std::collate(3)

okay so this is the std::collate(3) page from the C++ Standard Libary manual, and bestie we are about to make locale collation make sense 💅✨

💖 NAME 💖

std::collate - std::collate — yes, that’s literally the NAME line, it’s giving minimal and mysterious, periodt.

✨ Synopsis ✨

Defined in header <locale>
template< class CharT >
class collate;

okay so std::collate is the class that wraps up locale-specific collation (that’s comparison, bestie) 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. iconic behavior, ngl.

there’s also a little diagram situation: std-collate-inheritance.svg — the Inheritance diagram 🦋

🌀 Specializations 🌀

The standard library is guaranteed to provide the following specializations — and any locale object is required to implement them, no cap:

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 🧸

• 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).

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source/version/date check, bestie: http://cppreference.com, 2024.06.10, page std::collate(3) — mwah, love u, bye 💋🫶