Write numbers to a file in lua in binary format

I have a big array with numbers I would like to write to a file.

But if I do this:

local out = io.open("file.bin", "wb")
local i = 4324234

I am just writing the number as a string to the file. How do I write the correct bytes for the number to file. And how can I later read from it.


Try this

function writebytes(f,x)
    local b4=string.char(x%256) x=(x-x%256)/256
    local b3=string.char(x%256) x=(x-x%256)/256
    local b2=string.char(x%256) x=(x-x%256)/256
    local b1=string.char(x%256) x=(x-x%256)/256


and also this

function bytes(x)
    local b4=x%256  x=(x-x%256)/256
    local b3=x%256  x=(x-x%256)/256
    local b2=x%256  x=(x-x%256)/256
    local b1=x%256  x=(x-x%256)/256
    return string.char(b1,b2,b3,b4)


These work for 32-bit integers and output the most significant byte first. Adapt as needed.

You could use lua struct for more fine-grained control over binary conversion.

local struct = require('struct')

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