std::collate (3) - Linux Manuals

std::collate: std::collate


std::collate - std::collate


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.
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)

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

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


// Run this code

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

  int main()
      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';


  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 facet
operator() (public member function of std::locale)
               creates a collate facet for the named locale
collate_byname (class template)