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PROLOG
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.
NAME
mbtowc — convert a character to a wide-character code
SYNOPSIS
#include <stdlib.h> int mbtowc(wchar_t *restrict pwc, const char *restrict s, size_t n);
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 not a null pointer, mbtowc() shall determine the number of bytes that constitute the character
pointed to by s. It shall then determine the wide-character code for the value of type wchar_t that
corresponds to that character. (The value of the wide-character code corresponding to the null byte is
0.) 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. 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. 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().
The mbtowc() function need not be thread-safe.
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).
In no case shall the value returned be greater than n or the value of the {MB_CUR_MAX} macro.
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.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
mblen(), mbstowcs(), 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 .