Is uppercase string always of the same length as the original one?

Question

• Is the length of an unicode uppercase string always the same as the length of an original string, no matter what culture is used?

• Is the length of an unicode lowercase string always the same as the length of an original string, no matter what culture is used?

In other words, is the following true in C#?

text.ToUpper(CultureInfo.CurrentCulture).Length == text.Length
text.ToLower(CultureInfo.CurrentCulture).Length == text.Length

Note that I'm not interested about the number of bytes: the question about that is already answered.

Answer 1

The answers to the questions are “No” and “Yes”, as far as Unicode Standard is concerned.

For example, when converting to uppercase, “ß” U+00DF LATIN SMALL LETTER SHARP S is mapped to two characters “SS” by Unicode mapping rules. It is possible to map it to the single character “ẞ” U+1E9E LATIN CAPITAL LETTER SHARP S, but that’s not the default (and not common at all). Another example is that “fi” U+FB01 LATIN SMALL LIGATURE FI is mapped to “FI”.

In the opposite direction, there is no default mapping that would change the number of characters. See Character Properties, Case Mappings & Names FAQ, which links to the file SpecialCasing.txt that contains all deviations from simple one-to-one mappings. The only rules there that would make the lowercase string different from an uppercase original are a few optional rules related to Lithuanian practices.