[CSE10200] Programming Basis ( 프로그래밍기초 ) Chapter 9. Seungkyu Lee. Assistant Professor, Dept. of Computer Engineering Kyung Hee University

Transcription

1 [CSE10200] Programming Basis ( 프로그래밍기초 ) Chapter 9 Seungkyu Lee Assistant Professor, Dept. of Computer Engineering Kyung Hee University

2 CHAPTER 9 Pointers #1~2

3 Pointer int main () { int a; int b; int c; int* ptr; a = 1000; b = 2000; c = 3000; ptr = &a; } int a int b int c memory address int* ptr of a

4 Pointer and data int* ptr; int a=5; ptr = &a; a 5 ptr 1004 값의주소는? 주소의값은? cout << *ptr; cout << &ptr; cout << *a; (error)

5 Pass by value

6 Pass by reference

7 Pass by address(pointers)

8 Pointers to arrays a same &a[0] a is a pointer only to the first element, not the whole array

9 Dereferencing array pointers

10 Two dimension array and pointer int Dim2[3][4] Dim2[0] =*(Dim2+0) =Dim2+0? Dim2[0]+1 = *Dim FF FF14 It s a Pointer to Pointer Points to start of array 0013FF FF1C Dim2 Dim2[1] =*(Dim2+1) =Dim2+1? 0013FF FF FF FF2C 4 Dim2[2] =*(Dim2+2) =Dim2+2? 0013FF FF FF FF3C

11 Two dimension array and pointer int Dim2[3][4] *(Dim2[1]+1) *(*(Dim2+1)+1) 0013FF FF FF FF1C Dim2[1]+1 *(Dim2+1) FF FF FF FF2C FF FF FF FF3C

12 CHAPTER 9 Pointers #3

13 Memory allocation

14 A conceptual view of memory

15 Memory management functions

16 Note: You can refer to dynamic memory only through a pointer.

17 new memory allocation for a single data item

18 Memory allocation for an array

19 Freeing memory

20 Note: Memory allocated by new must be released with delete, and memory allocated by new[ ] must be released with delete[ ].

21 #include<iostream> using namespace std; int main() { int *ptr = new int[10]; for (int i=0;i<10;i++) *(ptr+i) = i; for (int i=0;i<10;i++) cout << *(ptr+i) << ' '; delete[] ptr; cout << endl; for (int i=0;i<10;i++) cout << *(ptr+i) << ' '; } return 0;

22 Array of pointers: A ragged array

23 Dynamic vs. static memory allocation Array Dynamic Memory Allocation using Pointer Declaration int arrayvar[50]; int* ptrvar; Memory Allocation Memory Release Too much data case Too small data case Pros Cons Not required (automatically at program execution) Impossible (memory reserved until termination) Impossible to increase memory size Impossible to decrease Memory size Easy to programming using just an INDEX Fixed memory space (Big program), Weak for unexpected memory request ptrvar = new int[50]; delete ptrvar; Easy (allocate more memory) Easy (release and maintain small memory) Optimized memory usage Complex to manage pointers (side effect expected)

24 Common Errors int* a[5] vs int (*a)[5] int* a,b,c; //only a is a pointer int* ptr; *ptr=5; //error

25 Common Errors #include <iostream> using namespace std; void myfun(int a[3][3]); int main() { int a[3][3]; cout << a << ' ' << *a << ' ' << &a[0] << endl; int** b; int* c; //b=a; //c=a; c=*a; cout << c << endl; myfun(a); return 0; } void myfun(int suba[3][3]) { cout << suba << ' ' << *suba << ' ' << &suba[0] << endl; }

26 Definitions Linked List A data structure in which each element is dynamically allocated and in which elements point to each other to define a linear relationship Singly- or doubly-linked Stack, queue, circular list 26

27 Linked List 값 주소 27

28 Linked List struct listitem { int ; listitem *; }; 28

29 Linked List (continued) Items of list are usually same type Generally obtained from new operator Each item points to item Last item points to null Need head to point to first item! Payload of item may be almost anything A single member or multiple members Any type of object whose size is known at compile time Including struct, union, char * or other pointers 29

30 #include <iostream> using namespace std; struct NodeType { int component; NodeType* link; }; int main(){ NodeType* head; NodeType* newnodeptr; NodeType* currptr; // External pointer to list // Pointer to newest node // Pointer to last node cout << "Enter 4 integer value." << endl; head = new NodeType; cin >> head->component; currptr = head; for(int count = 1; count <= 3; count++){ newnodeptr = new NodeType; cin >> newnodeptr->component; currptr->link = newnodeptr; currptr = newnodeptr; } // Create new node // Set its component value // Link node into list // Set currptr to last node currptr->link = NULL; currptr = head; // Mark end of list } for(int count = 0; count <= 3; count++){ cout << "currptr->component: " << currptr->component << endl; currptr = currptr->link; } return 0; 30

31 Linked List (continued) struct listitem { int ; listitem *; }; listitem *head; 31

32 Adding an Item to a List listitem *p, *q; Add an item pointed to by q after item pointed to by p (Neither p nor q is NULL) 32

33 Adding an Item to a List listitem *addafter(listitem *p, listitem *q){ q -> = p -> ; p -> = q; return p; } 33

34 Adding an Item to a List listitem *addafter(listitem *p, listitem *q){ q -> = p -> ; p -> = q; return p; } 34

35 Adding an Item to a List listitem *addafter(listitem *p, listitem *q){ q -> = p -> ; p -> = q; return p; } 35

36 Adding an Item to a List (continued) listitem *addafter(listitem *p, listitem *q){ if (p && q) { q -> = p -> ; p -> = q; } return p; } 36

37 Doubly-Linked List struct listitem { int ; listitem *prev; listitem *; }; listitem *head, *tail; prev prev prev prev 37

38 Other Kinds of List Structures Queue FIFO (First In, First Out) Items added at end Items removed from beginning Stack LIFO (Last In, First Out) Items added at beginning, removed from beginning Circular list Last item points to first item Head may point to first or last item Items added to end, removed from beginning Linked Lists in C and C++ CS-2303, C-Term