这是我在这里的第一个问题。我无法理解这个程序中的几行代码。
自定义销毁函数指针是我无法理解的。
我已经评论了“需要帮助 #1 和需要帮助 #2”，我需要代码方面的帮助。
任何帮助将不胜感激，我将非常感谢任何可以帮助我理解这些代码的人。
#ifndef LIST_H
#define LIST_H
#include <stdio.h>
typedef struct _ListElmt
{
void *data;
struct ListElmt *next;
} ListElmt;
typedef struct _List
{
int size;
int (*match)(const void *key1, const void *key2);
void (*destroy)(void *data);
ListElmt *head;
ListElmt *tail;
} List;
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);
int list_size(const List *list);
ListElmt *list_head(const List *list);
ListElmt *list_tail(const List *list);
int list_is_head(const ListElmt *element);
int list_is_tail(const ListElmt *element);
void *list_data(const ListElmt *element);
ListElmt *list_next(const ListElmt *element);
#endif
这是list.c
#include <stdlib.h>
#include <string.h>
#include "List.h"
/* Need Help #1: The destroy function pointer is called here when the list is initialized and I need some explanation on how this works */
void list_init(List *list, void (*destroy)(void *data))
{
list->size = 0;
list->destroy = destroy;
list->head = NULL;
list->tail = NULL;
return;
}
void list_destroy(List *list)
{
void *data;
while (list_size(list) > 0)
{
if (list_rem_next(list, NULL, (void **) &data) == 0&& list->destroy != NULL)
{
list->destroy(data);
/* Need Help #2: The above line - how this works. I have no idea how this works because I haven't seen any code like that before. Also kindly let me know if this is recursion or not.*/
}
}
memset(list, 0, sizeof(List));
return;
}
int list_ins_next(List *list, ListElmt *element, const void *data)
{
ListElmt *new_element;
if ((new_element = (ListElmt *) malloc(sizeof(ListElmt))) == NULL ) // not yet understanded
return -1;
new_element->data = (void *) data;
if (element == NULL )
{
if (list_size(list) == 0)
list->tail = new_element;
new_element->next = list->head;
list->head = new_element;
}
else
{
if (element->next == NULL )
list->tail = new_element;
new_element->next = element->next;
element->next = new_element;
}
list->size++;
return 0;
}
int list_rem_next(List *list, ListElmt *element, void **data)
{
ListElmt *old_element;
if (list_size(list) == 0)
return -1;
if (element == NULL )
{ // Handle removal of the head
*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 else
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(old_element);
list->size--;
return 0;
}