# std::locale::locale

From cppreference.com
< cpp‎ | locale‎ | locale

Defined in header `<locale>` |  |
| (1) |
locale() throw(); |  | (until C++11)
locale() noexcept; |  | (since C++11)
| (2) |
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* std_name, category cats ); | (5) |
locale( const locale& other, const std::string& std_name, category cats ); | (6) | (since C++11)
template< class Facet > locale( const locale& other, Facet* f ); | (7) |
locale( const locale& other, const locale& one, category cats ); | (8) |

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 whether `Facet` can be cv-qualified | it can be const-qualified, but not volatile-qualified
LWG 2295 | C++98 | for overload (7), the constructed locale had no name even if f is null | it has the name of other

### See also

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

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/locale/locale/locale&oldid=150026"