Passing binary strings with ActiveX

hello.

I am making an ActiveX control in MFC that is supposed to work with Visual Basic.

I want to make a function in the control that will return a binary string of non-constant size (unsigned char*)

Let's just make the example easy...
In the control there is a function called:
GetFileData(LPCSTR FileName)

how would i return the innards of the file to the user correctly? and this is a binary file, not a text file.

thanks in advance

and i want to pass it back to the VB user as 'String' not as a byte array.

If you pass it back as a null-terminated char* then VB will be able to interpret it as a string.

but since this is a binary string, it may contain nulls in it allready. I want to return a varible declared as string in VB that is basically Unsigned Char* in C++.
does that make sence?

I'd probably have a C prototype similar to this:

Code:

---

void GetData(unsigned char** ppubData, unsigned long *pulLength);

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Then in VB:

Code:

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Declare Sub GetData ... (ByRef ppubData() As Byte, ByRef pulLength As Long)
Dim dat() as Byte
Dim len as long

GetData dat, len

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I can't check that at the moment, but I think the theory's fairly sound.

ok if anyone cares, this is how you do it with MFC C++

in the ActiveX control or DLL you setup a function like so:

Code:

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BSTR ReturnBinaryString()
{
        CString strResult;
       
        //Buffer the string to how ever long
        strResult.GetBufferSetLength(10);

        //theres a null at position 3 of the 10 byte string
        strResult.SetAt(3, '\0');

        //return a SYSSTRING so you do not get dealloction leak
        //(System will take care of deallocation for you)
        return strResult.AllocSysString();

        //now in VB this will return as a string of 10 bytes with a null at position 3.
}

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*whew*