Originální popis anglicky: 
wctob - try to represent a wide character as a single byte
Návod, kniha: Linux Programmer's Manual
#include <wchar.h>
 
int wctob(wint_t c);
The 
wctob function tests whether the multi-byte representation of the
  wide character 
c, starting in the initial state, consists of a single
  byte. If so, it is returned as an unsigned char.
Never use this function. It cannot help you in writing internationalized
  programs. Internationalized programs must never distinguish single-byte and
  multi-byte characters.
The 
wctob function returns the single-byte representation of 
c, if
  it exists, of EOF otherwise.
ISO/ANSI C, UNIX98
wctomb(3)
The behaviour of 
wctob depends on the LC_CTYPE category of the current
  locale.
This function should never be used. Internationalized programs must never
  distinguish single-byte and multi-byte characters. Use the function
  
wctomb instead.