Question

我尝试从该行添加书籍并将其存储在链接列表中。但是，当我尝试这样做时，它会继续从文件中读取。

我在语句if (current == NULL)之前添加了一个print语句，它返回一个空链表。

读完文件后，我可以得到正确的结果，但一旦弹出if循环，当前节点就会再次变空。

以下是代码：

typedef struct _Book
{
    int ISBN;
    char Title[20];
    char Author[20];
    char Description[40];
    int CopiesAtCSU;


    struct _Book *next;
} Book;

int add(Book **listHead,int ISBN,char *Title,char *Author, int CopiesAtCsu, char *description,  int sortIndx){
    current = listHead; 
    prev = null; 
    newNode = null;

    newNode = malloc(sizeof(Book));
    newNode->ISBN = ISBN;
    //newNode->Title = Title;
    strcpy(newNode->Title, Title);
    //newNode->Author = Author;
    strcpy(newNode->Author, Author);
    newNode->CopiesAtCSU = CopiesAtCsu;
    //newNode->Description = description;
    strcpy(newNode->Description, description);
    newNode->next = NULL;

    if (*listHead == NULL){
    current = newNode;
    printf("\n check current in the loop: \n");
    displayBookList(current);
    listHead = current;
    printf("\n ");
    }
}

display是一种方法，只需打印链表中的所有项目。

Answer 1

我认为当您分配到列表头时，您错过了取消引用。

In [45]: %timeit uniques = np.sort(pd.unique(df.values.ravel()))
1 loops, best of 3: 933 ms per loop

In [46]: %timeit  dfc = df.apply(lambda x: x.astype('category', categories=uniques))
1 loops, best of 3: 1.35 s per loop

但是，在您的问题中，您在if语句后面说，当前显示为空。这与上面的错误无关。你能展示一下if (*listHead == NULL){ current = newNode; printf("\n check current in the loop: \n"); displayBookList(current); *listHead = current; // <------- ERROR: This needs to be dereferenced. In your code you do listhead=current without the dereference. printf("\n "); }方法吗？我非常确定您的问题在于解除引用和间接级别：即使在第一行，您也不应该displayBookList()而不是current = *listhead？

Answer 2

您的代码有点不完整。目前尚不清楚是否要插入列表的前面或末尾。

要在前面插入，newNode->next必须设置为*listHead。

要在最后插入，newNode->next必须设置为NULL。您必须找到指向现有列表中最后一个节点的指针，因此您需要for循环。

我提供了两种方式：

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

typedef struct _Book {
    int ISBN;
    char Title[20];
    char Author[20];
    char Description[40];
    int CopiesAtCSU;

    struct _Book *next;
} Book;

void
add_to_front(Book **listHead,int ISBN,char *Title,char *Author,int CopiesAtCsu,
    char *description, int sortIndx)
{
    Book *newNode;

    newNode = malloc(sizeof(Book));

    newNode->ISBN = ISBN;
    strcpy(newNode->Title, Title);
    strcpy(newNode->Author, Author);
    newNode->CopiesAtCSU = CopiesAtCsu;
    strcpy(newNode->Description, description);

    newNode->next = *listHead;
    *listHead = newNode;
}

void
add_to_back(Book **listHead,int ISBN,char *Title,char *Author,int CopiesAtCsu,
    char *description, int sortIndx)
{
    Book *newNode;
    Book *cur;
    Book *prev;

    newNode = malloc(sizeof(Book));

    newNode->ISBN = ISBN;
    strcpy(newNode->Title, Title);
    strcpy(newNode->Author, Author);
    newNode->CopiesAtCSU = CopiesAtCsu;
    strcpy(newNode->Description, description);

    prev = NULL;
    for (cur = *listHead;  cur != NULL;  cur = cur->next)
        prev = cur;

    newNode->next = NULL;

    if (prev != NULL)
        prev->next = newNode;
    else
        *listHead = newNode;
}

链表添加功能不存储数据

2 个答案: