endl and flushing the buffer

Question

In the C++ primer book, in chapter (1), it mentions the following:

endl is a special value, called a manipulator, that when written t

Answer 1

When using std::cout, the operand used after the output operator ( << ) are stored in a buffer and are not displayed onto the stdin (usually terminal, or the command prompt) until it comes across std::endl or std::cin, which causes the buffer to be flushed, in the sense, display/output the contents of the buffer onto the stdin.

Consider this program:

#include 
#include 

int main(void)
{
    std::cout << "Hello, world";
    sleep(2);
    std::cout << std::endl;

    return 0;
}

The output obtained will be:

after 2 seconds

Hello, World