int main { fstream fout("data.dat", ios::in | ios::out | ios::binary); Names name; <--- not a pointer name.s1.assign("abc"); name.s2.assign("xyz"); fout.write((char*)name, sizeof(Names)); <--- never thought you can cast fout.close a structure to a pointer to } char. Either this works for weird reasons, or you made a mistake copying (char *)&name.

Stack-based variables, as opposed to heap-based variables (i.e., those created with new), are cleaned up when the variable goes out of scope. "Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

And there's a strange thing that: If I write: fstream *fout; fout = new fstream("data.dat", ios::in | ios::out | ios::binary); if (!fout->is_open()) { cout << " can't open the file" << endl; return 1; } fout->write((const char*)name, sizeof(Names)); ---> the result is "can't open the file"; But if I don't check if the file is open. fstream *fout; fout = new fstream("data.dat", ios::in | ios::out | ios::binary); fout->write((const char*)name, sizeof(Names)); --> there's no error but there's no file created. I think if the file doesn't exist, the instruction "fout->write((const char*)name, sizeof(Names));" should cause an error. Right?

You could also take a look at aggregation and containment if you are trying to perform it from the server side. It is not necessarily that COM doesn't support good programming practice, the whole reason for the development of COM was to insulate the client from the details of implementation; thus implementation inheritance is out of the question since it requires too much detailed information over how the "insides" work. COM does support interface inheritance, which is developed through aggregation and containment. These tools allow you to specialize COM interfaces.

Hi, thank you for your help. But the problem comes from the following code: SafeArrayCreateVector(VT_DISPATCH, 0, length);. If I hide this code, no problem any more. If the code is SafeArrayCreateVector(VT_INT, 0, length); or SafeArrayCreateVector(VT_BSTR, 0, length);.., no problem. So eventhough I wrap the return value into VARIANT type, I still have to call SafeArrayCreateVector(VT_DISPATCH, 0, length);, then the problem is still there. Do you know how to solve it, or is there any other ways to create a vector of IDispatch*? Thank you. Nga

Hi. If, for example, you want to throw an exception from a certain method "Test()" of a certain COM interface "IMyInterface", a possible simple solution is proposed below. You can use either the macro "_com_raise_error(...)" or the command "throw _com_error(...)" inside the method "Test()" for throwing an exception. In the "client" of your "Test()" method, you can catch this exception as a "_com_error". In the following you can find a code example. Hoping this could help, Manuele Server ====== #include "comdef.h" ... // -------------------------------------------------------------------------- STDMETHODIMP CMyInterface::Test( int p_Int ) { HRESULT l_HR = S_OK; // Let's suppose we want to throw an exception if the // parameter is zero. if ( p_Int == 0 ) { // Create a new error info object and fill it. ICreateErrorInfo* l_CreateErrorInfo = NULL; GUID l_GUID = CLSID_MyInterface; l_HR = CreateErrorInfo( &l_CreateErrorInfo ); if ( ! SUCCEEDED( l_HR ) ) { return E_FAIL; } l_CreateErrorInfo->SetDescription( L"Descrizione Errore" ); l_CreateErrorInfo->SetGUID( l_GUID ); l_CreateErrorInfo->SetHelpContext( 0 ); l_CreateErrorInfo->SetHelpFile( L"HelpFile" ); l_CreateErrorInfo->SetSource( L"Source" ); IErrorInfo* l_ErrorInfo = NULL; l_HR = l_CreateErrorInfo->QueryInterface( IID_IErrorInfo, ( void** ) &l_ErrorInfo ); if ( ! SUCCEEDED( l_HR ) ) { return E_FAIL; } l_CreateErrorInfo->Release(); // Throw the just created error info object. // Alternatively, here you can use // "_com_raise_error( E_FAIL, l_ErrorInfo );" as well. throw _com_error( E_FAIL, l_ErrorInfo ); return E_FAIL; } return S_OK; } Client ====== #import "..." no_namespace // -------------------------------------------------------------------------- int main(int argc, char* argv[]) { HRESULT l_HR = S_OK; IMyInterfacePtr l_MyPtr = NULL; l_HR = CoInitialize( NULL ; if ( ! SUCCEEDED( l_HR ) ) { return E_FAIL; } l_HR = l_MyPtr.CreateInstance( __uuidof(MyInterface) ); if ( ! SUCCEEDED( l_HR ) ) { return E_FAIL; } try { l_HR = l_MyPtr->Test( 0 ); } catch( _com_error e ) { // Here, you can get information made available // by interface IErrorInfo _bstr_t l_Description = e.Description(); DWORD l_HelpContext = e.HelpContext(); _bstr_t l_HelpFile = e.HelpFile(); _bstr_t l_Source = e.Source(); GUID

You need to read either (or both) Essential IDL and Essential COM, or at a minimum, look for examples on MSDN and other sites (like this one) which use SAFEARRAYs. Google for SAFEARRAY SAMPLE or SAFEARRAY SOURCE which should help you get started. Alternatively, my rates for training (if you're UK based) are quite competitive :) Steve S Developer for hire