windows.h 和 MFC
为什么我不能在 afx(MFC) 项目中包含 windows.h?
Why can't I include windows.h in afx(MFC) projects?
推荐答案
通常，MFC 应用程序代码包括 afx.h 或 afxwin.h(后者包括前者).windows.h 的前两行是
Typically, MFC application code includes afx.h or afxwin.h (the latter includes former). First two lines of windows.h are
#ifndef _WINDOWS_
#define _WINDOWS_
这意味着如果包含此标头，则定义 _WINDOWS_.Afx.h 包含 afxver_.h 且此标头包含 afxv_w32.h 包含以下代码:
which means that _WINDOWS_ becomes defined if this header is included.
Afx.h includes afxver_.h and this header includes afxv_w32.h which contains following code:
#ifdef _WINDOWS_
#error WINDOWS.H already included. MFC apps must not #include <windows.h>
#endif
...
#include <windows.h>
因此，如果您在 MFC 头文件之前包含 windows.h，您将在编译时生成此错误，并且如您所见，如果您包含 afxwin.h 你不需要自己包含 windows.h - afxv_w32.h 已经包含了它.
So, if you include windows.h before MFC headers, you'll get this error generated in compile time and, as you can see, if you include afxwin.h you don't need to include windows.h yourself - it will already be included by afxv_w32.h.
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