Re: Channel 9 video: Visual C++ 10 is the new 6

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sun, 23 Nov 2008 14:33:05 -0600

Message-ID:

<kffji49mvnhdgfgip4n0qephp24fau0b0b@4ax.com>

On Sat, 22 Nov 2008 00:09:19 +0100, "Giovanni Dicanio"
<giovanniDOTdicanio@REMOVEMEgmail.com> wrote:

I recall reading that when they invented MFC they wanted to avoid "bloated"
v-tables with lots of virtual functions to speed things up; but probably
with dual-core CPUs with clock at 2-3 GHz becoming mainstream this is not a
problem anymore.

It wasn't the clock speed so much as it was memory. Consider a vtbl with
(say) 1000 slots multiplied by several dozen derived classes in MFC alone,
most of which would override just a handful of virtual functions. Message
maps are a *lot* more efficient in terms of space. Also, modifying a base
class message map doesn't always require recompiling every derived class,
while things are more complicated for virtual functions.

Undoubtly, I think that the virtual methods are more elegant than message
maps.

Every MFC programmer should be able to describe what's wrong with the
following and how to fix it:

MyListBox c_lb;
....
CListBox& lb = c_lb;
lb.InsertString(...);

Or more generally:

MyWindow mw;
....
CWnd& w = mw;
w.OnSomeMessage(...);

--
Doug Harrison
Visual C++ MVP