A File Manager extension sends an FM_GETSELCOUNTLFN message to retrieve the number of selected files in the active File Manager window (either the directory window or the Search Results window). The count includes files that have long filenames.
FM_GETSELCOUNTLFN wParam = 0; // not used, must be zero lParam = 0; // not used, must be zero
This message has no parameters.
The return value is the number of selected files.
Only extensions that support long filenames (for example, network-aware extensions) should use this message.