Ignoring accented letters in string comparison

Question

I need to compare 2 strings in C# and treat accented letters the same as non-accented letters. For example:

string s1 = "hello";
string s2 = "héllo";

s1.Equals(s2, StringComparison.InvariantCultureIgnoreCase);
s1.Equals(s2, StringComparison.OrdinalIgnoreCase);

These 2 strings need to be the same (as far as my application is concerned), but both of these statements evaluate to false. Is there a way in C# to do this?

Answer 1

EDIT 2012-01-20: Oh boy! The solution was so much simpler and has been in the framework nearly forever. As pointed out by knightpfhor :

string.Compare(s1, s2, CultureInfo.CurrentCulture, CompareOptions.IgnoreNonSpace);

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Here's a function that strips diacritics from a string:

static string RemoveDiacritics(string text)
{
  string formD = text.Normalize(NormalizationForm.FormD);
  StringBuilder sb = new StringBuilder();

  foreach (char ch in formD)
  {
    UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(ch);
    if (uc != UnicodeCategory.NonSpacingMark)
    {
      sb.Append(ch);
    }
  }

  return sb.ToString().Normalize(NormalizationForm.FormC);
}

More details on MichKap's blog (RIP...).

The principle is that is it turns 'é' into 2 successive chars 'e', acute. It then iterates through the chars and skips the diacritics.

"héllo" becomes "he<acute>llo", which in turn becomes "hello".

Debug.Assert("hello"==RemoveDiacritics("héllo"));

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Note: Here's a more compact .NET4+ friendly version of the same function:

static string RemoveDiacritics(string text)
{
  return string.Concat( 
      text.Normalize(NormalizationForm.FormD)
      .Where(ch => CharUnicodeInfo.GetUnicodeCategory(ch)!=
                                    UnicodeCategory.NonSpacingMark)
    ).Normalize(NormalizationForm.FormC);
}