socket );
                PlayerLeft( ThisPlayer );
            }
            catch ( int )
            {
                World.MessageBuffer.push_back( "Unlogged in socket " +
jml::StrmConvert( Socket ) + " disconnected." );
            }
        }

        break;