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std::has_facet(3) C++ Standard Libary std::has_facet(3) NAME std::has_facet - std::has_facet Synopsis Defined in header <locale> template< class Facet > (until C++11) bool has_facet( const locale& loc ) throw(); template< class Facet > (since C++11) bool has_facet( const locale& loc ) noexcept; Checks if the locale loc implements the facet Facet. The program is ill-formed if Facet is not a facet or it is a volatile-qualified facet. Parameters loc - the locale object to query Return value Returns true if the facet Facet was installed in the locale loc, false otherwise. Notes std::has_facet must return true for all locales loc if Facet is one of the standard facets given here. Example // Run this code #include <iostream> #include <locale> // minimal custom facet struct myfacet : public std::locale::facet { static std::locale::id id; }; std::locale::id myfacet::id; int main() { // loc is a "C" locale with myfacet added std::locale loc(std::locale::classic(), new myfacet); std::cout << std::boolalpha << "Can loc classify chars? " << std::has_facet<std::ctype<char>>(loc) << '\n' << "Can loc classify char32_t? " << std::has_facet<std::ctype<char32_t>>(loc) << '\n' << "Does loc implement myfacet? " << std::has_facet<myfacet>(loc) << '\n'; } Output: Can loc classify chars? true Can loc classify char32_t? false Does loc implement myfacet? true Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 436 C++98 it was unclear whether Facet it can be const- qualified, but not can be cv-qualified volatile-qualified See also locale set of polymorphic facets that encapsulate cultural dif- ferences (class) use_facet obtains a facet from a locale (function template) http://cppreference.com 2024.06.10 std::has_facet(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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