Question

我需要创建一个带有Sentinel节点的循环双向链表，该节点应该从文件中读取数据并将其插入列表中，而不是使用它执行某些操作。现在我被困在一个简单的打印功能上，由于某些原因不能从列表打印。文件中的数据采用字符串形式，例如：“流行的排序算法，冒泡排序，合并排序，“空行”等

到目前为止，这是我的代码：

头文件包含：

typedef struct NODE {
 struct NODE *prev;
 char *value;
 struct NODE *next;
} NODE;

typedef struct LIST {
 int count;
 struct NODE *next;
 struct NODE *prev;
 } LIST;

int InsertEnd(NODE *head, char * value, int *lineCount);
void printLines(int *lineCount);
void Traverse(NODE *head);

主要包含：

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


int main()
{
    int lineCount = 0;
    NODE *head;

    head = (NODE *)malloc(sizeof(NODE)); /* creates head node dynamically */

    head->next = NULL;   /* points to first element */
    head->prev = NULL;   /* points to last element */
    head->value = "HEAD"; /* not needed, but it was pretty useful when debugging */

    //*********BEGIN OF OPEN FILE FUNCTION
    FILE* fp;
    char *fname = NULL;
    fname = (char *)malloc(200); <<<<<===== I would prefer to set the size dynamically adjusting but I dont know how

        printf("Reading file input.txt\n");

    //Checks if the file us unable to be opened, then it shows the error message
    if ( !(fp = fopen("input.txt", "r")))
    {
        printf("\nError, Unable to open the file for reading \n");
        exit(100);
    }

    //*********BEGIN OF READ FROM FILE FUNCTION

    while (!feof(fp))
    {
        fgets(fname, 150, fp);  //reads the file and stores in buffer

        fname[strlen(fname) - 1] = '\0'; // reduces empty strings for input

        if (fname != '\0')
        {

            InsertEnd(head, fname, &lineCount);
        //printf("%s\n", head->next->value);  <<<<==== If uncomment this print function would work properly but only in this context

        }
        else
        {
            printf("Error'\n"); // For debugging
        }

    }
    Traverse(head); // Print Function Should Be Working in Here
    printf("Debugging print\n");
    printLines(&lineCount); // Shows Line Count
    return 0;
}
// Function inserts a new node at the end of the LIST
int InsertEnd(NODE *head, char * value, int* lineCount)
{
    int lineCounter = *lineCount;
    /* create new node */
    NODE *newnode;
    newnode = (struct NODE *)malloc(sizeof( struct NODE));
    newnode->value = value;
    /* placing new node in LIST */
    if (head->next == NULL) /* LIST was empty */
    {
        newnode->next = head;
        newnode->prev = head;
        head->next = newnode;
        head->prev = newnode;
        lineCounter++;               // Increment line counter
    }
    else /* LIST wasn't empty */
    {
        newnode->next = head;
        newnode->prev = head->prev;
        head->prev->next = newnode; /* adjust node that was previously last */
        head->prev = newnode;       /* adjust head node */
        lineCounter++;                // Increment line counter
    }
    *lineCount = lineCounter;
    return lineCount;
}


// This function prints how many lines there are in the LIST, but I need to get rid of the empty spaces
void printLines(int *lineCount)
{
 printf("Line counter is %d", *lineCount);  // Shows the number of lines, but doesn't skip empty ones.
}


void Traverse(NODE *head)
{
    NODE *current = head;

    printf("Forward:");
    while (current!= head->prev)
    {
        printf("%s \n", current->value);

        current = current->next;
    }
    printf("\n");
}

因此，到目前为止，我有几个问题：

1）我最需要删除列表中的空字符串。什么是更好的方法，在阅读时摆脱它们或在打印时不显示？我该怎么做呢？

2）如何修复我的打印（遍历）功能，那里有什么问题？

3）此外所有这一切都应该通过菜单管理器进行，这会提示命令（我认为这是正确的）。但是有些功能我不知道如何实现。例如，当使用命中“I”时，它应该调用Insert函数并提示用户输入另外两个值，然后在适当的位置插入。我该怎么办？示例“I 1 8”

4）与前一个类似，应该有List函数，它应该在特定值之间打印行。用户输入格式应包含在“L to”列表中。例“L 2 5”

5）与之前类似，应该有一个包含格式为“D”的删除功能。例“D 3 7”

6）最后一个是格式为“S”的保存功能示例“S output.txt”

感谢您的帮助！

Answer 1

我在代码中至少看到了这些问题，

在main()

 if (fname != '\0')

这应该是

 if (fname[0] != '\0')

在InsertEnd()

newnode->value = value;

应该是

newnode->value = strdup(value);

Answer 2

在您的代码中，应该有一些正确性，根据您的请求，您需要动态分配缓冲区，但不知道file长度，因此可以通过这个实现非常有用＃

int sz;
printf("Reading file input.txt\n");

//Checks if the file us unable to be opened, then it shows the error message
if ( !(fp = fopen("sample.txt", "r")))
{
    printf("\nError, Unable to open the file for reading \n");
    exit(100);
}

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

printf("size of file %d\n",sz);

fname = (char *)malloc(sz);
rewind(fp);

现在，为了阅读您检查fname到\0的文件内容不正确我更正了您的while..loop。

while (!feof(fp))
{
    if(fgets(fname,256, fp) != 0)
    {
        fname[strlen(fname) - 1] = '\0'; // reduces empty strings for input
        InsertEnd(head, fname, &lineCount);
    }
    else
    {
        printf("Error'\n"); // For debugging
    }
}

圆形双向链表，打印功能

2 个答案: