std:: has_facet

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

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

#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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also