一段很经典话

              How can an oprerating send a message to a program?

 

           When I say that "Windows sends a message to the program"I mean that Windows calls a funtion within the program-a funtion that you write and which is an essential part of your program's code. The parameters to this function describe the particular message that is being sent by Windows and received by your program. This function in your program is known as the "window procedure"