C / C++ / MFC

Multiple inheritance in MFC

4-Jul-07 10:13

What is menat by the fact that windows handles are passed from one thread to another. What does it imply and when is it used? Also why is it that if the wrapping C++ windows objects are passed from one thread to another unexpected results occur.

Re: Passing Handles

David Crow5-Jul-07 3:07

David Crow

5-Jul-07 3:07

Passing a pointer to a CWnd object between threads is not safe since the CWnd object is not created by the other thread(s).

Thread uses local storage to map window handles, therefore object that was passed by a pointer may have (and most certainly do) different handle mapped to it. Use handle of a window attached to the CWnd object instead, and post/send messages using this handle.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

General DLL questions

ForNow4-Jul-07 9:52

ForNow

4-Jul-07 9:52

I am desgning an addition of Visual Studio makefile solution which contains only one project

I figure I'll make my code another project in C++ maybe use .NET (the orignal code/project/solution is C)

The project I am writting contains 3 classes

The first Class is Global as there is only 1 instance
by that I mean it should be able to be accessed by all functions within the project('s) there are locking mechinism to ensure single threading/proper access

I thought about writting this CLass as a DLL

Few questions come to mind

1) can I keep all three class in the same project

2) Should I export and import the entire class e.g.
Class _declspec(dllexport) DllClass
{
and conversely in the program using the DLL

Class _declspec(dllimport) DllClass
{
or maybe only certin methods or data members

3) do I need to decalre all members and methods
as static

4) Do I a LoadLibrary/GetProcAddress ??
if I use the dllexport/dllimport do I still need
to do a LoadLibrary/GetprocAddress call ??

Thankx in advance

tom groezer4-Jul-07 9:28

4-Jul-07 9:28

Why multiple inheritance is not corrected by using virtual inheritance of the COject class in MFC. The explanation in MFC is not very clear.

Mark Salsbery4-Jul-07 9:31

4-Jul-07 9:31

Have you seen this?

TN016: Using C++ Multiple Inheritance with MFC[^]

Mark

Mark Salsbery
Microsoft MVP - Visual C++

"Go that way, really fast. If something gets in your way, turn."

tom groezer4-Jul-07 10:19

4-Jul-07 10:19

Yes the MSDN tech note looks more of a specification. I would like to know more substantial information. And stuff like when there could be a case when MI has to be used. When I need to derive a class from two classes whose base class is CWnd. Why this scenario is going to fail?

David Crow5-Jul-07 3:13

David Crow

5-Jul-07 3:13

tom groezer wrote:
When I need to derive a class from two classes whose base class is CWnd. Why this scenario is going to fail?

This paragraph sums it up quite nicely:

The CObject::IsKindOf member function will not correctly determine the type of an object if it has multiple base classes. Therefore, you cannot use CObject as a virtual base class, and all calls to CObject member functions such as Serialize and operator new will need to have scope qualifiers so that C++ can disambiguate the appropriate function call. If you do find the need to use MI within MFC, then you should be sure to make the class containing the CObject base class the left-most class in the list of base classes.

By deriving from two CWnd classes, references to CObject member functions will be ambiguous, and will need to be dealt with explicitly.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Mark Salsbery5-Jul-07 10:54

how to use "OnNewDocument" from cview or cmainframe class

5-Jul-07 10:54

Thanks for that Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++

"Go that way, really fast. If something gets in your way, turn."

chaitannya_m4-Jul-07 9:18

chaitannya_m

4-Jul-07 9:18

Hi everyone,
I am using an activex control which i have inserted onto a formview of an mdi application.when i press File->new option i get a new window with the activex in it. Now i want to implement the same funtionality on a button press. i want the same results as that of File->New.How do i achieve it from the CFormView or the Cmainframe class.

