Subject: Re: Question about open/read-byte...
From: Erik Naggum <>
Date: Sun, 16 Dec 2001 18:44:16 GMT
Newsgroups: comp.lang.lisp
Message-ID: <>

* Cory Spencer <>
| I'm a relative Lisp newbie, and for the past several hours have been
| struggling with opening a binary file, and reading the data back as a
| series of 6-bit bytes.  The line that has been giving me problems is:
|   (setq stream (open "foo" :element-type '(unsigned-byte 6)))
| and whever it executes, always prints something along the lines of:
|   *** - file #P"/home/cspencer/foo" is not an integer file
| Grr.  Could someone please point out the error of my ways?

  You seem to be using CLISP, but have not used CLISP to write the file.
  CLISP supports arbitrarily sized bytes in a file by starting the file
  with the number of bytes as a 32-bit binary number.  It is so sad that
  Unix does not support file meta-information.  It does not keep the byte
  size in the file similarly, so if you lie to open about the element-type,
  you will run into a mismatch between the stored size and the actual size
  in terms of specified byte size, but fortunately, this does not apply to
  multiples-of-8-bit-byte files.  If you want to read 6-bit bytes from a
  file that does not begin with the prerequisite prefix, you need to copy
  its contents to a new file that startes with the 32-bit prefix.  Since
  you cannot change the element-type of a stream in mid-flight, you may
  need to write four 8-bit 0 bytes to your output file, copy the input file
  as 8-bit bytes, then reopen as a 32-bit file in overwrite mode, and write
  the file size of the input file in 6-bit bytes.  Pretty damn ugly, but
  such is life when people make bad technical decisions.

  The past is not more important than the future, despite what your culture
  has taught you.  Your future observations, conclusions, and beliefs are
  more important to you than those in your past ever will be.  The world is
  changing so fast the balance between the past and the future has shifted.