30 Localization library [localization]

30.1 General [localization.general]

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This Clause describes components that C++ programs may use to encapsulate (and therefore be more portable when confronting) cultural differences.
The locale facility includes internationalization support for character classification and string collation, numeric, monetary, and date/time formatting and parsing, and message retrieval.
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The following subclauses describe components for locales themselves, the standard facets, and facilities from the C library, as summarized in Table 107.
Table 107: Localization library summary [tab:localization.summary]
Subclause
Header
Locales
<locale>
Standard locale categories
C library locales
<clocale>
Text encodings identification
<text_encoding>

30.2 Header <locale> synopsis [locale.syn]

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namespace std { // [locale], locale class locale; template<class Facet> const Facet& use_facet(const locale&); template<class Facet> bool has_facet(const locale&) noexcept; // [locale.convenience], convenience interfaces template<class charT> bool isspace (charT c, const locale& loc); template<class charT> bool isprint (charT c, const locale& loc); template<class charT> bool iscntrl (charT c, const locale& loc); template<class charT> bool isupper (charT c, const locale& loc); template<class charT> bool islower (charT c, const locale& loc); template<class charT> bool isalpha (charT c, const locale& loc); template<class charT> bool isdigit (charT c, const locale& loc); template<class charT> bool ispunct (charT c, const locale& loc); template<class charT> bool isxdigit(charT c, const locale& loc); template<class charT> bool isalnum (charT c, const locale& loc); template<class charT> bool isgraph (charT c, const locale& loc); template<class charT> bool isblank (charT c, const locale& loc); template<class charT> charT toupper(charT c, const locale& loc); template<class charT> charT tolower(charT c, const locale& loc); // [category.ctype], ctype class ctype_base; template<class charT> class ctype; template<> class ctype<char>; // specialization template<class charT> class ctype_byname; class codecvt_base; template<class internT, class externT, class stateT> class codecvt; template<class internT, class externT, class stateT> class codecvt_byname; // [category.numeric], numeric template<class charT, class InputIterator = istreambuf_iterator<charT>> class num_get; template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class num_put; template<class charT> class numpunct; template<class charT> class numpunct_byname; // [category.collate], collation template<class charT> class collate; template<class charT> class collate_byname; // [category.time], date and time class time_base; template<class charT, class InputIterator = istreambuf_iterator<charT>> class time_get; template<class charT, class InputIterator = istreambuf_iterator<charT>> class time_get_byname; template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class time_put; template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class time_put_byname; // [category.monetary], money class money_base; template<class charT, class InputIterator = istreambuf_iterator<charT>> class money_get; template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class money_put; template<class charT, bool Intl = false> class moneypunct; template<class charT, bool Intl = false> class moneypunct_byname; // [category.messages], message retrieval class messages_base; template<class charT> class messages; template<class charT> class messages_byname; }
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The header <locale> defines classes and declares functions that encapsulate and manipulate the information peculiar to a locale.235
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In this subclause, the type name tm is an incomplete type that is defined in <ctime>.

30.3 Locales [locales]

30.3.1 Class locale [locale]

30.3.1.1 General [locale.general]

namespace std { class locale { public: // [locale.types], types // [locale.facet], class locale​::​facet class facet; // [locale.id], class locale​::​id class id; // [locale.category], type locale​::​category using category = int; static const category // values assigned here are for exposition only none = 0, collate = 0x010, ctype = 0x020, monetary = 0x040, numeric = 0x080, time = 0x100, messages = 0x200, all = collate | ctype | monetary | numeric | time | messages; // [locale.cons], construct/copy/destroy locale() noexcept; locale(const locale& other) noexcept; explicit locale(const char* std_name); explicit locale(const string& std_name); locale(const locale& other, const char* std_name, category); locale(const locale& other, const string& std_name, category); template<class Facet> locale(const locale& other, Facet* f); locale(const locale& other, const locale& one, category); ~locale(); // not virtual const locale& operator=(const locale& other) noexcept; // [locale.members], locale operations template<class Facet> locale combine(const locale& other) const; string name() const; 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], global locale objects static locale global(const locale&); static const locale& classic(); }; }
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Class locale implements a type-safe polymorphic set of facets, indexed by facet type.
In other words, a facet has a dual role: in one sense, it's just a class interface; at the same time, it's an index into a locale's set of facets.
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Access to the facets of a locale is via two function templates, use_facet<> and has_facet<>.
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[Example 1: 
An iostream operator<< can be implemented as:236 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; }
— end example]
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In the call to use_facet<Facet>(loc), the type argument chooses a facet, making available all members of the named type.
If Facet is not present in a locale, it throws the standard exception bad_cast.
A C++ program can check if a locale implements a particular facet with the function template has_facet<Facet>().
User-defined facets may be installed in a locale, and used identically as may standard facets.
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[Note 1: 
All locale semantics are accessed via use_facet<> and has_facet<>, except that:
  • (5.1)
    A member operator template operator()(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 the standard collections, to collate strings.
  • (5.2)
    Convenient global interfaces are provided for traditional ctype functions such as isdigit() and isspace(), so that given a locale object loc a C++ program can call isspace(c, loc).
    (This eases upgrading existing extractors ([istream.formatted]).)
— end note]
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Once a facet reference is obtained from a locale object by calling use_facet<>, that reference remains usable, and the results from member functions of it may be cached and re-used, as long as some locale object refers to that facet.
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In successive calls to a locale facet member function on a facet object installed in the same locale, the returned result shall be identical.
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A locale constructed from a name string (such as "POSIX"), or from parts of two named locales, has a name; all others do not.
Named locales may be compared for equality; an unnamed locale is equal only to (copies of) itself.
For an unnamed locale, locale​::​name() returns the string "*".
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Whether there is one global locale object for the entire program or one global locale object per thread is implementation-defined.
Implementations should provide one global locale object per thread.
If there is a single global locale object for the entire program, implementations are not required to avoid data races on it ([res.on.data.races]).
236)236)
Note that in the call to put, the stream is implicitly converted to an ostreambuf_iterator<charT, traits>.

30.3.1.2 Types [locale.types]

30.3.1.2.1 Type locale​::​category [locale.category]

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using category = int;
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Valid category values include the locale member bitmask elements collate, ctype, monetary, numeric, time, and messages, each of which represents a single locale category.
In addition, locale member bitmask constant none is defined as zero and represents no category.
And locale member bitmask constant all is defined such that the expression (collate | ctype | monetary | numeric | time | messages | all) == all is true, and represents the union of all categories.
Further, the expression (X | Y), where X and Y each represent a single category, represents the union of the two categories.
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locale member functions expecting a category argument require one of the category values defined above, or the union of two or more such values.
Such a category value identifies a set of locale categories.
Each locale category, in turn, identifies a set of locale facets, including at least those shown in Table 108.
Table 108: Locale category facets [tab:locale.category.facets]
Category
Includes facets
collate
collate<char>, collate<wchar_t>
ctype
ctype<char>, ctype<wchar_t>
codecvt<char, char, mbstate_t>
codecvt<wchar_t, char, mbstate_t>
monetary
moneypunct<char>, moneypunct<wchar_t>
moneypunct<char, true>, moneypunct<wchar_t, true>
money_get<char>, money_get<wchar_t>
money_put<char>, money_put<wchar_t>
numeric
numpunct<char>, numpunct<wchar_t>
num_get<char>, num_get<wchar_t>
num_put<char>, num_put<wchar_t>
time
time_get<char>, time_get<wchar_t>
time_put<char>, time_put<wchar_t>
messages
messages<char>, messages<wchar_t>
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For any locale loc either constructed, or returned by locale​::​classic(), and any facet Facet shown in Table 108, has_facet<Facet>(loc) is true.
Each locale member function which takes a locale​::​category argument operates on the corresponding set of facets.
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An implementation is required to provide those specializations for facet templates identified as members of a category, and for those shown in Table 109.
Table 109: Required specializations [tab:locale.spec]
Category
Includes facets
collate
collate_byname<char>, collate_byname<wchar_t>
ctype
ctype_byname<char>, ctype_byname<wchar_t>
codecvt_byname<char, char, mbstate_t>
codecvt_byname<wchar_t, char, mbstate_t>
monetary
moneypunct_byname<char, International>
moneypunct_byname<wchar_t, International>
money_get<C, InputIterator>
money_put<C, OutputIterator>
numeric
numpunct_byname<char>, numpunct_byname<wchar_t>
num_get<C, InputIterator>, num_put<C, OutputIterator>
time
time_get<char, InputIterator>
time_get_byname<char, InputIterator>
time_get<wchar_t, InputIterator>
time_get_byname<wchar_t, InputIterator>
time_put<char, OutputIterator>
time_put_byname<char, OutputIterator>
time_put<wchar_t, OutputIterator>
time_put_byname<wchar_t, OutputIterator>
messages
messages_byname<char>, messages_byname<wchar_t>
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The provided implementation of members of facets num_get<charT> and num_put<charT> calls use_facet<F>(l) only for facet F of types numpunct<charT> and ctype<charT>, and for locale l the value obtained by calling member getloc() on the ios_base& argument to these functions.
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In declarations of facets, a template parameter with name InputIterator or OutputIterator indicates the set of all possible specializations on parameters that meet the Cpp17InputIterator requirements or Cpp17OutputIterator requirements, respectively ([iterator.requirements]).
A template parameter with name C represents the set of types containing char, wchar_t, and any other implementation-defined character container types ([defns.character.container]) that meet the requirements for a character on which any of the iostream components can be instantiated.
A template parameter with name International represents the set of all possible specializations on a bool parameter.

30.3.1.2.2 Class locale​::​facet [locale.facet]

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namespace std { class locale::facet { protected: explicit facet(size_t refs = 0); virtual ~facet(); facet(const facet&) = delete; void operator=(const facet&) = delete; }; }
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Class facet is the base class for locale feature sets.
A class is a facet if it is publicly derived from another facet, or if it is a class derived from locale​::​facet and contains a publicly accessible declaration as follows:237 static ::std::locale::id id;
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Template parameters in this Clause which are required to be facets are those named Facet in declarations.
A program that passes a type that is not a facet, or a type that refers to a volatile-qualified facet, as an (explicit or deduced) template parameter to a locale function expecting a facet, is ill-formed.
A const-qualified facet is a valid template argument to any locale function that expects a Facet template parameter.
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The refs argument to the constructor is used for lifetime management.
For refs == 0, the implementation performs delete static_cast<locale​::​facet*>(f) (where f is a pointer to the facet) when the last locale object containing the facet is destroyed; for refs == 1, the implementation never destroys the facet.
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Constructors of all facets defined in this Clause take such an argument and pass it along to their facet base class constructor.
All one-argument constructors defined in this Clause are explicit, preventing their participation in implicit conversions.
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For some standard facets a standard “…_byname” class, derived from it, implements the virtual function semantics equivalent to that facet of the locale constructed by locale(const char*) with the same name.
Each such facet provides a constructor that takes a const char* argument, which names the locale, and a refs argument, which is passed to the base class constructor.
Each such facet also provides a constructor that takes a string argument str and a refs argument, which has the same effect as calling the first constructor with the two arguments str.c_str() and refs.
If there is no “…_byname” version of a facet, the base class implements named locale semantics itself by reference to other facets.
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This is a complete list of requirements; there are no other requirements.
Thus, a facet class need not have a public copy constructor, assignment, default constructor, destructor, etc.

30.3.1.2.3 Class locale​::​id [locale.id]

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namespace std { class locale::id { public: id(); void operator=(const id&) = delete; id(const id&) = delete; }; }
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The class locale​::​id provides identification of a locale facet interface, used as an index for lookup and to encapsulate initialization.
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[Note 1: 
Because facets are used by iostreams, potentially while static constructors are running, their initialization cannot depend on programmed static initialization.
One initialization strategy is for locale to initialize each facet's id member the first time an instance of the facet is installed into a locale.
This depends only on static storage being zero before constructors run ([basic.start.static]).
— end note]

30.3.1.3 Constructors and destructor [locale.cons]

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locale() noexcept;
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Effects: Constructs a copy of the argument last passed to locale​::​global(locale&), if it has been called; else, the resulting facets have virtual function semantics identical to those of locale​::​classic().
[Note 1: 
This constructor yields a copy of the current global locale.
It is commonly used as a default argument for function parameters of type const locale&.
— end note]
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explicit locale(const char* std_name);
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Effects: Constructs a locale using standard C locale names, e.g., "POSIX".
The resulting locale implements semantics defined to be associated with that name.
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Throws: runtime_error if the argument is not valid, or is null.
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Remarks: The set of valid string argument values is "C", "", and any implementation-defined values.
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explicit locale(const string& std_name);
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Effects: Equivalent to locale(std_name.c_str()).
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locale(const locale& other, const char* std_name, category cats);
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Preconditions: cats is a valid category value ([locale.category]).
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Effects: Constructs a locale as a copy of other except for the facets identified by the category argument, which instead implement the same semantics as locale(std_name).
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Throws: runtime_error if the second argument is not valid, or is null.
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Remarks: The locale has a name if and only if other has a name.
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locale(const locale& other, const string& std_name, category cats);
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Effects: Equivalent to locale(other, std_name.c_str(), cats).
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template<class Facet> locale(const locale& other, Facet* f);
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Effects: Constructs a locale incorporating all facets from the first argument except that of type Facet, and installs the second argument as the remaining facet.
If f is null, the resulting object is a copy of other.
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Remarks: If f is null, the resulting locale has the same name as other.
Otherwise, the resulting locale has no name.
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locale(const locale& other, const locale& one, category cats);
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Preconditions: cats is a valid category value.
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Effects: Constructs a locale incorporating all facets from the first argument except those that implement cats, which are instead incorporated from the second argument.
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Remarks: If cats is equal to locale​::​none, the resulting locale has a name if and only if the first argument has a name.
Otherwise, the resulting locale has a name if and only if the first two arguments both have names.
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const locale& operator=(const locale& other) noexcept;
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Effects: Creates a copy of other, replacing the current value.
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Returns: *this.

