参考：COM技术内幕
DllGetClassObject
https://msdn.microsoft.com/en-us/library/windows/desktop/ms680760.aspx
If a call to the CoGetClassObject function finds the class object that is to be loaded in a DLL,
CoGetClassObject uses the DLL‘s exported DllGetClassObject function.
IClassFactory
https://msdn.microsoft.com/en-us/library/windows/desktop/ms694364.aspx
After calling the CoGetClassObject function to get an IClassFactory interface pointer to the class object,
call the CreateInstance method of this interface to create an object.
CoCreateInstance
https://msdn.microsoft.com/en-us/library/windows/desktop/ms686615.aspx
CoCreateInstance等价
{
CoGetClassObject(rclsid, dwClsContext, NULL, IID_IClassFactory, &pCF);
hresult = pCF->CreateInstance(pUnkOuter, riid, ppvObj
pCF->Release();
}
CoGetClassObject: 将在注册表中查找指定的组件。找到之后，它将装载实现此组件的DLL。
装载成功之后，它将调用在DLL服务器中实现的DllGetClassObject。
DllGetClassObject: 此函数的作用是创建响应的类场。
查询IClassFactory接口，并将其返回给CoCreateInstance。
CoCreateInstance将使用此接口来调用IClassFactory::CreateInstance函数
IClassFactory::CreateInstance调用了new操作符来创建指定的组件，并查询组件的IX接口。
//客户调用COM流程：
CoCreateInstace(rclsid,NULL,dwClsContext,IID_IX,(void**)&pIX); //IX* pIX
|--> CoGetClassObject(rclsid, dwClsContext, NULL, IID_IClassFactory, &pCF) //IClassFactory* pCF
|--> DllGetClassObject(rclsid,IID_IClassFactory,&pCF)
|--> CFactory* pFactory = new CFactory();
|--> pFactory->QueryInterface(IID_IClassFactory,&pCF); //返回类场指针IClassFactory* pCF
|--> pCF->CreateInstance(pUnkOuter, IID_IX, &pIX); //IX* pIX 组件接口指针pIX
pIX->Fx();
注意：.def模块定义文件
LIBRARY "ComComponent"
EXPORTS
DllCanUnloadNow PRIVATE
DllGetClassObject PRIVATE
DllRegisterServer PRIVATE
DllUnregisterServer PRIVATE