30 Localization library [localization]

30.6 Text encodings identification [text.encoding]

30.6.2 Class text_encoding [text.encoding.class] Members [text.encoding.members]

constexpr explicit text_encoding(string_view enc) noexcept;
  • 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.
  • 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.
  • enc.compare(name_) == 0 is true.
constexpr text_encoding(id i) noexcept;
Preconditions: i has the value of one of the enumerators of id.
  • mib_ == i is true.
  • 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;
Returns: mib_.
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 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 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.
β€” 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.
β€” 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 b encoded 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 β€œCharset Alias Matching” algorithm described in the Unicode Technical Standard 22[bib].
β€” 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); β€” end example]