Undefined reference to function (linker error)

Question

Hi i read the other questions and answers about undefined reference.But still i'm not able to find out what are the problems with my code. I have a simple linked list code wherein i add the integers to the tail and after that i display them. Here is my code "head.h"

#ifndef __HEAD_H_INCLUDE
#define __HEAD_H_INCLUDE

class Node {
int info;
Node *next;
};

class imple {
public:
    imple();
    void addToTail(int );
    void display(void);
private:
    Node *head,*tail;
};

#endif

"implementaion.cpp"

#include<iostream>
#include "head.h"

imple::imple(){
head=tail=0;
}

void imple::addToTail(int key){
if(tail==0)
    {tail=head=new Node();
    info=key;next=0;}
else
{
    tail->next=new Node();
    info=key;next=0;
    tail=tail->next;
}
}

void imple::display(){
Node *temp;
for(temp=head;temp->next !=0;temp=temp->next)
{
    std::cout<<temp->info << "   ";
}
}

"main.cpp"

#include<iostream>
#include "head.h"

int main(){
Node node;
imple ab;
for(int i=0;i<5;i++)
ab.addToTail(i);
ab.display();
}

Everytime i compile i get this error

"/tmp/cc20Z1ZH.o: In function main': lmain.cpp:(.text+0x10): undefined reference toimple::imple()' lmain.cpp:(.text+0x2a): undefined reference to imple::addToTail(int)' lmain.cpp:(.text+0x45): undefined reference toimple::display()' collect2: ld returned 1 exit status"

Your answers and suggestions will be helpful

What does your command line look like ? Are you actually compiling implementaion.cpp ? — Paul R
– Paul R, Commented Oct 20, 2015 at 7:37
Possible duplicate of What is an undefined reference/unresolved external symbol error and how do I fix it? — Niall
– Niall, Commented Oct 20, 2015 at 7:44

cadaniluk · Accepted Answer · 2015-10-20 07:42:42Z

3

In short, you may use

g++ main.cpp implementation.cpp -o out

You need to include implementation.cppin your building process and make the function definitions accessible to the linker. That is, compile it with

g++ -c implementation.cpp -o implementation.o

and

g++ -c main.cpp -o main.o

and link them together with

g++ main.o implementation.o -o out

answered Oct 20, 2015 at 7:42

cadaniluk

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Comments

alexeykuzmin0 · Accepted Answer · 2015-10-20 07:42:34Z

0

Try using

g++ main.cpp implementaion.cpp

Probably this will help

answered Oct 20, 2015 at 7:42

alexeykuzmin0

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Comments

Noorbala7418 · Accepted Answer · 2019-12-31 12:35:06Z

0

You can create a run file with:

g++ -o main implementation.cpp main.cpp

and run it with :

./main

edited Dec 31, 2019 at 12:35

answered Dec 29, 2019 at 21:18

Noorbala7418

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1 Comment

Nate Radebaugh Over a year ago

Looks like you forgot to finish your thought here? I'm confused by this answer.

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