#include <stdlib.h> size_t wcstombs(char *restrict s, const wchar_t *restrict pwcs, size_t n);
The wcstombs() function converts the sequence of wide-character codes from the array pointed to by pwcs into a sequence of characters and stores 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 is converted as if by a call to wctomb(3C).
The behavior of this function is affected by the LC_CTYPE category of the current locale.
No more than n bytes will 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() returns 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() returns (size_t)-1. Otherwise, wcstombs() returns the number of bytes stored in the character array, not including any terminating null byte. The array will not be null-terminated if the value returned is n.
The wcstombs() function may fail if:
A wide-character code does not correspond to a valid character.
See attributes(5) for descriptions of the following attributes: