ftell, fgetpos, etc.

[Hendrik Boom <hendrik@topoi.pooq.com>]

I need to write code that creates, reads, and writes a random-access binary
file, said binary file to be readable and writable on several machines,
which may have different byte sex, but will certainly have different
native word size (32 vs 64 bit).  Addresses of positions in the file
*will* have to be written into the file.

The machines on which this software will have to run presently use
Debian or Debian-derived Linux distributions. (386, AMD64, maemo).

Now I know how to handle different byte sex (use shifts and masks to
decompose data and recompose it in the chosen file-format -- anyone have a
metter method?).

What I don't know is how to seek around the file in a machine-independent
manner, and avoid future headaches.

I can certainly hack up something that works for now, and will have to be
replaced if the files to be handled ever get huge.  But I'd like to know
if there's a recommended way of doing it.

As far as I can tell, the two regimes available are

(a) use fgetpos and fsetpos
  This will presumably do random access to anything the machine's file
  system will handle, but the disk address I get from fgetpos are
  unliky to be usable on another system.
(b) use ftell and fseek
  Now these will solve the problem as long as my files stay small.
  They provide byte counts from the start of the file, which are
  semantically independent of the platform, but are just long int, which,
  last I heard, was 32 bits almost everywhere (and, because of the sign
  bit are limited to 31 bits in practise).

Is there something else available?  Is there another way to use the tools
I have already mentioned?  Is there a clean way to move to 64-bit
relatively system-independent disk addresses?  Is there a standard way?
 
-- hendrik