Re: Question - C / C++ / MFC Discussion Boards

toxcct29-Mar-06 3:53

29-Mar-06 3:53

1. calls the CPaintDC contructor which receives a CWnd* parameter, and initializes it with the this pointer passed,

2. calls the CPaintDC default constructor...

Re: What is the difference??

includeh1029-Mar-06 4:43

includeh10

29-Mar-06 4:43

DC is related to Window, in other words, we say "a DC of a window".

1) the DC of "this" window - similar to ::GetDC(this->m_hWnd);
2) the DC of screen - similar to ::GetDC(0).

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Includeh10

Question

big_denny_20029-Mar-06 3:33

big_denny_200

29-Mar-06 3:33

Hi all

I have such question :

I often see following things in other people's code :

object.SomeFunction(BS_STYLE1 | BS_STYLE2 | BS_STYLE3)

and then after execution all those three styles are set to

the object.

How is this implemented inside the function ?

Can anybody clarify, or bring an example ?

thank you.

PS. For example this API uses such thing too :

ListView_SetExtendedListViewStyle(m_list, LVS_EX_FULLROWSELECT | LVS_EX_GRIDLINES );

Re: Question

khan++29-Mar-06 3:50

khan++

29-Mar-06 3:50

Actually it is a DWORD in the function:
void ListView_SetExtendedListViewStyle(HWND hwndLV,DWORD dwExStyle);
And this one is:
#define LVS_EX_FULLROWSELECT 0x00000020

this is this.

Re: Question

big_denny_20029-Mar-06 3:58

big_denny_200

29-Mar-06 3:58

thank you khan, but my question was how is it achieved inside the function that after writing

LVS_EX_FULLROWSELECT | LVS_EX_GRIDLINES

both styles are set.

And if I write only LVS_EX_FULLROWSELECT then only this style is set.

Re: Question

khan++29-Mar-06 4:08

khan++

29-Mar-06 4:08

Actually it is just a parameter like any other. The actual code inside the function handles the values passed, which can be anything.
It maybe like:

void func(DWORD dwStyle)
{
//save the dwStyle value to an internal variable maybe:
 m_dwStyle = dwStyle;
//Issue a redraw message to reflect the changed style.
 RedrawWindow();//etc

}

//some draw function for the control:

void Draw()
{
 if (m_dwStyle & LVS_EX_FULLROWSELECT)
 {
 //draw it differently
 }
 else
 {
 //draw it normally.
 }
}

this is this.

Re: Question

Gavin Taylor29-Mar-06 4:12

Gavin Taylor

29-Mar-06 4:12

It's called BitWise. CP has loads of articles on it if you do a search, however this is[^] a particulary good one.

All the function is doing is something like:

void SomeFunction( DWORD dwFlags )
{
	if( dwFlags & BS_STYLE2 )
	{ // Do something as style 2 was set
		DoSomething( );
	}
}

Gavin Taylor
w: http://www.gavspace.com

Re: Question

toxcct29-Mar-06 4:34

toxcct

29-Mar-06 4:34

i don't exactly get you ; however, if i understand well, you want to know this :
let go deeper in the instruction BS_STYLE1 | BS_STYLE3 | BS_STYLE6.

firstly, we need to know what are defined those constants like.
let's consider they're declared this way :

enum {
    BS_STYLE1 =  1,
    BS_STYLE2 =  2,
    BS_STYLE3 =  4,
    BS_STYLE4 =  8,
    BS_STYLE5 = 16,
    BS_STYLE6 = 32
};

to understand why these constants' values are chosen, we must go in binary representation to understand :

 1 -> 0b 00000000 00000000 00000000 00000001
 2 -> 0b 00000000 00000000 00000000 00000010
 4 -> 0b 00000000 00000000 00000000 00000100
 8 -> 0b 00000000 00000000 00000000 00001000
16 -> 0b 00000000 00000000 00000000 00010000
32 -> 0b 00000000 00000000 00000000 00100000

notice that for those special values that are multiples of 2, only one bit is set at a time, all the others are equal to 0.
the interrest in this is that each bit is a flag for a functionnality (style here), and we can mix them in once variable to avoid using as many booleans as we need flags.
for example, see the following case :

 0b 00000000 00000000 00000000 00100101
 
Flags of <code>Style6</code>, <code>Style3</code> and <code>Style1</code> are set

now, as we don't handle binary directly in C++, we use bitwise operators instead.
what you see as that vertical bar | is the bitwise OR operator.
the OR operator works like this :

 x y  |
--------
 0 0  0
 0 1  1
 1 0  1
 1 1  1

in the case of the instruction BS_STYLE1 | BS_STYLE3 | BS_STYLE6, it so ORs like this :

 0b 00000000 00000000 00000000 00000001   <- BS_STYLE1
 0b 00000000 00000000 00000000 00000100   <- BS_STYLE3
 0b 00000000 00000000 00000000 00100000   <- BS_STYLE6
-----------------------------------------------
 0b 00000000 00000000 00000000 00100101   <- BS_STYLE1 | BS_STYLE3 | BS_STYLE6

Now, the "mix value" is constructed, we can pass it to a function.
but how does the function know which bits are set, and which are not ?
easy... follow me !

