Description

   The wcstombs function converts a sequence of codes corresponding
   to multibyte characters from the array pointed to by pwcs to a
   sequence of multibyte characters that are stored into the array
   pointed to by s, up to a maximum of n bytes. The value returned
   is equal to the number of characters converted or a -1 if an
   error occurred.

   This function is affected by the LC_CTYPE category of the
   program's current locale.

   If s is NULL, this function call is a counting operation and n is
   ignored.

   See also wctomb.