# Pretty printing binary ints **URL:** \ **Category:** Ecosystem\ **Tags:** pretty-printing, printf, format\ **Created:** [December 29, 2021, 12:45am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062 "2021-12-29T00:45:46Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [December 29, 2021, 12:45am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/1 "2021-12-29T00:45:47Z")
Stdlib’s Printf allows you to print `int`s as unsigned octals or hexadecimals, but not as unsigned binary integers. Does anyone have a library that can pretty print `int`s as binary ints? I’m in the middle of writing one, but thought I’d ask just in case I missed something. Ideally I’m looking for something that would output `0b1_0010` or simply `10010` when I run `Printf.printf "%a" pp_binary_int 18`. Bonus points if there’s a way to specify minimum widths: `0b0001_0010` for `Printf.printf "%a" (pp_binary_int ~min_width:8) 18`. ---
**Author:** ![yawaramin](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/yawaramin/32/3384_2.png) [@yawaramin](https://discuss.ocaml.org/u/yawaramin)\ **Post date:** [December 29, 2021, 2:01am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/2 "2021-12-29T02:01:48Z")
Interesting, looks like `Printf` at one point supported it but then it was removed: [minor feature request: printf and binary digits · Issue #6249 · ocaml/ocaml · GitHub](https://github.com/ocaml/ocaml/issues/6249) ---
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [December 29, 2021, 2:29am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/3 "2021-12-29T02:29:12Z")
> There doesn’t seem to be much demand for this feature. If someone can come up with a compelling argument, a good choice of letter (given that B and b are already taken), and a patch, we might include it. Hmm… My use case is that I’m abusing int as a small bit-vector and need it for debugging. I don’t think this would count as “much demand”. ---
**Author:** ![Chet\_Murthy](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/chet_murthy/32/1501_2.png) [@Chet\_Murthy](https://discuss.ocaml.org/u/Chet_Murthy)\ **Post date:** [December 29, 2021, 3:48am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/4 "2021-12-29T03:48:42Z")
When pretty-printing stuff in anger, I’ve more-or-less stopped using Printf in favor of Fmt. It’s got enough bells-and-whistles that even for printing single lines, it’s the way to go. But either way, you can just use the “provide a function that converts to string” (for Fmt, "provide a function that pretty-prints) method to provide custom pretty-printers for your special types. I hope that was clear; if not, I can give an example. It’s not as sweet at “%b”, but then again, it’s not very painful either. ---
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [December 29, 2021, 4:12am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/5 "2021-12-29T04:12:14Z")
Oh, I already use `Fmt` when I’m pretty-printing complicated types. Love that library! I’m still going to have to write a function that converts ints to (strings of) binary ints. ---
**Author:** ![Chet\_Murthy](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/chet_murthy/32/1501_2.png) [@Chet\_Murthy](https://discuss.ocaml.org/u/Chet_Murthy)\ **Post date:** [December 29, 2021, 4:32am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/6 "2021-12-29T04:32:17Z")
I haven’t looked at that issue, but maybe you could scoop up the code [that got removed] from the associated PR ? Just a thought _grin_. ---
**Author:** ![nojb](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/nojb/32/519_2.png) [@nojb](https://discuss.ocaml.org/u/nojb)\ **Post date:** [December 29, 2021, 8:52am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/7 "2021-12-29T08:52:57Z")
> [@ifazk](#): > > I’m still going to have to write a function that converts ints to (strings of) binary ints. This is code that I have used in the past (from memory): ```auto let int_size = Sys.word_size - 1 let int2bin = let buf = Bytes.create int_size in fun n -> for i = 0 to int_size - 1 do let pos = int_size - 1 - i in Bytes.set buf pos (if n land (1 lsl i) != 0 then '1' else '0') done; (* skip leading zeros *) match Bytes.index_opt buf '1' with | None -> "0b0" | Some i -> "0b" ^ Bytes.sub_string buf i (int_size - i) ``` Cheers, Nicolas ---
**Author:** ![XVilka](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/xvilka/32/5334_2.png) [@XVilka](https://discuss.ocaml.org/u/XVilka)\ **Post date:** [December 29, 2021, 12:04pm UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/8 "2021-12-29T12:04:33Z")
Another option is to use `Bitvector` code from BAP [bap/lib/bitvec at master · BinaryAnalysisPlatform/bap · GitHub](https://github.com/BinaryAnalysisPlatform/bap/tree/master/lib/bitvec) ---
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [December 29, 2021, 4:18pm UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/9 "2021-12-29T16:18:46Z")
Done with my library: [GitHub - ifazk/pp-binary-ints: An OCaml library for pretty printing ints as unsigned binary integers](https://github.com/ifazk/pp-binary-ints). Will post an announcement once’s the opam PR goes through. I made it very customizable. - You can print with `0b` prefixes and `_` separators. - You can choose to print zeros just like the non-zeros, with prefixes and separators. - If you use zero padding, you can control how many leading zeros show up with the `~min_width` argument. - It correctly handles the edge cases when adding `_` separators: you won’t get leading underscores. - And of course, it includes pretty printers that work with `Format` and `Fmt`, not just `to_string` functions. The “zeros just like the non-zeros” needs some explanation. I noticed some inconsistencies when printing zero with `Printf`. ```ocaml # Printf.printf "%0#11d" 4444444;; 004_444_444- : unit = () # Printf.printf "%0#11d" 0;; 00000000000- : unit = () ``` Notice the `00000000000`, I would have expected `000_000_000`. I made both behaviours available. ---
**Author:** ![Maelan](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/maelan/32/1184_2.png) [@Maelan](https://discuss.ocaml.org/u/Maelan)\ **Post date:** [January 3, 2022, 11:05am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/10 "2022-01-03T11:05:02Z")
> [@ifazk](#): > > The “zeros just like the non-zeros” needs some explanation. I noticed some inconsistencies when printing zero with `Printf` . I would call this a bug. Did you consider reporting it? ---
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [January 4, 2022, 12:30am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/11 "2022-01-04T00:30:52Z")
No, I later realized that the two aren’t inconsistent. `Stdlib` takes “zero-padding” a little to literally. Notice what happens when we use a much longer width. ```ocaml # Printf.printf "%0#22d" 4444444;; 00000000000004_444_444- : unit = () # Printf.printf "%0#22d" 0;; 0000000000000000000000- : unit = () ``` ---
**Author:** ![Maelan](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/maelan/32/1184_2.png) [@Maelan](https://discuss.ocaml.org/u/Maelan)\ **Post date:** [January 4, 2022, 2:37pm UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/12 "2022-01-04T14:37:12Z")
Still, I would expect padding zeros to be thousand-separated (that leaves the corner case when the mandated width is a multiple of 4, where you’d start with an underscore, but in that case we can blame the user for mandating an inadequate width with the alternate format). NB: I just noticed another unexpected behavior: the `+` and `` flags (prefix non-negative numbers with a plus or a space, for alignment purposes) disable the alternate format altogether. ---
**Author:** ![ifazk](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/ifazk/32/836_2.png) [@ifazk](https://discuss.ocaml.org/u/ifazk)\ **Post date:** [January 5, 2022, 8:25am UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/13 "2022-01-05T08:25:07Z")
For zero padding, it looks like this is known and intended behaviour, meant to keep things simple in `Stdlib`. [Printf: alternative format for integers by ygrek · Pull Request #1182 · ocaml/ocaml · GitHub](https://github.com/ocaml/ocaml/pull/1182). For better handling, at least [this comment](https://github.com/ocaml/ocaml/pull/1182#issuecomment-392511939) believes it should be handled by external libraries. Looks like `+` and `` flags are not allowed to be used together and only there for legacy-behaviour. Try passing the `-strict-formats` flag to the `ocaml` toplevel or the compiler. ---
**Author:** ![anentropic](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/anentropic/32/2509_2.png) [@anentropic](https://discuss.ocaml.org/u/anentropic)\ **Post date:** [November 1, 2022, 12:44pm UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/14 "2022-11-01T12:44:31Z")
> [@nojb](#): > > `let int_size = Sys.word_size - 1` On my system (macos 12.6, OCaml 4.14) `Sys.int_size` and `Sys.word_size - 1` both return `63` Just curious if there is a reason for using the latter over the former? ---
**Author:** ![nojb](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/nojb/32/519_2.png) [@nojb](https://discuss.ocaml.org/u/nojb)\ **Post date:** [November 1, 2022, 1:12pm UTC](https://discuss.ocaml.org/t/pretty-printing-binary-ints/9062/15 "2022-11-01T13:12:07Z")
No, there isn’t. In fact, it is better to use `Sys.int_size` which is correct even for other backends such as `js_of_ocaml` (which uses 32-bit integers). Cheers, Nicolas