StdAfx + 头文件 - MFC 应用程序中的包含顺序

2021-12-22 00:00:00 compiler-errors visual-c++ c++ mfc stdafx.h

我使用的是 Visual Studio 2005.我创建了一个名为StdAfx 依赖"的基于 MFC 的控制台应用程序.IDE 为我创建了以下文件.

I am using Visual Studio 2005. I created an MFC based console application named "StdAfx dependancy". The IDE created the following files for me.

  1. 资源.h
  2. StdAfx Dependancy.h
  3. stdafx.h
  4. StdAfx Dependancy.cpp
  5. stdafx.cpp

我添加了另一个类 CHelper 和 Helper.h 和 Helper.cpp，如下所示.

I added another class CHelper with Helper.h and Helper.cpp as below.

Helper.h:

#pragma once

class CHelper
{
public:
    CHelper(void);
    ~CHelper(void);
};

Helper.cpp

#include "StdAfx.h"
#include "Helper.h"

CHelper::CHelper(void)
{
}

CHelper::~CHelper(void)
{
}

我在主函数中为CHelper创建了一个对象；为此，我在 StdAfx Dependancy.cpp 的第一行中添加了 Header.h 文件，如下所示；我收到了以下错误.

I created an object for CHelper in the main function; to achieve this I added Header.h file in the first line of StdAfx Dependancy.cpp as below; and I got the following errors.

d:codesstdafx 依赖项stdafx依赖stdafx依赖.cpp(33):错误 C2065:CHelper":未声明标识符
d:codesstdafx依赖stdafx 依赖stdafxdependancy.cpp(33):错误 C2146:语法错误:缺少；"前标识符myHelper"
d:codesstdafx依赖stdafx 依赖stdafxdependancy.cpp(33):错误 C2065:'myHelper' : 未声明的标识符

d:codesstdafx dependancystdafx dependancystdafx dependancy.cpp(33) : error C2065: 'CHelper' : undeclared identifier
d:codesstdafx dependancystdafx dependancystdafx dependancy.cpp(33) : error C2146: syntax error : missing ';' before identifier 'myHelper'
d:codesstdafx dependancystdafx dependancystdafx dependancy.cpp(33) : error C2065: 'myHelper' : undeclared identifier

但是当我在 stdafx.h 之后包含它时，错误消失了.为什么?

But when I include it after stdafx.h, the error vanishes. Why?

// Stdafx dependancy.cpp : Defines the entry point for the console application.
//

#include "Helper.h"

#include "stdafx.h"
#include "Stdafx dependancy.h"

// #include "Helper.h" --> If I include it here, there is no compilation error

#ifdef _DEBUG
#define new DEBUG_NEW
#endif


// The one and only application object

CWinApp theApp;

using namespace std;

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
    int nRetCode = 0;

    // initialize MFC and print and error on failure
    if (!AfxWinInit(::GetModuleHandle(NULL), NULL, ::GetCommandLine(), 0))
    {
        // TODO: change error code to suit your needs
        _tprintf(_T("Fatal Error: MFC initialization failed
"));
        nRetCode = 1;
    }
    else
    {
        CHelper myHelper;
    }

    return nRetCode;
}

推荐答案

这个链接一定会给你一些线索.stdafx.h 的目的

This link must give you some clue. Purpose of stdafx.h

在之前定义的行#include "stdafx.h" 被编译器忽略.因此，如果您想真正包含这些文件，那么您需要将它们包含在 #include "stdafx.h" 之后.

The lines defined before the #include "stdafx.h" are ignored by the compiler. So if you want to actually include those files then you need to include them after the #include "stdafx.h".

希望它很清楚.

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