std::locale::locale(3)

NAME
std::locale::locale - std::locale::locale

Synopsis
   Defined in header <locale>
   locale() throw(); (until C++11)
   locale() noexcept; (since C++11)
   locale( const locale& other ) throw(); (until C++11)
   locale( const locale& other ) noexcept; (since C++11)
   explicit locale( const char* std_name ); (3)
   explicit locale( const std::string& std_name ); (4) (since C++11)
   locale( const locale& other, const char* (1) (5)
   std_name, category cats ); (2)
   locale( const locale& other, const std::string& (6) (since C++11)
   std_name, category cats );
   template< class Facet > (7)
   locale( const locale& other, Facet* f );
   locale( const locale& other, const locale& one, (8)
   category cats );
   Constructs a new locale object.
   1) Default constructor. Constructs a copy of the global C++ locale, which is the
   locale most recently used as the argument to std::locale::global or a copy of
   std::locale::classic() if no call to std::locale::global has been made.
   2) Copy constructor. Constructs a copy of other.
   3,4) Constructs a copy of the system locale with specified std_name (such as "C", or
   "POSIX", or "en_US.UTF-8", or "English_US.1251"), if such locale is supported by the
   operating system. The locale constructed in this manner has a name.
   4) Equivalent to locale(std_name.c_str()).
   5) Constructs a copy of other except for all the facets identified by the cats
   argument, which are copied from the system locale identified by its std_name. The
   locale constructed in this manner has a name if and only if other has a name.
   6) Equivalent to locale(other, std_name.c_str(), cats).
   7) Constructs a copy of other except for the facet of type Facet (typically deduced
   from the type of the argument) which is installed from f. If f is a null pointer,
   the constructed locale is a full copy of other. The program is ill-formed if Facet
   is not a facet or it is a volatile-qualified facet.
   If f is null, the constructed locale has the same name as other. Otherwise, the
   constructed locale has no name.
   8) Constructs a copy of other except for all the facets identified by the cats
   argument, which are copied from one.
   If cats is equal to locale::none, the constructed locale has a name if and only if
   other has a name. Otherwise, the constructed locale has a name if and only if other
   and one both have names.

Parameters
   other - another locale to copy
   std_name - name of the system locale to use
   f - pointer to a facet to merge with other
   cats - the facet categories used to identify the facets to merge with other
   one - another locale to take facets from

Exceptions
   3,5) std::runtime_error if the operating system has no locale named std_name or if
   std_name is a null pointer.
   4,6) std::runtime_error if the operating system has no locale named std_name.

Notes
   Overload (7) is typically called with its second argument, f, obtained directly from
   a new-expression: the locale is responsible for calling the matching delete from its
   own destructor.

Example
// Run this code
 #include <codecvt>
 #include <iostream>
 #include <locale>
 std::ostream& operator<< (std::ostream& os, std::locale const& loc)
 {
     if (loc.name().length() <= 80)
         return os << loc.name() << '\n';
     for (const auto c : loc.name())
         c != ';' ? os << c : os << "\n ";
     return os << '\n';
 }
 int main()
 {
     // l1 is a copy of the classic "C" locale
     std::locale l1;
     // l2 is a unicode locale
     std::locale l2("en_US.UTF-8");
     // l3 is "C" except for ctype, which is unicode
     std::locale l3(l1, l2, std::locale::ctype);
     // l4 is "C" except for codecvt
     std::locale l4(l1, new std::codecvt_utf8<wchar_t>);
     std::cout
         << "Locale names:\n"
         << "l1: " << l1 << "l2: " << l2
         << "l3: " << l3 << "l4: " << l4;
 }

Possible output:
 Locale names:
 l1: C
 l2: en_US.UTF-8
 l3: LC_CTYPE=en_US.UTF-8
     LC_NUMERIC=C
     LC_TIME=C
     LC_COLLATE=C
     LC_MONETARY=C
     LC_MESSAGES=C
     LC_PAPER=C
     LC_NAME=C
     LC_ADDRESS=C
     LC_TELEPHONE=C
     LC_MEASUREMENT=C
     LC_IDENTIFICATION=C
 l4: *
   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 for overload (7), it was unclear it can be const-qualified,
                       whether Facet can be cv-qualified but not volatile-qualified
   LWG 2295 C++98 for overload (7), the constructed it has the name of other
                       locale had no name even if f is null

See also
   destructor destructs the locale and the facets whose reference count becomes zero
                (public member function)

External links
   1. List of Windows locale names.
   2. List of Linux locale names.