mbstate_t(3type)

✨ mbstate_t — multi-byte-character conversion state ✨

okay bestie, gather round, we're talking about mbstate_t from the 3type section 💖

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📚 LIBRARY

Standard C library (libc) — the O.G., the blueprint, the main character 👑

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🎀 SYNOPSIS

#include <wchar.h>

typedef /* ... */  mbstate_t;

yes, that's the whole thing. a typedef with vibes and secrets 🫶 the /* ... */ is doing a LOT of heavy lifting there and honestly? respect.

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💅 DESCRIPTION

so here's the tea: when you're converting characters between the multibyte representation and the wide character representation, you need conversion state, and the type for that is mbstate_t. 🌸

and like, converting a string uses a finite-state machine, right? so when that conversion gets interrupted after it's fully converted some number of characters, it might need to save a state for handling the rest of the characters later. this whole conversion-state situation is genuinely necessary for encodings like ISO/IEC 2022 and UTF-7. no cap. 😭

The initial state is the state at the beginning of conversion of a string. and there are two kinds of state, bestie:

• the one used by multibyte → wide character conversion functions, like mbsrtowcs(3) ⭐
• and the one used by wide character → multibyte conversion functions, like wcsrtombs(3) 🌈

but plot twist: they both fit in a mbstate_t, and they both have the same representation for an initial state. iconic behaviour tbh.

Now, for 8-bit encodings: every state is equivalent to the initial state. periodt. 💜

But for multibyte encodings like UTF-8, EUC-*, BIG5, or SJIS? 👀 Here's the split:

• the wide character → multibyte conversion functions never produce non-initial states
• but the multibyte → wide-character conversion functions like mbrtowc(3) do produce non-initial states when they get interrupted in the middle of a character

One possible way to create an mbstate_t in initial state is to set it to zero:

mbstate_t state;
memset(&state, 0, sizeof(state));

On Linux, the following works as well, but might generate compiler warnings:

mbstate_t state = { 0 };

ok so fair warning bestie: that second one is lowkey sketchy on the warning front 🙈 it does work on Linux, but your compiler may come for you. don't say I didn't tell you.

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📜 STANDARDS

C11, POSIX.1-2024.

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🕰️ HISTORY

SUSv2, C99, POSIX.1-2001. ancient lore fr fr 💀

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👀 SEE ALSO

• mbrlen(3)
• mbrtowc(3)
• mbsinit(3)
• mbsrtowcs(3)
• wcrtomb(3)
• wcsrtombs(3)

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and that's the whole page, bestie!! you ate that 🍓✨ this was brought to you by Linux man-pages 6.20, dated 2026-02-08 — the iconic source material, no cap, we stan 💖🎀🦋👑