Let's go from the bottom up. An interface is simply a group of functions. Those functions are called methods. Interface names start with I, for example IShellLink. In C++, an interface is written as an abstract base class that has only pure virtual functions.
Interfaces may inherit from other interfaces. Inheritance works just like single inheritance in C++. Multiple inheritance is not allowed with interfaces.
Interfaces只能使用單inheritance.
A coclass (short for component object class) is contained in a DLL or EXE, and contains the code behind one or more interfaces. The coclass is said to implement those interfaces. A COM object is an instance of a coclass in memory. Note that a COM "class" is not the same as a C++ "class", although it is often the case that the implementation of a COM class is a C++ class.
coclass 組件對象類。存在于dll或者exe中。coclass可以包跨一個或者多個interfaces。
一個com對象是一個初始后在內存中的實例。
A COM server is a binary (DLL or EXE) that contains on or more coclasses.
A class ID, or CLSID, is a GUID that names a coclass. An interface ID, or IID, is a GUID that names an interface.
guid的兩用
An HRESULT is an integral type used by COM to return error and success codes. It is not a "handle" to anything, despite the H prefix. I'll have more to say about HRESULTs and how to test them later on.
Finally, the COM library is the part of the OS that you interact with when doing COM-related stuff. Often, the COM library is referred to as just "COM," but I will not do that here, to avoid confusion.
com library 是操作系統的一部分
The Base Interface - IUnknown
com的服務器端的Iclassfactory的接口是用來產生對象的實例的接口，如果有（也必須有）一個class是由這個接口派生的,如果com對象是進程內組建對象的話，必須實現DllGetClassObject的方法。在client端通過CoCreateInstance，CoCreateInstanceEx,CoGetClassObject三種方法中的一個。把參數clisid，iid和ppv傳給DllGetClassObject方法。由DllGetClassObject創建類廠，并返回類廠對象接口指針。
CoCreateInstance，CoCreateInstanceEx,CoGetClassObject的區別。
CoGetClassObject 這個是最原始也是最基本的方法，他的參數包跨IID_IClassFactory.
CoCreateInstance 比較常用的方法，參數使用IID_IUnknown,從而隱藏了IClassFactory的細節
CoCreateInstanceEx，使用了一個接口數組，因此可以返回多個接口。