30.3.1.4 Members [locale.members]

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template<class Facet> locale combine(const locale& other) const;
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Effects: Constructs a locale incorporating all facets from *this except for that one facet of other that is identified by Facet.
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Returns: The newly created locale.
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Throws: runtime_error if has_facet<Facet>(other) is false.
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Remarks: The resulting locale has no name.
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string name() const;
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Returns: The name of *this, if it has one; otherwise, the string "*".
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text_encoding encoding() const;
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Mandates: CHAR_BIT == 8 is true.
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Returns: A text_encoding object representing the implementation-defined encoding scheme associated with the locale *this.

30.3.1.5 Operators [locale.operators]

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bool operator==(const locale& other) const;
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Returns: true if both arguments are the same locale, or one is a copy of the other, or each has a name and the names are identical; false otherwise.
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template<class charT, class traits, class Allocator> bool operator()(const basic_string<charT, traits, Allocator>& s1, const basic_string<charT, traits, Allocator>& s2) const;
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Effects: Compares two strings according to the collate<charT> facet.
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Returns: use_facet<collate<charT>>(*this).compare(s1.data(), s1.data() + s1.size(), s2.data(), s2.data() + s2.size()) < 0
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Remarks: This member operator template (and therefore locale itself) meets the requirements for a comparator predicate template argument ([algorithms]) applied to strings.
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[Example 1: 
A vector of strings v can be collated according to collation rules in locale loc simply by ([alg.sort], [vector]): std::sort(v.begin(), v.end(), loc);
— end example]

30.3.1.6 Static members [locale.statics]

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static locale global(const locale& loc);
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Effects: Sets the global locale to its argument.
Causes future calls to the constructor locale() to return a copy of the argument.
If the argument has a name, does setlocale(LC_ALL, loc.name().c_str()); otherwise, the effect on the C locale, if any, is implementation-defined.
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Returns: The previous value of locale().
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Remarks: No library function other than locale​::​global() affects the value returned by locale().
[Note 1: 
See [c.locales] for data race considerations when setlocale is invoked.
— end note]
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static const locale& classic();
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The "C" locale.
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Returns: A locale that implements the classic "C" locale semantics, equivalent to the value locale("C").
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Remarks: This locale, its facets, and their member functions, do not change with time.

30.3.2 locale globals [locale.global.templates]

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template<class Facet> const Facet& use_facet(const locale& loc);
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Mandates: Facet is a facet class whose definition contains the public static member id as defined in [locale.facet].
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Returns: A reference to the corresponding facet of loc, if present.
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Throws: bad_cast if has_facet<Facet>(loc) is false.
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Remarks: The reference returned remains valid at least as long as any copy of loc exists.
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template<class Facet> bool has_facet(const locale& loc) noexcept;
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Returns: true if the facet requested is present in loc; otherwise false.

30.3.3 Convenience interfaces [locale.convenience]

30.3.3.1 Character classification [classification]

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template<class charT> bool isspace (charT c, const locale& loc); template<class charT> bool isprint (charT c, const locale& loc); template<class charT> bool iscntrl (charT c, const locale& loc); template<class charT> bool isupper (charT c, const locale& loc); template<class charT> bool islower (charT c, const locale& loc); template<class charT> bool isalpha (charT c, const locale& loc); template<class charT> bool isdigit (charT c, const locale& loc); template<class charT> bool ispunct (charT c, const locale& loc); template<class charT> bool isxdigit(charT c, const locale& loc); template<class charT> bool isalnum (charT c, const locale& loc); template<class charT> bool isgraph (charT c, const locale& loc); template<class charT> bool isblank (charT c, const locale& loc);
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Each of these functions isF returns the result of the expression: use_facet<ctype<charT>>(loc).is(ctype_base::F, c) where F is the ctype_base​::​mask value corresponding to that function ([category.ctype]).238
238)238)
When used in a loop, it is faster to cache the ctype<> facet and use it directly, or use the vector form of ctype<>​::​is.

30.3.3.2 Character conversions [conversions.character]

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template<class charT> charT toupper(charT c, const locale& loc);
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Returns: use_facet<ctype<charT>>(loc).toupper(c).
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template<class charT> charT tolower(charT c, const locale& loc);
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Returns: use_facet<ctype<charT>>(loc).tolower(c).

30.4 Standard locale categories [locale.categories]

30.4.1 General [locale.categories.general]

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Each of the standard categories includes a family of facets.
Some of these implement formatting or parsing of a datum, for use by standard or users' iostream operators << and >>, as members put() and get(), respectively.
Each such member function takes an ios_base& argument whose members flags(), precision(), and width(), specify the format of the corresponding datum ([ios.base]).
Those functions which need to use other facets call its member getloc() to retrieve the locale imbued there.
Formatting facets use the character argument fill to fill out the specified width where necessary.
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The put() members make no provision for error reporting.
(Any failures of the OutputIterator argument can be extracted from the returned iterator.)
The get() members take an ios_base​::​iostate& argument whose value they ignore, but set to ios_base​::​failbit in case of a parse error.
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Within [locale.categories] it is unspecified whether one virtual function calls another virtual function.

30.4.2 The ctype category [category.ctype]

30.4.2.1 General [category.ctype.general]

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namespace std { class ctype_base { public: using mask = see below; // numeric values are for exposition only. static constexpr mask space = 1 << 0; static constexpr mask print = 1 << 1; static constexpr mask cntrl = 1 << 2; static constexpr mask upper = 1 << 3; static constexpr mask lower = 1 << 4; static constexpr mask alpha = 1 << 5; static constexpr mask digit = 1 << 6; static constexpr mask punct = 1 << 7; static constexpr mask xdigit = 1 << 8; static constexpr mask blank = 1 << 9; static constexpr mask alnum = alpha | digit; static constexpr mask graph = alnum | punct; }; }
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The type mask is a bitmask type.

30.4.2.2 Class template ctype [locale.ctype]

30.4.2.2.1 General [locale.ctype.general]

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namespace std { template<class charT> class ctype : public locale::facet, public ctype_base { public: using char_type = charT; explicit ctype(size_t refs = 0); bool is(mask m, charT c) const; const charT* is(const charT* low, const charT* high, mask* vec) const; const charT* scan_is(mask m, const charT* low, const charT* high) const; const charT* scan_not(mask m, const charT* low, const charT* high) const; charT toupper(charT c) const; const charT* toupper(charT* low, const charT* high) const; charT tolower(charT c) const; const charT* tolower(charT* low, const charT* high) const; charT widen(char c) const; const char* widen(const char* low, const char* high, charT* to) const; char narrow(charT c, char dfault) const; const charT* narrow(const charT* low, const charT* high, char dfault, char* to) const; static locale::id id; protected: ~ctype(); virtual bool do_is(mask m, charT c) const; virtual const charT* do_is(const charT* low, const charT* high, mask* vec) const; virtual const charT* do_scan_is(mask m, const charT* low, const charT* high) const; virtual const charT* do_scan_not(mask m, const charT* low, const charT* high) const; virtual charT do_toupper(charT) const; virtual const charT* do_toupper(charT* low, const charT* high) const; virtual charT do_tolower(charT) const; virtual const charT* do_tolower(charT* low, const charT* high) const; virtual charT do_widen(char) const; virtual const char* do_widen(const char* low, const char* high, charT* dest) const; virtual char do_narrow(charT, char dfault) const; virtual const charT* do_narrow(const charT* low, const charT* high, char dfault, char* dest) const; }; }
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Class ctype encapsulates the C library <cctype> features.
istream members are required to use ctype<> for character classing during input parsing.
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The specializations required in Table 108 ([locale.category]), namely ctype<char> and ctype<wchar_t>, implement character classing appropriate to the implementation's native character set.

30.4.2.2.2 ctype members [locale.ctype.members]

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bool is(mask m, charT c) const; const charT* is(const charT* low, const charT* high, mask* vec) const;
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Returns: do_is(m, c) or do_is(low, high, vec).
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const charT* scan_is(mask m, const charT* low, const charT* high) const;
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Returns: do_scan_is(m, low, high).
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const charT* scan_not(mask m, const charT* low, const charT* high) const;
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Returns: do_scan_not(m, low, high).
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charT toupper(charT c) const; const charT* toupper(charT* low, const charT* high) const;
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Returns: do_toupper(c) or do_toupper(low, high).
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charT tolower(charT c) const; const charT* tolower(charT* low, const charT* high) const;
5
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Returns: do_tolower(c) or do_tolower(low, high).
🔗
charT widen(char c) const; const char* widen(const char* low, const char* high, charT* to) const;
6
#
Returns: do_widen(c) or do_widen(low, high, to).
🔗
char narrow(charT c, char dfault) const; const charT* narrow(const charT* low, const charT* high, char dfault, char* to) const;
7
#
Returns: do_narrow(c, dfault) or do_narrow(low, high, dfault, to).

30.4.2.2.3 ctype virtual functions [locale.ctype.virtuals]

🔗
bool do_is(mask m, charT c) const; const charT* do_is(const charT* low, const charT* high, mask* vec) const;
1
#
Effects: Classifies a character or sequence of characters.
For each argument character, identifies a value M of type ctype_base​::​mask.
The second form identifies a value M of type ctype_base​::​mask for each *p where (low <= p && p < high), and places it into vec[p - low].
2
#
Returns: The first form returns the result of the expression (M & m) != 0; i.e., true if the character has the characteristics specified.
The second form returns high.
🔗
const charT* do_scan_is(mask m, const charT* low, const charT* high) const;
3
#
Effects: Locates a character in a buffer that conforms to a classification m.
4
#
Returns: The smallest pointer p in the range [low, high) such that is(m, *p) would return true; otherwise, returns high.
🔗
const charT* do_scan_not(mask m, const charT* low, const charT* high) const;
5
#
Effects: Locates a character in a buffer that fails to conform to a classification m.
6
#
Returns: The smallest pointer p, if any, in the range [low, high) such that is(m, *p) would return false; otherwise, returns high.
🔗
charT do_toupper(charT c) const; const charT* do_toupper(charT* low, const charT* high) const;
7
#
Effects: Converts a character or characters to upper case.
The second form replaces each character *p in the range [low, high) for which a corresponding upper-case character exists, with that character.
8
#
Returns: The first form returns the corresponding upper-case character if it is known to exist, or its argument if not.
The second form returns high.
🔗
charT do_tolower(charT c) const; const charT* do_tolower(charT* low, const charT* high) const;
9
#
Effects: Converts a character or characters to lower case.
The second form replaces each character *p in the range [low, high) and for which a corresponding lower-case character exists, with that character.
10
#
Returns: The first form returns the corresponding lower-case character if it is known to exist, or its argument if not.
The second form returns high.
🔗
charT do_widen(char c) const; const char* do_widen(const char* low, const char* high, charT* dest) const;
11
#
Effects: Applies the simplest reasonable transformation from a char value or sequence of char values to the corresponding charT value or values.239
The only characters for which unique transformations are required are those in the basic character set ([lex.charset]).
For any named ctype category with a ctype<charT> facet ctc and valid ctype_base​::​mask value M, (ctc.​is(M, c) || !is(M, do_widen(c)) ) is true.240
The second form transforms each character *p in the range [low, high), placing the result in dest[p - low].
12
#
Returns: The first form returns the transformed value.
The second form returns high.
🔗
char do_narrow(charT c, char dfault) const; const charT* do_narrow(const charT* low, const charT* high, char dfault, char* dest) const;
13
#
Effects: Applies the simplest reasonable transformation from a charT value or sequence of charT values to the corresponding char value or values.
For any character c in the basic character set ([lex.charset]) the transformation is such that do_widen(do_narrow(c, 0)) == c
For any named ctype category with a ctype<char> facet ctc however, and ctype_base​::​mask value M, (is(M, c) || !ctc.is(M, do_narrow(c, dfault)) ) is true (unless do_narrow returns dfault).
In addition, for any digit character c, the expression (do_narrow(c, dfault) - '0') evaluates to the digit value of the character.
The second form transforms each character *p in the range [low, high), placing the result (or dfault if no simple transformation is readily available) in dest[p - low].
14
#
Returns: The first form returns the transformed value; or dfault if no mapping is readily available.
The second form returns high.
239)239)
The parameter c of do_widen is intended to accept values derived from character-literals for conversion to the locale's encoding.
240)240)
In other words, the transformed character is not a member of any character classification that c is not also a member of.

