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wcstombs — convert a wide-character string to a character string
size_t wcstombs(char *restrict s, const wchar_t *restrict pwcs,
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
The wcstombs() function shall fail if:
- A wide-character code does not correspond to a valid character.
The following sections are informative.
mblen(), mbtowc(), mbstowcs(),
The Base Definitions volume of POSIX.1‐2008,
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 .
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