Help Understanding Some Basics
I just recently bought the book:
Mastering Algorithms with C
A Link to the book
In it, the author provides code for some basic data structures. I am in the process of transcribing them to my machine using vim. Along the way I am attempting to write some basic programs using these data structures just to test my knowledge and help my understanding more.
However, I have run into a bit of a problem. I am unable to figure out how to use the very first one. I will provide you with the code if you can please explain to me how exactly I am to use these structures. I am a bit new to C, but I am really trying here. Any help would be much appreciated.
list.h
Code:
/**
* list.h
**/
#ifndef LIST_H
#define LIST_H
/**
* Define a structure for linked list elements
**/
typedef struct ListElmt_ {
void *data;
struct ListElmt_ *next;
} ListElmt;
/**
* Define a structure for linked lists
**/
typedef struct List_ {
int size;
int (*match)(const void *key1, const void *key2);
void (*destroy)(void *data);
ListElmt *head;
ListElmt *tail;
} List;
/**
* Public Interface
**/
void list_init(List *list, void (*destroy)(void *data));
void list_destroy(List *list);
int list_ins_next(List *list, ListElmt *element, const void *data);
int list_rem_next(List *list, ListElmt *element, void **data);
#define list_size(list) ((list)->size)
#define list_head(list) ((list)->head)
#define list_tail(list) ((list)->tail)
#define list_is_head(list, element) ((element) == (list)->head ? 1 : 0)
#define list_is_tail(list, elememt) ((element) == (list)->tail ? 1 : 0)
#define list_data(element) ((element)->data)
#define list_next(element) ((element)->next)
#endif
Code:
/**
* list.c
**/
#include <stdlib.h>
#include <string.h>
#include "list.h"
/**
* list_init
**/
void list_init(List *list, void (*destroy)(void *data)) {
/**
* initializes the list
**/
list->size = 0;
list->destroy = destroy;
list->head = NULL;
list->tail = NULL;
return;
}
/**
* list_destroy
**/
void list_destroy(List *list) {
void *data;
/**
* remove each element
**/
while (list_size(list) > 0) {
if (list_rem_next(list, NULL, (void **)&data) == 0 && list->destroy != NULL) {
/**
* Call a user-defined function to free dynamically allocated data.
**/
list->destroy(data);
}
}
/**
* No operations are allowed now, but clear the structer as a precaution.
**/
memset(list, 0, sizeof(List));
return;
}
/**
* list_ins_next
**/
int list_ins_next(List *list, ListElmt *element, const void *data) {
ListElmt *new_element;
/**
* Allocate storage for the element.
**/
if ((new_element = (ListElmt *)malloc(sizeOf(ListElmt))) == NULL)
return -1;
/**
* Insert the element into the list.
**/
new_element->data = (void *)data;
if (element == NULL) {
/**
* Handle insertion at the head of the list.
**/
if (list_size(list) == 0)
list->tail = new_element;
new_element->next = list->head;
list->head = new_element;
}
else {
/**
* Handle insertion somewhere other than at the head.
**/
if (element->next == NULL)
list->tail = new_element;
new_element->next = element->next;
element->next = new_element;
}
/**
* Adjust the size of the list to account for the inserted element.
**/
list->size++;
return 0;
}
/**
* list_rem_next
**/
int list_rem_next(List *list, ListElmt *element, void **data) {
ListElmt *old_element;
/**
* Do not allow removal from an empty list.
**/
if (list_size(list) ==0)
return -1;
/**
* Remove the element from the list.
**/
if (element == NULL) {
/**
* Handle removal from the head of the list.
**/
*data = list->head->data;
old_element = list->head;
list->head = list->head->next;
if (list_size(list) == 1)
list->tail = NULL;
}
else {
/**
* Handle removal from somewhere other than the head.
**/
if (element->next == NULL)
return -1;
*data = element->next->data;
old_element = element->next;
element->next = element->next->next;
if (element->next == NULL)
list->tail = element;
}
/**
* Free the storage allocated by the abstract datatype.
**/
free(old_element);
/**
* Adjust the size of the list to account for the removed element.
**/
list->size--;
return 0;
}
This is my basic testprog.c
I am mainly just trying to take baby steps so I can get something to atleast compile. However, I am having issues understanding the correct usage of the list_init function.
Code:
int main() {
List mainList;
void *data;
mainList = list_init(&mainList,free(&data));
return 0;
}
I am having a tough time understanding the function pointer concept i suppose. I understand it is a pointer to a function, but the function must have arguments passed to it. What am I supposed to pass to the free() macro to get this to compile and also properly use it when i call list_destroy.
Thanks in advance!!!
