Question

我正在使用以下数据结构在双向链表上编写程序：

Person

在以下函数中，我将文本文件中的数据读取到链表，文件内容如下所示：

typedef struct telephoneBookNode {
    int id;
    char name[NAME_LENGTH];
    char telephone[TELEPHONE_LENGTH];
    struct telephoneBookNode * previousNode;
    struct telephoneBookNode * nextNode;
} TelephoneBookNode;

typedef struct telephoneBookList {
    TelephoneBookNode * head;
    TelephoneBookNode * tail;
    TelephoneBookNode * current;
} TelephoneBookList;

这是创建列表的功能，问题可能在这里：它不会向列表添加新节点，它只是用新的节点替换第一个节点。最后，链表只有1条记录，这是文本文件中的最后一条记录。我该如何修复代码？谢谢！

/*100, Alice, 0411112222
101, Bob, 0411112222
102, Ali, 0411112223*/

TelephoneBookList * commandLoad(char* fileName) {
    TelephoneBookList *(*createList)(TelephoneBookNode*, char[]) = createTelephoneBookList;

    char entry[100], *temp1, *temp2;
    TelephoneBookList* aList = NULL;
    TelephoneBookNode* aNode = NULL;
    FILE* telephoneListFile = NULL;
    int countEntry = 0;
    Boolean check;

    telephoneListFile = fopen(fileName, "r");

    if (!telephoneListFile)
        return NULL;
    else {
        while (fgets(entry, 100, telephoneListFile)) {
            temp2 = strcpy(temp2, entry);
            temp1 = strtok(entry, "\n");
            check = addressBookEntryCheck(temp1);

            if (!check)
                return NULL;
            else
                //here I pass aNode pointer to the below function
                aList = (*createList)(aNode, temp2);
        }
        fclose(telephoneListFile);
        printf("printed"); //This line is reached when program complied
        return aList;
    }
}

这是检查条目的功能：

TelephoneBookList * createTelephoneBookList(TelephoneBookNode* node, char entry[]) {
    TelephoneBookList* aList = malloc(sizeof *aList);
    TelephoneBookNode* aNode = (TelephoneBookNode*) malloc(sizeof *aNode);
    char *tokens;

    tokens = strtok(entry, ", ");
    aNode->id = atoi(tokens);

    tokens = strtok(NULL, ", ");
    strcpy(aNode->name, tokens);

    tokens = strtok(NULL, ", ");
    strcpy(aNode->telephone, tokens); //Just assigning values to a node

    //program always go to this block, means `node` is always null
    if (node == NULL) {
        aNode->nextNode = NULL;
        aNode->previousNode = NULL;
        node = aNode;

        aList->current = node;
        aList->head = node;
        aList->tail = node;
    }
    else { //This block is not reached
        while (node->nextNode)
            node = node->nextNode;

        node->nextNode = aNode;
        aNode->previousNode = node;

        aList->tail = node->nextNode;
    }
    return aList;
}

Answer 1

//program always go to this block, means `node` is always null
    if (node == NULL) {
    ....

这是因为函数的调用者传递了aNode并且它永远不会在该循环中发生变化。因此，它始终会传递aNode NULL的相同值。

我没有详细查看代码的逻辑，但我认为您可能希望通过aList->head或者您已经通过aList，所以只需使用它。

Answer 2

每次致电

createTelephoneBookList

您创建了一个新列表

TelephoneBookList* aList = malloc(sizeof *aList);

您还要复制到未初始化的指针

temp2 = strcpy(temp2, entry);

我建议你创建一个函数来创建列表标题，一个函数来添加新项目，例如。

aList = createList()
while (fgets(entry,sizeof(entry),fp)!=NULL)
{
  if (!addEntry(aList,entry))
  {
    fprintf(stderr, "failed additem item %s\n", entry);
  }
}
...

在addEntry中解析字符串

int id = 0;
char name[NAME_LENGTH];
char telephone[TELEPHONE_LENGTH];

p = strtok(entry, ","); // id
if (p != NULL) 
{  
  id = atoi(p);
  p = strtok(NULL, ","); // name, store to temporary string
  if (p != NULL )
  {
    strcpy(name,p);
    p = strtok(NULL, ","); // telephone number, store to temporary string
    if ( p != NULL )
    {
      strcpy(telephone,p);

      // here you can allocate the new node
    }
  }
}

// disclaimer omitted checks for length etc which any good program should have. also make sure you have room for \0

如果上述任何strtok失败，则返回0，否则分配新条目

TelephoneBookNode* aNode = malloc(sizeof(TelephoneBookNode));
aNode->id = id;
strcpy(aNode->name, name); 
strcpy(aNode->telephone, telephone);

然后添加到您的aList

C - 双向链表始终为空

2 个答案: