Lua true Binary I/O

Question

I read this question, and I checked it myself.

I use the following snippet:

f = io.open("file.file", "wb")
f:write(1.34)
f:close()

This creates the file, into which 1.34 is written. This is same as : 00110001 00101110 00110011 00110100 , that is binary codes for the digit 1, the decinal point, then 3 and finally 4.

However, I would like to have printed 00111111 10101100 11001100 11001101, which is a true float representation. How do I do so?

I'm not sure I understand the question entirely but you might need something like [lpack](http://www.tecgraf.puc-rio.br/~lhf/ftp/lua/#lpack) (or similar) for this. — Etan Reisner, Jul 23 '14 at 17:50
@EgorSkriptunoff's answer is not valid for lua 5.1, but is valid in lua 5.2. (I have no idea if it is correct.) — Etan Reisner, Jul 23 '14 at 17:51
BTW, you can simply store 17 decimal digits of the number `f:write(('%.17g'):format(1.34))` to avoid any rounding errors and receive exactly the same number with `tonumber`. This works in Lua 5.1 — Egor Skriptunoff, Jul 23 '14 at 18:23
@EgorSkriptunoff and the corresponding read command would be f:read(('%.17g'):format(1.34)) ? — Sean, Jul 23 '14 at 19:36
I thumbed you down for using a roundabout way of saying that the string "3.14" was written into the file. You could have said it plainly instead of forcing us to run your code. — Niccolo M., Jul 24 '14 at 10:45
@NiccoloM. I believe it is a good practice, as mentioned in Stackoverflow guidlines, to give example of the used code. I personally, when seeing the snippet will unambiguously understand, regardless of formulation of the description of problem, what is happening - without running the code. So moderator please assist me, to understand what it is about the "Forcing" mentioned here. — Sean, Jul 24 '14 at 11:47
@Sean: I apologize for being rude. I reverted my unjustified thumb down. Mea culpa. You posted simple code. Then, instead of writing `into which "1.34" is written` or `... the string "1.34" is written`, you wrote `into which 1.34 is written`, which necessitated your explaining the nature of this unspecified 1.34, and caused me to question my own understanding of the code. Since I'm impatient in nature I gave up grokking your "windy" explanation and just run the code. My thumb down was retribution. Again I apologize. Probably all people here would find the fault in me, not in you ;-) — Niccolo M., Jul 24 '14 at 21:38
(Hmmm... the site won't let me revert my thumbdown. It seems the question has to be edited first. Sorry.) — Niccolo M., Jul 24 '14 at 21:41
That is okey. The discussion should serve as a clarification. — Sean, Jul 25 '14 at 16:35

score 2 · Answer 1 · edited May 23 '17 at 12:13

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You may need to convert it to binary representation, using something similar to this answer. This discussion on serialization of lua numbers may also be useful.

edited May 23 '17 at 12:13

Community

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answered Jul 23 '14 at 19:54

Paul Kulchenko

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Lua true Binary I/O

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