问题：
What is the difference between an abstract function and a virtual function? 抽象函数和虚函数有什么区别？ In which cases is it recommended to use virtual or abstract? 建议在哪种情况下使用虚拟或抽象？ Which one is the best approach? 哪种方法最好？
解决方案：
参考一： https://stackoom.com/question/1dqF/抽象函数和虚函数有什么区别参考二： https://oldbug.net/q/1dqF/What-is-the-difference-between-an-abstract-function-and-a-virtual-function
来源：oschina
链接：https://my.oschina.net/stackoom/blog/3217467