Malloc and free in linkedlist recursion function

Question

I know that for every malloc there must be a free(), but in case of an existing linkedlist passed in a recursive function to insert a new node inside the linkedlist how would you free that? I'm using valgrind and it shows me that i must free the malloc

So my function has as parameters a char * and the pointer to the list passed as **, I did some research and it was needed to be passed like this in order to get the new nodes inserted even tho a pointer only worked well

void showDir(char *name, linkedList **list) {
    DIR *dir;
    struct dirent *entry;

    if (!(dir = opendir(name))) return;

    while ((entry = readdir(dir)) != NULL) {
        if (entry->d_type == DT_DIR) {
            char path[1024];
            if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
                continue;
            snprintf(path, sizeof(path), "%s/%s", name, entry->d_name);
            showDir(path, list);
        }
        linkedList *node = malloc(sizeof(linkedList));
        if (!node) {
            printf("Error!");
        }
        node->next = NULL;
        char filePath[1024];
        snprintf(filePath, sizeof(filePath), "%s/%s", name, entry->d_name);
        node->path = malloc(strlen(filePath) + 1);
        strcpy(node->path, filePath);
        if (*list) {
            int found = 0;
            for (linkedList *ptr = *list; ptr != NULL; ptr = ptr->next) {
                if (strcmp(ptr->path, filePath) == 0) {
                    found = 1;
                }
                if (ptr->next == NULL && found == 0) {
                    ptr->next = node;
                    break;
                }
            }
        } else {
            *list = node;
        }
    }
    closedir(dir);
}

I'm calling the recursive function like this showDir(ptr->path, &list); and freeing it like this

linkedList *ptr = list;
    while (ptr != NULL) {
        linkedList *next = ptr->next;
        free(ptr->path);
        free(ptr);
        ptr = next;
    }

Of course the list passed in the initial call is already filled up!

Thanks for the reading and hope you can help to understand what I'm doing wrong in here!

--EDIT

==1914== 64 (24 direct, 40 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 14
==1914==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1914==    by 0x10A633: showDir(filestat.c:512)
==1914==    by 0x10A629: showDir(filestat.c:510)
==1914==    by 0x10A629: showDir(filestat.c:510)
==1914==    by 0x109581: main (filestat.c:186)

Don't know if that's what you're running into (include the Valgrind report), but it appears that you don't free the newly allocated node if it's found. — 500 - Internal Server Error
– 500 - Internal Server Error, Commented Jul 4, 2019 at 18:57
The function showDir right now does not seem to be calling it self recursively. But to answer your question, unless there's some reallocation going on, you can easily free the list after the function call. You can also free when you do reallocation inside the function. — sassy_rog
– sassy_rog, Commented Jul 4, 2019 at 18:59
@SASSY_ROG What do you mean with I can easily free the list after the function call? I need the list for later use and can't free it, if i free the node after allocating it and inserting inside the linkedlist it will segment fault. — Rasputin
– Rasputin, Commented Jul 4, 2019 at 19:08
What is the state of list prior to the call showDir(ptr->path, &list);? Amend post and provide a minimal reproducible example — chux
– chux, Commented Jul 4, 2019 at 21:16

Alan Barrett II · Accepted Answer · 2019-07-04 19:10:27Z

1

Create a tmp pointer. This way as you free them you can still move though the struct.

If you don't create a temp pointer to the address of the struct you are losing access to the rest of the nodes.

    void freeList(struct node* head)
{
   struct node* tmp;

   while (head != NULL)
    {
       tmp = head;
       head = head->next;
       free(tmp);
    }

}

C: How to free nodes in the linked list?

answered Jul 4, 2019 at 19:10

Alan Barrett II

655 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

500 - Internal Server Error Over a year ago

The OP does do this.

dreamcrash · Accepted Answer · 2021-03-11 07:34:58Z

1

To free a Linkedlist recursively you can do it as follows:

void freeList(struct node* head){
    if(head != NULL){
      freeList(head->next);
      free(head);
    }
}

edited Mar 11, 2021 at 7:34

answered Mar 8, 2021 at 14:46

dreamcrash

52.6k26 gold badges114 silver badges138 bronze badges

Collectives™ on Stack Overflow

Malloc and free in linkedlist recursion function

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related