I'm attempting a managed implementation of a COM interface, which
enumerates structures... (The interface is ISyncMgrEnumItems, defined
in MobSync.idl, for anyone who wants to play along.)
Here's the relevant snippet of IDL:
HRESULT Next(
[in] ULONG celt,
[out, size_is(celt), length_is(*pceltFetched)]
LPSYNCMGRITEM rgelt,
[out] ULONG *pceltFetched);
SYNCMGRITEM is a (fairly hefty) struct composed of simple, blittable
types, including an in-place character array:
typedef struct _tagSYNCMGRITEM {
DWORD cbSize;
DWORD dwFlags;
SYNCMGRITEMID ItemID;
DWORD dwItemState;
HICON hIcon;
WCHAR wszItemName[128];
FILETIME ftLastUpdate;
} SYNCMGRITEM, *LPSYNCMGRITEM;
The Problem: I'm not sure what to make of the 'LPSYNCMGRITEM rgelt'
parameter in the method declaration. It's a top-level pointer to an
array, but it's an [out] parameter. So if I declare it with the C#
'out' keyword, I believe I'll end up with one too many levels of
indirection:
int Next(
int celt,
out SyncMgrItem[] rgelt, // pointer-to-a-pointer?
out int pceltFetched);
Will UnmanagedType.ByValArray rectify this?
int Next(
int celt,
[MarshalAs(UnmanagedType.ByValArray)] out SyncMgrItem[] rgelt,
out int pceltFetched);
Or, should I model it as a top-level pointer to an array, and specify
the direction with the [Out] attribute?
int Next(
int celt,
[Out] SyncMgrItem[] rgelt,
out int pceltFetched);
And in either case, how should I specify the size -- SizeParamIndex?
Which param?
Thanks in advance, interop gurus...
-Shawn
http://msdn.com/tabletpc
http://windojitsu.com
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