Re: Specification of the problem. - C / C++ / MFC Discussion Boards

Michael Dunn10-Dec-01 16:41

10-Dec-01 16:41

The difference is that the first version has a non-const this pointer, so the returned value is a reference to an array value. That means you can change the contents of the Matrix, such as:

void f ( Matrix& m )
{
  m(2,5) = 3.14;  // calls double& Matrix::operator()
}

But in the second, this is const, thus the return value cannot reference the object. So this code is illegal:

void g ( const Matrix& m )
{
  m(4,1) = 42;  // calls double Matrix::operator() const
                     // error, can't assign to a plain double
}

--Mike--
http://home.inreach.com/mdunn/
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How can I make address of a member-function (__cdecl *)???

10-Dec-01 9:39

One function accepts an address of another as a parameter, I want to use a member-function of a class as the parameter, but I have this error: cannot convert parameter 1 from 'void (void)' to 'int (__cdecl *)(void)'

There's an example (MVSC++6) (Compilation gives the error)

typedef void(*fntFunc)();

class CMy
{
public:
CMy(){};
~CMy(){};
void Func();
};

void CMy::Func(){}

void CallIt(fntFunc fn)
{
fn();
}

int main(int argc, char* argv[])
{
CMy my;
CallIt(my.Func);
}

Thanks a lot. http://sjcomp.virtualave.net

Re: How can I make address of a member-function (__cdecl *)???

Joaquín M López Muñoz10-Dec-01 10:05

Joaquín M López Muñoz

10-Dec-01 10:05

Two issues here:

Your Func method has to be static if you want to pass it on as a regular function pointer. Check Mike Dunn's C++ FAQ for details.
Once you hace declared your method static, you can set its calling convention like this:
```
class CMy{
  ...
  static void __cdecl Func();
};
```

Hope this helps.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Here's how

Ravi Bhavnani10-Dec-01 10:13

Ravi Bhavnani

10-Dec-01 10:13

Joaquín is right.

A standard solution to this common problem is to have 2 static items: (1) a pointer to a CMy object and (2) a function of the type you expect to pass as a parameter, eg:

static CMy* pMy = NULL;
 
static void StaticFunc()
{
  if (pMy != NULL) {
     pMy->Func();
  }
}

Then, have a CMy object set the static pMy to "this" before you pass StaticFunc() to CallIt(), eg:

CMy my;
pMy = &my;
CallIt (&StaticFunc);

Hope this helps.

/ravi

"There is always one more bug..."
ravib@ravib.com
http://www.ravib.com

Re: How can I make address of a member-function (__cdecl *)???

Ravi Bhavnani10-Dec-01 10:15

Ravi Bhavnani

10-Dec-01 10:15

I'm probably stating the obvious here, but my solution is slightly different from Joaquin's in that CMy's member function doesn't have to be static.

/ravi

"There is always one more bug..."
ravib@ravib.com
http://www.ravib.com

Re: How can I make address of a member-function (__cdecl *)???

Fazlul Kabir10-Dec-01 10:40

Fazlul Kabir

10-Dec-01 10:40

This should help..
INFO: Creating a Function Pointer to a C++ Member Function

// Fazlul

Get RadVC today! Play RAD in VC++
http://www.capitolsoft.com

Specification of the problem.

10-Dec-01 12:15

Thanks everyone for assistance, it solves the problem as I state it, but the situation I have is like this: I have a function which is predefined and this function takes a callback function as parameter. I'm creating class, each copy of which should have it's own call back function. (I'm using glut (for OpenGL) and I'm creating window class whcih uses glut functions, and I'd like glut call a member-function of the class.)

Let's say I have function
void CallIt( void(*func)(ini,int)) );

And I can not change it.

The problem is that I want to have a couple of classes which are waiting for the callback, and CallIt doesn't provide inforamtion what class set the callback Cry | :((

(

And as understood I can use only static functions or global functions and I can use class specific functions to link with CallIt.

