std::use_facet - cppreference.com (original) (raw)

| | | | | ----------------------------------------------------------------------------------------------------------------------------------------------------- | | | | template< class Facet > const Facet& use_facet( const std::locale& loc ); | | |

Obtains a reference to a facet implemented by loc.

The program is ill-formed if Facet is not a facet whose definition contains the public static member **id** or it is a volatile-qualified facet.

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[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] Notes

A std::locale object should not be a temporary if a reference to the Facet object obtained from use_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 object auto& f = std::use_facet<std::moneypunct<char, true>>(loc); foo(f.curr_symbol()); // OK: f internally uses a reference to existing locale object.

[edit] Example

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

#include #include   int main() { for (const char* 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 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.

[edit] See also

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