declare-statement_1.vb

    Declare Function getUserName Lib "advapi32.dll" Alias "GetUserNameA" (
        ByVal lpBuffer As String, ByRef nSize As Integer) As Integer
    Sub getUser()
        Dim buffer As String = New String(CChar(" "), 25)
        Dim retVal As Integer = getUserName(buffer, 25)
        Dim userName As String = Strings.Left(buffer, InStr(buffer, Chr(0)) - 1)
        MsgBox(userName)
    End Sub