I dont' see a way to do it, right now, but hope I'm wrong.

Regards, Alexander.

Re: Specification of the problem.

Joaquín M López Muñoz10-Dec-01 22:33

Joaquín M López Muñoz

10-Dec-01 22:33

Well, the standard solution is to provide a pointer to the class when you register your function (this is usually called a callback parameter): this callback parameter can be used by your static callback function to transfer the function call to the actual class responsible for doing the job.
Unfortunately, GLUT seems not to provide any mechanism to store any callback parameter on callback registration. But do not abandon any hope, there's still a way (if a little convoluted) to retrieve the class, via glutGetWindow(). The idea is having a map associating windows IDs with classes, and having the static method dispatch to the appropriate class using this map. This is s little piece of pseudocode that describes the process using the glutMouseFunc callback:

class MyGlutWindow{
private:
  static std::map<int,MyGlutWindow*> ID2MyGlutWindow;
public:
  MyGlutWindow(){
    ...
    ID2MyGlutWindow[glutGetWindow()]=this; // associates current GLUT window ID to myself
  }
  static void __cdecl glutMouseFuncCallback(int button,int state,int x, int y){
   ID2MyGlutWindow[glutGetWindow()]->doGlutMouseFuncCallback(button,state,x,y);
  }
  void doGlutMouseFuncCallback(int button,int state,int x, int y){
    ...
  }
};

There are some details missing (cleanup when windows are destroyed, for instance), but the basics are here, I hope you get the idea and find it useful.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Specification of the problem.

11-Dec-01 6:15

Thanks a lot! It really helps Smile | :)

Have not thought about such aproach. Thanks.

Regards, Alexander

Re: char* byte* DLL-VC++ and Delphi Please help !

Joaquín M López Muñoz10-Dec-01 9:37

Joaquín M López Muñoz

10-Dec-01 9:37

Well I'm no Delphi expert, but I guess the best thing to do is having the array allocated (even statically) on the Delphi client. Just like this:

var
  myarray packed array [1..801] of char;
  ...
begin
  ...
  TheDLLFuntion(...,@(myarray[1]),...);
  ...
end;

where TheDLLFunction accepts a char * (a ^char in Delphi).
As I said before, I'm no expert in Delphi, so forgive me if this is off-topic (or simply incorrect).

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

PS: Has anybody had problems trying to reply other posts? For some reason I'm not being able and have been forced to post the reply on a new thread.

USB support for VC++????

Johnny_8910-Dec-01 8:23

Johnny_89

10-Dec-01 8:23

Are there API functions available to access a USB port? Just as we have CreateFile() for the serial port?

CMenu::CheckMenuItem(...)???

Rickard Andersson²⁰10-Dec-01 7:38

Rickard Andersson²⁰

10-Dec-01 7:38

I wonder how to check an item in a menu?

(this code in OnInitDialog())
CMenu menu;
menu.LoadMenu(IDR_POPUP);
menu.CheckMenuItem(ID_POPUP_ALLTIDVERST,MF_CHECKED | MF_BYCOMMAND);

Isn't the the menu allready created from start?
Or do I have to overriden some function?

It wont be selected?
The menu is a tray menu...

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

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

Re: CMenu::CheckMenuItem(...)???

Christian Graus10-Dec-01 11:12

Christian Graus

10-Dec-01 11:12

This menu is being created and then destroyed right away. To check or uncheck an item, you need to use the OnCmdUI handler, or you need to check it in OnContextMenu, just before you show it.

Christian

After all, there's nothing wrong with an elite as long as I'm allowed to be part of it!! - Mike Burston Oct 23, 2001

Sonork ID 100.10002:MeanManOzI live in Bob's HungOut now

Re: CMenu::CheckMenuItem(...)???

Ravi Bhavnani11-Dec-01 5:18

Ravi Bhavnani

11-Dec-01 5:18

If you're not using ON_COMMAND_UI handlers (i.e: if you have a standalone menu or are building a dialog based app), you can use CMenu::ModifyMenu() to check/disable/gray a menu item.

