source: vendor/glibc-tests/glibc/stdio-common/tst-fmemopen.c

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>

#define TEST_FILE "test-1"

int
main (void)
{
  const char blah[] = "BLAH";
  FILE *fp;
  char *mmap_data;
  int ch, fd;
  struct stat fs;
  const char *cp;

  /* setup the physical file, and use it */
  if ((fp = fopen (TEST_FILE, "w+")) == NULL)
    exit (1);
  if (fwrite (blah, 1, strlen (blah), fp) != strlen (blah))
    exit (2);

  rewind (fp);
  printf ("file: ");
  cp = blah;
  while ((ch = getc (fp)) != EOF)
    {
      fputc (ch, stdout);
      if (ch != *cp)
        {
          printf ("\ncharacter %td: '%c' instead of '%c'\n",
                  cp - blah, ch, *cp);
          exit (1);
        }
      ++cp;
    }
  fputc ('\n', stdout);
  if (ferror (fp))
    {
      puts ("fp: error");
      exit (1);
    }
  if (feof (fp))
    printf ("fp: EOF\n");
  else
    {
      puts ("not EOF");
      exit (1);
    }
  fclose (fp);

  /* Now, mmap the file into a buffer, and do that too */
  if ((fd = open (TEST_FILE, O_RDONLY)) == -1)
    exit (3);
  if (fstat (fd, &fs) == -1)
    exit (4);

  if ((mmap_data = (char *) mmap (NULL, fs.st_size, PROT_READ,
                                  MAP_SHARED, fd, 0)) == MAP_FAILED)
    {
      if (errno == ENOSYS)
        exit (0);
      exit (5);
    }

  if ((fp = fmemopen (mmap_data, fs.st_size, "r")) == NULL)
    exit (1);

  printf ("mem: ");
  cp = blah;
  while ((ch = getc (fp)) != EOF)
    {
      fputc (ch, stdout);
      if (ch != *cp)
        {
          printf ("%td character: '%c' instead of '%c'\n",
                  cp - blah, ch, *cp);
          exit (1);
        }
      ++cp;
    }

  fputc ('\n', stdout);

  if (ferror (fp))
    {
      puts ("fp: error");
      exit (1);
    }
  if (feof (fp))
    printf ("fp: EOF\n");
  else
    {
      puts ("not EOF");
      exit (1);
    }

  fclose (fp);

  munmap (mmap_data, fs.st_size);

  unlink (TEST_FILE);

  return 0;
}