iostream

iostream is a header in the C++ standard library that provides facilities for input and output through streams. It declares the standard stream objects used for console I/O and defines the core streaming interfaces that enable formatted communication between programs and their I/O devices.

Standard streams defined in iostream include std::cin for input, std::cout for output, std::cerr for error reporting, and std::clog for logging. Wide-character variants (std::wcin, std::wcout, std::wcerr, std::wclog) are provided as well. These objects are generally instances of the template classes std::basic_istream and std::basic_ostream, and they support chained operations using the insertion (<<) and extraction (>>) operators.

The header also supports formatting control through stream state, flags, and manipulators. Typical usage involves sending data to std::cout or reading from std::cin, with standard operators overloaded for many built-in and user-defined types. The iostream facilities form the basis for more specialized streams, including file streams (provided by <fstream>) and string streams (provided by <sstream>).

Implementations of iostream are part of the C++ standard library and are designed to be portable across compilers. Performance considerations include the ability to synchronize or decouple C and C++ standard I/O when mixing libraries; by default, iostreams may be synchronized with C stdio for compatibility.