# Newbie question - how to write out specific bytes to an IO stream? **URL:** \ **Category:** Ruby\ **Created:** [November 7, 2007, 1:59am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445 "2007-11-07T01:59:33Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 1:59am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/1 "2007-11-07T01:59:33Z")
Hello – I’m trying to write out specific byte sequences over the wire / to a file / etc. Let’s say for example that I wanted to write out 99 111 108 108 105 110 as a simple, six byte sequence to a file. In Java, I might use the byte primitive, but it seems that in Ruby you have Fixnum and then a Float for fractions. If I simply create a Fixnum using the 99 literal, I think that that will create more than an 8-bit sequence when I write out to the file. Any ideas on how to do this? ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 2:37am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/2 "2007-11-07T02:37:34Z")
On 11/6/07, Collin VanDyck [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > when I write out to the file. > > Any ideas on how to do this? String objects are arrays of bytes, so you could simply do… num\_string = “99 111 108 108 105 110” byte\_string = num\_string.split.map! {|word| word.to\_i.chr}.join # Now, to illustrate… byte\_string.class # gives String byte[0] # gives 99, the base 10 representation of 1100011 # note that each byte can store numbers up to 255 puts byte\_string # gives collin If you want to store the 1’s and 0’s as a text string, you can use the Integer#to\_s(2) method. hth, Todd ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 2:55am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/3 "2007-11-07T02:55:40Z")
On Nov 6, 6:42 pm, Collin VanDyck [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > when I write out to the file. > > Any ideas on how to do this? I _think_ you’ll want to use Array#pack. E.g., to write them out in big-endian order: > a = [99, 111, 108, 108, 105, 110].pack ‘n\*’ > =\> “\000c\000o\000l\000l\000i\000n” > file.write a If you want little-endian, use ‘s\*’ (or ‘S\*’ for unsigned) instead of ‘n\*’. See [RDoc Documentation](http://ruby-doc.org/core/) and check Array#pack for more details on the directives. ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 3:39am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/4 "2007-11-07T03:39:34Z")
On 11/6/07, yermej [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > literal, I think that that will create more than an 8-bit sequence > > If you want little-endian, use ‘s\*’ (or ‘S\*’ for unsigned) instead of > ‘n\*’. See [RDoc Documentation](http://ruby-doc.org/core/) and check Array#pack for more > details on the directives. Hmm, I was thinking about #pack, but your example creates 12 bytes. ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 3:53am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/5 "2007-11-07T03:53:35Z")
Thank you for your replies! Both methods seem to work equally well, but I’m seeming to favor the pack method because i can just push in my random bytes (0-255) into an array. I decided to use pack “C\*” though, because I think that the C\* directive will limit the packed members to 8 bits, if I’m not mistaken. ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 4:25am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/6 "2007-11-07T04:25:08Z")
On 11/6/07, Collin VanDyck [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Thank you for your replies! > > Both methods seem to work equally well, but I’m seeming to favor the > pack method because i can just push in my random bytes (0-255) into an > array. I decided to use pack “C\*” though, because I think that the C\* > directive will limit the packed members to 8 bits, if I’m not mistaken. Good choice! Todd ---
**Author:** ![Collin\_VanDyck](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/839c29/32.png) [@Collin\_VanDyck](https://www.ruby-forum.com/u/Collin_VanDyck)\ **Post date:** [November 7, 2007, 11:30am UTC](https://www.ruby-forum.com/t/newbie-question-how-to-write-out-specific-bytes-to-an-io-stream/119445/7 "2007-11-07T11:30:18Z")
Todd B. wrote: > > > Float for fractions. If I simply create a Fixnum using the 99 > > > If you want little-endian, use ‘s\*’ (or ‘S\*’ for unsigned) instead of > > > ‘n\*’. See [RDoc Documentation](http://ruby-doc.org/core/) and check Array#pack for more > > > details on the directives. > > Hmm, I was thinking about #pack, but your example creates 12 bytes. That’s because n isn’t the code for a byte - you want c or C, for signed or unsigned char: irb(main):004:0\> a = [1, 2, 3, 4, 5, 6].pack ‘C\*’ =\> “\001\002\003\004\005\006”