Using InvariantCultureIgnoreCase instead of ToUpper for case-insensitive string comparisons

Question

On this page, a commenter writes:

Do NOT ever use .ToUpper to insure comparing strings is case-insensitive.

Instead of this:

type.Name.ToUpper() == (controllerName.ToUpper() + "Controller".ToUpper())) 

Do this:

type.Name.Equals(controllerName + "Controller", 
     StringComparison.InvariantCultureIgnoreCase)

Why is this way preferred?

Answer 1

In short, it's optimized by the CLR (less memory as well).

Further, uppercase comparison is more optimized than ToLower(), if that tiny degree of performance matters.

In response to your example there is a faster way yet:

String.Equals(type.Name, controllerName + "Controller", 
              StringComparison.InvariantCultureIgnoreCase);

Answer 2

Here is the answer in details .. The Turkey Test (read section 3)

As discussed by lots and lots of people, the "I" in Turkish behaves differently than in most languages. Per the Unicode standard, our lowercase "i" becomes "İ" (U+0130 "Latin Capital Letter I With Dot Above") when it moves to uppercase. Similarly, our uppercase "I" becomes "ı" (U+0131 "Latin Small Letter Dotless I") when it moves to lowercase.

Fix: Again, use an ordinal (raw byte) comparer, or invariant culture for comparisons unless you absolutely need culturally based linguistic comparisons (which give you uppercase I's with dots in Turkey)

And according to microsoft you should not even be using the Invariant... but the Ordinal... ( New Recommendations for Using Strings in Microsoft .NET 2.0 )