Which Version of StringComparer to use

Question

If I want to have a case-insensitive string-keyed dictionary, which version of StringComparer should I use given these constraints:

• The keys in the dictionary come from either C# code or config files written in english locale only (either US, or UK)
• The software is internationalized and will run in different locales

I normally use StringComparer.InvariantCultureIgnoreCase but wasn't sure if that is the correct case. Here is example code:

Dictionary< string, object> stuff = new Dictionary< string, object>(StringComparer.InvariantCultureIgnoreCase);

Answer 1

There are three kinds of comparers:

• Culture-aware
• Culture invariant
• Ordinal

Each comparer has a case-sensitive as well as a case-insensitive version.

An ordinal comparer uses ordinal values of characters. This is the fastest comparer, it should be used for internal purposes.

A culture-aware comparer considers aspects that are specific to the culture of the current thread. It knows the "Turkish i", "Spanish LL", etc. problems. It should be used for UI strings.

The culture invariant comparer is actually not defined and can produce unpredictable results, and thus should never be used at all.

References

1. New Recommendations for Using Strings in Microsoft .NET 2.0

Answer 2

This MSDN article covers everything you could possibly want to know in great depth, including the Turkish-I problem.

It's been a while since I read it, so I'm off to do so again. See you in an hour!

Answer 3

The concept of "case insensitive" is a linguistic one, and so it doesn't make sense without a culture.

See this blog for more information.

That said if you are just talking about strings using the latin alphabet then you will probably get away with the InvariantCulture.

It is probably best to create the dictionary with StringComparer.CurrentCulture, though. This will allow "ß" to match "ss" in your dictionary under a German culture, for example.