143 lines
6.6 KiB
Markdown
143 lines
6.6 KiB
Markdown
[locale.general]
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# 28 Text processing library [[text]](./#text)
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## 28.3 Localization library [[localization]](localization#locale.general)
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### 28.3.3 Locales [[locales]](locales#locale.general)
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#### 28.3.3.1 Class locale [[locale]](locale#general)
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#### 28.3.3.1.1 General [locale.general]
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namespace std {class locale {public:// [[locale.types]](locale.types "28.3.3.1.2 Types"), types// [[locale.facet]](locale.facet "28.3.3.1.2.2 Class locale::facet"), class locale::facetclass facet; // [[locale.id]](locale.id "28.3.3.1.2.3 Class locale::id"), class locale::idclass id; // [[locale.category]](locale.category "28.3.3.1.2.1 Type locale::category"), type locale::categoryusing category = int; static const category // values assigned here are for exposition only none = 0,
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collate = 0x010, ctype = 0x020,
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monetary = 0x040, numeric = 0x080,
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time = 0x100, messages = 0x200,
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all = collate | ctype | monetary | numeric | time | messages; // [[locale.cons]](locale.cons "28.3.3.1.3 Constructors and destructor"), construct/copy/destroy locale() noexcept;
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locale(const locale& other) noexcept; explicit locale(const char* std_name); explicit locale(const string& std_name);
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locale(const locale& other, const char* std_name, category);
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locale(const locale& other, const string& std_name, category); template<class Facet> locale(const locale& other, Facet* f);
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locale(const locale& other, const locale& one, category); ~locale(); // not virtualconst locale& operator=(const locale& other) noexcept; // [[locale.members]](locale.members "28.3.3.1.4 Members"), locale operationstemplate<class Facet> locale combine(const locale& other) const;
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string name() const;
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text_encoding encoding() const; bool operator==(const locale& other) const; template<class charT, class traits, class Allocator>bool operator()(const basic_string<charT, traits, Allocator>& s1, const basic_string<charT, traits, Allocator>& s2) const; // [[locale.statics]](locale.statics "28.3.3.1.6 Static members"), global locale objectsstatic locale global(const locale&); static const locale& classic(); };}
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L520)
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Class locale implements a type-safe polymorphic set of facets,
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indexed by facet *type*[.](#1.sentence-1)
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In other words, a facet has a dual role:
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in one sense, it's just a class interface;
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at the same time, it's an index into a locale's set of facets[.](#1.sentence-2)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L527)
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Access to the facets of a locale is via two function templates,use_facet<> and has_facet<>[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L531)
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[*Example [1](#example-1)*:
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An iostream operator<< can be implemented as:[214](#footnote-214 "Note that in the call to put, the stream is implicitly converted to an ostreambuf_iterator<charT, traits>.")
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template<class charT, class traits> basic_ostream<charT, traits>&operator<< (basic_ostream<charT, traits>& s, Date d) {typename basic_ostream<charT, traits>::sentry cerberos(s); if (cerberos) { tm tmbuf; d.extract(tmbuf); bool failed = use_facet<time_put<charT, ostreambuf_iterator<charT, traits>>>( s.getloc()).put(s, s, s.fill(), &tmbuf, 'x').failed(); if (failed) s.setstate(s.badbit); // can throw}return s;} â *end example*]
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L558)
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In the call to use_facet<Facet>(loc),
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the type argument chooses a facet,
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making available all members of the named type[.](#4.sentence-1)
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If Facet is not present in a locale,
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it throws the standard exception bad_cast[.](#4.sentence-2)
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A C++ program can check if a locale implements a particular facet
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with the function template has_facet<Facet>()[.](#4.sentence-3)
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User-defined facets may be installed in a locale, and
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used identically as may standard facets[.](#4.sentence-4)
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L569)
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[*Note [1](#note-1)*:
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All locale semantics are accessed viause_facet<> and has_facet<>,
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except that:
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- [(5.1)](#5.1)
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A member operator templateoperator()(const basic_string<C, T, A>&, const basic_string<C, T, A>&) is provided so that a locale can be used as a predicate argument to
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the standard collections, to collate strings.
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- [(5.2)](#5.2)
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Convenient global interfaces are provided for
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traditional ctype functions such asisdigit() and isspace(),
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so that given a locale object loc a C++ program can call isspace(c, loc). (This eases upgrading existing extractors ([[istream.formatted]](istream.formatted "31.7.5.3 Formatted input functions"))[.](#5.2.sentence-2))
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â *end note*]
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L593)
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Once a facet reference is obtained from a locale object
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by calling use_facet<>,
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that reference remains usable,
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and the results from member functions of it may be cached and re-used,
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as long as some locale object refers to that facet[.](#6.sentence-1)
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L600)
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In successive calls to a locale facet member function
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on a facet object installed in the same locale,
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the returned result shall be identical[.](#7.sentence-1)
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[8](#8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L605)
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A locale constructed
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from a name string (such as "POSIX"), or
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from parts of two named locales, has a name;
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all others do not[.](#8.sentence-1)
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Named locales may be compared for equality;
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an unnamed locale is equal only to (copies of) itself[.](#8.sentence-2)
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For an unnamed locale, locale::name() returns the string "*"[.](#8.sentence-3)
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[9](#9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L614)
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Whether there is
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one global locale object for the entire program or
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one global locale object per thread
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is implementation-defined[.](#9.sentence-1)
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Implementations should provide one global locale object per thread[.](#9.sentence-2)
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If there is a single global locale object for the entire program,
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implementations are not required to
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avoid data races on it ([[res.on.data.races]](res.on.data.races "16.4.6.10 Data race avoidance"))[.](#9.sentence-3)
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[214)](#footnote-214)[214)](#footnoteref-214)
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Note that in the call to put,
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the stream is implicitly converted
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to an ostreambuf_iterator<charT, traits>[.](#footnote-214.sentence-1)
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