namespace std { template<> struct char_traits<char>; template<> struct char_traits<char16_t>; template<> struct char_traits<char32_t>; template<> struct char_traits<wchar_t>; }
The header <string> shall define four specializations of the class template char_traits: char_traits<char>, char_traits<char16_t>, char_traits<char32_t>, and char_traits<wchar_t>.
The requirements for the members of these specializations are given in Clause [char.traits.require].
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; 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 char_type* move(char_type* s1, const char_type* s2, size_t n); static char_type* copy(char_type* s1, const char_type* s2, size_t n); static 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 defined types for int_type, pos_type, off_type, and state_type shall be int, streampos, streamoff, and mbstate_t respectively.
The type streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].
The type streamoff shall be an implementation-defined type that satisfies the requirements for off_type in [iostreams.limits.pos] and [iostream.forward].
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 shall be defined identically to the built-in operator =. The two-argument members eq and lt shall be defined identically to the built-in operators == and < for type unsigned char.
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; 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 char_type* move(char_type* s1, const char_type* s2, size_t n); static char_type* copy(char_type* s1, const char_type* s2, size_t n); static 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 u16streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].
The two-argument members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.
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; 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 char_type* move(char_type* s1, const char_type* s2, size_t n); static char_type* copy(char_type* s1, const char_type* s2, size_t n); static 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 u32streampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].
The two-argument members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.
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; 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 char_type* move(char_type* s1, const char_type* s2, size_t n); static char_type* copy(char_type* s1, const char_type* s2, size_t n); static 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 defined types for int_type, pos_type, and state_type shall be wint_t, wstreampos, and mbstate_t respectively.
The type wstreampos shall be an implementation-defined type that satisfies the requirements for pos_type in [iostreams.limits.pos] and [iostream.forward].
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 members assign, eq, and lt shall be defined identically to the built-in operators =, ==, and < respectively.