Question

I have my C list, and i implemented the push_back function:

bool_t push_back_clist(clist_ptr pList, void* item)
{
    if(pList)
    {
        node_ptr pNode = new_node(item, pList->sizeof_item);
        if(!pNode) return FALSE;

        if(!pList->head)
            pList->head = pList->tail = pNode;
        else
        {
            pList->tail->next = pNode;
            pNode->prev = pList->tail;
            pList->tail = pNode;
        }

        pList->size++;
        return TRUE;
    }

    return FALSE;
}

static node_ptr new_node(void* data, size_t sizeof_item)
{
    node_ptr pNode = (node_ptr) malloc(sizeof(node_t));
    if(!pNode) return NULL;

     pNode->data = malloc(sizeof_item);

     if(!pNode->data)
     {
         free(pNode);
         return NULL;
     }

     memcpy(pNode->data, data, sizeof_item);
     pNode->next = pNode->prev = NULL;
     return pNode;
}

It works, but when I compared my push_back_clist function with std::list.push_back method I noticed that my function requires about twice as long. Why? How could i improve the performance of my function?
Thanks.

Answer 1

You can allocate your data and node in a single go to save on the number of malloc calls.

char* mem = malloc(sizeof(node_t)+sizeof_item);
// Check alloc here...
node_ptr pNode = (node_ptr)mem;
pNode->data = mem+sizeof(node_t);