Long story short: I made a Template Double-Linked List, and putting lists inside of other lists causes issues. This question has been solved.
I'm testing Double-Linked-Lists as templates, and I'm running into an issue where placing a linked list inside of another linked list gives the following error:
(Microsoft Visual Studio 2010 Express)
Windows has triggered a breakpoint in linkListTesting.exe. This may be due to a corruption of the heap, which indicates a bug in linkListTesting.exe or any of the DLLs it has loaded. This may also be due to the user pressing F12 while linkListTesting.exe has focus. The output window may have more diagnostic information.
Searching for this particular error yielded results along the lines of, "make sure you don't use uninitialized variables," -in this scenario, when I tell a list to push_back / push_front, etc, it should initialize the list for me. (Not pressing F12, so that scenario's out.)
Here's my main cpp->
#include "vcLLMK2.h"
int main(int argc, char *argv[])
{
vcList<vcList<int>> a;
vcList<int> b;
b.push_back(1);
a.push_back(b);
//ERROR HAPPENS HERE APPARENTLY
return 0;
}
Pushing back (or front, tried that too) a new entry (in this case, '1') into 'b' works great. No crashes, no silliness. Pushing 'b' into 'a' causes the application to spit out the aforementioned error, trigger a breakpoint, and die.
I've recently started playing around with SDL, and intend on using a list as a container for 16 layers, which are basically lists of sprites/tiles/etc to render. The mode of thought is that the program will iterate through each entry in the layer-containing list, then render each object in the contained layer before moving on to the next.
"Why not just use std::list?" -Because that's cheating.
Although it's pretty likely that those who answer in this thread will be able to point out each of the glaring flaws in my list's structure and implementation that I'm blissfully unaware of, what I'm most concerned about is what-in-particular is causing this peculiar error and how to remedy it. That said, my question for you folks is what is wrong with the linked-list setup that I've built that causes the above cpp to error at runtime?
The Linked List structure below is the culmination of reading the following pages:
http://www.codeproject.com/Articles/26631/Using-C-templates-for-functions-and-operators
http://www.cprogramming.com/tutorial/lesson15.html
http://geekswithblogs.net/MarkPearl/archive/2010/02/20/linked-lists-in-c.aspx
Turning it into a template is mostly the result of creative interpretation of this page:
http://www.cplusplus.com/doc/tutorial/templates/
Here's my Link-List template class, with lots of comments->
#pragma once
#ifndef vcLLMK2_H_INCLUDED
#define vcLLMK2_H_INCLUDED
#define NULL 0
//THIS IS ALL OUR NODE SHOULD EVER NEED
template <class T>
struct vcListNode
{
public:
T data;
vcListNode<T> *next;
vcListNode<T> *prev;
};
template <class T>
struct vcList
{
public:
vcListNode<T> *root;//the list's "start"
vcListNode<T> *end;//the list's "end"
vcListNode<T> *cur;//used to bounce around amongst entries
int size();//returns number of non-null entries
int count;//because keeping track of these is easier than iterating through every time
void setAt(T,int);//sets data in a node
void push_front(T);//inserts a new node at the beginning of the list
void push_back(T);//same thing but back of list
void removeAt(int);//kills a node at an arbitrary spot in the list
void clear();//deletes all of the nodes in the list
T getAt(int);//returns data from a node in the list
vcList<T>& operator = (const vcList<T>&);//used for setting list a's contents to list b
//EDIT COPYCONSTRUCTOR
vcList<T>(const vcList<T>&);//copyconstructor
vcList();// : root(NULL),end(root),cur(NULL),count(0){};
~vcList();
};
//constructor - sets everything to null and count to zero on init
template <class T>
vcList<T>::vcList()
{
root=NULL;
cur=NULL;
end=NULL;
count=0;
}
//destructor - deletes all nodes
template <class T>
vcList<T>::~vcList()
{
clear();
}
//deletes all nodes from root to end
template <class T>
void vcList<T>::clear()
{
if(root==NULL)//assume list has nothing in it, abort
return;
//set current targeted entry to root
cur = root;
//as long as we have somewhere to go...
