CODEWITHSUNDEEP
c
raj
raj

Reputation: 13

copying the structure in the linked list

Here I am copying the structure from one node to another but when I encounter the last node I will have a segmentation fault since temp_clsf->next in memcpy will be pointing to a invalid location, how can I fix this? I cant free temp_clsf as it is not dynamic allocation.

while(temp_clsf!=NULL)
{
    memcpy(&temp_clsf, &temp_clsf->next, sizeof(struct classifier));
    if(temp_clsf->next ==NULL)
        return;
    else
        temp_clsf = temp_clsf->next;
}

Upvotes: 0

Views: 789

Answers (5)

pmg
pmg

Reputation: 108968

Inside the loop, keep a pointer to the previous node. When the loop ends, update that node with a pointer to NULL

/* pseudo-code */
while () {
    prev = curr;
    /* ... */
}
prev->next = NULL;

Upvotes: 1

BMitch
BMitch

Reputation: 263469

It looks like you are doing a shift of items, potentially to remove one. If this was an ordered array, there would be no need to use a next pointer. I'm not sure what other static allocation you are using, but you can simply do the following to remove the single item temp_clsf->next:

temp_clsf->next=temp_clsf->next->next;

Upvotes: 0

dubnde
dubnde

Reputation: 4431

Potentially, temp_clsf->next could be NULL so move the NULL check before the memcpy

while(temp_clsf != NULL)
{
    if(temp_clsf->next == NULL)
    {
        return;
    }

    memcpy(&temp_clsf, &temp_clsf->next, sizeof(struct classifier));

    temp_clsf = temp_clsf->next;
}

Update: temp_clsf and temp_clsf->next look like pointers to me. So your memcpy is taking address of pointers and overwriting what is there. Is this your intention? Not sure what sizeof(struct classifier) is as we do not have the structure types in your example.

Upvotes: 0

Azodious
Azodious

Reputation: 13872

use following condition in while.

while(temp_clsf->next!=NULL)

Upvotes: 0

pmg
pmg

Reputation: 108968

Just move the copy after the if ...

 while(temp_clsf!=NULL)
    {
    if(temp_clsf->next ==NULL)
    return;
    //else
    memcpy(&temp_clsf, &temp_clsf->next, sizeof(struct classifier));
    temp_clsf = temp_clsf->next;
    }

Upvotes: 0

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