双向链表分段故障打印向后

I am trying to delete a node at a specific location but I keep getting a segmentation fault 11.

我试图删除特定位置的节点，但我不断收到分段错误11。

I am reading the position and value from a file.

我正在从文件中读取位置和值。

Here is my code:

这是我的代码：

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

typedef struct node {
  float val;
  struct node *prev;
  struct node *next;
}node_t;

void printForward(node_t *head) {
  node_t *current = head;

  while (current != NULL) {
    printf("%.2f\n", current->val);
    current = current->next;
  }
}

void printBackward(node_t *head) {
  node_t *current = head;

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

  while (current != NULL) {
    printf("%.2f\n", current->val);
    current = current->prev;
  }
}


void deleteAtPos(node_t **head, int pos) {
  int i;
  node_t *current = *head;
  node_t *temp = NULL;

  if (pos == 0) {
    temp = (*head)->next;
    free(*head);
    (*head) = temp;
    (*head)->prev = NULL;
    return;
  }

    for (i = 0; i < (pos - 1); i++) {
      if (current->next != NULL) {
        current = current->next;
      }
    }

      temp = current->next;
      current->next = temp->next;
      free(temp);
}


// Fix insert at position
void insertAtPos(node_t **head, int pos, float val) {
  int i;
  node_t *newNode = malloc(sizeof(node_t));
  node_t *current = *head;
  newNode->val = val;

  if (pos == 0) {
    newNode->next = (*head);
    newNode->prev = NULL;
    (*head)->prev = newNode;
    (*head) = newNode;
    return;
  }

  for (i = 0; i < pos; i++) {
    if (current->next != NULL) {
      current = current->next;
    }
    else {
      printf("Node does not exist\n");
      break;
    }
  }

  current->prev->next = newNode;
  newNode->prev = current->prev;
  newNode->next = current;
  current->prev = newNode;
}

void addEnd(node_t **head, float val) {
  node_t *current = *head;
  node_t *newNode = malloc(sizeof(node_t));
  newNode->next = NULL;
  newNode->val = val;

  if (*head == NULL) {
    *head = newNode;
    newNode->prev = NULL;
    return;
  }

  while (current->next != NULL) {
    current = current->next;
  }
  current->next = newNode;
  newNode->prev = current;
}

int main(int argc, char *argv[]) {
  if (argc != 2) {
    printf("Error");
  }

  node_t *head = NULL;

  FILE *fp;
  int i = 0, x;
  float valLine1, valLine2, valLine3;
  char buffer[200], *token, *del = ",";
  float posVals[200], delPos[200];
  fp = fopen(argv[1], "r");

  fgets(buffer, sizeof(buffer), fp);
    token = strtok(buffer, del);
    while (token != NULL) {
      valLine1 = atof(token);
      addEnd(&head, valLine1);
      token = strtok(NULL, del);
    }

    printForward(head);
    printf("\n");


    del = ":,";
    fgets(buffer, sizeof(buffer), fp);
    token = strtok(buffer, del);
    while (token != NULL) {
      valLine2 = atof(token);
      posVals[i] = valLine2;
      token = strtok(NULL, del);
      i++;
    }

    for (x = 0; x < i; x += 2) {
      insertAtPos(&head, posVals[x + 1], posVals[x]);
    }
    printForward(head);

    fgets(buffer, sizeof(buffer), fp);
    i = 0;
    token = strtok(buffer, del);
    while (token != NULL) {
      valLine3 = atof(token);
      delPos[i] = valLine3;
      token = strtok(NULL, del);
      i++;
    }
    printf("\n");


    for (x = 0; x < i; x++) {
      deleteAtPos(&head, delPos[x]);
    }



    printForward(head);
    printf("\n");
    printBackward(head);

    fclose(fp);


}

The trouble is with my deleteAtPos function but I can't figure out why.

麻烦在于我的deleteAtPos功能，但我无法弄清楚原因。

Here is the output:

这是输出：

24.00
0.04
17.00
-200.10
34.60
0.00
Segmentation fault: 11

And here is the contents of the file:

这是文件的内容：

17,32.5,12,0,34.6,-200.1,17,0.04,24
1:2,4.1:5,-12:4
3,5,0

Please help!

请帮忙！

Thank you

谢谢

2 个解决方案

#1

I have modified your deleteAtPos() function now you can delete at any position and your backward() function will print correct values.

我已经修改了你的deleteAtPos（）函数，现在你可以在任何位置删除你的back（）函数将打印正确的值。

void deleteAtPos(node_t **head, int pos) {
  int i;
  node_t *current = *head;
  node_t *temp = NULL;    

  if (pos == 0) {
    temp = (*head)->next;
    free(*head);
    (*head) = temp;
    (*head)->prev = NULL;
    return;
  }

    for (i = 0; i < (pos - 1); i++) {
      if (current->next != NULL) {
        current = current->next;
      }
    }


    temp = current;
    if(current->next==NULL)
    {
        current->prev->next = current->next;
    }
    else
    {
        current->prev->next = current->next;
        current->next->prev = current->prev;
    }

    free(temp);
}

#2

You are saying the trouble is with deleteAtPos. But your code is very far from an SSCCE, so I don't want to isolate the problem for you - you should do that, and most of the time, during the process of isolation, you will find the answer. If not, you can then post the question here.

你说的是deleteAtPos的麻烦。但是你的代码离SSCCE很远，所以我不想为你隔离问题 - 你应该这样做，而且大多数时候，在隔离过程中，你会找到答案。如果没有，您可以在此处发布问题。

Therefore I will just list the things I can see are wrong with deleteAtPos and maybe if you fix all of them, the problem will disappear.

因此，我将列出我可以看到的deleteAtPos错误的东西，也许如果你修复所有这些，问题就会消失。

1. You are not handling the situation where *head is NULL, the list has 0 elements. This would surely segfault.

   你没有处理* head为NULL的情况，列表有0个元素。这肯定是段错误的。

2. You are not checking that pos >= 0.

   你没有检查pos> = 0。

3. You are not correctly handling the case where your list has one element, either. Another segfault.

   您没有正确处理列表中包含一个元素的情况。另一个段错误。

4. You are not correctly handling the case where pos is the end of your list. Another segfault.

   您没有正确处理pos是列表末尾的情况。另一个段错误。