iostreams

Iostreams refers to the C++ standard library facilities that implement input and output using stream objects. It provides a hierarchy of stream classes and associated buffers that decouple I/O operations from the underlying devices, enabling formatted and unformatted I/O through a uniform interface.

Core classes include basic_istream, basic_ostream, and basic_iostream, templates parameterized by character type and traits. Common specializations include istream, ostream, iostream and their wide-character counterparts. The standard objects std::cin, std::cout, std::cerr, and std::clog are instances of these classes and serve as primary entry points for input and output. I/O is typically performed with the insertion operator (<<) and the extraction operator (>>) which dispatch to the appropriate virtual functions to format data or parse input.

Internally, iostreams rely on stream buffers (std::streambuf) and formatting state embedded in i/o manipulators such as std::endl, std::setw, std::setfill, and std::setprecision. The library tracks state flags (eofbit, failbit, badbit, good) and can throw exceptions if enabled via std::ios_base::exceptions. The ecosystem also includes string streams (std::stringstream) for in-memory I/O and file streams (std::ifstream, std::ofstream, std::fstream) which extend the same interface to files.

Design and usage emphasize type safety and extensibility, with locale support and facets that influence formatting and parsing. Iostreams form a cohesive alternative to printf-style I/O in C++ and are a fundamental part of the standard library, widely used for console I/O, logging, and data serialization in portable C++ programs.