interface ITest : IDispatch{
    [id(1), helpstring("method ADD")] HRESULT ADD([in] LONG x, [in] LONG y, LONG* z);
    [id(2), helpstring("method UpperCase")] HRESULT UpperCase([in] CHAR A, CHAR* B);
    [id(3), helpstring("method LowerCase")] HRESULT LowerCase([in] BSTR A, BSTR* B);
    [id(4), helpstring("method Change")] HRESULT Change([in] VARIANT A, [out] VARIANT* B);
};

 MIDL_INTERFACE("52CA8A5C-593D-4E2E-B58F-BB6C6604EAF2")
    ITest : public IDispatch
    {
    public:
        virtual /**//* [helpstring][id] */ HRESULT STDMETHODCALLTYPE ADD( 
            /**//* [in] */ LONG x,
            /**//* [in] */ LONG y,
            LONG *z) = 0;
        
        virtual /**//* [helpstring][id] */ HRESULT STDMETHODCALLTYPE UpperCase( 
            /**//* [in] */ CHAR A,
            CHAR *B) = 0;
        
        virtual /**//* [helpstring][id] */ HRESULT STDMETHODCALLTYPE LowerCase( 
            /**//* [in] */ BSTR A,
            BSTR *B) = 0;
        
        virtual /**//* [helpstring][id] */ HRESULT STDMETHODCALLTYPE Change( 
            /**//* [in] */ VARIANT A,
            /**//* [out] */ VARIANT *B) = 0;
        
    };

在Test中实现以上接口函数。

二 在C#中的使用方法

1）使用IDE中的reference来reference com，这个之前com必须先注册：


2）使用命令TLBIMP ATLCOM.tlb /out:C:\ATLCOM.dll ,然后referece生成的DLL（tblmp命令帮你注册com）。

3）TypeLibConverter 类
TypeLibConverter 类（位于 System.Runtime.InteropServices 命名空间中）提供了将类型库中的 coclass 和接口转换为程序集中的元数据的方法。此 API 将生成与 Tlbimp.exe 相同的元数据输出。不过，与 Tlbimp.exe 不同的是，TypeLibConverter 类可以将内存中的类型库转换为元数据。

 4）自定义包装
当类型库不可用或不正确时，一种可选的做法是在托管源代码中创建类或接口的重复定义。然后，用面向运行库的编译器来编译源代码以生成程序集中的元数据。
要手动定义 COM 类型，必须具备下列各项：

所定义的 coclass 和接口的精确描述。
可生成正确 .NET Framework 类定义的编译器，如 C# 编译器。
有关类型库到程序集转换规则的知识。

编写自定义包装是一种较少使用的高级技术。有关生成自定义包装的其他信息，请参见自定义标准包装。

三 在C#的client调用COM提供的接口，我们可以看到在C#中COM的接口和函数被变换为如下：
Member of atlcom.TestClass：
public TestClass();   
public virtual void ADD(int x, int y, ref int z);
public virtual void UpperCase(sbyte A, ref sbyte B);
public virtual void Change(object A, out object B) ;  
public virtual void LowerCase(string A, ref string B);

四 更多可以参考：http://www.codeproject.com/dotnet/cominterop.asp

What is OLE?
OLE (Object Linking and Embedding) is Microsoft's component document technology. With OLE, it is possible to dynamically link files and applications together. An object is a combination of data and the application needed to modify that data. Objects can be embedded in or linked to documents created with a different application.

For instance, an Excel spreadsheet can be embedded within a Microsoft Word document using OLE. Double-clicking the embedded spreadsheet will launch Excel and allow the user to modify the sheet.

Some applications include small applets that are used to create objects. For instance, Microsoft Word includes a drawing tool (MS Draw) and a tool for manipulating characters as art (Text Art) which can be launched only via OLE.

For more information, visit Microsoft's Developer Network page at: http://msdn.microsoft.com/default.aspx

What are COM, COM+, and DCOM?
COM (Component Object Model) is Microsoft's component software architecture developed primarily for Windows. It is the foundation upon which OLE and ActiveX are based, and provides a means to re-use code without requiring re-compilation. In COM, a component is a platform-specific binary file that compliant applications and other components can utilize. Programs incorporating a component's services never have access to its internal data structure, but instead include pointers to its standardized interface. Thus, it is possible for components to interact with each other regardless of how they work or what language they are written in.

COM+ is an enhanced version of COM that provides better security and improved performance. DCOM (Distributed Component Object Model) is an extension of COM that allows applications and components to communicate with each other over a network.

For more detailed information about COM, COM+, DCOM, and related technologies, visit: http://www.microsoft.com/com/default.mspx

What is ActiveX?
ActiveX is a term Microsoft uses to describe a number of its COM technologies. However, when most people say "ActiveX", they are really referring to ActiveX controls, Microsoft's answer to Java applets. The two technologies are similar in that they are designed to be downloaded and executed by web browsers. The difference is that while ActiveX controls can interface with Microsoft Windows better than Java can, they offer very little cross-platform support.

For more information about ActiveX controls as well as other ActiveX technologies, visit Microsoft's page at: http://www.microsoft.com/com/default.mspx CNET maintains a library of ActiveX controls, available at the following address: http://www.download.com/2001-2206-0.html?legacy=cnet

What are ActiveX controls?
ActiveX controls are small program building blocks that can be used to create distributed applications that work over the Internet through web browsers. Examples include customized applications for gathering data, viewing certain kinds of files, and displaying animation.

The ActiveX programming specification is an extension of Microsoft Windows and the Object Linking and Embedding (OLE) API. ActiveX applications are used mainly with Microsoft's Internet Explorer web browser.

Like Java applets, programs that use ActiveX controls run on the client computer, not the server.

For more information about ActiveX controls as well as other ActiveX technologies, visit Microsoft's page at: http://www.microsoft.com/com/default.mspx

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
A software architecture developed by Microsoft to build component-based applications. COM objects are discrete components, each with a unique identity, which expose interfaces that allow applications and other components to access their features. COM objects are more versatile than Win32 DLLs because they are completely language-independent, have built-in interprocess communications capability, and easily fit into an object-oriented program design. COM was first released in 1993 with OLE2, largely to replace the interprocess communication mechanism DDE used by the initial release of OLE. ActiveX also is based on COM.