From: "Chris Günther" <cg_@...>
Date: 2005-03-22T20:29:51+09:00
Subject: Re: Reading and writing a binary file

Thanks Robert,

you are absolutely right with your remarks using a block. The code I 
posted was just a small copied fraction of the real code, in which I 
cannor use a block because the same fd will be stored in a hash for 
later usage by another method.
Anyway, meanwhile I found the cause of this problem (again you are 
right, it was not in the code I posted) , but now I have another related 
problem that tricks my mind. I am trying to patch binary data in a file.
Unfortunately the data I am patching is not the data I get when reading 
it back from the patched binary file.
Any ideas??



Thanks again in advance,
Chris





#!/usr/bin/env ruby

FNAME, FSIZE, OFFSET, VALUE = 'foooo.dat', 1024, 32,
[?c,?a,?f,?e].pack('cccc')

File.open(FNAME,"ab+") {|fd|
     fd.pos=0
     bin_data = [0].pack('c')*FSIZE
     fd.write(bin_data)
}

File.truncate(FNAME,FSIZE)

File.open(FNAME,"ab+") {|fd|
     fd.pos=0
     data=fd.read(FSIZE)
     data[OFFSET,VALUE.length]=VALUE
     fd.pos=0
     fd.write(data)
     p "written modified piece of data = '#{data[OFFSET,VALUE.length]}'"
}

File.truncate(FNAME,FSIZE)
File.open(FNAME,"ab+") {|fd|
     fd.pos=OFFSET
     patched=fd.read(VALUE.length)
     p "read modified piece of data = '#{patched}'"
     puts "Oooops !!!" unless VALUE==patched
}