std::has_facet (3) Linux Manual Page

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.

Parameters

loc – the locale object to query

Return value

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

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

See also

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