“std::endl” vs “\n”

Question

Many C++ books contain example code like this...

std::cout << \"Test line\" << std::endl;

...so I\'ve always done that too. But

Answer 1

With reference This is an output-only I/O manipulator.

std::endl Inserts a newline character into the output sequence os and flushes it as if by calling os.put(os.widen('\n')) followed by os.flush().

When to use:

This manipulator may be used to produce a line of output immediately,

e.g.

when displaying output from a long-running process, logging activity of multiple threads or logging activity of a program that may crash unexpectedly.

Also

An explicit flush of std::cout is also necessary before a call to std::system, if the spawned process performs any screen I/O. In most other usual interactive I/O scenarios, std::endl is redundant when used with std::cout because any input from std::cin, output to std::cerr, or program termination forces a call to std::cout.flush(). Use of std::endl in place of '\n', encouraged by some sources, may significantly degrade output performance.