Yup, that's the hacky solution :)
I modified my example after copying it and didn't fix the last part. Here's
a working version:
julia> err = ccall( (:midiOutGetDevCapsA, :Winmm), Uint64, (Ptr{Uint64},
Ref{Mid
iOutCaps}, Uint32), 0, output_struct, sizeof(output_struct))
WARNING: convert(::Type{Ptr}, ::Int64) methods should be converted to be
methods
of unsafe_convert
in depwarn at deprecated.jl:73
in unsafe_convert at no file:398
in anonymous at no file
while loading no file, in expression starting on line 0
0x0000000000000000
julia> bytestring(Ptr{Cchar}(pointer_from_objref(output_struct[].szPname)))
"Microsoft GS Wavetable Synth"
(for some reason I haven't investigated yet, passing the device id as a Ref
doesn't work)
Possibly of interest, I have some example code calling a few Win32 API
functions here:
https://github.com/ihnorton/Win32GUIDemo.jl
https://github.com/ihnorton/COMCall.jl
(there are also some examples in base, the implementation of `download` for
example)
On Mon, Sep 7, 2015 at 10:29 AM, Joel Hobson <[email protected]> wrote:
> Sorry about the last post - I'm new, so it was caught in the moderation
> filter. I actually wrote it before Tony and Isaiah posted.
> Isaiah - That looks promising, thanks! It's been a long time since I've
> used C, so I completely missed that szPname isn't a pointer.
>
> On Sunday, 6 September 2015 17:37:01 UTC-4, Joel Hobson wrote:
>
>> Hi all,
>>
>> I'm trying to use some C functions, but I'm running into trouble using
>> the results.
>>
>> This is the function I'm trying to call:
>> https://msdn.microsoft.com/en-us/library/dd798469(v=vs.85).aspx
>> And this is the struct that it's expecting a pointer to:
>> https://msdn.microsoft.com/en-us/library/dd798467(v=vs.85).aspx
>>
>> Here's my struct definition in Julia:
>>
>> type MidiOutCaps
>> wMid::Uint16
>> wPid::Uint16
>> vDriverVersion::Uint32
>> szPname::Ptr{Uint8}
>> wTechnology::Uint16
>> wVoices::Uint16
>> wNotes::Uint16
>> wChannelMask::Uint16
>> dwSupport::Uint32
>>
>> MidiOutCaps() = new(0, 0, 0, Array(Uint8, 32), 0, 0, 0, 0, 0)
>> end
>>
>> And the function for loading it:
>>
>> function getoutputdeviceswindows()
>> numberofdevices = ccall( (:midiOutGetNumDevs, :Winmm), Int32, ())
>>
>> for i in [0:numberofdevices-1]
>> output_struct = MidiOutCaps()
>>
>> err = ccall( (:midiOutGetDevCapsA, :Winmm), Uint32, (Ptr{Uint32},
>> Ptr{MidiOutCaps}, Uint32), i, &output_struct, sizeof(output_struct))
>>
>> println("Err is $(err)")
>> println("Result is $(output_struct)")
>>
>> println("Result name is $(unsafe_load(output_struct.szPname, 0))")
>> end
>> end
>>
>> Both ccalls execute without error, and it appears to populate the struct
>> correctly, but when I try to do an unsafe load on the szPname, Julia
>> crashes and I get this:
>>
>> Please submit a bug report with steps to reproduce this fault, and any
>> error messages that follow (in their entirety). Thanks.
>> Exception: EXCEPTION_ACCESS_VIOLATION at 0xdbc6d34 -- unsafe_load at
>> pointer.jl:45
>> unsafe_load at pointer.jl:45
>> jlcall_unsafe_load_1323 at (unknown line)
>> jl_apply_generic at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> jl_interpret_toplevel_expr at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> jl_interpret_toplevel_thunk_with at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> jl_eval_with_compiler_p at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> jl_f_top_eval at C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll
>> (unknown line)
>> eval_user_input at REPL.jl:53
>> jlcall_eval_user_input_1054 at (unknown line)
>> jl_apply_generic at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> anonymous at task.jl:95
>> jl_handle_stack_switch at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> julia_trampoline at
>> C:\Users\Joel\AppData\Local\Julia-0.3.9\bin\libjulia.dll (unknown line)
>> unknown function (ip: 4202784)
>> unknown function (ip: 4199370)
>> unknown function (ip: 4199672)
>> BaseThreadInitThunk at C:\WINDOWS\system32\KERNEL32.DLL (unknown line)
>> RtlUserThreadStart at C:\WINDOWS\SYSTEM32\ntdll.dll (unknown line)
>> RtlUserThreadStart at C:\WINDOWS\SYSTEM32\ntdll.dll (unknown line)
>>
>> I suspect that it's a problem with my code and not Julia, which is why I
>> haven't submitted a bug report yet.
>>
>> I've tried just setting szPname to 0 instead of an array, and I've tried
>> different index values for unsafe_load, but no luck. Any ideas where I'm
>> going wrong? The only other issue I can see is that MSDN defines szPname to
>> be an array of TCHARs, but according to the MSDN, TCHAR is just a char.
>> https://msdn.microsoft.com/en-us/library/office/cc842072.aspx
>>
>> Thanks!
>>
>>
>>
>>
