23 Strings library [strings]

23.2 Character traits [char.traits]

23.2.4 char_­traits specializations [char.traits.specializations]

23.2.4.1 General [char.traits.specializations.general]

namespace std { template<> struct char_traits<char>; template<> struct char_traits<char8_t>; template<> struct char_traits<char16_t>; template<> struct char_traits<char32_t>; template<> struct char_traits<wchar_t>; }
The header <string> defines five specializations of the class template char_­traits: char_­traits<char>, char_­traits<char8_­t>, char_­traits<char16_­t>, char_­traits<char32_­t>, and char_­traits<wchar_­t>.

23.2.4.2 struct char_­traits<char> [char.traits.specializations.char]

namespace std { template<> struct char_traits<char> { using char_type = char; using int_type = int; using off_type = streamoff; using pos_type = streampos; using state_type = mbstate_t; using comparison_category = strong_ordering; static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr bool eq(char_type c1, char_type c2) noexcept; static constexpr bool lt(char_type c1, char_type c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a); static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* assign(char_type* s, size_t n, char_type a); static constexpr int_type not_eof(int_type c) noexcept; static constexpr char_type to_char_type(int_type c) noexcept; static constexpr int_type to_int_type(char_type c) noexcept; static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept; static constexpr int_type eof() noexcept; }; }
The type mbstate_­t is defined in <cwchar> and can represent any of the conversion states that can occur in an implementation-defined set of supported multibyte character encoding rules.
The two-argument member assign is defined identically to the built-in operator =.
The two-argument members eq and lt are defined identically to the built-in operators == and < for type unsigned char.
The member eof() returns EOF.

23.2.4.3 struct char_­traits<char8_­t> [char.traits.specializations.char8.t]

namespace std { template<> struct char_traits<char8_t> { using char_type = char8_t; using int_type = unsigned int; using off_type = streamoff; using pos_type = u8streampos; using state_type = mbstate_t; using comparison_category = strong_ordering; static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr bool eq(char_type c1, char_type c2) noexcept; static constexpr bool lt(char_type c1, char_type c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a); static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* assign(char_type* s, size_t n, char_type a); static constexpr int_type not_eof(int_type c) noexcept; static constexpr char_type to_char_type(int_type c) noexcept; static constexpr int_type to_int_type(char_type c) noexcept; static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept; static constexpr int_type eof() noexcept; }; }
The two-argument members assign, eq, and lt are defined identically to the built-in operators =, ==, and < respectively.
The member eof() returns an implementation-defined constant that cannot appear as a valid UTF-8 code unit.

23.2.4.4 struct char_­traits<char16_­t> [char.traits.specializations.char16.t]

namespace std { template<> struct char_traits<char16_t> { using char_type = char16_t; using int_type = uint_least16_t; using off_type = streamoff; using pos_type = u16streampos; using state_type = mbstate_t; using comparison_category = strong_ordering; static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr bool eq(char_type c1, char_type c2) noexcept; static constexpr bool lt(char_type c1, char_type c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a); static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* assign(char_type* s, size_t n, char_type a); static constexpr int_type not_eof(int_type c) noexcept; static constexpr char_type to_char_type(int_type c) noexcept; static constexpr int_type to_int_type(char_type c) noexcept; static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept; static constexpr int_type eof() noexcept; }; }
The two-argument members assign, eq, and lt are defined identically to the built-in operators =, ==, and <, respectively.
The member eof() returns an implementation-defined constant that cannot appear as a valid UTF-16 code unit.

23.2.4.5 struct char_­traits<char32_­t> [char.traits.specializations.char32.t]

namespace std { template<> struct char_traits<char32_t> { using char_type = char32_t; using int_type = uint_least32_t; using off_type = streamoff; using pos_type = u32streampos; using state_type = mbstate_t; using comparison_category = strong_ordering; static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr bool eq(char_type c1, char_type c2) noexcept; static constexpr bool lt(char_type c1, char_type c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a); static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* assign(char_type* s, size_t n, char_type a); static constexpr int_type not_eof(int_type c) noexcept; static constexpr char_type to_char_type(int_type c) noexcept; static constexpr int_type to_int_type(char_type c) noexcept; static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept; static constexpr int_type eof() noexcept; }; }
The two-argument members assign, eq, and lt are defined identically to the built-in operators =, ==, and <, respectively.
The member eof() returns an implementation-defined constant that cannot appear as a Unicode code point.

23.2.4.6 struct char_­traits<wchar_­t> [char.traits.specializations.wchar.t]

namespace std { template<> struct char_traits<wchar_t> { using char_type = wchar_t; using int_type = wint_t; using off_type = streamoff; using pos_type = wstreampos; using state_type = mbstate_t; using comparison_category = strong_ordering; static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr bool eq(char_type c1, char_type c2) noexcept; static constexpr bool lt(char_type c1, char_type c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a); static constexpr char_type* move(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* copy(char_type* s1, const char_type* s2, size_t n); static constexpr char_type* assign(char_type* s, size_t n, char_type a); static constexpr int_type not_eof(int_type c) noexcept; static constexpr char_type to_char_type(int_type c) noexcept; static constexpr int_type to_int_type(char_type c) noexcept; static constexpr bool eq_int_type(int_type c1, int_type c2) noexcept; static constexpr int_type eof() noexcept; }; }
The two-argument members assign, eq, and lt are defined identically to the built-in operators =, ==, and <, respectively.
The member eof() returns WEOF.