Undefined Reference to

Question

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:

Answer 1

I was getting this error because my cpp files was not added in the CMakeLists.txt file

Answer 2

1. Usually headers guards are for header files (i.e., .h ) not for source files ( i.e., .cpp ).
2. Include the necessary standard headers and namespaces in source files.

LinearNode.h:

#ifndef LINEARNODE_H
#define LINEARNODE_H

class LinearNode
{
    // .....
};

#endif

LinearNode.cpp:

#include "LinearNode.h"
#include <iostream>
using namespace std;
// And now the definitions

LinkedList.h:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

class LinearNode; // Forward Declaration
class LinkedList
{
    // ...
};

#endif

LinkedList.cpp

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

// Definitions

test.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.out

Answer 3

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();
}

Answer 4

g++ test.cpp LinearNode.cpp LinkedList.cpp -o test

Answer 5

I 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.

Answer 6

Try to remove the constructor and destructors, it's working for me....