[英]Read linked list from a file and load the data
I wrote a C code to implement a dictionary using linked-list(nodes are in sorted order) I want to save the data to a file and be able to reload the data when I run the program next time. 我编写了一个C代码以使用链表实现字典(节点按排序顺序),我想将数据保存到文件中,并在下次运行程序时能够重新加载数据。 I'm having trouble loading the data from file. 我无法从文件加载数据。 Here is my code for reading and writing data: 这是我用于读取和写入数据的代码:
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);
}
I can't load data from the file to the linked list. 我无法将数据从文件加载到链接列表。 Code is not working. 代码不起作用。 I can't figure out where the problem is.. 我不知道问题出在哪里。
Here's how I'm writing the data to the file : 这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);
}
I've used sizeof
, instead of strlen
, it's a string. 我用过sizeof
,而不是strlen
,它是一个字符串。 It'll have null character at the end - no problem with string. 它的结尾将为空字符-字符串没有问题。 It'll consume more memory though. 它会消耗更多的内存。
try this (untested): 试试这个(未试用):
void ReadData(struct node **head){//or struct node *ReadData(void){ ... return head; }
struct node temp = { .next = NULL };//{ {0}, {{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);
//...
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