std::collate

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Localization library

Locales and facets
Locales
has_facet use_facet	locale
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
ctype facets
ctype ctype<char> ctype_byname	codecvt codecvt_byname
numeric facets
num_get num_put	numpunct numpunct_byname
collate facets
collate	collate_byname
time facets
time_get time_put	time_get_byname time_put_byname
monetary facets
money_get money_put	moneypunct moneypunct_byname
messages facets
messages	messages_byname

Character classification and conversion
Character classification
isspace isblank (C++11) iscntrl	isupper islower isalpha	ispunct isdigit isxdigit	isalnum isprint isgraph

Character conversions

toupper

tolower

String and stream conversions

wstring_convert (C++11/17/26*)

wbuffer_convert (C++11/17/26*)

Text encoding identifications

text_encoding (C++26)

Unicode conversion facets

codecvt_utf8 (C++11/17/26*)

codecvt_utf16 (C++11/17/26*)

codecvt_utf8_utf16 (C++11/17/26*)

codecvt_mode (C++11/17/26*)

C library locales
LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME	setlocale localeconv lconv

 

std::collate

Member functions

collate::collate

collate::~collate

collate::comparecollate::do_compare

collate::transformcollate::do_transform

collate::hashcollate::do_hash

 

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

Specializations

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

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

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

Example

Run this code

#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

See also

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