int ipfx( int need = 0 );
A nonzero return value if the operation was successful; 0 if the stream’s error state is nonzero, in which case the function does nothing.
Zero if called from formatted input functions; otherwise the minimum number of characters needed.
This input prefix function is called by input functions prior to extracting data from the stream. Formatted input functions call ipfx( 0 ), while unformatted input functions usually call ipfx( 1 ).
Any ios object tied to this stream is flushed if need = 0 or if there are fewer than need characters in the input buffer. Also, ipfx extracts leading white space if ios::skipws is set.
See Also istream::isfx