Codeblocks c++ undefined reference error, class is defined

Question

Hey guys I asked a question the other day about some c++ code that I couldn't get to work. I took everyones advice as to how to create objects in c++ but now I get undefined reference errors. I am using the latest code blocks version and using that to compile. I have read that this is caused by not linking some files during compilation, and that it means I have defined the class in the header file but not in the code, which confuses me because from my understanding (a profs example) I am declaring the objects.

Header File MathObject.h

class MathObject{
private:
    int num1;
    int num2;

public:
    int sum();
    MathObject(int n, int m);
};

MathObject file MathObject.cpp

#include <iostream>
#include "MathObject.h"
using namespace std;

MathObject :: MathObject(int n, int m){
    num1 = n;
    num2 = m;
}

int MathObject :: sum(){
    return num1+num2;
}

Main File

#include <iostream>
#include "MathObject.h"
using namespace std;

int main(int args, char *argv[]){
    MathObject *mo = new MathObject(3,4);
    int sum = mo -> sum();

    MathObject mo2(3,4);

    //cout << sum << endl;
    return 0;
}

The undefined reference is for all calls to anything in the MathObject class, I have been searching for a small c++ example that I can understand. (The syntax is so different from java)

This used to happen when I tried to use multiple files in c, could this be an issue with my computer?

@RedAlert, Do you mean with an include statement? I thought you only need to include the header file. — Michael Miner
– Michael Miner, Commented Jun 17, 2014 at 0:21
an include statement would probably resolve this issue, but that's not how you want to fix it. You need to compile both source files as part of your project, not just main.cpp — Red Alert
– Red Alert, Commented Jun 17, 2014 at 2:06

Drew Dormann · Accepted Answer · 2014-06-17 00:33:23Z

9

In the "Projects" tab in codeblocks, right-click your project's name and select "Add Files..."

Alternately, you can choose "Add files..." from "Project" in the application's main menu.

Use this to add all of your source files to your project.

Currently MathObject.cpp is missing from that list, so it's not getting compiled or linked.

edited Jun 17, 2014 at 0:33

answered Jun 17, 2014 at 0:28

Drew Dormann

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3 Comments

Michael Miner Over a year ago

oddly, clicking the "Add Files" under "Project" does nothing. The system or ide does not hang, it is simply as if there is no action set for that selection.

Ganapathy Over a year ago

Make sure you've selected all required files under Project > Properties > Build targets > Build target files

Seungju Over a year ago

If this does not work then right click each files and click add to active project . Then it would be added to the project manually.

Ruslan Gerasimov · Accepted Answer · 2014-06-17 00:26:47Z

0

g++ MathObject.cpp main.cpp -o main

answered Jun 17, 2014 at 0:26

Ruslan Gerasimov

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3 Comments

Michael Miner Over a year ago

tried, this. I did a cd to the folder all the files are in and typed your line exactly as you have and I am told that g++ is not a recognized command

David G Over a year ago

@MichaelMiner Add the path to the MinGW/bin folder to the PATH environment variable.

Ruslan Gerasimov Over a year ago

What is your platfrom\operating system? It is just the example that you need to include MathObject.cpp file to compiling. I ran it from Linux, which has g++ compiler by default.

impulse · Accepted Answer · 2015-06-22 09:47:46Z

0

Found a solution from code::blocks forum:

-Project -> "Build Options

-Make sure the correct target is highlighted on the left side; if you do not know select the project, top one.

-Select Tab "Search Directories"

-Select Sub-Tab "Compiler"

-"Add" the path to the folder that contains the header. Single Folder per line.

Just add your current folder or location of your header file to the path.

Link: http://forums.codeblocks.org/index.php?topic=14713.0

answered Jun 22, 2015 at 9:47

impulse

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Comments

Hunterrr · Accepted Answer · 2018-12-16 16:10:52Z

0

You can do this simply by adding .cpp file of the class in main.cpp.

#include <iostream>
#include "MathObject.h"
#include "MathObject.cpp"
using namespace std;

int main(int args, char *argv[]){
    MathObject *mo = new MathObject(3,4);
    int sum = mo -> sum();

    MathObject mo2(3,4);

    //cout << sum << endl;
    return 0;
}

answered Dec 16, 2018 at 16:10

Hunterrr

1

Comments

Nardos Wehabe · Accepted Answer · 2020-08-17 11:44:11Z

0

To fix undefined reference error :-

Settings -> compiler... -> Build options finally mark "Explicitly add currently compiling file's directory to compiler search dirs"

answered Aug 17, 2020 at 11:44

Nardos Wehabe

1

1 Comment

help-info.de Over a year ago

Welcome to Stack Overflow! Please note you are answering a very old and already answered question. Here is a guide on How to Answer.

Esteban E · Accepted Answer · 2014-06-17 00:34:38Z

-3

I try this and works fine!

MAIN.cpp

#include <iostream>
#include "MathObject.h"
using namespace std;

int main(int args, char *argv[]){
    MathObject *mo = new MathObject(3,4);
    int sum = mo->sum();

    MathObject mo2(3,4);
    int sum2 = mo2.sum();

    cout << sum << endl;
    cout << sum2 << endl;
    system("pause");
    return 0;
}

MathObject.h

class MathObject
{
private:
    int num1;
    int num2;
public:
    MathObject(void);
    ~MathObject(void);
    int sum();
    MathObject(int n, int m);
};

MathObject.cpp

#include "MathObject.h"

MathObject::MathObject(void)
{
}

MathObject::~MathObject(void)
{
}
int MathObject::sum(){
    return num1+num2;
}
MathObject::MathObject(int n, int m){
    num1 = n;
    num2 = m;
}

Compile with:

g++ MathObject.cpp main.cpp -o main.exe

edited Jun 17, 2014 at 0:34

answered Jun 17, 2014 at 0:26

Esteban E

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5 Comments

Michael Miner Over a year ago

using yours, I still get unreferenced errors, could it be my compiler or ide?

David G Over a year ago

This does not answer the question. The OP is obviously experiencing something different from you on his compiler and simply asserting that it "works for you" doesn't help the situation.

Esteban E Over a year ago

i forgot comment how i compile it: g++ MathObject.cpp main.cpp -o main.exe

Michael Miner Over a year ago

if yours works, does that not mean mine should as well? I have tried compiling it that way but still nothing

Esteban E Over a year ago

then you could give more details of your problem, the exact error that gives the compiler or any clue...

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