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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MBRTOWC(3P) POSIX Programmer's Manual MBRTOWC(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
mbrtowc — convert a character to a wide-character code
(restartable)
#include <wchar.h>
size_t mbrtowc(wchar_t *restrict pwc, const char *restrict s,
size_t n, mbstate_t *restrict ps);
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.
If s is a null pointer, the mbrtowc() function shall be equivalent
to the call:
mbrtowc(NULL, "", 1, ps)
In this case, the values of the arguments pwc and n are ignored.
If s is not a null pointer, the mbrtowc() function shall inspect
at most n bytes beginning at the byte pointed to by s to determine
the number of bytes needed to complete the next character
(including any shift sequences). 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.
If the corresponding wide character is the null wide character,
the resulting state described shall be the initial conversion
state.
If ps is a null pointer, the mbrtowc() function 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. The
implementation shall behave as if no function defined in this
volume of POSIX.1‐2017 calls mbrtowc().
The behavior of this function is affected by the LC_CTYPE category
of the current locale.
The mbrtowc() function need not be thread-safe if called with a
NULL ps argument.
The mbrtowc() function shall not change the setting of errno if
successful.
The mbrtowc() function 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.
The mbrtowc() 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 mbrtowc() function may fail if:
EINVAL ps points to an object that contains an invalid conversion
state.
The following sections are informative.
None.
None.
None.
None.
mbsinit(3p), mbsrtowcs(3p)
The Base Definitions volume of POSIX.1‐2017, wchar.h(0p)
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 .
IEEE/The Open Group 2017 MBRTOWC(3P)
Pages that refer to this page: wchar.h(0p), fwprintf(3p), mbrlen(3p), mbsinit(3p), mbsrtowcs(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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