wcswidth —
number of column positions in wide-character string
Standard C Library (libc, -lc)
#include <wchar.h>
int
  
  wcswidth(const
    wchar_t *pwcs, size_t
    n);
The wcswidth() function determines the number of column
  positions required for the first n characters of
  pwcs, or until a nul wide character (L'\0') is
  encountered.
The wcswidth() function returns 0 if
  pwcs is an empty string (L""), -1 if a
  non-printing wide character is encountered, otherwise it returns the number of
  column positions occupied.
The wcswidth() function conforms to
  IEEE Std 1003.1-2001 (“POSIX.1”).