std::collate - cppreference.com

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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

Specializations

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


`std::collate<char>`	implements lexicographical ordering of byte strings
`std::collate<wchar_t>`	implements lexicographical ordering of wide strings

Nested types

Type	Definition
`char_type`	`CharT`
`string_type`	`std::basic_string<CharT>`

Data members

Member	Description
std::locale::id `id` [static]	the identifier of the facet

Member functions

Protected member functions

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

Example

#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

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