NAME¶

std::collate - std::collate

Synopsis¶

Defined in header <locale>
template< class CharT >
class collate;

Class std::collate encapsulates locale-specific collation (comparison) and hashing
of strings. This facet is used by std::basic_regex and can be applied, by means of
std::locale::operator(), directly to all standard algorithms that expect a string
comparison predicate.

std-collate-inheritance.svg

Inheritance diagram

Specializations¶

The standard library is guaranteed to provide the following specializations (they
are required to be implemented by any locale object):

Defined in header <locale>
std::collate<char> implements lexicographical ordering of byte strings
std::collate<wchar_t> implements lexicographical ordering of wide strings

Member types¶

Member type Definition
char_type CharT
string_type std::basic_string<CharT>

Member functions¶

constructor constructs a new collate facet
(public member function)
destructor destructs a collate facet
(protected member function)
compare invokes do_compare
(public member function)
transform invokes do_transform
(public member function)
hash invokes do_hash
(public member function)

Member objects¶

static std::locale::id id id of the locale
(public member object)

Protected member functions¶

do_compare compares two strings using this facet's collation rules
[virtual] (virtual protected member function)
do_transform transforms a string so that collation can be replaced by comparison
[virtual] (virtual protected member function)
do_hash generates an integer hash value using this facet's collation rules
[virtual] (virtual protected member function)

Example¶

// Run this code

#include <algorithm>
#include <iostream>
#include <locale>
#include <string>
#include <vector>

int main()
{
std::locale::global(std::locale("en_US.utf8"));
std::wcout.imbue(std::locale(""));
std::vector<std::wstring> v{
L"ar", L"zebra", L"\u00f6grupp", L"Zebra",
L"\u00e4ngel",L"\u00e5r", L"f\u00f6rnamn"
};

std::wcout << "Default locale collation order: ";
std::sort(v.begin(), v.end());
for (auto s : v)
std::wcout << s << ' ';
std::wcout << '\n';

std::wcout << "English locale collation order: ";
std::sort(v.begin(), v.end(), std::locale("en_US.UTF-8"));
for (auto s : v)
std::wcout << s << ' ';
std::wcout << '\n';

std::wcout << "Swedish locale collation order: ";
std::sort(v.begin(), v.end(), std::locale("sv_SE.UTF-8"));
for (auto s : v)
std::wcout << s << ' ';
std::wcout << '\n';
}

Output:¶

Default locale collation order: Zebra ar förnamn zebra ängel år ögrupp
English locale collation order: ängel ar år förnamn ögrupp zebra Zebra
Swedish locale collation order: ar förnamn zebra Zebra år ängel ögrupp

See also¶

lexicographically compares two strings using this locale's collate
operator() facet
(public member function of std::locale)
collate_byname represents the system-supplied std::collate for the named locale
(class template)