Marshalling for C struct with arrays

[Markus Stiller]

Could someone give me an hint?

I have trouble with mashaling of a struct. I can set values in struct
(byVAL) but cant read from the struct. Its an long pointer struct in a
c dll.

thats my struct where is correct i guess

'-----------------------------------
' structure declarations
' xl event
<StructLayout(LayoutKind.Sequential, Pack:=1)> Structure s_xlEvent
Public tag As Byte
Public chanIndex As Byte
Public transID As Short
Public porthandle As Short
Public reserved As Short
Public timestamp As UInt64
<FieldOffset(0)> Public tagdata_can_msg As s_xl_can_msg
<FieldOffset(0)> Public tagdata_chipstate As s_xl_chipstate
<FieldOffset(0)> Public tagdata_lin_msg As s_xl_lin_msg_api
<FieldOffset(0)> Public tagdata_sync_pulse As s_xl_sync_pulse
<FieldOffset(0)> Public tagdata_daio_data As s_xl_daio_data
<FieldOffset(0)> Public tagdata_transceiver As
s_xl_transceiver
End Structure


Structure s_xl_can_msg
Public id As UInt32
Public flags As Short
Public dlc As Short
Public res1 As UInt64
<MarshalAs(UnmanagedType.ByValArray, SizeConst:=8)> Public
data As Byte()
Public res2 As UInt64
End Structure


' function to fill/set struct with array - this is successful

Public Declare Function xlCanTransmit Lib "vxlapi.dll" (ByVal
PortHandle As UInt32, ByVal accessmask As UInt64, ByRef messageCount
As UInt16, <MarshalAs(UnmanagedType.LPArray)> ByVal pMessages As
s_xlEvent()) As Byte

' function to read frome struct with array - this is the problem

Public Declare Function xlReceive Lib "vxlapi.dll" (ByVal PortHandle
As UInt32, ByRef pEventCount As UInt16,
<MarshalAs(UnmanagedType.LPArray)> ByRef pMessages As s_xlEvent()) As
Byte

Problem SizeParamIndex is not allowed to with byref parameter
Any suggestions?

 

[Mattias Sjögren]

Markus,

What does the original native function signature look like? Are you
sure that pMessages should be ByRef in the xlReceive function?



Mattias

 

[Markus Stiller]

the original function is that. The driver dll I ask is an c dll and
will give me a pointer back to this structure. I saw that the call is
successful and values are returned in the debug messages of dll.

#ifdef DYNAMIC_XLDRIVER_DLL
typedef XLstatus (_EXPORT_API *XLRECEIVE) (
XLportHandle portHandle,
unsigned int *pEventCount,
XLevent *pEvents);
#else
XLstatus _EXPORT_DECL xlReceive(
XLportHandle portHandle,
unsigned int *pEventCount,
XLevent *pEvents);
#endif

Markus

 

[Mattias Sjögren]

Markus,

Looks like the array should be passed ByVal after all. Try this

Public Declare Function xlReceive Lib "vxlapi.dll" (ByVal PortHandle
As UInt32, ByRef pEventCount As UInt16, <Out> ByVal pMessages As
s_xlEvent()) As Byte



Mattias