Error marshalling data

[gborges]

Hi all!

I am trying to code something more efficient, and so, I try do not use a loop in order to marshal the data which the app receives.

It throws an exception which I do not know how to handle it.

Does someone can help me?

I attach here a piece of relevant code and the error message. During the execution of this line:

Marshal.PtrToStructure(dst, finputDoublebuffer);

it occurs an exception.

Thank you in advance
Gustavo

    public class ds_param_value_buffer : Object {
        public ds_param_value_buffer(int sz) { 
		values = new ds_param_value[sz];
        }

        public ds_param_value [] values;
    };

	...
	public class DS {

        private ds_param_value_buffer finputDoublebuffer;   

        public DS() {
		...
		finputDoublebuffer = new ds_param_value_buffer((int)Constants.DSMAXDATAVISINPUTPARAMS);		
	}

	public static IntPtr IntPtr_Offset(IntPtr src,int offset) {
            switch (IntPtr.Size) {
                case 4:
                    return new IntPtr(src.ToInt64() + offset);
                case 8:
                    return new IntPtr(src.ToInt64() + offset);
                default:
                    throw new NotSupportedException("This is running on a machine where pointers are " 
                                                    + IntPtr.Size 
                                                    );
            }
        }

        private void MarshalIncommingData(){
            // manual marshalling to convert native incomming data to managed data
            IntPtr dst;            

            dst = IntPtr_Offset(funmanagedinputbuffer,0);
/////////////////
            Marshal.PtrToStructure(dst, finputDoublebuffer); //ERROR HERE
/////////////////
	    return;
        }


        private ds_status handle_data() {
		...
                switch(status){
                    case ds_status.DS_OK:
                        // Do manual marshalling of the incomming data
                        MarshalIncommingData();
                        if (fOnEvtData != null) {
                            // Fire "on data" event
                            EvtDataArgs args = new EvtDataArgs(timestamp, ref finputDoublebuffer);
                            fDispatcher.Invoke(DispatcherPriority.Normal, fOnEvtData, this, args);
                            args = null;
                        }
                        break;
		    ...
                }//switch  
		...
                return status;
        }

	...
	}

Error Message:
System.ArgumentException was unhandled
  Message="The specified structure must be blittable or have layout information.\r\nParameter name: structure"
  Source="mscorlib"
  ParamName="structure"
  StackTrace:
       at System.Runtime.InteropServices.Marshal.PtrToStructureHelper(IntPtr ptr, Object structure, Boolean allowValueClasses)
       at System.Runtime.InteropServices.Marshal.PtrToStructure(IntPtr ptr, Object structure)
       at DSI.DS.MarshalIncommingData() in DS.cs:line 827
       at DSI.DS.handle_data() in DS.cs:line 847
       at DSI.DS.handle_event(ds_dv_event_type evt, StringBuilder errmsgbuf) in DS.cs:line 980
       at DSI.DS.ds_evt_deamon() in DS.cs:line 1024
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

[darwen]

Basically the structure (which you haven't shown) has types in it that .NET can't automatically turn into native types.

Post the structure and maybe I can help further.

Darwen.

[darwen]

Oops - sorry, just noticed your structure (or class) in your post above.

Firstly - it's a class which won't work with PtrToStructure because (and no prizes for guessing this one) ITS NOT A STRUCTURE ! ITS A CLASS !

OK you might not know that there are big differences between structures and classes in .NET - unlike C++ where they're the same things.

FYI PtrToStructure works with structures. Not classes.

Turn it into a struct and try again.

Darwen.

[vcdebugger]

Even after changing it to Struct if still the problem repeats, then there might be mismatch between the structure fields between application and the unmanaged side