Extract MS-DOS 8.0 disk image

extract.c

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

#define SECTOR		512
#define BOOTMAGIC	0xaa55

char disk[SECTOR*2880];

int
main(int argc, const char *argv[])
{
  char name[48];
  FILE *f;
  int c;

  snprintf(name, 48, "%s/System32/diskcopy.dll", getenv("SystemRoot"));
  if (argc > 1)
    f = fopen(argv[1], "rb");
  else
    f = fopen(name, "rb");

  if (f == NULL) {
    perror("Error: cannot open DLL");
    return 1;
  }

  while ((c = getc(f)) != EOF) {
    if (c == (BOOTMAGIC & 0xff)) {
      c = getc(f);
      if (c == BOOTMAGIC >> 8) {
	puts("Found boot sector!");
	goto found;
      }
    }
  }

  fputs("Error: cannot find boot sector\n", stderr);
  return 1;

found:
  fseek(f, -SECTOR, SEEK_CUR);
  fread(disk, SECTOR, 2880, f);
  fclose(f);

  f = fopen("msdos.img", "wb");
  fwrite(disk, SECTOR, 2880, f);
  fclose(f);

  return 0;
}