/ravi

"There is always one more bug..."
ravib@ravib.com
http://www.ravib.com

char* byte* DLL-VC++ and Delphi Please help !

mimi10-Dec-01 7:36

mimi

10-Dec-01 7:36

My function (in my DLL-VC) have to return to the Delphi client program a array of 801 characters . BYTE arr[801]
that 801 can include everyone from the characters that exist and even NULL s

since Delphi have not type BYTE* or CString

The problem:

If my function gets char* and try to write into,
it gives error "access invalidation..." at Delphi

If the function returns char* ,
the Delphi program don't know where the string terminate because that string can contain some NULLs that confuses the program.

How it possible that the function vc++ could to give array of characters at constant length (as 801 bytes) for Delphi program ???

Create a CBitmap object, draw in it, save in (.bmp file)

Remi Morin10-Dec-01 7:34

Remi Morin

10-Dec-01 7:34

in my Document class the function serialize... I wan,t to save my data as a monochrome bitmap so I do

void CWoopDoc::Serialize(CArchive& ar)
{
	if (ar.IsStoring())
	{
		//I need a bitmap object
      CBitmap BitMapTemp;
      //a device context to draw on it
      CDC CBitmapDC;  
      CBitmap* OldBitMap;
      
      //initialisation of the dc
      CBitmapDC.CreateCompatibleDC(NULL);
      
//here I'm not sure of that... I guess
      
      //I create an array of bytes for the bitmap
      void * bitmapbitstemp = malloc( Size_X*Size_Y / sizeof(BYTE));
      
      //here I create the bitmap
      BitMapTemp.CreateBitmap(Size_X,Size_Y,1,1,bitmapbitstemp);

		//I send my bitmap to the DC and save the old one
      OldBitMap = CBitmapDC.SelectObject(&BitMapTemp);
     
     //(... I draw in it)
     
      //now I wan't to save it
      
      //I need a bitmapInfoHeader and A bitMap File Header
      BITMAPFILEHEADER BmpFileH;
      BITMAPINFOHEADER bmpInfoH;
      BITMAP bm;
      BitMapTemp.GetBitmap(&bm);     //<--here I'm unable the get the bitmap bits, but the creation return true!!!
      BmpFileH.biBitCount = bm.bmBitsPixel;
      BmpFileH.biCompression = BI_RGB;
      BmpFileH.biHeight = bm.bmHeight;
      BmpFileH.biPlanes = bm.bmPlanes;
      BmpFileH.biWidth = bm.bmWidth;
      BmpFileH.biSizeImage = BI_RGB;
      BmpFileH.biClrUsed = 0;
      BmpFileH.biClrImportant = 2;
      BmpFileH.biXPelsPerMeter = 0;
      BmpFileH.biYPelsPerMeter = 0;
      BmpFileH.biSize = sizeof(BmpFileH);

      bmpInfoH.bfOffBits = sizeof(bmpInfoH)+sizeof(BmpFileH);
      bmpInfoH.bfSize = bm.bmWidthBytes;
      bmpInfoH.bfType = ('M' << 8 | 'B');
      bmpInfoH.bfReserved1 = 0;
      bmpInfoH.bfReserved2 = 0;
      
      ar.Write(&BmpFileH,sizeof(BmpFileH));
      ar.Write(&bmpInfoH,sizeof(bmpInfoH));
      //here I need to write the byte them self... but bm.bmBits are always NULL
      ar.Write(bm.bmBits,bm.bmWidthBytes);  
      
      //destroying...
      CBitmapDC.SelectObject(OldBitMap);

      delete bitmapbitstemp;
   }
	else
	{
		// TODO: add loading code here
	}
}

BitMapTemp.Serialize(ar); //do not work...

any help will be fine...

