Key Highlights of the Blog- Understand linked lists from the ground up, how they work in memory and why they’re different from arrays.
- Learn all major types of linked lists in C++ (singly, doubly, circular) with clear visuals and real code examples.
- Master core operations like traversal, insertion, deletion, and searching with time–space clarity.
- Discover how linked lists are used in the real world through stacks, queues, graphs, and memory management.
- Know when not to use linked lists and choose the right data structure confidently in real programs.
Introduction
Have you ever wondered how applications add data quickly without moving thousands of elements? Or how memory is dynamically managed by systems without squandering space? That’s where linked list in C++ quietly power things behind the scenes.
As you move beyond basic programming, you will realize that real-world software rarely deals with fixed-size data. Data grows, shrinks, and changes constantly, and arrays alone can’t handle that efficiently. This is exactly why linked lists in C++ exist.
In this guide, you are going to learn how linked lists work at a memory level, how different types behave, and how to perform essential operations safely and efficiently. By the end, you won’t just know linked lists, you’ll understand when and why to use them, which is what truly matters as a growing programmer.
Introduction to Linked Lists
A linked list represents a type of linear data structure that utilizes non-contiguous memory regions are used to hold items, or nodes. Each node contains data and a pointer (reference) to the next node in the sequence.
This structure allows efficient insertion and deletion of elements, especially when compared to arrays that require shifting elements.
Linked List Representation in C++
A collection of nodes kept in non-contiguous memory regions is called a linked list in C++. In order to enable dynamic connections between elements, each node has a data field to store information and one or more pointers, also known as links, that record the addresses of other nodes.
Components of a Node
- Data Field: Stores the value or information for that node.
- Pointer(s): Stores the memory address of the next (and possibly previous) node in the list.
The node is typically defined using a struct or class in C++. For example:
class Node { public: int data; // data field Node* next; // next pointer (address of next node) };
The Head Pointer
The head is a special pointer that always points to the first node in the linked list. If the list is empty, the head is set to nullptr. All operations like traversal, insertion, and deletion typically start from the head.
Types of Linked List Structures
- Singly Linked List:
- Each node contains a data field and a single next pointer.
- The next pointer stores the address of the next node.
- Traversal is possible only in one direction—from head to the last node (which points to nullptr).
- Doubly Linked List:
- A data field, a next pointer, and a prior pointer are all present in each node.
- The address of the preceding node is stored in the previous pointer, while the address of the following node is stored in the next pointer.
- permits both-way traversal.
- Circular Linked List:
- Can be singly or doubly linked.
- The next pointer of the final node in a circular singly linked list points back to the head rather than nullptr.
- In a circular doubly linked list, both the next and previous pointers of the last and first nodes form a circle.
Memory Representation
Linked lists are stored in non-contiguous memory locations. Every node in a linked list can be found anywhere in memory, in contrast to arrays, where items are kept together. By storing the addresses of linked nodes, the pointers preserve the logical order.
Key Terms in Context:
- address: The memory location of a node, stored in pointers.
- node: The fundamental building block containing data and pointers.
- head: Pointer to the first node.
- next pointer: Points to the next node.
- previous pointer: (in doubly/circular lists) Points to the previous node.
- structure: The organization of data and pointers within each node.
Summary Table:
| List Type |
Data Field |
Next Pointer |
Previous Pointer |
Last Node Points To |
| Singly Linked List |
Yes |
Yes |
No |
nullptr |
| Doubly Linked List |
Yes |
Yes |
Yes |
nullptr |
| Circular Linked List |
Yes |
Yes |
Optional |
Head (forms a loop) |
Types of Linked List in C++
There are three useful linked list types in C++. Each one has its own requirements, which are as follows:
1. Singly Linked List
A Singly Linked List is a linear data structure where each node points only to the next node. Traversal is possible only in one direction, from the first node to the last. It is simple and uses less memory because each node stores just one pointer.