Lets say we want to know if the bit of BS_STYLE1 is set from the mix we get in parameter (let's call it MIX_VAR.
we must create a maskwhich we'll AND with the :

STYLE1_MASK = 0b 00000000 00000000 00000000 00000001

as you see, the mask is the same as the STYLE constant, so in practice, you'll never see defined such mask :

MIX_VAR  -> 0b 00000000 00000000 00000000 00100101
MASK1    -> 0b 00000000 00000000 00000000 00000001
           ----------------------------------------
<code>Bitwise AND</code> 0b 00000000 00000000 00000000 00000001

if the result is equal to the STYLE1, then it is because the bit was set. otherwise, you get 0.

ok, now, in practice, here is how you'll often see it :

void fooFunc(DWORD dwMix) {
    if (BS_STYLE1 & dwMix) == BS_STYLE1) {
        //Apply style 1
    }
    else if (BS_STYLE2 & dwMix) == BS_STYLE2) {
        //Apply style 2
    }
    else if (BS_STYLE3 & dwMix) == BS_STYLE3) {
        //Apply style 3
    }
    //etc...
}

wow, that's very long finally... hum, well, i hope it will help, truly ! Cool | :cool:

Re: Question

Eytukan29-Mar-06 5:29

Eytukan

29-Mar-06 5:29

Nice !

VuNic

Re: Question

Wes Aday29-Mar-06 6:26

Wes Aday

29-Mar-06 6:26

Excellent explanation!

Why is common sense not common?

Never argue with an idiot. They will drag you down to their level where they are an expert.

Re: Question

big_denny_20029-Mar-06 6:57

big_denny_200

29-Mar-06 6:57

i think you should write an article on this Smile | :)

thanks

Re: Question

toxcct29-Mar-06 20:16

toxcct

29-Mar-06 20:16

ok, in the todo list Wink | ;)

thanks

About sending mail

mkoliv29-Mar-06 3:32

mkoliv

29-Mar-06 3:32

Thanks

modified 28-Sep-16 7:28am.

Re: About sending mail

David Crow29-Mar-06 4:43

David Crow

29-Mar-06 4:43

Have you tried posing this question here, or downloading the latest version from here? Do you have access to an SMTP server?

Oliver Shikaloski wrote:
...I can only send mails that are the same type like mine.

Do you mean in your same domain?

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

Message Closed

29-Mar-06 21:44

mkoliv

29-Mar-06 21:44

Message Closed

modified 28-Sep-16 7:28am.

Re: About sending mail

David Crow30-Mar-06 1:57

David Crow

30-Mar-06 1:57

oliver_mak wrote:
How do I fix this problem?

By trying my other three suggestions perhaps.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

TreeView Control Problem

gbruyneel29-Mar-06 3:00

gbruyneel

29-Mar-06 3:00

Hello
I have Visual studio 2005. I have created a Win32app project with a dialogbox containing a treeview control. As I would like to have the dialogbox in the client part of my window i have added the handle of WM_CREATE message in the MainWndProc like this :

switch (message)<br />
	{<br />
	HANDLE_MSG(hWnd, WM_CREATE,  WndProc_OnCreate);

and I have wrote :

BOOL WndProc_OnCreate(HWND hwnd,LPCREATESTRUCT ct)<br />
{<br />
    HWND g_hViewDir;<br />
    g_hViewDir = CreateDialog(hInst, MAKEINTRESOURCE(IDD_SHOWDIR), hwnd, ShowdirDlgProc);<br />
    if(g_hViewDir != NULL)<br />
    {<br />
      ...<br />
    }<br />
    else<br />
     return FALSE;<br />
return TRUE;<br />
}

No compilation error. When i launch the app the dialog does not appear. I have investigate and found that the error message comes out of the CreateDialog function and says : Error 1407 : Unknown window Class Confused | :confused:

????
Could someone help.

Re: TreeView Control Problem

Gavin Taylor29-Mar-06 3:27

Gavin Taylor

29-Mar-06 3:27

Check your linking into the Common Control library comctrl32.lib and calling InitCommonControlsEx[^] to initialize the library, finally also check your passing ICC_TREEVIEW_CLASSES as a flag so it knows to load the correct classes.

