# L-10 MCS 507 Wed 13 Sep 2023 : callqsort.jl

"""
We will wrap the C function qsort.

void qsort(void *base, size_t nmemb, size_t size,
           int (*compare)(const void*, const void*));

The C qsort needs a callback function compare,
to define the order between the elements to be sorted.
"""

"""
    mycompare(a, b)

Comparison function (Julia) to pass to qsort (C).
"""
function mycompare(a, b)::Cint
    return (a < b) ? -1 : ((a > b) ? +1 : 0)
end

# To pass this Julia function to C,
# we use the macro @function.

mycompare_c = @cfunction(mycompare, Cint, (Ref{Cdouble}, Ref{Cdouble}));

println("A random sequence of numbers :")
A = rand(16, 1)
println(A)

println("Calling qsort ...")

ccall(:qsort, Cvoid, (Ptr{Cdouble}, Csize_t, Csize_t, Ptr{Cvoid}),
      A, length(A), sizeof(eltype(A)), mycompare_c)

println("The sorted sequence :")
println(A)