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
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>.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
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.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
.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
.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
.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.