error C2065: 'cout' : undeclared identifier

Question

I am working on the 'driver' part of my programing assignment and i keep getting this absurd error:

error C2065: 'cout' : undeclared identifier

I have even tried using the std::cout but I get another error that says:

IntelliSense: namespace "std" has no member "cout"

When I have declared using namespace std, included iostream and I even tried to use ostream

#include <iostream>
using namespace std;

int main () {
    cout << "hey" << endl;
 return 0;
}

I'm using Visual Studio 2010 and running Windows 7. All of the .h files have using namespace std and include iostream and ostream.

Answer 1

In Visual Studio you must #include "stdafx.h" and be the first include of the cpp file. For instance:

These will not work.

#include <iostream>
using namespace std;
int main () {
    cout << "hey" << endl;
    return 0;
}




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

This will do.

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

Here is a great answer on what the stdafx.h header does.

Answer 2

write this code, it works perfectly..

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

using namespace std;

int main()
{
 cout<<"Hello World!";
  return 0;
}

Answer 3

I had same problem on Visual Studio C++ 2010. It's easy to fix. Above the main() function just replace the standard include lines with this below but with the pound symbol in front of the includes.

# include "stdafx.h"
# include <iostream>
using  namespace std;

Answer 4

The include "stdafx.h" is ok

But you can't use cout unless you have included using namespace std

If you have not included namespace std you have to write std::cout instead of simple cout

Answer 5

If the only file you include is iostream and it still says undefined, then maybe iostream doesn't contain what it's supposed to. Is it possible that you have an empty file coincidentally named "iostream" in your project?

Answer 6

I've seen similar things happen when I was using the .c file extension with C++ code. Other than that, I'd have to agree with everyone about a buggy installation. Does it work if you try to compile the project with an earlier release of VS? Try VC++ Express 2008. Its free on msdn.

Answer 7

I have seen that if you use

#include <iostream.h>

then you will get the problem.

If you use

#include <iostream>  

(notice - without the .h)

then you will not get the problem you mentioned.

Answer 8

If you started a project requiring the #include "stdafx.h" line, put it first.

Answer 9

Such a silly solution in my case:

// Example a
#include <iostream>    
#include "stdafx.h"

The above was odered as per example a, when I changed it to resemble example b below...

// Example b
#include "stdafx.h"
#include <iostream>  

My code compiled like a charm. Try it, guaranteed to work.

Answer 10

before you begin this program get rid of all the code and do a simple hello world inside of main. Only include iostream and using namespace std;. Little by little add to it to find your issue.

cout << "hi" << endl;

Answer 11

The code below compiles and runs properly for me using gcc. Try copy/pasting this and see if it works.

#include <iostream>
using namespace std;

int bob (int a) { cout << "hey" << endl; return 0; };

int main () {
    int a = 1;
    bob(a);
    return 0;
}

Answer 12

I have VS2010, Beta 1 and Beta 2 (one on my work machine and one at home), and I've used std plenty without issues. Try typing:

std::

And see if Intellisense gives you anything. If it gives you the usual stuff (abort, abs, acos, etc.), except for cout, well then, that is quite a puzzler. Definitely look into your C++ headers in that case.

Beyond that, I would just add to make sure you're running a regular, empty project (not CLR, where Intellisense is crippled), and that you've actually attempted to build the project at least once. As I mentioned in a comment, VS2010 parses files once you've added an include; it could be that something stuck the parser and it didn't "find" cout right away. (In which case, try restarting VS maybe?)

Answer 13

I had the same issue when starting a ms c++ 2010 project from scratch - I removed all of the header files generated by ms and but used:

#include "stdafx.h"
#include <iostream>
using namespace std;

int main() {
   cout << "hey" << endl;
   return 0;
}

I had to include stdafx.h as it caused an error not having it in.

Answer 14

Try it, it will work. I checked it in Windows XP, Visual Studio 2010 Express.

#include "stdafx.h"
#include <iostream>
using namespace std;

void main( ) 
{
   int i = 0;
   cout << "Enter a number: ";
   cin >> i;
}

Answer 15

Take the code

#include <iostream>
using namespace std;

out of your .cpp file, create a header file and put this in the .h file. Then add

#include "whatever your header file is named.h"

at the top of your .cpp code. Then run it again.

Answer 16

When you created your project, you did not set 'use precompiled headers' correctly. Change it in properties->C/C++->precompiled headers.

Answer 17

In Visual studio use all your header filer below "stdafx.h".

Answer 18

Are you sure it's compiling as C++? Check your file name (it should end in .cpp). Check your project settings.

There's simply nothing wrong with your program, and cout is in namespace std. Your installation of VS 2010 Beta 2 is defective, and I don't think it's just your installation.

I don't think VS 2010 is ready for C++ yet. The standard "Hello, World" program didn't work on Beta 1. I just tried creating a test Win32 console application, and the generated test.cpp file didn't have a main() function.

I've got a really, really bad feeling about VS 2010.

Answer 19

Just use printf!

Include stdio.h in your stdafx.h header file for printf.

Answer 20

Include the std library by inserting the following line at the top of your code:

using namespace std;

Answer 21

is normally stored in the C:\Program Files\Microsoft Visual Studio 8\VC\include folder. First check if it is still there. Then choose Tools + Options, Projects and Solutions, VC++ Directories, choose "Include files" in the "Show Directories for" combobox and double-check that $(VCInstallDir)include is on top of the list.

Answer 22

I came here because I had the same problem, but when I did #include "stdafx.h" it said it did not find that file.
What did the trick for me was: #include <algorithm>.
I use Microsoft Visual Studio 2008.
These are the things that you can use then, incl. 'count': Link

Answer 23

Had this problem, when header files declared "using namespace std;", seems to be confusing for GNU compiler; anyway is bad style!

Solution was providing std::cout ... in headers and moving "using namespace std" to the implementation file.

Answer 24

I ran across this error after just having installed vs 2010 and just trying to get a nearly identical program to work.

I've done vanilla C coding on unix-style boxes before, decided I'd play with this a bit myself.

The first program I tried was:

#include "stdafx.h"


int _tmain(int argc, _TCHAR* argv[])
{
    cout << "Hello World!";
    return 0;
}

The big thing to notice here... if you've EVER done any C coding,

int _tmain(int argc, _TCHAR* argv[])

Looks weird. it should be:

int main( int argc, char ** argv )

In my case I just changed the program to:

#include <iostream>
using namespace std;

int main()
{
     cout << "Hello world from  VS 2010!\n";
     return 0;
}

And it worked fine.

Note: Use CTRL + F5 so that the console window sticks around so you can see the results.

Answer 25

In VS2017, stdafx.h seems to be replaced by pch.h see this article,

so use:

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

using namespace std;

int main() {
    cout << "Enter 2 numbers:" << endl;

Answer 26

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It was the compiler - I'm now using Eclipse Galileo and the program works like a wonder

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