From: "Mark J. Reed" <markjreed@...>
Date: 2003-12-05T11:57:05+09:00
Subject: Re: how to navigate in a file ?

On Fri, Dec 05, 2003 at 01:58:22AM +0100, Boris BXS Schulz wrote:
> Hi,
> 
> I would like to open a binary file and read its contents.
> The opening is no problem, but if I wanted to jump to a specific byte, 
> how would I do that ? Also, how would I read this specific byte ? I have 
> some code reading the byte, but it quite ugly. Is there something like 
> DATA.readbyte(position) ?

What you're looking for is File#seek(offset).  For instance:

foo.rb(main):001:0> # Create a binary file where the byte at position N = N
foo.rb(main):002:0* File.open("binfile", "wb") do
foo.rb(main):003:1*     |f|
foo.rb(main):004:1*     256.times do
foo.rb(main):005:2* 	    |b|
foo.rb(main):006:2* 	    f.write(b.chr)
foo.rb(main):007:2>     end
foo.rb(main):008:1> end
=> 256
foo.rb(main):009:0> 
foo.rb(main):010:0* # Seek to position 128 and read the byte there
foo.rb(main):011:0* File.open("binfile", "rb") do
foo.rb(main):012:1*     |f|
foo.rb(main):013:1*     f.seek(128)
foo.rb(main):014:1>     b = f.getc
foo.rb(main):015:1>     puts b
foo.rb(main):016:1> end
128
=> nil
foo.rb(main):017:0> 

-Mark