DLL Functions

DLL Functions

A DLL must implement the following functions so that it can be registered, unregistered, and loaded into memory.

• DllMain: The DLL entry point. The name DllMain is a placeholder for the library-defined function name. The DirectShow implementation uses the name DllEntryPoint. For more information, see the Platform SDK.
• DllGetClassObject: Creates a class factory instance. Described in the previous sections.
• DllCanUnloadNow: Queries whether the DLL can safely be unloaded.
• DllRegisterServer: Creates registry entries for the DLL.
• DllUnregisterServer: Removes registry entries for the DLL.

Of these, the first three are implemented by DirectShow. If your factory template provides an initialization function in the m_lpfnInit member variable, that function is called from inside the DLL entry-point function. For more information on when the system calls the DLL entry-point function, see DllMain in the Platform SDK.

You must implement DllRegisterServer and DllUnregisterServer, but DirectShow provides a function named AMovieDllRegisterServer2 that does the necessary work. Your component can simply wrap this function, as shown in the following example:

STDAPI DllRegisterServer()
{
    return AMovieDllRegisterServer2( TRUE );
}

STDAPI DllUnregisterServer()
{
    return AMovieDllRegisterServer2( FALSE );
}

However, within DllRegisterServer and DllUnregisterServer you can customize the registration process as needed. If your DLL contains a filter, you might need to do some additional work. For more information, see How to Register DirectShow Filters.

In your module-definition (.def) file, export all the DLL functions except for the entry-point function. The following is an example .def file:

EXPORTS
    DllGetClassObject PRIVATE
    DllCanUnloadNow PRIVATE
    DllRegisterServer PRIVATE
    DllUnregisterServer PRIVATE

You can register the DLL using the Regsvr32.exe utility.