如何在非MFC程序中使用MFC类——解决#error : WINDOWS.H already included.

我想在WinProc函数中使用CFileDialog类，于是#include <afxdlgs.h>以后编译，出现了以下错误：

c:/program files/microsoft visual studio/vc98/mfc/include/afxv_w32.h(14) : fatal error C1189: #error : WINDOWS.H already included. MFC apps must not #include <windows.h>

于是， 我在VC6.0集成环境中的菜单项project下的setting中设置使用MFC例"use mfc in a shared DLL"

即：

project->setting->general->Microsoft Foundation Classed: 选择 Use MFC in a shared DLL"

同时，加入：

#include <afxwin.h>//使用MFC
#include "afxdlgs.h"//使用CFileDialog类需要包含它

#include "cv.h"
#include "cxcore.h"
#include "highgui.h"
#include "stdafx.h"
#include "resource.h"
#include "commdlg.h"
#include "direct.h"
#include "stdio.h"
#include "LbqSVM1.h"
#include "HogOfImage.h"
#include "Winbase.h"

#include <afxwin.h>
#include "afxdlgs.h"

后编译错误依然存在，于是把顺序调换一下：

#include <afxwin.h>
#include "afxdlgs.h"

#include "cv.h"
#include "cxcore.h"
#include "highgui.h"
#include "stdafx.h"
#include "resource.h"
#include "commdlg.h"
#include "direct.h"
#include "stdio.h"
#include "LbqSVM1.h"
#include "HogOfImage.h"
#include "Winbase.h"

编译通过！

学会两点：

1、在project->setting->general->Microsoft Foundation Classed: 选择 Use MFC in a shared DLL

2、#include 顺序调换可能会解决问题