In generic terms, we refer to char, char16_t, and char32_t as code units. A character may use several code units: between 1 and 4 code units in UTF-8, and between 1 and 2 code units in UTF-16LE and ...

With multi-byte, variable-width character strings, the usual functions like strlen fall apart. Unicode’s combining characters also causes problems when it comes to comparison and collation of text.