Ok, I found embedding.c. Allocating Julia arrays as given in the example
there works. In Julia, I specify the return type of the C function as Any,
and I get a nice tuple.
On Thursday, April 10, 2014 12:30:18 AM UTC-7, Dominique Orban wrote:
>
> Thanks for the suggestions. Changing the return type results in complaints
> from Julia:
>
> ERROR: error compiling anonymous: in anonymous: ccall: missing return type
>
>
> or
>
> ERROR: error compiling anonymous: error interpreting ccall return type:type
> cannot be constructed
>
>
>
> Using a single variable name on the left-hand side is an improvement and I
> was just experimenting with that. Perhaps unsafe_pointer_to_objref() is
> relevant here, but it gave me a segfault...
>
> On Thursday, April 10, 2014 12:25:40 AM UTC-7, Tobias Knopp wrote:
>>
>> Hi, this is more a guess but could you try changing the return type in
>> ccall to NTuple{3,Ptr{Any}}? Or maybe just Tuple. Further you could try
>> using on the left hand site only a single variable name, i.e.
>>
>> tup = = ccall((:my_c_function, "mylib"), Tuple, ())
>>
>> Am Donnerstag, 10. April 2014 09:15:30 UTC+2 schrieb Dominique Orban:
>>>
>>> My use case is a C function that creates a sparse matrix in triplet form
>>> (rows, cols, vals). What's the appropriate way to return this to Julia?
>>> I've tried the following, thinking that Julia accepts C pointers as return
>>> values, so why not tuples of C pointers:
>>>
>>> jl_value_t *my_c_function(void) {
>>>
>>> jl_tuple_t *tuple = jl_alloc_tuple(3);
>>> long *rows, *cols;
>>> double *vals;
>>>
>>> // allocate and populate rows, cols and vals...
>>>
>>> jl_tupleset(tuple, 0, rows);
>>> jl_tupleset(tuple, 1, cols);
>>> jl_tupleset(tuple, 2, vals);
>>>
>>> return (jl_value_t*)tuple;
>>> }
>>>
>>> (The intention is then to call ptr_to_array() on each component of the
>>> tuple.) In Julia, I call this C function as follows:
>>>
>>> (rows, cols, vals) = ccall((:my_c_function, "mylib"), Ptr{Any}, ())
>>>
>>> But that gives me
>>>
>>> ERROR: no method start(Ptr{Any})
>>>
>>> I'm sure there's more than one mistake in that code, but I'm not finding
>>> documentation on the Julia API.
>>>
>>> Thanks!
>>>
>>
