INFO: How Regsvr32.exe Registers and Unregisters COM DLLs

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Article ID: 207132 - View products that this article applies to.
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SUMMARY

This article describes how the RegSvr32.exe program registers and unregisters a Component Object Model (COM) dynamic-link library (DLL). You can use this information to troubleshoot errors that occur when you try to use RegSvr32.exe program with your COM DLL.

MORE INFORMATION

RegSvr32.exe calls the following Win32 functions in this order:
  • OleInitialize
  • LoadLibrary to load the DLL
  • DllRegisterServer or DllUnregisterServer
  • FreeLibrary
  • OleUninitialize
Most often, RegSvr32.exe fails because the LoadLibrary, DllRegisterServer, or DllUnregisterServer function fails. LoadLibrary can fail if the DLL is not in the specified path, or if the specified path is incorrect. LoadLibrary can also fail if one of the dependencies of the DLL that you are trying to load is not met; in other words, if a dependent DLL is not present or is not in the specified path.

NOTE: You can use the Depends.exe tool to check whether or not all of the dependencies of your DLL are met. Depends.exe is included with the Microsoft Platform Software Development Kit (SDK), which ships with Microsoft Visual Studio.

Your DLL must implement DllRegisterServer and DllUnregisterServer, which contain the logic that is necessary to add or delete the required registry entries for the COM component. RegSvr32.exe finds the entry point to these functions, and calls them appropriately.

NOTE: If you use the Microsoft Active Template Library (ATL) Wizard to create the COM DLL, the Wizard generates the necessary code for DllRegisterServer and DllUnregisterServer.

If you use Microsoft Visual C++, refer to the Platform SDK sample at \Platform SDK\Samples\Com\Fundamentals\Async\Server.

Step-by-Step Example

The following sample describes registry functions that you can use to register and unregister your COM DLL.

You can also write your own code to do what RegSvr32.exe does. This helps to identify, isolate, and troubleshoot errors more easily.

To create a Win32 Application that you can use to register or unregister your COM DLL, perform the following steps:
  1. In Visual C++, create a new Win32 Application named Register. Accept all of the defaults.
  2. Create a new .cpp file named Register.cpp, and add it to the project.
  3. Paste the following code in Register.cpp:
    #include <tchar.h>
    #include <afxole.h>
    #include <stdlib.h>
    
    #define FAIL_ARGS    1
    #define FAIL_OLE     2
    #define FAIL_LOAD    3
    #define FAIL_ENTRY   4
    #define FAIL_REG     5 
    
    static char szAppName[] = "Register";
    static char szUsage[] = "\n\nUsage: Register [/u] dllname";
    static char szDllRegSvr[] = "DllRegisterServer";
    static char szDllUnregSvr[] = "DllUnregisterServer"; 
    
    int PASCAL WinMain(
    		   HINSTANCE hInstance, 
    		   HINSTANCE hPrev, 
    		   LPSTR pszCmdLine, 
    		   int nCmdShow)
    {   
    	int iReturn = 0;       
    	HRESULT (FAR STDAPICALLTYPE * lpDllEntryPoint)(void);  
    	static TCHAR szMsgBuffer[_MAX_PATH*4];         
    	BOOL bVisualC = FALSE; 
    	BOOL bSilent = FALSE;  
    	BOOL bUnregister = FALSE;      
    	LPSTR pszDllEntryPoint = szDllRegSvr;  
    	LPSTR pszDllName = NULL;
    	char szCmdLineCopy[_MAX_PATH]; 
    	strcpy(szCmdLineCopy, pszCmdLine);             
    	LPSTR pszTmp = szCmdLineCopy;  
    	LPSTR pszTok;          
    	
    	while ((pszTok = strtok(pszTmp, " \t")) != NULL)       
    	{                                
    		pszTmp = NULL; 
    		
    		if ((pszTok[0] == '-') || (pszTok[0] == '/'))
    		{      
    			switch (pszTok[1])     
    			{      
    			case 'v':      
    			case 'V':
    				bVisualC = TRUE;
    				break;         
    			case 's':      
    			case 'S':
    				bSilent = TRUE;
    				break;         
    			case 'u':      
    			case 'U':
    				bUnregister = TRUE;
    				pszDllEntryPoint = szDllUnregSvr;
    				break;         
    			default:
    				wsprintf(szMsgBuffer, 
    					"Unrecognized flag: %s%s", 
    					pszTok, 
    					(LPCSTR)szUsage);
    				if (!bSilent)  
    					MessageBox(NULL, 
    					   szMsgBuffer, 
    					   szAppName, 
    					   MB_TASKMODAL | MB_ICONEXCLAMATION);
    				return FAIL_ARGS;      
    			}
    		}
    		else
    		{      
    			if (pszDllName == NULL)
    				pszDllName = pszTok;   
    			else   
    			{
    				wsprintf(szMsgBuffer, 
    					"Extra argument on command line: %s%s", 
    					pszTok, 
    					(LPCSTR)szUsage);
    				if (!bSilent)  
    					MessageBox(NULL, 
    					   szMsgBuffer, 
    					   szAppName, 
    					   MB_TASKMODAL | MB_ICONEXCLAMATION);
    				return FAIL_ARGS;      
    			}
    		}      
    	}      
    	
