Multiple Definition Error

I recently started teaching myself C++ from varrious tutorials and books, and once I felt I had a decent understanding of syntax, input, output and classes, I figured I'd try to write a basic text adventure console app.

The class definition seems to work fine, but I keep getting a "multiple definition" error on the testRoom instance I create, despite the fact that it's only created once.

At first I thought I might be calling the file twice (I'm keeping the list of rooms in a separate header file), but that is not the case. I've looked online and can't seem to figure out what is wrong with it...

source.cpp

Code:

/*
  Name: Text Adventure
  Copyright: None
  Author: Timothy Sassone
  Date: 14/02/09 22:42
  Description: A basic text adventure engine, written to practice basic C++ skills.
*/

#include <iostream>
#include <vector> //I plan on using a vector to hold the rooms
#include <string>

#include "roomDef.cpp"
#include "roomListing.cpp"

int main() 
{
    bool quit = 0;
    while(quit==0)
    {
                  //Main loop
                  quit=1;
    }
    
    return 0;
}

roomDef.cpp

Code:

#ifndef ROOM_DEF //Prevents repeated class definition
#define ROOM_DEF

#include <iostream>
#include <string>

using namespace std;

class Room {
      private:
              string itsName;
              string itsDesc;
              
      public:
             
             string getName() {
                    return itsName;
             }                    
             string getDesc() {
                    return itsDesc;
             }
             
             void setName(string newName) {
                  itsName=newName;
             }
             void setDesc(string newDesc) {
                  itsDesc=newDesc;
             }
             
             Room(string name, string desc) { //constructor
                         itsName=name;
                         itsDesc=desc;
             }
             ~Room() {}; //Destructor
};

#endif

roomListing.cpp

Code:

#ifndef ROOM_LIST //Prevents repeat definitions.
#define ROOM_LIST

#include "roomDef.cpp" //So I have access to the Room class

Room testroom1("1", "2");  //Create two test rooms
Room testroom2("2", "3");

#endif

I'm compiling with Dev-C++, and the error it gives is:
multiple definition of `testroom1'
first is defined here
multiple definition of `testroom2'
first is defined here
ld returned 1 exit status
C:\Documents and Settings\Timothy Sassone\Text Adventure\Makefile.win [Build Error] ["Text] Error 1

Neither of the "first defined here" errors is giving me a line or even file name. Any idea why it is giving me this error?

Thank you for your time,
Timothy

Do not include cpp files.

Read this and the section of your text which explains writing header files. If you don't have a book, you really ought to get one.

Wow, this is exactly my problem.

Except that I'm not including the CPP file. I'm only including the .h file and it's still giving me the error.

Unfortunately the error is way too fast to give a proper example. Lemme try to make a small example.

util.h

Code:

#ifndef UTILS_H_INCLUDED
#define UTILS_H_INCLUDED
int someglobalarray[5];

int somefuntionthatusesarray(int foo);
#endif

util.cpp

Code:

#include <stuff>
#include "util.h"

int somefuntionthatusesarray(int foo){
  return someglobalarray[foo];
}

main.cpp

Code:

#include <stuff>
#include "util.h"

int main () {
  someglobalarray[0] = 1;
  someglobalarray[1] = 2;
  someglobalarray[2] = 3;
  someglobalarray[3] = 4;
  someglobalarray[4] = 5;

  return somefuntionthatusesarray(3);
}

Okay, obviously I haven't compiled this, but I think it illustrates the problem. If I could compile this I compile this I would get:

Code:

-------------- Build: Release in numbrixgenerator ---------------

Linking console executable: bin\Release\whatever.exe
obj\Release\main.o:main.cpp:(.bss+0x4): multiple definition of `_someglobalarray'
obj\Release\util.o:utils.cpp:(.bss+0x0): first defined here
collect2: ld returned 1 exit status
Process terminated with status 1 (0 minutes, 1 seconds)
0 errors, 0 warnings

And no EXE.

Hu?

The problem is that you are defining someglobalarray in the header, so it is defined in each source file that includes the header. If you really need a global variable to be shared across source files, declare it extern in the header, and define it in exactly one source file.

Your first example was including cpp files, hence whiteflag's response.

The array someglobalarray is defined in every source file that #include's util.h. If more than one source file does that (and both util.cpp and main.cpp do in your latest example) that array is multiply defined. Which is exactly what your linker is telling you.

Declare someglobalarray as extern in util.h, and place a definition (without the extern keyword) in exactly one of your source files which #include's that header.

I'm currently borrowing a (slightly dated) copy of Sam's Teach Yourself C++ from the local library. However, it's a few years old, and some of the syntax is a bit off. Being one of the early editions, there are a couple typos as well. It's getting the point accross, but I'm have to get most of my syntax help elsewhere. It didn't really explain when/why you use .h instead of .cpp

Oh well, it works now, thanks everyone!

Tim

Originally Posted by grumpy

The array someglobalarray is defined in every source file that #include's util.h. If more than one source file does that (and both util.cpp and main.cpp do in your latest example) that array is multiply defined. Which is exactly what your linker is telling you.

Declare someglobalarray as extern in util.h, and place a definition (without the extern keyword) in exactly one of your source files which #include's that header.

Ah, thank you, thank you, thank you.

So like this:
util.h

Code:

#ifndef UTILS_H_INCLUDED
#define UTILS_H_INCLUDED

extern int someglobalarray[5];

int somefuntionthatusesarray(int foo);
#endif

util.cpp

Code:

#include <stuff>
#include "util.h"

int someglobalarray[5];

int somefuntionthatusesarray(int foo){
  return someglobalarray[foo];
}

main.cpp

Code:

#include <stuff>
#include "util.h"

int main () {
  someglobalarray[0] = 1;
  someglobalarray[1] = 2;
  someglobalarray[2] = 3;
  someglobalarray[3] = 4;
  someglobalarray[4] = 5;

  return somefuntionthatusesarray(3);
}

Yes, that seems to get it compiled. Thanks again, you guys, as always, are great.

But you are aware that globals should be avoided, yes?

Originally Posted by Elysia

But you are aware that globals should be avoided, yes?

Sigh. Yes mother.

Thing is I know how I should have done it differently, but at this point a global was a cheaper solution. And it works. Besides, I finally found a use for externs.

No, don't take it as an order. Just take into consideration.
Easy solutions can easily break when things scale up in complexity.
It's a suggestion, and an advice, and a question to see if you are aware of the consequences.