Question

In C#, you can compare two strings with String.Equals and supply a StringComparison.

I’ve recently been looking to update my archaic method of comparing ToLower() because I read that it doesn’t work on all languages/cultures.

From what I can tell, the comparison types are used to determine order when confronted with a list containing aé and ae as to which should appear first (some cultures order things differently).

With string.Equals, ordering is not important. Therefore is it safe to assume that many of the options are irrelevent, and only [Ordinal] and [Ordinal]IgnoreCase are important?

The MSDN article for String.Equals says

The comparisonType parameter indicates whether the comparison should
use the current or invariant culture, honor or ignore the case of the
two strings being compared, or use word or ordinal sort rules.

string.Equals(myString, theirString, StringComparison.OrdinalIgnoreCase)

I’d also be interested to know how the sort method works internally, does it use String.Compare to work out the relative positioning of two strings?

Answer 1

Case insensitive comparisons are culture dependent. For example using Turkish culture, i is not lowercase for I. With that culture I is paired with ı, and İ is paired with i. See Dotted and dotless I on Wikipedia.

There are a number of weird effects related to culture sensitive string operations. For example "KonNy".StartsWith("Kon") can return false.

So I recommend switching to culture insensitive operations even for seemingly harmless operations.

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And even with culture insensitive operations there is plenty of unintuitive behavior in unicode, such as multiple representations of the same glyph, different codepoints that look identical, zero-width characters that are ignored by some operations, but observed by others,…