2. case conversion - is locale dependent - for example if the locale is Turkish then upper("i")=="İ" while upper("i")="I" for other languages.
Simple case conversions are the easy 1:1 language- and context-agnostic mappings.
I can't do the more complex conversions because they depend on specific languages and contexts.
Thankfully case folding is not language- nor context-dependent, and is probably what most people want rather than case conversion.
Then don't do case conversion! Do just case folding. For such "simple" and incorrect case conversion I don't need sophisticated Unicode library, I can use use standard operating system API and even std::locale::ctype very successfully (which I do in Boost.Locale if user prefers to use non-icu based backend) Case conversion is: - context dependent: Greek letter "Σ" is converted to "σ" or to "ς", according to position in the word. - locale dependent: Turkish i goes to İ - not 1-to-1: German ß goes to SS in upper case. So if you don't do this right, just don't do it. I'm not sure about case-folding but AFAIK it is not 1-to-1 as well - but I may be wrong.
Yes, it definitely is; but you could still have a "general" collation that would work well enough for most languages.
For general collation that works "well" in most languages I can use strcmp... I don't need Unicode library for this. Artyom