wcwidth: determine columns needed for a wide character

a.c

#ifndef _GNU_SOURCE
# define _GNU_SOURCE 1
#endif
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wchar.h>

int main(int argc, char *argv[])
{
  setlocale(LC_ALL, "");
  mbstate_t ps;
  const char *argv1 = argv[1];
  int n = strlen(argv1);
  wchar_t *wargv = (wchar_t *)malloc(sizeof(wchar_t)*n);
  memset(&ps, 0, sizeof ps);
  size_t g = mbsrtowcs(wargv, &argv1, n, &ps);
  if (g == (size_t)-1)
    fprintf(stderr, "invalid multibyte sequence has been encountered\n");
  else
    for (int i = 0; i < g; i++)
      printf("%lc: %d\n", wargv[i], wcwidth(wargv[i]));
  free(wargv);
  return 0;
}

cc a.c -o a
./a $'\U1f632中a0 x'