std::char_traits

 

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char_traits

 

Defined in header <string>
template<     class CharT > class char_traits;

The char_traits class defines the stream and string operation properties of a character type, such as the types used for manipulating the characters and character strings, as well as all the common operations for the given character type.

Member types

Type	Definition
char_type	CharT
int_type	an integer type that can hold all values of char_type plus EOF
off_type	implementation-defined
pos_type	implementation-defined
state_type	implementation-defined

Member functions

Signature	Effects / Return value	Complexity
void assign(CharT &r, CharT a) noexcept	assigns r = a	constant
constexpr bool eq(CharT a, CharT b) noexcept	shall return true if a and b are equivalent	constant
constexpr bool lt( CharT a, CharT b ) noexcept	shall return true if a is less than b	constant
char_type *assign(CharT *p, size_t n, CharT a)	shall assign value a to character string [p, p+n). Shall return p	linear
char_type *move(CharT *p, const CharT *q, size_t n)	shall assign character string [q, q+n) to character string [p, p+n). Shall return p. Performs correctly even if [p, p+n) and [q, q+n) overlap.	linear
char_type *copy(CharT *p, const CharT *q, size_t n)	shall assign character string [q, q+n) to character string [p, p+n). Shall return p. q shall not be in [p, p+n)	linear
int compare(const CharT *p, const CharT *q, size_t n)	shall return ​0​ if character strings [p, p+n) and [q, q+n) are equal, shall return negative value if [p, p+n) is less than [q, q+n) and shall return positive value if [p, p+n) is greater than [q, q+n). The comparison is done lexicographically, using eq and lt functions.	linear
size_t length(const char_type* s)	shall return the position of the terminating Char() (i.e. null-character)	linear
const char_type *find(const CharT *p, size_t n, CharT a)	shall return the pointer to the first character of value a in character string p	linear
constexpr char_type to_char_type(int_type a) noexcept	shall return equivalent value of char_type type. If there is no such value, return value is unspecified	constant
constexpr int_type to_int_type(char_type a) noexcept	shall return equivalent value of int_type type.	constant
constexpr bool eq_int_type(int_type a, int_type b) noexcept	shall return false if one of a or b equals eof() and the other is not. Shall return true if a equals b. Return value is unspecified in other cases.	constant
constexpr int_type eof() noexcept	shall return a value not equal to any value of type char_type	constant
constexpr bool not_eof(int_type a) noexcept	shall return false if a and eof() are equivalent	constant

(constexpr and noexcept specification were added in C++11)

There is class template char_traits defined, which serves as a basis for explicit instantiations. It fulfills all requirements of Traits concept.

Also, several specializations are defined for most common character types which which has to specify the following members:

Instantiation	char_type	int_type	off_type	pos_type	state_type
char_traits<char>	char	int	streamoff	streampos	mbstate_t
char_traits<wchar_t>	wchar_t	wint_t	wstreamoff	wstreampos	mbstate_t
char_traits<char16_t> (C++11)	char16_t	int_least16_t	streamoff	u16streampos	mbstate_t
char_traits<char32_t> (C++11)	char32_t	int_least32_t	streamoff	u32streampos	mbstate_t

See also

basic_string	stores and manipulates sequences of characters (class template)