std::locale::operator()(3)

🎀 std::locale::operator()(3) 🎀

okay bestie, this one is from the C++ Standard Libary manual — header spelling, iykyk 💀 — and it’s literally about using a locale as a comparator. no cap, it’s iconic.

🌸 NAME 🌸

std::locale::operator() — and the NAME line is literally std::locale::operator() - std::locale::operator(), so yeah, it’s giving “I contain multitudes” 💅.

✨ 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;

okay so what does it do? it compares two string arguments s1 and s2 according to the lexicographic comparison rules defined by this locale’s std::collate<CharT> facet. and the glow-up? 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). periodt 💖

🫶 Parameters 🫶

• s1 — the first string to compare, aka the one on the left.
• s2 — the second string to compare, aka the one on the right.

💖 Return value 💖

true if s1 is lexicographically less than s2, false otherwise. that’s it, that’s the tea 🍵.

🧚 Possible implementation 🧚

here’s the possible implementation, copied exactly — line breaks and all, bestie, do not come for me:

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). obsessed with a facet that does compare + hash, honestly iconic 🌈.

okay that’s the whole page, bestie 💖 source: http://cppreference.com · version/date: 2024.06.10 · page: std::locale::operator()(3) — mwah, slay 🫶