Example:
List: 10 -> 20 -> 30 -> 40
Singly linked list in C program:
#include <iostream>
using namespace std;
// Define a node
class Node {
public:
int data;
Node* next;
Node(int val) { // Constructor
data = val;
next = nullptr;
}
};
// Define the singly linked list
class SinglyLinkedList {
public:
Node* head;
SinglyLinkedList() {
head = nullptr;
}
// Add a node at the end
void append(int val) {
Node* new_node = new Node(val);
if (!head) {
head = new_node;
return;
}
Node* current = head;
while (current->next != nullptr) {
current = current->next;
}
current->next = new_node;
}
// Display the list
void display() {
Node* current = head;
while (current != nullptr) {
cout << current->data << " -> ";
current = current->next;
}
cout << "NULL" << endl;
}
};
// Main function
int main() {
SinglyLinkedList sll;
sll.append(10);
sll.append(20);
sll.append(30);
sll.append(40);
sll.display();
return 0;
}
Output:
10 -> 20 -> 30 -> 40 -> NULL
2. Doubly Linked List
Each node in a doubly linked list in C++ is connected to both the nodes immediately before and following it. This allows movement in both forward and backward directions. It is slightly more complex and uses more memory since each node holds two pointers.
Example:
List: 10 <-> 20 <-> 30 <-> 40
Doubly linked list in c program:
#include <iostream>
using namespace std;
// Define a node
class Node {
public:
int data;
Node* next;
Node* prev;
Node(int val) {
data = val;
next = nullptr;
prev = nullptr;
}
};
// Define the doubly linked list
class DoublyLinkedList {
public:
Node* head;
DoublyLinkedList() {
head = nullptr;
}
// Add a node at the end
void append(int val) {
Node* new_node = new Node(val);
if (!head) {
head = new_node;
return;
}
Node* current = head;
while (current->next != nullptr) {
current = current->next;
}
current->next = new_node;
new_node->prev = current;
}
// Display the list forward
void displayForward() {
Node* current = head;
while (current != nullptr) {
cout << current->data << " <-> ";
current = current->next;
}
cout << "NULL" << endl;
}
// Display the list backward
void displayBackward() {
Node* current = head;
if (!current) return;
// Move to the last node
while (current->next != nullptr) {
current = current->next;
}
// Print backward
while (current != nullptr) {
cout << current->data << " <-> ";
current = current->prev;
}
cout << "NULL" << endl;
}
};
// Main function
int main() {
DoublyLinkedList dll;
dll.append(10);
dll.append(20);
dll.append(30);
dll.append(40);
cout << "Forward: ";
dll.displayForward();
cout << "Backward: ";
dll.displayBackward();
return 0;
}
Output:
Forward: 10 <-> 20 <-> 30 <-> 40 <-> NULL
Backward: 40 <-> 30 <-> 20 <-> 10 <-> NULL
3. Circular Linked List (CLL)
A circular linked list is one where the last node loops back to the first node, thereby creating a circle. It is a nice structure to have when you want to go through the list endlessly without ever stopping. Also, a circular linked list can be either singly or doubly linked.
Example (Singly Circular):
List: 10 -> 20 -> 30 -> 40 -> back to 10
Code:
#include <iostream>
using namespace std;
// Define a node
class Node {
public:
int data;
Node* next;
Node(int val) {
data = val;
next = nullptr;
}
};
// Define the circular linked list
class CircularLinkedList {
public:
Node* head;
CircularLinkedList() {
head = nullptr;
}
// Add a node at the end
void append(int val) {
Node* new_node = new Node(val);
if (!head) {
head = new_node;
new_node->next = head; // Point to itself
return;
}
Node* current = head;
while (current->next != head) {
current = current->next;
}
current->next = new_node;
new_node->next = head;
}
// Display the list
void display() {
if (!head) return;
Node* current = head;
do {
cout << current->data << " -> ";
current = current->next;
} while (current != head);
cout << "(back to head)" << endl;
}
};
// Main function
int main() {
CircularLinkedList cll;
cll.append(10);
cll.append(20);
cll.append(30);
cll.append(40);
cll.display();
return 0;
}
Output:
10 -> 20 -> 30 -> 40 -> (back to head)
Linked List Operations
Linked lists are flexible data structures implemented through nodes that are linked using pointers. The four basic operations that you can perform on a linked list are traversal, insertion, deletion, and searching. These operations' understanding is a prerequisite for handling data in C++ in an efficient and safe manner.
Traversal
The process of traversing a linked list involves visiting each node, usually beginning at the head (the first node) and follows the pointers until the list's end (NULL for conventional lists, or the head again for circular lists) is reached.
Logic:
- Set a pointer to the head node.
- While the pointer is not NULL:
- Process the data in the current node.
- Move the pointer to the next node.
Use Cases: Displaying all elements, searching, or applying any operation to each node.
Time Complexity: O(n), at which n is the number of nodes.
