🚀 go-pugleaf

In article <BuL6E4.2wq@csn.org> c4craig@teal.csn.org (Craig Anderson) writes:
>How should I port a DOS call to chsize() to STD C / POSIX?
>In SunOS and BSD/386 I find:
>int ftruncate(int fd, off_t length)
>  truncate a file to a specified length

I hope that the POSIX standard has ftruncate(), but let's hope this will
be answered by someone who knows.

If you want to be portable to most ANSI C implementations (including those
which are not POSIX conforming) then the answer is ugly.  Use fopen() to
create a new file with some name that you think will be acceptable (e.g.
will be located on the same physical device and partition and probably
directory as the old file), copy the contents of the old file to the new
one, stop where you want it truncated, fclose() the new file, remove() the
old one, and rename() the new one.  There is no guarantee that this will
work (disk space might be exceeded or the implementation can return failure
status for any reasons it wishes) but this is as close as you can get.
This will probably lose the file permissions and various other OS-dependent
stuff that were set on the old file.

I would define a few flags at compile time and do stuff like
#if have_unix_fds && have_ftruncate
  status = ftruncate(fileno(my_file), where);
#else
  all that garbage
#endif

>In DOS Turbo C++ I find:
>int chsize(int handle,k long size)
>  Changes the file size.

If you only want to port to POSIX conforming systems, you'll have UNIX-style
file descriptor numbers (which are probably the same as handles) and, I hope,
ftruncate.  If you want to port to all ANSI C implementations, you'll have
to change all of your handles to use stdio-style files.
--
Norman Diamond       diamond@jit081.enet.dec.com
If this were the company's opinion, I wouldn't be allowed to post it.
"Yeah -- bad wiring.  That was probably it.  Very bad."