wcwidth —
number of column positions of a wide-character code
Standard C Library (libc, -lc)
#include <wchar.h>
int
  
  wcwidth(wchar_t
    wc);
The wcwidth() function determines the number of column
  positions required to display the wide character wc.
The wcwidth() function returns 0 if the
  wc argument is a nul wide character (L'\0'), -1 if
  wc is not printable, otherwise it returns the number of
  column positions the character occupies.
This code fragment reads text from standard input and breaks lines that are more
  than 20 column positions wide, similar to the
  fold(1) utility:
wint_t ch;
int column, w;
column = 0;
while ((ch = getwchar()) != WEOF) {
	w = wcwidth(ch);
	if (w > 0 && column + w >= 20) {
		putwchar(L'\n');
		column = 0;
	}
	putwchar(ch);
	if (ch == L'\n')
		column = 0;
	else if (w > 0)
		column += w;
}
 
The wcwidth() function conforms to IEEE
  Std 1003.1-2001 (“POSIX.1”).