Ruby - read bytes from a file, convert to integer

Question

I am trying to read unsigned integers from a file (stored as serial bytes) and convert them to integers. I tried this:

file = File.new(filename,"r")
num = file.read(2).unpack("S") #read an unsigned short
puts num #value  will be less than expected

What am I doing wrong here?

Answer 1

Ok, I got it for work:

num = file.read(8).unpack("N")

Thank you for your help.

Answer 2

You do not read enough bytes. As you say in the commentary to the tadman, you get 202instead3405691582

Note that the first 2 bytes 0xCAFEBABEare equal 0xCA=202

If you really want all 8 bytes to be in the same number, you need to read more than unsigned short

to try

num = file.read(8).unpack("L_")

, long 8 , .

Answer 3

, The Pickaxe? (Ruby 1.9, . 44)

File.open("testfile") 
do |file|
    file.each_byte {|ch| print "#{ch.chr}:#{ch} " }
end

each_byte .

Answer 4

, Ruby, DSL- , , , , - .

, . ( , ):

• BitStruct
• BinData

Answer 5

, , Windows. , .

open(filename, "rb") do |file|
  num = file.read(2).unpack("S")
  puts num
end

"endian" . , PowerPC, Mac, IBM Power, PS3 Sun Sparc.

Can you post an example of how this is “less”? Usually there is an obvious template for data.

For example, if you want 0x1234, but you get 0x3412, this will be an end problem.

Answer 6

In what format are the numbers stored in the file? Is it in the hex? Your code looks correct to me.