The FTP data structure

$\textstyle \parbox{0.49\textwidth}{int \underline{\bf sock}\index{sock}}$ $\textstyle \parbox{0.49\textwidth}{--- descriptor of a command channel to the server;\hfill}$
$\textstyle \parbox{0.49\textwidth}{FILE *\underline{\bf data}\index{data}}$ $\textstyle \parbox{0.49\textwidth}{--- pointer to data structure, which describes data channel to the server;\hfill}$
$\textstyle \parbox{0.49\textwidth}{int \underline{\bf errno}\index{errno}}$ $\textstyle \parbox{0.49\textwidth}{ --- last returned value. When value is lower than 1, an error occurred;\hfill}$
$\textstyle \parbox{0.49\textwidth}{char \underline{\bf mode}\index{mode}}$ $\textstyle \parbox{0.49\textwidth}{--- type of transfer;\hfill}$
$\textstyle \parbox{0.49\textwidth}{int ch}$ $\textstyle \parbox{0.49\textwidth}{--- help variable. Is used to convert ASCII files;\hfill}$
$\textstyle \parbox{0.49\textwidth}{STATUS (*func)()}$ $\textstyle \parbox{0.49\textwidth}{--- pointer to an error handler. It is called
when status from the server is bad;\hfill}$
$\textstyle \parbox{0.49\textwidth}{STATUS (*debug)()}$ $\textstyle \parbox{0.49\textwidth}{--- pointer to a debug handler. Is called from
functions of sending/receiving messages to/from server;\hfill}$
$\textstyle \parbox{0.49\textwidth}{STATUS (*IO)()}$ $\textstyle \parbox{0.49\textwidth}{--- pointer to Input/Output error handler. Is called when channel to server is broken.\hfill}$