Check size in bytes of variable using Julia

Question

Question: How do I check the size in bytes of a variable using Julia?

What I've tried: In Matlab, the whos() function provided this information, but in Julia that just provides the variable names and module. Browsing the standard library in the Julia manual, sizeof() looked promising, but it only appears to provide the size of the canonical binary representation, rather than the current variable.

waTeim waTeim · Accepted Answer · 2015-02-09T07:11:10

sizeof works on variables too

sizeof(a::Array{T,N})

returns the size of the array times the element size.

julia> x = [1 2 3 4]
1x4 Array{Int64,2}:
 1  2  3  4

julia> sizeof(x)
32

julia> x = Int8[1 2 3 4]
1x4 Array{Int8,2}:
 1  2  3  4

julia> sizeof(x)
4

sizeof(B::BitArray{N})

returns chunks; each chunk is 8 bytes so can represent up to 64 bits

julia> x = BitArray(36);
julia> sizeof(x)
8 

julia> x = BitArray(65);
julia> sizeof(x)
16

sizeof(s::ASCIIString) and sizeof(s::UTF8String)

return the number of characters in the string (1 byte/char).

julia> sizeof("hello world")
11

sizeof(s::UTF16String) and sizeof(s::UTF32String)

Same as above but with 2 and 4 bytes/character respectively.

julia> x = utf32("abcd");
julia> sizeof(x)
16

Accordingly other strings

sizeof(s::SubString{ASCIIString}) at string.jl:590
sizeof(s::SubString{UTF8String}) at string.jl:591
sizeof(s::RepString) at string.jl:690
sizeof(s::RevString{T<:AbstractString}) at string.jl:737
sizeof(s::RopeString) at string.jl:802
sizeof(s::AbstractString) at string.jl:71

core values

returns the number of bytes each variable uses

julia> x = Int64(0);
julia> sizeof(x)
8

julia> x = Int8(0);
julia> sizeof(x)
1

julia> x = Float16(0);
julia> sizeof(x)
2

julia> x = sizeof(Float64)
8

one would expect, but note that Julia characters are wide characters

julia> sizeof('a')
4

getBytes

For cases where the layout is more complex and/or not contiguous. Here's a function that will iterate over the fields of a variable (if any) and return of sum of all of the sizeof results which should be the total number of bytes allocated.

getBytes(x::DataType) = sizeof(x);

function getBytes(x)
   total = 0;
   fieldNames = fieldnames(typeof(x));
   if fieldNames == []
      return sizeof(x);
   else
     for fieldName in fieldNames
        total += getBytes(getfield(x,fieldName));
     end
     return total;
   end
end

using it

create an instance of a random-ish type...

julia> type X a::Vector{Int64}; b::Date end

julia> x = X([i for i = 1:50],now())
X([1,2,3,4,5,6,7,8,9,10  …  41,42,43,44,45,46,47,48,49,50],2015-02-09)

julia> getBytes(x)
408