1. CPS 393 Introduction to Unix and C
START OF WEEK 12 (C-6)
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Course material created by D. Woit

2. Course material created by D. Woit
Linked Lists
Generally, a list could be described as:
__ ____ ____ ____ ____
| -|-->|e1|-|-->|e2|-|--->|e3|-|--> >|en|-|
List
where ei is the ith element on the list.
Therefore, the list a b c can be:
__ ____ ____ ____
| -|-->|a |-|-->|b |-|--->|c |-|
A "null" pointer signifies end of list (NULL from stdio.h)
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3. Course material created by D. Woit
example
/*Source list.c
Making the list is done "by hand" here for illustration, but you would normally write a function, such as Add, so that a call such as Add(List,'a') would add an 'a' to the List
New element is added to the head of the list */
#include <stdio.h>
#include <stdlib.h>
typedef struct node NodeType;
struct node {
char ch;
NodeType *next; };
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4. Course material created by D. Woit
int main(void) {
NodeType *Node, //a list node
*List, //a list
*ptr; //a temp var to move along a list, node by node
List=NULL; // initially empty list
Node=(NodeType *) malloc(sizeof(NodeType)); //we add first node
Node->ch='a';
Node->next=NULL; // current end of list
printf("Node.ch: %c\n", Node->ch); //or (*Node).ch
printf("Node.next: %p\n", Node->next);
List=Node ; // pointer to list is updated
printf("List.ch: %c\n", List->ch);
printf("List.next: %p\n", List->next);
// now |.|->|a|-|
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5. Course material created by D. Woit
Node=(NodeType *) malloc(sizeof(NodeType)); //we add second node
Node->ch='b'; // data field is set to ‘b’
Node->next=NULL; // for the time being
Node->next=List; // now this node is set to point to the old head of the list
List=Node; // and head of the list is set to point to the new node
// now |.|->|b|-|->|a|-|
/*print out list*/
printf(" \nList is:\n \n ");
for (ptr=List; ptr!=NULL; ) {
printf(" %c ", ptr->ch);
ptr=ptr->next; }
printf("\n");
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6. Course material created by D. Woit
printf(" \nDetail :\n \n");
for (ptr=List; ptr!=NULL; ) {
printf("List.ch: %c\n", ptr->ch);
printf("List.next: %p\n", ptr->next);
ptr=ptr->next; }
return 0;
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7. Course material created by D. Woit
Add
Can make a function Add(list, char) to put char on front of list
/*Source add.h
header file for add.c */
typedef struct node NodeType;
struct node {
char ch;
NodeType *next; };
void Add(NodeType **L, char c);
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8. Course material created by D. Woit
Source add.c
/*Source add.c
function to add a char to the front of a list */
#include <stdio.h>
#include <stdlib.h>
#include "add.h“
/*Note: need to pass address of L so that it is call by value
if just passed *L, any changes to L inside function would
be lost upon function return. e.g., calling add(List,ch)
would not cause List to be changed after add return
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9. Course material created by D. Woit
void Add(NodeType **L, char c) {
NodeType *new;
new=(NodeType *) malloc(sizeof(NodeType)); //needs error checking
new->ch=c;
new->next=*L;
*L=new; }
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10. Course material created by D. Woit
addmain.c
/*Source addmain.c
program to use function Add (in file add.c) to add to front
of a list */
#include <stdio.h>
#include "add.h"
int main(void) {
NodeType *Node, //a pair
*List, //a list
*ptr; //a temp var to move along a list, pair by pair
char ch; //char to add to front of list
List=NULL;
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11. Course material created by D. Woit
for (ch='a'; ch<'f';ch++) //add a b c d e, each to front of list
Add(&List,ch); //call by value, so List changed
printf("List is: "); /*print list*/
for (ptr=List; ptr!=NULL; ) {
printf(" %c ", ptr->ch);
ptr=ptr->next; }
printf("\n");
return 0;
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12. Course material created by D. Woit
Searching
/*source: search.c
Search a list to determine if given character is in list*/
int Srch(NodeType *L, char item) {
NodeType *p;
for (p=L; p != NULL; p = p->next)
if (p->ch == item) return 1;
return 0; }
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13. We can alter addmain.c to do a search:
//Source addmainS.c
#include <stdio.h>
#include "add.h“
#include “srch.h”
void main(void) {
NodeType *Node, *List, *ptr;
char ch, item;
List=NULL;
for (ch='a'; ch<'f';ch++)
Add(&List,ch);
printf("List is: ");
for (ptr=List; ptr!=NULL; ) {
printf(" %c ", ptr->ch);
ptr=ptr->next; }
printf("\n");
/*search for a given item in list*/
printf("Enter char to search for: ");
scanf("%c",&item);
if ((Srch(List,item))==1) printf("found\n");
else printf("not found\n");
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14. Course material created by D. Woit
HMWK:
Write a version of Add that does not mutate (change) the list; instead,
it should return a new list.