Insertion
Insertion adds a new node to the linked list. Depending on where you want to insert, the logic varies:
- At the Beginning:
- Create a new node.
- Point its next pointer to the current head.
- Update head to the new node.
- Efficient for linked lists; takes constant time O(1).
- At the End:
- Create a new node.
- Traverse to the last node (where next is NULL).
- Set the last node’s next pointer to the new node.
- Takes O(n) time due to traversal.
- After a Given Node:
- Traverse to the specified node.
- Create a new node.
- Point its next to the specified node’s next.
- Update the specified node’s next to the new node.
Edge Cases: Inserting into an empty list, inserting before/after head or tail.
Deletion
Deletion removes a node from the linked list and safely reconnects the remaining nodes.
- At the Beginning:
- Update head to point to the second node.
- Delete the original head node.
- O(1) time.
- At the End:
- Traverse to the second-last node.
- Set its next pointer to NULL.
- Delete the last node.
- O(n) time.
- Specific Node (by value):
- Traverse the list to find the node.
- Keep track of the previous node.
- Update the previous node’s next to skip the node to be deleted.
- Delete the target node.
- O(n) time.
Edge Cases: Deleting from an empty list, deleting the only node, deleting head or tail.
Searching
Searching checks if a node containing a specific value exists in the list.
Logic:
- Start from the head.
- Traverse each node, comparing its data with the target value.
- If found, return the node or its position.
- If not found by the end, indicate failure.
Time Complexity: O(n).
Updating
Once a node is found, typically through a search, it can be updated by changing the value stored in its data field. Updating is useful when data needs to be corrected or modified without changing the structure of the list.
Time and Space Complexity Summary
| Operation |
Best Case |
Worst Case |
Space Complexity |
| Traversal |
O(1) |
O(n) |
O(1) |
| Insertion* |
O(1) |
O(n) |
O(1) |
| Deletion* |
O(1) |
O(n) |
O(1) |
| Searching |
O(1) |
O(n) |
O(1) |
Note: Insertion and deletion take O(1) time when performed at the head of the list. They become O(n) when done at the end or at a specific position, as traversal is required.
Key Terms in Context:
- linkedlist class/node class: Wrap up the logic of handling nodes and their pointers.
- head: Pointer to the first node; starting point for most operations.
- tail: Last node in the list; its next pointer is NULL.
- pointer: Used for linking nodes and walking through the list.
- space complexity: Because each node requires memory for data and a pointer, the space complexity is O(n).
- Time complexity: Depends on the operation and position as indicated in the table above.
Linked List in C++ Standard Library
C++ provides a built-in doubly linked list implementation called std::list, available in the <list> header. The Standard Template Library (STL) includes it.
Basic Example:
#include <iostream>
#include <list>
int main() {
std::list<int> myList = {1, 2, 3};
// Insert at the front
myList.push_front(0);
// Insert at the back
myList.push_back(4);
// Display the list
for (int value : myList) {
std::cout << value << " ";
}
std::cout << std::endl;
return 0;
}
Advantages and Disadvantages of Linked Lists
Linked lists offer several benefits and limitations compared to other data structures such as arrays, stacks, and queues. Understanding these helps in choosing the right structure for your application.
Advantages of Linked Lists
- Dynamic Memory Allocation
- Linked lists use dynamic memory allocation, so nodes are created as needed.
- This allows for a flexible size; the list can grow or shrink at runtime without needing to pre-declare the size.
- Efficient Insertions and Deletions
- Inserting or deleting nodes is efficient, especially at the beginning or middle of the list.
- Unlike arrays, no shifting of elements is required due to the use of pointers connecting non-contiguous nodes.
- Non-Contiguous Structure
- Nodes are stored in non-contiguous memory locations.
- This makes linked lists ideal when memory is fragmented or when continuous memory allocation is not possible.
- Resource Release
- Memory for each node can be explicitly released (freed) when it is no longer needed, reducing memory wastage.
- Implementation of Other Structures
- Linked lists form the basis for advanced data structures like stack, queue, and deque (double-ended queue).
Disadvantages of Linked Lists
- Extra Memory Overhead
- In contrast to arrays, every node in a linked list needs extra memory to store one or more pointers.
- No Direct Access
- O(n) time complexity results from having to traverse the list from the head node in order to access an entry.
- Random access in O(1) time is possible with arrays.
- Complex Node Structure and Management
- The node structure and pointer management make linked lists more complex to implement and debug.
- Mistakes in pointer manipulation can lead to issues like memory leaks or dangling pointers.
