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REGISTER - Component Object Registration |
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The REGISTER sample builds a simple REGISTER.EXE utility that is used in subsequent code samples to invoke DLL- or EXE-housed COM servers and command them to register or unregister their components in the system registry.
For functional descriptions and a tutorial code tour of REGISTER, see the Code Tour section in REGISTER.HTM. For details on the external user operation of REGISTER, see both the Usage and Operation sections in REGISTER.HTM. To read REGISTER.HTM, run TUTORIAL.EXE in the main tutorial directory and click the REGISTER lesson in the table of lessons. You can also achieve the same thing by clicking the REGISTER.HTM file after locating the main tutorial directory in the Windows Explorer.
In general, to set up your system to build and test the code samples in this COM Tutorial series, see the global TUTORIAL.HTM file for details. The accompanying makefile (MAKEFILE) is Microsoft NMAKE-compatible. To create a debug build, issue the NMAKE command in the Command Prompt window.
REGISTER.EXE is an application that you can run directly from Windows or from the Command Prompt. REGISTER is usually run from the Command Prompt in one of the following forms:
register myserver.dll - To register the DLL server.
register /u myserver.dll - To unregister the DLL server.
register /e myserver.exe - To register the EXE server.
register /u /e myserver.exe - To unregister the EXE server.
The REGISTER application operates transparently except when an error occurs. If an error occurs, a modal error dialog box is displayed with one of the following errors:
REGISTER.EXE: COM initialization failed REGISTER.EXE: DLL Unregister failed REGISTER.EXE: DLL Registration failed REGISTER.EXE: DLL Load Library failed REGISTER.EXE: WinExec of EXE server failed
This utility is designed to be used by installation programs that must register the COM components housed inside COM servers (either EXE or DLL). In this code sample series, REGISTER is invoked by the makefiles of each server code sample to register the components offered by the server. For example, the DLLSERVE code sample makefile supports NMAKE REGISTER and NMAKE UNREGISTER options to register and unregister its components.
Files Description
REGISTER.TXT Short sample description.
MAKEFILE The generic makefile for building the code sample.
REGISTER.H The include file for the REGISTER application.
Contains
string literals and Resource identifiers.
REGISTER.CPP The main implementation file for REGISTER.EXE. Has
WinMain
and CMainWindow implementation.
REGISTER.RC The application resource definition file.
REGISTER.ICO The application icon resource.
REGISTER is a simple utility that is used in subsequent samples to register COM servers. Before a COM component can be used by a client, its server must be loaded and running. Because the client doesn't load the servers directly, the client doesn't need specific information about the location of the components. All the client needs are the CLSIDs and Interface GUIDs (IIDs) of the components. The client presents to COM a CLSID for a component and an interface IID for the services sought. COM takes care of finding and loading the appropriate server, creating a COM object instance of the desired component, and providing the client with the requested interface to the object.
COM can perform these tasks only if the components have been previously registered. There are currently two principal ways to register a component. In the first method, you provide a .REG file that contains the registry entries for your components. The eventual user of the components can then use a utility like the Registry Editor (REGEDIT.EXE in Windows 95, REGEDT32.EXE in Windows NT) to process the .REG file and register the components. A disadvantage of this method is that the .REG file must contain specific paths to the server executables, so the .REG file may have to be edited when the components are installed.
The second method solves this problem by having the components register themselves. Self-registration is thus built into the component's server and is accessed through a standard protocol. With this method, the entries for the path to the server are dynamically determined by the server itself; no editing of .REG files is required. Though it takes a little more work to implement the server housing, self-registration is recommended and is used throughout this code sample series.
The specifics of self-registration will be covered when first encountered in the series: in the DLLSERVE lesson for DLL in-process servers, and in the LOCSERVE lesson for EXE local servers.
The REGISTER.EXE utility in this lesson is used to load a specified server and invoke its self-registration facilities. This application is so simple that no main window or message loop is required. The only user interface that might be needed is a set of message dialog boxes to notify the user of error conditions.
The main content of the program is in REGISTER.CPP. Almost all the work is done in the WinMain function. The program scans its own command line options to determine the kind of COM server to load and whether the server should be registered or unregistered. The following while loop does this:
...
while (ch = *psz)
{
BOOL bStop = FALSE;
switch (ch)
{
case '\t':
case '\n':
case '\r':
case ' ':
// Skip any white space.
psz = SkipAnsiString(psz, TRUE);
continue;
case '/':
case '-':
// Check what option this is, then skip to next whitespace.
ch = *(++psz);
if ('u' == ch)
bUnreg = TRUE;
if ('e' == ch)
bEXE = TRUE;
psz = SkipAnsiString(psz, FALSE);
continue;
default:
bStop = TRUE;
break;
}
if (bStop)
break;
psz++;
}
...