30.4.2.3 Class template ctype_byname [locale.ctype.byname]

🔗
namespace std { template<class charT> class ctype_byname : public ctype<charT> { public: using mask = typename ctype<charT>::mask; explicit ctype_byname(const char*, size_t refs = 0); explicit ctype_byname(const string&, size_t refs = 0); protected: ~ctype_byname(); }; }

30.4.2.4 ctype<char> specialization [facet.ctype.special]

30.4.2.4.1 General [facet.ctype.special.general]

🔗
namespace std { template<> class ctype<char> : public locale::facet, public ctype_base { public: using char_type = char; explicit ctype(const mask* tab = nullptr, bool del = false, size_t refs = 0); bool is(mask m, char c) const; const char* is(const char* low, const char* high, mask* vec) const; const char* scan_is (mask m, const char* low, const char* high) const; const char* scan_not(mask m, const char* low, const char* high) const; char toupper(char c) const; const char* toupper(char* low, const char* high) const; char tolower(char c) const; const char* tolower(char* low, const char* high) const; char widen(char c) const; const char* widen(const char* low, const char* high, char* to) const; char narrow(char c, char dfault) const; const char* narrow(const char* low, const char* high, char dfault, char* to) const; static locale::id id; static const size_t table_size = implementation-defined; const mask* table() const noexcept; static const mask* classic_table() noexcept; protected: ~ctype(); virtual char do_toupper(char c) const; virtual const char* do_toupper(char* low, const char* high) const; virtual char do_tolower(char c) const; virtual const char* do_tolower(char* low, const char* high) const; virtual char do_widen(char c) const; virtual const char* do_widen(const char* low, const char* high, char* to) const; virtual char do_narrow(char c, char dfault) const; virtual const char* do_narrow(const char* low, const char* high, char dfault, char* to) const; }; }
1
#
A specialization ctype<char> is provided so that the member functions on type char can be implemented inline.241
The implementation-defined value of member table_size is at least 256.
241)241)
Only the char (not unsigned char and signed char) form is provided.
The specialization is specified in the standard, and not left as an implementation detail, because it affects the derivation interface for ctype<char>.

30.4.2.4.2 Destructor [facet.ctype.char.dtor]

🔗
~ctype();
1
#
Effects: If the constructor's first argument was nonzero, and its second argument was true, does delete [] table().

30.4.2.4.3 Members [facet.ctype.char.members]

1
#
In the following member descriptions, for unsigned char values v where v >= table_size, table()[v] is assumed to have an implementation-specific value (possibly different for each such value v) without performing the array lookup.
🔗
explicit ctype(const mask* tbl = nullptr, bool del = false, size_t refs = 0);
2
#
Preconditions: Either tbl == nullptr is true or [tbl, tbl+table_size) is a valid range.
3
#
Effects: Passes its refs argument to its base class constructor.
🔗
bool is(mask m, char c) const; const char* is(const char* low, const char* high, mask* vec) const;
4
#
Effects: The second form, for all *p in the range [low, high), assigns into vec[p - low] the value table()[(unsigned char)*p].
5
#
Returns: The first form returns table()[(unsigned char)c] & m; the second form returns high.
🔗
const char* scan_is(mask m, const char* low, const char* high) const;
6
#
Returns: The smallest p in the range [low, high) such that table()[(unsigned char) *p] & m is true.
🔗
const char* scan_not(mask m, const char* low, const char* high) const;
7
#
Returns: The smallest p in the range [low, high) such that table()[(unsigned char) *p] & m is false.
🔗
char toupper(char c) const; const char* toupper(char* low, const char* high) const;
8
#
Returns: do_toupper(c) or do_toupper(low, high), respectively.
🔗
char tolower(char c) const; const char* tolower(char* low, const char* high) const;
9
#
Returns: do_tolower(c) or do_tolower(low, high), respectively.
🔗
char widen(char c) const; const char* widen(const char* low, const char* high, char* to) const;
10
#
Returns: do_widen(c) or do_widen(low, high, to), respectively.
🔗
char narrow(char c, char dfault) const; const char* narrow(const char* low, const char* high, char dfault, char* to) const;
11
#
Returns: do_narrow(c, dfault) or do_narrow(low, high, dfault, to), respectively.
🔗
const mask* table() const noexcept;
12
#
Returns: The first constructor argument, if it was nonzero, otherwise classic_table().

30.4.2.4.4 Static members [facet.ctype.char.statics]

🔗
static const mask* classic_table() noexcept;
1
#
Returns: A pointer to the initial element of an array of size table_size which represents the classifications of characters in the "C" locale.

30.4.2.4.5 Virtual functions [facet.ctype.char.virtuals]

🔗
char do_toupper(char) const; const char* do_toupper(char* low, const char* high) const; char do_tolower(char) const; const char* do_tolower(char* low, const char* high) const; virtual char do_widen(char c) const; virtual const char* do_widen(const char* low, const char* high, char* to) const; virtual char do_narrow(char c, char dfault) const; virtual const char* do_narrow(const char* low, const char* high, char dfault, char* to) const;
1
#
These functions are described identically as those members of the same name in the ctype class template ([locale.ctype.members]).

30.4.2.5 Class template codecvt [locale.codecvt]

30.4.2.5.1 General [locale.codecvt.general]

🔗
namespace std { class codecvt_base { public: enum result { ok, partial, error, noconv }; }; template<class internT, class externT, class stateT> class codecvt : public locale::facet, public codecvt_base { public: using intern_type = internT; using extern_type = externT; using state_type = stateT; explicit codecvt(size_t refs = 0); result out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const; result unshift( stateT& state, externT* to, externT* to_end, externT*& to_next) const; result in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const; int encoding() const noexcept; bool always_noconv() const noexcept; int length(stateT&, const externT* from, const externT* end, size_t max) const; int max_length() const noexcept; static locale::id id; protected: ~codecvt(); virtual result do_out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const; virtual result do_in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const; virtual result do_unshift( stateT& state, externT* to, externT* to_end, externT*& to_next) const; virtual int do_encoding() const noexcept; virtual bool do_always_noconv() const noexcept; virtual int do_length(stateT&, const externT* from, const externT* end, size_t max) const; virtual int do_max_length() const noexcept; }; }
1
#
The class codecvt<internT, externT, stateT> is for use when converting from one character encoding to another, such as from wide characters to multibyte characters or between wide character encodings such as UTF-32 and EUC.
2
#
The stateT argument selects the pair of character encodings being mapped between.
3
#
The specializations required in Table 108 ([locale.category]) convert the implementation-defined native character set.
codecvt<char, char, mbstate_t> implements a degenerate conversion; it does not convert at all.
codecvt<wchar_t, char, mbstate_t> converts between the native character sets for ordinary and wide characters.
Specializations on mbstate_t perform conversion between encodings known to the library implementer.
Other encodings can be converted by specializing on a program-defined stateT type.
Objects of type stateT can contain any state that is useful to communicate to or from the specialized do_in or do_out members.

30.4.2.5.2 Members [locale.codecvt.members]

🔗
result out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const;
1
#
Returns: do_out(state, from, from_end, from_next, to, to_end, to_next).
🔗
result unshift(stateT& state, externT* to, externT* to_end, externT*& to_next) const;
2
#
Returns: do_unshift(state, to, to_end, to_next).
🔗
result in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const;
3
#
Returns: do_in(state, from, from_end, from_next, to, to_end, to_next).
🔗
int encoding() const noexcept;
4
#
Returns: do_encoding().
🔗
bool always_noconv() const noexcept;
5
#
Returns: do_always_noconv().
🔗
int length(stateT& state, const externT* from, const externT* from_end, size_t max) const;
6
#
Returns: do_length(state, from, from_end, max).
🔗
int max_length() const noexcept;
7
#
Returns: do_max_length().

30.4.2.5.3 Virtual functions [locale.codecvt.virtuals]

🔗
result do_out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const; result do_in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const;
1
#
Preconditions: (from <= from_end && to <= to_end) is well-defined and true; state is initialized, if at the beginning of a sequence, or else is equal to the result of converting the preceding characters in the sequence.
2
#
Effects: Translates characters in the source range [from, from_end), placing the results in sequential positions starting at destination to.
Converts no more than (from_end - from) source elements, and stores no more than (to_end - to) destination elements.
3
#
Stops if it encounters a character it cannot convert.
It always leaves the from_next and to_next pointers pointing one beyond the last element successfully converted.
If returns noconv, internT and externT are the same type and the converted sequence is identical to the input sequence [from, from_next).
to_next is set equal to to, the value of state is unchanged, and there are no changes to the values in [to, to_end).
4
#
A codecvt facet that is used by basic_filebuf ([file.streams]) shall have the property that if do_out(state, from, from_end, from_next, to, to_end, to_next) would return ok, where from != from_end, then do_out(state, from, from + 1, from_next, to, to_end, to_next) shall also return ok, and that if do_in(state, from, from_end, from_next, to, to_end, to_next) would return ok, where to != to_end, then do_in(state, from, from_end, from_next, to, to + 1, to_next) shall also return ok.242
[Note 1: 
As a result of operations on state, it can return ok or partial and set from_next == from and to_next != to.
— end note]
5
#
Returns: An enumeration value, as summarized in Table 110.
Table 110: do_in/do_out result values [tab:locale.codecvt.inout]
Value
Meaning
ok
completed the conversion
partial
not all source characters converted
error
encountered a character in [from, from_end) that cannot be converted
noconv
internT and externT are the same type, and input sequence is identical to converted sequence
A return value of partial, if (from_next == from_end), indicates that either the destination sequence has not absorbed all the available destination elements, or that additional source elements are needed before another destination element can be produced.
6
#
Remarks: Its operations on state are unspecified.
[Note 2: 
This argument can be used, for example, to maintain shift state, to specify conversion options (such as count only), or to identify a cache of seek offsets.
— end note]
🔗
result do_unshift(stateT& state, externT* to, externT* to_end, externT*& to_next) const;
7
#
Preconditions: (to <= to_end) is well-defined and true; state is initialized, if at the beginning of a sequence, or else is equal to the result of converting the preceding characters in the sequence.
8
#
Effects: Places characters starting at to that should be appended to terminate a sequence when the current stateT is given by state.243
Stores no more than (to_end - to) destination elements, and leaves the to_next pointer pointing one beyond the last element successfully stored.
9
#
Returns: An enumeration value, as summarized in Table 111.
Table 111: do_unshift result values [tab:locale.codecvt.unshift]
Value
Meaning
ok
completed the sequence
partial
space for more than to_end - to destination elements was needed to terminate a sequence given the value of state
error
an unspecified error has occurred
noconv
no termination is needed for this state_type
🔗
int do_encoding() const noexcept;
10
#
Returns: -1 if the encoding of the externT sequence is state-dependent; else the constant number of externT characters needed to produce an internal character; or 0 if this number is not a constant.244
🔗
bool do_always_noconv() const noexcept;
11
#
Returns: true if do_in() and do_out() return noconv for all valid argument values.
codecvt<char, char, mbstate_t> returns true.
🔗
int do_length(stateT& state, const externT* from, const externT* from_end, size_t max) const;
12
#
Preconditions: (from <= from_end) is well-defined and true; state is initialized, if at the beginning of a sequence, or else is equal to the result of converting the preceding characters in the sequence.
13
#
Effects: The effect on the state argument is as if it called do_in(state, from, from_end, from, to, to+max, to) for to pointing to a buffer of at least max elements.
14
#
Returns: (from_next-from) where from_next is the largest value in the range [from, from_end] such that the sequence of values in the range [from, from_next) represents max or fewer valid complete characters of type internT.
The specialization codecvt<char, char, mbstate_t>, returns the lesser of max and (from_end-from).
🔗
int do_max_length() const noexcept;
15
#
Returns: The maximum value that do_length(state, from, from_end, 1) can return for any valid range [from, from_end) and stateT value state.
The specialization codecvt<char, char, mbstate_t>​::​do_max_length() returns 1.
242)242)
Informally, this means that basic_filebuf assumes that the mappings from internal to external characters is 1 to N: that a codecvt facet that is used by basic_filebuf can translate characters one internal character at a time.
243)243)
Typically these will be characters to return the state to stateT().
244)244)
If encoding() yields -1, then more than max_length() externT elements can be consumed when producing a single internT character, and additional externT elements can appear at the end of a sequence after those that yield the final internT character.

