Re: global variables - C / C++ / MFC Discussion Boards

dolph_loe22-Jun-04 5:20

22-Jun-04 5:20

I have some global variables in my program, but some of them (pointers) suddenly change without me doing it.. How is this possible?

øivind

Re: global variables

Johan Rosengren22-Jun-04 5:28

Johan Rosengren

22-Jun-04 5:28

By being overwritten, for example. In MSVC++ 6.0, you can set breakpoints on memory changing, this might help you. From the help file:

1. From the Edit menu, click Breakpoints.
2. Click the Data tab of the Breakpoints dialog box.
3. In the Expression text box, type the dereferenced pointer variable name (*p or p->next, for example).
4. Click OK to set the breakpoint.

You might want to consult the help file further (search for Breakpoint AND memory AND change, for example).

Re: global variables

dolph_loe22-Jun-04 6:42

dolph_loe

22-Jun-04 6:42

Ok.... dont know if i'm doing things the wrong way, but MSVC.NET gives me the message:

The following breakpoint cannot be set:
When 'g_resManager' changes
Data breakpoints are not supported in the Common Language Runtime.

I also tried to dereference g_resManager (which is a pointer) but that gave the same result..

Confused | :confused:

Re: global variables

Johan Rosengren22-Jun-04 8:29

Johan Rosengren

22-Jun-04 8:29

Being the happy non-owner of MSVC.NET, I must direct you to the documentation for it. You want to set a breakpoint, and you want to set it when either the variable or the memory address changes. Search, man, search!

Re: global variables

jmkhael22-Jun-04 5:29

jmkhael

22-Jun-04 5:29

In the debugger, put a conditional breakpoint to see who or what is changing it

Papa

while (TRUE)
Papa.WillLove ( Bebe ) ;

Re: global variables

David Crow22-Jun-04 5:53

David Crow

22-Jun-04 5:53

Have you single-stepped through the code to see which statement is writing to the memory address in question? Consider the following:

1) char c1 = 'D'; // 0x0012e7d8
2) char c2 = 'C'; // 0x0012e7d4
3) int *i3 = (int *) &c2; // point to the address of c2
4) *i3 = 1234567; // change the value at c2's address, thus stepping on c1

We never directly wrote to c1 or c2, but c1 got changed indirectly. Setting a breakpoint on the first two statements would not show you anything as the "damage" does not happen until the fourth statement. Make sense?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: global variables

dolph_loe22-Jun-04 6:59

dolph_loe

22-Jun-04 6:59

makes sense Smile | :)

Re: global variables

Henry miller22-Jun-04 8:15

Henry miller

22-Jun-04 8:15

Either you are doing it but just don't know your code well enough to to recall where. (This happens more often than you would think), or you are overwriting it thourgh some memory that isn't as big as you think it is. Look for a global array near that point that is one member too small or some such.

You might be able to get a clue by seeing what it was changed to. Pull up your debugger after this happens, and look in memory to see if there is something supicious, not just with the variable overwritten, but also others near that location. If it is a string you have a good clue.

Your confusion on how to find these is one of the lesser reasons to consider global variables evil. (There is sometimes no way to get around them, but the less you have the better, and any you can get rid of is generally good practice)

Good luck.

Modeless Dialogs & Z order

Mark Kinsley22-Jun-04 4:47

Mark Kinsley

22-Jun-04 4:47

I have a simple dialog app which creates a child window as follows:

CModeless_testDlg *pDlg = new CModeless_testDlg;
pDlg->Create(IDD_MODELESS_TEST_DIALOG,this);
pDlg->ShowWindow(SW_SHOW);

The problem is that the child window is always on top of the parent window, even after selecting the parent. Is it possible to override this behaviour?

(I've set the parent dialog's 'Clip children' style but this does not seem to help. I also tried calls to change the Z order with no effect)

Any suggestions?

Mark

Yet another hardware engineer gone soft...

Re: Modeless Dialogs & Z order

V.22-Jun-04 4:57

22-Jun-04 4:57

Maybe there is a better way, but you could destroy&recreate the one you want on top?

"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimi Hendrix

Re: Modeless Dialogs & Z order

PJ Arends22-Jun-04 5:26

PJ Arends

22-Jun-04 5:26

Make your modeless dialog a child of the desktop.

pDlg->Create(IDD_MODELESS_TEST_DIALOG, NULL);

Sonork 100.11743 Chicken Little

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

Within you lies the power for good - Use it!

Re: Modeless Dialogs & Z order

Mark Kinsley22-Jun-04 5:49

Mark Kinsley

22-Jun-04 5:49

Thanks for the suggestion, I tried that but it does not seem to make any difference.

Re: Modeless Dialogs & Z order

PJ Arends22-Jun-04 10:12

PJ Arends

22-Jun-04 10:12

How about:

pDlg->Create(IDD_MODELESS_TEST_DIALOG, GetDesktopWindow());

Sonork 100.11743 Chicken Little

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

Within you lies the power for good - Use it!

