/* Author: Ruud Harmsen, August 2021.

   Explanation: https://rudhar.com/sfreview/siworin/siworin15.htm

   Meant to illustrate this bug:
   https://sourceware.org/bugzilla/show_bug.cgi?id=28258
 */

#include <stdio.h>
#include <locale.h>
#include <wchar.h>
#include <errno.h>

#define REPERR(LINE, ERRNO) { \
   fprintf(stderr, "Line %3d, error %d ", (LINE), (ERRNO)); \
   perror(NULL);}

int main (int argc, char **argv)
{
   static char bytes[] = u8"á";
   FILE *fp;
   int i;
   wint_t cw;
   int retval;

   if (!setlocale(LC_ALL, "en_US.UTF-8"))
      REPERR(__LINE__, errno);

   /* Write the test string to disk. */
   fp = fopen("in", "w"); fwrite(bytes, 1, sizeof bytes - 1, fp); fclose(fp);
   /* Reopen for reading. */
   fp = fopen("in", "r");
   for (i = argc > 1 ? 0 : 1; i < sizeof bytes && bytes[i]; i++)
   {
      fprintf(stderr, "Line %3d, i = %d\n", __LINE__, i);
      if ((retval = fseek(fp, i, SEEK_SET)) < 0)
         REPERR(__LINE__, errno);
      fprintf(stderr, "Line %3d, i = %d\n", __LINE__, i);

      cw = fgetwc(fp);
      if (ferror(fp)) {REPERR(__LINE__, errno); clearerr(fp);}
   }
   fclose(fp);
   return 0;
}