基于 WinSock 的网络聊天软件的设计与实现 专业班级：网络工程**** 姓名：** 学号：*******
Most messages in Windows are strictly defined and apply to all programs. For example, a
WM_CREATE message is sent when a window is being created, a WM_LBUTTONDOWN
message is sent when the user presses the left mouse button, a WM_CHAR message is sent
when the user types a character, and a WM_CLOSE message is sent when the user closes a
window. All messages have two 32-bit parameters that convey information such as cursor
coordinates, key code, and so forth. Windows sends WM_COMMAND messages to the
appropriate window in response to user menu choices, dialog button clicks, and so on.
Command message parameters vary depending on the window's menu layout. You can define
your own messages, which your program can send to any window on the desktop. These user-
defined messages actually make C++ look a little like Smalltalk.
Don't worry yet about how these messages are connected to your code. That's the job of the
application framework. Be aware, though, that the Windows message processing requirement
imposes a lot of structure on your program. Don't try to force your Windows programs to look
like your old MS-DOS programs. Study the examples in this book, and then be prepared to
start fresh.
1.2 The Windows Graphics Device Interface
Many MS-DOS programs wrote directly to the video memory and the printer port. The
disadvantage of this technique was the need to supply driver software for every video board
and every printer model. Windows introduced a layer of abstraction called the Graphics
Device Interface (GDI). Windows provides the video and printer drivers, so your program
doesn't need to know the type of video board and printer attached to the system. Instead of
addressing the hardware, your program calls GDI functions that reference a data structure
called a device context. Windows maps the device context structure to a physical device and
issues the appropriate input/output instructions. The GDI is almost as fast as direct video
access, and it allows different applications written for Windows to share the display.
1.3 Resource-Based Programming
To do data-driven programming in MS-DOS, you must either code the data as initialization
constants or provide separate data files for your program to read. When you program for
Windows, you store data in a resource file using a number of established formats. The linker
2
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