Hello all. I am new to D and loving the experience so far.
I am trying to make use of a C library from Canon that provides a
header and a pre-compiled binary containing implementations of
declarations found in the header. I used the excellent guide at
https://www.gamedev.net/articles/programming/general-and-gameplay-programming/binding-d-to-c-r3122/ to get started and so far I can initialize the library and embed it within my D application. So far so great!
Where I am running into problems is creating D bindings for this
function declaration:
// EDSDK.h
EdsError EDSAPI EdsGetCameraList(EdsCameraListRef*
outCameraListRef);
//
If accepts a pointer to EdsCameraListRef that is declared as:
// EDSDKTypes.h
typedef struct __EdsObject* EdsBaseRef;
typedef EdsBaseRef EdsCameraListRef;
//
From my reading I learned that EdsCameraListRef is an alias of an
alias for an opaque pointer. It allowed the library writers to
declare an object for use that the end-user would not have access
to the implementation of. These are the D bindings I created:
// edsdk.d
struct EdsBaseRef;
alias EdsBaseRef EdsCameraListRef;
alias uint EdsUInt32;
extern (System):
EdsError EdsGetCameraList(EdsCameraListRef*);
EdsError EdsGetChildCount(EdsBaseRef*, EdsUInt32*);
EdsUInt32 EdsRelease(EdsBaseRef*);
//
Calling the functions using the bindings and the following code
results in invalid pointer errors however (reported from the
library):
// camera_list.d
import edsdk;
class CameraList
{
private EdsCameraListRef* list;
private EdsUInt32 _count = 0;
this()
{
// Returns EDS_ERR_INVALID_POINTER
EdsGetCameraList(list);
// Returns EDS_ERR_INVALID_HANDLE
EdsGetChildCount(list, &_count);
}
~this()
{
EdsRelease(list);
}
final uint count()
{
return cast(uint) _count;
}
}
//
What did I do wrong in constructing the bindings? If it helps the
library provides a function called EdsRelease for cleaning-up
allocated objects. Is the management of pointers between D and C
the issue? Please forgive me if I've mangled that concept.