Re: how to use "OnNewDocument" from cview or cmainframe class

Mark Salsbery4-Jul-07 9:47

Re: how to use "OnNewDocument" from cview or cmainframe class

4-Jul-07 9:47

Maybe something like this:

if (AfxGetApp()->m_pDocManager)
   AfxGetApp()->m_pDocManager->OnFileNew();

Mark

Mark Salsbery
Microsoft MVP - Visual C++

"Go that way, really fast. If something gets in your way, turn."

chaitannya_m4-Jul-07 16:21

chaitannya_m

4-Jul-07 16:21

O' My God that really worked like magic.. But how do i get a pointer to each view. I want to pass data to the view

Re: how to use "OnNewDocument" from cview or cmainframe class

Mark Salsbery5-Jul-07 6:53

5-Jul-07 6:53

I'm glad it worked. That's how MFC does it but it's using an undocumented variable (although
it's worked for as long as I can remember).

You probably could just give your button the id ID_FILE_NEW and it would have worked like magic
too Smile | :)

I thought for sure someone here would jump on me for that one LOL.

chaitannya_m wrote:
But how do i get a pointer to each view. I want to pass data to the view

Which view? The one just created?

The view just created should be the active view. To get the active view in MDI;

// this is the MFC example from the docs
 
CMDIFrameWnd *pFrame = 
             (CMDIFrameWnd*)AfxGetApp()->m_pMainWnd;
 
// Get the active MDI child window.
CMDIChildWnd *pChild = 
             (CMDIChildWnd *) pFrame->GetActiveFrame();
 
// or CMDIChildWnd *pChild = pFrame->MDIGetActive();
 
// Get the active view attached to the active MDI child
// window.
CMyView *pView = (CMyView *) pChild->GetActiveView();

To iterate through all views, one way is to iterate through all documents and their associated
views:

// Iterate through doc templates
 
POSITION DocTemplatePos = AfxGetApp()->GetFirstDocTemplatePosition();
while (DocTemplatePos != NULL)
{
   CDocTemplate *pTmpl = AfxGetApp()->GetNextDocTemplate(DocTemplatePos);
 
   // Iterate through documents for the current template
 
   POSITION DocPos = pTmpl->GetFirstDocPosition();
   while (DocPos != NULL)
   {
      CDocument *pDoc = pTmpl->GetNextDoc(DocPos);
 
      // Iterate through views for the current document
 
      // You could use CDocument::UpdateAllViews() or ...
 
      POSITION ViewPos = pDoc->GetFirstViewPosition();
      while (ViewPos != NULL)
      {
         CView *pView = pDoc->GetNextView(ViewPos);
 
         // Do something with the current view
      }
   }
}

Mark Salsbery
Microsoft MVP - Visual C++

"Go that way, really fast. If something gets in your way, turn."

C++ data structures

tom groezer4-Jul-07 8:54

CString::Replace Problem [modified]

4-Jul-07 8:54

What are the best books to start knowing about data structures from a begineer point of view with emphasis on hands on rather than the theoritical aspect? Any help would be highly appreciated.

Re: C++ data structures

Maximilien4-Jul-07 9:06

Maximilien

4-Jul-07 9:06

you will need a little bit of theoretical aspect to get you going.

I suggest this book :

Introduction to Algorithms ( by Thomas H. Cormen (Author), Charles E. Leiserson (Author), Ronald L. Rivest (Author), Clifford Stein (Author))

http://www.amazon.com/Introduction-Algorithms-Thomas-H-Cormen/dp/0262032937/ref=pd_sim_b_1_img/002-3852795-0448009[^]

Maximilien Lincourt
Your Head A Splode - Strong Bad

Re: C++ data structures

David Crow5-Jul-07 3:15

David Crow

5-Jul-07 3:15

tom groezer wrote:
What are the best books

What's good for others may not be good for you, and vice versa.

What's wrong with this?

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

lparsonson4-Jul-07 5:58

lparsonson

4-Jul-07 5:58

Hi all,

I'm trying to use the Replace function of the CString class, and it seems to be mostly fine, except it's ballsing up in one particular instance. I can't see what I'm doind different, but for some reason it doesn't like this:

CString PostCode;

m_PostCode.GetLine(0, PostCode.GetBuffer(m_PostCode.LineLength(0)), m_PostCode.LineLength(0));
PostCode.Replace("'", "''");

where m_PostCode is a member of the class this code is called from, being an instance of CEdit. I can't see anything that I'm doing differently to any other times I'm using the Replace function, but in this instance it just won't replace ' with ''.

Any ideas? I can't seem to find anything that suggests this is a known issue.

Thanks!

Louis.

