basicostream

basic_ostream is a class template in the C++ standard library that provides the interface for output streams. It forms the basis for character-output streams, coordinating writing to an underlying stream buffer and offering formatting controls and insertion operations used by higher-level stream classes.

Template parameters are charT, the character type (for example char or wchar_t), and Traits, the character traits type (defaulting to std::char_traits<charT>). basic_ostream inherits from std::basic_ios<charT, Traits> and relies on a stream buffer (std::basic_streambuf<charT, Traits>), accessed via rdbuf(), to perform the actual I/O.

It supplies member functions for direct writing, such as put and write, and for controlling output positioning with seekp and tellp. It also exposes formatting state—width, precision, fill and the format flags—through setf, unsetf and related accessors. The insertion operators (operator<<) for a wide range of types ultimately dispatch through these facilities and the num_put locale facet to render values as text.

std::ostream is a common instantiation of basic_ostream<char>, while std::wostream uses wchar_t. The template also underpins other aliases and specializations, allowing different character encodings to be written through the same interface.

Concrete stream types such as std::cout, std::cin, std::ofstream, and std::ostringstream derive from basic_ostream, providing writable output to the console, files, or in-memory buffers. The class plays a central role in the iostreams library by coordinating formatting, buffering, and the insertion-based output interface used throughout C++.