Computer Systems and Networks

Transcription

1 University of the Pacific LECTURE 5: C PROGRAMMING Computer Systems and Networks Dr. Pallipuram (vpallipuramkrishnamani@pacific.edu)

2 Today s Class o Pointer basics o Pointers and mul;- dimensional arrays o malloc, calloc, free o Pointers and data structures o Structures o linked lists o File I/O in C o C challenge o Deadline: Friday 15 th Sept, :59 PM

3 Pointer ArithmeEc Only addition and subtraction are allowed with pointers. All pointers increase and decrease by the length of the data-type they point to. Example: If an integer pointer, iptr holds address 32, then after the expression iptr++, iptr will hold 36 (assuming integer is 4 bytes).

4 Problem 1 The name of the array is actually a pointer pointing to the first element of the array. printf( \n %u:array+3); //prints? printf( \n %u:*(array+3)); //prints?

5 Pointers and FuncEons: Call by value vs. Call by reference Call by value main() a5,b6; update(a,b); printf( %d,a); update(int a, int b) aa-b; these are just copies. No change to original variables modification to actual variable Call by reference (pointer) main() a5,b6; update(&a,&b); printf( %d,a); update(int *a,int *b) *a*a-*b;

6 Malloc 1D int *array; //array of integers array (int *)malloc(sizeof(int)*5); address: value: array[0] array[1] array[2] array[3] array[4] array (pointer variable) value: 60 pointer s addr: 32

7 Malloc 2D Allocate 4x5 integers (important for lab 4) int **array; //a double pointer array (int **)malloc(sizeof(int *)*4); for(i0;i<4;i++) array[i] (int *)malloc(sizeof(int)*5); an array of integer pointers array of ints array of ints array of ints array of ints

8 Malloc 3D int ***array; //a triple pointer an array of double pointers a matrix of single pointers a cuboid of integers

9 Problem 2 Dynamically allocate space for a 3-D color image of width, w; height, h; color channel, c. Any pixel is accessed as image[height][width][c].

10 Calloc() void * calloc(int count, int size) Basically the same as malloc! Imagine you want an array of elements Argument 1: # of elements to allocate Argument 2: Size of each element in bytes Return value: Pointer to the region

11 Realloc() void * realloc(void *ptr, int size); Resize a dynamic region of memory Note that it might move to a new address! Argument: Pointer to the original region Argument 2: Desired size in bytes of new region Return value: Pointer to the new region It might be at the same address if you made it smaller It might be at a new address if you made it larger

12 #include <stdlib.h> Include this library to use malloc, realloc, and calloc!

13 free() Why do we need to call free() a?er calling malloc()? Memory leak malloc() cannot re- use that space ever, because its internal bookkeeping s;ll thinks that region is used Will only be recovered upon termina;ng program Opera;ng system wipes out all the memory allocated to your process (stack, heap, etc )

14 C Structures Structures are a nice way to bring certain related items together struct database int id_number; int age; float salary; ; int main() struct database employee; //an object employee.age 22; employee.id_number 1; employee.salary ;

15 Problem 3 Declare a structure called coordinate that contains two integers denoting the (height,width) location of a pixel in an image matrix. Inside main, create a structure object called and set it s values to (220,360).

16 Pointers and Structures Singly Linked Lists are a bunch of dynamically allocated structures (Nodes) connected to each other Node link stores the address of the node data link addr: Head Tail

17 Doubly Linked Lists prev. link Node data link data Head 243 data data 437 Tail

18 Example CreaEng a doubly linked list for the data: struct coordinate Write a function called: create_list to create a doubly linked list for the structure, coordinate, containing height and width information for a pixel. This function should be called to add a new coordinate to the list. The list should be doubly linked. Additionally, the list should have a head (first node) and a tail (last node) for easy traversal.

19 struct double_list struct coordinate coord; struct double_list *,*prev;; main() //Something something struct coordinate ; struct double_list *head,*tail; head; tail; No List yet

20 struct double_list struct coordinate coord; struct double_list *,*prev; main() //Something something struct coordinate ; struct double_list *head,*tail; head; tail; //something something //a loop to push random s to list 3 times for(i0;i<3;i++) //something something creates s create_list(&head, &tail, );

21 void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp;

22 Let s execute the three iteraeons

23 void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 0 nothing yet

24 void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 0 nothing yet

25 void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 0 nothing yet

26 void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 0 nothing yet

27 head tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 0 nothing yet

28 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

29 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

30 head temp tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

31 head temp tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

32 head temp tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

33 head tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 1 one item on the list

34 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

35 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

36 head tail t temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

37 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

38 head tail temp void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

39 head tail void create_list(struct double_list **head, struct double_list **tail, struct coordinate ) //call by reference if(*head) //nothing on the list yet (*head)(struct double_list *)malloc(sizeof(struct double_list)); (*head)->; (*head)->prev; (*head)->coord; (*tail)(*head); //tail and head are same when only 1 item else temp (struct double_list *)malloc(sizeof(struct double_list)); temp-> ; temp->previous *tail; temp->coord; (*tail)-> temp; (*tail)temp; iteration 2 two items on the list

40 and so on!

41 Problem 4 Write a C function that traverses the doubly linked list you just created and prints the data. Start the traversal from the head.

42 void print_list(struct double_list *head) //call by value. No change to list temphead; while(temp!) printf( \n %d %d,(temp->coord).height, (temp->coord).width; temptemp->;

43 Problem 5 Let us simulate a queue (FIFO list). The linked list function we wrote already creates a queue. Write a C function that returns the first element (struct coordinate type), removes the node, and adjusts the linked list.

44 struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ;

45 head tail struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; Let s call this function three times

46 head temp tail struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

47 head tail temp struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

48 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

49 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

50 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

51 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

52 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; first call

53 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

54 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

55 temp struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; head if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

56 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

57 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

58 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

59 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; second call

60 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

61 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

62 temp struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; head if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

63 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

64 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

65 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; third call

66 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; if(temp) //nothing on the list yet printf( \n Nothing to exit.. ); exit(0); else temp->coord; (*head)(*head)->; free(temp); if((*head)!) (*head)->prev; return ; what will happen on the fourth call?

67 File I/O

68 #include<stdio.h> int main() FILE *ptr_file; char buf[1000]; ptr_file fopen("input.txt","r"); if (!ptr_file) return 1; while (fgets(buf,1000, ptr_file)!) printf("%s",buf); fclose(ptr_file); return 0;

69 Problem 6: File I/O FuncEons o fopen opens a text file. o fclose closes a text file. o feof o fgets reads a string from a file. o fwrite o fgetc reads a character from a file. o fputc prints a character to a file.