Dynamic Memory & Linked Lists
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The document discusses dynamic memory allocation and linked lists in programming, highlighting the limitations of static arrays and the benefits of dynamic allocation using 'new' and 'delete' operators. It outlines the structure and types of linked lists, such as singly, doubly, and circular linked lists, as well as their advantages and disadvantages compared to arrays. Additionally, it emphasizes the applications of linked lists in various data structures and algorithms.
![Explicitly freeing memory in C++:
The ‘delete’ Operator
• Used to free memory allocated with new operator
• The delete operator should be called on a pointer to
dynamically allocated memory when it is no longer needed
• Can delete a single variable/object or an array
delete PointerName;
delete [] ArrayName;
• After delete is called on a memory region, that region should
no longer be accessed by the program
• Convention is to set pointer to deleted memory to NULL
Any new must have a corresponding delete --- if not, the
program has memory leak.
New and delete may not be in the same routine.](https://image.slidesharecdn.com/week5-dynamicmemorylinkedlist-191013065814/85/Dynamic-Memory-Linked-Lists-11-320.jpg)
![Example
• int main()
• {
• // Below variables are allocated memory
• // dynamically.
• int *ptr1 = new int;
• int *ptr2 = new int[10];
•
• // Dynamically allocated memory is
• // deallocated
• delete ptr1;
• delete [] ptr2;
• }](https://image.slidesharecdn.com/week5-dynamicmemorylinkedlist-191013065814/85/Dynamic-Memory-Linked-Lists-13-320.jpg)
Dynamic Memory & Linked Lists
- 1. Dynamic Memory & Linked List Prepared by: Afaq Mansoor Khan BSSE III- Group A Session 2017-21 IMSciences, Peshawar.
- 2. Last Lecture Summary • Selection Sort, • Insertion Sort, • Algorithms Analysis • Merge Sort Algorithm, • Merge Sort Analysis
- 3. Objectives Overview • Dynamic Memory Allocation • Introduction to Linked List
- 4. 4 Problem with Arrays • Sometimes ▫ Amount of data cannot be predicted beforehand ▫ Number of data items keeps changing during program execution • Example: Search for an element in an array of N elements • One solution: find the maximum possible value of N and allocate an array of N elements ▫ Wasteful of memory space, as N may be much smaller in some executions ▫ Example: maximum value of N may be 10,000, but a particular run may need to search only among 100 elements Using array of size 10,000 always wastes memory in most cases
- 5. Better Solution • Dynamic memory allocation ▫ Know how much memory is needed after the program is run Example: ask the user to enter from keyboard ▫ Dynamically allocate only the amount of memory needed 5
- 6. Memory Allocation There are essentially two types of memory allocation 1. Static 2. Dynamic
- 7. Memory Allocation - Static Static – Done by the compiler automatically (implicitly). o Global variables or objects -- memory is allocated at the start of the program, and freed when program exits; alive throughout program execution 1. Can be access anywhere in the program. o Local variables (inside a routine) – memory is allocated when the routine starts and freed when the routine returns. 1. A local variable cannot be accessed from another routine. o Allocation and free are done implicitly. o No need to explicitly manage memory is nice, but has limitations! 1. Using static allocation, the array size must be fixed.
- 8. Memory Allocation - Dynamic Wouldn’t it be nice to be able to have an array whose size can be adjusted depending on needs. Dynamic memory allocation deals with this situation. Dynamic – Done explicitly by programmer. Programmer explicitly requests the system to allocate memory and return starting address of memory allocated (what is this?). This address can be used by the programmer to access the allocated memory. When done using memory, it must be explicitly freed.
- 9. Explicitly allocating memory in C++: The ‘new’ Operator • Used to dynamically allocate memory • Can be used to allocate a single variable/object or an array of variables/objects • The new operator returns pointer to the type allocated • Before the assignment, the pointer may or may not point to a legitimate memory • After the assignment, the pointer points to a legitimate memory.
