Wininet中的ftp类不支持断点续传,只支持http的断点续传。The MFC class CInternetFile provides a base class for the CHttpFile and CGopherFile file classes.
CInternetFile::Seek()的注释:At this time, a call to this member function is only supported for data associated with CHttpFile objects. It is not supported for FTP or gopher requests. If you call Seek for one of these unsupported services, it will pass back you to the Win32 error code ERROR_INTERNET_INVALID_OPERATION.