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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
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NAME
mbrtowc — convert a character to a wide-character code (restartable)
SYNOPSIS
#include <wchar.h> size_t mbrtowc(wchar_t *restrict pwc, const char *restrict s, size_t n, mbstate_t *restrict ps);
DESCRIPTION
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.
RETURN VALUE
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.
ERRORS
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.
EXAMPLES
None.
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 .