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std::collate

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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.

cpp/locale/locale/facetstd-collate-inheritance.svg
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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.

Contents

[edit] Member types

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

[edit] Member functions

constructs a new collate facet
(public member function)
destructs a collate facet
(protected member function)
invokes do_compare
(public member function) [edit]
invokes do_transform
(public member function) [edit]
invokes do_hash
(public member function) [edit]

[edit] Member objects

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

[edit] Protected member functions

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

[edit] Example

#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

[edit] See also

lexicographically compares two strings using this locale's collate facet
(public member function of std::locale) [edit]
creates a collate facet for the named locale
(class template)