util-linux/include/widechar.h

/* Declarations for wide characters */
/* This file must be included last because the redefinition of wchar_t may
   cause conflicts when system include files were included after it. */

#ifdef ENABLE_WIDECHAR

# include <wchar.h>
# include <wctype.h>
#if 0 /* for testing on platforms without built-in wide character support */
#  include <libutf8.h>
#endif

#if 1
/* explicit prototypes, since sometimes <wchar.h> does not give them */
extern int wcwidth (wchar_t c);         /* old: wint_t c */
extern int wcswidth (const wchar_t *s, size_t n);
extern size_t wcslen (const wchar_t *s);
extern wchar_t *wcsdup (const wchar_t *s);
#endif

#else

# include <ctype.h>
  /* Fallback for types */
# define wchar_t char
# define wint_t int
# define WEOF EOF
  /* Fallback for input operations */
# define fgetwc fgetc
# define getwc getc
# define getwchar getchar
# define fgetws fgets
  /* Fallback for output operations */
# define fputwc fputc
# define putwc putc
# define putwchar putchar
# define fputws fputs
  /* Fallback for character classification */
# define iswgraph isgraph
# define iswprint isprint
# define iswspace isspace
  /* Fallback for string functions */
# define wcschr strchr
# define wcsdup strdup
# define wcslen strlen

# define wcwidth(c) 1

#endif