30 Localization library [localization]

30.6 Text encodings identification [text.encoding]

30.6.2 Class text_encoding [text.encoding.class]

30.6.2.3 Members [text.encoding.members]

constexpr explicit text_encoding(string_view enc) noexcept;

Preconditions:

(1.1)
enc represents a string in the ordinary literal encoding consisting only of elements of the basic character set ([lex.charset]).
(1.2)
enc.size() <= max_name_length is true.
(1.3)
enc.contains('\0') is false.

Postconditions:

(2.1)
If there exists a primary name or alias a of a known registered character encoding such that comp-name(a, enc) is true, mib_ has the value of the enumerator of id associated with that registered character encoding.

Otherwise, mib_ == id::other is true.
(2.2)
enc.compare(name_) == 0 is true.

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constexpr text_encoding(id i) noexcept;

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

Postconditions:

(4.1)
mib_ == i is true.
(4.2)
If (mib_ == id::unknown || mib_ == id::other) is true, strlen(name_) == 0 is true.

Otherwise, ranges::contains(aliases(), string_view(name_)) is true.

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constexpr id mib() const noexcept;

Returns: mib_.

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constexpr const char* name() const noexcept;

Returns: name_ if (name_[0] != '\0') is true, and nullptr otherwise.

Remarks: If name() == nullptr is false, name() is an ntbs and accessing elements of name_ outside of the range

name() + [0, strlen(name()) + 1)

is undefined behavior.

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

Returns: r.

[Note 1:

The order of aliases in r is unspecified.

— end note]

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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]).

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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]).

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template<id i>
  static bool environment_is();

Mandates: CHAR_BIT == 8 is true.

Returns: environment() == i.

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static constexpr bool comp-name(string_view a, string_view b);

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

(19.1)
all elements that are not digits or letters ([character.seq.general]),
(19.2)
character case, and
(19.3)
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]