Re: Pure virtual destructor ? - C / C++ / MFC Discussion Boards

eyalle23-Jun-10 0:29

23-Jun-10 0:29

Hello all
I've implemented a class dervied from CRecordset.
this class gets the DB and sql query and retrives data.
everything was working fine, untill i've decided to delete the data directly from the DB.
when i'm running the same code, the class retrives the same data, although the data is erased.
what's the problem ??

CSpecificGraphsRS rsSpeGraphs(&m_db);
    strQuery.Format("SELECT * FROM GRAPHS ORDER BY GRAPH_ID"); //empty result query
rsSpeGraphs.Open(CRecordset::snapshot, strQuery, CRecordset::none);
while (!rsSpeGraphs.IsEOF())
{
           //gets in this while although the query is empty in DB
           //but actually the value is passed
          //seems like it keeps it somewhere in the memory
      genGraphDisplay.strGraphId = rsSpeGraphs.m_GRAPH_ID;
    }

Re: CRecordset old data problem

loyal ginger23-Jun-10 1:52

loyal ginger

23-Jun-10 1:52

Did you make sure your program is accessing the same database that you directly deleted data from? Sometimes multiple test databases are used and the wrong one may be modified, making you believe that the program is not working.

Re: CRecordset old data problem

eyalle23-Jun-10 2:14

eyalle

23-Jun-10 2:14

yes i did,
they access the same DB.

Re: CRecordset old data problem

David Crow23-Jun-10 3:48

David Crow

23-Jun-10 3:48

Are the records in the set truly deleted? Try:

while (! rsSpeGraphs.IsEOF())
{
    if (rsSpeGraphs.IsDeleted())
        TRACE(_T("Recod is deleted.\n"));
  
    rsSpeGraphs.MoveNext();
}

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Pure virtual destructor ?

krishna_CP23-Jun-10 0:17

krishna_CP

23-Jun-10 0:17

HI,

What is pure virtual destructor?

what is the use of using pure virtual destructor ?

Thanks,
Krish.

Re: Pure virtual destructor ?

CPallini23-Jun-10 0:40

CPallini

23-Jun-10 0:40

See, for instance, the competitors...[^].

Personally, I think you should always use virtual destructors. No need to have pure virtual destructors (see [^]).

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[My articles]

Re: Pure virtual destructor ?

C^hris L^osinger23-Jun-10 1:30

C^hris L^osinger

23-Jun-10 1:30

LMGTFY[^]

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Re: Pure virtual destructor ?

Aescleal23-Jun-10 6:52

Aescleal

23-Jun-10 6:52

A pure virtual destructor is any destructor marked as virtual with = 0 after it's signature, e.g:

class T
{
    public:
        virtual ~T() = 0;
};

Making a destructor pure virtual means very little more than making the destructor virtual (and you do that to make sure the correct destructor is called when you delete an object through a base class pointer). The additional bit is that it means the derived class has to define it's own destructor and not rely on the base class one.

One additional wrinkle is that all pure virtual destructors have to have an implementation, unlike normal pure virtual member functions which don't have to have one.

Cheers,

Ash

Mainframe loses focus with modeless dialogs in MFC application

David Ayllon23-Jun-10 0:06

David Ayllon

23-Jun-10 0:06

Hi,

I have developed and application based on modeless dialogs (the view is a formview and the others are CDialog and I show and hide them as corresponds). But I have a problem because when a modeless dialog has the caption, the mainframe loses it and I cannot access to the menu and toolbar from acceleratos because they don't have the caption.
How could I keep always caption on the mainframe? Maybe all dialogs can be defined as formview?

Thank in advance

Re: Mainframe loses focus with modeless dialogs in MFC application

Richard MacCutchan23-Jun-10 3:05

Richard MacCutchan

23-Jun-10 3:05

Don't make the dialog a child of your main window, set its parent window to NULL. In that way it will be a child of the desktop and will not take the focus from your main window.

It's time for a new signature.

Re: Mainframe loses focus with modeless dialogs in MFC application

manchukuo23-Jun-10 16:31

manchukuo

23-Jun-10 16:31

Or you can leave it like child of your window and put return FALSE in OnInitDialogfunction

Re: Mainframe loses focus with modeless dialogs in MFC application

Richard MacCutchan23-Jun-10 21:45

Richard MacCutchan

23-Jun-10 21:45

What?

It's time for a new signature.

Re: Mainframe loses focus with modeless dialogs in MFC application

David Ayllon23-Jun-10 23:46

David Ayllon

23-Jun-10 23:46

Hi,

Thank you for your help, but unfortunately it didn't work.

I set:

BOOL CDlgListaPt::Create()
{
return CDialog::Create(CDlgListaPt::IDD);
this->SetParent(NULL);
}
and also tried in Oninitdialog method but the mainframe lose caption

my dialog is a popup non-modal dialog that is created from the view (what is a formview)
If I change the dialog style to child, the mainframe keeps caption but I cannot control de dialog.

The other solution returning false in oninitdialog it didn't work either.

Regards

threads

jt_snjy0722-Jun-10 23:42

jt_snjy07

22-Jun-10 23:42

how many threads can possibly be made in a program please explian launguage wise

Re: threads

CPallini22-Jun-10 23:55

CPallini

22-Jun-10 23:55

CreateThread documentation [^], Remarks section:

The number of threads a process can create is limited by the available virtual memory. By default, every thread has one megabyte of stack space. Therefore, you can create at most 2,048 threads. If you reduce the default stack size, you can create more threads. However, your application will have better performance if you create one thread per processor and build queues of requests for which the application maintains the context information. A thread would process all requests in a queue before processing requests in the next queue.

Re: threads

«_Superman_»23-Jun-10 0:09

«_Superman_»

23-Jun-10 0:09

Read this blog entry - Pushing the Limits of Windows: Processes and Threads[^]

«_Superman_»

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Re: threads

El Corazon23-Jun-10 6:36

El Corazon

23-Jun-10 6:36

jt_snjy07 wrote:
how many threads can possibly be made in a program please explian launguage wise

http://www.nvidia.com/object/fermi_architecture.html[^]

Thousands, many thousands.... probably not the architecture you meant.... but you didn't specify any limits. Smile | :)

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Re: threads

Aescleal23-Jun-10 6:50

Aescleal

23-Jun-10 6:50

It depends on the thread library's implementation. For example if you were mad enough to create a user mode library then the number of threads would depend on how many thread contexts you could fit into memory in one process. If you're using kernel threads then it depends on how the OS is implemented and how many thread contexts it reserves space for.

Cheers,

Ash

Re: threads

Stephen Hewitt1-Jul-10 18:54

Stephen Hewitt

1-Jul-10 18:54

Whenever I hear this question (it comes up a lot) I immediately suspect it's from someone who's application is using way too many.

Steve

C calling convention importance

rupeshkp72822-Jun-10 23:13

rupeshkp728

22-Jun-10 23:13

C calling convention we all know defines a way how the parameters are pushed onto the stack.
My question is when and how does this C calling conventions matters to a user?
When the user will have to bother about the calling conventions in his project?

Re: C calling convention importance

Cedric Moonen22-Jun-10 23:52

Cedric Moonen

22-Jun-10 23:52

For instance when you write a dll that could be used in programs which are using another calling convention. Typically, using a C dll in a VB program.

Cédric Moonen
Software developer

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Re: C calling convention importance

rupeshkp72823-Jun-10 1:29

rupeshkp728

23-Jun-10 1:29

ok thanks cedric

Is time for QT?

lxkjlzz22-Jun-10 22:34

lxkjlzz

22-Jun-10 22:34