C / C++ / MFC

Niklas L22-Jul-10 6:03

22-Jul-10 6:03

Actually there are scenarios where this is useful, like exposing methods from private and protected inheritance. A sort of forwarding.

class Base
{
public:
    string name() const;
};
class Derived : protected Base
{
public:
    string name() const { return Base::name(); }
};

Edit: The reason being of course to change the access level of a method.

Moak22-Jul-10 14:30

Moak

22-Jul-10 14:30

Just a thought: As someone who prefers composition over inheritance, I can hardly think of a case using protected/private inheritance. Not sure when I used it last time. Also see Stackoverflow[^].

Cheers Smile | :)

/Moak

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Aescleal22-Jul-10 20:15

22-Jul-10 20:15

It's more likely to be used to open up a protected function in the base class. I've seen that a lot in MFC code and it gives me the willies:

class base
{
    protected:
        virtual void a();
};

class derived : public base
{
    public:
        virtual void b()
        {
             a();
        }
};

You can also do it using using declarations but that's scary as well.

Cheers,

Ash

Moak23-Jul-10 0:25

Moak

23-Jul-10 0:25

Begs for a redesign/refactoring of the interface, if you ask me. Big Grin | :-D

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Niklas L22-Jul-10 22:44

22-Jul-10 22:44

I have actually never inherited in any other way than public as far as I can recall, but elevating the access level of a function does not need protected or private inheritance though.

Aescleal22-Jul-10 20:17

22-Jul-10 20:17

In this case I'd almost certainly rewrite the base class to provide what I want than hack the derived class. I know there are social reasons why it may be preferable to forward calls like that but it leaves a bad taste in my mouth.

Actually the real bad taste is implementation inheritance but in the world of GUI frameworks people are very stuck in the early 90s.

Cheers,

Ash

Niklas L22-Jul-10 23:11

22-Jul-10 23:11

Unfortunately, far from all classes can be rewritten (for several reasons other than social)

I have used this for access level elevation a couple of times (probably more than two) in about 17 years, so it's not really common, but I believe there is a use for it.

There are of course also other reasons to implement a method in terms of the base class implementation. Code generation tools does it all the time. Mostly along with ToDo comments.

Aescleal23-Jul-10 4:13

23-Jul-10 4:13

The only time you can't rewrite a base class is when you haven't got the code for it. The rest of the reasons are all social.

Just out of interest anything you can do with inheritance (of concrete base classes) in the context of code generation you could a lot more cleanly do with composition. MFC, as one example, wouldn't be such a mess of deriving from concrete classes if they'd have done that. However there wasn't the C++ expertise around in 1991 that there is now so you can't blame them in hindsight.

Cheers,

Ash

Niklas L23-Jul-10 11:36

23-Jul-10 11:36

I think the social bit got lost in translation. I was looking upon social as political, and not economical, which I assume now you include in social?

Aescleal23-Jul-10 19:36

how to play audio and video

23-Jul-10 19:36

I tend to include economic reasons as social, although as a supposed engineer perhaps I shouldn't.

Cheers,

Ash

MKC00222-Jul-10 3:11

MKC002

22-Jul-10 3:11

In MFC application, I want to play audio and video file on my dialog. Audio/video file like mp3,vob,wav,flv,wma,dat,avi etc
Is there any example available

Re: how to play audio and video

Cool_Dev22-Jul-10 3:19

Cool_Dev

22-Jul-10 3:19

Directshow is one simple option. You can play any media file, provided its codec is present in the system.

refer this CP article

msdn documentation here

Its now part of windows sdk, no need to use DirectX sdk 9.0.

Re: how to play audio and video

MKC00222-Jul-10 23:18

MKC002

22-Jul-10 23:18

Thanks for the link
It's working for avi and mp3 files
is there any sample for other audio/video files like dat,vob,slv

Re: how to play audio and video

Cool_Dev3-Aug-10 2:24

Cool_Dev

3-Aug-10 2:24

well.. directshow is not a format bounded architecture. You just need to have the codec for the audio/video format you need to play. Directshow's intelligent connect mechanism will do the rest for you.

Making a driver WITHOUT wdf [Solved myself!]

Iain Clarke, Warrior Programmer22-Jul-10 2:51

Iain Clarke, Warrior Programmer

22-Jul-10 2:51

Edit: Solved myself, after a flash of inspiration!
Just removed the "KMDF_VERSION_MAJOR=1" line from SOURCE file.
Sigh...

-------------------

Good afternoon all.

I'm trying to make a driver to run on XP. I've trawled the web, and ended up with the following ultra minimal code:

#include <ntddk.h>

NTSTATUS driverCleanupFunction (IN PDRIVER_OBJECT pDriverObject);


NTSTATUS DriverEntry (IN PDRIVER_OBJECT pDriverObject, IN PUNICODE_STRING strRegistryPath)
{
	strRegistryPath = strRegistryPath;
	pDriverObject->DriverUnload = driverCleanupFunction;
	DbgPrint ("Iain: Driver starting\n");
	return STATUS_SUCCESS;
}

NTSTATUS driverCleanupFunction (IN PDRIVER_OBJECT pDriverObject)
{
	pDriverObject = pDriverObject;
	DbgPrint ("Iain: Driver stopping\n");
	return STATUS_SUCCESS;
}

As you can see it doesn't do a whole bunch. I do plan on adding some functionality!

