Computer Systems and Networks

Transcription

1 LECTURE 6: C PROGRAMMING Computer Systems and Networks Dr. Pallipuram (vpallipuramkrishnamani@pacific.edu) University of the Pacific

2 Today s Class o Recap from last class o File I/O o What happens during a malloc and free o String Operations

3 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;

4 Let s execute the three iteragons

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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

16 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

17 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

18 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

19 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

20 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

21 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

22 and so on!

23 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.

24 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 ;

25 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

26 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

27 head temp struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

28 temp tail 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

29 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

30 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

31 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

32 head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

33 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

34 temp head struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

35 temp struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

36 tail 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

37 tail 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

38 tail 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

39 struct coordinate exit_queue(struct double_list **head) //call by reference struct coordinate ; temp*head; tail 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

40 tail 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

41 tail 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

42 tail 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

43 tail 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

44 tail 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

45 tail 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

46 tail 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?

47 DO NOT want program to access tail either head struct coordinate exit_queue(struct double_list **head, struct double_list **tail) //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; else (*tail); return ; tail

48 Problem 1 How would you modify the exit_queue function to simulate a stack function, pop()?

49 File I/O

50 #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;

51 Problem 2: File I/O FuncGons 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.

52 C program memory management

53 Memory Management OS creates virtual memory space for process when started Region is huge (full 32 or 64 bit space) Not fully mapped to physical memory Otherwise you could only fit 1 program in memory 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Virtual Memory Space for new process 0x

54 Memory Management OS loads in the program from disk Text region Program code Data region Program fixed data 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Data (Program data) Text (Program code) 0x

55 Memory Management Stack created to track program funcmon calls and local variables 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Stack Data (Program data) Text (Program code) 0x

56 Memory Management Heap created to store dynamic memory from malloc()and related funcmons Not to scale this unused region is huge! 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Stack (Unused / unmapped virtual memory) Heap Data (Program data) Text (Program code) 0x

57 Memory Management Program starts running malloc() allocates some memory 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Stack (Unused / unmapped virtual memory) Heap Data (Program data) Text (Program code) 0x

58 Memory Management Original heap space eventually fills up malloc() requests addimonal space from the kernel by using brk() system call New spac e 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Stack (Unused / unmapped virtual memory) Heap Data (Program data) Text (Program code) 0x

59 Memory Management Program terminates OS expunges enmre virtual address space Everything is deleted 0xFFFFFFFFFFFFFFFF (32 or 64 bit) Stack (Unused / unmapped virtual memory) Heap Data (Program data) Text (Program code) 0x

60 String OperaGons

61 C Strings There is no such thing as a string in C! What do you get? An array of characters Terminated by the null character '\0' Must manipulate element by element Not enough room in the array? Need a bigger array

62 Arrays of Characters char phrase[]"math"; phrase phrase[0] phrase[1] phrase[2] phrase[3] phrase[4] M A T H \0 Null terminator character (End of string) 62

63 Arrays of Characters phrase char phrase[8]"math"; phrase[0] phrase[1] phrase[2] phrase[3] phrase[4] phrase[5] phrase[6] phrase[7] M A T H \0????????? printf("%s\n", phrase); Prints until it reaches the \0 character!

64 Problem Helpful Library for Character Arrays #include <string.h> Useful funcmons strcpy - strcmp strlen strcat -

65 String Copy char phrase1[] "Math"; char phrase2[8]; strcpy(phrase2, phrase1); phrase1 phrase1[0] phrase1[1] phrase1[2] phrase1[3] phrase1[4] M A T H \0 phrase2 phrase2[0] phrase2[1] phrase2[2] phrase2[3] phrase2[4] phrase2[5] phrase2[6] phrase2[7] M A T H \0?????????

66 String ConcatenaGon char phrase1[8] Comp ; char phrase2[] Sci ; strcat(phrase1, phrase2); phrase1 phrase1[0] phrase1[1] phrase1[2] phrase1[3] phrase1[4] C O M P S phrase1[5] phrase1[6] phrase1[7] C I \0 phrase2 phrase2[0] phrase2[1] phrase2[2] phrase2[3] S C I \0 You cannot do this: phrase2 phrase1+phrase2;

67 ctype Library Useful for character manipulamon #include <ctype.h> toupper(char) / tolower(char) Converts character to uppercase or lowercase Example: char c toupper('a'); printf("%c", c); // A

68 ctype Library isalpha(char) Is the character a le\er? isdigit(char) Is the character a number 0-9? isspace(char) Is the character whitespace? (space or newline character) ispunct(char) Is the character punctuamon? (technically, a visible character that is not whitespace, a le\er, or a number) and several other variamons

69 Problem 4: What is the output of the C snippet below? main( ) char s[ ] "CPP programmers! You know C!" ; printf ( "\n%s", &s[2] ) ; printf ( "\n%s", s ) ; printf ( "\n%c", s[2] ) ;

70 Problem 5: Write a C snippet to reverse a string char *string; printf( \n Enter the string %s,string); /* Your code snippet here */ printf( \n The reverse string is %s,string);

71 What s the Error? char *a malloc(128*sizeof(char)); char *b malloc(128*sizeof(char)); b a; free(a); free(b);

72 What s the (PotenGal) Error? char *a malloc(128*sizeof(char)); datalen <some value...> // Copy datalen bytes // starting at *data to *a memcpy(a, data, datalen);

73 What s the Error? ptr (char *) malloc(strlen(string_a)); strcpy(ptr, string_a);

74 In- class ParGcipaGon: What s the Error? int *get_ii() int ii 2; return &ii; main() int *ii; ii get_ii();... Do stuff using ii pointer

75

76 You are ready for Lab 4!

77 Useful Knowledge Simple structures 2-D array dynamic allocation and access String manipulation functions PRE-LAB DUE ON 26 th September: * Everything except for the game logic. However, your program should repeatedly display the grid and terminate when the special word "exit" is entered by the user. I will perform the check-off.