How do I create a "Virtual" Device Context? - C / C++ / MFC Discussion Boards

Re: Converting int to CString

Joaquín M López Muñoz14-Dec-01 4:59

Joaquín M López Muñoz

14-Dec-01 4:59

The following snippet of code is useful for writing numeric values into std::strings:

#include <sstream>
template <typename T> inline std::string tostring(const T& t)
{
  std::ostringstream ostr;
  ostr<<t;
  return ostr.str();
}

It must be trivial to adapt it for MFC CStrings.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Converting int to CString

Cam14-Dec-01 5:09

Cam

14-Dec-01 5:09

Ahh...yes, if I'm going to be doing a lot of conversions like that, a template would be a very good idea. But I don't really understand that code...I don't get what the binary shift does...but isn't there a more direct route?

~Cam Desautels (BinaryUprising.com)

Re: Converting int to CString

Alvaro Mendez14-Dec-01 5:16

Alvaro Mendez

14-Dec-01 5:16

Here's the most direct way, short of writing your own little function to do it:

CString Day;
Day.Format(_T("%d"), theTime.GetDay());

Regards,
Alvaro

Re: Converting int to CString

Cam14-Dec-01 5:48

Cam

14-Dec-01 5:48

Ahhh

, thank you.

~Cam Desautels (BinaryUprising.com)

How to Change the 'Caption' of a CPropertyPage

14-Dec-01 3:39

Hi there,

can somebody tell me how to Change 'Capiton' text of a CPropertyPage at Runtime.

this

m_psp.pszTitle = "Test";

or this

SetWindowText("Test");

dosn't work

Thanks

Claus

Re: How to Change the 'Caption' of a CPropertyPage

Joaquín M López Muñoz14-Dec-01 4:23

Joaquín M López Muñoz

14-Dec-01 4:23

Check MSDN article Q141487:How to Change the Text in the Tabs of a CPropertySheet.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Creating Excel files

14-Dec-01 2:21

Hello all!

Anybody knows how to create Excel (BIFF) files without Excel (directly write to file)?

I find source code only in Pascal Frown | :-(

((
Need C++ ...

Help!!! Smile | :)

))

Dmitry.

How do I create a "Virtual" Device Context?

Jon Hulatt14-Dec-01 2:04

Jon Hulatt

14-Dec-01 2:04

Hi,

I'm trying to write a bitmap conversion program that reads the bits of a bitmap file and writes them to another file in my custom format.

Because the user's bitmap might not be the required size, i want to scale it to cater for this eventuality.

The CDC::StretchBlt function is good for this, I've used it before. But how can I use this function, when i have no device contect to work with? I am not displaying the bitmap to the screen at any point.

How can i create memory device contexts from nowhere, that are suitable for my bitmap manipulation needs?

Thanks

Jon

Sorry to dissapoint you all with my lack of a witty or poignant signature.

Re: How do I create a "Virtual" Device Context?

Joaquín M López Muñoz14-Dec-01 2:11

Joaquín M López Muñoz

14-Dec-01 2:11

::CreateCompatibleDC(NULL) will do, I guess.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: How do I create a "Virtual" Device Context?

Jon Hulatt14-Dec-01 3:18

Jon Hulatt

14-Dec-01 3:18

Thanks for that info. It kind of works, but my stretchblt doesn't!
see:

CDC srcDC,destDC;

srcDC.CreateCompatibleDC(NULL);
destDC.CreateCompatibleDC(&srcDC);
destDC.SetStretchBltMode(COLORONCOLOR);
srcDC.SelectObject(m_Bitmap);
destDC.StretchBlt(0,0,WALLPAPER_SIZE_X,WALLPAPER_SIZE_Y,&srcDC,0,0,bm.bmWidth,bm.bmHeight, SRCCOPY);

int x,y;
for (y=0; y<WALLPAPER_SIZE_Y;y++)
{
    for (x=0;x<WALLPAPER_SIZE_X;x++)
    {
        m_PreviewPane.p_ImgData[ (WALLPAPER_SIZE_X * y) + x ]=destDC.GetPixel(x,y);
    }
}

OK. Let me explain what's happening here. I create a source device contect as you suggested, and a destination dc compatible with it. I select my source bitmap into the source device context (srcDC). I then try to strechblt, to scale the image to be WALLPAPER_SIZE_X by WALLPAPER_SIZE_Y in size. bm is a BITMAP structure, containing the source bitmap information.

Tracing through this in the debugger, everything seems valid. bm.bmWidth * bmHeight contain correct source size info, etc etc. But the stretchblt function returns 0 (which is a failure). GetLastError returns 0 as well, if i try that.

The nested loops at the bottom read the scaled bitmap into a previously allocated array. destDC.GetPixel always returns (COLORREF) 0xFFFFFFFF. if i change that line to use srcDC.GetPixel, It returns the proper data from my bitmap.

Basically, I have no idea why stretchblt is failing, and no ideas of how to trace through the problem.

Any help greatly appreciated.

Thanks

Jon

Sorry to dissapoint you all with my lack of a witty or poignant signature.

Re: How do I create a "Virtual" Device Context?

Jon Hulatt14-Dec-01 3:31

Jon Hulatt

14-Dec-01 3:31

I fixed this now by using the CBitmapDC class from this site!

http://www.codeproject.com/bitmap/bitmapdc.asp#xx49439xx

Thanks all

Sorry to dissapoint you all with my lack of a witty or poignant signature.

Accessing .MDB files

Cris14-Dec-01 2:02

Cris

14-Dec-01 2:02

Anybody knows if is possible install with VC++ code the MS Jet 3.5 to access MDB files ? How could I make this ?

Thanks,
Cristiano ...