- Cache Inefficiency
- Compared to arrays, which benefit from spatial locality, linked lists may perform worse in the cache due to non-contiguous storage.
- Overhead in Simple Use Cases
- Arrays or vectors could be better for situations where the size is fixed or seldom fluctuates, or when quick random access is required.
Use Cases and Applications of Linked Lists in C++
| Feature |
Linked List |
Array |
| Size |
Can grow or shrink dynamically |
Fixed size (unless resized) |
| Memory Layout |
Stored in separate locations |
Stored in continuous memory |
| Insert/Delete (Front) |
Very fast — O(1) |
Slower — O(n) |
| Insert/Delete (Middle/End) |
Slower — O(n) |
Slower — O(n) |
| Access Elements |
Must traverse — O(n) |
Direct access — O(1) |
| Extra Memory Used |
More (stores pointers) |
Less |
When to Use Linked Lists:
When the number of elements is unknown ahead of time and your application necessitates frequent insertions and removals, particularly at the start or middle of a collection, linked lists are an excellent option.
When Not to Use Linked Lists:
Arrays or vectors could be better if your program requires quick random access, little memory overhead, or cache-friendly data structures.
Use Cases and Applications of Linked Lists in C++
- Implementing Stacks and Queues: Stacks (LIFO structures) and queues (FIFO structures), whose items are often added and withdrawn at the ends, are typically constructed using linked lists.
- Adjacency Lists in Graphs: In graph algorithms, linked lists efficiently store neighbours of a node. Every node in the graph points to a linked list of connected nodes.
- Undo/Redo Functionality: Linked lists are used by programs such as text editors to monitor changes. Every operation is a node, making it simple to move forward (redo) or backward (undo).
- Memory Management (Free Lists): Operating systems use linked lists to manage free blocks of memory. A free list is a linked list where each node represents an available memory chunk.
- Polynomial Arithmetic: Polynomials are represented as linked lists, where each node holds a term (coefficient and exponent), making term addition and multiplication simple.
Conclusion
A linked list in C++ is an important data structure, providing flexibility, dynamic memory management, and efficient insertion/deletion operations. Robust software development requires an understanding of its implementation, variances, and best practices. Learning linked lists gives the foundation for more complex data structures and algorithms, whether utilizing raw pointers for learning or smart pointers for production code.
Points to Remember
- Linked lists hold data in separate memory locations and use pointers to connect the data, rather than indexes.
- Insertions and deletions are efficient, especially at the beginning of the list.
- Traversal is required for access; there is no direct indexing like arrays.
- Each linked list type solves a different problem (singly = simple, doubly = bidirectional, circular = cyclic use cases).
- Deciding to use linked lists instead of arrays is a matter of flexibility rather than speed. Put them to use where the changes have to be dynamic.
Frequently Asked Questions
1. What is a Linked List, and why is it important in C++?
A linked list is an example of linear data structure in which nodes are not kept in contiguous memory but rather are connected via pointers. It is essential to C++ programming and system architecture because it enables dynamic memory management and effective insertion or deletion.
2. What are the main types of Linked Lists?
Circular linked lists (last node refers to first), doubly linked lists (two-way pointers), and singly linked lists (one-way pointers) are the three primary varieties. Depending on traversal and memory requirements, each kind fulfils a distinct purpose.
3. How do you implement a basic Linked List in C++?
Creating a Node class or struct containing data and a pointer is the first step. Then, to ensure smooth abstraction and code reuse, you create a LinkedList class to handle nodes using methods like insert, delete, print, and search.
4. How does insertion work in a Linked List?
A list can be inserted at the start, middle, or end. Unlike arrays, where data must be shifted, it entails modifying the pointers of existing nodes to incorporate the new node without severing the relationship.
5. What is the difference between std::list and a custom linked list?
std::list from the C++ STL is a ready-made doubly linked list, optimized for frequent insertions and deletions. A custom linked list gives you full control for learning or when specific custom behaviors are needed.
6. What are real-world applications of Linked Lists?
Linked lists are used in implementing stacks, queues, graph adjacency lists, undo/redo systems, memory management, and polynomial arithmetic wherever dynamic data structures are needed.
7. Why should you master Linked Lists in C++?
Mastering linked lists is an excellent way to prepare for more challenging topics, such as graphs, trees, dynamic memory, and system architecture at a lower level. It's a necessary milestone in your journey to becoming a proficient and confident C++ programmer.
