Defines the class template basic_istream, which mediates extractions for the iostreams, and the class template basic_iostream, which mediates both insertions and extractions. The header also defines a related manipulator. This header file is typically included for you by another iostreams header; you rarely have to include it directly.
The class template describes an object that controls extraction of elements and encoded objects from a stream buffer with elements of type Elem, also known as char_type, whose character traits are determined by the class Tr, also known as traits_type.