Undefined Reference to
Matthew Barrera 
When I compile my code for a linked list, I get a bunch of undefined reference errors. The code is below. I have been compiling with both of these statements:
g++ test.cpp as well as
g++ LinearNode.h LinearNode.cpp LinkedList.h LinkedList.cpp test.cpp I really do not understand why I am getting these errors because I am really rusty on classes in C++. I could really use some help.
LinearNode.h:
#ifndef LINEARNODE_H
#define LINEARNODE_H
#include<iostream>
using namespace std;
class LinearNode
{ public: //Constructor for the LinearNode class that takes no arguments LinearNode(); //Constructor for the LinearNode class that takes the element as an argument LinearNode(int el); //returns the next node in the set. LinearNode* getNext(); //returns the previous node in the set LinearNode* getPrevious(); //sets the next element in the set void setNext(LinearNode* node); //sets the previous element in the set void setPrevious(LinearNode* node); //sets the element of the node void setElement(int el); //gets the element of the node int getElement(); private: LinearNode* next; LinearNode* previous; int element;
};//ends the LinearNode class
#endifLinearNode.cpp:
#ifndef LINEARNODE_cpp
#define LINEARNODE_cpp
#include<iostream>
#include"LinearNode.h"
using namespace std;
//Constructor for LinearNode, sets next and element to initialized states
LinearNode::LinearNode()
{ next = NULL; element = 0;
}//ends LinearNode default constructor
//Constructor for LinearNode takes an element as argument.
LinearNode::LinearNode(int el)
{ next = NULL; previous = NULL; element = 0;
}//ends LinearNode constructor
//returns the next element in the structure
LinearNode* LinearNode::getNext()
{ return next;
}//ends getNext function
//returns previous element in structure
LinearNode* LinearNode::getPrevious()
{ return previous;
}//ends getPrevious function
//sets the next variable for the node
void LinearNode::setNext(LinearNode* node)
{ next = node;
}//ends the setNext function
//sets previous for the node
void LinearNode::setPrevious(LinearNode* node)
{ previous = node;
}//ends the setPrevious function
//returns element of the node
int LinearNode::getElement()
{ return element;
}//ends the getelement function
//sets the element of the node
void LinearNode::setElement(int el)
{ element = el;
}//ends the setElement function
#endifLinkedList.h:
#ifndef LINKEDLIST_H
#define LINKEDLIST_H
#include<iostream>
#include"LinearNode.h"
using namespace std;
class LinkedList
{ public: LinkedList(); void add(int element); int removie (int element); private: int count; LinearNode *contents;
};//ends the class linked list
#endifLinkedList.cpp:
#ifndef LINKEDLIST_CPP
#define LINKEDLIST_CPP
#include<iostream>
#include"LinearNode.h"
#include"LinkedList.h"
using namespace std;
//linkedlist constructor for an empty linked list
LinkedList::LinkedList()
{ count = 0; contents = NULL;
}//ends the constructor
//adds an element to the front of the linked list
void LinkedList::add(int element)
{ int found = 0, current = 0; while( (found == 0) && (current !=count) ) { if (contents.getElement() == element) found = 1; else { contents = contents.getNext(); current++; }//ends the else statement }//ends the while loop if (found == 0) { LinearNode node = new LinearNode(element); node.setNext(contents); contents.setPrevious(node); count++; }//ends the found == 0 if statment
}//ends the add function
//this function removes one element from the linked list.
int LinearNode::remove(int element)
{ int found = 0; if (count == 0) cout << "The list is empty" << endl; else { if (contents.getElement() == element) { result = contents.getElement(); contents = contents.getNext(); }//ends the contents.getElement() == element else { previous = contents; current = contents.getNext(); for (int index = 0; ( (index < count) && (found == 0) )index++) if (current.getElement() = element) found = 1; else { previous = current; current = current.getNext(); }//ends the else statement if (found == 0) cout << "The element is not in the list" << endl; else { result = current.getElement(); previous.setNext(current.getNext()); }//ends else statement }//ends the else stamtement count--; }//ends the else statement of count == 0 return result;
}//ends the remove function
#endiftest.cpp:
#include<iostream>
#include"LinearNode.h"
#include"LinkedList.h"
using namespace std;
int main()
{ LinearNode node1, node2, node3, move; LinkedList list; node1.setElement(1); node2.setElement(2); node3.setElement(3);
} 6 Answers
- Usually headers guards are for header files (i.e.,
.h) not for source files ( i.e.,.cpp). - Include the necessary standard headers and namespaces in source files.
LinearNode.h:
#ifndef LINEARNODE_H
#define LINEARNODE_H
class LinearNode
{ // .....
};
#endifLinearNode.cpp:
#include "LinearNode.h"
#include <iostream>
using namespace std;
// And now the definitionsLinkedList.h:
#ifndef LINKEDLIST_H
#define LINKEDLIST_H
class LinearNode; // Forward Declaration
class LinkedList
{ // ...
};
#endifLinkedList.cpp
#include "LinearNode.h"
#include "LinkedList.h"
#include <iostream>
using namespace std;
// Definitionstest.cpp is source file is fine. Note that header files are never compiled. Assuming all the files are in a single folder -
g++ LinearNode.cpp LinkedList.cpp test.cpp -o exe.outI was getting this error because my cpp files was not added in the CMakeLists.txt file
g++ test.cpp LinearNode.cpp LinkedList.cpp -o testI had this issue when I forgot to add the new .h/.c file I created to the meson recipe so this is just a friendly reminder.
Another way to get this error is by accidentally writing the definition of something in an anonymous namespace:
foo.h:
namespace foo { void bar();
}foo.cc:
namespace foo { namespace { // wrong void bar() { cout << "hello"; }; }
}other.cc file:
#include "foo.h"
void baz() { foo::bar();
}Try to remove the constructor and destructors, it's working for me....
