Various parts of the standard are marked as OPTIONAL, so you do not need to support them to have a compliant implementation. This includes, at the moment, any k

Various parts of the standard are marked as OPTIONAL, so you do not need to support them to have a compliant implementation. This includes, at the moment, any kind of Unicode. You may be aware that C and C++ are still used in legacy environments... "legacy" in the sense that these environments have been in continuous use for a long time. > __STDC_ISO_10646__ > An integer literal of the form yyyymmL (for example, 199712L). If this symbol is defined, then every character in the Unicode required set, when stored in an object of type wchar_t, has the same value as the code point of that character. The Unicode required set consists of all the characters that are defined by ISO/IEC 10646, along with all amendments and technical corrigenda as of the specified year and month. You can see the wording, "if this symbol is defined". Note that even if your implementation supports Unicode, and has all sorts of character conversion tables and character property tables, you can easily arrange for those to be statically linked, and only included if actually used. This is normally how standard libraries work in programming environments for resource-constrained systems like microcontrollers. Another interesting macro is the __STDC_HOSTED__ macro--basically, if __STDC_HOSTED__ is missing, then large chunks of the library will not be available. Still completely standards-compliant.