how can get evaluated value

I am trying this source. reference these.

2012 SOLIDWORKS API Help - Add Component and Mate Example (C++ COM)

2015 SOLIDWORKS API Help - Get Custom Properties of Referenced Part (VB.NET)

2015 SOLIDWORKS API Help - Traverse Bodies (C++/CLI)

2015 SOLIDWORKS API Help - Get Object's Persistent Reference ID Example (C++)

CComPtr<ISldWorks> swApp;

CComPtr<IModelDoc2> swModel;

CComPtr<IModelDocExtension> swDocExt;

CComPtr<ICustomPropertyManager> cusmgr;

long lErrors;

long lWarnings;

long lMateError;
CComBSTR sAssemblyName(L"c:\\Program Files\\test.sldasm");

CComBSTR sDefaultConfiguration(L"Default");

hres = swApp.CoCreateInstance(__uuidof(SldWorks), NULL, CLSCTX_LOCAL_SERVER);
CString con = "";

//swApp->IActivateDoc3((_bstr_t)con,VARIANT_FALSE,&lErrors, &swModel);
swApp->get_IActiveDoc2(&swModel);
swModel->get_Extension(&swDocExt);
  swDocExt->get_CustomPropertyManager((_bstr_t)con, &cusmgr);

I expect to success to write like that.

But it can't get swModel both get_IActiveDoc2 and IActiveDoc2.

According to 2015 SOLIDWORKS API Help - Get Object's Persistent Reference ID Example (C++)

CComPtr<ISldWorks> swApp;

if(swApp.CoCreateInstance(L"SldWorks.Application", NULL, CLSCTX_LOCAL_SERVER) != S_OK){

return(0);

}

CComPtr<IModelDoc2> swDoc;

swApp->get_IActiveDoc2(&swDoc);

It is just create instance swApp next call get_IactiveDoc2.

I think that i doing same thing.But my source don't insert any thing to swModel.

swModel is null after swApp->get_IActiveDoc2 or swApp->IActivateDoc3 steady.

And happen error swModel->get_Extension(&swDocExt) becuase swModel is null.

I am really confusing.