wcstombs — convert
    a wide-character string to a character string
Standard C Library (libc, -lc)
#include
    <stdlib.h>
size_t
  
  wcstombs(char * restrict
    mbstring, const wchar_t * restrict wcstring,
    size_t nbytes);
The
    wcstombs()
    function converts a wide character string wcstring
    into a multibyte character string, mbstring, beginning
    in the initial conversion state. Up to nbytes bytes
    are stored in mbstring. Partial multibyte characters
    at the end of the string are not stored. The multibyte character string is
    null terminated if there is room.
The wcstombs() function returns the number
    of bytes converted (not including any terminating null), if successful,
    otherwise it returns (size_t)-1.
The wcstombs() function will fail if:
  - [
EILSEQ] 
  - An invalid wide character was encountered.
 
  - [
EINVAL] 
  - The conversion state is invalid.
 
The wcstombs() function conforms to
    ISO/IEC 9899:1999
  (“ISO C99”).