C++ COM实现之一 创建一个DLL

COM是一种接口技术，它提供了一种方法用于客户程序进行调用。COM原理和技术的文章已经很多了，就不过多讲解了，这里只注重实现。下面分几步对进程内COM组件进行编码实现以达到对实现一个COM的清晰的认识，目的是通过COM接口方法调用DLL中的函数。

首先，创建一个标准的win32 DLL项目mycom，dllmain入口实现如下

01.DWORD g_dwAttachedProcesses = 0L;   // # of attached processes   
02.DWORD g_dwPageSize = 0L;            // System page size   
03.HINSTANCE g_hInstance = 0L;         // Instance Handle   
04.LONG g_cLock =  0L;         // # of outstanding objects   
05.BOOL APIENTRY DllMain( HMODULE hModule,   
06.                       DWORD  ul_reason_for_call,   
07.                       LPVOID lpReserved   
08.                     )   
09.{   
10.    BOOL        fRetVal = FALSE;   
11.    SYSTEM_INFO SystemInformation;   
12.    switch(ul_reason_for_call)   
13.    {   
14.    case DLL_PROCESS_ATTACH:   
15.        // Assume successfully initialized   
16.        fRetVal = TRUE;   
17.        // Do one-time initialization when first process attaches   
18.        if(!g_dwAttachedProcesses)   
19.        {   
20.            g_hInstance = (HINSTANCE)hModule;   
21.            // Get the system page size   
22.            if(!g_dwPageSize)   
23.            {   
24.                GetSystemInfo( &SystemInformation );    // can't fail   
25.                g_dwPageSize = SystemInformation.dwPageSize;   
26.            }   
27.        }   
28.        // Do per-process initialization here...   
29.           
30.        // Remember that another process successfully attached   
31.        g_dwAttachedProcesses++;   
32.        break;   
33.    case DLL_THREAD_ATTACH:   
34.        // Clean up when the last process is going away   
35.        if(g_dwAttachedProcesses == 1)   
36.        {   
37.        }   
38.        // Do per-process clean up here...   
39.        // Remember that a process has detached   
40.        g_dwAttachedProcesses--;   
41.        break;   
42.    case DLL_THREAD_DETACH:   
43.    case DLL_PROCESS_DETACH:   
44.        break;   
45.    }   
46.    return fRetVal;   
47.}  

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/zhoujianhei/archive/2010/07/30/5777404.aspx

在工程中添加没有mycom.DEF文件用于导出COM接口函数，如下：

01.LIBRARY "mycom"  
02.EXPORTS    
03.; EntryName [=InternalName] [@Ordinal] [NONAME] [CONSTANT]   
04.; This is the entry point that DllMainCRTStartup calls   
05.DllMain @12    
06.; Standard OLE exports   
07.DllGetClassObject       PRIVATE   
08.DllCanUnloadNow         PRIVATE   
09.; For self-registration.   
10.DllRegisterServer       PRIVATE   
11.DllUnregisterServer     PRIVATE  

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/zhoujianhei/archive/2010/07/30/5777404.aspx

DllMain 函数可以不导出。

其次，在mycom.cpp中实现导出函数，如下：

01.STDAPI DllUnregisterServer(void)   
02.{   
03.    return S_OK;   
04.}   
05.STDAPI DllRegisterServer(void)   
06.{   
07.    return S_OK;   
08.}   
09.STDAPI DllCanUnloadNow(void)   
10.{   
11.    if(!g_cLock)   
12.        return S_OK;   
13.    return S_FALSE;   
14.}   
15.STDAPI DllGetClassObject(REFCLSID rclsid ,REFIID riid,void **ppv)   
16.{   
17.    return CLASS_E_CLASSNOTAVAILABLE;   
18.}  

通过以上步骤，一个基本的DLL创建完成，这还不能称之为COM，仅仅是一个DLL导出了几个空函数而已。