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I was poking around in the MFC source code and found the following line:
pCmdUI->SetCheck(!!m_bHelpMode);
Very strange. Any idea why the !! is used? I thought it may be some weird optimization performance thing then I found the line:
ASSERT(!!GetView()->GetRichEditCtrl().GetModify() == !!bModified);
And of course optimization in an ASSERT is quite pointless.
Anybody hazard a guess?
Joel
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The construct will ensure that direct comparisons to TRUE will evaluate correctly (so long as TRUE is defined as !FALSE)(which it should be).
Of course, you shouldn't be doing direct comparisons to TRUE anyway... My thoughts are these lines were written by some dipshit maintenance programmer straight out of a party school, but hey, maybe this passes for wit at MS... 
--------
Well actually they are sort of interesting Nish, on Nudes
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I guess that this's a way for cripted code... for esample:
asm{
mov ax,1
NOP
NOP
NOP
mov bx,ax
...
};
this's equal to:
asm{
mov ax,1
mov bx,ax
...
};
because NOP don't work operations.
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yah but we used to write stuff like that for diff reasons
either the code was self-modifying at run time
or its a virus with space for random mutations to fool the pattern matchers ... errrrr not that i know anything about writing viruses
---
situations to avoid #37:
"good morning ... how many sugars do you take in your coffee ... and what was your name again?"
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! returns a bool, so !!x returns true if x != 0, false if x == 0. Basically it turns a non-bool into its bool equivalent.
--Mike--
Actual sign at the laundromat I go to: "No tinting or dying"
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My really out-of-date homepage
Big fan of Alyson Hannigan and Jamie Salé.
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This is the one I'm going with, converting BOOL to bool in a compact form. Still both examples in MFC do not seem to need to do this!
Joel
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One of the many reasons I don't spend much time poking around inside of MFC. I'm afraid I might learn something I don't want to know.
"There's a slew of slip 'twixt cup and lip"
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I've seen some comments here mixing Windows SDK BOOL and C++ bool.
To make that part perfectly clear, the second "!" inverts the logic of the statement it's applied to, first converting "m_bHelpMode" to a C++ bool and then negating that bool. The first "!" then negates/inverts that bool. So once "!m_bHelpMode" is evaluated the value of the expression is a plain C++ bool.
The whole expression if then converted to int (since according to MSDN SetCheck takes an int).
What it really says (or should say) is
pCmdUI->SetCheck(m_bHelpMode != FALSE ? 1 : 0);
Since as we all know true evaluates to the integral value 1 and false evaluates to the integral value 0.
You then touch on the area of optimizations. However mad it seems, MSVC6 actually generates different code for the following functions (go ahead, try both /O1 and /O2)!
bool foo1(int a) { return a == 0; }
bool foo2(int a) { return (a == 0) ? true : false; }
I'd love to see if this part of the MS Compiler optimizer has been fixed in VC7!
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I think a lot of people forget that SetCheck isn't a BOOL. It is actually a tri-state. Like you said, the '!!' forces a 0 or 1 value.
The other example is doing the same thing.
Tim Smith
I know what you're thinking punk, you're thinking did he spell check this document? Well, to tell you the truth I kinda forgot myself in all this excitement. But being this here's CodeProject, the most powerful forums in the world and would blow your head clean off, you've got to ask yourself one question, Do I feel lucky? Well do ya punk?
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Hi.
I am working on my first "real" Windows program. I am at a point in the implementing process where I see a need to multithread one specific job. I will give a good example of something that is very similar to what I am to implement. I will then give my thoughts on a possible solution. I have no prior experience with multithreading, but Jeff Prosise's book does wonders.
I am design a dialog box with a progress bar *very similar* to
the one you see when you download a file using IE. When you download a large file (your download bandwidth is slow), you can see the progress of the download process. The process bar is easy to implement. The part that makes IE progress bar special is you can *still use* IE during the download process. The key is multithread.
Here is my design.
-----
-User activate a feature (via menu)
-View creates a dialogbox w/ progressbar (position 0)
-Dialogbox sends a message to MainFrm.
-MainFrm redirect message to View
-View calls function in Document to begin data processing
-View also passes the function a pointer to dialogbox
-Document starts a new thread (worker thread)
-Thread begin processing data
-Thread sends message back to Document when applicable
-Document calls updated progressbar via pointer to dialog
-----
Again, this is my first experiment with multithread. Is there anything wrong with the design above? I left some small features out. I will include it soon.
Thanks,
Kuphryn
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Some details are missing to make a full evaluation of this approach, but IMHO the possibility of a deadlock is lurking in your design.
If your dialog features a cancel button, and you implement it like this:
void CProgressDialog::OnCancel()
{
signal the thread to die;
wait for the signal to die with WaitForMultipleObject or some similar API;
}then there's a possible deadlock here. Suppose the user presses the Canel button and CProgressDialog::OnCancel is called. If right after the thread is signalled to die the thread happens to be in an update call to the document, and the updating process involves sending (explicitly or implicitly) some message to CProgressDialog, then you've hit a deadlock, as the thread won't answer the termination signal until it's returned from the update call, and CProgressDialog won't process any further messages until it returns from CProgressDialog::OnCancel. You got it? In general, to avoid such deadlocks between a worker thread and the GUI part of a program, it is advisable to have the worker thread post messages to the GUI instead of sending them in a blocking fashion.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Thanks.
