C / C++ / MFC

Question re: overriding functions and default arguments

11-May-05 7:46

How about sharing it with the rest of us?

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Re: Abort

Ansari A. Halim11-May-05 7:48

Ansari A. Halim

11-May-05 7:48

There is no problem with the code check out the range of numerator and denominator ur providing.

Re: Abort

Anonymous12-May-05 6:40

Anonymous

12-May-05 6:40

The numerator and denominator were within range, but the debugger was stopping the program from working propperly.

Budric B.11-May-05 6:10

Budric B.

11-May-05 6:10

Hi,
I want to do something like this, but not sure what the behavior will be:

<br />
class A<br />
{<br />
  virtual void Init(int width, int height) = 0;<br />
};<br />
class B<br />
{<br />
  virtual void Init(int width = 640, int height = 480);<br />
};<br />
class C<br />
{<br />
  virtual void Init(int width = 800, int height = 600);<br />
};<br />

Does this mean if I say:

<br />
B *var1 = new B();<br />
A *pvar1 = &myB;<br />
pvar1->Init();  //call with default parameters 640,480<br />
pvar1->Init(320,240);  //call class B's implementation<br />

This will call the correct function?

Re: Question re: overriding functions and default arguments

David Crow11-May-05 6:14

Re: Question re: overriding functions and default arguments

11-May-05 6:14

The easiest way to answer this type of question is to set a breakpoint within each Init() method and see how/when they are called.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

S. Senthil Kumar11-May-05 7:03

S. Senthil Kumar

11-May-05 7:03

I assume that B derives from A. In that case, it will call the correct function (the one in B).

Default parameters are only significant at the calling point. If you don't provide parameters, the compiler puts them in for you. So pvar1->Init() will get compiled as pvar1->Init(640, 480); and will call B's implementation.

Regards
Senthil
_____________________________
My Blog | My Articles | WinMacro

Re: Question re: overriding functions and default arguments

Ansari A. Halim11-May-05 8:07

Ansari A. Halim

11-May-05 8:07

what is myB?

Re: Question re: overriding functions and default arguments

Ryan Binns11-May-05 18:09

Ryan Binns

11-May-05 18:09

This is not a good idea. Good programming practice is to always use the same default values for overridden methods, or better yet, don't use default values for virtual methods. Have you tried to compile this? I don't think it will compile. The compiler doesn't know that pvar1 is actually of type B, so it will check the parameters against the Init method in class A, and fail, because there are no defaults. The defaults for the method in class B will only be used if you call the method through a variable of type B.

Generally, if you don't know what will happen, don't do it, because it will make someone else's life difficult when they come to maintain it and also don't know what will happen.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

DLL and CTypedPtrList problem

Andrew Hoole11-May-05 5:38

Andrew Hoole

11-May-05 5:38

Hi All

I have run out of ideas can anyone help me.

I have created a extension DLL for a Patient selection dialog. When the dialog opens it initializes a list with with patient details. The user can then select one of the patients and the dialog closes and then the program can query the dialog before its destruction to get the index of the patient who was selected.

void CTestApp::OnFileOpen()
{
CLantisPatientSelectDlg dlg;

if(dlg.DoModal() == IDOK){
m_nPatID1 = dlg.GetPatID1();
}
}

To try and be tidy in the OnOK() member function of my class derived from CDialog I delete all of the list.

void CLantisPatientSelectDlg::OnOK()
{
int nIndex;
CPatientDetails *pPatientDetails;
CListCtrl *pList = (CListCtrl *)GetDlgItem(IDC_PATIENTLIST);

nIndex = pList->GetSelectionMark();
if(nIndex != -1){
POSITION pos = m_lpPatients.FindIndex(nIndex);
if(pos != NULL){
pPatientDetails = m_lpPatients.GetAt(pos);
m_nSelectedPatID1 = pPatientDetails->m_Pat_ID1;
}
} else {
m_nSelectedPatID1 = -1;
}

// Get any background list loading to terminate
m_bTerminateLoad = true;
::WaitForSingleObject(m_hListLoadingThread,INFINITE);

DeletePatientList();

CDialog::OnOK();
}

void CLantisPatientSelectDlg::DeletePatientList()
{
CPatientDetails *pPatientDetails;
POSITION pos = m_lpPatients.GetHeadPosition();
while(pos != NULL){
pPatientDetails = m_lpPatients.RemoveHead();
delete pPatientDetails;
pos = m_lpPatients.GetHeadPosition();
}
}

Now all of this seems to work alright until it comes to the end of the OnFileOpen() function at which point the instance of the dialog goes out of scope and the system deletes it. At this point the list which was cleared before and had 0 elements now seems to have a count of -1 (0xFFFFFFFF) and the routine to get rid of it crashes.

