Redefinition error with multiple derived classes in the main

Question

I have an Object base class, and I have several derived classes called Item, Person, and Location.

Because each of these are derived from Object I need to include Object.h in each of their header files, and I include all of the derived classes in my main.

Because I am doing that I am getting a redefinition error.

What I want to know is what is the correct way to include these files to avoid this error?

Thanks!

EDIT:

object.h

using namespace std;

class Object{
    string name;
    string description;

    public:
        Object();
        Object(string name, string description);
        void set_name(string name);
        void set_description(string description);
        string get_name();
        string get_description();
        ~Object();
};

item.h

using namespace std;

#include "object.h"

class Item : public Object{
    public:
        Item();
        Item(string name, string description);

};

locale.h

using namespace std;

#include "object.h"

class Locale : public Object{
    public:
        Locale();
        Locale(string name, string description);
};

main.cpp

#include <iostream>
#include <string>

#include "locale.h"
#include "item.h"


using namespace std;

int main(){
    return 0;
}

What is the *exact* error message? And please show a (simplified) version of your code. — Oliver Charlesworth, Feb 26 '12 at 21:04
Ok, you'll need to show some code. Check out http://sscce.org first (it's about boiling your code down to the best possible format for Stack Overflow). — Oliver Charlesworth, Feb 26 '12 at 21:06
I know what is causing the error. object.h is getting defined twice. I want to know what the correct format for including header files is for this circumstance. — jasonaburton, Feb 26 '12 at 21:10
Please do not import namespaces inside header files - this is a pretty invasive thing to do, every file that includes that header will automatically import the whole namespace. — Wojciech Cierpucha, Feb 26 '12 at 21:12

score 8 · Accepted Answer · answered Feb 26 '12 at 21:06

8

Strange, everybody I've met that hits this problem does not have a slightest idea what is going on and you have properly analysed the problem.

Read this: http://en.wikipedia.org/wiki/Include_guard

answered Feb 26 '12 at 21:06

Wojciech Cierpucha

790
6
11

score 8 · Answer 2 · answered Feb 26 '12 at 21:08

You should add include guards to your headers. This prevents headers from being included twice. For example, at the the top of the Object.h header, you would put,

#ifndef _OBJECT_H
#define _OBJECT_H

and then you end the header with,

#endif

If the header has already been included, the text between #ifndef and #endif is dropped.

score 4 · Answer 3 · answered Feb 26 '12 at 21:07

4

If you haven't got them in place already, you need to put include guards into you header files to prevent including the same files multiple times (which would redefine the classes).

answered Feb 26 '12 at 21:07

Timo Geusch

24,095
5
52
70

Redefinition error with multiple derived classes in the main

3 Answers3