C / C++ / MFC

28-Dec-07 4:00

(Update: Problem solved)

I'm trying to use CDC::GetWindow to get a pointer to a CWnd object to perform some tests but CDC::GetWindow() returns NULL. I'm trying to derive the CDC from the Graphics object passed into a function as follows...

void SomeFunction(Graphics& graphics)
{
	HDC hDC=graphics.GetHDC();
	CDC* pDC=CDC::FromHandle(hDC);

	if (pDC) {

		CWnd* pWnd=pDC->GetWindow();
		if (pWnd) {

			// Never gets here
		}
	}

	graphics.ReleaseHDC(hDC);
}

Can anyone tell me the folly of my ways?
thanks in advance

modified on Friday, December 28, 2007 11:17:40 AM

CPallini28-Dec-07 4:46

28-Dec-07 4:46

Why are you doing that (i.e. have you no control on Graphics object instance?)?
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

bob1697228-Dec-07 5:03

28-Dec-07 5:03

I'm passing the graphics object around to drawing functions in classes that have no knowledge of who is using them. Those other classes, however, are interested in knowing whether the window the Graphics object is drawing to has the input focus so they can perform their drawing actions differently.

I'm just trying to minimize the number of parameters I'm passing around.

CPallini28-Dec-07 5:08

28-Dec-07 5:08

Well, I don't think that a Graphics object is a good transport medium for a CWnd one. Pass needed parameters packed in a struct.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

bob1697228-Dec-07 5:17

28-Dec-07 5:17

I realized what I was doing wrong.

I'm using a memDC so there is no window associated with the underlying DC.

Thanks for the response.
I apologize for my oversight. Blush | :O

bob1697228-Dec-07 5:29

28-Dec-07 5:29

Since the graphics object has the HDC, and the HDC knows which HWND it is associated with (if any) it seems reasonable to say the overhead of digging the HDC out and creating a struct and setting it up are approximately even.

Granted, I screwed it up but the concept seems sound if one can assert the HDC is associated with a window and not just a memory buffer.

Anyway, thanks for your advice as many opinions usually lead to a solution directly or indirectly.

CPallini28-Dec-07 5:44

28-Dec-07 5:44

I'm happy you've found a solution.
BTW a device context maybe associated to the whole screen, so you can get no window anyway (you can state as a precondition that screen DCs are banned!)
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

Hamid_RT28-Dec-07 4:50

Hamid_RT

28-Dec-07 4:50

Do you want to get handle to a control?

bob1697228-Dec-07 5:06

28-Dec-07 5:06

No, I'm just trying to get a generic window handle for the window the Graphics object drawing commands will effect.

I'm trying to minimize the number of parameters to each function and since the Graphics object is being passed in, I was hoping to use the associated DC to track down the window.

bob1697228-Dec-07 5:18

Off-topic: Happy new year

28-Dec-07 5:18

I realized what I was doing wrong.

I'm using a memDC so there is no window associated with the underlying DC.

I apologize for my oversight. Blush | :O

CPallini1-Jan-08 3:38

can anybody tell me What happens if an exception is throws from an, object's constructor and object's destructor?

1-Jan-08 3:38

Hamid. wrote:
Hi CPallini
Happy New Year
I wanted to send the card postal for you but I didnt have your mail address but anyway I wish good year with health for you and your family

I'm sorry, but the link for the above message, is broken hence I cannot reply to the right place. Anyway I'm happy about your message and I wish you and your family a Happy New Year.

Best Wishes Again,
Carlo.

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

philiptabraham28-Dec-07 1:49

philiptabraham

28-Dec-07 1:49

can anybody tell me
What happens if an exception is throws from an, object's constructor and object's destructor?

thanks in dvance

Re: can anybody tell me What happens if an exception is throws from an, object's constructor and object's destructor?

CPallini28-Dec-07 2:12

Re: can anybody tell me What happens if an exception is throws from an, object's constructor and object's destructor?

28-Dec-07 2:12

Ask George_George: he made a extensive study about... Big Grin | :-D

Seriously, IMHO opinion, the object consumer has to care about of that possibility exactly like it does with standard method thrown exceptions. A difference maybe the fact that object construction/destruction sometimes happens implicitly (and is somehow hidden to the consumer itself).
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

peterchen28-Dec-07 2:27

peterchen

28-Dec-07 2:27

[1] Constructor
The object will never be created. Destructor is NOT called. If you allocated ressources before the exception is thrown, they are NOT freed.

[2] Destructors
Technically, the object is left in an undefined state. Likely, Accessing it afterwards will fail, and resources may leak.