Addendum:

I've noticed that it occurs with other CString/CEdit pairs like this, but if I copy the contents of the CString into a new CString, then run the Replace function of the new string it works fine. Am I missing something here?

-- modified at 12:05 Wednesday 4th July, 2007

Re: CString::Replace Problem

Mark Salsbery4-Jul-07 7:02

Re: CString::Replace Problem

4-Jul-07 7:02

Maybe try calling

PostCode.ReleaseBuffer(m_PostCode.LineLength(0));

before calling Replace()

Mark

Mark Salsbery
Microsoft MVP - Visual C++

"Go that way, really fast. If something gets in your way, turn."

lparsonson5-Jul-07 4:54

lparsonson

5-Jul-07 4:54

Yes, this worked like a charm!

Thanks a lot Mark, very speedy response!

Louis.

CStatic drawing interrupted... Worker, UI Threads????

Greg Ellis4-Jul-07 5:41

Greg Ellis

4-Jul-07 5:41

Hey Guys,

I have an MFC CStatic derived class that has a public member function Draw();. Draw uses GDI to draw stuff to the CStatic window. I call this Draw method from a multimedia timer (timeSetEvent) to continually update the display.

My problems is that When my main app is doing a lot of work the drawing is sometimes interrupted when I load files. So I put the lengthy process of loading files in a worker thread, but the drawing is still "jerky" when loading a file. Is there anything else I can do to ensure that my CStatic is always drawing? Is this something I need a user interface thread for?

Thanks,
Greg

Re: CStatic drawing interrupted... Worker, UI Threads????

Matthew Faithfull4-Jul-07 6:27

Matthew Faithfull

4-Jul-07 6:27

I'm not certain what you're trying to achieve here as genuinely constant redrawing would preclude you doing anything else anyway but you may have run up against a perenial problem with the MFC architecture. Essentailly anything done to the user interface is done on the main thread even if you call it from a worker thread. I would definitely suggest doing the file loading on a worker thread before getting into the absolute minefield of multiple user interface threads.

Nothing is exactly what it seems but everything with seems can be unpicked.

Re: CStatic drawing interrupted... Worker, UI Threads????

Greg Ellis4-Jul-07 6:35

Greg Ellis

4-Jul-07 6:35

Basically I have two music files playing (video and/or audio) I am showing a scrolling waveform as the song is playing in realtime (using GDI). I need this waveform to always scroll. When loading a file into the second player while the first player is playing the scrolling waveform is being interrupted. I just need that waveform to always be scrolling.

So MFC always draws from the main thread no matter what? That's no good for me. Is my only option UI threads?

Re: CStatic drawing interrupted... Worker, UI Threads????

Matthew Faithfull4-Jul-07 6:55

Matthew Faithfull

4-Jul-07 6:55

If you're doing that sort of thing and you want it really smooth I'd consider DirectX/OpenGL or perhaps just doing everything except the drawing in lower priority background threads and relying on having enough hardware under the bonnet to keep up. Double buffering may be your friend aswell when it comes to getting smooth display updates. i.e. draw it all to an off screen Bitmap and then blit that to the screen in one go. With a bit of manipulation perhaps you could do the scrolling in the bitmap memory aswell without having to redraw the old parts of the waveform.
It's a while since I did much PC based MFC but I certainly wouldn't have recommended it for the sort of app your describing when I did. Having said that there may be other issues causing your problems. Are you using a cyclic or fixed buffer that doesn't do any heap allocation while in use to store your waveform? If not you're going to get horrible performance glitches from the memory allocator for example.
Are you maxing out your current hardware? If you check the performance monitor while your app is the only one running and it's flat out at 100% then either you've got some ineffecient code or you're trying to push your hardware beyond what it can achieve. Ultimately all such jolts and flickers are down to something being blocked either by synchronisation or a bandwidth limit somewhere. Unless something is resource stealing. In that regard watch out for the Quicktime tray icon app if you use DirectX it can steal the graphics card from you every few seconds and cause horrible jitter.

Nothing is exactly what it seems but everything with seems can be unpicked.

Re: CStatic drawing interrupted... Worker, UI Threads???? [modified]

Mark Salsbery4-Jul-07 7:08