cout is not a member of std

Question

I'm practicing using mulitple files and header files etc. So I have this project which takes two numbers and then adds them. Pretty simple.

Here are my files:

main.cpp

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

int main()
{
    int x = readNumber();
    int y = readNumber();

    writeAnswer(x + y);

    return(0);
}

io.cpp

int readNumber()
{
    int x;

    std::cout << "Number: ";
    std::cin >> x;

    return x;
}

void writeAnswer(int x)
{
    std::cout << "Answer: ";
    std::cout << x;
}

add.h

#ifndef ADD_H_INCLUDED
#define ADD_H_INCLUDED

int readNumber();
void writeAnswer(int x);

#endif // #ifndef ADD_H_INCLUDED

The error is showing up in io.cpp. The exact errors are:

Does anyone have any idea why this may be happening? Thanks.

EDIT: I made a small project yesterday with the same amount of files (2 .cpp and 1.h) and I didn't include the iostream header in the other .cpp and it still compiled and ran fine.

Re your edit: then you compiled that project differently. Including iostream in your second cpp file is **required** as you have it here. Maybe you had that include in the `.h` file last time around. — Mat, Jul 07 '12 at 14:58
Yeah, it's working great now, thanks for the quick responses everyone! :) — Paul Hannon, Jul 07 '12 at 15:01

score 426 · Accepted Answer · answered Jul 07 '12 at 14:45

426

add #include <iostream> to the start of io.cpp too.

answered Jul 07 '12 at 14:45

unkulunkulu

11,576
2
31
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6

iostream has to be included (directly or indirectly). Otherwise how would the compiler know where to find std::cout. – A. K. Jul 07 '12 at 14:56
1

I understand what you're saying. Thanks. Though how did I get my other proj. to work without including it in the other .cpp too? I updated OP at the bottom. – Paul Hannon Jul 07 '12 at 14:58
2

You´ve probably included it indirectly. It is ALWAYS required. – Sebastian Hoffmann Jul 07 '12 at 14:58
2

I needed to include it in a .h file as well!! Thanks – user391339 Dec 20 '14 at 03:06
4

also it has to be included after `stdafx.h`, not before – Alex Apr 15 '18 at 20:30

score 26 · Answer 2 · edited Aug 13 '22 at 11:55

26

If you're using pre-compiled headers with Microsoft's compiler (MSVC), remember that it must be:

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

and not the other way around:

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

In other words, the pre-compiled header include file must always come first. (The compiler should give you an error specifically explaining this if you forget.)

edited Aug 13 '22 at 11:55

Cody Gray - on strike

239,200
50
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574

answered Sep 20 '18 at 19:41

Jukes

407
4
5

score 1 · Answer 3 · answered May 22 '18 at 17:26

1

I had a similar issue and it turned out that i had to add an extra entry in cmake to include the files.

Since i was also using the zmq library I had to add this to the included libraries as well.

answered May 22 '18 at 17:26

Marco Rubio

71
3

cout is not a member of std

3 Answers3

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