Managing input streams: class istream
Class istream objects are specialized for input; as for ostream, they are derived from ios, so you can use any of the general-purpose methods from that base class. Declarations for this class also come from iostream.h.
See the following documentation’s discussion for more information.
istream::istream () Constructor
When used without arguments, the istream constructor simply initializes the ios object and initializes the input counter (the value reported by istream::gcount) to 0.
istream::istream (streambuf* sb [, ostream tie]) Constructor < 5c8 /PRE>
You can also call the constructor with one or two arguments. The first argument, sb, is a streambuf*; if you supply this pointer, the constructor uses that streambuf for input. You can use the second optional argument tie to specify a related output stream as the initial value for ios::tie.
If you use this constructor, the argument, sb, is not destroyed (or deleted or closed) when the ostream is destroyed.