| Localization library | |||||||||||||||||||||||||
| Regular expressions library(C++11) | |||||||||||||||||||||||||
| Formatting library(C++20) | |||||||||||||||||||||||||
| Null-terminated sequence utilities | |||||||||||||||||||||||||
| Byte strings | |||||||||||||||||||||||||
| Multibyte strings | |||||||||||||||||||||||||
| Wide strings | |||||||||||||||||||||||||
| Primitive numeric conversions | |||||||||||||||||||||||||
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| Text encoding identifications | |||||||||||||||||||||||||
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Defined in header <locale> | ||
template<class Facet> const Facet& use_facet(conststd::locale& loc); | ||
Obtains a reference to a facet implemented byloc.
The program is ill-formed if Facet is not afacet whose definition contains the public static memberid or it is a volatile-qualified facet.
Contents |
| loc | - | the locale object to query |
Returns a reference to the facet. The reference returned by this function is valid as long as anystd::locale object refers to that facet.
std::bad_cast ifstd::has_facet<Facet>(loc)==false.
Astd::locale object should not be a temporary if a reference to theFacet object obtained fromuse_facet is used after the end of statement:
// BAD:auto& f= std::use_facet<std::moneypunct<char,true>>(std::locale{"no_NO.UTF-8"});foo(f.curr_symbol());// Error: f internally uses a dangling reference// to a std::locale object that no longer exists.// GOOD:auto loc=std::locale{"is_IS.UTF-8"};// OK: a non-temporary objectauto& f= std::use_facet<std::moneypunct<char,true>>(loc);foo(f.curr_symbol());// OK: f internally uses a reference to existing locale object.
Display the 3-letter currency name used by the user's preferred locale.
#include <iostream>#include <locale> int main(){for(constchar* name:{"en_US.UTF-8","de_DE.UTF-8","en_GB.UTF-8"})std::cout<<"Your currency string is "<< std::use_facet<std::moneypunct<char,true>>(std::locale{name}).curr_symbol()<<'\n';}
Output:
Your currency string is USDYour currency string is EURYour currency string is GBP
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 31 | C++98 | the returned reference remained usable as long as the locale value itself exists | the returned reference remains usable as long as some locale object refers to that facet |
| LWG 38 | C++98 | Facet was not required to have a direct memberid | required |
| LWG 436 | C++98 | it was unclear whetherFacet can be cv-qualified | it can be const-qualified, but not volatile-qualified |
| set of polymorphic facets that encapsulate cultural differences (class)[edit] | |
| checks if a locale implements a specific facet (function template)[edit] |
