(Redefinition error) Create multiple inherting classes from one baseclass in C++

Question

Greetings oh mighty coders,

I am a beginner and in a bit of trouble here.

There is my baseclass (sensor.h):

class sensor
{
private:
   int sensor_id;
   string sensor_name;
   string sensor_type;
   float reading;

public:

   sensor();
   sensor(int, char*, char*);
   ~sensor();

/* Few extra methods here */

};

... and I want to create 4 other classes that inherit from my baseclass sensor (temperaturesensor, humiditysensor... and so on).

 #include "sensor.h"


class temperaturesensor:public sensor
{
public:
   Temperatursensor(int, char*,char*);
   ~Temperatursensor();

/* Few extra methods here */

};

Thing is: Every single one of these classes has to be in its own .cpp/.h file and then be included and used in my main.cpp.

using namespace std;
#include <xyz.h>
/* Other libaries here */
          ....
#include "temperaturesensor.h"
#include "humiditysensor.h"

int main()
{
    sensor* station[2];


    station [0] = new temperaturesensor(x,y,z);
    station [1] = new humiditysensor(x,y,z);
}

If I include one of them it's no biggie. However: If I use multiple ones I get an redefinition error.

error C2011: 'sensor': 'class' typeredefinition c:\users\name\desktop\project\sensor.h 14

error c2011: 'temperaturesensor' : 'class' typeredefinition

What can I do to workaround this? Note that I am not allowed to use #pragma once

Sorry for my stupidity and thanks in advance!

You can use standard *include guards* in place of the non-portable `#pragma once`. — Bathsheba, Jun 29 '17 at 15:52
Welcome to Stack Overflow. Please take the time to read [The Tour](http://stackoverflow.com/tour) and refer to the material from the [Help Center](http://stackoverflow.com/help/asking) what and how you can ask here. — πάντα ῥεῖ, Jun 29 '17 at 15:53
You do have [*include guards*](https://en.wikipedia.org/wiki/Include_guard) or [`#pragma once`](https://en.wikipedia.org/wiki/Pragma_once) in your header files? — Some programmer dude, Jun 29 '17 at 15:53
And can you please edit your question *show* the errors? Copy-paste them (as text). — Some programmer dude, Jun 29 '17 at 15:53
Since you are using `std::string` in your class, use `std::string` in your constructor's parameters. The compiler can convert `char *` to `std::string`, so you can call the constructor with character literals. — Thomas Matthews, Jun 29 '17 at 15:56
Btw, `station[2]` is an out-of-bounds access and hence undefined behaviour. What you presumably meant was to use indices `0` and `1`, not `1` and `2`. — Walter, Jun 29 '17 at 15:58

21koizyd · Accepted Answer · 2017-06-29T16:02:52.750

2

You must use:

#ifndef FILE_H
#define FILE_H

.. normal code here

#endif

or

#pragma once

but too, I think, that sensor schould be abstract class and you schould use virtual destructor. One more think is that array is numerate from 0.

edited Jun 29 '17 at 16:02

answered Jun 29 '17 at 15:57

21koizyd

1,843
12
25

Good catch for indexing of the array! However, I do not see the need for an abstract base class. – AGN Gazer Jun 29 '17 at 16:01
1

Don't create symbols with a leading underscore followed by an upper-case letter, [those are reserved in all scopes](http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier). – Some programmer dude Jun 29 '17 at 16:01
@AGNGazer I see that class abstract sensor and specialization to particular sensors – 21koizyd Jun 29 '17 at 16:04

score 0 · Answer 2 · answered Jun 29 '17 at 15:53

you forgot to use the include guards in your header class, this is redefining your base class everytime you use it.

so, just do a

#pragma once

or a normal include guard

#ifndef YOURFILENAME_H
#define YOURFILENAME_H

.. normal code here

#endif

Then you will not have the multiple definition error.

score 0 · Answer 3 · answered Jun 29 '17 at 15:56

0

The definition of the class sensor is coming from both "temperaturesensor.h" and "humiditysensor.h". Use guards https://en.wikipedia.org/wiki/Include_guard or #pragma once: https://en.wikipedia.org/wiki/Pragma_once

answered Jun 29 '17 at 15:56

AGN Gazer

8,025
2
27
45

(Redefinition error) Create multiple inherting classes from one baseclass in C++

3 Answers3