The function prototype could be NodeType *Add(NodeType *L, char c);
Write functions for first and rest as follows:
first returns a copy of the first item on the
list (error if empty list)
rest returns a list that is the given list with the first item removed.
(error if empty list).
first should return a character and rest should return a list.
Write fucntion InsertO which inserts a given item into a list, keeping
the list in order.
Write function SrchO which searches an ordered list for the given item.
Note that if the item is not in the list, search can terminate as soon
as it finds an item larger than the searched-for item.
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15. Course material created by D. Woit
ADTs
-Normally, programmer supplies object code and definitions (.o and .h file) for an ADT. User writes a main which includes the .h and compiles their main with the given .o
-So user does not see source code.
-e.g., C sqrt function. WE use it by including math.h and then compiling our main with the math object code using -lm
(other object code included automatically, e.g., for printf, etc, but we still need definitions, eg., stdio.h)
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16. Course material created by D. Woit
USER PROGRAM:
/*Source userlistADT.c
compile: gcc userlistADT.c listADT.o */
#include <stdio.h>
#include <stdlib.h>
#include "listADT.h"
int main(void) {
List L;
init(&L);
add(&L,'a'); add(&L,'b'); add(&L,'c');
print(L);
printf("Length is %d\n",length(L));
return 0; }
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17. Course material created by D. Woit
PROGRAMMER CODE:
/*Source listADT.h */
typedef struct node NodeType;
struct node {
char ch;
NodeType *next; };
typedef struct {
int length;
NodeType *head;
} List;
void init(List *L) ;
void add(List *L, char c) ;
void print(List L) ;
int length(List L) ;
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18. Course material created by D. Woit
listADT.c
void add(List *L, char c) {
NodeType *new;
new=(NodeType *) malloc(sizeof(NodeType));
new->ch=c;
new->next=L->head;
L->head=new;
L->length++; }
void print(List L) {
int i; NodeType *p;
printf("List is: ");
for (i=0,p=L.head; i<L.length; i++,p=p->next) {
printf(" %c ", p->ch);
putchar('\n');
/*Source listADT.c
a user compiles listADT.o with their main to use a list ADT */
#include <stdio.h>
#include <stdlib.h>
#include "listADT.h"
void init(List *L) {
L->length=0;
L->head=NULL; }
int length(List L) {
return L.length;
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19. Hiding all Implementation Details
-If selling Off-The-Shelf code to a 3rd party, want to completely hide the implementation details from user (3rd party).
-How? User only gets ADT.h and ADT.o. User includes ADT.h in main and compiles main with ADT.o (has no source code ADT.c)
ADT.h has no ADT implementation details, only (void *)
ADT.o has ADT implementation details (structs etc), and
casts the (void *) to (ADT *) as necessary within ADT functions
-example:
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20. Example of how to hide details of ADT from user
/*Source: main.c
example of how to hide details of ADT from user
by keeping struct details out of complex.h, and only in complex.c */
#include <stdio.h>
#include <stdlib.h>
#include "complex.h"
int main (void) {
complex *m;
set(&m,7,2);
print(m);
return 0; }
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21. Course material created by D. Woit
void set(complex **a, int v, int w) {
priv_complex *new;
new=(priv_complex *)malloc(sizeof(priv_complex));
(*new).i=v;
(*new).j=w;
(*a)=(void *)new; }
void print(complex *a) {
printf("%d+%di\n", (*(priv_complex *)a).i, (*(priv_complex *)a).j);
//Source complex.h
typedef void *complex;
void set(complex **a,int i, int j) ;
void print(complex *a) ;
//Source complex.c
#include <stdio.h>
#include <stdlib.h>
#include "complex.h"
typedef struct {
int i;
int j;
} priv_complex;
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