std::locale::operator()

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Localizations library

Locales and facets
locale
use_facet	has_facet
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11) wbuffer_convert (C++11)
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
Facet categories
ctype ctype<char> codecvt collate messages time_get time_put	num_get num_put numpunct money_get money_put moneypunct
Locale-specific facets
ctype_byname codecvt_byname messages_byname collate_byname	time_get_byname time_put_byname numpunct_byname moneypunct_byname
Code conversion facets
codecvt_utf8 (C++11) codecvt_utf16 (C++11)	codecvt_utf8_utf16 (C++11) codecvt_mode (C++11)
C locale
setlocale localeconv lconv	LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME

 

std::locale

Member types

locale::id

locale::facet

Member functions

locale::locale

locale::~locale

locale::operator=

locale::combine

locale::name

locale::operator==locale::operator!=

locale::operator()

Static member functions

locale::global

locale::classic

 

template< class CharT, class Traits, class Alloc > bool operator()( const basic_string<CharT,Traits,Alloc>& s1,                  const basic_string<CharT,Traits,Alloc>& s2) const;

Compares two string arguments s1 and s2 according to the lexicographic comparison rules defined by this locale's std::collate<charT> facet. This operator allows any locale object that has a collate facet to be used as a binary predicate in the standard algorithms (such as std::sort) and ordered containers (such as std::set)

Parameters

s1	-	the first string to compare
s2	-	the second string to compare

Return value

true if s1 is lexicographically less than s2, false otherwise.

Possible implementation

template<class CharT, class Traits, class Alloc > bool operator()(const std::basic_string<CharT,Traits,Alloc>& s1, const std::basic_string<CharT,Traits,Alloc>& s2) const; { return std::use_facet<std::collate<CharT>>(*this).compare( s1.data(), s1.data() + s1.size(), s2.data(), s2.data() + s2.size() ) < 0; }

Example

A vector of strings can be sorted according to a non-default locale by using the locale object as comparator:

Run this code

#include <locale>
#include <algorithm>
#include <vector>
#include <string>
#include <cassert>
 
int main()
{
    std::vector<std::wstring> v = {L"жил", L"был", L"кот"};
    std::sort(v.begin(), v.end(), std::locale("ru_RU.UTF8"));
    assert(v[0] == L"был");
    assert(v[1] == L"жил");
    assert(v[2] == L"кот");
}

See also

collate

defines lexicographical comparison and hashing of strings (class template)