C / C++ / MFC

16-May-01 13:50

I wrote an OCX (that dynamically links MFC) using VC6. I wrote a test app that exercises the OCX in VC6, and the OCX appears to work fine.

I then wrote a test app in VB6, and this is where my sad story begins.

The OCX has some string properties, and these properties have Get/Set functions associated with them. If you're at all familiar with VB, you know that while you're running your app (from the VC6 IDE), you can hover your mouse over an OCX property name and a toolitip will popup giving you the value/contents of that property. For all but one property, this works fine, but when I try to hover the mouse over one of them (happens to be a string that holds an IP address), it *crashes the VB IDE*. After a little experimenting, I found that if I deleted the periods from the IP address in the string (did this in the OCX itself in the Get() function), it worked fine.

In the OCX, my Get/Set functions look like this:

CString m_sXXXProperty;

//---------------------------------------------------------//
VARIANT CMyOcxCtrl::GetXXXProperty() 
{
	_variant_t vaResult;
	vaResult = (const char*)m_sXXXProperty;
	return vaResult;
}

//---------------------------------------------------------//
void CMyOcxCtrl::SetXXXProperty(const VARIANT FAR& newValue) 
{
	_variant_t vTemp(newValue);
	m_sXXXProperty = vTemp.bstrVal;
	SetModifiedFlag();
}

First, I need to knbow if I'm doing anything wrong in the code above. Second, I need to know why in hell the dots in the IP address would cause a crash in VB.

In the VB test app, I cycle through a counter (also retrieved from the OCX) to retrieve other strings (using the same mechanism described above), but these strings are not properties. After I have called a retrieval function, the string in the VB app contains the expected text. However, when IO put that string into a listbox, all I get is the first character shown in the listbox.

I don't know much about VB, and really prefer not to know any more than I need to get this test app working as expected. I strongly suspect that my problem lies in the OCX functions that return the strings.

Keep in mind that this OCX works *fine* from the VC6 test application.

Any help would be appreciated.

Dark Angel17-May-01 10:27

Dark Angel

17-May-01 10:27

Disclaimer: I've never written a COM object with MFC.

I think that some of the problem might be that you are passing a CString back to VB. VB is probably looking for a BSTR. COM works with UNICODE, not ascii, so that may be the first problem: The result is getting turned into a bunch of non-ascii UNICODE characters. Since Unicode is looking for a 16-bit null character, VB is probably not finding one and is blowing up. I don't know why this would work in C++.

I don't know if MFC does any conversions or not...take a look at the _bstr_t data type and break out the USES_CONVERSION and associated macros (OLE2T etc).

If you are only seeing the first character, that is likely some sort of Unicode / ascii conversion problem. COM works with Unicode. If the Unicode is converted to ascii without "proper conversion", it will display the first character only because the ASCII character set occupies the unicode positions 0-255.

The string "ABC" in unicode would have the byte pattern "A\0B\0C\0"

hope this helps.

If you need to pass strings to a VB app, why not use the BSTR type in your C++ component? That will map to a VB String variable directly.

"Harland Pepper, would you stop naming nuts" - Harland Pepper

Carlos Antollini17-May-01 10:49

Carlos Antollini

17-May-01 10:49

I think that you need this....

CString m_strProperty = _T("");

STDMETHODIMP CCPerson::get_Property(BSTR *pVal)
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())

// TODO: Add your implementation code here
::SysFreeString(*pVal);
*pVal = m_strProperty.AllocSysString();
return S_OK;
}

STDMETHODIMP CCPerson::put_Property(BSTR newVal)
{
AFX_MANAGE_STATE(AfxGetStaticModuleState())

// TODO: Add your implementation code here
m_strProperty = newVal;
return S_OK;
}

Cheers.

Carlos Antollini.

#realJSOP17-May-01 10:53

17-May-01 10:53

This isn't a COM object as much as it is an OCX. The Get/Set functions were inserted by ClassWizard, and they accept/return VARIANT's. I'm using the _variant_t wrapper class because it's easier to work with (or so I thought).

Reading disk directly under Win32

21-May-01 21:31

in the code you show that you are using VARIANT return type for your property;
may be the vb ide gets an ip-address wrong as anumber (with to many dots in it).
Try using BSTR (*) ? as return type to get a real vb string, (or may be you only
need to set vaResult.vt to the right variant type constant) Blush | :O

Wirawan Purwanto16-May-01 13:20

Wirawan Purwanto

16-May-01 13:20

This is a question on system programming (like Windows API, hardware programming, etc).

How to read a disk directly in Windows (under Win32)? I need the following equivalent of DOS functions:

INT 25h/26h -- absolute disk read/write (i.e. reading logical disk sector)

INT 13h -- physical disk sector read/write

I need the equivalence of INT 25/26 *very badly*. Especially the READ function. This should be something trivial. If you know an URL containing this info, I would appreciate it.

Assume I will write the program under generic C++ program (GNU C++). But if you know something, you can assume other things if you want, but *I don't* have Delphi, MSVC, etc.... Frown | :-(

Please... I need someone help me find the right reference.

Thanks,
Wirawan

Re: Reading disk directly under Win32

Tomasz Sowinski17-May-01 4:51

Tomasz Sowinski

17-May-01 4:51

Just curious: why do you need this functionality?
Cheers,

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

Deleting strings from listboxes?

16-May-01 12:40

I have a list box in my project and i need the user to be abel to delete an object from the listbox but you can only delete a strings if you know the number place where the string is in in the box. How can i have the project find the number sting when the string is clicked?
Cool | :cool:

Justin

Re: Deleting strings from listboxes?

Christian Graus16-May-01 12:55

Christian Graus

16-May-01 12:55

GetCurSel returns the current selection index. So you go m_List.DeleteString(m_List.GetCurSel());

Christian

I've learned that you cannot make someone love you. All you can do is stalk them and hope they panic and give in.

The early bird may get the worm, but it's the second mouse that gets the cheese.

16-May-01 12:47

If your going to make this like you are why don't you do it in QBASIC. It would be so simple you could finish it in a few minutes. If you want I can help you do it in QBASIC, E-MAIL me @ rcdude10tc3@aol.com, c ya Cool | :cool:

Justin

#realJSOP17-May-01 2:31

17-May-01 2:31

1) You haven't told us what you want help for.

2) This looks like a school homework assignment. I have a real problem finishing someone's homework for them. If this is an incorrect assumption, I'll apologize now, but I don't want to see CodeProject become a haven for folks too lazy to learn how to do stuff on their own (when it's necessary for them to do so).

#realJSOP17-May-01 4:41

17-May-01 4:41

Well, don't you think asking specific questions would get you a specific answer a lot freakin faster? If you cop an attitude, you'll get attitude back.

[attitude]
Go somewhere else if you want someone to finish your homework assignment for you. I have a idea, go ask your instructor.
[/attitude]

yawn...