C / C++ / MFC

16-Jan-02 1:19

I have been working on an app for weeks now and I am in final stages of development. Suddenly things are going haywire.

The situation I am at is that variables in the app are changing without any code being called to cause the change. For example, BOOL value is set to FALSE in the constructor - I come to check it later in the app (having set a breakpoint on the only function which changes the value) and it has changed to TRUE without the function being called. This is happening across a few different variables.

Any ideas - I really need help with this cause I'm going out of my mind.

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

Phil.Benson16-Jan-02 1:31

Phil.Benson

16-Jan-02 1:31

Does this "unusual" behaviour only happen in the "Release" version, or also in the "Debug" version.

I had similar problems, where a function bool foo(DWORD& dwValue) was called, the dwValue was not used, and when the function returned there was only "Garbage" in dwValue.

This strange behaviour happens because VS in the "Debug" version, allocates more memory for variables etc (usually before and after the actual variable) AND initialises it.

In the release version is does not.

James Spibey16-Jan-02 1:36

16-Jan-02 1:36

Thanks for the response. Unfortunately, this is in the debug version. I have checked and the variables all get initialised properley in their constructors but the value has changed by the time I come to check it.

Is there a way to set a breakpoint on a value so that when it is accessed/modified I get notified?

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

Matt Gullett16-Jan-02 2:05

Matt Gullett

16-Jan-02 2:05

The best way is to have a method of your class expose the variable (ie. Set/Get).

Also, it could well be that you are corrupting your memory in an unexpected way. I would place a DWORD value around the BOOL value like below.

DWORD dwTest1;
BOOL bValue;
DWORD dwTest2;

Then when I initialized the bValue I would also initialize the dwTest1 and dwTest2 to some unlikely value.

bValue = TRUE;
dwTest1 = 0xfefe;
dwTest2 = 0xfefe;

The other thing you can do is add 2 data members to the class one static and one not static.

static int iStartingPoint;
int iPointOfStart;

Initialize iStartingPoint to zero.
Then in your constructor, set iPointOfStart = iStartingPoint and increment iStartingPoint.

When you check the value of bValue you will 1) know if memory is getting overwritten by checking dwTest1 and dwTest2 and you will know if you are working with the same object you were working with before (check iPointOfStart}

Just my $0.02.

Thanks,

Matt Gullett

James Spibey16-Jan-02 2:54

16-Jan-02 2:54

Right, I think I found the error but I don't know what's causing it. The BOOL bValue has the value of decimal 20 rather than 1 or zero and the two DWORDs have changed their value.

Now, how can I trap when this is happens?

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

FIXED WOO-HOO

James Spibey16-Jan-02 3:03

16-Jan-02 3:03

Thanks to all that helped but I got it. Only took me 9 hours Smile | :)

For those interested it was a simple index out of bounds. I had two constants defined as the maximum sizes of two arrays I was using and I was looping through one array (and writing to it ) using the wrong max size.

Anyway, thanks again everyone.

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

Re: FIXED WOO-HOO

Matt Gullett16-Jan-02 3:33

Matt Gullett

16-Jan-02 3:33

Great!

I was justing working on my repost. I was going to tell you to check for...

arValules[10];

for (int i = 0; i <= 10; i++)
...

I used to do this all of the time.

Anyway, glad you solved your problem.

Matt Gullett

Tim Smith16-Jan-02 2:13

Tim Smith

16-Jan-02 2:13

A few things to check.

1. Rogue pointer - You have a pointer that hasn't been properly initialized that is trashing another variable when used.

2. Use of deallocated memory - You deallocate memory, that memory is then allocated to your new object. However, another piece of code is still trying to access the old object thus trashing the data in the new.

3. You are returning a pointer to a stack object.

4. Your object is located on the stack and another buffer (such as a character string) isn't large enough to hold an array of data. Thus when you write this data into the buffer, you trash other objects on the stack. This can also happen with allocated memory.

Tim Smith
Descartes Systems Sciences, Inc.

James Spibey16-Jan-02 2:26

Setting Control Focus Within Property Sheet

16-Jan-02 2:26

Thanks for the response. I have actually run the code through boundschecker and it didn't throw up any of the above.

A quick expanation of the code - it's a CWnd derived class which includes a load of CUIElemnt objects which represent GUI objects. When I receive OnMouseDown messages I call PointInRect for each element and if they report that the click was within their bounding rect, I call Clicked() on that element. On the next OnMouseUp messages I scan for the clicked element, perform an action and then call Release() on that element.

