All the iostream classes in the ios hierarchy depend on an attached streambuf class for the actual I/O processing. This class is an abstract class, but the iostream class library contains the following derived buffer classes for use with streams:
filebuf
Buffered disk file I/O.
strstreambuf
Stream data held entirely within an in-memory byte array.
stdiobuf
Disk I/O with buffering done by the underlying standard I/O system.
All streambuf objects, when configured for buffered processing, maintain a fixed memory buffer, called a reserve area, that can be dynamically partitioned into a get area for input and a put area for output. These areas may or may not overlap. Protected member functions allow access and manipulation of a get pointer for character retrieval and a put pointer for character storage. The exact behavior of the buffers and pointers depends on the implementation of the derived class.
The capabilities of the iostream classes can be extended significantly through the derivation of new streambuf classes. The ios class tree supplies the programming interface and all formatting features, but the streambuf class does the real work. The ios classes call the streambuf public members, including a set of virtual functions.
The streambuf class provides a default implementation of certain virtual member functions. The “Default Implementation” section for each such function suggests function behavior for the derived class.
#include <iostream.h>