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'System & API - How to Return a volume's serial number
Option Explicit
 
Private Const MAX_FILENAME_LEN = 256
 
Private Declare Function GetVolumeInformation& Lib "kernel32" Alias "GetVolumeInformationA" _
    (ByVal lpRootPathName As String, ByVal pVolumeNameBuffer As String, _
    ByVal nVolumeNameSize As Long, lpVolumeSerialNumber As Long, lpMaximumComponentLength As Long, _
    lpFileSystemFlags As Long, ByVal lpFileSystemNameBuffer As String, _
    ByVal nFileSystemNameSize As Long)
 
Public Function GetSerialNumber(ByVal sDriveLetter As String) As Long
    Dim lSerial As Long, I As Long, J As Long
    Dim s As String * MAX_FILENAME_LEN
    Dim s2 As String * MAX_FILENAME_LEN
    Call GetVolumeInformation(sDriveLetter & ":\" & Chr$(0), s, MAX_FILENAME_LEN, lSerial, I, J, _
        s2, MAX_FILENAME_LEN)
    GetSerialNumber = lSerial
End Function