MBTOWC(3P)

💖 MBTOWC(3P) 💖

okay bestie, so this one lives in the POSIX Programmer's Manual — that's the manual it belongs to — and it's the mbtowc page, no cap. Sit down, grab a strawberry 🍓, we're decoding characters together.

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🌸 PROLOG 🌸

Real talk before we start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so like, consult the corresponding Linux manual page for the actual Linux behavior, okay? — or honestly the interface may not even be implemented on Linux at all. 🙈 It's giving "check your own system first."

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✨ NAME ✨

mbtowc — convert a character to a wide-character code. that's the whole job, she's focused, she's iconic 💅

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🎀 SYNOPSIS 🎀

#include <stdlib.h>

int mbtowc(wchar_t *restrict pwc, const char *restrict s, size_t n);

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🦋 DESCRIPTION 🦋

First thing, bestie, so we're all on the same page: 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. And this volume of POSIX.1‐2017 defers to the ISO C standard. So if they ever beef, the ISO C standard wins. periodt.

Now the actual vibe. If s is not a null pointer, mbtowc() shall determine the number of bytes that constitute the character pointed to by s. Then it shall determine the wide-character code for the value of type wchar_t that corresponds to that character. (Heads up: the value of the wide-character code corresponding to the null byte is 0.) And if the character is valid and pwc is not a null pointer, mbtowc() shall store the wide-character code in the object pointed to by pwc. 🫶

The behavior of this function is affected by the LC_CTYPE category of the current locale — so yes, locale girlies, this is your moment.

For a state-dependent encoding, this function is placed into its initial state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer shall cause the internal state of the function to be altered as necessary. A call with s as a null pointer shall cause this function to return a non-zero value if encodings have state dependency, and 0 otherwise. If the implementation employs special bytes to change the shift state, these bytes shall not produce separate wide-character codes, but shall be grouped with an adjacent character. Changing the LC_CTYPE category causes the shift state of this function to be unspecified. 😭 And at most n bytes of the array pointed to by s shall be examined.

The implementation shall behave as if no function defined in this volume of POSIX.1‐2017 calls mbtowc().

⚠️ important: the mbtowc() function need not be thread-safe. not me warning you about threading again, but here we are 💀

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🔥 RETURN VALUE 🔥

• If s is a null pointer, mbtowc() shall return a non-zero or 0 value, if character encodings, respectively, do or do not have state-dependent encodings.
• If s is not a null pointer, mbtowc() shall either:
  • return 0 (if s points to the null byte), or
  • return the number of bytes that constitute the converted character (if the next n or fewer bytes form a valid character), or
  • return -1 and shall set errno to indicate the error (if they do not form a valid character).

And in no case shall the value returned be greater than n or the value of the {MB_CUR_MAX} macro. that's the ceiling, bestie, no going over 👑

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💜 ERRORS 💜

The mbtowc() 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.

The following sections are informative. 👀 (yes, that's literally what it says — everything after this is the informative bonus content)

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🌈 EXAMPLES 🌈

None. 😌 she said no examples today, we're keeping it mysterious

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💅 APPLICATION USAGE 💅

None. nothing to add, she's lowkey perfect as is

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🧚 RATIONALE 🧚

None. no justification needed, she simply is

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⭐ FUTURE DIRECTIONS ⭐

None. the future is bright but this page is staying exactly the same

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🌸 SEE ALSO 🌸

• mblen()
• mbstowcs()
• wctomb()
• wcstombs()

Also: The Base Definitions volume of POSIX.1‐2017, <stdlib.h>. go read your header files, bestie, it's self care 🫶

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👑 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 .

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and that's the whole page, bestie ✨ courtesy of IEEE/The Open Group, 2017, and yeah — the footer says MBTOWC(3P) too, so you know exactly which page you're on. mwah 💋 🦋