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

Two standalone (locale-independent) specializations are provided by the standard
library:

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

In addition, every locale object constructed in a C++ program implements its own
(locale-specific) versions of these specializations.

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

int main()
{
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