具有读取txt的c中的链表结构

Question

I upload picture above. I ask question, how can I read from txt files to add linked list with structs. I try this but how can I declare for basket.txt and produce .txt

FILE *fp
char CustomerName[20];
char CustomerSurname[20];
int  CustomerId;
struct Customer *current = NULL, *head = NULL;
fp = fopen("customer.txt", "r");

while (fscanf(fp, "%d\t%s\t%s", &CustomerId, CustomerName, CustomerSurname) != EOF) {
    struct Customer *ReadList;
    ReadList = (struct Customer *)malloc(sizeof(struct Customer));
    ReadList->NextPtr = NULL;
    ReadList->CustomerId = CustomerId;
    ReadList->CustomerName = strdup(CustomerName);
    ReadList->CustomerSurname = strdup(CustomerSurname);
    if (head == NULL) {
        current = head = ReadList;
    } else {
        current = current->NextPtr = ReadList;
    }
}
fclose(fp);

Answer 1

There is a subtile problem in your code: the way you parse the input file is incorrect:

while (fscanf(fp, "%d\t%s\t%s", &CustomerId, CustomerName, CustomerSurname) != EOF)

• you should protect from buffer overflows in CustomerName and CustomerSurname by telling fscanf the maximum number of characters to store into these arrays: use format "%d\\t%19s\\t%19s" for that.
• you only check for fscanf complete failure at end of file, where it would return EOF , but it returns the number of fields parsed and you should check for this to be 3 . If fscanf fails to parse an integer for the first field, it will return 0 and the contents of all fields will be unchanged. You will loop indefinitely adding the same new record to the list, until you crash when malloc will eventually return NULL , which you do not test.
• The \\t character in the format string will match any sequence of white space characters in the file, not just the TAB character. This may be different from what you expect. Note that %d and %s both ignore leading white space characters, so the \\t characters in the format string are completely redundant.

There are other issues, such as

• You do not check for fopen failure
• You do not check for memory allocation failure

Here is an improved version:

FILE *fp
char CustomerName[20];
char CustomerSurname[20];
int  CustomerId;
int res;
struct Customer *current = NULL, *head = NULL;
fp = fopen("customer.txt", "r");
if (fp == NULL) {
    fprintf(stderr, "cannot open input file\n");
    return 1;
}

while ((res = fscanf(fp, "%d\t%19s\t%19s", &CustomerId, CustomerName, CustomerSurname)) == 3) {
    struct Customer *ReadList = malloc(sizeof(*ReadList));
    if (ReadList == NULL) {
        fprintf(stderr, "cannot allocate memory for customer\n");
        fclose(fp);
        return 1;
    }
    ReadList->NextPtr = NULL;
    ReadList->CustomerId = CustomerId;
    ReadList->CustomerName = strdup(CustomerName);
    ReadList->CustomerSurname = strdup(CustomerSurname);
    if (ReadReadList->CustomerName == NULL || ReadList->CustomerSurname == NULL) {
        fprintf(stderr, "cannot allocate memory for customer fields\n");
        fclose(fp);
        return 1;
    }
    if (head == NULL) {
        current = head = ReadList;
    } else {
        current = current->NextPtr = ReadList;
    }
}
if (res != EOF) {
    fprintf(stderr, "input file has incorrect format\n");
    fclose(fp);
    return 1;
}
fclose(fp);