- if you want to pass a pointer to the *complete* Julia type, including the
type tag, use pointer_from_objref. From the manual:
Julia values v can be converted to jl_value_t*pointers, as Ptr{Void}, by
> calling pointer_from_objref(v).
- if you want to pass a pointer to a C-compatible struct, tell ccall that
is what you want, and use the "&" symbol before the variable. From the
manual:
struct T* (where T represents an appropriately defined bits type)Ptr{T} (call
> using &variable_name in the parameter list)
Here is an example:
https://gist.github.com/ihnorton/1c1338a22fb3d143fa7f
Really the best way to work through these things is to write small examples
where you can control everything, and see what happens. Trying to figure it
out on the go in a large system with many moving pieces is a recipe for
frustration.
On Sun, Jan 18, 2015 at 9:28 AM, J Luis <jmfl...@gmail.com> wrote:
> Thank you very much Jiahao. That's indeed the result I want
>
> ... but sorry, I'm still confused. Why doesn't the other way work too? At
> the end it also gets composite type with the same members but with a
> whatever in their values.
>
> Also, I have here a case where it worked with unsafe_load() but crashes if
> I use unsafe_pointer_to_objref() (note that 'image' is a pointer to a
> composite type)
>
> https://github.com/joa-quim/IUP.jl/blob/master/examples/im_view_.jl#L106
>
> I read and reread the docs but find confusing what is a *memory address
> of a Julia object* is that apparently is different to the pointer
> obtained with convert()
>
>
> domingo, 18 de Janeiro de 2015 às 06:17:11 UTC, Jiahao Chen escreveu:
>
>> I don't think the conversion does what you want. Instead you may be
>> looking for this:
>>
>> julia> type foo a::Int; b::Int end
>>
>> julia> tp=foo(2,3)
>> foo(2,3)
>>
>> julia> p=pointer_from_objref(tp)
>> Ptr{Void} @0x00007fa70872e188
>>
>> julia> pt=unsafe_pointer_to_objref(p)
>> foo(2,3)
>>
>> Thanks,
>>
>> Jiahao Chen
>> Staff Research Scientist
>> MIT Computer Science and Artificial Intelligence Laboratory
>>
>
