关于_WIN32_WINNT
本打算了解一下纤程内容，在试图使用 ConvertThreadToFiber的时候，编译总是出错，提示信息如下：error C2065: 'ConvertThreadToFiber' : undeclared identifier，编译器告诉我“函数未声明”。于是转而查看MSDN，有内容如下：
Requirements:
Windows NT/2000: Requires Windows NT 3.51 SP3 or later.
Windows 95/98: Requires Windows 98.
Header: Declared in Winbase.h; include Windows.h.
Library: Use Kernel32.lib.
但明明已经#include <Windows.h>了。不得已，又经Windows.h进入Winbase.h中，查看源码，见声明之前有条件编译语 句：#if(_WIN32_WINNT >= 0x0400)，由此发现我的程序并没有声明宏_WIN32_WINNT。最终在StdAfx.h文件的#include <windows.h>语句之前添加语句：
#define _WIN32_WINNT 0x0400
编译通过。
理解_WIN32_WINNT的作用：
需要你自已在stdafx.h头文件中定义。编译器根据此宏来确定windows的版本，如果你需要使用高版本的WIN32函数,只有你定义了此宏后才能使用
Windows XP _WIN32_WINNT>=0x0501
Windows 2000 _WIN32_WINNT>=0x0500
Windows NT 4.0 _WIN32_WINNT>=0x0400
Windows Me _WIN32_WINDOWS=0x0490
Windows 98 _WIN32_WINDOWS>=0x0410
Internet Explorer 6.0 _WIN32_IE>=0x0600
Internet Explorer 5.01, 5.5 _WIN32_IE>=0x0501
Internet Explorer 5.0, 5.0a, 5.0b _WIN32_IE>=0x0500
Internet Explorer 4.01 _WIN32_IE>=0x0401
Internet Explorer 4.0 _WIN32_IE>=0x0400
Internet Explorer 3.0, 3.01, 3.02 _WIN32_IE>=0x0300
PS:当然也可以在程序的C++的预处理器中设置。
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MSDN中的描述
Using the SDK Headers
This version of the Microsoft® Platform SDK enables you to create applications that run on Microsoft Windows® 95, Microsoft Windows NT® 4.0, Windows® 98, Windows Millennium Edition (Windows Me), Windows 2000, Windows XP, and Windows .NET Server 2003 family. You can also create 64-bit applications. The header files use data types that allow you to build both 32- and 64-bit versions of your application from a single source code base. For more information, see Getting Ready for 64-bit Windows.
Microsoft® Visual C++® includes content from the edition of the Platform SDK that was current at the time Visual C++ was released. Therefore, if you install the latest Platform SDK, you may end up with multiple versions of the same header files on your computer. To ensure that you are using the latest version of the SDK header files, follow the directions included in Installing the Platform SDK with Visual Studio. Otherwise, you will receive the following error when compiling code that uses features that were introduced after Visual C++ was released: error C2065: undeclared identifier.
Certain functions that depend on a particular version of Windows are declared using conditional code. This enables you to use the compiler to detect whether your application uses functions that are not supported on its target version(s) of Windows. To compile an application that uses these functions, you must define the appropriate macros. Otherwise, you will receive the C2065 error message. The following table indicates the macros you must define to target each system.
Minimum system required Macros to define
Windows .NET Server 2003 family _WIN32_WINNT>=0x0502
Windows XP _WIN32_WINNT>=0x0501
Windows 2000 _WIN32_WINNT>=0x0500
Windows NT 4.0 _WIN32_WINNT>=0x0400
Windows Me _WIN32_WINDOWS=0x0490
Windows 98 _WIN32_WINDOWS>=0x0410
Internet Explorer 6.0 _WIN32_IE>=0x0600
Internet Explorer 5.01, 5.5 _WIN32_IE>=0x0501
Internet Explorer 5.0, 5.0a, 5.0b _WIN32_IE>=0x0500
Internet Explorer 4.01 _WIN32_IE>=0x0401
Internet Explorer 4.0 _WIN32_IE>=0x0400
Internet Explorer 3.0, 3.01, 3.02 _WIN32_IE>=0x0300
For example, to use the features specifically marked for Windows 2000 in the header files, you need to explicitly define _WIN32_WINNT as 0x0500 or greater. You can define the symbols using the #define statement in each source file, or by specifying the /D_WIN32_WINNT=0x0500 compiler option supported by Visual C++.
Visual C++ 6.0: To specify compiler options, go to the Projects menu and click Settings, then select the C/C++ tab.
Visual C++ 7.0: To specify compiler options, go to the Projects menu and click Properties.
The macros in Win32.mak can help you define the correct macros. The value of _WIN32_WINNT depends on the platform you choose to target. For more information, see Building Applications Using Win32.mak.