Virtual function not behaving like it should

[Laww]

Hi, not sure I did well posting here instead of the Beginners' subforum. Oh well.

Long story short, I have these two classes:

class Motion
{
    protected : 
 
    / * Things */
 
    public :
 
    virtual void Delete(void);
    void foo(void);
 
    /* Things */
};
 
class DoubleMotion : public Motion
{
    public :
 
    void Delete(void);
};

The function 'foo' contains "Delete();" somewhere in the code.

Then I create a few objects:

deque<Motion> someDeQue;

/* Things, then we enter a for loop */

DoubleMotion* NewMotion = new DoubleMotion(...);
someDeQue.push_back(*NewMotion); 

/* This is done several times */

Then I use the function foo like that:

someDeQue[0].foo();

and no matter what I do, it always uses Motion::Delete, instead of DoubleMotion::Delete().

Would you know what the problem is? Thanks!

[cire]

Your deque is only capable of holding Motion objects, so that is all that will ever be stored in it.

// http://ideone.com/1oWD0K
#include <iostream>

struct base
{
    virtual void print_type() const {
        std::cout << "base\n";
    }
};

struct derived : public base
{
    void print_type() const {
        std::cout << "derived\n";
    }
};

int main()
{
    base b; // b is an object of type base.  It can never be anything else.
    b.print_type();

    derived d;
    d.print_type();

    b = d; // If we set b equal to an object of type derived, it is still an object of type base.
    b.print_type();

    base* ptr = &b;     // ptr is a pointer to some class in the base hierarchy
    ptr->print_type();  // if we point it a a base class object, we get base class behavior

    ptr = &d;           // if we point it a derived class object, we get derived class behavior
    ptr->print_type();
}

Store pointers in your container (preferably of the smart variety.)

Google "object slicing"

[Laww]

You are a life saver!!!

Thank you very much :)