Analogue of python's: array.array('H', file.read(n_bytes))

Questions / Help
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1

First, let’s say, that n_bytes = 2 and we do not need an array, then it’s pretty simple to write in elixir:

<<data :: bytes-size(2), _ :: binary>> = file
res = :binary.decode_unsigned(data)

Let’s return to python line: array.array('H', file.read(n_bytes))
It returns 2-byte array of numbers. ‘H’ means 2 byte.

So the question is, how to make the same in elixir?

Thanks in advance

2

Hello,

You could try something like that :

data = IO.read(file, 2)
array = for <<part::bytes-size(2) <- data>>, do: :binary.decode_unsigned(part)
3

You should also be able to get an integer directly too:

for <<part::integer-unsigned-size(2) <- data>>, do: part
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4

Thanks for your response. It might be:

for <<part::integer-unsigned-size(16) <- data>>, do: part

As size means bits, not bytes. By the way integer-unsigned-size is big endian. Any way to code the same with little endian?

5

Thank, that works, as you can specify big and little endian.

6

Yes you can add the endianness directly in the form @josevalim gave :

for <<part::little-integer-unsigned-size(16) <- data>>, do: part

All possibilities are described here: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#<<>>/1

1 Like