Thread: Deleting derived classes

Hi, i am writing a client for some protocol which has several messages defined. Ive been passing these messages around in a list of type <Message*>, whilst each individual message is derived from Message, let me give a quick example of this, with a message called GRMFYI

Code:

int main (int argc, char** argv)
{
        DatReader* dat = NULL;
        GameState* gs = NULL;

        uint8_t* inpacket;
        int packet_size = loadpacket (&inpacket);

        uint8_t* tmp = new uint8_t[packet_size];
        memcpy (tmp, inpacket, packet_size);

        NetworkMessage* inmsg = new NetworkMessage (packet_size, tmp);
        inmsg->setPos (4);

        Message* m = new GRMFYI (inmsg, gs, dat);

        delete m;
        delete inpacket;
        delete inmsg;
        return 0;
}

this is stripped down to absolute basics, but basically when i run valgrind GRMFYI wont be freed, i assume because Message and GRMFYI are different. I can only guess that the wrong deconstructor is being called, as frees are done based on structures in memory (i think). If instead of

Code:

        Message* m = new GRMFYI (inmsg, gs, dat);

i use

Code:

        GRMFYI* m = new GRMFYI (inmsg, gs, dat);

valgrind gives me a happy pat on the back. My question is is there a way to delete a derived class if you only have a pointer to the base class and are unaware of how the class was derived.

The two obvious solutions are to have an virtual killme () function which does delete this or to add a deleteMessage function to the message factory (i already have one producing the derived classes).
Thankyou

You simply need to make sure that the destructor (note spelling) of 'Message' itself is virtual (which means it's derived classes will also have a virtual destructor). This is standard practice for classes that need to be deleted through a pointer to their base type. It should make the code work correctly, and prevent complaints from valgrind.

it is virtual, and i think i know what your talking about. The problem is im deleteing the base class, not the derived class.
I know that when you delete a derived class the constructor of the base class is also called.

For anyones interest i took the latter approach and gave factories the ability to delete messages by looking up their ids and then choosing an appropriate type to cast to before deleting them.

lol ur right, the classes in question didnt have deconstructors, ::smacks himself over the head::

thank god for source control...