30.4.2.6 Class template codecvt_byname [locale.codecvt.byname]

🔗
namespace std { template<class internT, class externT, class stateT> class codecvt_byname : public codecvt<internT, externT, stateT> { public: explicit codecvt_byname(const char*, size_t refs = 0); explicit codecvt_byname(const string&, size_t refs = 0); protected: ~codecvt_byname(); }; }

30.4.3 The numeric category [category.numeric]

30.4.3.1 General [category.numeric.general]

1
#
The classes num_get<> and num_put<> handle numeric formatting and parsing.
Virtual functions are provided for several numeric types.
Implementations may (but are not required to) delegate extraction of smaller types to extractors for larger types.245
2
#
All specifications of member functions for num_put and num_get in the subclauses of [category.numeric] only apply to the specializations required in Tables 108 and 109 ([locale.category]), namely num_get<char>, num_get<wchar_t>, num_get<C, InputIterator>, num_put<char>, num_put<wchar_t>, and num_put<C, OutputIterator>.
These specializations refer to the ios_base& argument for formatting specifications ([locale.categories]), and to its imbued locale for the numpunct<> facet to identify all numeric punctuation preferences, and also for the ctype<> facet to perform character classification.
3
#
Extractor and inserter members of the standard iostreams use num_get<> and num_put<> member functions for formatting and parsing numeric values ([istream.formatted.reqmts], [ostream.formatted.reqmts]).
245)245)
Parsing "-1" correctly into, e.g., an unsigned short requires that the corresponding member get() at least extract the sign before delegating.

30.4.3.2 Class template num_get [locale.num.get]

30.4.3.2.1 General [locale.num.get.general]

🔗
namespace std { template<class charT, class InputIterator = istreambuf_iterator<charT>> class num_get : public locale::facet { public: using char_type = charT; using iter_type = InputIterator; explicit num_get(size_t refs = 0); iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, bool& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, long& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, long long& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, unsigned short& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, unsigned int& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, unsigned long& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, unsigned long long& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, float& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, double& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, long double& v) const; iter_type get(iter_type in, iter_type end, ios_base&, ios_base::iostate& err, void*& v) const; static locale::id id; protected: ~num_get(); virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, bool& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, long& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, long long& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, unsigned short& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, unsigned int& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, unsigned long& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, unsigned long long& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, float& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, double& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, long double& v) const; virtual iter_type do_get(iter_type, iter_type, ios_base&, ios_base::iostate& err, void*& v) const; }; }
1
#
The facet num_get is used to parse numeric values from an input sequence such as an istream.

30.4.3.2.2 Members [facet.num.get.members]

🔗
iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;
1
#
Returns: do_get(in, end, str, err, val).

30.4.3.2.3 Virtual functions [facet.num.get.virtuals]

🔗
iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;
1
#
Effects: Reads characters from in, interpreting them according to str.flags(), use_facet<ctype<​charT>>(loc), and use_facet<numpunct<charT>>(loc), where loc is str.getloc().
2
#
The details of this operation occur in three stages:
  • (2.1)
    Stage 1: Determine a conversion specifier.
  • (2.2)
    Stage 2: Extract characters from in and determine a corresponding char value for the format expected by the conversion specification determined in stage 1.
  • (2.3)
    Stage 3: Store results.
3
#
The details of the stages are presented below.
  • Stage 1:
    The function initializes local variables via fmtflags flags = str.flags(); fmtflags basefield = (flags & ios_base::basefield); fmtflags uppercase = (flags & ios_base::uppercase); fmtflags boolalpha = (flags & ios_base::boolalpha);
    For conversion to an integral type, the function determines the integral conversion specifier as indicated in Table 112.
    The table is ordered.
    That is, the first line whose condition is true applies.
    Table 112: Integer conversions [tab:facet.num.get.int]
    State
    stdio equivalent
    basefield == oct
    %o
    basefield == hex
    %X
    basefield == 0
    %i
    signed integral type
    %d
    unsigned integral type
    %u
    For conversions to a floating-point type the specifier is %g.
    For conversions to void* the specifier is %p.
    A length modifier is added to the conversion specification, if needed, as indicated in Table 113.
    Table 113: Length modifier [tab:facet.num.get.length]
    Type
    Length modifier
    short
    h
    unsigned short
    h
    long
    l
    unsigned long
    l
    long long
    ll
    unsigned long long
    ll
    double
    l
    long double
    L
  • Stage 2:
    If in == end then stage 2 terminates.
    Otherwise a charT is taken from in and local variables are initialized as if by char_type ct = *in; char c = src[find(atoms, atoms + sizeof(src) - 1, ct) - atoms]; if (ct == use_facet<numpunct<charT>>(loc).decimal_point()) c = '.'; bool discard = ct == use_facet<numpunct<charT>>(loc).thousands_sep() && use_facet<numpunct<charT>>(loc).grouping().length() != 0; where the values src and atoms are defined as if by: static const char src[] = "0123456789abcdefpxABCDEFPX+-"; char_type atoms[sizeof(src)]; use_facet<ctype<charT>>(loc).widen(src, src + sizeof(src), atoms); for this value of loc.
    If discard is true, then if '.' has not yet been accumulated, then the position of the character is remembered, but the character is otherwise ignored.
    Otherwise, if '.' has already been accumulated, the character is discarded and Stage 2 terminates.
    If it is not discarded, then a check is made to determine if c is allowed as the next character of an input field of the conversion specifier returned by Stage 1.
    If so, it is accumulated.
    If the character is either discarded or accumulated then in is advanced by ++in and processing returns to the beginning of stage 2.
    [Example 1: 
    Given an input sequence of "0x1a.bp+07p",
    • (3.2.1)
      if the conversion specifier returned by Stage 1 is %d, "0" is accumulated;
    • (3.2.2)
      if the conversion specifier returned by Stage 1 is %i, "0x1a" are accumulated;
    • (3.2.3)
      if the conversion specifier returned by Stage 1 is %g, "0x1a.bp+07" are accumulated.
    In all cases, the remainder is left in the input.
    — end example]
  • Stage 3:
    The sequence of chars accumulated in stage 2 (the field) is converted to a numeric value by the rules of one of the functions declared in the header <cstdlib>:
    • (3.3.1)
      For a signed integer value, the function strtoll.
    • (3.3.2)
      For an unsigned integer value, the function strtoull.
    • (3.3.3)
      For a float value, the function strtof.
    • (3.3.4)
      For a double value, the function strtod.
    • (3.3.5)
      For a long double value, the function strtold.
    The numeric value to be stored can be one of:
    • (3.3.6)
      zero, if the conversion function does not convert the entire field.
    • (3.3.7)
      the most positive (or negative) representable value, if the field to be converted to a signed integer type represents a value too large positive (or negative) to be represented in val.
    • (3.3.8)
      the most positive representable value, if the field to be converted to an unsigned integer type represents a value that cannot be represented in val.
    • (3.3.9)
      the converted value, otherwise.
    The resultant numeric value is stored in val.
    If the conversion function does not convert the entire field, or if the field represents a value outside the range of representable values, ios_base​::​failbit is assigned to err.
4
#
Digit grouping is checked.
That is, the positions of discarded separators are examined for consistency with use_facet<numpunct<charT>>(loc).grouping().
If they are not consistent then ios_base​::​failbit is assigned to err.
5
#
In any case, if stage 2 processing was terminated by the test for in == end then err |= ios_base​::​eofbit is performed.
🔗
iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const;
6
#
Effects: If (str.flags()&ios_base​::​boolalpha) == 0 then input proceeds as it would for a long except that if a value is being stored into val, the value is determined according to the following: If the value to be stored is 0 then false is stored.
If the value is 1 then true is stored.
Otherwise true is stored and ios_base​::​failbit is assigned to err.
7
#
Otherwise target sequences are determined “as if” by calling the members falsename() and truename() of the facet obtained by use_facet<numpunct<charT>>(str.getloc()).
Successive characters in the range [in, end) (see [sequence.reqmts]) are obtained and matched against corresponding positions in the target sequences only as necessary to identify a unique match.
The input iterator in is compared to end only when necessary to obtain a character.
If a target sequence is uniquely matched, val is set to the corresponding value.
Otherwise false is stored and ios_base​::​failbit is assigned to err.
8
#
The in iterator is always left pointing one position beyond the last character successfully matched.
If val is set, then err is set to str.goodbit; or to str.eofbit if, when seeking another character to match, it is found that (in == end).
If val is not set, then err is set to str.failbit; or to (str.failbit|str.eofbit) if the reason for the failure was that (in == end).
[Example 2: 
For targets true: "a" and false: "abb", the input sequence "a" yields val == true and err == str.eofbit; the input sequence "abc" yields err = str.failbit, with in ending at the 'c' element.
For targets true: "1" and false: "0", the input sequence "1" yields val == true and err == str.goodbit.
For empty targets (""), any input sequence yields err == str.failbit.
— end example]
9
#
Returns: in.

30.4.3.3 Class template num_put [locale.nm.put]

30.4.3.3.1 General [locale.nm.put.general]

🔗
namespace std { template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class num_put : public locale::facet { public: using char_type = charT; using iter_type = OutputIterator; explicit num_put(size_t refs = 0); iter_type put(iter_type s, ios_base& f, char_type fill, bool v) const; iter_type put(iter_type s, ios_base& f, char_type fill, long v) const; iter_type put(iter_type s, ios_base& f, char_type fill, long long v) const; iter_type put(iter_type s, ios_base& f, char_type fill, unsigned long v) const; iter_type put(iter_type s, ios_base& f, char_type fill, unsigned long long v) const; iter_type put(iter_type s, ios_base& f, char_type fill, double v) const; iter_type put(iter_type s, ios_base& f, char_type fill, long double v) const; iter_type put(iter_type s, ios_base& f, char_type fill, const void* v) const; static locale::id id; protected: ~num_put(); virtual iter_type do_put(iter_type, ios_base&, char_type fill, bool v) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, long v) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, long long v) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, unsigned long) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, unsigned long long) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, double v) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, long double v) const; virtual iter_type do_put(iter_type, ios_base&, char_type fill, const void* v) const; }; }
1
#
The facet num_put is used to format numeric values to a character sequence such as an ostream.

30.4.3.3.2 Members [facet.num.put.members]

🔗
iter_type put(iter_type out, ios_base& str, char_type fill, bool val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, unsigned long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, unsigned long long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, double val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long double val) const; iter_type put(iter_type out, ios_base& str, char_type fill, const void* val) const;
1
#
Returns: do_put(out, str, fill, val).

