How To Pass Binary Data Between an ActiveX Control and VB
ID: Q154172
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The information in this article applies to:
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Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1, 4.2
SUMMARY
This article will demonstrate how to pass an array of bytes between Visual
Basic and an ActiveX (OLE) Control. This is accomplished by creating a
method that takes a VARIANT parameter that will contain a SafeArray of
bytes.
MORE INFORMATION
Exchanging data in this manner is useful for both raw data and as a
technique for passing data structures.
WARNING: Passing data structures in this manner can pose problems if it
contains pointers.
Sample Code
/* Compile options needed : None
*/
// Automation method in the control BinData.
void CBinDataCtrl::VBtoVCtoVB(const VARIANT FAR& Buffer)
{
// Verify the Variant contains SafeArray of Bytes
if (Buffer.vt == (VT_ARRAY | VT_UI1)) {
long Dims = SafeArrayGetDim(Buffer.parray);
long UpperBounds;
long LowerBounds;
if (Dims == 1) {
SafeArrayGetLBound(Buffer.parray, 1, &LowerBounds);
SafeArrayGetUBound(Buffer.parray, 1, &UpperBounds);
// Use LowerBounds and UpperBounds to force a specific
// Array size as shown here or they can be used to
// dynamically create the buffer.
if ((LowerBounds == 0) && (UpperBounds == 512)) {
// Reference pointer for accessing the SafeArray
unsigned char* buff;
// Variable to store the data from the SafeArray
// could be a global variable or member of CBinDataCtrl
// Shown as a local variable for demonstration purpose only
unsigned char m_abBinaryData[512];
SafeArrayAccessData (Buffer.parray, (void**)&buff);
for (int i = 0; i < 512; i++) {
// Handle the binary data in the buffers
// Copying the data passed from VB to VC.
m_abBinaryData[i] = buff[i];
// Modifying the data to be passed back to VB
buff[i] = 0;
}
SafeArrayUnaccessData (Buffer.parray);
return;
}
}
}
AfxMessageBox ("Invalid parameter passed in VBtoVC method.\n" +
"The array may only have a single dimension.\n" +
"The array must contain 512 bytes.");
}
NOTE: Code for Visual Basic 4.0 where BinData is the name of the control:
Private Sub Form_Load()
Dim buf(512) As Byte
For i = 0 To 511
buf(i) = 50
Next i
BinData1.VBtoVCtoVB buf
End Sub
REFERENCES
For more information, please see the following articles in the Microsoft
Knowledge Base:
Q122287
Limits of VB 3.0 & Disptest as Automation Controllers
Q131046
SAMPLE: BINARY: Transfer Binary Data Using OLE Automation
Q131086
SAMPLE: SAFEARAY: Use of Safe Arrays in Automation
Q140202
SAMPLE: MFCARRAY: Using Safe Arrays in MFC Automation
Q122289
Passing Structures in OLE Automation
Microsoft Systems Journal, June 1996, "Q&A OLE" by Don Box.
Additional query words:
2.00 2.10 2.20 4.00 4.10 4.20 kbinf array Visual Basic 4.00 binary data byte
Keywords : kbole kbCtrl
Version : 2.00 2.10 2.20 4.00 4.10 4.20
Platform : NT WINDOWS
Issue type :