Remi Morin
Rmorin@Operamail.com
Remi.Morin@Lyrtech.com

Re: Create a CBitmap object, draw in it, save in (.bmp file)

Bill Wilson10-Dec-01 7:42

Bill Wilson

10-Dec-01 7:42

Are you sure you're drawing in the correct map? Using CBitMapDC->LineTo etc?

It sounds as if there is nothing in BitMapTemp.

Hope this helps,
Bill

How to insert characters in a CRichEditViewed application?

davilism10-Dec-01 7:33

davilism

10-Dec-01 7:33

Hi, all, I have problem doing a replacement of text in my text editor using
CRichEditView class. I want to replace some text that the user types but
have no idea what functions I can use. I am aware of the
GetRichEditCtrl( ).Paste, which can paste a copied text at the position of
the caret, but how do I insert a not clipboard stuff, such as a CString
object.

Peace, no war

How to move the caret in CRichEditViewed application?

davilism10-Dec-01 7:32

davilism

10-Dec-01 7:32

Hi, all, I'm programming a text editor with spell check using MFC's
CRichEditView class. Anybody knows how to move the caret?
My usage is that when the user types a word that is found spelled wrong, the
editor has to move its caret to the word's beginning position and replace
the word. I'm new to Windows programming. I have no idea how to move the
caret and replace the word. I tried typing SetCaretPos( ) and ShowCaret( )
in the CMainFrame derived from CFrameWnd, but it didn't actually move the
caret. The caret seemed to change its postion to the one I set in
SetCaretPos( ), but when I used GetRichEditCtrl( ).Paste to paste a text for
a test, the text was pasted at the position as if I didn't do the
SetCaretPos( ).

Peace, no war

Re: How to move the caret in CRichEditViewed application?

squizz10-Dec-01 10:05

squizz

10-Dec-01 10:05

try :
GetRichEditCtrl().SetSel(caretPos, caretPos);

Re: How to move the caret in CRichEditViewed application?

davilism10-Dec-01 17:19

davilism

10-Dec-01 17:19

Thanks, squizz, this is great.

Can't use RTTI

Chen Jiadong10-Dec-01 7:05

Chen Jiadong

10-Dec-01 7:05

hi, all
i derived a class from CObject, and also let it support "runtime type information"(RTTI), so i did these:
// Derived.h
class CDerived : public CObject{
DECLARE_DYNAMIC(CDerived)
public:
CDerived(){};
~CDerived(){};
}
// Derived.cpp
IMPLEMENT_DYNAMIC(CObject, CDerived)

but there are a warning and a error:
Derived.cpp(19) : warning C4273: 'public: static struct CRuntimeClass const CObject::classCObject' : inconsistent dll linkage. dllexport assumed.
Derived.cpp(19) : error C2491: 'CObject::classCObject' : definition of dllimport static data member not allowed

can you tell me why?
thank you!
Confused | :confused:

Re: Can't use RTTI

Ernest Laurentin10-Dec-01 8:04

Ernest Laurentin

10-Dec-01 8:04

Hello Grant,
I think you make a little mistake:

you typed:
IMPLEMENT_DYNAMIC(CObject, CDerived)
instead:
IMPLEMENT_DYNAMIC(CDerived, CObject)
Hope that help!

Re: Can't use RTTI

Chen Jiadong10-Dec-01 19:10

Chen Jiadong

10-Dec-01 19:10

Thank you very much, thank you all.
such a silly question, ha...

Re: Can't use RTTI

Christian Graus10-Dec-01 10:00

Christian Graus

10-Dec-01 10:00

RTTI information is a feature of the C++ language that requires no M$ macros or classes. Just use dynamic_cast, and if the return is NULL, the object was not of the type you were casting to.

The M$ version, like the M$ container classes, were a stopgap, not a replacement.

Christian

After all, there's nothing wrong with an elite as long as I'm allowed to be part of it!! - Mike Burston Oct 23, 2001

Sonork ID 100.10002:MeanManOzI live in Bob's HungOut now

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.