30.4.3.3.3 Virtual functions [facet.num.put.virtuals]

🔗
iter_type do_put(iter_type out, ios_base& str, char_type fill, long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, long long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, unsigned long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, unsigned long long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, double val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, long double val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, const void* val) const;
1
#
Effects: Writes characters to the sequence out, formatting val as desired.
In the following description, loc names a local variable initialized as locale loc = str.getloc();
2
#
The details of this operation occur in several stages:
  • (2.1)
    Stage 1: Determine a printf conversion specifier spec and determine the characters that would be printed by printf ([c.files]) given this conversion specifier for printf(spec, val) assuming that the current locale is the "C" locale.
  • (2.2)
    Stage 2: Adjust the representation by converting each char determined by stage 1 to a charT using a conversion and values returned by members of use_facet<numpunct<charT>>(loc).
  • (2.3)
    Stage 3: Determine where padding is required.
  • (2.4)
    Stage 4: Insert the sequence into the out.
3
#
Detailed descriptions of each stage follow.
4
#
Returns: out.
5
#
  • Stage 1:
    The first action of stage 1 is to determine a conversion specifier.
    The tables that describe this determination use the following local variables
    fmtflags flags = str.flags(); fmtflags basefield = (flags & (ios_base::basefield)); fmtflags uppercase = (flags & (ios_base::uppercase)); fmtflags floatfield = (flags & (ios_base::floatfield)); fmtflags showpos = (flags & (ios_base::showpos)); fmtflags showbase = (flags & (ios_base::showbase)); fmtflags showpoint = (flags & (ios_base::showpoint));
    All tables used in describing stage 1 are ordered.
    That is, the first line whose condition is true applies.
    A line without a condition is the default behavior when none of the earlier lines apply.
    For conversion from an integral type other than a character type, the function determines the integral conversion specifier as indicated in Table 114.
    Table 114: Integer conversions [tab:facet.num.put.int]
    State
    stdio equivalent
    basefield == ios_base​::​oct
    %o
    (basefield == ios_base​::​hex) && !uppercase
    %x
    (basefield == ios_base​::​hex)
    %X
    for a signed integral type
    %d
    for an unsigned integral type
    %u
    For conversion from a floating-point type, the function determines the floating-point conversion specifier as indicated in Table 115.
    Table 115: Floating-point conversions [tab:facet.num.put.fp]
    State
    stdio equivalent
    floatfield == ios_base​::​fixed
    %f
    floatfield == ios_base​::​scientific && !uppercase
    %e
    floatfield == ios_base​::​scientific
    %E
    floatfield == (ios_base​::​fixed | ios_base​::​scientific) && !uppercase
    %a
    floatfield == (ios_base​::​fixed | ios_base​::​scientific)
    %A
    !uppercase
    %g
    otherwise
    %G
    For conversions from an integral or floating-point type a length modifier is added to the conversion specifier as indicated in Table 116.
    Table 116: Length modifier [tab:facet.num.put.length]
    Type
    Length modifier
    long
    l
    long long
    ll
    unsigned long
    l
    unsigned long long
    ll
    long double
    L
    otherwise
    none
    The conversion specifier has the following optional additional qualifiers prepended as indicated in Table 117.
    Table 117: Numeric conversions [tab:facet.num.put.conv]
    Type(s)
    State
    stdio equivalent
    an integral type
    showpos
    +
    showbase
    #
    a floating-point type
    showpos
    +
    showpoint
    #
    For conversion from a floating-point type, if floatfield != (ios_base​::​fixed | ios_base​::​​scientific), str.precision() is specified as precision in the conversion specification.
    Otherwise, no precision is specified.
    For conversion from void* the specifier is %p.
    The representations at the end of stage 1 consists of the char's that would be printed by a call of printf(s, val) where s is the conversion specifier determined above.
  • Stage 2:
    Any character c other than a decimal point(.) is converted to a charT via use_facet<ctype<charT>>(loc).widen(c)
    A local variable punct is initialized via const numpunct<charT>& punct = use_facet<numpunct<charT>>(loc);
    For arithmetic types, punct.thousands_sep() characters are inserted into the sequence as determined by the value returned by punct.do_grouping() using the method described in [facet.numpunct.virtuals].
    Decimal point characters(.) are replaced by punct.decimal_point().
  • Stage 3:
    A local variable is initialized as fmtflags adjustfield = (flags & (ios_base::adjustfield));
    The location of any padding246 is determined according to Table 118.
    Table 118: Fill padding [tab:facet.num.put.fill]
    State
    Location
    adjustfield == ios_base​::​left
    pad after
    adjustfield == ios_base​::​right
    pad before
    adjustfield == internal and a sign occurs in the representation
    pad after the sign
    adjustfield == internal and representation after stage 1 began with 0x or 0X
    pad after x or X
    otherwise
    pad before
    If str.width() is nonzero and the number of charT's in the sequence after stage 2 is less than str.​width(), then enough fill characters are added to the sequence at the position indicated for padding to bring the length of the sequence to str.width().
    str.width(0) is called.
  • Stage 4:
    The sequence of charT's at the end of stage 3 are output via *out++ = c
🔗
iter_type do_put(iter_type out, ios_base& str, char_type fill, bool val) const;
6
#
Returns: If (str.flags() & ios_base​::​boolalpha) == 0 returns do_put(out, str, fill,
(int)val), otherwise obtains a string s as if by string_type s = val ? use_facet<numpunct<charT>>(loc).truename() : use_facet<numpunct<charT>>(loc).falsename(); and then inserts each character c of s into out via *out++ = c and returns out.
246)246)
The conversion specification #o generates a leading 0 which is not a padding character.

30.4.4 The numeric punctuation facet [facet.numpunct]

30.4.4.1 Class template numpunct [locale.numpunct]

30.4.4.1.1 General [locale.numpunct.general]

🔗
namespace std { template<class charT> class numpunct : public locale::facet { public: using char_type = charT; using string_type = basic_string<charT>; explicit numpunct(size_t refs = 0); char_type decimal_point() const; char_type thousands_sep() const; string grouping() const; string_type truename() const; string_type falsename() const; static locale::id id; protected: ~numpunct(); // virtual virtual char_type do_decimal_point() const; virtual char_type do_thousands_sep() const; virtual string do_grouping() const; virtual string_type do_truename() const; // for bool virtual string_type do_falsename() const; // for bool }; }
1
#
numpunct<> specifies numeric punctuation.
The specializations required in Table 108 ([locale.category]), namely numpunct<​wchar_t> and numpunct<char>, provide classic "C" numeric formats, i.e., they contain information equivalent to that contained in the "C" locale or their wide character counterparts as if obtained by a call to widen.
2
#
The syntax for number formats is as follows, where digit represents the radix set specified by the fmtflags argument value, and thousands-sep and decimal-point are the results of corresponding numpunct<charT> members.
Integer values have the format:
intval:
sign units
sign:
+
-
units:
digits
digits thousands-sep units
digits:
digit digits
and floating-point values have:
floatval:
sign units fractional exponent
sign decimal-point digits exponent
fractional:
decimal-point digits
exponent:
e sign digits
e:
e
E
where the number of digits between thousands-seps is as specified by do_grouping().
For parsing, if the digits portion contains no thousands-separators, no grouping constraint is applied.

30.4.4.1.2 Members [facet.numpunct.members]

🔗
char_type decimal_point() const;
1
#
Returns: do_decimal_point().
🔗
char_type thousands_sep() const;
2
#
Returns: do_thousands_sep().
🔗
string grouping() const;
3
#
Returns: do_grouping().
🔗
string_type truename() const; string_type falsename() const;
4
#
Returns: do_truename() or do_falsename(), respectively.

30.4.4.1.3 Virtual functions [facet.numpunct.virtuals]

🔗
char_type do_decimal_point() const;
1
#
Returns: A character for use as the decimal radix separator.
The required specializations return '.' or L'.'.
🔗
char_type do_thousands_sep() const;
2
#
Returns: A character for use as the digit group separator.
The required specializations return ',' or L','.
🔗
string do_grouping() const;
3
#
Returns: A string vec used as a vector of integer values, in which each element vec[i] represents the number of digits247 in the group at position i, starting with position 0 as the rightmost group.
If vec.size() <= i, the number is the same as group (i - 1); if (i < 0 || vec[i] <= 0 || vec[i] == CHAR_MAX), the size of the digit group is unlimited.
4
#
The required specializations return the empty string, indicating no grouping.
🔗
string_type do_truename() const; string_type do_falsename() const;
5
#
Returns: A string representing the name of the boolean value true or false, respectively.
6
#
In the base class implementation these names are "true" and "false", or L"true" and L"false".
247)247)
Thus, the string "\003" specifies groups of 3 digits each, and "3" probably indicates groups of 51 (!) digits each, because 51 is the ASCII value of "3".

30.4.4.2 Class template numpunct_byname [locale.numpunct.byname]

🔗
namespace std { template<class charT> class numpunct_byname : public numpunct<charT> { // this class is specialized for char and wchar_t. public: using char_type = charT; using string_type = basic_string<charT>; explicit numpunct_byname(const char*, size_t refs = 0); explicit numpunct_byname(const string&, size_t refs = 0); protected: ~numpunct_byname(); }; }

30.4.5 The collate category [category.collate]

30.4.5.1 Class template collate [locale.collate]

30.4.5.1.1 General [locale.collate.general]

🔗
namespace std { template<class charT> class collate : public locale::facet { public: using char_type = charT; using string_type = basic_string<charT>; explicit collate(size_t refs = 0); int compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const; string_type transform(const charT* low, const charT* high) const; long hash(const charT* low, const charT* high) const; static locale::id id; protected: ~collate(); virtual int do_compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const; virtual string_type do_transform(const charT* low, const charT* high) const; virtual long do_hash (const charT* low, const charT* high) const; }; }
1
#
The class collate<charT> provides features for use in the collation (comparison) and hashing of strings.
A locale member function template, operator(), uses the collate facet to allow a locale to act directly as the predicate argument for standard algorithms ([algorithms]) and containers operating on strings.
The specializations required in Table 108 ([locale.category]), namely collate<char> and collate<wchar_t>, apply lexicographical ordering ([alg.lex.comparison]).
2
#
Each function compares a string of characters *p in the range [low, high).

30.4.5.1.2 Members [locale.collate.members]

🔗
int compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;
1
#
Returns: do_compare(low1, high1, low2, high2).
🔗
string_type transform(const charT* low, const charT* high) const;
2
#
Returns: do_transform(low, high).
🔗
long hash(const charT* low, const charT* high) const;
3
#
Returns: do_hash(low, high).

30.4.5.1.3 Virtual functions [locale.collate.virtuals]

🔗
int do_compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;
1
#
Returns: 1 if the first string is greater than the second, -1 if less, zero otherwise.
The specializations required in Table 108 ([locale.category]), namely collate<char> and collate<wchar_t>, implement a lexicographical comparison ([alg.lex.comparison]).
🔗
string_type do_transform(const charT* low, const charT* high) const;
2
#
Returns: A basic_string<charT> value that, compared lexicographically with the result of calling transform() on another string, yields the same result as calling do_compare() on the same two strings.248
🔗
long do_hash(const charT* low, const charT* high) const;
3
#
Returns: An integer value equal to the result of calling hash() on any other string for which do_compare() returns 0 (equal) when passed the two strings.
4
#
Recommended practice: The probability that the result equals that for another string which does not compare equal should be very small, approaching (1.0/numeric_limits<unsigned long>​::​max()).
248)248)
This function is useful when one string is being compared to many other strings.

30.4.5.2 Class template collate_byname [locale.collate.byname]

🔗
namespace std { template<class charT> class collate_byname : public collate<charT> { public: using string_type = basic_string<charT>; explicit collate_byname(const char*, size_t refs = 0); explicit collate_byname(const string&, size_t refs = 0); protected: ~collate_byname(); }; }

30.4.6 The time category [category.time]

30.4.6.1 General [category.time.general]

1
#
Templates time_get<charT, InputIterator> and time_put<charT, OutputIterator> provide date and time formatting and parsing.
All specifications of member functions for time_put and time_get in the subclauses of [category.time] only apply to the specializations required in Tables 108 and 109 ([locale.category]).
Their members use their ios_base&, ios_base​::​iostate&, and fill arguments as described in [locale.categories], and the ctype<> facet, to determine formatting details.

30.4.6.2 Class template time_get [locale.time.get]

30.4.6.2.1 General [locale.time.get.general]

🔗
namespace std { class time_base { public: enum dateorder { no_order, dmy, mdy, ymd, ydm }; }; template<class charT, class InputIterator = istreambuf_iterator<charT>> class time_get : public locale::facet, public time_base { public: using char_type = charT; using iter_type = InputIterator; explicit time_get(size_t refs = 0); dateorder date_order() const { return do_date_order(); } iter_type get_time(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t) const; iter_type get_date(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t) const; iter_type get_weekday(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t) const; iter_type get_monthname(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t) const; iter_type get_year(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t) const; iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier = 0) const; iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, const char_type* fmt, const char_type* fmtend) const; static locale::id id; protected: ~time_get(); virtual dateorder do_date_order() const; virtual iter_type do_get_time(iter_type s, iter_type end, ios_base&, ios_base::iostate& err, tm* t) const; virtual iter_type do_get_date(iter_type s, iter_type end, ios_base&, ios_base::iostate& err, tm* t) const; virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_base&, ios_base::iostate& err, tm* t) const; virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_base&, ios_base::iostate& err, tm* t) const; virtual iter_type do_get_year(iter_type s, iter_type end, ios_base&, ios_base::iostate& err, tm* t) const; virtual iter_type do_get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier) const; }; }
1
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time_get is used to parse a character sequence, extracting components of a time or date into a tm object.
Each get member parses a format as produced by a corresponding format specifier to time_put<>​::​put.
If the sequence being parsed matches the correct format, the corresponding members of the tm argument are set to the values used to produce the sequence; otherwise either an error is reported or unspecified values are assigned.249
2
#
If the end iterator is reached during parsing by any of the get() member functions, the member sets ios_base​::​eofbit in err.
249)249)
In other words, user confirmation is required for reliable parsing of user-entered dates and times, but machine-generated formats can be parsed reliably.
This allows parsers to be aggressive about interpreting user variations on standard formats.

30.4.6.2.2 Members [locale.time.get.members]

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dateorder date_order() const;
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Returns: do_date_order().
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iter_type get_time(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
2
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Returns: do_get_time(s, end, str, err, t).
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iter_type get_date(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
3
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Returns: do_get_date(s, end, str, err, t).
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iter_type get_weekday(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const; iter_type get_monthname(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
4
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Returns: do_get_weekday(s, end, str, err, t) or do_get_monthname(s, end, str, err, t).
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iter_type get_year(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
5
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Returns: do_get_year(s, end, str, err, t).
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iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier = 0) const;
6
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Returns: do_get(s, end, f, err, t, format, modifier).
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iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, const char_type* fmt, const char_type* fmtend) const;
7
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Preconditions: [fmt, fmtend) is a valid range.
8
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Effects: The function starts by evaluating err = ios_base​::​goodbit.
It then enters a loop, reading zero or more characters from s at each iteration.
Unless otherwise specified below, the loop terminates when the first of the following conditions holds:
  • (8.1)
    The expression fmt == fmtend evaluates to true.
  • (8.2)
    The expression err == ios_base​::​goodbit evaluates to false.
  • (8.3)
    The expression s == end evaluates to true, in which case the function evaluates err = ios_base​::​eofbit | ios_base​::​failbit.
  • (8.4)
    The next element of fmt is equal to '%', optionally followed by a modifier character, followed by a conversion specifier character, format, together forming a conversion specification valid for the POSIX function strptime.
    If the number of elements in the range [fmt, fmtend) is not sufficient to unambiguously determine whether the conversion specification is complete and valid, the function evaluates err = ios_base​::​failbit.
    Otherwise, the function evaluates s = do_get(s, end, f, err, t, format, modifier), where the value of modifier is '\0' when the optional modifier is absent from the conversion specification.
    If err == ios_base​::​goodbit holds after the evaluation of the expression, the function increments fmt to point just past the end of the conversion specification and continues looping.
  • (8.5)
    The expression isspace(*fmt, f.getloc()) evaluates to true, in which case the function first increments fmt until fmt == fmtend || !isspace(*fmt, f.getloc()) evaluates to true, then advances s until s == end || !isspace(*s, f.getloc()) is true, and finally resumes looping.
  • (8.6)
    The next character read from s matches the element pointed to by fmt in a case-insensitive comparison, in which case the function evaluates ++fmt, ++s and continues looping.
    Otherwise, the function evaluates err = ios_base​::​failbit.
9
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[Note 1: 
The function uses the ctype<charT> facet installed in f's locale to determine valid whitespace characters.
It is unspecified by what means the function performs case-insensitive comparison or whether multi-character sequences are considered while doing so.
— end note]
10
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Returns: s.

