# Bug in julia zeros() side effects

**URL:** <https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [February 25, 2022, 2:32am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046 "2022-02-25T02:32:13Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![herm](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/herm/32/14268_2.png) [@herm](https://discourse.julialang.org/u/herm)\
**Post date:** [February 25, 2022, 2:32am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046/1 "2022-02-25T02:32:13Z")

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Julia Version 1.7.2 (2022-02-06)

I experienced some side effects of the initialization with zeros.  
Good to know…

# buggy

function compute\_k1!(nfft::Int64,kvec::Vector{ComplexF64})  
kvec=zeros(ComplexF64,nfft)  
for i=1:nfft  
kvec[i]=i+1im  
end  
end

# no bug

function compute\_k2!(nfft::Int64,kvec::Vector{ComplexF64})  
for i=1:nfft  
kvec[i]=i+1im  
end  
end

nfft=10  
kvec1=zeros(ComplexF64,nfft)  
compute\_k1!(nfft,kvec1)  
println(kvec1)  
kvec2=zeros(ComplexF64,nfft)  
compute\_k2!(nfft,kvec2)  
println(kvec2)

first println  
10-element Vector{ComplexF64}:  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
0.0 + 0.0im  
second println  
ComplexF64[1.0 + 1.0im, 2.0 + 1.0im, 3.0 + 1.0im, 4.0 + 1.0im, 5.0 + 1.0im, 6.0 + 1.0im, 7.0 + 1.0im, 8.0 + 1.0im, 9.0 + 1.0im, 10.0 + 1.0im]

Obviously there is side effects on using zeros…

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<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [February 25, 2022, 2:33am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046/2 "2022-02-25T02:33:32Z")

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This isn’t a bug. This is just that Julia is pass by sharing.

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**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [February 25, 2022, 3:20am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046/3 "2022-02-25T03:20:34Z")

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In the function `compute_k1!` you create a local array which masks `kvec`  
passed as argument. The argument is not modified. Delete the line which  
calls `zeros`. If you really want to set `kvec` to zero on that line, use `kvec .= zero(eltype(kvec))`.

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<div class="post-metadata">

**Author:** ![herm](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/herm/32/14268_2.png) [@herm](https://discourse.julialang.org/u/herm)\
**Post date:** [February 26, 2022, 9:30am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046/4 "2022-02-26T09:30:09Z")

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> [@PetrKryslUCSD](#):
>
> `kvec .= zero(eltype(kvec))` .

Thank you for the response, topics closed

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**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [February 26, 2022, 9:48am UTC](https://discourse.julialang.org/t/bug-in-julia-zeros-side-effects/77046/5 "2022-02-26T09:48:14Z")

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