NAME¶

std::locale::operator() - std::locale::operator()

Synopsis¶

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

int main()
{
std::vector<std::wstring> v = {L"жил", L"был", L"пёс"};
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"пёс");
}

See also¶

collate defines lexicographical comparison and hashing of strings
(class template)