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

#define with_open_file(var, path, mode)                         \
  /* loop control */                                            \
  for (int with_open_file_run = 1;                              \
       with_open_file_run; )                                    \
  /* save path, so that it is only evaluated once. */           \
  for (char *with_open_file_path = (path);                      \
       with_open_file_run; )                                    \
  /* open the file and setup the cleanup */                     \
  for (FILE *with_open_file_file                                \
         __attribute__((cleanup (with_open_file_cleanup)))      \
         = fopen (with_open_file_path, (mode));                 \
       with_open_file_run; )                                    \
  /* call helper function to crash and burn, when               \
     the file could not be opened. */                           \
  for (with_open_file_ensure (with_open_file_file,              \
                              with_open_file_path);             \
       with_open_file_run; )                                    \
  /* define the given var and bind it to the file */            \
  for (FILE *var = with_open_file_file;                         \
       with_open_file_run;                                      \
       with_open_file_run = 0) /* all done */

static void with_open_file_cleanup (FILE **f)
{
  if (*f) fclose (*f);
}

static void with_open_file_ensure (FILE *f, const char *path)
{
  if (!f)
    {
      fprintf (stderr, "Cannot open file \"%s\": %s\n",
               path,
               strerror (errno));
      exit (1);
    }
}

/* -- Demo ----------------------------------------------------------------- */

int main (int argc, char **argv)
{
  if (argc != 2)
    {
      fprintf (stderr, "Supply a file name as command line argument.\n");
      exit (1);
    }

  with_open_file (f, argv[1], "r")
    {
      printf ("File is open: f = %p\n", f);
    }

  return 0;
}