Re: Preventing memory and resource leaks with GDI Objects ???

"Tom Serface" <>
Fri, 12 Mar 2010 12:25:12 -0800
Hi Peter,

You can have different font objects if you want to have multiple fonts set
up. You are right about not deleting it when it is selected, but I don't
think you'd want that to happen. It typically make my font objects members
of the class so they are always persistent while the class object is...
Also, the assertion messages won't display for release builds which is
convenient, but if you get them in debug you would definitely want to fix
the problem.


"Peter Olcott" <> wrote in message

"Joseph M. Newcomer" <> wrote in message

As I indicated in an earlier reply, you cannot call DeleteObject on any
object which is
selected into a DC. It won't do the deletion.

Apparently this is no longer true under Windows 7. I spent several hours
re-arranging my code to meet your specification, and ended up having to
change it back. When I tested it against your prior post:

   If you have an object like CFont,
   you cannot create more than one
   font in it unles you call DeleteObject
   explivitly, or you will get an assertion failure.

and got an assertion failure when I removed the DeleteObject() for a CFont
object that was currently selected into a MemoryDC. This apparently shows
that DeleteObject() must work (at least for CFont) even if the CFont is
currently selected into a MemoryDC.

I had great difficulty trying to unselect the CFont and CBitmap objects.
(see my prior post) The only way that I knew to unselect a GDI object was
to select another GDI object. Since I had no other object, I tried to
select an empty one. This did not work.

It is you responsibility to make sure the
objec tis not seelected. I suggest SaveDC/RestoreDC to make sure any
object selected are

On Wed, 10 Mar 2010 17:49:56 -0600, "Peter Olcott"
<> wrote:

"Tom Serface" <> wrote in message

Yeah, that's it... Lots of time people forget to call
that. I turn on the GDI Objects column in Task Manager so
I can watch what my program is doing.

Can I execute CBitmap::DeleteObject() while the CBitmap is
currently selected into a DC?
(This is just before I create another CBitmap to be selected
into the same DC).


"Peter Olcott" <> wrote in message

"Peter Olcott" <> wrote in message

"Tom Serface" <> wrote in message

You will have to manage the resources somehow and
someplace, but I don't think it matters how or where.
I think you get like 5000 GDI resources before they run
out and I think that number is shared among programs.
Still converting them is no worse that destroying and
recreating them, but you'll have to destroy them
ultimately at some point, or, if the number is not to
arduous you could let them get recovered when the
program exits (but I'm not a big fan of that behavior).


The main thing that I want to do is to manually free any
memory or resources that the CBitmap object is using. I
don't know what resources it is using, and I don't know
how to free them.

I think that I got it: Simply call the inherited member

"Peter Olcott" <> wrote in message

I am have built a general purpose bitmap/image
handling class and want to add TextOut() capability to
this class. To do this I must convert some of my GDI
local function variables into GDI object member
variables. This means that I must be able to re-use
several GDI objects, instead of constructing them and
destroying them after a single use.

What issues are raised with resource and memory leaks
by using CDC and CBitmap objects? How are these
issues mitigated?

Joseph M. Newcomer [MVP]
MVP Tips:

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