export SHGLQ!
function SHGLQ!(zero::AbstractVector{Cdouble}, w::AbstractVector{Cdouble},
                plx::Optional{AbstractArray{Cdouble,2}}, lmax::Integer;
                norm::Integer=1, csphase::Integer=1, cnorm::Integer=0,
                exitstatus::Optional{Ref{<:Integer}}=nothing)
    @assert length(zero) ≥ lmax + 1
    @assert length(w) == length(zero)
    @assert lmax ≥ 0
    if plx !== nothing
        @assert size(plx) == (lmax + 1, (lmax + 1) * (lmax + 2) ÷ 2)
    end
    @assert norm ∈ (1, 2, 3, 4)
    @assert csphase ∈ (1, -1)
    @assert cnorm ∈ (0, 1)
    exitstatus′ = Ref{Cint}()
    ccall((:SHGLQ, libSHTOOLS), Cvoid,
          (Cint, Ptr{Cdouble}, Ptr{Cdouble}, Ptr{Cdouble}, Ref{Cint}, Ref{Cint},
           Ref{Cint}, Ref{Cint}), lmax, zero, w, optional(plx, Ptr{Cdouble}()),
          norm, csphase, cnorm, exitstatus′)
    if exitstatus === nothing
        exitstatus′[] ≠ 0 && error("SHGLQ!: Error code $(exitstatus′[])")
    else
        exitstatus[] = exitstatus′[]
    end
    return zero, w
end

export SHGLQ
function SHGLQ(plx::Optional{AbstractArray{Cdouble,2}}, lmax::Integer;
               norm::Integer=1, csphase::Integer=1, cnorm::Integer=0,
               exitstatus::Optional{Ref{<:Integer}}=nothing)
    @assert lmax ≥ 0
    zero = Array{Cdouble}(undef, lmax + 1)
    w = Array{Cdouble}(undef, lmax + 1)
    if plx !== nothing
        @assert size(plx) == (lmax + 1, (lmax + 1) * (lmax + 2) ÷ 2)
    end
    SHGLQ!(zero, w, plx, lmax; norm=norm, csphase=csphase, cnorm=cnorm,
           exitstatus=exitstatus)
    return zero, w

end

end
@testset "SHGLQ" begin
    zero, w = SHGLQ(nothing, 4)