30.4.6.2.3 Virtual functions [locale.time.get.virtuals]

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dateorder do_date_order() const;
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Returns: An enumeration value indicating the preferred order of components for those date formats that are composed of day, month, and year.250
Returns no_order if the date format specified by 'x' contains other variable components (e.g., Julian day, week number, week day).
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iter_type do_get_time(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
2
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Effects: Reads characters starting at s until it has extracted those tm members, and remaining format characters, used by time_put<>​::​put to produce the format specified by "%H:%M:%S", or until it encounters an error or end of sequence.
3
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Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid time.
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iter_type do_get_date(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
4
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Effects: Reads characters starting at s until it has extracted those tm members and remaining format characters used by time_put<>​::​put to produce one of the following formats, or until it encounters an error.
The format depends on the value returned by date_order() as shown in Table 119.
Table 119: do_get_date effects [tab:locale.time.get.dogetdate]
date_order()
Format
no_order
"%m%d%y"
dmy
"%d%m%y"
mdy
"%m%d%y"
ymd
"%y%m%d"
ydm
"%y%d%m"
5
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An implementation may also accept additional implementation-defined formats.
6
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Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid date.
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iter_type do_get_weekday(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const; iter_type do_get_monthname(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
7
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Effects: Reads characters starting at s until it has extracted the (perhaps abbreviated) name of a weekday or month.
If it finds an abbreviation that is followed by characters that can match a full name, it continues reading until it matches the full name or fails.
It sets the appropriate tm member accordingly.
8
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Returns: An iterator pointing immediately beyond the last character recognized as part of a valid name.
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iter_type do_get_year(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;
9
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Effects: Reads characters starting at s until it has extracted an unambiguous year identifier.
It is implementation-defined whether two-digit year numbers are accepted, and (if so) what century they are assumed to lie in.
Sets the t->tm_year member accordingly.
10
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Returns: An iterator pointing immediately beyond the last character recognized as part of a valid year identifier.
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iter_type do_get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier) const;
11
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Preconditions: t points to an object.
12
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Effects: The function starts by evaluating err = ios_base​::​goodbit.
It then reads characters starting at s until it encounters an error, or until it has extracted and assigned those tm members, and any remaining format characters, corresponding to a conversion specification appropriate for the POSIX function strptime, formed by concatenating '%', the modifier character, when non-NUL, and the format character.
When the concatenation fails to yield a complete valid directive the function leaves the object pointed to by t unchanged and evaluates err |= ios_base​::​failbit.
When s == end evaluates to true after reading a character the function evaluates err |= ios_base​::​eofbit.
13
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For complex conversion specifications such as %c, %x, or %X, or conversion specifications that involve the optional modifiers E or O, when the function is unable to unambiguously determine some or all tm members from the input sequence [s, end), it evaluates err |= ios_base​::​eofbit.
In such cases the values of those tm members are unspecified and may be outside their valid range.
14
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Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid input sequence for the given format and modifier.
15
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Remarks: It is unspecified whether multiple calls to do_get() with the address of the same tm object will update the current contents of the object or simply overwrite its members.
Portable programs should zero out the object before invoking the function.
250)250)
This function is intended as a convenience only, for common formats, and can return no_order in valid locales.

30.4.6.3 Class template time_get_byname [locale.time.get.byname]

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namespace std { template<class charT, class InputIterator = istreambuf_iterator<charT>> class time_get_byname : public time_get<charT, InputIterator> { public: using dateorder = time_base::dateorder; using iter_type = InputIterator; explicit time_get_byname(const char*, size_t refs = 0); explicit time_get_byname(const string&, size_t refs = 0); protected: ~time_get_byname(); }; }

30.4.6.4 Class template time_put [locale.time.put]

30.4.6.4.1 General [locale.time.put.general]

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namespace std { template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class time_put : public locale::facet { public: using char_type = charT; using iter_type = OutputIterator; explicit time_put(size_t refs = 0); // the following is implemented in terms of other member functions. iter_type put(iter_type s, ios_base& f, char_type fill, const tm* tmb, const charT* pattern, const charT* pat_end) const; iter_type put(iter_type s, ios_base& f, char_type fill, const tm* tmb, char format, char modifier = 0) const; static locale::id id; protected: ~time_put(); virtual iter_type do_put(iter_type s, ios_base&, char_type, const tm* t, char format, char modifier) const; }; }

30.4.6.4.2 Members [locale.time.put.members]

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iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t, const charT* pattern, const charT* pat_end) const; iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t, char format, char modifier = 0) const;
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Effects: The first form steps through the sequence from pattern to pat_end, identifying characters that are part of a format sequence.
Each character that is not part of a format sequence is written to s immediately, and each format sequence, as it is identified, results in a call to do_put; thus, format elements and other characters are interleaved in the output in the order in which they appear in the pattern.
Format sequences are identified by converting each character c to a char value as if by ct.narrow(c, 0), where ct is a reference to ctype<charT> obtained from str.getloc().
The first character of each sequence is equal to '%', followed by an optional modifier character mod251 and a format specifier character spec as defined for the function strftime.
If no modifier character is present, mod is zero.
For each valid format sequence identified, calls do_put(s, str, fill, t, spec, mod).
2
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The second form calls do_put(s, str, fill, t, format, modifier).
3
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[Note 1: 
The fill argument can be used in the implementation-defined formats or by derivations.
A space character is a reasonable default for this argument.
— end note]
4
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Returns: An iterator pointing immediately after the last character produced.
251)251)
Although the C programming language defines no modifiers, most vendors do.

30.4.6.4.3 Virtual functions [locale.time.put.virtuals]

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iter_type do_put(iter_type s, ios_base&, char_type fill, const tm* t, char format, char modifier) const;
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Effects: Formats the contents of the parameter t into characters placed on the output sequence s.
Formatting is controlled by the parameters format and modifier, interpreted identically as the format specifiers in the string argument to the standard library function strftime(), except that the sequence of characters produced for those specifiers that are described as depending on the C locale are instead implementation-defined.
[Note 1: 
Interpretation of the modifier argument is implementation-defined.
— end note]
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Returns: An iterator pointing immediately after the last character produced.
[Note 2: 
The fill argument can be used in the implementation-defined formats or by derivations.
A space character is a reasonable default for this argument.
— end note]
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Recommended practice: Interpretation of the modifier should follow POSIX conventions.
Implementations should refer to other standards such as POSIX for a specification of the character sequences produced for those specifiers described as depending on the C locale.

30.4.6.5 Class template time_put_byname [locale.time.put.byname]

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namespace std { template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class time_put_byname : public time_put<charT, OutputIterator> { public: using char_type = charT; using iter_type = OutputIterator; explicit time_put_byname(const char*, size_t refs = 0); explicit time_put_byname(const string&, size_t refs = 0); protected: ~time_put_byname(); }; }

30.4.7 The monetary category [category.monetary]

30.4.7.1 General [category.monetary.general]

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These templates handle monetary formats.
A template parameter indicates whether local or international monetary formats are to be used.
2
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All specifications of member functions for money_put and money_get in the subclauses of [category.monetary] only apply to the specializations required in Tables 108 and 109 ([locale.category]).
Their members use their ios_base&, ios_base​::​iostate&, and fill arguments as described in [locale.categories], and the moneypunct<> and ctype<> facets, to determine formatting details.

30.4.7.2 Class template money_get [locale.money.get]

30.4.7.2.1 General [locale.money.get.general]

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namespace std { template<class charT, class InputIterator = istreambuf_iterator<charT>> class money_get : public locale::facet { public: using char_type = charT; using iter_type = InputIterator; using string_type = basic_string<charT>; explicit money_get(size_t refs = 0); iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, long double& units) const; iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, string_type& digits) const; static locale::id id; protected: ~money_get(); virtual iter_type do_get(iter_type, iter_type, bool, ios_base&, ios_base::iostate& err, long double& units) const; virtual iter_type do_get(iter_type, iter_type, bool, ios_base&, ios_base::iostate& err, string_type& digits) const; }; }

30.4.7.2.2 Members [locale.money.get.members]

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iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, long double& quant) const; iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, string_type& quant) const;
1
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Returns: do_get(s, end, intl, f, err, quant).

30.4.7.2.3 Virtual functions [locale.money.get.virtuals]

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iter_type do_get(iter_type s, iter_type end, bool intl, ios_base& str, ios_base::iostate& err, long double& units) const; iter_type do_get(iter_type s, iter_type end, bool intl, ios_base& str, ios_base::iostate& err, string_type& digits) const;
1
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Effects: Reads characters from s to parse and construct a monetary value according to the format specified by a moneypunct<charT, Intl> facet reference mp and the character mapping specified by a ctype<charT> facet reference ct obtained from the locale returned by str.getloc(), and str.flags().
If a valid sequence is recognized, does not change err; otherwise, sets err to (err|str.failbit), or (err|str.failbit|str.eofbit) if no more characters are available, and does not change units or digits.
Uses the pattern returned by mp.neg_format() to parse all values.
The result is returned as an integral value stored in units or as a sequence of digits possibly preceded by a minus sign (as produced by ct.widen(c) where c is '-' or in the range from '0' through '9' (inclusive)) stored in digits.
[Example 1: 
The sequence $1,056.23 in a common United States locale would yield, for units, 105623, or, for digits, "105623".
— end example]
If mp.grouping() indicates that no thousands separators are permitted, any such characters are not read, and parsing is terminated at the point where they first appear.
Otherwise, thousands separators are optional; if present, they are checked for correct placement only after all format components have been read.
2
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Where money_base​::​space or money_base​::​none appears as the last element in the format pattern, no whitespace is consumed.
Otherwise, where money_base​::​space appears in any of the initial elements of the format pattern, at least one whitespace character is required.
Where money_base​::​none appears in any of the initial elements of the format pattern, whitespace is allowed but not required.
If (str.flags() & str.showbase) is false, the currency symbol is optional and is consumed only if other characters are needed to complete the format; otherwise, the currency symbol is required.
3
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If the first character (if any) in the string pos returned by mp.positive_sign() or the string neg returned by mp.negative_sign() is recognized in the position indicated by sign in the format pattern, it is consumed and any remaining characters in the string are required after all the other format components.
[Example 2: 
If showbase is off, then for a neg value of "()" and a currency symbol of "L", in "(100 L)" the "L" is consumed; but if neg is "-", the "L" in "-100 L" is not consumed.
— end example]
If pos or neg is empty, the sign component is optional, and if no sign is detected, the result is given the sign that corresponds to the source of the empty string.
Otherwise, the character in the indicated position must match the first character of pos or neg, and the result is given the corresponding sign.
If the first character of pos is equal to the first character of neg, or if both strings are empty, the result is given a positive sign.
4
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Digits in the numeric monetary component are extracted and placed in digits, or into a character buffer buf1 for conversion to produce a value for units, in the order in which they appear, preceded by a minus sign if and only if the result is negative.
The value units is produced as if by252 for (int i = 0; i < n; ++i) buf2[i] = src[find(atoms, atoms+sizeof(src), buf1[i]) - atoms]; buf2[n] = 0; sscanf(buf2, "%Lf", &units); where n is the number of characters placed in buf1, buf2 is a character buffer, and the values src and atoms are defined as if by static const char src[] = "0123456789-"; charT atoms[sizeof(src)]; ct.widen(src, src + sizeof(src) - 1, atoms);
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Returns: An iterator pointing immediately beyond the last character recognized as part of a valid monetary quantity.
252)252)
The semantics here are different from ct.narrow.

