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.
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.1‐2008 defers to the ISO C standard.
The wcstombs() function shall convert the sequence of wide-character
codes that are in the array pointed to by pwcs into a sequence of
characters that begins in the initial shift state and store these
characters into the array pointed to by s, stopping if a character
would exceed the limit of n total bytes or if a null byte is stored.
Each wide-character code shall be converted as if by a call to
wctomb(), except that the shift state of wctomb() shall not be
The behavior of this function shall be affected by the LC_CTYPE
category of the current locale.
No more than n bytes shall be modified in the array pointed to by s.
If copying takes place between objects that overlap, the behavior is
undefined. If s is a null pointer, wcstombs() shall return the
length required to convert the entire array regardless of the value
of n, but no values are stored.
If a wide-character code is encountered that does not correspond to a
valid character (of one or more bytes each), wcstombs() shall return
(size_t)−1. Otherwise, wcstombs() shall return the number of bytes
stored in the character array, not including any terminating null
byte. The array shall not be null-terminated if the value returned is
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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
IEEE/The Open Group 2013 WCSTOMBS(3P)