Interoperability between COM client and .NET Server

[Bobby2001]

I am looking into the COM Interoperating Sample from MSDN:
COM Client and .NET Server:

msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconexposingnetframeworkcomponentstocom.asp

The .NET Server defines ILoan interface which is implemented by Loan class in C#.
The function "ComputePayment" defined and implemented as follows:
namespace LoanLib {

public interface ILoan {
...
double ComputeOpeningBalance();
...
};

public class Loan : ILoan {
...
public double ComputePayment() {
Payment = Util.Round(OpeningBalance * (Rate / (1 -
Math.Pow((1 + Rate), - Term))), 2);
return Payment;
}
...
};
}

Here is question:

When this function is called from VC++ 6.0 client, the signature of this function is quite different.

pILoan->ComputePayment(&payment);

The return value is moved to the end of argument list. Can anyone explain
why this is happening? Thanks

[jwalto1]

Hi Bobby,

Its COM. COM always returns a HRESULT (hopefully S_OK). The parameter that the client receives back (such as VB or VBScript) is passed as an [out, retval] parameter.

See http://www.codeguru.com/forum/showthread.php?t=302058

Jeff