Hi all,
I’m having trouble getting an open/write/close cycle to actually put the
correct data in the file. Here’s some code that illustrates the problem:
x = "012345678\n"
10.times do
len = 0
begin
len = File.stat( 'junk').size
rescue
len = 0
end
puts len.to_s
f = File.open 'crapper', 'w'
f.seek len
f.write x
f.close
end
produces:
0
10
20
30
40
50
60
70
80
90
as output. However, the file ‘junk’ is filled with zeroes, except for
the last 10 bytes, which are what you’d expect them to be:
puma:~> od -h junk
0000000 0000 0000 0000 0000 0000 0000 0000 0000
*
0000120 0000 0000 0000 0000 0000 3130 3332 3534
0000140 3736 0a38
0000144
puma:~>
Anyone know what I’m doing wrong? I tried using sysseek and syswrite,
but I got the same results. Is Ruby’s internal buffering screwing me up
here somehow? TIA.
–
Toby DiPasquale
On 24-Mar-06, at 11:43 AM, Toby DiPasquale wrote:
len = 0
end
60
70
80
90
as output. However, the file ‘junk’ is filled with zeroes, except for
the last 10 bytes, which are what you’d expect them to be:
opening a file for writing truncates it. Does this, opening it for
reading & writing, do what you want?
x = “012345678\n”
10.times do
len = 0
begin
len = File.stat( ‘junk’).size
rescue
len = 0
end
puts len.to_s
f = File.open ‘junk’,File::RDWR|File::CREAT
f.seek len
f.write x
f.close
end
Mike
–
Mike S. [email protected]
http://www.stok.ca/~mike/
The “`Stok’ disclaimers” apply.
len = File.stat( 'junk').size
f = File.open 'crapper', 'w'
Are there really 2 files? or is this a typo?
The docs on IO::open says tha using the ‘w’ mode cause the file to be
truncated if it exists.
You need to look at ‘a’ mode
cheers
On Mar 24, 2006, at 10:43 AM, Toby DiPasquale wrote:
begin
len = File.stat( ‘junk’).size
rescue
len = 0
end
puts len.to_s
f = File.open ‘crapper’, ‘w’
f.seek len
The above procedure seems like a complex way to do:
File.open(“junk”, “a”)…
Will that work for you?
James Edward G. II
Mike S. wrote:
opening a file for writing truncates it.
ARRRGH! I’m a moron. Of course, you are right. Thanks for the mental
clue-by-four.
–
Toby DiPasquale
James G. wrote:
The above procedure seems like a complex way to do:
File.open(“junk”, “a”)…
Will that work for you?
No, the above code was just a small example to illustrate the issue. The
real code does lots more before and after each write.
–
Toby DiPasquale
Toby DiPasquale wrote:
From above:
- f = File.open ‘crapper’, ‘w’
- f = File.open ‘junk’, ‘w’
Sorry.
Not a problem.
When I run your snippet i get:
ruby -w fwrite-test.rb
0
11
22
33
44
55
66
77
88
99
It looks like seeking on an empty file fills it with null data. Not
sure if thats a Ruby thing or a feature of the underlying IO libs.
change the ‘w’ to an ‘a’ (an delete the current ‘junk’ file)
and the file produced looks like:
012345678
012345678
012345678
012345678
012345678
012345678
012345678
012345678
012345678
012345678
cheers