Re: Does anyone know what this text means? (related to C4251 warning)

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"Doug Harrison [MVP]" <dsh@xxxxxxxx> wrote in message
news:pbcki3p750upnqmsi78sdb1a91qep4kvjo@xxxxxxxxxx
On Thu, 1 Nov 2007 08:38:35 -0500, "Ben Voigt [C++ MVP]"
<rbv@xxxxxxxxxxxxx> wrote:

BTW David's way is what the article is referring to. Inheritance is done
via aggregation and implementing the same public interface.

That's not "inheritance" in the C++ sense of the word.

It isn't type derivation, but it is inheritance in the OOP sense of the
word.

[snip]

Doug's way, although it might avoid the warning, does all the things the
warning is designed to discourage (exports class members, violates
one-definition rule, etc).

It doesn't just "avoid the warning". What I talked about in the last
paragraph of my message lets you use the class as a real C++ class,
instead
of some clumsy COM simulation. Not everything is a nail.

That's misleading. What you could say is "it's a real Visual C++ 8.0 class
dynamically linking the debug runtime library, with 4-byte packing, and
STL_CHECKED_ITERATORS=0"... if those are in fact the compiler options used.
Whereas the source code for a real C++ class can be used in any C++ program
and compiled with any C++ standard-compliant compiler.

[snip]


Where did what I posted violate the ODR, BTW?

The definition of class X is different between the provider and consumer.

Every single use of dllimport/dllexport on a type violates the ODR.
Sometimes you can get away with it, sometimes not.


--
Doug Harrison
Visual C++ MVP


.

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