Указатели Связанные списки C

Question

Я сделал это правильно? Я получаю странные ошибки здесь ...

 
linked.c: In function ‘push’: 
linked.c:50:19: warning: assignment from incompatible pointer type [enabled by default] 
linked.c: In function ‘main’: 
linked.c:146:9: error: incompatible type for argument 1 of ‘push’ 
linked.c:45:6: note: expected ‘struct node **’ but argument is of type ‘struct node’ 
~/swen250/CLinkedList$ gcc -o linked linked.c 
linked.c: In function ‘push’: 
linked.c:50:19: warning: assignment from incompatible pointer type [enabled by default] 
~/swen250/CLinkedList$ gcc -o linked linked.c 
linked.c: In function ‘pop’: 
linked.c:63:19: error: request for member ‘data’ in something not a structure or union 
linked.c:64:20: error: request for member ‘next’ in something not a structure or union 
linked.c: In function ‘copyList’: 
linked.c:106:9: warning: passing argument 1 of ‘appendNode’ from incompatible pointer type [enabled by default] 
linked.c:75:6: note: expected ‘struct node **’ but argument is of type ‘struct node *’ 

#include <stdio.h> 
#include <stdlib.h> 

struct node { 
    int data; 
    struct node* next; 
}; 

static int length(struct node** head); 
static void push(struct node** head, int data); 
static int pop(struct node** head); 
static void appendNode(struct node** head, int data); 
static struct node *copyList(struct node** head); 
static void printList(struct node** head); 



/************************************************************ 
length - return length of a list 
************************************************************/ 
int length(struct node** head) { 
    int count = 0; 
    struct node* current = NULL; 

    current = *head; 
    while (current != NULL) { 
     current = current->next; 
     ++count; 
    } 

    return count; 
} 


/************************************************************ 
push - add new node at beginning of list 
************************************************************/ 
void push(struct node** head, int data) { 
    struct node* new_ptr = NULL; 

    new_ptr = (struct node*)malloc(sizeof(struct node)); 
    new_ptr->data = data; 
    new_ptr->next = *head; 

    *head = new_ptr; 
} 

/************************************************************ 
pop - delete node at beginning of non-empty list and return its data 
************************************************************/ 
int pop(struct node** head) { 
    int val = 0; 
    struct node* temp = NULL; 

    if (*head != NULL) { 
     val = head->data; 
     temp = head->next; 
     free(head); 
     *head = temp; 
    } 

    return(val); 
} 

/************************************************************ 
appendNode - add new node at end of list 
************************************************************/ 
void appendNode(struct node** head, int data) { 
    struct node* current = NULL; 
    struct node* previous = NULL; 
    struct node* new_ptr = NULL; 

    current = *head; 
    previous = current; 
    while (current != NULL) { 
     previous = current; 
     current = current->next; 
    } 

    new_ptr = (struct node*)malloc(sizeof(struct node)); 
    new_ptr->data = data; 
    new_ptr->next = NULL; 

    previous = new_ptr; 

} 

/************************************************************ 
copyList - return new copy of list 
************************************************************/ 
struct node* copyList(struct node** head) { 
    struct node* copy = NULL; 
    struct node* current = NULL; 
    struct node* new_ptr = NULL; 

    /* Copy current head to copy */ 
    current = *head; 
    while (current != NULL) { 
     appendNode(copy, current->data); 
     current = current->next; 
    } 

    return copy; 
} 


/************************************************************ 
printList - print linked list as "List: < 2, 5, 6 >" (example) 
************************************************************/ 
void printList(struct node** head) { 
    struct node* current = NULL; 

    printf("List: < "); 

    current = *head; 
    if (current == NULL) 
     printf("none "); 

    while (current != NULL) { 
     printf("%d", current->data); 
     current = current->next; 
     if (current != NULL) 
      printf(", "); 
    } 

    printf(" >\n"); 
} 

void main() { 
    int i;      // index used for loops 
    struct node *list_a;  // a new list 
    struct node *list_a_copy; // copy of list 
    list_a = NULL;    // initialize empty list 
    list_a_copy = NULL;   // initialize empy list 


    // test push 
    for (i = 0; i < 4; ++i) 
     push(&list_a, i); 

    // test length 
    printf("Length of list = %d\n", length(&list_a)); 

    // test print head list 
    printf("head:\n"); 
    printList(&list_a); 

    // test append node 
    for (i = 4; i < 8; ++i) 
     appendNode(&list_a, i); 

    // test print head list 
    printf("head(append):\n"); 
    printList(&list_a); 

    // make a copy of list 
    list_a_copy = copyList(&list_a); 

    // test pop head list 
    for (i = 0; i < 4; ++i) 
     printf("%d popped\n", pop(&list_a)); 

    // test print copy list 
    printf("head copy:\n"); 
    printList(&list_a_copy); 

    // test pop copy list 
    for (i = 0; i < 4; ++i) 
     printf("%d popped\n", pop(&list_a_copy)); 

} 

Answer 1

Из журнала ошибок, я заметил, что у вас есть несовместимые типы кратные времени. Это поможет, если вы разместите свой файл main.cpp.

p.s Как сказал Майк Г, двойной указатель действительно чрезмерен. Вы можете реализовать связанный список, используя один указатель.

