static / Dynamic casting and references/pointers

[MisterEd]

Hi,

I'm getting a bit confused while looking at static_cast and dynamic_cast while using references and pointers. I could really do with an idiots guide with plenty of examples to clear things up.

I understand that:

- static_cast has no RTTI checking (and so does not have the associated overhead)

- dynamic_cast uses RTTI checking and so is safer, although this does incur an overhead at runtime

- dynamic_cast can only be used with pointers and references

Is there anything important I'm missing when comparing static vs dynamic casts?


I understand what pointers and references are but could do with some clarification on the following points:


Can you cast from a pointer to a reference?

Can you cast from a reference to a pointer?

Can you cast from an object to a pointer?

Can you cast from an object to a reference?


Is the main use of dynamic_cast then to cast base class pointers/references to derived class pointers/references and vice versa?



Any help would be appreciated!

Cheers!

[helios]

Can you cast from a pointer to a reference?

No, but you can initialize references from pointers provided that the pointed-to type (including constness) is the same.

Can you cast from a reference to a pointer?

No, but you can get a pointer from a reference using the address-of operator.

Can you cast from an object to a pointer?

No, but see the previous point.

Can you cast from an object to a reference?

No, but you can initialize references to objects.

[S6k9GNh0]

helios is trying to say that your using the incorrect terminology. It's casting if your turning something into something else. Yes, pun intended because that's where it came from.

A pointer to a reference. NOTE that it didn't cast anything. It grabbed the data that was already available:

int * pInteger = new int;
int &myRef = *pInteger; //myRef now controls the allocated space of pInteger.
//I don't normally use references but this should be right... 

A reference to a pointer:

int myInt = 0;
int &myRef = myInt;
int * pInteger = &myRef; //myRef is a reference to myInt. It can also give you the adress since that's what a reference is after all. 

Object to pointer:

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

int main()
{
   MyClass aClass;
   MyClass *pClass = &aClass;
}

I don't really think an example of the last one is needed...

[MisterEd]

thanks for both the replies!

I think it's slowly becoming clearer.

I was specifically interested in what you can and can't do with the static_cast and dynamic_cast operators...

So I think that's clearer now...

Cheers!