With psz pointing to the command line input, the loop scans for '/u' or '/e' to determine respectively whether unregistration or an EXE server is specified. The default is to register a DLL server. SkipAnsiString is a utility function defined locally in this module that can either skip over whitespace characters or skip to the next whitespace character. This entire application is compiled for the ANSI character set and uses the appropriate versions of Win32 API calls. This is simply because the pszCmdLine command line is available to WinMain only in ANSI. The makefile ignores any request to compile this program for Unicode.
As the while loop scans the command line, the bUnreg and bEXE Boolean flags are assigned. They are then used to determine the execution of the remaining code in WinMain. For the default case of a DLL server (bEXE == FALSE), the following code runs:
// Because we load the DLL server into our own (ie, REGISTER.EXE)
// process space, call to initialize the COM Library. Use the
// SUCCEEDED macro to detect success. If fails, then exit
// application with error message.
if (SUCCEEDED(CoInitialize(NULL)))
{
HINSTANCE hMod;
// Load the Server DLL into our process space.
hMod = LoadLibraryA(psz);
if (NULL != hMod)
{
HRESULT (STDAPICALLTYPE *pfn)(void);
if (bUnreg)
{
(FARPROC&)pfn = GetProcAddress(hMod,
"DllUnregisterServer");
if (NULL != pfn)
iFail = FAILED((*pfn)());
if (iFail)
ErrorBoxID(hInstance, IDS_DLLUNREG_FAIL);
else
{
// Show a timed message box indicating registration
success.
DelayBox(hInstance, MAKEINTRESOURCE(IDD_SUCCESS_MSG),
NULL);
}
}
else
{
(FARPROC&)pfn = GetProcAddress(hMod,
"DllRegisterServer");
if (NULL != pfn)
iFail = FAILED((*pfn)());
if (iFail)
ErrorBoxID(hInstance, IDS_DLLREG_FAIL);
else
{
// Show a timed message box indicating registration
success.
DelayBox(hInstance, MAKEINTRESOURCE(IDD_SUCCESS_MSG),
NULL);
}
}
CoFreeLibrary(hMod);
}
else
ErrorBoxID(hInstance, IDS_LOADLIB_FAIL);
// We're exiting this app so shut down the COM Library.
CoUninitialize();
}
else
ErrorBoxID(hInstance, IDS_OLEINITFAILED);
Because the DLL server will probably make calls to COM services, the program calls the CoInitialize function to initialize the COM service libraries. After the /u and /e switches are found or not, the code treats the remainder of the command line pointed to by psz as the path to the DLL server. The server is then explicity loaded with a LoadLibraryA call. If /u was specified, GetProcAddress is called to obtain the address of the DllUnregisterServer function. If the function is found, it is called to actually get the server to unregister its components. If /u is not specified, the DllRegisterServer function is found and called. The loaded server DLL is freed after use, and the COM library is uninitialized.
For the case of an EXE server (bEXE == TRUE) the following code runs.
if (bEXE)
{
UINT uError;
CHAR szEXE[MAX_PATH];
wsprintfA(
szEXE,
"%s %s",
psz,
bUnreg ? "/UNREGSERVER" : "/REGSERVER");
// We WinExec the .EXE server passing /unregserver or
/regserver.
uError = WinExec(szEXE, SW_HIDE);
if (uError < 32)
{
ErrorBoxID(hInstance, IDS_EXERUN_FAIL);
iFail = FALSE;
}
else
{
// Show a timed message box indicating registration success.
DelayBox(hInstance, MAKEINTRESOURCE(IDD_SUCCESS_MSG), NULL);
}
}
The EXE server is started by a call to WinExec with the appropriate command line option, /UNREGSERVER or /REGSERVER. The server is run with SW_HIDE because only an internal service of the server is being requested, and no user interface is required.
For both EXE and DLL servers, APPUTIL's DelayBox function is used to show a success message box for a few seconds if the registration is successful.
One final note about self-registration. For tutorial purposes, this lesson shows the internal operation of a self-registering utility for both EXE and DLL COM servers. A similar utility, REGSVR32.EXE, is provided as part of the Platform SDK in the \MSSDK\BIN directory. REGSVR32 can be used to register in-process COM server DLLs and marshaling server DLLs. The Microsoft Visual C++® product (version 4.x and above) also includes this utility.
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