Valid filename check. What is the best way?

Question

See subject of positing for question.

1) I recall seeing a really cool option in VB.NET using LINQ to match using "LIKE%'

2) I know regular expressions will work and I suspect that will result in the shortest code and probably won't be too hard to read for such a simple test.

Here's what I did. Warning: You're gonna hate it.

Private Shared Function FileNameIsOk(ByVal fileName As String) As Boolean

    For Position As Integer = 0 To fileName.Length - 1

        Dim Character As String = fileName.Substring(Position, 1).ToUpper
        Dim AsciiCharacter As Integer = Asc(Character)

        Select Case True

            Case Character = "_" 'allow _
            Case Character = "." 'allow .
            Case AsciiCharacter >= Asc("A") And AsciiCharacter <= Asc("A") 'Allow alphas
            Case AsciiCharacter >= Asc("0") AndAlso AsciiCharacter <= Asc("9") 'allow digits

            Case Else 'otherwise, invalid character
                Return False

        End Select

    Next

    Return True

End Function

Answer 1

Frankly, I'd just use the FileInfo object built in to .NET, and check for an exception for invalidity. See this reference for details.

Answer 2

It is a regex and C# but:

using System;
using System.Text.RegularExpressions;

/// <summary>
/// Gets whether the specified path is a valid absolute file path.
/// </summary>
/// <param name="path">Any path. OK if null or empty.</param>
static public bool IsValidPath( string path )
{
    Regex r = new Regex( @"^(([a-zA-Z]\:)|(\\))(\\{1}|((\\{1})[^\\]([^/:*?<>""|]*))+)$" );
    return r.IsMatch( path );
}

Answer 3

How about Path.GetInvalidFileNameChars and Path.GetInvalidPathChars?

Public Shared Function FilenameIsOK(ByVal fileNameAndPath as String) as Boolean
    Dim fileName = Path.GetFileName(fileNameAndPath)
    Dim directory = Path.GetDirectoryName(fileNameAndPath)
    For each c in Path.GetInvalidFileNameChars()
        If fileName.Contains(c) Then
            Return False
        End If
    Next
    For each c in Path.GetInvalidPathChars()
        If directory.Contains(c) Then
            Return False
        End If
    Next
    Return True
End Function

Answer 4

Even though this is quite old, it's still valid, and I ended up here looking for the solution to how to check the filename for invalid characters. I looked at the accepted answer and found a few holes.

Hopefully these modifications are of some use to someone else.

Public Function FilenameIsOK(ByVal fileNameAndPath As String) As Boolean
    Dim fileName As String = String.Empty
    Dim theDirectory As String = fileNameAndPath

    Dim p As Char = Path.DirectorySeparatorChar

    Dim splitPath() As String
    splitPath = fileNameAndPath.Split(p)
    If splitPath.Length > 1 Then
        fileName = splitPath(splitPath.Length - 1)
        theDirectory = String.Join(p, splitPath, 0, splitPath.Length - 1)
    End If

    For Each c As Char In Path.GetInvalidFileNameChars()
        If fileName.Contains(c) Then
            Return False
        End If
    Next

    For Each c As Char In Path.GetInvalidPathChars()
        If theDirectory.Contains(c) Then
            Return False
        End If
    Next
    Return True
End Function