Std::collate (3) Linux Manual Page

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

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

Member objects

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

Protected member functions

do_compare compares two strings using this facet’s collation rules
(virtual protected member function)
[virtual]

do_transform transforms a string so that collation can be replaced by comparison
(virtual protected member function)
[virtual]

do_hash generates an integer hash value using this facet’s collation rules
(virtual protected member function)
[virtual]

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

std::collate (3) Linux Manual Page