C2065'cout'：未声明的标识符[关闭]

Posted 2021-04-24

所以我是C ++的完整菜鸟，我正在尝试为作业制作一个简单的“Hello world”程序。我的代码如下：

#include "stdafx.h"
#include <iostream>
using namespace std;
int main() {
    cout<<"hello world!";
    return 0;
}

出于某种原因，VS2017在cout上抛出一个错误，说这是未定义的。我已经对旧帖子做了一些关于此的阅读，并在#include "stdafx.h中添加，看看是否会按照旧建议解决它，但它继续给我错误。有任何想法吗？

编辑：

再一次完整的菜鸟，但是当我搜索它时会出现多个版本的stdafx.h，这里看起来像是“主要”的：

  // stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently,
// but are changed infrequently

#pragma once

#ifndef STRICT
#define STRICT
#endif

#include "targetver.h"

[!if SERVICE_APP]
#define _ATL_FREE_THREADED
[!else]
#define _ATL_APARTMENT_THREADED
[!endif]

#define _ATL_NO_AUTOMATIC_NAMESPACE

#define _ATL_CSTRING_EXPLICIT_CONSTRUCTORS  // some CString constructors will be explicit

[!if PREVIEW_HANDLER || THUMBNAIL_HANDLER || SEARCH_HANDLER]
#ifdef _MANAGED
#error File type handlers cannot be built as managed assemblies.  Set the Common Language Runtime options to no CLR support in project properties.
#endif

#ifndef _UNICODE
#error File type handlers must be built Unicode.  Set the Character Set option to Unicode in project properties.
#endif

#define SHARED_HANDLERS

[!endif]
[!if SUPPORT_MFC]
#include <afxwin.h>
#include <afxext.h>
#include <afxole.h>
#include <afxodlgs.h>
#include <afxrich.h>
#include <afxhtml.h>
#include <afxcview.h>
#include <afxwinappex.h>
#include <afxframewndex.h>
#include <afxmdiframewndex.h>

#ifndef _AFX_NO_OLE_SUPPORT
#include <afxdisp.h>        // MFC Automation classes
#endif // _AFX_NO_OLE_SUPPORT
[!endif]
[!if SUPPORT_COMPLUS]

#include <comsvcs.h>
[!endif]

#define ATL_NO_ASSERT_ON_DESTROY_NONEXISTENT_WINDOW

#include "resource.h"
#include <atlbase.h>
#include <atlcom.h>
#include <atlctl.h>

答案

error C2065: 'cout': undeclared identifier是缺乏#include <iostream>的结果。第一个原因可能是stdafx.h内容。你提供的那个，我不太确定它与你的main.cpp /项目有什么关系。让我们从一个新项目开始：... VS2017 IDE：创建新项目，ConsoleApplication项目类型，并用您的main()函数替换。

VS2017 IDE（15.8.2）全新的ConsoleApplication项目：ConsoleApplication1

// ConsoleApplication1.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {

    cout << "hello world!";
    return 0;
}

stdafx.h :(由IDE生成）

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//

#pragma once

#include "targetver.h"


// TODO: reference additional headers your program requires here

stdafx.cpp :(由IDE生成）

// stdafx.cpp : source file that includes just the standard includes
// ConsoleApplication1.pch will be the pre-compiled header
// stdafx.obj will contain the pre-compiled type information

#include "stdafx.h"

// TODO: reference any additional headers you need in STDAFX.H
// and not in this file

targetver.h :(由IDE生成）

#pragma once

// Including SDKDDKVer.h defines the highest available Windows platform.

// If you wish to build your application for a previous Windows platform, include WinSDKVer.h and
// set the _WIN32_WINNT macro to the platform you wish to support before including SDKDDKVer.h.

#include <SDKDDKVer.h>

**此代码运行完美。 **

--

“当我搜索它时会出现多个版本的stdafx.h” - 你的意思是什么？在你的项目中？在网上？你不能只从互联网上拿一个stdafx.h。 stdafx.h内容是根据项目量身定制的，而不是通用的。例如，我在上面提供的是IDE默认的新ConsoleApplication项目stdafx.h。您可以根据项目需要添加到文件中。