C2065 'cout'：未声明的标识符

C2065 'cout': undeclared identifier

本文关键字：标识符 未声明 cout C2065      更新时间：2023-10-16

所以我是一个完全的菜鸟C++，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抛出错误，说它是未定义的。我已经阅读了一些关于此的旧帖子，并添加了#include "stdafx.h，看看这是否会按照旧建议解决它，但它继续给我错误。有什么想法吗？

编辑：

再次是一个完整的菜鸟，但是当我搜索它时会出现多个版本的stdafx.h，这是看起来像"主要"版本的内容：

// 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>

error C2065: 'cout': undeclared identifier是缺少#include <iostream>的结果。第一个原因可能是内容stdafx.h。您提供的那个，我不太确定它与您的main.cpp/项目有何关系。让我们从一个新的项目开始：...VS2017 IDE：创建新项目，ConsoleApplication 项目类型，并将main()函数替换为您的函数。

VS2017 IDE(15.8.2(全新控制台应用程序项目：控制台应用程序1

// 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">- 你是什么意思？在您的项目中？在互联网上？你不能只从互联网上拿一个stdafx.h。stdafx.h内容是按项目量身定制的，而不是通用的。例如，我上面提供的是IDE默认的新控制台应用程序项目stdafx.h。您可以根据项目需要添加到文件中。

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