elements. The final call to qsort looks like this: julia> A = [1.3, -2.7, 4.4, 3.1] 4-element Array{Float64,1}: 1.3 -2.7 4.4 3.1 julia> ccall(:qsort, Cvoid, (Ptr{Cdouble}, Csize_t, Csize_t, Ptr{Cvoid}) Array{Float64,1}: 36.2. MAPPING C TYPES TO JULIA 319 -2.7 1.3 3.1 4.4 As can be seen, A is changed to the sorted array [-2.7, 1.3, 3.1, 4.4]. Note that Julia takes care of conver�ng the array to a Ptr{Cdouble}) usually also require fine-grained control over the factoriza�on of A. Examples julia> A = [1 2.2 4; 3.1 0.2 3; 4 1 2]; julia> X = [1; 2.5; 3]; julia> Y = zero(X); julia> ldiv!(Y, qr(A), X); julia> Y

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Variables 7 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4CHAPTER

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Variables 7 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4CHAPTER

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Installation 7 3.1 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Mac related from your PATH variable and then install Julia with one of the methods described below. 3.1 Windows On Windows Julia can be installed directly from the Windows store here. One can also install -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 As the

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Installation 7 3.1 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Mac related from your PATH variable and then install Julia with one of the methods described below. 3.1 Windows On Windows Julia can be installed directly from the Windows store here. One can also install -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 As the

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Variables 6 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 CHAPTER

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Variables 7 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 CHAPTER

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Variables 6 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 CHAPTER

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Variables 7 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 CHAPTER

Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Variables 7 3.1 Allowed Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Assignment 0 julia> sqrt = 4 ERROR: cannot assign a value to imported variable Base.sqrt from module Main 3.1 Allowed Variable Names Variable names must begin with a letter (A-Z or a-z), underscore, or a subset -2.7, 4.4, 3.1]; julia> @ccall qsort(A::Ptr{Cdouble}, length(A)::Csize_t, sizeof(eltype(A))::Csize_t, mycompare_c::Ptr{Cvoid})::Cvoid �→ julia> A 4-element Vector{Float64}: -2.7 1.3 3.1 4.4 CHAPTER