c - C-双链表始终为null

我正在双链表上编写一个具有以下数据结构的程序：

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;

在以下函数中，我将数据从文本文件读取到链接列表，文件内容如下所示：

/*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;
    }
}

这是创建列表的函数，问题可能在这里：它没有向列表中添加新节点，只是用新节点替换第一个节点。最后，链接列表只有一条记录，这是文本文件中的最后一条记录。我怎样才能修改代码？谢谢您！

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;
}

这是检查条目的函数：

Boolean addressBookEntryCheck(char entry[]) {
    char *tokens;

    tokens = strtok(entry, ", ");

    if(!tokens || strlen(tokens) < 1 || strlen(tokens) > 3)
        return FALSE;
    else {
        if (!isNumber(tokens))
            return FALSE;
        else {
            tokens = strtok(NULL, ", ");

            if (!tokens)
                return FALSE;
            else
            {
                tokens = strtok(NULL, ", ");

                if (!tokens)
                    return FALSE;
                else if (!isNumber(tokens) || strlen(tokens) != 10)
                    return FALSE;
                else
                    return TRUE;
            }
        }
    }
}

最佳答案

每次你打电话

createTelephoneBookList

创建新列表

TelephoneBookList* aList = malloc(sizeof *aList);

还可以复制到未初始化的指针

temp2 = strcpy(temp2, entry);

我建议您创建一个函数来创建列表标题，一个函数来添加新项，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

如果上面的任何一个strtok失败，返回0，否则分配一个新条目

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

然后添加到您的aList

关于c - C-双链表始终为null，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/37201613/