Endl

endl is a manipulator in the C++ standard library used with output streams, such as std::cout. It inserts a newline character into the stream and then flushes the stream. The manipulator is defined in the header <ostream> (and is typically included via <iostream>).

Usage: It is applied with the insertion operator, for example: std::cout << "Hello" << std::endl; This writes the newline and immediately flushes the stream, ensuring all buffered output is delivered to the underlying device. Flushing can be important for interactive programs and for making logs appear promptly, but it can incur performance costs when used repeatedly in tight loops.

By contrast, writing "\n" inserts only a newline without flushing. If a flush is desired without inserting a newline, std::flush can be used. The behavior of endl is independent of platform newline conventions; for narrow streams it inserts the character '\n', and for wide streams it inserts L'\n'. The actual newline representation in a file may depend on the system, but endl always performs a flush after inserting the appropriate newline character.

Guidance: in performance-sensitive code, prefer '\n' over endl unless an immediate flush is required. Use endl when you need to ensure the user sees prompts or diagnostic messages promptly. endl is a portable standard feature of the C++ iostream library.