namespace std {
class locale {
public:
class facet;
class id;
using category = int;
static const category none = 0,
collate = 0x010, ctype = 0x020,
monetary = 0x040, numeric = 0x080,
time = 0x100, messages = 0x200,
all = collate | ctype | monetary | numeric | time | messages;
locale() noexcept;
locale(const locale& other) noexcept;
explicit locale(const char* std_name);
explicit locale(const string& std_name);
locale(const locale& other, const char* std_name, category);
locale(const locale& other, const string& std_name, category);
template <class Facet> locale(const locale& other, Facet* f);
locale(const locale& other, const locale& one, category);
~locale(); const locale& operator=(const locale& other) noexcept;
template <class Facet> locale combine(const locale& other) const;
basic_string<char> name() const;
bool operator==(const locale& other) const;
bool operator!=(const locale& other) const;
template <class charT, class traits, class Allocator>
bool operator()(const basic_string<charT, traits, Allocator>& s1,
const basic_string<charT, traits, Allocator>& s2) const;
static locale global(const locale&);
static const locale& classic();
};
}Class
locale
implements a type-safe polymorphic set of facets, indexed by facet
type.In other words, a facet has a dual role: in one
sense, it's just a class interface; at the same time, it's an index
into a locale's set of facets
.Access to the facets of a
locale
is via two function templates,
use_facet<>
and
has_facet<>.[
Example: An iostream
operator<<
might be implemented as:
template <class charT, class traits>
basic_ostream<charT, traits>&
operator<< (basic_ostream<charT, traits>& s, Date d) {
typename basic_ostream<charT, traits>::sentry cerberos(s);
if (cerberos) {
ios_base::iostate err = ios_base::iostate::goodbit;
tm tmbuf; d.extract(tmbuf);
use_facet<time_put<charT, ostreambuf_iterator<charT, traits>> >(
s.getloc()).put(s, s, s.fill(), err, &tmbuf, 'x');
s.setstate(err); }
return s;
} —
end example ]
In the call to
use_facet<Facet>(loc),
the type argument chooses a facet, making available all members
of the named type
.If
Facet
is not present in a
locale,
it throws the standard exception
bad_cast.A C++ program can check if a locale implements a particular
facet with the
function template
has_facet<Facet>().User-defined facets may be installed in a locale, and used identically as
may standard facets (
[facets.examples])
.[
Note: All locale semantics are accessed via
use_facet<>
and
has_facet<>,
except that:
A member operator template
operator()(const basic_string<C, T, A>&, const basic_string<C, T, A>&)
is provided so that a locale may be used as a predicate argument to
the standard collections, to collate strings
.Convenient global interfaces are provided for traditional
ctype
functions such as
isdigit()
and
isspace(),
so that given a locale
object
loc a C++ program can call
isspace(c, loc).
—
end note ]
Once a facet reference is obtained from a locale object by calling
use_facet<>,
that reference remains usable, and the results from member functions
of it may be cached and re-used, as long as some locale object refers
to that facet
.In successive calls to a locale facet member function on a facet object
installed in the same locale, the returned result shall be identical
.A
locale
constructed from a name string (such as
"POSIX"), or from parts of
two named locales, has a name; all others do not
.Named locales may be compared for equality; an unnamed locale is equal
only to (copies of) itself
.For an unnamed locale,
locale::name()
returns the string
"*".Whether there is one global locale object for the entire program or one global locale
object per thread is
implementation-defined
.Implementations should provide one global locale object per
thread
.If there is a single global locale object for the entire program,
implementations are not required to avoid data races on it (
[res.on.data.races])
.using category = int;
Valid
category
values include the
locale
member bitmask elements
collate,
ctype,
monetary,
numeric,
time,
and
messages,
each of which represents a single locale category
. In addition,
locale
member bitmask constant
none
is defined as zero and represents no category
.And
locale
member bitmask constant
all
is defined such that the expression
(collate | ctype | monetary | numeric | time | messages | all) == all
is
true,
and represents the union of all categories
.Further, the expression
(X | Y),
where
X
and
Y
each represent a single category, represents the union of the two categories
.locale
member functions expecting a
category
argument require one of the
category
values defined above, or the union of two or more such values
. Such a
category
value identifies a set of locale categories
.Each locale category,
in turn, identifies a set of locale facets, including at least those
shown in Table
64.Table
64 — Locale category facets
Category | Includes facets |
collate | collate<char>, collate<wchar_t> |
ctype | ctype<char>, ctype<wchar_t> |
| codecvt<char, char, mbstate_t> |
