# Convert a number to a byte array

**URL:** <https://discourse.julialang.org/t/convert-a-number-to-a-byte-array/111867>\
**Category:** New to Julia\
**Created:** [March 20, 2024, 11:26am UTC](https://discourse.julialang.org/t/convert-a-number-to-a-byte-array/111867 "2024-03-20T11:26:32Z")\
**Posts on this page:** 1\
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**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [March 20, 2024, 12:06pm UTC](https://discourse.julialang.org/t/convert-a-number-to-a-byte-array/111867/7 "2024-03-20T12:06:42Z")

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You can’t use `reinterpret` because a `BigInt` is stored as a pointer and some lengths, but you can get at the raw bytes in a variety of ways, from low-level (exploit the raw pointer) to high-level. The best-documented way is to use the [`digits!` function](https://docs.julialang.org/en/v1/base/numbers/#Base.digits!):

```julia
julia> a = big(11)^100
137806123398222701841183371720896367762643312000384664331464775521549852095523076769401159497458526446001

jjulia> digits!(Vector{UInt8}(undef, ndigits(a; base=256)), a, base=256)
44-element Vector{UInt8}:
 0xb1
 0xe1
 0x4f
 0x64
 0xe2
 0x52
 0xe1
    ⋮
 0xcc
 0xf1
 0x0e
 0x71
 0xd8
 0x03

```

See also the discussion in [BigInt to bytes](https://discourse.julialang.org/t/bigint-to-bytes/91107) — since that discussion, `digits!` got optimized using `mpz_export` as explained in the thread.

What are you trying to accomplish?

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