Hi Isaiah, I have actually read your previous e-mails and they were very helpful! I am able to construct structs in Julia and pass them to C by mirroring the struct layout as a Julia immutable, but I still couldn't manage to get results back from C.
I tried writing a simple library to make figuring this out easier ( https://gist.github.com/jfsantos/9136352) but it seems the null pointer I pass to C is not changed after ccall (i.e., it is still a pointer to C_NULL) (please ignore the last few lines in test_ccall.jl, they are supposed to work only after I am able to convert the pointer to Cdvec). Could you point out where is my mistake? Thanks! -- João Felipe Santos On Fri, Feb 21, 2014 at 10:30 AM, Isaiah Norton <isaiah.nor...@gmail.com>wrote: > Sorry, I misread - ignore what I said about (1). > > > On Fri, Feb 21, 2014 at 10:25 AM, Isaiah Norton > <isaiah.nor...@gmail.com>wrote: > >> For (1) see here: >> >> http://julia.readthedocs.org/en/latest/manual/calling-c-and-fortran-code/#passing-pointers-for-modifying-inputs >> >> For (2) you do basically the same thing (varout = Ptr[C_NULL]). You need >> to have the struct layout mirrored as an immutable in Julia... search the >> list history for my name, for a very recent email with a detailed >> explanation. >> >> >> On Fri, Feb 21, 2014 at 10:13 AM, John Myles White < >> johnmyleswh...@gmail.com> wrote: >> >>> Re (1), check out the section on the & operator in the docs: >>> http://julia.readthedocs.org/en/latest/manual/calling-c-and-fortran-code/ >>> >>> It took me a while to figure out to use that operator, but I think it's >>> what you'll need. >>> >>> Not sure about (2). >>> >>> -- John >>> >>> On Feb 21, 2014, at 7:06 AM, João Felipe Santos <joao....@gmail.com> >>> wrote: >>> >>> > Hi, >>> > >>> > I am using ccall to write a wrapper for a C library in Julia and have >>> a couple of questions: >>> > >>> > 1. One of the functions I am wrapping gets several pointers to long >>> and double as arguments. Let's say I have a function signature as: >>> > >>> > int my_function(long* a, double* b). >>> > >>> > From the manual, I understood that I have to wrap it as: >>> > >>> > ccall((:my_function, "mylib"), Cint, (Ptr{Clong}, Ptr{Cdouble}, a, b) >>> > >>> > with a and b being Vector{Int64} and Vector{Float64} in Julia. >>> However, when I try to use this, I am getting back this error message: "no >>> method convert(Type{Int64}, Array{Int64,1})", which is weird, since I don't >>> try to do this conversion anywhere. What am I doing wrong? >>> > >>> > 2. Some functions in my library return pointers to structs and I would >>> like to be able to read these structs from Julia. I implemented these >>> strucs as bittypes but I'm not sure on how can I pass an "empty pointer to >>> struct" and get back a pointer to a struct allocated in C after my ccall. >>> Is it possible? >>> > >>> > Best regards >>> > >>> > -- >>> > João Felipe Santos >>> >>> >> >
