[julia-users] "Arrays of unknown size are not supported."

[Andre Manoel]

Hi,

I'm trying to call the following C function from Julia using ccall

void sum(Problem *P) {
    int i;
    printf("n = %d, res = %g\n", P->n, P->res);
    for (i = 0; i < P->n; i++) {
        P->res += P->x[i];
        printf("x[i] = %g, res = %g\n", P->x[i], P->res);
    }
}

which takes as argument the following struct

typedef struct Problem {
    int n;
    double *x;
    double res;
} Problem;

My Julia code is

type Problem
    n::Cint
    x::Ref{Cdouble}
    res::Cdouble
end

x = [1.3, 2.7, 4.9]
p = Problem(length(x), x, 0.)
ccall((:sum, "test"), Void, (Ref{Problem},), p)
println(p.res)

While I can read the n and res variables from inside the C function, I 
can't read the x array. According 
to http://docs.julialang.org/en/release-0.4/manual/calling-c-and-fortran-code/, 
"arrays of unknown size are not supported.". Is that the case here? Does 
anyone know if it would be too hard to lift this restriction?

Thanks,
Andre