c++ - I am getting this error when i try to display my linkedlist

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Learn more about Teams What is an undefined reference/unresolved external symbol error and how do I fix it? (39 answers)

Closed 1 year ago .

I am getting this error :

C:\Users\DELL\AppData\Local\Temp\ccEQYgIh.o:ll_using_class.cpp:(.text+0x98): undefined reference to linkedlist::linkedlist(int*, int)' C:\Users\DELL\AppData\Local\Temp\ccEQYgIh.o:ll_using_class.cpp:(.text+0xaf): undefined reference to linkedlist::~linkedlist()' C:\Users\DELL\AppData\Local\Temp\ccEQYgIh.o:ll_using_class.cpp:(.text+0xc2): undefined reference to `linkedlist::~linkedlist()' collect2.exe: error: ld returned 1 exit status

That's not the error I get. I get " error: no declaration matches 'void linkedlist::display()' " but if I fix that by adding


    void display();

to the class definition I get the same error as you because you haven't implemented the constructor


    linkedlist(int A[], int n);

or the destructor


    ~linkedlist();

– Ted Lyngmo Aug 25, 2021 at 10:07 You wrote a destructor, but you didn't provide a definition (implementation) of that destructor. – Yksisarvinen Aug 25, 2021 at 10:13

You've defined


    void linkedlist::display()

but you haven't declared it in your class definition.

You've declared the constructor


    linkedlist(int A[], int n)

but you haven't defined it.

You've declared the destructor


    ~linkedlist()

but you haven't defined it.

Other notes:

The global


    node*


    head

is pointless.

The


    node

type doesn't need to be visible outside the


    linkedlist

class. I suggest hiding it by making the


    node

definition private in


    linkedlist

The


    display()

member function does not make changes to the


    linkedlist

object. Make such functions


    const

Example fixes:

#include <iostream>
#include <utility> // std::exchange
class linkedlist {
private:
    struct node {     // made definition private
        int data;
        node *next;
    node* first;
public:
    linkedlist();
    linkedlist(int A[], int n);
    linkedlist(const linkedlist&) = delete;            // copying not implemented
    linkedlist& operator=(const linkedlist&) = delete; // copying not implemented
    ~linkedlist();
    void add(int value); // a function to add a value to the linked list
    void display() const; // made const 
linkedlist::linkedlist() : first(nullptr) {}
linkedlist::linkedlist(int A[], int n) : first(nullptr) {
    for(size_t idx = 0; idx < n; ++idx) {
        add(A[idx]);                     // use the add() member function
linkedlist::~linkedlist() {
    while(first) { // delete all nodes
        delete std::exchange(first, first->next);
void linkedlist::add(int value) {
    // add a node by linking it in first
    first = new node{value, first};
void linkedlist::display() const {
    if(first) {
        std::cout << first->data;
        for(node* p = first->next; p; p = p->next) {
            std::cout << ' ' << p->data;
int main(){
    int A[]={2, 3, 4, 5, 6};
    linkedlist l(A, 5);
    l.display();
Output
6 5 4 3 2
                @NoobCoder You're welcome! Please don't change your question radically after you've gotten answers. The question + the answer now doesn't make sense and since this is a Q&A site, it won't help anyone else in its current state. I'll revert the change you made. You do have some problems though like for(int i=1;i<n;i++) which skips the first element. Arrays starts at element 0 in C++.
– Ted Lyngmo
                Aug 25, 2021 at 12:26
                ohkay understood i won't do it hereafter. also, im adding first element in the first node itself.
– NoobCoder
                Aug 25, 2021 at 12:29