COM C#, How to use C++ to call COM -

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i used online example of c# com , call through c++. following c# com code, 1 interface "icalc" , 1 class "calc".

namespace comlib { [guid("f40d7bc9-cf53-4613-aa5e-f269ad73808f")] [interfacetype(cominterfacetype.interfaceisidispatch)] public interface icalc {     [dispid(1)]     long factorial(int n); }  [guid("8ee38f2e-75be-4b45-87b6-3f6d15fdbbc5")] [classinterface(classinterfacetype.none)] [comsourceinterfaces(typeof(icalc))] [progid("mycalc")] public class calc : icalc {     long icalc.factorial(int n)     {         long fact = 1;         (int = 1; <= n; i++)             fact *= i;         return fact;     } } }

the following code in c++ call this function. worked. however, confused code in second line. "icalcptr" come from? or mechanism?

coinitialize(null);     comlib::icalcptr pcalc;     hresult hres = pcalc.createinstance(__uuidof(comlib::calc));     if(failed(hres))         printf("icalcptr::createinstance failed w/err 0x%08lx\n", hres);     else     {         printf("%d\n", pcalc->factorial(3));     }     system("pause");     couninitialize();     return 0;

if code works, because somewhere in c++ project, there following statement defined (it's automatic if used #import directive example):

_com_smartptr_typedef(icalc, __uuidof(icalc));

_com_smartptr_typedef macro defines "smart pointer" on icalc. it's microsoft visual c++ magical extension easier com support. official documentation here: _com_ptr_t class

a smart pointer referenced typedef definition provided _com_smartptr_typedef macro. macro takes interface name , iid , declares specialization of _com_ptr_t name of interface plus suffix of ptr.


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