23 Strings library [strings]

Subclause [char.traits] defines requirements on classes representing character traits, and defines a class template char_traits<charT>, along with five specializations, char_traits<char>, char_traits<char8_t>, char_traits<char16_t>, char_traits<char32_t>, and char_traits<wchar_t>, that meet those requirements.

Most classes specified in [string.classes], [string.view], and [input.output] need a set of related types and functions to complete the definition of their semantics.

These types and functions are provided as a set of member typedef-names and functions in the template parameter traits used by each such template.

Subclause [char.traits] defines the semantics of these members.

To specialize those templates to generate a string, string view, or iostream class to handle a particular character container type ([defns.character.container]) C, that and its related character traits class X are passed as a pair of parameters to the string, string view, or iostream template as parameters charT and traits.

If X​::​char_type is not the same type as C, the program is ill-formed.