I am using a different header file for the DLL'ed Dialog in the application which only lists the functions that have been exported.

Any ideas??

David Crow11-May-05 6:19

11-May-05 6:19

Delete the m_lpPatients list in the dialog's destructor. That way it gets cleaned up no matter if the OK, Cancel, or X button is used.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Andrew Hoole11-May-05 21:37

Andrew Hoole

11-May-05 21:37

Yeah I agree with you and I was doing that but it doesn't seem to be the problem. When it comes time to destruct the instance of the dialog the list, which is empty by this time, appears to have been corrupted in some way and hence can't delete properly.

I have just noticed something else. In the code section

void CTestApp::OnFileOpen()
{
CLantisPatientSelectDlg dlg;

if(dlg.DoModal() == IDOK){
m_nPatID1 = dlg.GetPatID1();
}
}

In my testing before posting I didn't have the
m_nPatID1 = dlg.GetPatID1();
line and hence my code went on to destruct the dlg instance immediately. Now with this code a new failure mode is occurring along with the old one which is generated when you Cancel out of the dialog. In the line highlighted above the dlg.GetPatID1() function runs correctly and returns an int but an access violation occurs when this return value is copied to the m_nPatID1 variable.

I must be doing something silly. I just can't see it.

Andrew

lynchspawn12-May-05 3:12

lynchspawn

12-May-05 3:12

Andrew Hoole wrote:
Now all of this seems to work alright until it comes to the end of the OnFileOpen() function at which point the instance of the dialog goes out of scope and the system deletes it. At this point the list which was cleared before and had 0 elements now seems to have a count of -1 (0xFFFFFFFF) and the routine to get rid of it crashes.

Do you also iterate through the list and delete items when the dialog is destroyed? It looks like you only do this when clicking OK so I'm confused about the part you wrote above stating that the system deletes the dialog and something happens to the list.

What does your GetPatID1() function do - just return the value of the int found during the OnOK() function or does it make use of the list also?

Does anything else access your list?

One last thought - is that style of iteration safe? I don't use lists very often and haven't seen that style of iteration before. I got so frustrated using lists recently (a similar crashing issue that I just couldn't figure out)- I just ended up going with a CTypedPtryArray. I know this won't always work but in my case, the list wasn't really needed and the array worked just fine (and I was able to move on).

If you do figure it out, please post what you found. Good luck!

create/write excell file, set column width

Andrew Hoole13-May-05 0:51

Andrew Hoole

13-May-05 0:51

Hi

I'm stilling working on this but have started a new post as the topic seems to have move on a bit. See DLL memory issue[^] post.

Andrew Hoole

chenggong11-May-05 4:45

chenggong

11-May-05 4:45

Hi, I want to use VC++ (6.0) to create an excel file,
add rows, and set each column to a certain width
so that when the file opens the data are in decent display.

Could you give me some code sample or application sample to do this?

Appreciate your time and help!

Re: create/write excell file, set column width

David Crow11-May-05 5:27

Win2k/WinXP password authentication

11-May-05 5:27

Google for examples of Office, specifically Excel, Automation.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

DarkCloud1411-May-05 4:00

DarkCloud14

11-May-05 4:00

Hi guys,

is it somehow possible to call the windows password dialog with an API Call
and check if the user entered the correct password ?!?

Or is it possible to get the encrypted password of the user currently logged in??

I want to add a password authentication to my application which uses/checks the
entered password against the users windows password...

Is that somehow possible ?!?

THX

Blake Miller11-May-05 4:18

Blake Miller

11-May-05 4:18

You can make your own dialog to collect the information, then call LogonUser to validate it. Don't forget to close the handle if it is successful.

David Crow11-May-05 4:34

11-May-05 4:34

Blake Miller wrote:
...call LogonUser to validate it.

Good idea, but the process that calls LogonUser() must have the SE_TCB_NAME privilege. This is not necessary with Windows XP. Another restriction is that LogonUser() is not available on Windows 9x or ME.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

DarkCloud1411-May-05 10:37

DarkCloud14

11-May-05 10:37

Nice this works fine Big Grin | :-D

I just needed it for Win2k/WinXP not Win98 so thats OK...

THX

David Crow11-May-05 10:58

11-May-05 10:58

How about LookupAccountName()?

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Blake Miller12-May-05 11:36

Blake Miller

12-May-05 11:36

Well, DarkCloud DID mention he wanted to test the password in the first message... I am curious in what sequence of function calls LookupAccountName would be used to verify the password?

David Crow13-May-05 2:05

13-May-05 2:05

Blake Miller wrote:
I am curious in what sequence of function calls LookupAccountName would be used to verify the password?

As am I. My post was in reference to someone wanting the domain of the current user. I think it was posted Wednesday or Thursday, but that post has been deleted. It's odd that my post would get (randomly) attached to another thread.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown