fhello-3.c

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

int main (void)
{
  FILE *f = fopen ("fhello.txt", "w");
  if (f)
    {
      fprintf (f, "Hello, world!\n");
      fclose (f);
    }
  else
    fprintf (stderr, "error #%d\n", errno);
  return 0;
}