- 11. Explicitly freeing memory in C++: The ‘delete’ Operator • Used to free memory allocated with new operator • The delete operator should be called on a pointer to dynamically allocated memory when it is no longer needed • Can delete a single variable/object or an array delete PointerName; delete [] ArrayName; • After delete is called on a memory region, that region should no longer be accessed by the program • Convention is to set pointer to deleted memory to NULL Any new must have a corresponding delete --- if not, the program has memory leak. New and delete may not be in the same routine.
- 13. Example • int main() • { • // Below variables are allocated memory • // dynamically. • int *ptr1 = new int; • int *ptr2 = new int[10]; • • // Dynamically allocated memory is • // deallocated • delete ptr1; • delete [] ptr2; • }
- 14. The Heap • Large area of memory controlled by the runtime system that is used to grant dynamic memory requests. • It is possible to allocate memory and “lose” the pointer to that region without freeing it. This is called a memory leak. • A memory leak can cause the heap to become full • If an attempt is made to allocate memory from the heap and there is not enough, an exception is generated (error)
- 15. Why use dynamic memory allocation? • Allows data (especially arrays) to take on variable sizes (e.g. ask the user how many numbers to store, then generate an array of integers exactly that size). • Allows locally created variables to live past end of routine. • Allows us to create many structures used in Data Structures and Algorithms
- 16. The . and -> operators • The dot operator is used to access an object’s members ▫ M1.Simplify(); ▫ M1.num = 5; • But how do we access an objects members if we only have a pointer to the object? • If we have M1_ptr = &M1, Perhaps we would use (*(M1_ptr)).Simplify() • A shorthand for this is the arrow operator • M1_ptr->Simplify() is equivalent to(*(M1_ptr)).Simplify()
- 17. Introduction to Linked Lists
- 18. Linked Lists • Linked List is a very commonly used linear data structure which consists of group of nodes in a sequence. • Each node holds its own data and the address of the next node hence forming a chain like structure. • Linked Lists are used to create trees and graphs.
- 20. Types of Linked Lists There are 3 different implementations of Linked List available, they are: 1. Singly Linked List 2. Doubly Linked List 3. Circular Linked List
- 21. Singly Linked List • Singly linked lists contain nodes which have a data part as well as an address part i.e. next, which points to the next node in the sequence of nodes. • The operations we can perform on singly linked lists are insertion, deletion and traversal.
- 23. Doubly Linked List • In a doubly linked list, each node contains a data part and two addresses, one for the previous node and one for the next node.
- 25. Circular Linked List • In circular linked list the last node of the list holds the address of the first node hence forming a circular chain.
- 27. Advantages of Linked Lists • They are a dynamic in nature which allocates the memory when required. • Insertion and deletion operations can be easily implemented. • Linked List reduces the access time.
- 28. Disadvantages of Linked Lists • The memory is wasted as pointers require extra memory for storage. • No element can be accessed randomly; it has to access each node sequentially. • Reverse Traversing is difficult in linked list. • Not cache friendly. Since array elements are contiguous locations, there is locality of reference which is not there in case of linked lists.
- 29. Applications of Linked Lists • Linked lists are used to implement stacks, queues, graphs, etc. Linked lists let you insert elements at the beginning and end of the list. In Linked Lists we don't need to know the size in advance
- 30. Array vs Linked List • Both Linked List and Array are used to store linear data of similar type, but an array consumes contiguous memory locations allocated at compile time, i.e. at the time of declaration of array, while for a linked list, memory is assigned as and when data is added to it, which means at runtime.
- 31. On the left, we have Array and on the right, we have Linked List.
- 32. Summary • Dynamic Memory Allocation ▫ New Operator ▫ Delete Operator ▫ Heap ▫ dot . and -> operators • Introduction to Linked List ▫ Types ▫ Advantages ▫ Disadvantages ▫ Applications ▫ Difference between Array and Linked List
- 33. References • https://www.geeksforgeeks.org/what-is-dynamic- memory-allocation/ • https://www.geeksforgeeks.org/new-and-delete- operators-in-cpp-for-dynamic-memory/ • https://www.youtube.com/watch?v=texoDnnzWao • https://www.studytonight.com/data- structures/introduction-to-linked-list • https://www.geeksforgeeks.org/linked-list-set-1- introduction/