Passing data from C# to unmanaged C++ (using COM Interop)

Question

I'm using Com Interop method to communicate with unmanaged C++ and C#.

I need to send data to unmanaged C++ from C#.

Im already sending "bool" values values from C# & accessing it through "VARIANT_BOOL*" in c++.

I need to send a integer from C#. How can i access that integer value in unmanaged c++ side ?

for example:

C#

 public int myValue()
        {
            return 5;
        }

Unmanaged C++

CoInitialize(NULL);
MyNSpace::MyClassPtr IMyPointer;

 HRESULT  hRes =  IMyPointer.CreateInstance(MyNSpace::CLSID_MyClass);

if (hRes == S_OK)
{
//// ??? define x type

IMyPointer->myValue(x);

}

You might take a look at msdn.microsoft.com/en-us/library/aa910805.aspx, where you can find several com interop conform variant types. I would guess you should use VT_I4. But keep in mind that the length of your C++ integer type can differ from the default C# 32-Bit integer. (This depends on the compiler.) But usually it is handled by the definition of your VARIANT structure — Christoph Meißner
– Christoph Meißner, Commented Sep 30, 2013 at 10:05
Thanks.But ".tlh" file(generated by compiler) has diferent type defined. virtual HRESULT __stdcall myValue( /*[out,retval]*/ long * pRetVal ) = 0; — Devshan
– Devshan, Commented Sep 30, 2013 at 10:17
So you know that you need a long x; and call it with IMyPointer->myValue(&x); — Hans Passant
– Hans Passant, Commented Sep 30, 2013 at 10:25

borx · Accepted Answer · 2013-09-30 12:52:36Z

1

COM allows to use plain (native) integer types, for example LONG. COM LONG stands for 32-bit signed integer in C++. For example,

HRESULT myValue([out, retval] LONG* nOutVal);

In client (c++) code you just have to declare an ordinal int variable:

if (hRes == S_OK)
{
    int x;
    hRes = IMyPointer->myValue(x);

}

edited Sep 30, 2013 at 12:52

answered Sep 30, 2013 at 10:13

borx

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