This works OK for some elements but on one particular one, I get an access violation when I call Release on the mouse up. This is in addition to some elements returning TRUE to IsClicked when they haven't been Clicked(). I don't understand why I'm getting an access violation - I might expect it when using pointers but I'm not.

class CUIElement
{
public:
    BOOL PointInRect(CPoint point);
    void Clicked();
    void Release();
    BOOL IsClicked();

protected:
   BOOL m_bClicked;
};

CMyClass
{
public:
    ... Many Access Functions

Protected:
   CUIElement Button1;
   CUIElement Button2;
   CUIElement Button3;
   CUIElement Button4;
};

James Spibey

I love the word naked, it's brilliant isn't it, 'naked'. When I was a kid I used to write the word naked on a bit of paper hundreds of times and rub my face in it - Jeff, Coupling, BBC2

John Clump16-Jan-02 0:09

John Clump

16-Jan-02 0:09

Hi everyone. I have a dialog with a property sheet, with property pages, which I set up in the code below. The question I have is, how do I set the focus to a text box in the first property page when the dialog and then the property sheet is created afterwards. The idea is what when the dialog pops up, the focus is set to the edit box in the first property page in the property sheet, so the user can begin to enter data immediately, without having tomove the mouse or use the tab key to switch the focus from the OK button on the dialog to the edit box on the first property page.

<br />
        // property pages<br />
        CPpgOne* m_ppgOne;  // this one has the edit box<br />
        CPpgTwo* m_ppgTwo;<br />
        CPpgThree* m_ppgThree;<br />
	m_ppsMain.AddPage(m_ppgOne);<br />
	m_ppsMain.AddPage(m_ppgTwo);<br />
	m_ppsMain.AddPage(m_ppgThree);<br />
<br />
	// sets property sheet up<br />
        m_ppsMain.Create(this, WS_CHILD | WS_VISIBLE, 0);<br />
	m_ppsMain.ModifyStyleEx(0, WS_EX_CONTROLPARENT);<br />
	m_ppsMain.ModifyStyle(0, WS_TABSTOP);<br />
	CRect rcSheet;<br />
	GetDlgItem(IDC_PPS_PROPSHEET)->GetWindowRect(&rcSheet);<br />
	ScreenToClient(&rcSheet);<br />
	m_ppsMain.SetWindowPos(NULL, rcSheet.left- 7, rcSheet.top - 7, 0, 0,<br />
		SWP_NOZORDER | SWP_NOSIZE);<br />
<br />
   // in CPpgOne, there is a string tied to the edit box<br />
   // m_strTitle is ths string, IDC_EDT_TITLE is the control<br />
   // the edit box is just an ordinary edit box<br />

Every time I try and modify the focus anywhere, it always ends up on the OK button of the dialog the property sheet is on. Anyone have any ideas? I can provide more code if necessary.

Re: Setting Control Focus Within Property Sheet

Fred D.16-Jan-02 0:34

Fred D.

16-Jan-02 0:34

one way to do it is to use the CTRL + D when you are in the resource view and then set the order of your components.

so the first one has to be the edit box in your case and the last one the Ok button.

i hope it helps.

Fred

Re: Setting Control Focus Within Property Sheet

Roger Allen16-Jan-02 3:17

Roger Allen

16-Jan-02 3:17

Apart from settin gth tab order as suggested by Fred, you can set the control you want to have the focus in the OnInitDialog() function for the dialog by calling SetFocus() on that control. Remeber that you will need to return FALSe to let the CDialog class know that you set the focus to a control.

As your control is in a property page, you will need to get a pointer to that page in the OnInitDialog() and then a pointer to its control before being able to set the focus.

HTH

Roger Allen
Sonork 100.10016

If I'm not breathing, I'm either dead or holding my breath.

Enumerating All Visible Printers

jerry0davis15-Jan-02 23:43

jerry0davis

15-Jan-02 23:43

Anyone know how I can get a list of all local and network printers installed on a PC? I have a program that when it detects a fire, I'd like to print a fire report on every printer possible. Anyone got any ideas please? Thanks

Jeremy Davis
http://www.astad.org

567890123416-Jan-02 0:51

5678901234

16-Jan-02 0:51

See EnumPrinters and OpenPrinter.

jerry0davis16-Jan-02 3:34

jerry0davis

16-Jan-02 3:34

Alex Farber wrote:
See EnumPrinters and OpenPrinter.

Thanks! I'll try that. Wink | ;)

Jeremy Davis
http://www.astad.org

l a u r e n16-Jan-02 2:29

l a u r e n

16-Jan-02 2:29

sorry to sound like i'm laughing at you ... i'm not but i can't help but imagine the printouts:

"THERE IS A FIRE AND YOU SHOULD RUNNING THAT WAY!!!"

with an arrow pointing at the the nearest fire escape

Smile | :)

---
"every year we invent better idiot proof systems and every year they invent better idiots ... and the linux zealots still aren't being sterilized"