Visual Basic 6.0

Subtract One MessageSet from Another

Demonstrates the Chilkat MessageSet.Subtract method, which removes from this set every identifier whose numeric value is also present in another MessageSet. The only argument is the other set. This example starts with ids 1:10, subtracts 2,4,6, and prints what remains.

Background: A common IMAP pattern is "process everything except what I've already handled." Subtract makes that a single call: remove the already-processed ids from a working set. The comparison is numeric only and this object's HasUids is preserved, so for meaningful results both sets should hold the same id type from the same mailbox. Passing the same object clears the set; passing an empty set changes nothing.

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Visual Basic 6.0

Dim success As Long
success = 0

'  Demonstrates the MessageSet.Subtract method, which removes from this set every identifier
'  that is also present in another MessageSet.  The only argument is the other MessageSet.

Dim msgSet As New MessageSet

'  Start with messages 1 through 10.
success = msgSet.FromCompactString("1:10")
If (success = 0) Then
    Debug.Print msgSet.LastErrorText
    Exit Sub
End If

'  The identifiers that have already been processed and should be excluded.
Dim processed As New MessageSet
success = processed.FromCompactString("2,4,6")
If (success = 0) Then
    Debug.Print processed.LastErrorText
    Exit Sub
End If

'  Remove the already-processed identifiers from msgSet.
msgSet.Subtract processed

'  Show what remains.
Dim remaining As String
remaining = msgSet.ToCompactString()
Debug.Print remaining
'  Output: 1,3,5,7:10