Re: Modeless Dialogs & Z order

Mark Kinsley22-Jun-04 21:36

Mark Kinsley

22-Jun-04 21:36

Perfect, that works just right. Thanks for the help !

Modeless Dialogs

si_6922-Jun-04 4:10

si_69

22-Jun-04 4:10

hi All

i am calling a modeless dialog from my doc class using

CCPServerWait* m_pWaitDlg;
m_pWaitDlg = new CCPServerWait;
m_pWaitDlg->Create(IDD_DCPSERVER_WAIT);
m_pWaitDlg->m_wait_mes = "Confiming School Details...Please Wait";

m_pWaitDlg->UpdateData(FALSE);
m_pWaitDlg->CenterWindow(CWnd::GetDesktopWindow());

m_pWaitDlg->ShowWindow(SW_SHOW);
m_pWaitDlg->UpdateWindow();
m_pWaitDlg->DestroyWindow();

now i have used this code successfully in other applications but in the current one is throwing out an error
on updatedata

i noticed when i debug that hWnd is equalling ????????

anyone any ideas ???

ta

simon

Re: Modeless Dialogs

Johan Rosengren22-Jun-04 5:21

Johan Rosengren

22-Jun-04 5:21

si_69 wrote:
throwing out an error
on updatedata

It would be far easier to help you if you elaborated on this. With the amount of info given, I can only say that you probably have a bug Smile | :)

Re: Modeless Dialogs

David Crow22-Jun-04 5:59

David Crow

22-Jun-04 5:59

The reason this code fails is you are trying to manipulate a nonexistent window. Lose the call to UpdateData(). Instead, call SetWindowText(m_wait_mes) in the dialog's OnInitDialog() method. Move the CenterWindow() call to the OnInitDialog() method, too.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Modeless Dialogs

si_6923-Jun-04 1:17

si_69

23-Jun-04 1:17

thanks for that

before i display my modeless dialog, i call

ok = SQLCreateDataSource(m_hWnd,"CP_CMIS_CON");

now if i omit that, then my code works ok, but
with it then i get the errors

Re: Modeless Dialogs

David Crow23-Jun-04 2:04

David Crow

23-Jun-04 2:04

si_69 wrote:
ok = SQLCreateDataSource(m_hWnd,"CP_CMIS_CON");

What is the value of m_hWnd?

si_69 wrote:
...then i get the errors

And those errors are?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Modeless Dialogs

si_6923-Jun-04 2:28

si_69

23-Jun-04 2:28

im calling a dialog (dialog A) from OnNewDocument in my doc class

then in dialog A i call the

SQLCreateDataSource(m_hWnd,"CP_CMIS_CON");

m_hWnd is equalling to (when i step through)

m_hWnd 0x000f0664 {unused=??? } HWND__ *

this displays the Create DataSource dialog ok, the user creates a
datasource, once complete the user is back to dialog A

after OnOK has been called in dialog A, control goes back to
OnNewDocument and the modeless dialog is displayed

hope that makes sense

DavidCrow wrote:
And those errors are?

sorry i should have mentioned, these are the errors i was originally getting, when i first posted the message

thanks

si

Re: Modeless Dialogs

David Crow23-Jun-04 2:40

David Crow

23-Jun-04 2:40

si_69 wrote:
...these are the errors i was originally getting, when i first posted the message

But if you removed the call to UpdateData() and replaced it with a call to SetWindowText(), and moved it and the call to CenterWindow() to OnInitDialog(), you would not be getting the same errors.

Show us the OnNewDocument() and OnInitDialog() code.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

double and float problem

NMiceli22-Jun-04 3:50

NMiceli

22-Jun-04 3:50

Hi.
my problem:

<br />
double a=98;<br />
double b=100;<br />
double c=98/100;<br />
//then c=0.9799999999998 instead 0.98<br />

and why in delphi, vb, etc. i got the 0.98 but not in c++.
I even tried the /Op compiler setting and nothing.
I have readed the microsoft workaround of adding 1e-10 but does not work.
What should i do?.

Thanks in advance.

Re: double and float problem

Tim Smith22-Jun-04 4:01

Tim Smith

22-Jun-04 4:01

There is a very good chance that Delphi and VB are getting the exact same result but due to how they are displaying the number you as seeing a different result.

Floating point math is not exact.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: double and float problem

Antony M Kancidrowski22-Jun-04 4:20

Antony M Kancidrowski

22-Jun-04 4:20

double c=98/100;

would give

c = 0.0 as 98/100 is integer arithmetic, it is then case to double! Wink | ;)

OK,

double c=(a/b) + 0.0000000001;

will give c = 0.98

NOTE: This work around only makes the answer correct to 10dps.

If you change everything to float you will probably get a different answer. These calculations all depend on the format of the floating point number and its precision.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fuity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Re: double and float problem

David Crow22-Jun-04 6:09

David Crow

22-Jun-04 6:09

How a double (or float) is stored in memory and how it is displayed are two different things.

http://research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html

http://www.fact-index.com/f/fl/floating_point_1.html (see Problems with floating-point)

http://www.hal-pc.org/~clyndes/computer-arithmetic/floats.html

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

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