# IO.puts generates ArgumentError on binary

**URL:** <https://forum.elixirforum.com/t/io-puts-generates-argumenterror-on-binary/46020>\
**Category:** Questions\
**Tags:** troubleshooting, io\
**Created:** [February 14, 2022, 1:09am UTC](https://forum.elixirforum.com/t/io-puts-generates-argumenterror-on-binary/46020 "2022-02-14T01:09:58Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![bmitc](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/bmitc/32/28446_2.png) [@bmitc](https://forum.elixirforum.com/u/bmitc)\
**Post date:** [February 14, 2022, 1:09am UTC](https://forum.elixirforum.com/t/io-puts-generates-argumenterror-on-binary/46020/1 "2022-02-14T01:09:58Z")

</div>

Hello! I am having an issue where `IO.puts` on a specific binary is generating an `ArgumentError`.

```elixir
iex> IO.puts <<32, 32, 145, 225, 8, 179, 180, 12, 65, 83, 232, 51, 96, 25, 206, 113, 158, 163, 89, 233, 199, 129, 103, 78, 161, 83, 246, 125, 32, 250, 166, 202>>
** (ArgumentError) argument error
    (stdlib 3.16.1) io.erl:99: :io.put_chars(:standard_io, [<<32, 32, 145, 225, 8, 179, 180, 12, 65, 83, 232, 51, 96, 25, 206, 113, 158, 163, 89, 233, 199, 129, 103, 78, 161, 83, 246, 125, 32, 250, 166, 202>>, 10])
iex>

```

I am posting this in hopes of clarifying and checking my understanding, as I think I now understand why this is happening but am not 100% sure.

My understanding is that in Elixir, values of type `String.t()` are UTF-8 strings and are also of type `binary()`, but not necessarily the other way around in that all `binary()` are not `String.t()`. For example, you can have a binary which doesn’t represent a UTF-8 string. In Elixir, if a binary value represents a UTF-8 string, it is displayed as so, such as `<<75, 90>>` being displayed as `"KZ"`.

The input type of `IO.puts` is `chardata | String.Chars.t()`.

Is the `ArgumentError` above because the binary data doesn’t represent a UTF-8 string? Is encoding the binary to UTF-16 using `Base.encode16/1` a way to always display binaries as string data? What’s the general way one should “print” binary data in Elixir?

Is this right or is there something else going wrong?

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<div class="post-metadata">

**Author:** ![benwilson512](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/benwilson512/32/1457_2.png) [@benwilson512](https://forum.elixirforum.com/u/benwilson512)\
**Post date:** [February 14, 2022, 1:46am UTC](https://forum.elixirforum.com/t/io-puts-generates-argumenterror-on-binary/46020/2 "2022-02-14T01:46:41Z")

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> [@bmitc](#):
>
> Is the `ArgumentError` above because the binary data doesn’t represent a UTF-8 string?

Yes.

> [@bmitc](#):
>
> Is encoding the binary to UTF-16 using `Base.encode16/1` a way to always display binaries as string data?

That isn’t what `Base.encode16` does. Base.encode16 encodes a binary as a hexadecimal utf8 string. It will however always return a printable string, no matter what binary you give it.

---

<div class="post-metadata">

**Author:** ![bmitc](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/bmitc/32/28446_2.png) [@bmitc](https://forum.elixirforum.com/u/bmitc)\
**Post date:** [February 14, 2022, 2:31am UTC](https://forum.elixirforum.com/t/io-puts-generates-argumenterror-on-binary/46020/3 "2022-02-14T02:31:46Z")

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> [@benwilson512](#):
>
> > [@bmitc](#):
> >
> > Is encoding the binary to UTF-16 using `Base.encode16/1` a way to always display binaries as string data?
> 
> That isn’t what `Base.encode16` does. Base.encode16 encodes a binary as a hexadecimal utf8 string. It will however always return a printable string, no matter what binary you give it.

Yea, that’s what I meant. My wording may have been off a bit. I meant to just use `Base.encode16/1` as a way to convert any binary to a hexadecimal string.

Thank you for taking a look and confirming this! This was one of those situations where I got confused, typed up a draft, but then did more reading and sort of figured it out, but I wanted a gut check by posting here. Thanks again.