Programming Elixir ≥ 1.6

Binaries

Sometimes you need to access data as a sequence of bits and bytes. For example, the headers in JPEG and MP3 files contain fields where a single byte may encode two or three separate values.

Elixir supports this with the binary data type. Binary literals are enclosed between << and >>.

The basic syntax packs successive integers into bytes:

iex> bin = << 1, 2 >>
<<1, 2>>
iex> byte_size bin
2

You can add modifiers to control the type and size of each individual field. Here’s a single byte that contains three fields of widths 2, 4, and 2 bits. (The example uses some built-in libraries to show the result’s binary value.)

iex> bin = <<3 :: size(2), 5 :: size(4), 1 :: size(2)>>
<<213>>
iex> :io.format("~-8.2b~n", :binary ...