Re: Polymorphism

David Wilkinson <>
Mon, 17 Dec 2007 07:22:55 -0500
Alamelu wrote:

Thanks for your clarification.

1) C++ doesn't require the user to explicitily say dynamic_cast for derived
to base conversion. Is it users best pratise to say dynamic_cast during such

Base *pB1 = new Base;
Derived *pD1 = new Derived;
pB1 = pD1; // Doesn't require explicite dynamic_cast

When is the user supposed to explicitily say dynamic_cast, something like this
Base *pB = dynamic_cast<Derived*>(&D)

2) Why does c++ allow static_cast for base to derived conversion, when
actually will this be needed?


1. dynamic_cast is used for conversion from Base* to Dereived*. No cast
is necessary for converting Derived* to Base*.

dynamic_cast is never *needed*. You can always use static_cast if you
are *sure* of the type.

2. Not sure what your question is here. static_cast is generally
applicable where the conversion is (or might be) correct according to
the language. Converting Base* to Derived* is one such usage. Uses of
static_cast are portable.

OTOH, uses of reinterpret_cast are generally non-portable; for example
conversion of a pointer type to int.

David Wilkinson
Visual C++ MVP

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