| codecvt<char16_t, char, mbstate_t> |
| codecvt<char32_t, char, mbstate_t> |
| codecvt<wchar_t, char, mbstate_t> |
monetary | moneypunct<char>, moneypunct<wchar_t> |
| moneypunct<char, true>, moneypunct<wchar_t, true> |
| money_get<char>, money_get<wchar_t> |
| money_put<char>, money_put<wchar_t> |
numeric | numpunct<char>, numpunct<wchar_t> |
| num_get<char>, num_get<wchar_t> |
| num_put<char>, num_put<wchar_t> |
time | time_get<char>, time_get<wchar_t> |
| time_put<char>, time_put<wchar_t> |
messages | messages<char>, messages<wchar_t> |
For any locale
loc
either constructed, or returned by
locale::classic(),
and any facet
Facet
shown in Table
64,
has_facet<Facet>(loc)
is
true.Each
locale
member function which takes a
locale::category
argument operates on the corresponding set of facets
.An implementation is required to provide those specializations for
facet templates identified as members of a category, and for those
shown in Table
65.Table
65 — Required specializations
Category | Includes facets |
collate | collate_byname<char>, collate_byname<wchar_t> |
ctype | ctype_byname<char>, ctype_byname<wchar_t> |
| codecvt_byname<char, char, mbstate_t> |
| codecvt_byname<char16_t, char, mbstate_t> |
| codecvt_byname<char32_t, char, mbstate_t> |
| codecvt_byname<wchar_t, char, mbstate_t> |
monetary | moneypunct_byname<char, International> |
| moneypunct_byname<wchar_t, International> |
| money_get<C, InputIterator> |
| money_put<C, OutputIterator> |
numeric | numpunct_byname<char>, numpunct_byname<wchar_t> |
| num_get<C, InputIterator>, num_put<C, OutputIterator> |
time | time_get<char, InputIterator> |
| time_get_byname<char, InputIterator> |
| time_get<wchar_t, InputIterator> |
| time_get_byname<wchar_t, InputIterator> |
| time_put<char, OutputIterator> |
| time_put_byname<char, OutputIterator> |
| time_put<wchar_t, OutputIterator> |
| time_put_byname<wchar_t, OutputIterator> |
messages | messages_byname<char>, messages_byname<wchar_t> |
The provided implementation of members of facets
num_get<charT>
and
num_put<charT>
calls
use_facet<F>(l)
only for facet
F
of types
numpunct<charT>
and
ctype<charT>,
and for locale
l
the value obtained
by calling member
getloc()
on the
ios_base&
argument to these functions
.In declarations of facets, a template parameter with name
InputIterator
or
OutputIterator
indicates the set of
all possible specializations on parameters that satisfy the
requirements of an Input Iterator or an Output Iterator, respectively (
[iterator.requirements])
.A template parameter with name
C
represents the set
of types containing
char,
wchar_t, and any other
implementation-defined
character types that satisfy
the requirements for a character on which any of the iostream
components can be instantiated
.A template parameter with name
International
represents the set of all possible specializations on a bool parameter
.
namespace std {
class locale::facet {
protected:
explicit facet(size_t refs = 0);
virtual ~facet();
facet(const facet&) = delete;
void operator=(const facet&) = delete;
};
}Class
facet is the base class for locale feature sets
.A class is a
facet
if it is publicly derived from another facet, or
if it is a class derived from
locale::facet and
contains a publicly accessible declaration as follows:
static ::std::locale::id id;
Template parameters in this Clause which are required to be facets are those named
Facet
in declarations
.A program that passes a type that is
not
a facet, or a type that refers to a volatile-qualified facet, as an
(explicit or deduced) template parameter to a locale
function expecting a facet, is ill-formed
.A const-qualified facet is a
valid template argument to any locale function that expects a Facet template
parameter
.The
refs
argument to the constructor is used for lifetime management
.For
refs == 0,
the implementation performs
delete static_cast<locale::facet*>(f)
(where
f
is a pointer to the facet) when the last
locale
object containing the facet is destroyed;
for
refs == 1,
the implementation never destroys the facet
.Constructors of all
facets defined in this Clause take such an argument and pass it
along to their
facet
base class constructor
.All one-argument constructors defined
in this Clause are
explicit,
preventing their participation in automatic conversions
.For some standard facets a standard
“
…_byname”
class, derived from it, implements the virtual function semantics
equivalent to that facet of the locale constructed by
locale(const char*)
with the same name
.Each such facet provides a constructor that takes a
const char*
argument, which names the locale, and a
refs
argument, which is passed to the base class constructor
.Each such facet also provides a constructor that takes a
string argument
str and a
refs
argument, which has the same effect as calling the first constructor with the
two arguments
str.c_str() and
refs.If there is no
“
…_byname”
version of a facet, the base class implements named locale
semantics itself by reference to other facets
.
