c - 计算链表中的元素时出现段错误

Question

我是链表的新手，但我正在尝试创建一个包含 3 个元素的链表并编写一个函数来计算所述链表中元素的数量。我一直遇到段错误，但我不明白为什么。我们非常欢迎任何帮助。

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

typedef struct node {       // create a struct to build a 
    int             data;       // linked list
    struct node*    next;
};

struct node* BuildOneTwoThree() {
    struct node* head = NULL;           // pointers
    struct node* second = NULL;     // for 
    struct node* third = NULL;          // linked list

    // allocate memory on the heap for the 3 nodes
    head = malloc(sizeof(struct node));
    second = malloc(sizeof(struct node));
    third = malloc(sizeof(struct node));

    head->data = 1;     // set up 1st node
    head->next = second;

    second->data = 2;       // set up 2nd node
    second->next = third;

    third->data = 3;        // set up 3rd node
    third->next = NULL;

    return head;

}

void main(){
    int num = Length(BuildOneTwoThree);
    printf("Number of nodes:%d\n", num);

}

int Length(struct node* head) {
    struct node* current = head;    
    int count = 0;

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

Answer 1

线

int num = Length(BuildOneTwoThree);

需要

int num = Length(BuildOneTwoThree());
                                 ^^^ Missing the function call.

否则，您只是将函数指针指向 Length。

您可以通过在使用函数之前提供函数声明来避免此类错误。

struct node* BuildOneTwoThree();
int Length(struct node* head);

通过在文件顶部声明的函数，我从 gcc 得到以下消息:

soc.c: In function ‘main’:
soc.c:36:22: warning: passing argument 1 of ‘Length’ from incompatible pointer type [-Wincompatible-pointer-types]
     int num = Length(BuildOneTwoThree);
                      ^
soc.c:10:5: note: expected ‘struct node *’ but argument is of type ‘struct node * (*)()’
 int Length(struct node* head);

---

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

是不对的。这会产生 useless storage class specifier in empty declaration 警告。这需要要么

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

或

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

---

另外，main的返回类型需要是int，而不是void。