[BUG] File#rewind, File#syswrite, File#pos on Cygwin build

[Alan Davies]

On the cygwin build of ruby v1.8.0, I have encountered a strange bug
when using rewind, syswrite and pos. If you open a file in read/write
mode, read the contents, rewind, syswrite some data, then File#pos
always seems to return zero. This does not happen if you use the
windows build, or you replace 'syswrite' with 'write'.

e.g:

$ cat syswrite.rb
#!/bin/ruby

testStr = "hello\nthis is some example text\nblah blah blah"

# read it, rewind, then write it back again
File.open("out.txt", 'r+') do |file|
file.readlines
file.rewind
bytes = file.syswrite(testStr)
puts "#{bytes} bytes written"
puts "Now at position #{file.pos}"
end

$ ls > out.txt

$ syswrite.rb
46 bytes written
Now at position 0

[ts]

>>>>> "A" == Alan Davies <NOSPAMcs96and@yahoo.co.ukNOSPAM> writes:

A> On the cygwin build of ruby v1.8.0, I have encountered a strange bug
A> when using rewind, syswrite and pos. If you open a file in read/write
A> mode, read the contents, rewind, syswrite some data, then File#pos
A> always seems to return zero. This does not happen if you use the
A> windows build, or you replace 'syswrite' with 'write'.

try to add a flush

A> File.open("out.txt", 'r+') do |file|
A> file.readlines
A> file.rewind
A> bytes = file.syswrite(testStr)

file.flush

A> puts "#{bytes} bytes written"
A> puts "Now at position #{file.pos}"
A> end


Guy Decoux

[Robert Klemme]

"Alan Davies" <NOSPAMcs96and@yahoo.co.ukNOSPAM> schrieb im Newsbeitrag
news:3fba526d@primark.com...

> On the cygwin build of ruby v1.8.0, I have encountered a strange bug
> when using rewind, syswrite and pos. If you open a file in read/write
> mode, read the contents, rewind, syswrite some data, then File#pos
> always seems to return zero. This does not happen if you use the
> windows build, or you replace 'syswrite' with 'write'.

"Do not mix with other methods that write to ios or you may get
unpredictable results."
[url]http://www.rubycentral.com/book/ref_c_io.html#IO.syswrite[/url]

robert

[ts]

>>>>> "R" == Robert Klemme <bob.news@gmx.net> writes:

R> "Do not mix with other methods that write to ios or you may get
R> unpredictable results."
R> [url]http://www.rubycentral.com/book/ref_c_io.html#IO.syswrite[/url]

No, no.

moulon% cat b.rb
#!/usr/bin/ruby
testStr = "hello\nthis is some example text\nblah blah blah"

File.open("out.txt", 'r+') do |file|
file.readlines
puts "Now at position #{file.pos}"
file.rewind
puts "Now at position #{file.pos}"
bytes = file.syswrite(testStr)
puts "#{bytes} bytes written"
puts "Now at position #{file.pos}"
end
moulon%

moulon% ruby -v b.rb
ruby 1.8.0 (2003-08-04) [sparc-solaris2.7]
Now at position 3330
Now at position 0
46 bytes written
Now at position 46
moulon%

the problem is in cygwin and linux ...



Guy Decoux

[Alan Davies]

ts wrote:

> the problem is in cygwin and linux ...

Can we get this fixed in 1.8.1 then?