    	if (pszDllName == NULL)        
    	{
    		if (!bSilent)
    		{      
    			if (bVisualC)  
    			{
    				MessageBox(NULL, 
    				"This command is only valid when "
    				"an OLE Custom Control project is open.", 
    				bUnregister ? 
    				"Unregister Control" : "Register Control",
    				MB_TASKMODAL | MB_ICONEXCLAMATION);
    			}
    			else   
    			{
    				wsprintf(szMsgBuffer, 
    					_T("No DLL name specified%s"), 
    					(LPCSTR)szUsage);
    				MessageBox(NULL, 
    					szMsgBuffer, 
    					szAppName, 
    					MB_TASKMODAL | MB_ICONEXCLAMATION);
    			}
    		}
    		return FAIL_ARGS;      
    	}
    	
    	if (FAILED(OleInitialize(NULL)))       
    	{
    		if (!bSilent)  
    			MessageBox(NULL, 
    				"OleInitialize failed.", 
    				szAppName, 
    				MB_TASKMODAL | MB_ICONINFORMATION);
    		return FAIL_OLE;       
    	}              
    	
    	HINSTANCE hLib = LoadLibrary(pszDllName);      
    	
    	if (hLib < (HINSTANCE)HINSTANCE_ERROR) 
    	{
    		wsprintf(szMsgBuffer, 
    			"LoadLibary(\"%s\") failed.", 
    			pszDllName);
    		MessageBox(NULL, 
    			szMsgBuffer, 
    			szAppName, 
    			MB_TASKMODAL | MB_ICONEXCLAMATION);
    		iReturn = FAIL_LOAD;
    		goto CleanupOle;       
    	}
    	
    	(FARPROC&)lpDllEntryPoint = GetProcAddress(hLib, pszDllEntryPoint);
    	
    	if (lpDllEntryPoint == NULL)   
    	{
    #ifdef _WIN32
    		int nLen = strlen(pszDllName);
    		if ((nLen > 4) && 
    			(stricmp(pszDllName + nLen - 4, ".dll") != 0)  && 
    			(stricmp(pszDllName + nLen - 4, ".ocx") != 0))
    		{      
    			wsprintf(szMsgBuffer, 
    			"%s was loaded, but the %s entry point "
    			"was not found. %s does not appear to be "
    			"an .DLL or .OCX file.", 
    			pszDllName, 
    			pszDllEntryPoint, 
    			pszDllName);
    		}
    		else
    		{      
    			wsprintf(szMsgBuffer, 
    			"%s was loaded, but the %s entry point "
    			"was not found. %s may not be exported, "
    			"or a corrupt version may be in memory.  "
    			"Consider using PView to detect and remove it.",
    			pszDllName, 
    			pszDllEntryPoint, 
    			pszDllEntryPoint);
    		}
    #else
    		wsprintf(szMsgBuffer, 
    		"%s was loaded, but the %s entry point "
    		"was not found. %s may not be exported, "
    		"or a corrupt version may be in memory.  "
    		"Consider using WPS to detect and remove it.",
    		pszDllName, 
    		pszDllEntryPoint, 
    		pszDllEntryPoint);
    #endif
    		
    		if (!bSilent)  
    			MessageBox(NULL, 
    				szMsgBuffer, 
    				szAppName, 
    				MB_TASKMODAL | MB_ICONEXCLAMATION);
    		iReturn = FAIL_ENTRY;
    		
    		goto CleanupLibrary;   
    	}
    	
    	if (FAILED((*lpDllEntryPoint)()))      
    	{
    		wsprintf(szMsgBuffer, 
    			"%s in %s failed.", 
    			pszDllEntryPoint, 
    			pszDllName);
    		
    		if (!bSilent)  
    			MessageBox(NULL, 
    				szMsgBuffer, 
    				szAppName, 
    				MB_TASKMODAL | MB_ICONEXCLAMATION);
    		iReturn = FAIL_REG;
    		
    		goto CleanupLibrary;   
    	}      
    	
    	wsprintf(szMsgBuffer,
    		"%s in %s succeeded.", 
    		pszDllEntryPoint, 
    		pszDllName);     
    	
    	if (! bSilent)
    		MessageBox(NULL, 
    			szMsgBuffer, 
    			szAppName, 
    			MB_TASKMODAL | MB_ICONINFORMATION); 
    CleanupLibrary:     
    	FreeLibrary(hLib); 
    	
    CleanupOle: 
    	OleUninitialize();     
    	
    	return iReturn;
    }
    					
  4. Build the application, and use it to register or unregister your COM DLL.

REFERENCES

For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base:
140346 Possible Reasons for OLE Control Registration Failure
141824 INFO: Common Remote OLE Automation Errors
146219 HOWTO: Register an ActiveX Control (.ocx) Manually
185599 FIX: OleAut32.dll Is Unregistered Incorrectly

Properties

Article ID: 207132 - Last Review: February 23, 2007 - Revision: 2.5
APPLIES TO
  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows 2000 Datacenter Server
  • Microsoft Windows 95
  • Microsoft Windows 98 Standard Edition
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition
Keywords: 
kbinfo KB207132

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