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Showing content from https://cplusplus.com/reference/locale/ below:

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Localization library

In C++, locales are represented by an object of the locale class. Each of these locale objects contains all the information needed to use a set of culture-dependent features. But locale objects do not contain the features directly themselves as member functions: instead, a locale object contains information about which facet objects it selects, and is each one of these facet objects that implements specific features as member functions. This allows for features that are common to several locales to be shared by using the same facet objects, and makes them extensible, allowing custom facets to be added to locale objects.

Facets are divided into six standard categories:

Thus, the core of the localization functionality in C++ is implemented in the different facets. Facets are objects. These objects are managed automatically by the locale engine, therefore facet objects are generally neither constructed nor copied locally in a program (in fact a program is prevented to do so by their protected destructors). The most general way of accessing a particular feature of a facet associated with a locale is with the function use_facet:

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// using facet member directly:
myvar = use_facet < numpunct<char> > (mylocale).decimal_point();

// alias facet:
const numpunct<char>& myfacet = use_facet < numpunct<char> > (mylocale);
myvar = myfacet.decimal_point();

• is derived from class locale::facet (or from any class derived from it, like another facet).
• define a static member called id of type locale::id with a specific value.

All facet constructors include as second parameter (called refs in this reference) that defines whether the class deallocation is delegated to the locale engine, and hence it is automatically deleted when the last locale object where it is present is destroyed, or whether the program is in charge of its deletion at some point.

Some facet have an equivalent but ending with "_byname". These facet types are used by the localization engine to construct the appropriate facet objects when a named locale object is constructed.

All the standard facets are designed with public members that call virtual protected members with the same name, but preceded with "do_". The implementation of the operation itself lies in the virtual protected member function (so that derived class can easily overwrite it), while the non-virtual public function may implement platform-specific functionality not related to the operation itself, but necessary to allow the feature to work properly on the system.

All library implementations provide at least all the facets by default for the char and wchar_t types as template parameters for the facet's character type.

All library implementations provide at least all the facets by default for the

and

types as template parameters for the

. Additionally, the

facet is also required to support

and

.

use_facet

Access facet of locale (function template)

has_facet

Check if locale has facet (function template)

isspace

Check if character is a white-space (function)

isprint

Check if character is printable (function)

iscntrl

Check if character is a control character (function)

isupper

Check if character is uppercase letter (function)

islower

Check if character is lowercase letter (function)

isalpha

Check if character is alphabetic (function)

isdigit

Check if character is decimal digit (function)

ispunct

Check if character is a punctuation character (function)

isxdigit

Check if character is hexadecimal digit (function)

isalnum

Check if character is alphanumeric (function)

isgraph

Check if character has graphical representation (function)

isblank

Check if character is blank (function)

locale

Locale class (class)

ctype

Character type facet (class template)

ctype_byname

Character type facet (class template)

codecvt

Convert codeset facet (class template)

codecvt_byname

Convert codeset facet (class template)

num_get

Facet to parse numeric values (class template)

num_put

Facet to format numeric values (class template)

numpunct

Numeric punctuation facet (class template)

numpunct_byname

Numeric puntuation facet (class template)

collate

Facet to compare and hash strings (class template)

collate_byname

Facet to compare and hash strings (class template)

time_get

Facet to parse dates and times (class template)

time_get_byname

Facet to parse dates and times (class template)

time_put

Facet to format dates and times (class template)

time_put_byname

Facet to format dates and times (class template)

money_get

Facet to parse monetary expressions (class template)

money_put

Facet to format monetary expressions (class template)

moneypunct

Monetary punctuation facet (class template)

moneypunct_byname

Monetary punctuation facet (class template)

messages

Facet to access message catalogs (class template)

messages_byname

Facet to access message catalogs (class template)

ctype_base

Base class for ctype (class)

codecvt_base

Base class for codecvt (class)

time_base

Base class for time_get (class)

money_base

Base class for moneypunct (class)

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