How to pass a SAFEARRAY from C# to COM?

Question

I have an ATL COM Server, where the method for the interface is

CVivsBasic::UpdateSwitchPlan(BSTR plan_name, SAFEARRAY* plan)

And the IDL for this function looks like

typedef struct  
{   
    LONG time_to_play;
    BSTR ecportid;
} SwitchPlanItem;
HRESULT UpdateSwitchPlan([in] BSTR plan_name, [in] SAFEARRAY(SwitchPlanItem) plan) ;    

I tried to call it from C# like this:

        internal void UpdateSwitch(string plan_name, string ecportid)
    {
        SwitchPlanItem sp1;
        sp1.time_to_play = 33;
        sp1.ecportid = ecportid;

        SwitchPlanItem sp2;
        sp2.time_to_play = 33;
        sp2.ecportid = ecportid;

        SwitchPlanItem[] sps = { sp1, sp2 };

        sdk.UpdateSwitchPlan(plan_name, sps);
    }

But it crash. What is the correct way to pass a SAFEARRAY from C# to COM?

Answer 1

I think the problem here is that you're using a SAFEARRAY of user defined types (UDT), SAFEARRAY s of VARIANT , BSTR and IUnknown work out of the box but for UDT s you need to help the marshaller along. See this article in MSDN regarding Passing Safearray of UDTs .

Answer 2

I think the answer to this question is similar to this one: COM - [in] parameter as SAFEARRAY(STRUCT)

Basically, the C# client that is using an interface where SAFEARRAY(STRUCT) are passed in, has to define Embed Interop Types = False on the imported COM server reference properties.