Opening a new IE window

Rob Caldecott14-Dec-01 0:25

Rob Caldecott

14-Dec-01 0:25

I want to open a URL using a NEW IE window rather than any existing one being reused (same as SHIFT+clicking a link in IE). Currently, to open a URL, I simply use ShellExeute, e.g.:

ShellExecute(NULL, NULL, strURL, NULL, NULL, NULL);

However, calling the above twice means you blat the first URL with the second...

Re: Opening a new IE window

Philip Patrick14-Dec-01 14:21

Philip Patrick

14-Dec-01 14:21

First you need to determine what is the default browser on this machine. Check the "HKEY_CLASSES_ROOT\http\shell\open\command" in registry to find out it.
Next use your ShellExecute like this (in case the browser was MS Explorer):

ShellExecute(NULL, NULL, "iexplore.exe", strURL, NULL, NULL);

At least this way I did Smile | :)

Philip Patrick

ActiveX For Connecting Database

San13-Dec-01 23:50

San

13-Dec-01 23:50

Hi All,

I want to Create My own AciveX control which should work as teh usual database ActiveX Control.So Please give me the posssible suggessioon to create such a Component ie, what all are the Functions to be used for creating such an Application

Thanks in Advance

Sangeetha

Who have a example of setting a picture as background in CRichEditView?

white jungle13-Dec-01 23:03

white jungle

13-Dec-01 23:03

Please email to me a copy,Ok?
thank you !

Dummy dialog!

Rickard Andersson²⁰13-Dec-01 22:03

Rickard Andersson²⁰

13-Dec-01 22:03

If you create a edit box and the create a int varible for that. Then compile it and erase everything in the edit box, then a dialog box appears with a message that says "Write an integer" or something like that. But HOW TO GET AWAY FROM IT!! I don't want it!!

------------------------------
©0d3 ©®4©k3® - That's me! Smile | :)

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

Re: Dummy dialog!

Eugene Pustovoyt13-Dec-01 23:35

Eugene Pustovoyt

13-Dec-01 23:35

That is a work of the DDV function.
If you don't want have the message, you must fill edit box before close the dialog.

Best regards,
Eugene Pustovoyt
Big Grin | :-D

Sonork ID 100.10002:Yaumen

Re: Dummy dialog!

Nish Nishant13-Dec-01 23:47

Nish Nishant

13-Dec-01 23:47

Override OnOK() and put a zero into the member variable you have associated with the edit box so that DDV wont complain.

Nish

Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut

DLL questions

13-Dec-01 19:51

Is there a way to export an entire class in a .def file? I am working on a Unix-based project and there may be a need to port it to NT. I really want to avoid all the non-portable __declspec(dllexport) and all of those macros.

Also, could someone tell me how the heap manager works for DLLs? I've heard that all memory allocated from one DLL must be freed by that DLL because it may be using a different heap manager... That seems like a major problem if it's true. How do people develop plugin DLLs if that is the case? Do people provide destroy() methods on every object created by the DLL so that it can delete it?

Cheers,
Andy

Re: DLL questions

Nish Nishant13-Dec-01 20:10

Nish Nishant

13-Dec-01 20:10

Hi Andy

I cannot provide you a proper answer but sometimes people create their own heap from their DLLs. Thus those DLLs must delete their private heaps.

Look up HeapDestroy,HeapCreate

Nish

Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut

Re: DLL questions

Joaquín M López Muñoz13-Dec-01 23:57

Joaquín M López Muñoz

13-Dec-01 23:57

As far as I know, .DEFs do not provide any means to export a whole C++ class in one fell swoop. The closest you can get is exporting all of the member functions and variables, but this is pretty complicated due to name mangling. This article discusses the issue in greater detail and proposes alternative approaches.

As for the DLL heap manager, I'm afraid what you've heard is true: best way to avoid problems is ensuring that all that is allocated in the DLL is freed by the DLL itself (this post of mine explains what the issues with DLL private heaps are). The most usual technique to deal with this problem is to have exported factory methods like create() and their corresponding destroy()s, as you pointed out. An implication of this is that crossed DLL objects should not be created on the stack (i.e. their ctors should be declared protected).
If you still want to have classes that work safely across DLL boundaries but yet do not resort to create() methods, there's a solution: define and export new, delete and all ctors (including the copy constructor), and put the corresponding definitions in the .cpp file (so that they are not inlined). This way, all the allocation/deallocation works is ensured to be made inside the DLL.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: DLL questions

Nemanja Trifunovic14-Dec-01 5:03

Nemanja Trifunovic

14-Dec-01 5:03

Joaquín M López Muñoz wrote:
As for the DLL heap manager, I'm afraid what you've heard is true: best way to avoid problems is ensuring that all that is allocated in the DLL is freed by the DLL itself

Not at all. If you use the same version of CRT for the exe and the dll, you are safe. I do this all the time, and it works fine.

I vote pro drink Beer | [beer]

Re: DLL questions

Joaquín M López Muñoz14-Dec-01 6:12

Joaquín M López Muñoz

14-Dec-01 6:12

Well, my undersading of the situation (I explain it with much more detail here) is that the you're only safe if the CRT used is dynamically linked. Otherwise you end up with two (or more) CRT "instances", and two or more _crtheap private heaps. If I'm not wrong, it should be easy to prove this with a little test program/DLL combination producing a crash with statically linked CRTs.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: DLL questions

Nemanja Trifunovic14-Dec-01 6:37

Nemanja Trifunovic

14-Dec-01 6:37

Oh, I didn't look at your link. Sorry. Blush | :O

It is true that I always use dynamically linked CRT. That's why I never had any trouble.

I vote pro drink Beer | [beer]

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