它们是用于定义windows和Internet Explorer版本号的，用于区分不用版本的函数和参数。
在你编译程序时会根据不同的版本系统号，链接不同的函数和参数。
Minimum System Required Macros to Define
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Windows 95 and Windows NT 4.0 WINVER=0x0400
Windows 98 and Windows NT 4.0 _WIN32_WINDOWS=0x0410 and WINVER=0x0400
Windows NT 4.0 _WIN32_WINNT=0x0400 and WINVER=0x0400
Windows 98 _WIN32_WINDOWS=0x0410
Windows 2000 _WIN32_WINNT=0x0500 and WINVER=0x0500
Windows Me _WIN32_WINDOWS=0x0490
Windows XP and Windows .NET Server _WIN32_WINNT=0x0501 and WINVER=0x0501
Internet Explorer 3.0,3.01,3.02 _WIN32_IE=0x0300
Internet Explorer 4.0 _WIN32_IE=0x0400
Internet Explorer 4.01 _WIN32_IE=0x0401
Internet Explorer 5.0,5.0a,5.0b _WIN32_IE=0x0500
Internet Explorer 5.01,5.5 _WIN32_IE=0x0501
Internet Explorer 6.0 _WIN32_IE=0x0560 or _WIN32_IE=0x0600