Very point!
I do not quite understand what you meant with "sending them in a blocking fashion."
You were right on with OnCancel(). The way I planned to "signal the thread to die" is by using a boolean counter. OnCancel() would send a message to Doc. Doc would then set the counter to false. Meanwhile, the worker thread does its job only if counter is true.
Do you mean it is advisable to *post message* instead of *send message*?
Kuphryn
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I do not quite understand what you meant with "sending them in a blocking fashion."
SendMessage, when issued from a worker thread, does not return until the GUI thread processes the message sent. So if the GUI is stuck, SendMessage will wait forever. PostMessage, on the other hand, only leaves the message in the GUI thread message queue and returns immediately.
You were right on with OnCancel(). The way I planned to "signal the thread to die" is by using a boolean counter. OnCancel() would send a message to Doc. Doc would then set the counter to false. Meanwhile, the worker thread does its job only if counter is true.
The deadlock will happen only if OnCancel waits for the thread to actually die before returning (which is the proper way to proceed, on the other hand).
Do you mean it is advisable to *post message* instead of *send message*?
Yes. Be careful with the parameters accompanying a posted message --they mustn't be pointers to temporary variables.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Thanks for the valuable pointers.
I did not have time to work on that problem today (busy with other programs homeworks). I will try to work on it *soon* as in tomorrow or Friday at most.
I will post an update.
Kuphryn
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Hi there,
I have a pure win32 dialog with textboxes and static objects on it. The code is all done without MFC.
Now, the fonts seem rather huge, so I tried to modify them. I called
createfont at the beginning of my Dialog proc with various numbers
for the height variable and use various item for parameter 5. I do
as shown below:
SelectObject(hdc, CreateFont(12,2, 0, 0, FW_THIN, 0,0,0,
DEFAULT_CHARSET, OUT_CHARACTER_PRECIS, CLIP_CHARACTER_PRECIS, DEFAULT_QUALITY,DEFAULT_PITCH | FF_DONTCARE, _T("TimesNewRoman")));
and at the end of the proc, I delete it as following:
DeleteObject(SelectObject(hdc, GetStockObject(SYSTEM_FONT)));
But nothing changes. What am I doing wrong?
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You'll want to send a WM_SETFONT message to each control, specifying the font you wish to use.
--------
Well actually they are sort of interesting Nish, on Nudes
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Further to that, I have also created an edit control as following:
hwndEdit = CreateWindow( TEXT("edit"), tcLabel,
WS_CHILD | WS_VISIBLE | WS_BORDER | ES_LEFT | ES_AUTOHSCROLL ,
cxChar + 100, cyChar * (2 * i ) /* * (1 + 2 * i) */, 20 * cxChar + 100,
cyChar * (1.25), hwndDlg, (HMENU) i,
((LPCREATESTRUCT) lParam)->hInstance, NULL)
However, the following catch inside my dialog's WM_COMMAND catch statement, no longer works after creating my edit box :
if (HIWORD(wParam) == EN_CHANGE ||
HIWORD(wParam) == CBN_SELCHANGE)
When I click inside the text boxes, a couple of messages are generated, but they don't correspond to "EN_CHANGE". How would I find out what those messages are within VC btw? Any idea what this problem maybe?
thanks
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In Visual Studio .net, if you add a file to a project, then that file will appear at the end of the project, rather than appearing in alphabetical order. (VS6 alphabetizes the files.) Is there a property somewhere that can be set to fix this?
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Isn't it just that VC7 also takes into account the case of the filename? If so, this is a known bug.
source: nntp://microsoft.public.dotnet.langages.vc
IIRC it "will be fixed in a later release" but there were no promises of an sp fix (even that it would problably just adding an 'i' in the middle of a strcmp).
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I have noticed the same thing, but if I close my project, and opens it again, the files are sorted correctly.
- Anders
Money talks, but all mine ever says is "Goodbye!"
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OK, then this is another bug. You should probably report it to the NG I mentioned in my post.
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I would like to learn something about virtual desktops, but it's hard to find some articles or msdn info on it.
Is there some sort of function in Windows that makes it possible to switch desktops? As far as I know windows does support it completely, so it shouldn't be hard to code.
Got any links or information?
Cheers!
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It's not fully supported (f.ex. creating a new desktop still gets SystemParametersInfo to return the working area of a desktop with an Explorer bar), and you can't move windows from one desktop to another like you'd expect from any other OS, but you should have a look at the Win32 SDK sample "switcher". It's using CreateDesktop & co.
Note: You [obviously] need an NT kernel based OS for this.
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Thanks for the feedback, but I was looking for something that would work on both NT and 9x.
There are quite many apps out there that work on 95/98, so it must be possible. As the apps are fairly small I guess it doesn't take an awful lot of code to make it work.
I'll keep searching, if you got an idea please tell me.
Thanks in advance
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In Win9x it's completely unsupported. I've seen references to apps being _really_ ugly and to "switch desktop" they just grab a handle to any other apps window and move it to e.g. "appWnd.currpos - screenWidth", but I'd say yo get no friends from that approach even that it appears to work.
Now you know how some others do it. I just hope you don't do it yourself...
And even if you do, you'd have to track e.g. ALT+TAB to either not display the apps on "another desktop", or to swith desktop when alt-tabbing to an app on "another desktop".
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