Toggle little / big endian in unpack() in Ruby 1.8.7

Question

In Ruby 1.9.3, you can do

    "\x00\x01".unpack 'S' #=> 1 * 256 + 0 = 256, my machine use little endian by default
    "\x00\x01".unpack 'S>' #=> 0 * 256 + 1 = 1

But Ruby 1.8.7 doesn't have the ">" "<" annotation. So in 1.8.7, what is the best way to do unpack with big endian?

Have you got your examples mixed up? You’ve swapped the `x00` and `x01` bytes _and_ the format in the second example, they both equal 1. — matt, May 08 '14 at 01:42

score 0 · Answer 1 · answered May 08 '14 at 01:30

0

str = "\x00\x01"
puts str.unpack 'S'

p str.reverse
puts str.reverse.unpack 'S'


--output:--
256
"\001\000"
1

answered May 08 '14 at 01:30

7stud

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You should really add some explaination. – Numeron May 08 '14 at 01:55
My bad. I was also considering this method. The only down side here is that requires knowledge of the endianness of the machine. – user3580182 May 08 '14 at 05:57

score 0 · Answer 2 · answered May 08 '14 at 01:48

0

You can use n for network (big) endian 2 byte values (N for 4 byte ints) and v for little endian 2 byte integers (V for 4 bytes). See the docs.

"\x00\x01".unpack 'n'
# => [1] 
"\x00\x01".unpack 'v'
# => [256]

You really should look into upgrading your Ruby version if possible.

answered May 08 '14 at 01:48

matt

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Thanks. I should've pointed out - is there such a way to do it for signed integers? – user3580182 May 08 '14 at 05:51

Toggle little / big endian in unpack() in Ruby 1.8.7

2 Answers2