< cpp‎ | locale
Defined in header <locale>
template< class Facet >
bool has_facet( const locale& loc ) throw();
(until C++11)
template< class Facet >
bool has_facet( const locale& loc ) noexcept;
(since C++11)

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.


[edit] Parameters

loc - the locale object to query

[edit] Return value

Returns true if the facet Facet was installed in the locale loc, false otherwise.

[edit] Notes

std::has_facet must return true for all locales loc if Facet is one of the standard facets given here.

[edit] Example

#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';


Can loc classify chars? true
Can loc classify char32_t? false
Does loc implement myfacet? true

[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 436 C++98 it was unclear whether Facet can be cv-qualified it can be const-qualified, but not volatile-qualified

[edit] See also

set of polymorphic facets that encapsulate cultural differences
(class) [edit]
obtains a facet from a locale
(function template) [edit]