MBRTOWC(3POSIX)

🦋 PROLOG (aka the fine print bestie)

okay so real talk before we get into it 💖 this page is part of the POSIX Programmer's Manual (yes that's the manual name, we're being ✨official✨). But heads up: the Linux implementation of this interface may differ (so go consult the corresponding Linux manual page for the tea on Linux behavior), or honestly the interface may not even be implemented on Linux. vibe check accordingly. 🙈

---

✨ NAME ✨

mbrtowc — convert a character to a wide-character code (restartable)

like yes she converts, but she's the restartable one, iykyk 💅

---

🌸 SYNOPSIS 🌸

#include <wchar.h>

size_t mbrtowc(wchar_t *restrict pwc, const char *restrict s,
    size_t n, mbstate_t *restrict ps);

---

💖 DESCRIPTION 💖

okay so first thing: the functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

Now, if s is a null pointer, mbrtowc() shall be equivalent to the call:

mbrtowc(NULL, "", 1, ps)

and in this case, the values of the arguments pwc and n are ignored. (they're just there, sitting pretty, doing nothing 🎀)

If s is not a null pointer, mbrtowc() shall inspect at most n bytes beginning at the byte pointed to by s to figure out the number of bytes needed to complete the next character (including any shift sequences, yes those too). If the function determines that the next character is completed, it shall determine the value of the corresponding wide character and then, if pwc is not a null pointer, shall store that value in the object pointed to by pwc. And if the corresponding wide character is the null wide character, the resulting state described shall be the initial conversion state. slay.

If ps is a null pointer, mbrtowc() shall use its own internal mbstate_t object, which shall be initialized at program start-up to the initial conversion state. Otherwise, the mbstate_t object pointed to by ps shall be used to completely describe the current conversion state of the associated character sequence. And the implementation shall behave as if no function defined in this volume of POSIX.1‐2017 calls mbrtowc(). iconic, honestly.

The behavior of this function is affected by the LC_CTYPE category of the current locale. 🌈

⚠️ also: the mbrtowc() function need not be thread-safe if called with a NULL ps argument. so like, know that before you go wild in threads bestie 💀

And one more lil blessing: mbrtowc() shall not change the setting of errno if successful. 💜

---

👑 RETURN VALUE 👑

mbrtowc() shall return the first of the following that applies:

• 0 — If the next n or fewer bytes complete the character that corresponds to the null wide character (which is the value stored).
• between 1 and n inclusive — If the next n or fewer bytes complete a valid character (which is the value stored); the value returned shall be the number of bytes that complete the character.
• (size_t)-2 — If the next n bytes contribute to an incomplete but potentially valid character, and all n bytes have been processed (no value is stored). When n has at least the value of the {MB_CUR_MAX} macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
• (size_t)-1 — If an encoding error occurs, in which case the next n or fewer bytes do not contribute to a complete and valid character (no value is stored). In this case, [EILSEQ] shall be stored in errno and the conversion state is undefined. 😭 (undefined!! be careful!!)

---

🔥 ERRORS 🔥

mbrtowc() shall fail if:

• EILSEQ — An invalid character sequence is detected. In the POSIX locale an [EILSEQ] error cannot occur since all byte values are valid characters.

mbrtowc() may fail if:

• EINVAL — ps points to an object that contains an invalid conversion state.

📌 The following sections are informative.

---

🎀 EXAMPLES 🎀

None.

(yeah. nothing. empty. the void. she simply didn't provide any 💅)

---

🧚 APPLICATION USAGE 🧚

None.

---

⭐ RATIONALE ⭐

None.

---

🦋 FUTURE DIRECTIONS 🦋

None.

---

💜 SEE ALSO 💜

• mbsinit()
• mbsrtowcs()
• The Base Definitions volume of POSIX.1‐2017, <wchar.h>

---

🌸 COPYRIGHT 🌸

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

---

and that's the whole page bestie!! brought to you by IEEE/The Open Group, 2017, page MBRTOWC(3POSIX) — mwah, drink water, go convert some characters responsibly 🫶✨