On Sun, Jun 14, 2015 at 9:00 AM, Jan Strube <[email protected]> wrote:
> Thank you for your suggestions.
> I haven't tried Cxx.jl, since that apparently requires some effort
> installing a new LLVM, which makes it harder to convince others to use the
> bindings.
> Your second suggestion is unfortunately going in the wrong direction,
> taking a Julia array and passing it to C. It may be obvious to everybody
> else, but if the C code returns a Ptr{Ptr{Uint8}}, how can I convert this
> to an Array{String} on the Julia side?
>
That part is just about how to declare types for ccall. After you've got a
char**, you can just do the same you do in C to access them.
In julia, this is done with `unsafe_load`[3]
[3]
http://julia.readthedocs.org/en/latest/stdlib/c/?highlight=unsafe_load#Base.unsafe_load
> I read the manual back and forth, and I understand how to convert a
> Ptr{Uint8} to a String, using bytestring, but the extension to an Array
> eludes me.
>
>
>
>
> On Sunday, June 14, 2015 at 9:42:46 PM UTC+9, Yichao Yu wrote:
>
>>
>>
>> On Sun, Jun 14, 2015 at 2:04 AM, Jan Strube <[email protected]> wrote:
>>
>>> PPS: Sorry, the segfault actually is unrelated. Nevertheless, I can't
>>> figure out the right ccall signature.
>>>
>>
>> If you are on a new enough version, you can probably try Cxx.jl[1]
>> Otherwise, you probably need to do the conversion yourself. Have you
>> tried `Ptr{Ptr{Cchar}}`?[1]
>>
>> [1] https://github.com/Keno/Cxx.jl
>> [2]
>> http://julia.readthedocs.org/en/latest/manual/calling-c-and-fortran-code/?highlight=char**
>>
>>
>>>
>>>
>>> On Sunday, June 14, 2015 at 2:56:34 PM UTC+9, Jan Strube wrote:
>>>>
>>>> PS: My current attempt to return a char** from the vector<string> looks
>>>> like this:
>>>> I'm converting to a vector<const char*>, then returning the address of
>>>> the first element.
>>>>
>>>> const char* convert(const std::string& s)
>>>> {
>>>> return s.c_str();
>>>> }
>>>>
>>>> const char** lcevtgetcollectionnames( void* event ){
>>>> LCEventImpl* evt = static_cast<LCEventImpl*>(event);
>>>> const std::vector<std::string>* nameVec = evt->getCollectionNames();
>>>> std::vector<const char*>* names = new std::vector<const char*>;
>>>> std::transform(nameVec->begin(), nameVec->end(),
>>>> std::back_inserter(*names), convert);
>>>> return &(*names)[0];
>>>> }
>>>>
>>>>
>>>> On the Julia side I'm trying this signature:
>>>> ccall((:lcevtgetcollectionnames, "test.dylib"), Ptr{Cstring},
>>>> (Ptr{Void},), event)
>>>>
>>>> But this results in a seg fault
>>>>
>>>> signal (11): Segmentation fault: 11
>>>>
>>>> lcevtgetcollectionnames at /Users/stru821/Workdir/Julia/test.dylib
>>>> (unknown line)
>>>>
>>>> anonymous at no file:7
>>>>
>>>> jl_apply at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/./julia.h:1299
>>>>
>>>> jl_parse_eval_all at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/toplevel.c:573
>>>>
>>>> jl_load at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/toplevel.c:616
>>>>
>>>> include at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/lib/julia/sys.dylib
>>>> (unknown line)
>>>>
>>>> jl_apply at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/./julia.h:1299
>>>>
>>>> include_from_node1 at loading.jl:133
>>>>
>>>> jl_apply at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/gf.c:1632
>>>>
>>>> process_options at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/lib/julia/sys.dylib
>>>> (unknown line)
>>>>
>>>> _start at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/lib/julia/sys.dylib
>>>> (unknown line)
>>>>
>>>> jlcall__start_18703 at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/lib/julia/sys.dylib
>>>> (unknown line)
>>>>
>>>> jl_apply at
>>>> /Users/vagrant/buildbot/slave/package_osx10_9/build/src/./julia.h:1299
>>>>
>>>> true_main at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/bin/julia
>>>> (unknown line)
>>>>
>>>> main at
>>>> /Applications/Julia-0.4.0-dev-539c818c4e.app/Contents/Resources/julia/bin/julia
>>>> (unknown line)
>>>>
>>>> Segmentation fault: 11
>>>>
>>>>
>>>>
>>>>
>>>> On Sunday, June 14, 2015 at 2:43:24 PM UTC+9, Jan Strube wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I'm trying to wrap the LCIO file format http://lcio.desy.de/ in Julia.
>>>>> I have a proof of principle working and am starting to add more of the
>>>>> API.
>>>>>
>>>>> What totally stumps me is this signature:
>>>>> virtual const std::vector< std::string > *
>>>>> getCollectionNames
>>>>> <http://lcio.desy.de/v02-04-03/doc/doxygen_api/html/classEVENT_1_1LCEvent.html#a9128a3f65b8a94629c0cf5e77c0194ac>
>>>>> ()
>>>>> const =0
>>>>>
>>>>> http://lcio.desy.de/v02-04-03/doc/doxygen_api/html/classEVENT_1_1LCEvent.html#a9128a3f65b8a94629c0cf5e77c0194ac
>>>>>
>>>>> I've created a C library to call from Julia, so I'm happy to convert
>>>>> the return type to char**, but I just cannot figure out how to write a
>>>>> ccall that doesn't segfault.
>>>>> I've seen various examples how to convert a Julia array of strings to
>>>>> a char**, but couldn't find anything that converts a char** to Julia
>>>>> types.
>>>>>
>>>>> Any help is greatly appreciated.
>>>>>
>>>>> Jan
>>>>>
>>>>>
>>
