BlobToFile - Copy a BLOB field's contents to a binary file

' Copy a BLOB field's contents to a binary file.

Sub BlobToFile(fld As ADODB.Field, filename As String, _
    Optional ChunkSize As Long = 8192)
    Dim fnum As Integer, bytesLeft As Long, bytes As Long
    Dim tmp() As Byte
    
    ' Raise an error if the field doesn't support GetChunk.
    If (fld.Attributes And adFldLong) = 0 Then
        Err.Raise 1001, , "Field doesn't support the GetChunk method."
    End If
    ' Open the file;, delete it firstoverwrite it if necessary.' Delete the 
    ' file if it exists already, then create a new one.
    If Dir$(filename) <> "" Then Kill filename
    
    fnum = FreeFile
    Open filename For Binary As fnum
    ' Read the field's contents, and write it the data to the file.
    bytesLeft = fld.ActualSize
    
    Do While bytesLeft
        bytes = bytesLeft
        If bytes > ChunkSize Then bytes = ChunkSize
        tmp = fld.GetChunk(bytes)
        Put #fnum, , tmp
        bytesLeft = bytesLeft - bytes
    Loop
    
    Close #fnum
End Sub