Ah, I see! Your suggestion works indeed. Thanks :-)
Le mercredi 6 janvier 2016 05:25:30 UTC+1, Isaiah a écrit :
>
> This doesn't work because the `x::Ref` field is a pointer to the Julia
> object `x`, rather than a pointer to the data
>
> (modifying your code to print x):
>
> julia> ccall((:sum, "test"), Void, (Ref{Problem},), p)
> n = 3, res = 0
> x = 0x10d569d90
> ...
>
> julia> unsafe_pointer_to_objref(convert(Ptr{Void}, 0x10d569d90))
> Base.RefArray{Float64,Array{Float64,1},Void}([1.3,2.7,4.9],1,nothing)
>
>
> The following works, but if you hold the pointer or call back in to a
> Julia `cfunction` during the ccall, make sure that x is not garbage
> collected (for example, by holding a reference to it in a global array).
>
> type Problem
> n::Cint
> x::Ptr{Cdouble}
> res::Cdouble
> end
>
> ...
>
> p = Problem(length(x), pointer(x), 0.)
>
>
> On Mon, Jan 4, 2016 at 6:07 AM, Andre Manoel <[email protected]
> <javascript:>> wrote:
>
>> 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
>>
>
>
