Issue in casting

[Alexander Adam]

Hi all!

Not sure what I am doing wrong so someone might be able to help me out
here. I have a class model which looks like this:

struct A
{
...
};

struct B : public A
{
...
}

Now I have a simple function which looks like this:

A DoSomething()
{
return B(....);
}

And I am trying to cast it back to B from the outside:

....
A myClass = DoSomething();
B myClass2 = .... ??????

I've tried dynamic_cast etc. but it doesn't seem to work. What I am
doing wrong here? I'd like to avoid using dynamic_cast as I would like
to avoid having to use pointers (i.e. return A* instead of A).
Any idea?

thanks!
Alex

 

[Darío]

Hi all!

Not sure what I am doing wrong so someone might be able to help me out
here. I have a class model which looks like this:

struct A
{
..

};

struct B : public A
{
..

}

Now I have a simple function which looks like this:

A DoSomething()
{
  return B(....);

}

And I am trying to cast it back to B from the outside:

...
A myClass = DoSomething();
B myClass2 = .... ??????

I've tried dynamic_cast etc. but it doesn't seem to work. What I am
doing wrong here? I'd like to avoid using dynamic_cast as I would like
to avoid having to use pointers (i.e. return A* instead of A).

Why do you want to down cast?
That's a good question.

 

[peter koch]

Hi all!

Not sure what I am doing wrong so someone might be able to help me out
here. I have a class model which looks like this:

struct A
{
..

};

struct B : public A
{
..

}

Now I have a simple function which looks like this:

A DoSomething()
{
  return B(....);

}

And I am trying to cast it back to B from the outside:

...
A myClass = DoSomething();
B myClass2 = .... ??????

I've tried dynamic_cast etc. but it doesn't seem to work. What I am
doing wrong here? I'd like to avoid using dynamic_cast as I would like
to avoid having to use pointers (i.e. return A* instead of A).
Any idea?

thanks!
Alex

The problem is rather obvious, namely that DoSomething returns an
object of type A, not of type B. If you want to be able to return a B
object, you must return a pointer or a reference to A - not a value.

/Peter

 

[Rolf Magnus]

Hi all!

Not sure what I am doing wrong so someone might be able to help me out
here. I have a class model which looks like this:

struct A
{
..
};

struct B : public A
{
..
}

Now I have a simple function which looks like this:

A DoSomething()
{
return B(....);
}

And I am trying to cast it back to B from the outside:

You can't. You only returned a copy of the A part of your object from the
function, so an A is all that's left of it.

...
A myClass = DoSomething();
B myClass2 = .... ??????

I've tried dynamic_cast etc. but it doesn't seem to work. What I am
doing wrong here? I'd like to avoid using dynamic_cast as I would like
to avoid having to use pointers (i.e. return A* instead of A).

Why? Returning a pointer to a dynamically allocated B would be a solution.
As long as you return by value, there is nothing you can do to get what you
want.