namespace std {
class locale::id {
public:
id();
void operator=(const id&) = delete;
id(const id&) = delete;
};
}The class
locale::id provides identification of a locale facet
interface, used as an index for lookup
and to encapsulate initialization
.[
Note: Because facets are used by iostreams, potentially while static constructors are
running, their initialization cannot depend on programmed static
initialization
.One initialization strategy is for
locale
to initialize each facet's
id
member the first time an instance of the facet is installed into a locale
. —
end note ]
locale() noexcept;
Default constructor: a snapshot of the current global locale
.Effects:
Constructs a copy of the argument last passed to
locale::global(locale&),
if it has been called; else, the resulting facets have virtual
function semantics identical to those of
locale::classic(). [
Note: This constructor is commonly used as the default value for arguments
of functions that take a
const locale&
argument
. —
end note ]
locale(const locale& other) noexcept;
Effects:
Constructs a locale which is a copy of
other. explicit locale(const char* std_name);
Effects:
Constructs a locale using standard C locale names, e.g.,
"POSIX". The resulting locale implements semantics defined to be associated
with that name
.Throws:
runtime_error
if the argument is not valid, or is null
. Remarks:
The set of valid string argument values is
"C",
"",
and any
implementation-defined values
. explicit locale(const string& std_name);
Effects: The same as
locale(std_name.c_str()). locale(const locale& other, const char* std_name, category);
Effects:
Constructs a locale as a copy of
other
except for the facets identified by the
category
argument, which instead implement the same semantics as
locale(std_name). Throws:
runtime_error
if the argument is not valid, or is null
. Remarks:
The locale has a name if and only if
other
has a name
. locale(const locale& other, const string& std_name, category cat);
Effects: The same as
locale(other, std_name.c_str(), cat). template <class Facet> locale(const locale& other, Facet* f);
Effects:
Constructs a locale incorporating all facets from the first
argument except that of type
Facet,
and installs the second argument as the remaining facet
. If
f
is null, the resulting object is a copy of
other.Remarks:
The resulting locale has no name
. locale(const locale& other, const locale& one, category cats);
Effects:
Constructs a locale incorporating all facets from the first argument
except those that implement
cats,
which are instead incorporated from the second argument
. Remarks:
The resulting locale has a name if and only if the first two arguments
have names
. const locale& operator=(const locale& other) noexcept;
Effects:
Creates a copy of
other, replacing the current value
. ~locale();
A non-virtual destructor that throws no exceptions
.template <class Facet> locale combine(const locale& other) const;
Effects:
Constructs a locale incorporating
all facets from
*this
except for that one facet of
other
that is identified by
Facet. Returns:
The newly created locale
. Throws:
runtime_error
if
has_facet<Facet>(other)
is
false. Remarks:
The resulting locale has no name
. basic_string<char> name() const;
Returns:
The name of
*this,
if it has one; otherwise, the string
"*". bool operator==(const locale& other) const;
Returns:
true
if both arguments are the same locale, or one is a copy of the
other, or each has a name and the names are identical;
false
otherwise
. bool operator!=(const locale& other) const;
Returns: !(*this == other). template <class charT, class traits, class Allocator>
bool operator()(const basic_string<charT, traits, Allocator>& s1,
const basic_string<charT, traits, Allocator>& s2) const;
Effects:
Compares two strings according to the
collate<charT>
facet
. Remarks:
This member operator template (and therefore
locale
itself) satisfies requirements for a comparator predicate template argument
(Clause
[algorithms]) applied to strings
. Returns:
use_facet<collate<charT>>(*this).compare(s1.data(), s1.data() + s1.size(),
s2.data(), s2.data() + s2.size()) < 0 [
Example: A vector of strings
v
can be collated according to collation rules in locale
loc
simply by (
[alg.sort],
[vector]):
std::sort(v.begin(), v.end(), loc);
—
end example ]
static locale global(const locale& loc);
Sets the global locale to its argument
.Effects:
Causes future calls to the constructor
locale()
to return a copy of the argument
. If the argument has a name, does
setlocale(LC_ALL, loc.name().c_str());
otherwise, the effect on the C locale, if any, is
implementation-defined
.No library function other than
locale::global()
shall affect the value returned by
locale().[
Note: See
[c.locales] for data race considerations when
setlocale is invoked
. —
end note ]
Returns:
The previous value of
locale(). static const locale& classic();
Returns:
A locale that implements the classic
"C" locale semantics, equivalent
to the value
locale("C"). Remarks:
This locale, its facets, and their member functions, do not change
with time
.