Should this regex pattern throw an exception?

Question

Should this regex pattern throw an exception? Does for me.

^\d{3}[a-z]

The error is: parsing "^\d{3}[a" - Unterminated [] set.

I feel dumb. I don't get the error. (My RegexBuddy seems okay with it.)

A little more context which I hope doesn't cloud the issue:

I am writing this for a CLR user defined function in SQL Server:

[Microsoft.SqlServer.Server.SqlFunction(IsDeterministic=true)]
  public static SqlChars Match(
    SqlChars input,
    SqlString pattern,
    SqlInt32 matchNb,
    SqlString name,
    SqlBoolean compile,
    SqlBoolean ignoreCase,
    SqlBoolean multiline,
    SqlBoolean singleline
    )
  {
    if (input.IsNull || pattern.IsNull || matchNb.IsNull || name.IsNull)
      return SqlChars.Null; 

    RegexOptions options = RegexOptions.IgnorePatternWhitespace |
      (compile.Value ? RegexOptions.Compiled : 0) |
      (ignoreCase.Value ? RegexOptions.IgnoreCase : 0) |
      (multiline.Value ? RegexOptions.Multiline : 0) |
      (singleline.Value ? RegexOptions.Singleline : 0);

    Regex regex = new Regex(pattern.Value, options);
    MatchCollection matches = regex.Matches(new string(input.Value));

    if (matches.Count == 0 || matchNb.Value > (matches.Count-1))
      return SqlChars.Null;

    Match match = matches[matchNb.Value];

    int number;
    if (Int32.TryParse(name.Value, out number))
    {
      return (number > (match.Groups.Count - 1)) ? 
        SqlChars.Null :
        new SqlChars(match.Groups[number].Value);
    }
    else
    {
      return new SqlChars(match.Groups[name.Value].Value);
    }
  }

Setting it up with

CREATE FUNCTION Match(@input NVARCHAR(max), @pattern NVARCHAR(8), @matchNb INT, @name NVARCHAR(64), @compile BIT, @ignoreCase BIT, @multiline BIT, @singleline BIT)
RETURNS NVARCHAR(max)
AS EXTERNAL NAME [RegEx].[UserDefinedFunctions].[Match]
GO

And testing it with:

SELECT dbo.Match(
  N'123x45.6789' --@input
, N'^\d{3}[a-z]' --@pattern
,0 --@matchNb
,0 --@name
,0 --@compile
,1 --@ignoreCase
,0 --@multiline
,1 --@singleline
)

Answer 1

In your CREATE FUNCTION statement you are delcaring @pattern as NVARCHAR(8). This is truncating your pattern to 8 characters.