Order of header file inclusions and dependencies

Question

I'm just trying to test splitting code into multiple files.

I have:

//testMultiple.cpp

#include <string>
#include <iostream>
#include "testInclude.cpp"

int main(){
    std::cout << "hi";
}

and

//testInclude.cpp

class testClass{
    public:
        string x;
};

This is giving testInclude.cpp:3:9: error: ‘string’ does not name a type

I thought since it was including before it included the testInclude.cpp, string would be defined for use in testInclude.cpp.

Why are you including a `.cpp` file, instead of linking it with your `testMultiple.cpp`?? That's very unusual, and will break most buildsystems and IDE's. — πάντα ῥεῖ, Jul 28 '15 at 08:56
Because as far as I know, if you want to split your program into multiple files, you `#include` them — David Bandel, Jul 28 '15 at 08:57
No, that's wrong. You split them into a header file containing the class declarations, and a `.cpp` file containing the corresponding definitions. Other translation units (`.cpp` files) use `#include` to get the declarations from the header. — πάντα ῥεῖ, Jul 28 '15 at 09:00
@DavidBandel Maybe you should first read a few question, such as [this one](http://stackoverflow.com/questions/1945846/what-should-go-into-an-h-file). — undu, Jul 28 '15 at 09:01
@DavidBandel _"I had no idea it was a useless inclusion and string was actually defined in iostream."_No, you can't rely on this. If you use `std::string` use `#include `. — πάντα ῥεῖ, Jul 28 '15 at 09:03
Yes that says to put them in .h files. So I changed it to testInclude.h and that didn't fix anything — David Bandel, Jul 28 '15 at 09:05
Ok I figured out what I was doing wrong. I got it to work with #include in the header file like you said. So I'd just like to understand why I can't include vector in the main cpp, before I include the header file and the header file have access to vector. Does this mean if I have a bunch of code across a bunch of files, I have to include all my libraries and header files in each one? — David Bandel, Jul 28 '15 at 09:27
I had this idea, from all the examples and tutorials I went over that std was an iostream thing. I understand what a namespace is better now. I had the naive idea that needing to preface something with std:: without a `using namespace std` meant I was using something defined in iostream. — David Bandel, Jul 28 '15 at 09:43

score 2 · Answer 1 · edited Jul 28 '15 at 10:21

2

You need to use std::string instead of string.

edited Jul 28 '15 at 10:21

Patrick Hofman

153,850
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answered Jul 28 '15 at 08:49

Marcel

203
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8

That doesn't help me. It still won't use `` which is what I'm trying to do. – David Bandel Jul 28 '15 at 08:52
It's not enough here. He's declaring his class in a cpp, which is compiled. But it fails as string is unknown in the context of this cpp. – undu Jul 28 '15 at 08:59
I changed it to hpp and it still fails – David Bandel Jul 28 '15 at 09:03
I modified the code in the question. vector is a better example – David Bandel Jul 28 '15 at 09:06
Ok thanks. It worked your way. I just had a misunderstanding of where vector gets defined. – David Bandel Jul 28 '15 at 09:39

Nishant · Answer 2 · 2015-07-28T08:56:08.063

1

Use

class testClass{
    public:
        std::string x;
};

edited Jul 28 '15 at 08:56

answered Jul 28 '15 at 08:51

Nishant

1,635
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I already have `#include ` See my first file And I'm not trying to use the `` string. I'm trying to use the `` string. I simply want to split my code into multiple files. – David Bandel Jul 28 '15 at 08:55
@DavidBandel What do you mean _"I'm trying to use the `` string"_? I don't get what you want, the answer is correct. It's the way you try to organize your code that's wrong. – πάντα ῥεῖ Jul 28 '15 at 08:58
I am trying to put some code in another file, then include it, so that my code is split across multiple files. That's all. – David Bandel Jul 28 '15 at 09:02
Ok thanks. It worked your way. I just had a misunderstanding of where vector gets defined. – David Bandel Jul 28 '15 at 09:38

Sigve Kolbeinson · Accepted Answer · 2015-07-28T09:27:11.060

You're including a cpp file, not a hpp file. Common practice is to include header (h/hpp) files, not implementation (c/cpp) files.

If you only compile testMultiple.cpp, this should work. If the compiler is compiling testInclude.cpp separately, it will not see the `#include

Try renaming testInclude.cpp to testInclude.hpp and ensure it is not being compiled.

Here's an example:

///// testInclude.h
#include <vector>
class testClass{
    public:
         std::vector<int> x; // vector is in std namespace
};

///// testMultiple.cpp
// #include <vector> - gets this through testInclude.h
#include "testInclude.h"

int main(){
}

Order of header file inclusions and dependencies

3 Answers3