cout

Cout is the standard output stream in the C++ programming language. It is an object of type std::ostream defined in the iostream header and resides in the std namespace. std::cout writes data to the standard output, typically the console, and is usually globally accessible as std::cout.

Data is sent to cout using the insertion operator, operator<<, which is overloaded for built-in types as well as many standard library types. The operator<< returns a reference to the stream, enabling chaining of inserts in a single expression. Example: std::cout << "Hello, " << name << '!' << std::endl; This prints the string, the value of name, a exclamation mark, and a newline.

Formatting and manipulators: cout maintains a formatting state that includes width, precision, fill character, and format flags. Formatting can be controlled with manipulators from the iomanip header, such as std::setw, std::setprecision, std::hex, std::dec, and std::boolalpha. std::endl inserts a newline and flushes the stream, while std::flush flushes without adding a newline. For wide characters, std::wcout and related facilities are used.

Performance and behavior: By default, iostreams may be synchronized with the C stdio library, which can be disabled with std::ios::sync_with_stdio(false) to improve performance at the cost of interoperability with C I/O. std::cout is typically tied to std::cin, causing cout to flush before input operations. The stream also maintains error state flags (good, fail, bad, eof) that can be checked after operations.

User-defined types: To output custom types with cout, one typically provides an overloaded operator<< for std::ostream& and the type, enabling seamless streaming of objects.