#include <stdlib.h>
size_t wcstombs(char *restrict s, const wchar_t *restrict
pwcs,
size_t n);
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.
The wcstombs() function may fail if:
The following sections are informative.
mblen() , mbtowc() , mbstowcs() , wctomb() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>