CODEWITHSUNDEEP
cpointers
WillyCboi
WillyCboi

Reputation: 1

Unexpect behaviour with pointer array

im currently implementing a basic linked list structure on C.

Basically im parsing a txt file, and I buffer each line into a Node which contains a pointer to an array of integers. The problem is, that my data (the array of integers) doesn't save correctly / i don't know how to iterate through it correctly.

These are the structures that I use:

typedef struct Node
{
    struct Node* next; 
    struct Node* prev; 
    int* data; 
    int len; 
} Node;

typedef struct LinkedList
{
    Node* head; 
    Node* tail; 
} LinkedList;

and I use this method to create a new node from a buffered string:

int nodeManager(FILE* filePointer, char* buffer, char* token, LinkedList* linkedList)
{
    token = strtok(buffer, DELIMITER);
    int* data = (int*)malloc(sizeof(int));
    int dataIndex = 0;
    if (data == NULL)
    {
        fprintf(stderr, DATA_ALLOCATION_ERROR);
        freeLinkedList(linkedList);
        fclose(filePointer);
        return EXIT_FAILURE;
    }
    const char* insertPosition = token;
    while ((token = strtok(NULL, DELIMITER)))
    {
        data = realloc(data, dataIndex + 1);
        if (data == NULL) {
            fprintf(stderr, DATA_ALLOCATION_ERROR);
            freeLinkedList(linkedList);
            fclose(filePointer);
            return EXIT_FAILURE;
        }
        char *res;
        int num = (int) strtol(token, &res, 10);
        data[dataIndex] = num;
        dataIndex++;
    }
    Node* newNode = (Node*)malloc(sizeof(Node));
    if (newNode == NULL)
    {
        freeLinkedList(linkedList);
        free(data);
        fclose(filePointer);
        return EXIT_FAILURE;
    }
    newNode -> prev = NULL; newNode -> next = NULL;
    newNode -> len = dataIndex; newNode -> data = data;
    if(strcmp(insertPosition, INSERT_TO_START) == 0)
    {
        addToStartLinkedList(linkedList, newNode);
    }
    else
    {
        addToEndLinkedList(linkedList, newNode);
    }
    return EXIT_SUCCESS; // TODO - Change
}

A line of input looks like this:

start,1,2,3,4,5,6,7,10,22,44,55,66,66,77

for some reason, node -> data doesn't get all the values that I assign in this method and I can't really tell why.

I tried to print the values like this:

  for (int i = 0; i < newNode -> len; i++)
    {
        printf("%d,", (newNode -> data)[i]);
    }

However, as I said, something quite doesn't work with my assigment, or I just don't know how to access the values correctly.

Would love to get some insight - thanks.

Upvotes: 0

Views: 60

Answers (1)

4386427
4386427

Reputation: 44274

This part is wrong:

data = realloc(data, dataIndex + 1);

You have forgotten to multiply with sizeof(int) or better sizeof *p

BTW: Be careful about doing realloc directly into data. On failure realloc may return NULL and then you have a memory leak. You should use a temporary pointer like:

int * temp = realloc(data, SOME_SIZE); 
if (temp == NULL) 
{  
    // oh dear, add error handling here - maybe a return or whatever fits
} 
else 
{ 
    // All good
    data = temp; 
}

OT: Passing the file pointer to the function in order to be able to close the file is (IMO) a rather strange design. Instead, the caller should check the return value and close the file (if desired).

Upvotes: 1

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