Function pointer as a parameter of COM method

问题

I have created COM server in C++ that is used from C# application. Now I have to add one more method to my COM object and one of its parameter must be function pointer to callback function. C++ original function looks like this:

typedef int (__stdcall *tCallBackFunc)(int Param);

void MyFunc(void* CallBackFunc)
{
  int Param;
  //some code
  ((tCallBackFunc)(CallBackFunc))(Param); //call callback function
}

I need to add MyFunc as COM object method. VS VC++ "Add Method" dialog offers some predefined types for COM method parameter like "int*" or "bstr", I tried to define "CallBackFunc" parameter as "int*" type, but I was not able to make it work in C#:

public delegate int  tCallBackFunc(int Param);
...
tCallBackFunc cb; //I will initialize it when it is compiled
MyCOMObject.MyFunc(cb); //cannot find any way to cast cb to "ref int"

It seems I use wrong approach, is there a fast way to declare function pointer as parameter of COM object method in C++ and then use it in C#?

回答1:

The COM way is to make the parameter an interface pointer, and have the interface declare the callback function.

回答2:

+1 for Frederik's answer.

@Michael: It will prove a lot easier than your imagined solution. Especially with

object lifetimes
process boundaries
thread safety (apartment boundaries, IOW)
standards conformance (casting function pointers quickly enters the domain of Undefined Behaviour). Why should you worry? Standards conformance must concern you in case a compiler update introduces another optimization that makes your old (non-conformant) code break

来源：https://stackoverflow.com/questions/7875502/function-pointer-as-a-parameter-of-com-method

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