30.4.7.3 Class template money_put [locale.money.put]

30.4.7.3.1 General [locale.money.put.general]

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namespace std { template<class charT, class OutputIterator = ostreambuf_iterator<charT>> class money_put : public locale::facet { public: using char_type = charT; using iter_type = OutputIterator; using string_type = basic_string<charT>; explicit money_put(size_t refs = 0); iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, long double units) const; iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, const string_type& digits) const; static locale::id id; protected: ~money_put(); virtual iter_type do_put(iter_type, bool, ios_base&, char_type fill, long double units) const; virtual iter_type do_put(iter_type, bool, ios_base&, char_type fill, const string_type& digits) const; }; }

30.4.7.3.2 Members [locale.money.put.members]

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iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, long double quant) const; iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, const string_type& quant) const;
1
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Returns: do_put(s, intl, f, loc, quant).

30.4.7.3.3 Virtual functions [locale.money.put.virtuals]

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iter_type do_put(iter_type s, bool intl, ios_base& str, char_type fill, long double units) const; iter_type do_put(iter_type s, bool intl, ios_base& str, char_type fill, const string_type& digits) const;
1
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Effects: Writes characters to s according to the format specified by a moneypunct<charT, Intl> facet reference mp and the character mapping specified by a ctype<charT> facet reference ct obtained from the locale returned by str.getloc(), and str.flags().
The argument units is transformed into a sequence of wide characters as if by ct.widen(buf1, buf1 + sprintf(buf1, "%.0Lf", units), buf2) for character buffers buf1 and buf2.
If the first character in digits or buf2 is equal to ct.widen('-'), then the pattern used for formatting is the result of mp.neg_format(); otherwise the pattern is the result of mp.pos_format().
Digit characters are written, interspersed with any thousands separators and decimal point specified by the format, in the order they appear (after the optional leading minus sign) in digits or buf2.
In digits, only the optional leading minus sign and the immediately subsequent digit characters (as classified according to ct) are used; any trailing characters (including digits appearing after a non-digit character) are ignored.
Calls str.width(0).
2
#
Returns: An iterator pointing immediately after the last character produced.
3
#
Remarks: The currency symbol is generated if and only if (str.flags() & str.showbase) is nonzero.
If the number of characters generated for the specified format is less than the value returned by str.width() on entry to the function, then copies of fill are inserted as necessary to pad to the specified width.
For the value af equal to (str.flags() & str.adjustfield), if (af == str.internal) is true, the fill characters are placed where none or space appears in the formatting pattern; otherwise if (af == str.left) is true, they are placed after the other characters; otherwise, they are placed before the other characters.
[Note 1: 
It is possible, with some combinations of format patterns and flag values, to produce output that cannot be parsed using num_get<>​::​get.
— end note]

30.4.7.4 Class template moneypunct [locale.moneypunct]

30.4.7.4.1 General [locale.moneypunct.general]

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namespace std { class money_base { public: enum part { none, space, symbol, sign, value }; struct pattern { char field[4]; }; }; template<class charT, bool International = false> class moneypunct : public locale::facet, public money_base { public: using char_type = charT; using string_type = basic_string<charT>; explicit moneypunct(size_t refs = 0); charT decimal_point() const; charT thousands_sep() const; string grouping() const; string_type curr_symbol() const; string_type positive_sign() const; string_type negative_sign() const; int frac_digits() const; pattern pos_format() const; pattern neg_format() const; static locale::id id; static const bool intl = International; protected: ~moneypunct(); virtual charT do_decimal_point() const; virtual charT do_thousands_sep() const; virtual string do_grouping() const; virtual string_type do_curr_symbol() const; virtual string_type do_positive_sign() const; virtual string_type do_negative_sign() const; virtual int do_frac_digits() const; virtual pattern do_pos_format() const; virtual pattern do_neg_format() const; }; }
1
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The moneypunct<> facet defines monetary formatting parameters used by money_get<> and money_put<>.
A monetary format is a sequence of four components, specified by a pattern value p, such that the part value static_cast<part>(p.field[i]) determines the component of the format253 In the field member of a pattern object, each value symbol, sign, value, and either space or none appears exactly once.
The value none, if present, is not first; the value space, if present, is neither first nor last.
2
#
Where none or space appears, whitespace is permitted in the format, except where none appears at the end, in which case no whitespace is permitted.
The value space indicates that at least one space is required at that position.
Where symbol appears, the sequence of characters returned by curr_symbol() is permitted, and can be required.
Where sign appears, the first (if any) of the sequence of characters returned by positive_sign() or negative_sign() (respectively as the monetary value is non-negative or negative) is required.
Any remaining characters of the sign sequence are required after all other format components.
Where value appears, the absolute numeric monetary value is required.
3
#
The format of the numeric monetary value is a decimal number:
value:
units fractional
decimal-point digits
fractional:
decimal-point digits
if frac_digits() returns a positive value, or
value:
units
otherwise.
The symbol decimal-point indicates the character returned by decimal_point().
The other symbols are defined as follows:
units:
digits
digits thousands-sep units
digits:
adigit digits
In the syntax specification, the symbol adigit is any of the values ct.widen(c) for c in the range '0' through '9' (inclusive) and ct is a reference of type const ctype<charT>& obtained as described in the definitions of money_get<> and money_put<>.
The symbol thousands-sep is the character returned by thousands_sep().
The space character used is the value ct.widen(' ').
Whitespace characters are those characters c for which ci.is(space, c) returns true.
The number of digits required after the decimal point (if any) is exactly the value returned by frac_digits().
4
#
The placement of thousands-separator characters (if any) is determined by the value returned by grouping(), defined identically as the member numpunct<>​::​do_grouping().
253)253)
An array of char, rather than an array of part, is specified for pattern​::​field purely for efficiency.

30.4.7.4.2 Members [locale.moneypunct.members]

🔗
charT decimal_point() const; charT thousands_sep() const; string grouping() const; string_type curr_symbol() const; string_type positive_sign() const; string_type negative_sign() const; int frac_digits() const; pattern pos_format() const; pattern neg_format() const;
1
#
Each of these functions F returns the result of calling the corresponding virtual member function do_F().

30.4.7.4.3 Virtual functions [locale.moneypunct.virtuals]

🔗
charT do_decimal_point() const;
1
#
Returns: The radix separator to use in case do_frac_digits() is greater than zero.254
🔗
charT do_thousands_sep() const;
2
#
Returns: The digit group separator to use in case do_grouping() specifies a digit grouping pattern.255
🔗
string do_grouping() const;
3
#
Returns: A pattern defined identically as, but not necessarily equal to, the result of numpunct<charT>​::​​do_grouping().256
🔗
string_type do_curr_symbol() const;
4
#
Returns: A string to use as the currency identifier symbol.
[Note 1: 
For specializations where the second template parameter is true, this is typically four characters long: a three-letter code as specified by ISO 4217[bib] followed by a space.
— end note]
🔗
string_type do_positive_sign() const; string_type do_negative_sign() const;
5
#
Returns: do_positive_sign() returns the string to use to indicate a positive monetary value;257 do_negative_sign() returns the string to use to indicate a negative value.
🔗
int do_frac_digits() const;
6
#
Returns: The number of digits after the decimal radix separator, if any.258
🔗
pattern do_pos_format() const; pattern do_neg_format() const;
7
#
Returns: The specializations required in Table 109 ([locale.category]), namely
  • (7.1)
    moneypunct<char>,
  • (7.2)
    moneypunct<wchar_t>,
  • (7.3)
    moneypunct<char, true>, and
  • (7.4)
    moneypunct<wchar_t, true>,
return an object of type pattern initialized to { symbol, sign, none, value }.259
254)254)
In common U.S. locales this is '.'.
255)255)
In common U.S. locales this is ','.
256)256)
To specify grouping by 3s, the value is "\003" not "3".
257)257)
This is usually the empty string.
258)258)
In common U.S. locales, this is 2.
259)259)
Note that the international symbol returned by do_curr_symbol() usually contains a space, itself; for example, "USD ".

30.4.7.5 Class template moneypunct_byname [locale.moneypunct.byname]

🔗
namespace std { template<class charT, bool Intl = false> class moneypunct_byname : public moneypunct<charT, Intl> { public: using pattern = money_base::pattern; using string_type = basic_string<charT>; explicit moneypunct_byname(const char*, size_t refs = 0); explicit moneypunct_byname(const string&, size_t refs = 0); protected: ~moneypunct_byname(); }; }

30.4.8 The message retrieval category [category.messages]

30.4.8.1 General [category.messages.general]

1
#
Class messages<charT> implements retrieval of strings from message catalogs.

30.4.8.2 Class template messages [locale.messages]

30.4.8.2.1 General [locale.messages.general]

🔗
namespace std { class messages_base { public: using catalog = unspecified signed integer type; }; template<class charT> class messages : public locale::facet, public messages_base { public: using char_type = charT; using string_type = basic_string<charT>; explicit messages(size_t refs = 0); catalog open(const string& fn, const locale&) const; string_type get(catalog c, int set, int msgid, const string_type& dfault) const; void close(catalog c) const; static locale::id id; protected: ~messages(); virtual catalog do_open(const string&, const locale&) const; virtual string_type do_get(catalog, int set, int msgid, const string_type& dfault) const; virtual void do_close(catalog) const; }; }
1
#
Values of type messages_base​::​catalog usable as arguments to members get and close can be obtained only by calling member open.

30.4.8.2.2 Members [locale.messages.members]

🔗
catalog open(const string& name, const locale& loc) const;
1
#
Returns: do_open(name, loc).
🔗
string_type get(catalog cat, int set, int msgid, const string_type& dfault) const;
2
#
Returns: do_get(cat, set, msgid, dfault).
🔗
void close(catalog cat) const;
3
#
Effects: Calls do_close(cat).

30.4.8.2.3 Virtual functions [locale.messages.virtuals]

🔗
catalog do_open(const string& name, const locale& loc) const;
1
#
Returns: A value that may be passed to get() to retrieve a message from the message catalog identified by the string name according to an implementation-defined mapping.
The result can be used until it is passed to close().
2
#
Returns a value less than 0 if no such catalog can be opened.
3
#
Remarks: The locale argument loc is used for character set code conversion when retrieving messages, if needed.
🔗
string_type do_get(catalog cat, int set, int msgid, const string_type& dfault) const;
4
#
Preconditions: cat is a catalog obtained from open() and not yet closed.
5
#
Returns: A message identified by arguments set, msgid, and dfault, according to an implementation-defined mapping.
If no such message can be found, returns dfault.
🔗
void do_close(catalog cat) const;
6
#
Preconditions: cat is a catalog obtained from open() and not yet closed.
7
#
Effects: Releases unspecified resources associated with cat.
8
#
Remarks: The limit on such resources, if any, is implementation-defined.

30.4.8.3 Class template messages_byname [locale.messages.byname]

🔗
namespace std { template<class charT> class messages_byname : public messages<charT> { public: using catalog = messages_base::catalog; using string_type = basic_string<charT>; explicit messages_byname(const char*, size_t refs = 0); explicit messages_byname(const string&, size_t refs = 0); protected: ~messages_byname(); }; }

30.5 C library locales [c.locales]

30.5.1 Header <clocale> synopsis [clocale.syn]

namespace std { struct lconv; char* setlocale(int category, const char* locale); lconv* localeconv(); } #define NULL see [support.types.nullptr] #define LC_ALL see below #define LC_COLLATE see below #define LC_CTYPE see below #define LC_MONETARY see below #define LC_NUMERIC see below #define LC_TIME see below
1
#
The contents and meaning of the header <clocale> are the same as the C standard library header <locale.h>.

30.5.2 Data races [clocale.data.races]

1
#
Calls to the function setlocale may introduce a data race ([res.on.data.races]) with other calls to setlocale or with calls to the functions listed in Table 120.
See also: ISO/IEC 9899:2018, 7.11
Table 120: Potential setlocale data races [tab:setlocale.data.races]
fprintf
isprint
iswdigit
localeconv
tolower
fscanf
ispunct
iswgraph
mblen
toupper
isalnum
isspace
iswlower
mbstowcs
towlower
isalpha
isupper
iswprint
mbtowc
towupper
isblank
iswalnum
iswpunct
setlocale
wcscoll
iscntrl
iswalpha
iswspace
strcoll
wcstod
isdigit
iswblank
iswupper
strerror
wcstombs
isgraph
iswcntrl
iswxdigit
strtod
wcsxfrm
islower
iswctype
isxdigit
strxfrm
wctomb

30.6 Text encodings identification [text.encoding]

30.6.1 Header <text_encoding> synopsis [text.encoding.syn]

🔗
namespace std { struct text_encoding; // [text.encoding.hash], hash support template<class T> struct hash; template<> struct hash<text_encoding>; }

30.6.2 Class text_encoding [text.encoding.class]

30.6.2.1 Overview [text.encoding.overview]

1
#
The class text_encoding describes an interface for accessing the IANA Character Sets registry[bib].
🔗
namespace std { struct text_encoding { static constexpr size_t max_name_length = 63; // [text.encoding.id], enumeration text_encoding​::​id enum class id : int_least32_t { see below }; using enum id; constexpr text_encoding() = default; constexpr explicit text_encoding(string_view enc) noexcept; constexpr text_encoding(id i) noexcept; constexpr id mib() const noexcept; constexpr const char* name() const noexcept; struct aliases_view; constexpr aliases_view aliases() const noexcept; friend constexpr bool operator==(const text_encoding& a, const text_encoding& b) noexcept; friend constexpr bool operator==(const text_encoding& encoding, id i) noexcept; static consteval text_encoding literal() noexcept; static text_encoding environment(); template<id i> static bool environment_is(); private: id mib_ = id::unknown; // exposition only char name_[max_name_length + 1] = {0}; // exposition only static constexpr bool comp-name(string_view a, string_view b); // exposition only }; }
2
#
Class text_encoding is a trivially copyable type ([basic.types.general]).

