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std::use_facet

From cppreference.com
< cpp‎ | locale
Defined in header <locale>
template< class Facet >
const Facet& use_facet( const std::locale& loc );

Obtains a reference to a facet implemented by loc. Facet should be a facet class whose definition contains the public static member id.

Contents

[edit] Parameters

loc - the locale object to query

[edit] Return value

Returns a reference to the facet. The reference returned by this function is valid as long as any std::locale object refers to that facet.

[edit] Exceptions

std::bad_cast if std::has_facet<Facet>(loc) == false.

[edit] Example

Display the 3-letter currency name used by the user's preferred locale.

#include <iostream>
#include <locale>
 
int main()
{
    for (const char* name: {"en_US.UTF-8", "de_DE.UTF-8", "en_GB.UTF-8"})
    {
        std::locale loc = std::locale(name); // user's preferred locale
        std::cout << "Your currency string is "
                  << std::use_facet<std::moneypunct<char, true>>(loc).
                     curr_symbol() << '\n';
    }
}

Output:

Your currency string is USD
Your currency string is EUR
Your currency string is GBP

[edit] 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 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 there was no requirement on Facet requirement added

[edit] See also

set of polymorphic facets that encapsulate cultural differences
(class) [edit]
checks if a locale implements a specific facet
(function template) [edit]