Converting c++ printf formatting to/from VB .NET string formatting

I have some VB .NET software that interfaces to a load of old (but sound) COM objects. The VB provides a GU开发者_StackOverflowI for the COM objects, part of which consists of setting various options on the COM objects - several of which relate to string formatting.

I have a simple pair of VB .NET functions that convert basic %f, %d, %g formats to/from .NET equivalents using a large select case covering specific common strings, but they don't cover all formats. This is the kind of thing I have...

        ElseIf f = "%.3f" Then
            return "0.000"
        ElseIf f = "%.2f" Then
            return "0.00"
        ElseIf f = "%.1f" Then
            return "0.0"

Before I start diving in and making it more versatile with some parsing, does anyone know of a class (eg VB or C# .NET) that provides a decent ready-made implementation? Or perhaps some regexp wizadry could be used?

Many thanks

Tim

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Do you really need both formats, or is one format adopted by your users and the other is used inside the implementation details of your software -- but could go away if you had string formatting functions that recognized your users' options directly?

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You don't need to. Windows has that formatting built-in. You can simply P/Invoke wsprintf from User32.dll.

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Private Const _format_string = "\%(?<length>\d+)?(\.?(?<precision>\d+)?)(?<type>\w)"

Public Shared Function ToNet(format As String) As String
    Dim regex As New Regex(_format_string, RegexOptions.IgnoreCase _
                           Or RegexOptions.CultureInvariant _
                           Or RegexOptions.IgnorePatternWhitespace _
                           Or RegexOptions.Compiled)

    Dim m As Match = regex.Match(format)
    Dim numberTypeFormat As String = String.Empty
    Dim precision As Integer = 1
    Dim precisionFieldName As String = "precision"

    If m.Success Then
        Select Case m.Groups("type").Value
            Case "d", "i", "n", "u", "o"
                numberTypeFormat = "D"
                precisionFieldName = "length"

            Case "x", "X"
                numberTypeFormat = "X"

            Case "f", "F"
                numberTypeFormat = "N"
                precision = 6

            Case "e", "E"
                numberTypeFormat = "E"
                precision = 6

            Case "s"
                Throw New ArgumentException("String type format string not supported", "format")

        End Select

        If m.Groups(precisionFieldName).Success Then
            precision = Integer.Parse(m.Groups(precisionFieldName).Value)

        End If

        Return String.Format("{0}{1}", numberTypeFormat, precision)


    Else
        Throw New ArgumentException("C++ Format string not recognized", "format")

        Return String.Empty

    End If

End Function