std::wcsxfrm(3)

std::wcsxfrm(3) from the C++ Standard Libary — okay bestie, this is the wide-string transformation page, and it's lowkey iconic. Let's get into it 💅✨

🎀 NAME 🎀

std::wcsxfrm — std::wcsxfrm. That's it. Periodt. 💖

🌸 Synopsis 🌸

Defined in header <cwchar>
std::size_t wcsxfrm( wchar_t* dest, const wchar_t* src, std::size_t count );

So here's the vibe: it transforms the null-terminated wide string pointed to by src into the implementation-defined form such that comparing two transformed strings with std::wcscmp gives the same result as comparing the original strings with std::wcscoll, in the current C locale. Collation math, but make it fashion. 💫

The first count characters of the transformed string are written to destination, including the terminating null character, and the length of the full transformed string is returned, excluding the terminating null character. Read that twice, bestie — the count and the return value are not the same thing. 😭

If count is 0, then dest is allowed to be a null pointer. That's your little escape hatch. 🫶

🧚 Notes 🧚

• The correct length of the buffer that can receive the entire transformed string is 1 + std::wcsxfrm(nullptr, src, 0). Write that down, bestie 📝.
• This function is used when making multiple locale-dependent comparisons using the same wide string or set of wide strings, because it is more efficient to use std::wcsxfrm to transform all the strings just once, and subsequently compare the transformed wide strings with std::wcscmp. Efficiency slay. 🔥

💖 Parameters 💖

• dest — pointer to the first element of a wide null-terminated string to write the transformed string to.
• src — pointer to the null-terminated wide character string to transform.
• count — maximum number of characters to output.

🦋 Return value 🦋

The length of the transformed wide string, not including the terminating null-character. It's giving "length, but not that length." 💀

✨ Example ✨

Run this code, bestie:

#include <cwchar>
#include <iostream>

int main()
{
    std::setlocale(LC_ALL, "sv_SE.utf8");

    std::wstring in1 = L"\u00e5r";
    std::wstring out1(1 + std::wcsxfrm(nullptr, in1.c_str(), 0), L' ');
    std::wstring in2 = L"\u00e4ngel";
    std::wstring out2(1 + std::wcsxfrm(nullptr, in2.c_str(), 0), L' ');

    std::wcsxfrm(&out1[0], in1.c_str(), out1.size());
    std::wcsxfrm(&out2[0], in2.c_str(), out2.size());

    std::wcout << "In the Swedish locale: ";
    if (out1 < out2)
        std::wcout << in1 << " before " << in2 << '\n';
    else
        std::wcout << in2 << " before " << in1 << '\n';

    std::wcout << "In lexicographical comparison: ";
    if (in1 < in2)
        std::wcout << in1 << " before " << in2 << '\n';
    else
        std::wcout << in2 << " before " << in1 << '\n';

}

🌈 Output 🌈

In the Swedish locale: år before ängel
In lexicographical comparison: ängel before år

👑 See also 👑

• strxfrm — transform a string so that strcmp would produce the same result as strcoll (function)
• do_transform [virtual] — transforms a string so that collation can be replaced by comparison (virtual protected member function of std::collate<CharT>)
• wcscoll — compares two wide strings in accordance to the current locale (function)
• C documentation for wcsxfrm

Source/version/date: http://cppreference.com · 2024.06.10 · std::wcsxfrm(3) — bye bestie, go transform some wide strings responsibly 💋🫶