StdAfx + 头文件 - MFC 应用程序中包含的顺序

2022-01-12 00:00:00 compiler-errors visual-c++ c++ mfc stdafx.h

我正在使用 Visual Studio 2005.我创建了一个基于 MFC 的控制台应用程序，名为StdAfx 依赖".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

我用 Helper.h 和 Helper.cpp 添加了另一个类 CHelper，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；为了实现这一点，我在 StdAfx Dependancy.cpp 的第一行添加了 Header.h 文件，如下所示；我收到以下错误.

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 依赖关系stdafx依赖stdafx 依赖.cpp(33) :错误 C2065:'CHelper':未声明标识符
d:代码stdafx依赖stdafx 依赖stdafxdependancy.cpp(33):错误 C2146:语法错误:缺少 ';'前标识符myHelper"
d:代码stdafx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

这个链接一定能给你一些线索.stdafx.h的目的

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

之前定义的行#include "stdafx.h" 被编译器忽略.因此，如果您想实际包含这些文件，则需要在 #include "stdafx.h" 之后包含它们.

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".

希望清楚.

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