For some reason your release build is linked with the debug version of the MFC. You should find out why and fix that. A possible reason is linking with another DLL that depends on the MFC DLL and is a debug version itself.
With proper code, a debug build should also assert at that point (window handle NULL). However, it would not assert if the handle is not NULL but invalid (uninitialised variable). But then you usually get other runtime errors.
The assert macro is enabled in both the release and debug versions of the C run-time libraries when NDEBUG is not defined. When NDEBUG is defined, the macro is available but does not evaluate its argument and has no effect. When it is enabled, the assert macro calls _wassert for its implementation. Other assertion macros, _ASSERT, _ASSERTE and _ASSERT_EXPR, are also available, but they only evaluate the expressions passed to them when the _DEBUG macro has been defined and when they are in code linked with the debug version of the C run-time libraries.
My tip: Use them often (e.g. on top of functions for parameter checking and with function return values when there is no error handling). They are simply ignored in release builds but can save you a lot of debugging time.
How do I create a totally new MFC Control type? I take it that I have to create and register a new Window Class, with it's own Message Procedure, and thereafter write my own MFC/CPP around it as a Husk. Is there any way of deriving my own custom controls from CWnd directly and using the message map Macro's? As a new type of control it will need a resource to display it on screen, etc. How do I tie all this together.
It depends what you want your class to do. Take a look at the Hierarchy Chart | Microsoft Docs[^] and see if there is an existing control that you can derive from (even if it is CWnd), since the base class will provide lots of functionality.
Because all MFC controls are CWnd based you should use that as base class too. Then add the painting (OnPaint, OnEraseBackground), register the window class and add control specific message handlers as necessary.
I'm new to MFC and after passing several hours trying to solve a problem (that might seem simple to most of you), I decided to post my question here in order to get your help and hints.
I'm developing an MFC (C++) application using Visual Studio 2017. The application contains a main CDialog to communicate with a 2D Laser sensor using TCP/IP and to plot the points detected by the sensor on screen in real time (this is done on an IDC_PICTURE element with OnPaint() as the following:
// I create the pDC, memDC and the compatible device/bitmap
CDC* pDC = m_Picture.GetDC(); // m_picture is a member CStatic element in the main CDialog class
bmp.CreateCompatibleBitmap(pDC, PicW, PicH); // PicW, PicH are the width and height of the associated CRect member object in the class // After that, I get the points to plot in order to write them to my memDC//then, I copy the memDC to the device and delete the memDC, release the pDC
pDC->StretchBlt(0, 0, PicW, PicH, &memDC, 0, 0, PicW, PicH, SRCCOPY);
This previously mentioned code is working very well without problems with the main dialog.
Long story short, my problem is the following:
On that same dialog, I created a button that opens a secondary modeless dialog that contains another IDC_PICTURE element. The main goal of the secondary dialog is to plot a delayed version (t-n) of the points seen by the Laser sensor. My main problem is that I am not being able to show anything on the secondary IDC_PICTURE. Is it wrong to do the same thing applied on the main dialog (on another IDC_PICTURE, with anothe pDC and memDC)?
The secondary dialog is defined in a separate class of which I have created an instance in the (first) main CDialog class.
I have been looking everywhere on solutions that could look similar to my problem, but I haven't found anything. What exactly am I missing?
PS. sorry if my problem description isn't clear enough. My code is getting too big to be copied/pasted.. I'd be very happy if you have any hints / questions that might make me find the solution..
I guess that you trigger it in the main dialog when new data has been received from the sensor. You have to do it similar for the second modeless dialog (e.g. by triggering a repaint after new data has been passed).
I actually don't know what this message is or how to handle it.
Then you are definitely going to have problems, especially if you are trying to paint the controls at other times. If you do not understand how Window painting works in Windows then you will continue to have problems. I suggest you look for some tutorials on how it is done.
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