MBSTOWCS(3P)

🌸 MBSTOWCS(3P) — the POSIX Programmer's Manual, but make it a group chat 🌸

okay bestie, sit down, hydrate, because we're talking about mbstowcs() from the POSIX Programmer's Manual. she converts a character string into a wide-character string and honestly? she's iconic for it. 💅

---

💖 PROLOG 💖

so like, this manual page is part of the POSIX Programmer's Manual. heads up though: the Linux implementation of this interface may differ (so pls go consult the corresponding Linux manual page for the deets on Linux behavior), or the interface may not be implemented on Linux at all. no cap. 🙈

---

✨ NAME ✨

mbstowcs — convert a character string to a wide-character string

---

🎀 SYNOPSIS 🎀

#include <stdlib.h>

size_t mbstowcs(wchar_t *restrict pwcs, const char *restrict s,
    size_t n);

---

🦋 DESCRIPTION 🦋

okay so first things first: everything described on this reference page is aligned with the ISO C standard. if there's any conflict between the requirements here and the ISO C standard, that conflict is unintentional — not on purpose, not a vibe, just a whoopsie. and this volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

now the actual tea ☕: the mbstowcs() function shall convert a sequence of characters that begins in the initial shift state from the array pointed to by s into a sequence of corresponding wide-character codes, and shall store not more than n wide-character codes into the array pointed to by pwcs.

no characters that follow a null byte shall be examined or converted — and that null byte? it gets converted into a wide-character code with value 0. the way she just stops reading after that. 😌

each character shall be converted as if by a call to mbtowc(), except that the shift state of mbtowc() is not affected. she's not touching that shift state bestie, not even a little.

no more than n elements shall be modified in the array pointed to by pwcs.

🚨 if copying takes place between objects that overlap, the behavior is undefined. undefined behavior is not cute. do not do this.

the behavior of this function shall be affected by the LC_CTYPE category of the current locale. iykyk.

and here's a fun one: if pwcs is a null pointer, mbstowcs() shall return the length required to convert the entire array regardless of the value of n — but no values are stored. she's just doing a lil headcount for you, no writing. 👑

---

💀 RETURN VALUE 💀

if an invalid character is encountered, mbstowcs() shall return (size_t)-1 and shall set errno to indicate the error. sadness. 😭

otherwise? she shall return the number of the array elements modified (or required, if pwcs is null), not including a terminating 0 code, if any.

⚠️ and listen closely: the array shall not be zero-terminated if the value returned is n. so don't go assuming there's a lil 0 at the end, because there isn't. that's just how it is.

---

🍓 ERRORS 🍓

the mbstowcs() function 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. so if you're in the POSIX locale and you see this, something else is going on fr fr.

the following sections are informative. 📢

---

🌈 EXAMPLES 🌈

None.

---

🧚 APPLICATION USAGE 🧚

None.

---

💜 RATIONALE 💜

None.

---

⭐ FUTURE DIRECTIONS ⭐

None.

---

🔥 SEE ALSO 🔥

• mblen()
• mbtowc()
• wctomb()
• wcstombs()

The Base Definitions volume of POSIX.1‐2017, <stdlib.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 🫶 this lil masterpiece dropped in 2017, courtesy of IEEE/The Open Group, and it's living in the POSIX Programmer's Manual section 3P. stay wide-character-coded, mwah 💖✨🎀