[text.encoding.members] (original) (raw)

28 Text processing library [text]

28.4 Text encodings identification [text.encoding]

28.4.2 Class text_encoding [text.encoding.class]

28.4.2.3 Members [text.encoding.members]

constexpr explicit text_encoding(string_view enc) noexcept;

Preconditions:

• enc represents a string in the ordinary literal encoding consisting only of elements of the basic character set ([lex.charset]).
• enc.size() <= max_name_length is true.
• enc.contains('\0') is false.

Postconditions:

• If there exists a primary name or alias aof a known registered character encoding such that_comp-name_(a, enc) is true,mib_ has the value of the enumerator of idassociated with that registered character encoding.
  Otherwise, mib_ == id​::​other is true.
• enc.compare(name_) == 0 is true.

constexpr text_encoding(id i) noexcept;

Preconditions: i has the value of one of the enumerators of id.

Postconditions:

• If (mib_ == id​::​unknown || mib_ == id​::​other)is true,strlen(name_) == 0 is true.
  Otherwise,ranges​::​contains(aliases(), string_view(name_))is true.

constexpr id mib() const noexcept;

constexpr const char* name() const noexcept;

Remarks: name() is an ntbs and accessing elements of _name__outside of the range is undefined behavior.

constexpr aliases_view aliases() const noexcept;

Let r denote an instance of aliases_view.

If *this represents a known registered character encoding, then:

• r.front() is the primary name of the registered character encoding,
• r contains the aliases of the registered character encoding, and
• r does not contain duplicate values when compared with strcmp.

Otherwise, r is an empty range.

Each element in ris a non-null, non-empty ntbs encoded in the literal character encoding and comprising only characters from the basic character set.

[Note 1:

The order of aliases in r is unspecified.

— _end note_]

static consteval text_encoding literal() noexcept;

Mandates: CHAR_BIT == 8 is true.

Returns: A text_encoding object representing the ordinary character literal encoding ([lex.charset]).

static text_encoding environment();

Mandates: CHAR_BIT == 8 is true.

Returns: A text_encoding object representing the implementation-defined character encoding scheme of the environment.

On a POSIX implementation, this is the encoding scheme associated with the POSIX locale denoted by the empty string "".

[Note 2:

This function is not affected by calls to setlocale.

— _end note_]

Recommended practice: Implementations should return a value that is not affected by calls to the POSIX function setenv and other functions which can modify the environment ([support.runtime]).

template<id i> static bool environment_is();

Mandates: CHAR_BIT == 8 is true.

Returns: environment() == i.

static constexpr bool _comp-name_(string_view a, string_view b);

Returns: true if the two strings a and bencoded in the ordinary literal encoding are equal, ignoring, from left-to-right,

• all elements that are not digits or letters ([character.seq.general]),
• character case, and
• any sequence of one or more 0 characters not immediately preceded by a numeric prefix, where a numeric prefix is a sequence consisting of a digit in the range [1, 9] optionally followed by one or more elements which are not digits or letters,

and false otherwise.

[Note 3:

This comparison is identical to the “Charset Alias Matching” algorithm described in the Unicode Technical Standard 22[bib].

— _end note_]

[Example 1: static_assert(comp-name("UTF-8", "utf8") == true);static_assert(comp-name("u.t.f-008", "utf8") == true);static_assert(comp-name("ut8", "utf8") == false);static_assert(comp-name("utf-80", "utf8") == false); — _end example_]