[待解决]C++ primer中有关endl刷新输出流

Programmers often insert print statements during debugging. Such statements should always flush the stream. Forgetting to do so may cause output to be left in the buffer if the program crashes, leading to incorrect inferences about where the program crashed.

程序员经常在调试过程中插入输出语句，这些语句都应该刷新输出流。忘记刷新输出流可能会造成输出停留在缓冲区中，如果程序崩溃，将会导致程序错误推断崩溃位置。