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Visual Basic Code > Determine if file is a Windows or DOS executable

Determine if file is a Windows or DOS executable

To determine if an executable has been written for Windows or DOS you
need to check byte offset 24 in the file. If it contains 40h, it's a Windows executable.

Option Explicit

'Purpose     :  Determine if an executable has been written for Windows or DOS.
'Inputs      :  sFilePath                   The path and name of the executable.
'Outputs     :  Returns 1 if the file is a windows executable.
'               Returns 0 if the file is a DOS executable.
'               Returns -1 if the file doesn't exist.

Function FileWindows(ByVal sFilePath As String) As Long
    Dim lhwndFile As Integer
    Dim sTest As String * 1     'Buffer
    
    If Len(sFilePath) > 0 And Len(Dir$(sFilePath)) > 0 Then
        lhwndFile = FreeFile
        Open sFilePath For Binary As #lhwndFile
        Get lhwndFile, 25, sTest
        Close #lhwndFile
        FileWindows = Abs(Asc(sTest) = &H40&)
    Else
        'File doesn't exist
        FileWindows = -1
    End If

End Function

'Demonstration routine
Sub Test()
    Select Case FileWindows("C:\FootballAid.exe")
    Case 1
        MsgBox "Windows file"
    Case 0
        MsgBox "DOS file"
    Case -1
        MsgBox "file doesn't exist"
    End Select
End Sub