CComVariant

[Evan]

I have need in my ATL COM component to pass in
a VARIANT (at which point i assing it to a CComVariant)
the data is nothing special..just text...it's a BSTR
to support vbscript and vb clients. my question is this,
after passing this in (which works) i need to convert
the Variant to BYTE in order for a function to operate
on it (by reference).. I have tried mVar.ChangeType(VT_BYREF|VT_UI1,NULL)
which fails everytime..could someone show me what i'm doing
wrong (or another way to accomplish this)

BOOL changedata(BYTE *rawdata);

STDMETHODIMP Cmyobj::manip(VARIANT data, VARIANT *result)
{

BOOL success;
CComVariant mVar;

mVar = data;
if (! SUCCEEDED(mVar.ChangeType(VT_BYREF|VT_UI1,NULL))) {
return mVar.ChangeType(VT_BYREF|VT_UI1,NULL);
}

success = changedata(mVar.pbVal);

if (success) {
mVar.Detach(result);
return S_OK;
}
else {
return E_FAIL;
}
}

it always dies trying to change the variant to BYTE with a type
mismatch error, the changedata() function operates on the function
as a stream, and doesnt care if its text or symbols or whatever, as
long as it is BYTE

[Boris Karadjov]

"Evan" <evanh23@usa.net> wrote:
>
>I have need in my ATL COM component to pass in
>a VARIANT (at which point i assing it to a CComVariant)
>the data is nothing special..just text...it's a BSTR
>to support vbscript and vb clients. my question is this,
>after passing this in (which works) i need to convert
>the Variant to BYTE in order for a function to operate
>on it (by reference).. I have tried mVar.ChangeType(VT_BYREF|VT_UI1,NULL)
>which fails everytime..could someone show me what i'm doing
>wrong (or another way to accomplish this)

If you need to operate on a single byte, convert it to VT_UI1, not VT_BYREF|VT_UI1
and pass &V_UI1(&mVar) to your function.

If, on the other hand, you need to manipulate the whole string as an array
of bytes, simply cast it to (BYTE *) and pass SysStringLen(V_BSTR(&mVar))
* sizeof(OLECHAR) as the number of bytes.


Boris Karadjov
Brainbench MVP for Visual C++
http://www.brainbench.com