Practically, destructors should NEVER throw. It violates even the most basic exception safety guarantee: that objects remain destructable, no matter what.

For lots of more information, try the GOTW columns[^] that deal with exceptions

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
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linked list

LiYS28-Dec-07 1:04

LiYS

28-Dec-07 1:04

Hi all:

I have the following linked list in which head always pointed the last queue item. I'm thinking about the possibility to make the head points to the begining of the queue with the least possible changes.

<br />
class CQueue1 {<br />
public:<br />
    CQueue1(int nIndex);<br />
    static CQueue1* sm_pHead;<br />
    CQueue1* m_pNext;       <br />
};<br />
CQueue1* CQueue1::sm_pHead = NULL;<br />
CQueue1::CQueue1(int nIndex)<br />
{<br />
   m_pNext  = sm_pHead;    // The next node was at the head<br />
   sm_pHead = this;        // This node is now at the head<br />
}<br />

Thanks,

Re: linked list

CPallini28-Dec-07 1:10

HKEY_CURRENT_USER\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\ logon User Name cannot access from system process

28-Dec-07 1:10

LiYS wrote:
CQueue1::CQueue1(int nIndex)
{
m_pNext = sm_pHead; // The next node was at the head
sm_pHead = this; // This node is now at the head
}

?!?Uhm?!!

What do you want to do with the above code?

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

Re: linked list

Naveen28-Dec-07 1:43

Naveen

28-Dec-07 1:43

Change it as follows

CQueue1::CQueue1(int nIndex)<br />
{<br />
	CQueue1** pLast = &sm_pHead;<br />
	while( 0 != *pLast )<br />
	{<br />
	  pLast = &((*pLast)->m_pNext);<br />
	}<br />
	*pLast = this;<br />
	m_pNext = 0;<br />
}

nave

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Re: linked list

Nishad S28-Dec-07 2:31

Nishad S

28-Dec-07 2:31

It is better to avoid the while loop Smile | :)

- NS -
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vicky0000028-Dec-07 0:00

vicky00000

28-Dec-07 0:00

hai all
HKEY_CURRENT_USER\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\ logon User Name cannot access from system process I use the following code

LPCSTR szKey = _T("Software\\Microsoft\\Windows\\CurrentVersion\\Explorer");
LPCSTR szValueName = _T("Logon User Name");

//open the registry key
lRet = RegOpenKeyEx( HKEY_CURRENT_USER, szKey, 0, KEY_QUERY_VALUE, &hSubKey );
if( lRet == ERROR_SUCCESS)
{
dwBufLen = 256;
lRet = RegQueryValueEx( hSubKey, szValueName, NULL, NULL,
(LPBYTE) szValue, &dwBufLen);
}

pls help me

Advance thanks

Re: HKEY_CURRENT_USER\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\ logon User Name cannot access from system process

CPallini28-Dec-07 0:53

Re: HKEY_CURRENT_USER\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\ logon User Name cannot access from system process

28-Dec-07 0:53

vicky00000 wrote:
LPCSTR szKey = _T("Software\\Microsoft\\Windows\\CurrentVersion\\Explorer");
LPCSTR szValueName = _T("Logon User Name");

The above should be

LPCTSTR szKey = _T("Software\\Microsoft\\Windows\\CurrentVersion\\Explorer");
LPCTSTR szValueName = _T("Logon User Name");

And the code shown lacks some definitions like the one of the buffer (probably they are already present in your program, I don't know), anyway, the following code (practically identical to yours) is working fine on my system (XP):

TCHAR szValue[256];
LPCTSTR szKey = _T("Software\\Microsoft\\Windows\\CurrentVersion\\Explorer");
LPCTSTR szValueName = _T("Logon User Name");
HKEY hSubKey;
//open the registry key
LRESULT lRet = RegOpenKeyEx( HKEY_CURRENT_USER, szKey, 0, KEY_QUERY_VALUE, &hSubKey );
if( lRet == ERROR_SUCCESS)
{
  DWORD dwBufLen = 256;
  Ret = RegQueryValueEx( hSubKey, szValueName, NULL, NULL,(LPBYTE) szValue, &dwBufLen);
}

BTW whenever RegQueryValueEx fails is worthy to give a look at reported error.

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

vicky0000028-Dec-07 1:13

vicky00000

28-Dec-07 1:13

Thanks ur reply,
My code is exactly like u mentioned. This code will work correctly while it run by a normal process . It shows error while it run as system process. The error it shows is ERROR_FILE_NOT_FOUND

Re: HKEY_CURRENT_USER\Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\ logon User Name cannot access from system process

CPallini28-Dec-07 1:47