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 affected.
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.
The wcstombs() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
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 n.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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