Answer 2

Проблема в вашей функции pop() ... взгляните. вы назначаете

val=head->data; 
temp = head->next; 

также вы освободив голову, а затем переназначение.

вы должны сделать, как этот

val=(*head)->data; 
temp=(*head)->next; 

и освобождая память ... освободить темп и переназначить голову к его следующему.

Answer 3

Проблема связана с тем, как используются двойные указатели.

Вот полный рабочий код: Я сделал некоторые изменения на пути, как были использованы двойные указатели. Вы можете увидеть изменения в функции pop и copyList.

#include <stdio.h> 
#include <stdlib.h> 

struct node { 
    int data; 
    struct node* next; 
}; 

static int length(struct node** head); 
static void push(struct node** head, int data); 
static int pop(struct node** head); 
static void appendNode(struct node** head, int data); 
static struct node *copyList(struct node** head); 
static void printList(struct node** head); 



/************************************************************ 
length - return length of a list 
************************************************************/ 
int length(struct node** head) { 
    int count = 0; 
    struct node* current = NULL; 

    current = *head; 
    while (current != NULL) { 
    current = current->next; 
    ++count; 
    } 

    return count; 
} 


/************************************************************ 
push - add new node at beginning of list 
************************************************************/ 
void push(struct node** head, int data) { 
    struct node* new_ptr = NULL; 

    new_ptr = (struct node*)malloc(sizeof(struct node)); 
    new_ptr->data = data; 
    new_ptr->next = *head; 

    *head = new_ptr; 
} 

/************************************************************ 
pop - delete node at beginning of non-empty list and return its data 
************************************************************/ 
int pop(struct node** head) { 
    int val = 0; 
    struct node* temp = NULL; 

    if (*head != NULL) { 
    val = (*head)->data; 
    temp = (*head)->next; 
    free(*head); 
    *head = temp; 
    } 

    return(val); 
} 

/************************************************************ 
appendNode - add new node at end of list 
************************************************************/ 
void appendNode(struct node** head, int data) { 
    struct node* current = NULL; 
    struct node* previous = NULL; 
    struct node* new_ptr = NULL; 

    current = *head; 
    previous = current; 
    while (current != NULL) { 
    previous = current; 
    current = current->next; 
    } 

    new_ptr = (struct node*)malloc(sizeof(struct node)); 
    new_ptr->data = data; 
    new_ptr->next = NULL; 

    previous = new_ptr; 

} 

/************************************************************ 
copyList - return new copy of list 
************************************************************/ 
struct node* copyList(struct node** head) { 
    struct node* copy = NULL; 
    struct node* current = NULL; 
    struct node* new_ptr = NULL; 

    /* Copy current head to copy */ 
    current = *head; 
    while (current != NULL) { 
    appendNode(&copy, current->data); 
    current = current->next; 
    } 

    return copy; 
} 


/************************************************************ 
printList - print linked list as "List: < 2, 5, 6 >" (example) 
************************************************************/ 
void printList(struct node** head) { 
    struct node* current = NULL; 

    printf("List: < "); 

    current = *head; 
    if (current == NULL) 
    printf("none "); 

    while (current != NULL) { 
    printf("%d", current->data); 
    current = current->next; 
    if (current != NULL) 
     printf(", "); 
    } 

    printf(" >\n"); 
} 

void main() { 
    int i;      // index used for loops 
    struct node *list_a;  // a new list 
    struct node *list_a_copy; // copy of list 
    list_a = NULL;    // initialize empty list 
    list_a_copy = NULL;   // initialize empy list 


    // test push 
    for (i = 0; i < 4; ++i) 
    push(&list_a, i); 

    // test length 
    printf("Length of list = %d\n", length(&list_a)); 

    // test print head list 
    printf("head:\n"); 
    printList(&list_a); 

    // test append node 
    for (i = 4; i < 8; ++i) 
    appendNode(&list_a, i); 

    // test print head list 
    printf("head(append):\n"); 
    printList(&list_a); 

    // make a copy of list 
    list_a_copy = copyList(&list_a); 

    // test pop head list 
    for (i = 0; i < 4; ++i) 
    printf("%d popped\n", pop(&list_a)); 

    // test print copy list 
    printf("head copy:\n"); 
    printList(&list_a_copy); 

    // test pop copy list 
    for (i = 0; i < 4; ++i) 
    printf("%d popped\n", pop(&list_a_copy)); 
}