[REBOL] Re: Size?
From: antonr:lexicon at: 12-Dec-2004 2:23
In my tests on WinXP, it looks like
the sensible limit is 2147483647 == to-integer #{7FFFFFFF}
However, in my tests (see code below),
the size integer returned by INFO? wraps
around to -2147483648 and continues up from
there as you increase the file size, so at least
on WinXP you can get up to 4 Gigabytes (minus 1) and still accurately
test for size (albeit with a bit of careful integer hackery).
When 4Gig is reached, the size returned is zero.
If you further increase the file size from here,
then INFO? just gives a zero size result.
Anton.
> If the size of a file is larger than the max
> value of an integer, how can I then retrieve
> the size?
>
> Thank you
>
> Steffen
(watch out for unintended line wrapping...)
rebol [
Title: ""
File: %test-max-file.r
Date: 12-Dec-2004
Version: 1.0.0
Needs: []
Author: "Anton Rolls"
Language: 'English
Purpose: {Determine maximum file size which can be tested accurately}
Usage: {}
ToDo: {
-
}
History: [
1.0.0 [12-Dec-2004 {First version} "Anton"]
]
Notes: {
In rebol, file sizes are typically stored in signed integers.
Therefore the theoretical limit is:
2147483647 == to-integer #{7FFFFFFF}
}
]
file: %/L/big-rebol-file ; <- on a volume with enough space !!
; create a large string, but not so large it exhausts our memory
block-size: 1024 * 1024 * 16 ; 16 Megabytes
str: make string! block-size ; pre-allocate the string
insert/dup str "1" block-size ; <- fill the string
str-1: copy/part str back tail str ; <- one character less
if exists? file [delete file]
expected-size: 0
repeat n 255 [ ; (also try to 127)
print [n "^-Expected size:" expected-size "^-SIZE? size:" size? file]
write/append file str
expected-size: attempt [expected-size + block-size] ; catch integer
overflow errors
]
print ["SIZE? size:" size? file]
write/append file str-1 ; just below overflow limit
print ["SIZE? size:" size? file] ; <- size comes back as a negative number
write/append file "F" ; <- this causes the size integer overflow (number
becomes negative)
print ["SIZE? size:" size? file]
write/append file "1"
print ["SIZE? size:" size? file]
;halt
