In C# check that filename is *possibly* valid (not that it exists)

bool bOk = false;
try
{
  new System.IO.FileInfo(fileName);
  bOk = true;
}
catch (ArgumentException)
{
}
catch (System.IO.PathTooLongException)
{
}
catch (NotSupportedException)
{
}
if (!bOk)
{
  ...
}
else
{
  ...
}

Directory.GetLogicalDrives() // Returns an array of strings like "c:"
Path.GetInvalidFileNameChars() // Returns an array of characters that cannot be used in a file name
Path.GetInvalidPathChars() // Returns an array of characters that cannot be used in a path.

bool IsValidFilename(string testName)
{
    string regexString = "[" + Regex.Escape(Path.GetInvalidPathChars()) + "]";
    Regex containsABadCharacter = new Regex(regexString);

    if (containsABadCharacter.IsMatch(testName)
    {
        return false;
    }

    // Check for drive
    string pathRoot = Path.GetPathRoot(testName);
    if (Directory.GetLogicalDrives().Contains(pathRoot))
    {
        // etc
    }

    // other checks for UNC, drive-path format, etc

    return true;
}

char[] invalidChars = Path.GetInvalidFileNameChars(); //returns invalid charachters

Path.GetPathRoot(string); // will return the root.

System.IO.DriveInfo.GetDrives()

System.IO.Path.GetInvalidFileNameChars();
System.IO.Path.GetInvalidPathChars();