But I can't run it on my XP VM (you didn't expect me to mess about on a real machine to start with?), as the DDK's build has linked it with WDFLDR.sys.
I'm not using any of the WDF functionality. It's not installed on my basic XPsp3 VM (or the real XPsp3 machine to my left).

I've downloaded the DDK pretty recently (7600.16385.1).

I suspect I just have to use some sort of "#define NO_WDF_PLEASE" constant, but I have no clue what.

Any hints?

Cheers,

Iain.

I am one of "those foreigners coming over here and stealing our jobs". Yay me!

modified on Thursday, July 22, 2010 9:03 AM

PrintPreview in MFC SDI Application

tony_Udz21-Jul-10 23:05

tony_Udz

21-Jul-10 23:05

Hi,

I am facing problem in my project and to simulate this problem I have reproduced in sample application.

I have created a SDI MFC app with doc view architecture.
I am facing problem while Print preview.
While I close the preview Window, application hangs and after some time it crashed.
Following is the implementation of OnFilePrintPreview and OnEndPrintPreview:

void CSampleView::OnFilePrintPreview()
{
// must not create this on the frame. Must outlive this function
CPrintPreviewState* pState = new CPrintPreviewState;

// temporary remove the parent so that the DoPrintPreview() uses the mainframe
ShowWindow(SW_HIDE);

SetParent(NULL);

//AfxMessageBox("Before DoPrintPreview");
if (!DoPrintPreview(AFX_IDD_PREVIEW_TOOLBAR, this,
RUNTIME_CLASS(CPreviewView), pState))
{
//AfxMessageBox("After DoPrintPreview IF");
// In derived classes, reverse special window handling here for
// Preview failure case

TRACE0("Error: DoPrintPreview failed.\n");
AfxMessageBox(AFX_IDP_COMMAND_FAILURE);
delete pState; // preview failed to initialize, delete State now
}

//AfxMessageBox("After DoPrintPreview");

}

void CSampleView::OnEndPrintPreview( CDC* pDC, CPrintInfo* pInfo, POINT point, CPreviewView* pView)
{

pView->DestroyWindow();

SetParent(AfxGetApp()->m_pMainWnd);

AfxGetApp()->m_pMainWnd->ShowWindow(SW_SHOW);
AfxGetApp()->m_pMainWnd->UpdateWindow();

}

Please provide input on this if anybody has any idea on this.
Thanks in Advance!!

Regards,
Tony

Re: PrintPreview in MFC SDI Application

ErnestoNet22-Jul-10 7:23

ErnestoNet

22-Jul-10 7:23

Had this problem before. Dont remember exactly how I solved.

I think that, OnEndPrintPreview, call:

SetDlgCtrlID(AFX_IDW_PANE_FIRST);

I have an article, http://www.codeproject.com/KB/miscctrl/BasicAdminCP.aspx
In the utils folder, ViewPrintPreview.cpp there is code working.

it´s the journey, not the destination that matters

Re: PrintPreview in MFC SDI Application

tony_Udz22-Jul-10 18:54

tony_Udz

22-Jul-10 18:54

Thanks for your response.
It helped me partailly but I guess now I can solve that.

Once again thank you for your response!

Regards,
Tony

Re: PrintPreview in MFC SDI Application

ErnestoNet23-Jul-10 2:19

ErnestoNet

23-Jul-10 2:19

You´re welcome.
I spent a LOT of time making print preview work for different controls and situations.

it´s the journey, not the destination that matters

Wrapper Class

Benjamin Bruno21-Jul-10 22:39

Benjamin Bruno

21-Jul-10 22:39

Hi
How to create a wrapper class for an existing class?

thanks : Sniff | :^)

Sauro Viti21-Jul-10 22:44

Sauro Viti

21-Jul-10 22:44

Your question is too generic: it depends on your scenario.

Which kind of class do you want to wrap (COM object, ActiveX, ...)?
What is your target?

Niklas L21-Jul-10 23:01

21-Jul-10 23:01

Typically what you do is to create a new class exposing methods of an interface that you are interested in. Depending of what you want to wrap, the interface might be a C header file, a COM interface or another class, etc. The wrapper class often manages resource allocation and deallocation of the exposed interface, and this is often the most valuable aspect of wrapping. You can also make it easier to use the interface by bundling methods together as you see fit, removing rarely used parameters and such.

«_Superman_»21-Jul-10 23:12

«_Superman_»

21-Jul-10 23:12

As a member of the wrapper class, an object of the existing class is created.
The member object is then initialized in the constructor of the wrapper class.
From the methods of the wrapper class, the methods of the existing class will be called using the member object.

«_Superman_»

I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Aescleal21-Jul-10 23:13