The GetDefaultFilterExtList method gets the list of file name extensions that have been registered to use the default IFilter when no other IFilter has been registered for the file name extension.
HRESULT GetDefaultFilterExtList ( WCHAR const * pwcsOverride, WCHAR const * pwcsMachineName, WCHAR * pwszzBuf, DWORD * pdwSize);
[in] A pointer to a WCHAR that contains an override string, such as the application name.
[in] Not used. Value should be 0.
[out] A pointer to a WCHAR that receives one or more null-terminated file name extension strings. The last extension is terminated with two null characters.
[in, out] A pointer to a DWORD that on input contains the number of characters in pwczzBuf and on output receives the number of characters written to the buffer.
For a list of errors returned by SharePoint Portal Server IFilter registration objects, see Error Messages.
This method returns a list of file name extensions. When the SharePoint Portal Server content indexing service determines which IFilter to apply to a file, it first checks the IFilters registered for that file name extension, MIME type, and Class ID. If none of the assigned IFilters successfully processes the document, then the default IFilter is checked. The list of file name extensions includes those that were explicitly registered to use the default IFilter when no other registered IFilter successfully processes the document.
If the pwcsOverride string is not null, the method returns the file name extensions registered with that override string. The pwcsMachineName string indicates the computer name for which the list is returned.