Gavin Taylor
w: http://www.gavspace.com

Re: TreeView Control Problem

gbruyneel29-Mar-06 21:23

gbruyneel

29-Mar-06 21:23

Thanks a lot that solved my problem. But in the documentation of InitCommonControlsEx it says that it is not necessary to use it if we use a manifest. In that case i do not understand.

Smile | :)

How to access HKEY_CURRENT_USER from local system account?

khb29-Mar-06 1:54

khb

29-Mar-06 1:54

Hi together,

I have a big problem. I hope somebody can help me:

I implemented a service that runs under the local system account and checks if any screen blanker is activated. I use the following code:

bool result = false;
SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, (LPVOID) &result, 0);

This works fine on Win XP, but on Win 2000 the function always return true. It is a known bug according to article number 318781 on MSDN.

The suggested workaround is to look for the entry "SCRNSAVE.EXE" under the registry key "HKCU\Control Panel\Desktop" using the following two lines:

RegOpenKeyEx(HKEY_CURRENT_USER, "Control Panel\\Desktop", 0, KEY_READ, &hKeyScrSave);
RegQueryValueEx(hKeyScrSave, "SCRNSAVE.EXE", NULL, NULL, (LPBYTE) szData, &dwData);

Now the problem arises: As my service runs under the local system account, access to "HKEY_CURRENT_USER" is redirected to "HKEY_USERS\.DEFAULT". Dead | X|

So the result refers to the logon screen saver, which is (usually) always activated. But I only want this result if no user in logged in.

Therefore my question: Does anybody has a solution, how to check if a screen saver is active under 2000 like SystemParametersInfo(SPI_GETSCREENSAVEACTIVE) does it for XP? An idea how to access data under "HKEY_CURRENT_USER" from the local system account would also be very valuable for me.

Thank you very much for any hints,
Marcus.

Re: How to access HKEY_CURRENT_USER from local system account?

James R. Twine29-Mar-06 2:49

James R. Twine

29-Mar-06 2:49

   Two quick things - first SystemParametersInfo(...) does not use C++ types, so you should be passing the address of a BOOL (an int, or 4-bytes under 32-bit MS), not a bool (1-byte under 32-bit MS).

   Second, I am pretty sure that screen savers run on a separate desktop, the "screen saver desktop". Search MSDN for information on Window Stations and Desktops for more information.

   If I am correct, you might be able to determine which desktop is active, and from that determine if a screen saver is running.

   Peace!

-=- James

If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
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Re: How to access HKEY_CURRENT_USER from local system account?

khb29-Mar-06 3:08

khb

29-Mar-06 3:08

Hi James,

thank you very much for your reply!

Concerning the bool/BOOL issue: I'm actually using a BOOL. In my message, however, I cut & pasted the code from MSDN, which seems to contain several bugs/typos Frown | :(

Anyway, thanks for the hint.

Concerning the desktop issue: I think you are right. Some time ago I've read that the screen saver runs on another desktop. So I'll dig into that again Wink | ;)

Thank you again,
Marcus.

Re: How to access HKEY_CURRENT_USER from local system account?

David Crow29-Mar-06 3:16

David Crow

29-Mar-06 3:16

khb wrote:
SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, (LPVOID) &result, 0);

I think you want to check SPI_GETSCREENSAVERRUNNING instead.

khb wrote:
Now the problem arises: As my service runs under the local system account, access to "HKEY_CURRENT_USER" is redirected to "HKEY_USERS\.DEFAULT".

See MSDN article Q168877 for an example.

"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

Re: How to access HKEY_CURRENT_USER from local system account?

khb29-Mar-06 3:29

khb

29-Mar-06 3:29

Hi David,

I think that what I posted was correct. I want to check if a user has "installed" a screen saver so that I can expect that there is a change that it will start running somewhen. Anyway, I check if it is actually running, too.

The howto on Q168877 seems to be exactly what I was looking for, great!

Thank you,
Marcus.

Can I return an array of pointers of type unsigned char[]

Laughing Buddha29-Mar-06 1:52

Laughing Buddha

29-Mar-06 1:52

Hi,

I am creating an array of pointers that point to unsigned char arrays like so

unsigned char* data[3];

where
data[0] = new unsigned char[256];
data[1] = new unsigned char[256];
data[2] = new unsigned char[256];

I now want to return this pointer array data from one function. How can I do that? Or what way could I return data[0], data[1] and data[2]?

Thanks for any help cause am a bit stuck here

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