A callback function is essentially an event handler that is implemented by an application and called by the system. Microsoft® Windows® applications typically implement multiple callback functions, each one designed for a particular set of events. When an event occurs, the system notifies the application by calling the appropriate callback function. The callback function also usually has a parameter list that the system can use to pass the application more detailed information about the event. The most common example of a callback function is the window procedure. This function is used by the system to pass Windows messages to the applications that owns the window.
通样比如一些枚举函数也是通过CallBack实现的,比如枚举文件,系统只是告诉你找到了要找的文件这个事件,而如何处理完全有你的CallBack函数决定啊。