converting VARIANT to ...

[AndyMitchell]

I need to know how to get a VARIANT data type into something more useful like a char array or a CString. I have tried the following.

void CTestmodulesDlg::OnCheckResponseOK(VARIANT FAR* Response)
{
COleVariant MyVar;
char mc [10];
CString MyCStr;

MyVar.Attach (*Response);

mc [0] = *MyVar.pbVal;
mc [1] = *(MyVar.pbVal+1);
mc [2] = *(MyVar.pbVal+2);
mc [3] = *(MyVar.pbVal+3);
mc [4] = *(MyVar.pbVal+4);
mc [5] = 0;

MyCStr = MyVar.pbVal;
}

But looking at the mc array and the CString it seems that each element has a terminating 0 after it. For example if Response is "Hello" then it is stored as 'H',0,'e',0,'l',0,'l',0,'o',0.

Any suggestions?

[parksie]

No, that's correct.

OLE strings are Unicode, i.e. 16-bit. So, you end up with extra nulls embedded in the string - which is then terminated with a double null (i.e. a SINGLE null wchar_t character).

I think OLE strings have a length as well, so the terminator may not be there, I think I recall something in the MS docs saying not to rely on it.

[CornedBee]

To get the string out of a VARIANT, do this:
CString str;
str = (LPWSTR)Response->bstrVal;


Be aware that if the bstr does not contain a terminating 0, this method won't work. I#ll post a better method later.

[AndyMitchell]

Thanks for the tips. I how figured out how to do it:


void CTestmodulesDlg::OnCheckResponseOK(const VARIANT FAR& Response)
{
_variant_t MyVar (Response);
CString RespStr;

RespStr = MyVar.bstrVal;
////////////// or
CString RespStr (Response);
/////////////
}

No need for the cast.It's always easy when you know how.

[CornedBee]

As Jeff Prosise describes it, a BSTR is a counted UNICODE string. The character count is a WORD just before the first character. BSTR is a typedef of (unsigned int*), which points to the first character. This is why you can simply cast it to WCHAR*.
This would be the memory image of the string "Hello" (hex):

05 00 48 00 65 00 6c 00 6c 00 6f 00 00 00
count  'H'   'e'   'l'   'l'   'o'   '\0'
       ^
value of the BSTR var points here

Therefore, you can do

void BSTRtoCString(BSTR bstrIn, CString &strOut)
{
  WORD wCount = *(((WORD*)bstrIn) - 1);
  WCHAR *ws = new WCHAR[wCount + 1];
  memcpy(ws, bstrIn, wCount * sizeof(WCHAR));
  ws[wCount] = 0;
  strOut = ws;
  delete ws;
}

This should work, but I can't guarantee it.