Re: Common base class, reinterpret_cast, and aliasing

"Alf P. Steinbach" <>
Mon, 26 Mar 2007 10:11:19 CST
* Francis Glassborow:

You cannot use reinterpret_cast to change the type pointed to.

Well, you can in a special case, namely casting from POD* to
FirstMembersType* -- see paragraph something-or-other of the standard.

That's in support of old C code that emulated inheritance by containment.

With C++ inheritance the same is accomplished by a static_cast, that is,
instead of casting to an unrelated type, one casts to a base class.

Summing up the SPOCs (Special Pointer Ouch-what-was-that? Casts):

   * reinterpret_cast:
     Casting from POD* to FirstMembersType*.

   * dynamic_cast:
     Casting from Polymorphic* to MostDerived* by dynamic_cast<void*>.

   * C-style cast (note: can't be done using C++ named casts):
     Casting from Derived* to InaccessibleBase*.

Any good spaghetti soup should be generously spiced with one or more SPOCs.


- Alf

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