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Re: Patch - wrong casts, no cleanup in destructor

From: Dmitry <wipedout_at_yandex.ru>
Date: Fri, 04 Feb 2011 09:37:25 +0300

Hey.

03.02.2011, 22:18, "Stefan Küng" <tortoisesvn_at_gmail.com>:
>>  - C-style casts where static_casts would be safer (compiler will show an error if a cast is not possible in case of static_cast, but not in case of C-style cast)
> static_cast doesn't work here because ppv is a void pointer.

LOL, this one is very ironic. Yes, static_cast won't work in this very case, but not because "ppv" is of type "void**". "*ppv" is of type "void*", so any object pointer can be copied there even without an explicit cast.

The real reason why static_cast won't work here is because class CShellExt inside TortoiseOverlays only inherits from IShellIconOverlayIdentifier and so it doesn't implement most of the interfaces listed in the if-else comparison chain. In some branches of the if-else comparison C-style cast will work as reinterpret_cast (as in "shut up, stupid compiler, I demand you extinguish fire with kerosene") and the caller will be given a non-null pointer to an object that doesn't implement the requested interface.

That code is copied from CShellExt in TortoiseShell, where the class is indeed inherited from all those interfaces. static_cast works there - I copied that code into a separate project to test. If static_cast was used initially the compiler would prevent such unfortunate use of copy-paste.

Best wishes.
Dmitry.

> Stefan
>
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Received on 2011-02-04 07:37:39 CET

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