有时候，DefWindowProc处理完消息后会产生其它的消息。例如，假设使用者执行HELLOWIN，并且使用者最终单击了 Close按钮，或者假设用键盘或鼠标从系统菜单中选择了 Close， DefWindowProc处理这一键盘或者鼠标输入，在检测到使用者选择了Close选项之后，它给窗口消息处理程序发送一条WM_SYSCOMMAND消息。WndProc将这个消息传给DefWindowProc。DefWindowProc给窗口消息处理程序发送一条WM_CLOSE消息来响应之。WndProc再次将它传给DefWindowProc。DestroyWindow呼叫DestroyWindow来响应这条WM_CLOSE消息。DestroyWindow导致Windows给窗口消息处理程序发送一条WM_DESTROY消息。WndProc再呼叫PostQuitMessage，将一条WM_QUIT消息放入消息队列中，以此来响应此消息。这个消息导致WinMain中的消息循环终止，然后程序结束。
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Sometimes messages generate other messages as a result of DefWindowProc processing. For example, suppose you run HELLOWIN and you eventually click the Close button, or suppose you select Close from the system menu using either the keyboard or the mouse. DefWindowProc processes this keyboard or mouse input. When it detects that you have selected the Close option, it sends a WM_SYSCOMMAND message to the window procedure. WndProc passes this message to DefWindowProc. DefWindowProc responds by sending a WM_CLOSE message to the window procedure. WndProc again passes this message to DefWindowProc. DefWindowProc responds to the WM_CLOSE message by calling DestroyWindow. DestroyWindow causes Windows to send a WM_DESTROY message to the window procedure. WndProc finally responds to this message by calling PostQuitMessage to put a WM_QUIT message in the message queue. This message causes the message loop in WinMain to terminate and the program to end.
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