Re: Cleaning Up Memory DC ?

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 15 May 2006 19:33:15 -0400

Message-ID:

<Oh7#pfHeGHA.2456@TK2MSFTNGP04.phx.gbl>

Robert A. wrote:

Hi,

Like this:

CBitmap* oldBitmap=memDC.SelectObject(&memBitmap);

// then when cleaning up

memDC.SelectObject(oldBitmap);
memDC.DeleteDC();

...is that really necessary ? What happens if I delete the memory DC with
the bitmap still in it ?

Thanks.

"Jonathan Wood" <jwood@softcircuits.com> wrote in message
news:ulJeQLHeGHA.1272@TK2MSFTNGP03.phx.gbl...

You need to select back the previous bitmap before deleting yours.

Note that CBitmap should delete itself when the function returns.

--
Jonathan Wood
SoftCircuits Programming
http://www.softcircuits.com

"Robert A." <invalid@invalid.org> wrote in message
news:OzzJ6FHeGHA.3556@TK2MSFTNGP02.phx.gbl...

Hi guys,

Take a look:

CDC memDC;
CBitmap memBitmap;

memDC.CreateCompatibleDC(...);
memBitmap.CreateCompatibleBitmap(...);

memDC.SelectObject(&memBitmap);

// do my drawing and blit

// cleanup

memDC.DeleteDC();

...when I clean it up do I have to select the CBitmap out of the memory
DC, do I have to delete the CBitmap ? I thought I once read that if I
delete the memory DC with the bitmap in it everything will be fine. I've
never really been sure about this.

Thank you.

PS - I'm using VC6 (SP5) on XP Pro

Robert:

Jonathan gave you the answer. You do have to select the bitmap out of
the DC. You do not have to delete the DC because the C++ destructor does
it (this "RAII" feature of C++ is very useful).

What happens if you do not select the bitmap ouut of the DC? I'm not
quite sure with a local object like your memDC (maybe it does not matter
in this case), but is a general rule that you should always do this.

David Wilkinson