MBLEN(3P)

💖 MBLEN(3P) 💖

okay so bestie, welcome to the POSIX Programmer's Manual, and today's main character is mblen — the little function that counts how many bytes are in one character. she's short, she's sweet, she's got lore. let's get into it 🎀

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✨ PROLOG ✨

real talk before we even start, bestie: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go consult the corresponding Linux manual page for the deets on Linux behavior), or the interface may not be implemented on Linux at all. so don't come for me if Linux does its own thing 💅

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🌸 NAME 🌸

mblen — get number of bytes in a character

like. that's it. that's the whole job. she counts bytes in a character. iconic honestly 🦋

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⭐ SYNOPSIS ⭐

#include <stdlib.h>

int mblen(const char *s, size_t n);

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🎀 DESCRIPTION 🎀

okay so the lore: 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 💜

If s is not a null pointer, mblen() shall determine the number of bytes constituting the character pointed to by s. Except that the shift state of mbtowc() is not affected, it shall be equivalent to:

mbtowc((wchar_t *)0, s, n);

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

The behavior of this function is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, this function shall be 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. 🙈

heads up bestie: the mblen() function need not be thread-safe. she's not built for the group chat, she's built for the one-on-one 🫶

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💅 RETURN VALUE 💅

the receipts, in order:

• If s is a null pointer, mblen() 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, mblen() shall either:
  • return 0 (if s points to the null byte), or
  • return the number of bytes that constitute the character (if the next n or fewer bytes form a valid character), or
  • return -1 (if they do not form a valid character) and may set errno to indicate the error.

and in NO case shall the value returned be greater than n or the value of the {MB_CUR_MAX} macro. like she will not be overachieving, that's not the vibe 💀

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😭 ERRORS 😭

The mblen() function may 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.

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🌈 EXAMPLES 🌈

None.

ngl bestie, there is literally nothing here. move along 💜

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🧚 APPLICATION USAGE 🧚

None.

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👑 RATIONALE 👑

None.

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🦋 FUTURE DIRECTIONS 🦋

None.

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🔥 SEE ALSO 🔥

• mbtowc()
• mbstowcs()
• wctomb()
• wcstombs()

and also: The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

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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!! this one was brought to you by IEEE/The Open Group, 2017 — yeah, the footer era, we love a vintage moment. mwah, go count some bytes responsibly 💖✨