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：

DWORD g_dwAttachedProcesses = 0L;// # of attached processesDWORD g_dwPageSize = 0L;// System page sizeHINSTANCE g_hInstance = 0L; // Instance HandleLONG g_cLock = 0L;// # of outstanding objectsBOOL APIENTRY DllMain( HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved ){ BOOL fRetVal = FALSE; SYSTEM_INFO SystemInformation;switch(ul_reason_for_call){case DLL_PROCESS_ATTACH: // Assume successfully initialized fRetVal = TRUE; // Do one-time initialization when first process attaches if(!g_dwAttachedProcesses) {g_hInstance = (HINSTANCE)hModule;// Get the system page sizeif(!g_dwPageSize) {GetSystemInfo( &SystemInformation ); // can't failg_dwPageSize = SystemInformation.dwPageSize; } } // Do per-process initialization here... // Remember that another process successfully attached g_dwAttachedProcesses++;break;case DLL_THREAD_ATTACH: // Clean up when the last process is going away if(g_dwAttachedProcesses == 1) { } // Do per-process clean up here... // Remember that a process has detached g_dwAttachedProcesses--; break;case DLL_THREAD_DETACH:case DLL_PROCESS_DETACH:break;} return fRetVal;}

在工程中添加没有mycom.DEF文件用于导出COM接口函数，如下：

LIBRARY"mycom"EXPORTS ; EntryName [=InternalName] [@Ordinal] [NONAME] [CONSTANT]; This is the entry point that DllMainCRTStartup callsDllMain @12 ; Standard OLE exportsDllGetClassObjectPRIVATEDllCanUnloadNowPRIVATE; For self-registration.DllRegisterServerPRIVATEDllUnregisterServerPRIVATE

DllMain 函数可以不导出。

其次，在mycom.cpp中实现导出函数，如下：

STDAPI DllUnregisterServer(void){return S_OK;}STDAPI DllRegisterServer(void){return S_OK;}STDAPI DllCanUnloadNow(void){ if(!g_cLock) return S_OK;return S_FALSE;}STDAPI DllGetClassObject(REFCLSID rclsid ,REFIID riid,void **ppv){return CLASS_E_CLASSNOTAVAILABLE;}

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。

 

http://blog.csdn.net/zhoujianhei/archive/2010/07/30/5777404.aspx