Question

我编写了一个C代码来使用链表实现字典（节点按排序顺序）我想将数据保存到文件中，并且能够在下次运行程序时重新加载数据。我在从文件加载数据时遇到问题。这是我的读写数据代码：

struct node{
    char word[20];
    char meaning[5][100]; //2D array for saving multiple meanings of a word
    struct node *next;
};

void ReadData(struct node *head)
{
    struct node *tail;
    FILE *fp = fopen("dictionary.data", "rb");
    if(fp == NULL)
    {
        printf("Error opening file..\n");
        return;
    }
    while(!feof(fp))
    {
        tail = (struct node*)calloc(1, sizeof(struct node));
        fread(tail->word, sizeof(head->word), 1, fp);
        fread(tail->meaning, sizeof(head->meaning), 1, fp);
        if(head == NULL) //for fresh run head is initialized with NULL
        {
            tail->next = head;
            head = tail;
        }
        else
        {
            head->next = tail;
            head = head->next;
        }
    }
    fclose(fp);
}

我无法将文件中的数据加载到链接列表中。代码无效。我无法弄清问题在哪里..
以下是我将数据写入文件的方式：

/*I think this code is working because size of the file increases after running the code*/
void WriteData(struct node *head)
{
    FILE *fp = fopen("dictionary.data", "wb");
    if(fp == NULL)
    {
        printf("Error opening file..\n");
        return;
    }
    while(head != NULL)
    {
        fwrite(head->word, sizeof(head->word), 1, fp);
        fwrite(head->meaning, sizeof(head->meaning), 1, fp);
        head = head->next;
    }
    fclose(fp);
}

我使用的是sizeof，而不是strlen，它是一个字符串。它最后会有空字符 - 字符串没问题。它会消耗更多的内存。

Answer 1

试试这个（未经测试）：

void ReadData(struct node **head){//or struct node *ReadData(void){ ... return head; }
    struct node temp = { .next = NULL };//{ {0}, , NULL}
    struct node *hp, *curr;
    FILE *fp = fopen("dictionary.data", "rb");

    if(fp == NULL){
        printf("Error opening file..\n");
        return;
    }

    hp = *head;
    while(fread(temp.word, sizeof(temp.word), 1, fp) && fread(temp.meaning, sizeof(temp.meaning), 1, fp)){
        struct node *np = malloc(sizeof(*np));
        if(np == NULL){
            perror("couldn't make new node by malloc:");
            return ;//release list
        }
        *np = temp;

        if(hp == NULL){//for fresh run head is initialized with NULL
            curr = hp = np;
        } else {//If *head isn't NULL, you need to move to the last node first.
            curr = curr->next = np;
        }
    }
    fclose(fp);
    *head = hp;
}
//....................
int main(void){
    //...
    struct node *head = NULL;
    //...
    ReadData(&head);
    //...

从文件中读取链接列表并加载数据

1 个答案: