/* changes the case of each letter
   Illustrates accessing files with user specified buffers
    with fns defined in file control header file */
#include <ctype.h>
#include <fcntl.h>

#define	BUFSIZE	1024

main(int argc, char **argv)
{
  char mybuf[BUFSIZE], *p;
  int in_fd, out_fd, n;

  in_fd = open(argv[1], O_RDONLY); /* open for read only */
  out_fd = open(argv[2], O_WRONLY | O_EXCL | O_CREAT, 0600);
   /* open for write only or for create exclusively with file prot 600 */
  while ((n = read(in_fd, mybuf, BUFSIZE)) > 0) {
    /* use file identifier 0 - std input, 1 - std output, 2 - std error */
    for (p = mybuf; p - mybuf < n; ++p)
	if (islower(*p))
	   *p = toupper(*p);
	else if (isupper(*p))
	   *p = tolower(*p);
    write(out_fd, mybuf, n);
  }
  close(in_fd);
  close(out_fd);
}