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add an example of using sizeof on a struct with padding #47342

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Nov 3, 2022
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add an example of using sizeof on a struct with padding #47342

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11 changes: 11 additions & 0 deletions base/essentials.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -539,6 +539,17 @@ julia> sizeof(1.0)

julia> sizeof(collect(1.0:10.0))
80

julia> struct StructWithPadding
x::Int64
flag::Bool
end

julia> sizeof(StructWithPadding) # not the sum of `sizeof` of fields due to padding
16
Comment on lines +548 to +549
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Keno had proposed changing this (#46322), though we didn't finish

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So is this PR fine or is it an implementation detail of what number this should report when it comes to structs with padding?

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The exact number here is definitely an implementation detail. For example, on 32-bit platforms this returns:

julia> sizeof(StructWithPadding)
12


julia> sizeof(Int64) + sizeof(Bool) # different from above
9
```

If `DataType` `T` does not have a specific size, an error is thrown.
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