C / C++ / MFC

14-Aug-02 23:52

Hi,

I'm looking to catch an input error from a dialog box. I have edit boxes with doubles mapped to them so when letters are entered and the button is pressed the application automatically generates a MessageBox asking the user to enter a number. I want to catch this in order to be able to reset variables, etc. Is there a Message Handler for this?

Thanks,

Graham

Tomasz Sowinski15-Aug-02 0:07

15-Aug-02 0:07

gm_coll wrote:
I have edit boxes with doubles mapped to them so when letters are entered and the button is pressed the application automatically generates a MessageBox asking the user to enter a number

This is implemented in DDX_Text function. Calls to DDX_xxx functions are inserted in CYourDlg::DoDataExchange by ClassWizard. Unfortunately, there's no notification going back to your app when validation fails - MFC just displays a message box and throws CUserException, which is later catched in CWnd::UpdateData.

You basically have two options: catching CUserException (and throwing it again with argument-less 'throw') or doing data transfer/validation without DDX_ routines.

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

gm_coll15-Aug-02 0:32

15-Aug-02 0:32

Would I catch the CUserException in my BN_CLICKED message handler and carry out my additional functions before throwing the exception on?

Thanks in advance,

Graham

Tomasz Sowinski15-Aug-02 0:38

15-Aug-02 0:38

Data transfer/validation happens when UpdateData is called. MFC will call UpdateData for you in its OK handler. You may also call this method 'manually' in response to some event. Are you calling UpdateData yourself?

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

gm_coll15-Aug-02 1:09

15-Aug-02 1:09

I'm calling UpdateData() in my BN_CLICKED message handler to send the data from the controls to the variables. At the end of the function, after I have manipulated the variables, I call UpdateData(FALSE) to send the data back to the controls.

Tomasz Sowinski15-Aug-02 1:12

Re: Catching Dialog Box Errors - ignore previous post

15-Aug-02 1:12

Your first call to UpdateData should be in try..catch block. Please note that MFC throws 'CUserException *'.

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

Tomasz Sowinski15-Aug-02 1:13

Re: Catching Dialog Box Errors - ignore previous post

15-Aug-02 1:13

Sorry - you need to provide try..catch in DoDataExchange. Otherwise CWnd::UpdateData will catch and process the exception.

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

gm_coll15-Aug-02 1:25

Re: Catching Dialog Box Errors - ignore previous post

15-Aug-02 1:25

So within DoDataExchange I have to provide the code:

try
{
// code
}

catch (CUserException* e)
{
// carry out resetting of variables
}

Do I also have to throw the exception?

Thanks,

Graham

Tomasz Sowinski15-Aug-02 1:31

Re: Catching Dialog Box Errors - ignore previous post

15-Aug-02 1:31

gm_coll wrote:
Do I also have to throw the exception?

Yes. Just use 'throw' without arguments, which transfers control to upper-level catch handler.

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

gm_coll15-Aug-02 1:52

Re: Catching Dialog Box Errors - ignore previous post

15-Aug-02 1:52

Sorry, I'm still confused.

If I use a try..catch block in DoDataExchange what do I put in the try block, because what I am trying to do is transfer the data from the controls to the variables and this should already have happened. Will this not have already generated an exception when the data containing non-numeric characters is attempted to map to my double?

Tomasz Sowinski15-Aug-02 2:00

Smart Pointer implementation question

15-Aug-02 2:00

gm_coll wrote:
Will this not have already generated an exception when the data containing non-numeric characters is attempted to map to my double?

Yes, the exception was already generated and user has seen the MFC's message box. But you wanted to do something extra (at least this is what you originally posted). The catch block in DoDataExchange is your chance - you're getting control before DoDataExchange returns to CWnd::UpdateData.

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

pankajdaga14-Aug-02 23:50

pankajdaga

14-Aug-02 23:50

Hi,

I have a simple smart pointer implementation. Now, I want the pointer to allow type casting. For example, a derived class should be able to cast back to the base class etc. Any ideas on how to do this?

Here is the implementation so far:

template <class t="">
class SmartPtr
{
public:

/**
Default constructor.
*/
SmartPtr(): _p (0) {}

/**
Pass new directly as the argument
*/
SmartPtr (T* p): _p (p) {}

/**
Copy constructor
*/
SmartPtr(SmartPtr& source) :_p(source.Acquire())
{}

/**
Assignment operator: transfers ownership
*/
SmartPtr& operator= (SmartPtr& pSource)
{
if (_p != pSource._p)
{
delete _p;
_p = pSource.Acquire();
}
}

/**
Delete the pointer, when going out of scope.
The pointer does not get deleted if the owner has changed
*/
~XPtr () { delete _p; }

/**
Null out the pointer. So if the owner has changed and
this object goes out of scope, it does not delete the pointer.
*/
T* Acquire ()
{
T * pTmp = _p;
_p = 0;
return pTmp;
}

/**
for pointer like syntax
*/
T * operator->() { return _p; }

/**
Get the raw pointer
*/
T const & GetAccess () const { return *_p; }

private:
/**
The raw pointer
*/
T * _p;
};

Thanks,

Pankaj

Without struggle, there is no progress

Tomasz Sowinski14-Aug-02 23:59

14-Aug-02 23:59

Add 'operator T* () { return _p; }'

Tomasz Sowinski -- http://www.shooltz.com

Never argue with an idiot, he'll bring you to his level and beat you with experience.

pankajdaga16-Aug-02 1:45

pankajdaga

16-Aug-02 1:45

Thanks! That worked! However, how is it that we do not have to supply any return type? Does C++ automatically determine the return type according to the casting operator. Also, I did not know that a class function could be without a return type. However, it works! So obviously I need to learn a lot! Any input on this will be greatly appreciated!

Pankaj

Without struggle, there is no progress

Stuart Dootson15-Aug-02 11:15

Stuart Dootson

15-Aug-02 11:15

Without wishing to sound nasty or dificult or stupid...is this smart pointer implementation giving you anything more than auto_ptr in the Standard C++ Library - and if not, why not just use that?

Stuart Dootson

'Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p'

pankajdaga16-Aug-02 1:43

pankajdaga

16-Aug-02 1:43

I know I can use auto_ptr. I am not really using it in any project. It just feels good to know that you can implement this behavior sometime. Also, gives me a better understanding of the language and everything. Basically, just for educational purposes. That is all Smile | :)

Pankaj

Without struggle, there is no progress