std::locale::facet

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Localizations library

Locales and facets
Locales
has_facet use_facet	locale
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
ctype facets
ctype ctype_byname ctype<char>	codecvt codecvt_byname
numeric facets
num_get num_put	numpunct numpunct_byname
collate facets
collate	collate_byname
time facets
time_get time_get_byname	time_put time_put_byname
monetary facets
money_get money_put	moneypunct moneypunct_byname
messages facets
messages	messages_byname
Character classification and conversion
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11/17*) wbuffer_convert (C++11/17*)
Code conversion facets
codecvt_utf8 (C++11/17/26*) codecvt_utf16 (C++11/17/26*)	codecvt_utf8_utf16 (C++11/17/26*) codecvt_mode (C++11/17/26*)
C locale
LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME	setlocale localeconv lconv
Text encoding identifications
text_encoding (C++26)

 

std::locale

Member types

locale::id

locale::facet

Member functions

locale::locale

locale::~locale

locale::operator=

locale::combine

locale::name

locale::operator==locale::operator!= (until C++20)

locale::operator()

Static member functions

locale::global

locale::classic

 

Defined in header <locale>
class locale::facet;

std::locale::facet is the base class for facets. It provides a common base class so that locales could store pointers to the facets they implement in a single indexed container, and it abstracts support for facet reference counting.

Whenever a facet is added to a locale, the locale increments the reference count in the facet (through an implementation-specific mechanism). Whenever a locale is destructed or modified, it decrements the reference count in each facet it no longer implements. Whenever a facet's reference count becomes zero, the locale performs delete static_cast<std::locale::facet*>(f); where f is the pointer to the facet.

Facet class

A class is a facet if

• it is publicly derived from another facet, or
• it is a class derived from std::locale::facet and contains a publicly accessible declaration as follows:

static ::std::locale::id id;

Member functions

(constructor)	constructs a new facet with specified reference count (protected member function)
operator=	the copy assignment operator is deleted (protected member function)
(destructor) [virtual]	the destructor is protected virtual (virtual protected member function)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2694	C++98	the definition of 'facet' was removed by the resolution of LWG issue 436	added the definition back

See also

id	the facet index type: each facet class must declare or inherit a public static member of this type (class)