COM Marshalling Problem

[copperleaf]

I'm trying to send a byte array to an out-of-process COM object. On the receiving side, the byte array has invalid data.
Here is my IDL definition:

HRESULT setData([in] BSTR name, [in, size_is(dataLen)] BYTE* data, [in] LONG dataLen);

My calling implementation is:

  BYTE* data = (BYTE *) CoTaskMemAlloc(tDataLen);
  CopyMemory(data, tData, tDataLen);  
  bool rc = SUCCEEDED(object->setData(_bstr_t(name), data, tdataLen));  
  CoTaskMemFree(data);

The fields name and dataLen are passed through ok and the first byte of the array is passed through. Does anybody know what I need to change to get the whole array passed?

Regards,
Bill

[Igor Vartanov]

There's nothing suspicious so far in your code, and the problem may be somewhere else. Try to isolate your problem and replicate it in a short and simple compilable project, and post it here to let us see where the problem may be.

[OReubens]

I'm not entirely sure you can send a raw data array out to another process just like that.
it might work with an in-process COM server, but out of process will need some kind of marshalling telling the one process how many bytes of data to transfer between the process spaces of the 2 executables. just because your function has a DataLen, doesn't mean the whole COM marshalling system knows about this too.

Sending arrays through COM is usually done with a SAFEARRAY.

[Igor Vartanov]

In fact, it's okay to send raw bytes, and size_is(dataLen) makes the trick be possible. Proxy/Stub library is built in accordance with the IDL, and takes care of marshaling. See the sample: AtlBytes.zip

As I said, the problem's somewhere else.