30.6.2.2 General [text.encoding.general]

1
#
A registered character encoding is a character encoding scheme in the IANA Character Sets registry.
[Note 1: 
The IANA Character Sets registry uses the term “character sets” to refer to character encodings.
— end note]
The primary name of a registered character encoding is the name of that encoding specified in the IANA Character Sets registry.
2
#
The set of known registered character encodings contains every registered character encoding specified in the IANA Character Sets registry except for the following:
3
#
Each known registered character encoding is identified by an enumerator in text_encoding​::​id, and has a set of zero or more aliases.
4
#
The set of aliases of a known registered character encoding is an implementation-defined superset of the aliases specified in the IANA Character Sets registry.
The set of aliases for US-ASCII includes “ASCII”.
No two aliases or primary names of distinct registered character encodings are equivalent when compared by text_encoding​::​comp-name.
5
#
How a text_encoding object is determined to be representative of a character encoding scheme implemented in the translation or execution environment is implementation-defined.
6
#
An object e of type text_encoding such that e.mib() == text_encoding​::​id​::​unknown is false and e.mib() == text_encoding​::​id​::​other is false maintains the following invariants:
  • (6.1)
    e.name() == nullptr is false, and
  • (6.2)
    e.mib() == text_encoding(e.name()).mib() is true.
7
#
Recommended practice:
  • (7.1)
    Implementations should not consider registered encodings to be interchangeable.
    [Example 1: 
    Shift_JIS and Windows-31J denote different encodings.
    — end example]
  • (7.2)
    Implementations should not use the name of a registered encoding to describe another similar yet different non-registered encoding unless there is a precedent on that implementation.
    [Example 2: 
    Big5
    — end example]

30.6.2.3 Members [text.encoding.members]

🔗
constexpr explicit text_encoding(string_view enc) noexcept;
1
#
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.
2
#
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.
🔗
constexpr text_encoding(id i) noexcept;
3
#
Preconditions: i has the value of one of the enumerators of id.
4
#
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.
🔗
constexpr id mib() const noexcept;
5
#
Returns: mib_.
🔗
constexpr const char* name() const noexcept;
6
#
Returns: name_ if (name_[0] != '\0') is true, and nullptr otherwise.
7
#
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.
8
#
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.
9
#
Returns: r.
10
#
[Note 1: 
The order of aliases in r is unspecified.
— end note]
🔗
static consteval text_encoding literal() noexcept;
11
#
Mandates: CHAR_BIT == 8 is true.
12
#
Returns: A text_encoding object representing the ordinary character literal encoding ([lex.charset]).
🔗
static text_encoding environment();
13
#
Mandates: CHAR_BIT == 8 is true.
14
#
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 "".
15
#
[Note 2: 
This function is not affected by calls to setlocale.
— end note]
16
#
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();
17
#
Mandates: CHAR_BIT == 8 is true.
18
#
Returns: environment() == i.
🔗
static constexpr bool comp-name(string_view a, string_view b);
19
#
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]

30.6.2.4 Comparison functions [text.encoding.cmp]

🔗
friend constexpr bool operator==(const text_encoding& a, const text_encoding& b) noexcept;
1
#
Returns: If a.mib_ == id​::​other && b.mib_ == id​::​other is true, then comp-name(a.name_, b.name_).
Otherwise, a.mib_ == b.mib_.
🔗
friend constexpr bool operator==(const text_encoding& encoding, id i) noexcept;
2
#
Returns: encoding.mib_ == i.
3
#
Remarks: This operator induces an equivalence relation on its arguments if and only if i != id​::​other is true.

30.6.2.5 Class text_encoding​::​aliases_view [text.encoding.aliases]

🔗
struct text_encoding::aliases_view : ranges::view_interface<text_encoding::aliases_view> { constexpr implementation-defined begin() const; constexpr implementation-defined end() const; };
1
#
text_encoding​::​aliases_view models copyable, ranges​::​view, ranges​::​random_access_range, and ranges​::​borrowed_range.
2
#
Both ranges​::​range_value_t<text_encoding​::​aliases_view> and ranges​::​range_reference_t<text_encoding​::​aliases_view> denote const char*.
3
#
ranges​::​iterator_t<text_encoding​::​aliases_view> is a constexpr iterator ([iterator.requirements.general]).

30.6.2.6 Enumeration text_encoding​::​id [text.encoding.id]

🔗
namespace std { enum class text_encoding::id : int_least32_t { other = 1, unknown = 2, ASCII = 3, ISOLatin1 = 4, ISOLatin2 = 5, ISOLatin3 = 6, ISOLatin4 = 7, ISOLatinCyrillic = 8, ISOLatinArabic = 9, ISOLatinGreek = 10, ISOLatinHebrew = 11, ISOLatin5 = 12, ISOLatin6 = 13, ISOTextComm = 14, HalfWidthKatakana = 15, JISEncoding = 16, ShiftJIS = 17, EUCPkdFmtJapanese = 18, EUCFixWidJapanese = 19, ISO4UnitedKingdom = 20, ISO11SwedishForNames = 21, ISO15Italian = 22, ISO17Spanish = 23, ISO21German = 24, ISO60DanishNorwegian = 25, ISO69French = 26, ISO10646UTF1 = 27, ISO646basic1983 = 28, INVARIANT = 29, ISO2IntlRefVersion = 30, NATSSEFI = 31, NATSSEFIADD = 32, ISO10Swedish = 35, KSC56011987 = 36, ISO2022KR = 37, EUCKR = 38, ISO2022JP = 39, ISO2022JP2 = 40, ISO13JISC6220jp = 41, ISO14JISC6220ro = 42, ISO16Portuguese = 43, ISO18Greek7Old = 44, ISO19LatinGreek = 45, ISO25French = 46, ISO27LatinGreek1 = 47, ISO5427Cyrillic = 48, ISO42JISC62261978 = 49, ISO47BSViewdata = 50, ISO49INIS = 51, ISO50INIS8 = 52, ISO51INISCyrillic = 53, ISO54271981 = 54, ISO5428Greek = 55, ISO57GB1988 = 56, ISO58GB231280 = 57, ISO61Norwegian2 = 58, ISO70VideotexSupp1 = 59, ISO84Portuguese2 = 60, ISO85Spanish2 = 61, ISO86Hungarian = 62, ISO87JISX0208 = 63, ISO88Greek7 = 64, ISO89ASMO449 = 65, ISO90 = 66, ISO91JISC62291984a = 67, ISO92JISC62991984b = 68, ISO93JIS62291984badd = 69, ISO94JIS62291984hand = 70, ISO95JIS62291984handadd = 71, ISO96JISC62291984kana = 72, ISO2033 = 73, ISO99NAPLPS = 74, ISO102T617bit = 75, ISO103T618bit = 76, ISO111ECMACyrillic = 77, ISO121Canadian1 = 78, ISO122Canadian2 = 79, ISO123CSAZ24341985gr = 80, ISO88596E = 81, ISO88596I = 82, ISO128T101G2 = 83, ISO88598E = 84, ISO88598I = 85, ISO139CSN369103 = 86, ISO141JUSIB1002 = 87, ISO143IECP271 = 88, ISO146Serbian = 89, ISO147Macedonian = 90, ISO150 = 91, ISO151Cuba = 92, ISO6937Add = 93, ISO153GOST1976874 = 94, ISO8859Supp = 95, ISO10367Box = 96, ISO158Lap = 97, ISO159JISX02121990 = 98, ISO646Danish = 99, USDK = 100, DKUS = 101, KSC5636 = 102, Unicode11UTF7 = 103, ISO2022CN = 104, ISO2022CNEXT = 105, UTF8 = 106, ISO885913 = 109, ISO885914 = 110, ISO885915 = 111, ISO885916 = 112, GBK = 113, GB18030 = 114, OSDEBCDICDF0415 = 115, OSDEBCDICDF03IRV = 116, OSDEBCDICDF041 = 117, ISO115481 = 118, KZ1048 = 119, UCS2 = 1000, UCS4 = 1001, UnicodeASCII = 1002, UnicodeLatin1 = 1003, UnicodeJapanese = 1004, UnicodeIBM1261 = 1005, UnicodeIBM1268 = 1006, UnicodeIBM1276 = 1007, UnicodeIBM1264 = 1008, UnicodeIBM1265 = 1009, Unicode11 = 1010, SCSU = 1011, UTF7 = 1012, UTF16BE = 1013, UTF16LE = 1014, UTF16 = 1015, CESU8 = 1016, UTF32 = 1017, UTF32BE = 1018, UTF32LE = 1019, BOCU1 = 1020, UTF7IMAP = 1021, Windows30Latin1 = 2000, Windows31Latin1 = 2001, Windows31Latin2 = 2002, Windows31Latin5 = 2003, HPRoman8 = 2004, AdobeStandardEncoding = 2005, VenturaUS = 2006, VenturaInternational = 2007, DECMCS = 2008, PC850Multilingual = 2009, PC8DanishNorwegian = 2012, PC862LatinHebrew = 2013, PC8Turkish = 2014, IBMSymbols = 2015, IBMThai = 2016, HPLegal = 2017, HPPiFont = 2018, HPMath8 = 2019, HPPSMath = 2020, HPDesktop = 2021, VenturaMath = 2022, MicrosoftPublishing = 2023, Windows31J = 2024, GB2312 = 2025, Big5 = 2026, Macintosh = 2027, IBM037 = 2028, IBM038 = 2029, IBM273 = 2030, IBM274 = 2031, IBM275 = 2032, IBM277 = 2033, IBM278 = 2034, IBM280 = 2035, IBM281 = 2036, IBM284 = 2037, IBM285 = 2038, IBM290 = 2039, IBM297 = 2040, IBM420 = 2041, IBM423 = 2042, IBM424 = 2043, PC8CodePage437 = 2011, IBM500 = 2044, IBM851 = 2045, PCp852 = 2010, IBM855 = 2046, IBM857 = 2047, IBM860 = 2048, IBM861 = 2049, IBM863 = 2050, IBM864 = 2051, IBM865 = 2052, IBM868 = 2053, IBM869 = 2054, IBM870 = 2055, IBM871 = 2056, IBM880 = 2057, IBM891 = 2058, IBM903 = 2059, IBM904 = 2060, IBM905 = 2061, IBM918 = 2062, IBM1026 = 2063, IBMEBCDICATDE = 2064, EBCDICATDEA = 2065, EBCDICCAFR = 2066, EBCDICDKNO = 2067, EBCDICDKNOA = 2068, EBCDICFISE = 2069, EBCDICFISEA = 2070, EBCDICFR = 2071, EBCDICIT = 2072, EBCDICPT = 2073, EBCDICES = 2074, EBCDICESA = 2075, EBCDICESS = 2076, EBCDICUK = 2077, EBCDICUS = 2078, Unknown8BiT = 2079, Mnemonic = 2080, Mnem = 2081, VISCII = 2082, VIQR = 2083, KOI8R = 2084, HZGB2312 = 2085, IBM866 = 2086, PC775Baltic = 2087, KOI8U = 2088, IBM00858 = 2089, IBM00924 = 2090, IBM01140 = 2091, IBM01141 = 2092, IBM01142 = 2093, IBM01143 = 2094, IBM01144 = 2095, IBM01145 = 2096, IBM01146 = 2097, IBM01147 = 2098, IBM01148 = 2099, IBM01149 = 2100, Big5HKSCS = 2101, IBM1047 = 2102, PTCP154 = 2103, Amiga1251 = 2104, KOI7switched = 2105, BRF = 2106, TSCII = 2107, CP51932 = 2108, windows874 = 2109, windows1250 = 2250, windows1251 = 2251, windows1252 = 2252, windows1253 = 2253, windows1254 = 2254, windows1255 = 2255, windows1256 = 2256, windows1257 = 2257, windows1258 = 2258, TIS620 = 2259, CP50220 = 2260 }; }
[Note 1: 
The text_encoding​::​id enumeration contains an enumerator for each known registered character encoding.
For each encoding, the corresponding enumerator is derived from the alias beginning with “cs”, as follows
  • csUnicode is mapped to text_encoding​::​id​::​UCS2,
  • csIBBM904 is mapped to text_encoding​::​id​::​IBM904, and
  • the “cs” prefix is removed from other names.
— end note]

30.6.2.7 Hash support [text.encoding.hash]

🔗
template<> struct hash<text_encoding>;
1
#
The specialization is enabled ([unord.hash]).