[REBOL] [Fwd: SKIPping in a file]
From: joel:neely:fedex at: 8-Jul-2001 5:55
Hello, all!
Since Jeff had motivated me to dig out R/CUG2.3 and read up on
/DIRECT, I thought I'd take a shot at revising the "line reduction"
script for Aaron to read only the amount of data necessary for
the sample. (Not that I've ever been known to run an idea into
the ground! ;-)
In the course of playing with that idea, I ran into a puzzler
that I haven't sorted out yet. Any suggestions would be most
welcome!
This function
readhead: func [fn [file!] n [integer!] /local fi mybuf] [
fi: open/binary/direct fn
mybuf: copy/part fi n
close fi
mybuf
]
seems to do what I want -- read/return the first N bytes from FN
(as a BINARY! value, of course, but that's a non-issue for the
task at hand).
However, *this* function
readtail: func [fn [file!] n [integer!] /local sz rp fi mybuf] [
sz: get in info? fn 'size
rp: sz + 1 - n
print [sz rp]
fi: open/binary/direct fn
fi: skip fi rp
mybuf: copy/part fi n
close fi
mybuf
]
seems to perform the calculations for where to position into the
file (as witnessed by the debugging output from the first three
lines), but then hangs (immune to the escape key). It's burning
CPU cycles furiously according to top, but at least responds to
kill -15.
Trying a different approach, *this* function
readtailx: func [fn [file!] n [integer!] /local sz rp fi mybuf]
[
sz: get in info? fn 'size
rp: sz + 1 - n
print [sz rp]
fi: open/direct/binary/skip fn rp
mybuf: copy/part fi n
close fi
mybuf
]
again shows the correct size/readpoint calculations, but always
returns the *first* N bytes of the file, not the *last* N bytes.
Am I misreading R/CUG or doing something boneheaded here? Or
are /SKIP and SKIP broken in View 1.2.0.4.2 ?
-jn-
---------------------------------------------------------------
There are two types of science: physics and stamp collecting!
-- Sir Arthur Eddington
joel-dot-neely-at-fedex-dot-com
