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Tip of the Day
Language: VB7
Expertise: beginner
Jun 22, 2002

Write applications that take arguments

C# has a nice feature that VB.NET lacks: the ability to define a Main procedure that takes an array of strings, each one containig one of the arguments passed on the command line. It's easy to mimick this feature in VB, though.

In fact, while the Command function is still supported in VB.NET, you can retrieve command-line arguments more easily with the GetCommandLineArgs static method of the System.Environment class. This method parses the command-line text and returns individual arguments in an array of strings. Therefore you can have the "real" Sub Main procedure pass this array to a second Main procedure, which is where the real processing occurs. For example, the following code shows how you can build a console application that takes exactly two arguments:


Module Module1

    ' the "official" entry point 
    Sub Main()
        ' call the Main with arguments
        Main(Environment.GetCommandLineArgs())
    End Sub

    ' the "real" Main procedure
    Private Sub Main(ByVal args() As String)
        ' suppose that we expect two arguments, but there is always an
        ' extra argument that contains the EXE filename
        If args Is Nothing OrElse args.Length <> 3 Then
            Console.WriteLine("Syntax error.")
        Else
            ' use the arguments args(1) and args(2)
            ' ...
        End If
    End Sub

End Module
Keep in mind that the first command-line argument is always the complete filename of the running executable, therefore the first argument is args(1).

If you still need the entire command-line, without it being split in arguments, you can use the Environment.CommandLine static method. UPDATE: Richard Deeming and Burton Rodman wrote us to point at an alternative, and much cleaner way, to have your VB app take arguments. You just need to define a Sub Main that takes an array of strings:


Sub Main(ByVal args() As String) 
    ' Display arguments passed to the application
    Dim s As String 
    For Each s In args
        Console.WriteLine(s)
    Next
End Function

The args array will be filled with the command-line arguments, _
    excluding the name of the executable.
Francesco Balena
 
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