wctomb(3)

✨ wctomb(3) ✨

okay bestie, gather round, because we're talking about wctomb(3) — that's the manual page name AND the function name, yes it's giving title drop energy 💅. She lives in the Library Functions Manual, and she's part of the Standard C library (libc, link with -lc). 🎀

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🌸 NAME 🌸

wctomb — convert a wide character to a multibyte sequence 💖

📚 LIBRARY 📚

Standard C library (libc, -lc) 🫶

🦋 SYNOPSIS 🦋

#include <stdlib.h>

int wctomb(char *s, wchar_t wc);

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💫 DESCRIPTION 💫

okay so here's the tea ☕. This function has TWO whole modes depending on whether s is NULL, and honestly? main character behavior.

• If s is not NULL: wctomb() takes the wide character wc and converts it into its multibyte representation, then stores that at the very beginning of the character array that s points to. She also updates the shift state — which lives in a static anonymous variable that literally only the wctomb() function itself knows about (her little secret 🙈) — and then she returns the length of said multibyte representation. That means: the number of bytes written at s. ✨
• At most MB_CUR_MAX bytes will ever be written at s. And no, she will not double-check for you — the programmer must ensure that there is enough room to store the multibyte sequence at s. That's on you bestie, not her 😭
• If s is NULL: wctomb() resets that shift state (the one known only to this function) back to the initial state, and returns nonzero if the encoding has a nontrivial shift state, or zero if the encoding is stateless. 🌈

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🔥 RETURN VALUE 🔥

• If s is not NULL: wctomb() returns the number of bytes that have been written to the byte array at s. But!! if wc can not be represented as a multibyte sequence (according to the current locale), she returns -1. 💀
• If s is NULL: wctomb() returns nonzero if the encoding has nontrivial shift state, or zero if the encoding is stateless. no cap. ✨

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👑 ATTRIBUTES 👑

for the explanation of the terms used in this section, go check out attributes(7) — she's the source of truth 🫶

• Interface: wctomb()
• Attribute: Thread safety
• Value: MT-Unsafe race

so yeah, wctomb() is MT-Unsafe with a race situation. Not thread-safe, she said what she said 💀 be careful out there.

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🧚 VERSIONS 🧚

the function wcrtomb(3) provides a better interface to the same functionality. so like, she's the glow-up version. obsessed honestly. 💅

⭐ STANDARDS ⭐

C11, POSIX.1-2008. certified icon behavior ✨

🎀 HISTORY 🎀

POSIX.1-2001, C99. she's been around, she's got lore 📜

💜 NOTES 💜

the behavior of wctomb() depends on the LC_CTYPE category of the current locale. so locale vibes = output vibes, iykyk 🌸

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🌈 SEE ALSO 🌈

• MB_CUR_MAX(3)
• mblen(3)
• mbstowcs(3)
• mbtowc(3)
• wcrtomb(3)
• wcstombs(3)

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and that's the whole page bestie!! 🫶 she's from Linux man-pages 6.20, dated 2026-02-08, and she will always be wctomb(3) to us 💖 mwah, stan a multibyte conversion function, periodt. 🎀✨