std::wctomb(3)

💅 std::wctomb(3) — C++ Standard Libary, bestie

🌸 NAME

std::wctomb — std::wctomb. That's the name, periodt. We're keeping the double-name energy exactly as the original served it. 💖

✨ Synopsis

Okay so first things first: this icon lives in the header <cstdlib>, and the signature is literally:

int wctomb( char* s, wchar_t wc );

The way this works: it converts a wide character wc to multibyte encoding and stores it — including any shift sequences — in the char array whose first element is pointed to by s. No more than MB_CUR_MAX characters are stored. The conversion is affected by the current locale's LC_CTYPE category.

If wc is the null character, the null byte is written to s, preceded by any shift sequences necessary to restore the initial shift state.

If s is a null pointer, it resets the global conversion state and determines whether shift sequences are used. 🦋

🦋 Parameters

• s — pointer to the character array for output.
• wc — wide character to convert.

💖 Return value

If s is not a null pointer, it returns the number of bytes that are contained in the multibyte representation of wc, or -1 if wc is not a valid character.

If s is a null pointer, it resets its internal conversion state to represent the initial shift state and returns 0 if the current multibyte encoding is not state-dependent (does not use shift sequences), or a non-zero value if the current multibyte encoding is state-dependent (uses shift sequences). Slay. ✨

🧚 Notes

Each call to wctomb updates the internal global conversion state (a static object of type std::mbstate_t, only known to this function). If the multibyte encoding uses shift states, this function is not reentrant.

In any case, multiple threads should not call wctomb without synchronization: std::wcrtomb may be used instead. 💀 This is not the "just vibe and call it from every thread" situation, bestie.

🍓 Example

The original has a // Run this code label right here, so consider this your cue:

#include <clocale>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <string>

void print_wide(const std::wstring& wstr)
{
    bool shifts = std::wctomb(nullptr, 0); // reset the conversion state
    std::cout << "shift sequences are " << (shifts ? "" : "not" )
              << " used\n" << std::uppercase << std::setfill('0');
    for (const wchar_t wc : wstr)
    {
        std::string mb(MB_CUR_MAX, '\0');
        const int ret = std::wctomb(&mb[0], wc);
        const char* s = ret > 1 ? "s" : "";
        std::cout << "multibyte char '" << mb << "' is " << ret
                  << " byte" << s << ": [" << std::hex;
        for (int i{0}; i != ret; ++i)
        {
            const int c = 0xFF & mb[i];
            std::cout << (i ? " " : "") << std::setw(2) << c;
        }
        std::cout << "]\n" << std::dec;
    }
}

int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    // UTF-8 narrow multibyte encoding
    std::wstring wstr = L"z\u00df\u6c34\U0001d10b"; // or L"zß水𝄋"
    print_wide(wstr);
}

📤 Output

shift sequences are not used
multibyte char 'z' is 1 byte: [7A]
multibyte char 'ß' is 2 bytes: [C3 9F]
multibyte char '水' is 3 bytes: [E6 B0 B4]
multibyte char '𝄋' is 4 bytes: [F0 9D 84 8B]

🔥 See also

• mbtowc — converts the next multibyte character to wide character (function).
• wcrtomb — converts a wide character to its multibyte representation, given state (function).
• do_out — converts a string from InternT to ExternT, such as when writing to file [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>).
• C documentation for wctomb — yep, the C version, iykyk.

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Signing off from http://cppreference.com 💖 version 2024.06.10, on the std::wctomb(3) page. Mwah! 🫶✨