while(cur->next!=NULL)
{
//go there
cur=cur->next;
//and destroy where we were
delete cur->prev;
}
//then destroy ourselves because nihilism is good for memory
delete cur;
}
//used to set the contents of a list equal to those of another
template <class T>
vcList<T>& vcList<T>::operator= (const vcList<T> &fays)
{
//for starters, clear ourselves of any unwanted garbagedata
clear();
//check the import list's root entry
cur = fays.root;
//if the list containing the values we are importing is empty, we're done, move along
if(cur==NULL)
return *this;
//otherwise, make a new node - it's our new root
vcListNode<T> *newEntry = new vcListNode<T>;
newEntry->data = fays.root->data;
newEntry->prev = NULL;
newEntry->next = NULL;
//set root/end to the new entry
root = newEntry;
end = newEntry;
//update our count
count=1;
//fire through the import-list's entries
//cur starts at root
while(cur->next!=NULL)//(count<fays.count)
{
//move to next entry
cur=cur->next;
//add it to our list, push_back should update the location of 'end' for us
push_back(cur->data);
}
//we should be done here, so go ahead and return everything
return *this;
}
//this is mostly for convenience
template <class T>
int vcList<T>::size()
{
return count;
}
//adds a new entry to the front of our linked list
template <class T>
void vcList<T>::push_front(T info)
{
//eat some memory
vcListNode<T> *newEntry;
newEntry = new vcListNode<T>;
//set our memory and all that neat stuff
newEntry->data = info;
newEntry->next = root;
newEntry->prev = NULL;
//if our linked list is not empty
if(root!=NULL)
//set root's previous link to point at our new entry
root->prev = newEntry;
//if our linked list does not have an assigned end yet
if(end==NULL)
//assume it's empty and set end to our entry
end=newEntry;
//update the position of our root in the list, the beginning now begins at the beginning again
root = newEntry;
//and since we added something to the list, we should probably update our count of things in the list
count++;
}
//this finds an element in the pointer-chain and sets its information
template <class T>
void vcList<T>::setAt(T info,int index)
{
//set our target to the root
cur=root;
//run through the list's entries until we're where we're supposed to be
while(index>0)
{
cur=cur->next;
index--;
}
//set the data in the cell/node/whatever to our input
cur->data=info;
}
//returns the data contained in a node at a position in the list
template <class T>
T vcList<T>::getAt(int meBro)
{
//set target to root
cur=root;
//progress through the list
while(meBro>0)
{
cur=cur->next;
meBro--;
}
//dig the data out of the entry and return it
return cur->data;
}
//adds an element-containing node to the end of the list-chain
template <class T>
void vcList<T>::push_back(T info)
{
//if our list already has entries, end shouldn't be null
if(end!=NULL)
//so just target our end slot
cur=end;
//if our list is empty, however
else
//target the root instead
cur=root;
//create our new node, put stuff in it, etc
vcListNode<T> *newEntry;
newEntry = new vcListNode<T>;
newEntry->data = info;
//we're adding to the END of the list so make next null
newEntry->next = NULL;
//if cur is NOT null, then theoretically we're pointed at the end of the list
if(cur!=NULL)
//set our new entry's previous pointer to the end
newEntry->prev = cur;
//cur IS null, which means the list is empty
else
//set our entry's previous pointer to be null, duh
newEntry->prev = NULL;
//if the end of our list exists
if(end!=NULL)
{
//set the next entry in the list to point at our new entry
end->next = newEntry;
//then set end to target the new entry
end=newEntry;
}
//and if our list does not have an end yet for some reason (read as: it's empty)
else
{
//set the root to our new entry
root = newEntry;
//set the end to our new entry as well, since there's only one entry in the list
end = newEntry;
}
//update count of number of objects in list
count++;
}
//this deletes/removes/destroys/obliterates a node at a location in the list
template <class T>
void vcList<T>::removeAt(int index)
{
//for starters - is what we're trying to kill even here?
if(index>=count)
//NOPE GET OUT
return;
//later on it might speed things up to check whether the distance from end or root is shorter
//for now, just start at the beginning
//target the root
cur=root;
//move through the list to the specified entry
while(index>0)
{
index--;
cur=cur->next;
}
//if the previous entry exists
if(cur->prev!=NULL)
//point its next at the entry after this one
cur->prev->next=cur->next;
//if the previous entry is NULL, it means we're at the root
//so tell root to scoot forward one entry
//if there's a forward to scoot to
else if(cur->next != NULL)
root = cur->next;
//if the next entry exists
if(cur->next!=NULL)
//set the next entry's previous pointer to point at the entry before the targeted one
cur->next->prev=cur->prev;
//if the next entry does not exist, we must be at the end of the list
//so tell the end of the list to scoot back one slot
//if there's a back-one-slot to go to
else if(cur->prev!=NULL)
end = cur->prev;
//remove the entry at the targeted location
delete cur;
//decrement our count
count--;
}
//EDIT -> Copy Constructor
//copy constructor, similar as suggested to the operator=
template <class T>
vcList<T>::vcList(const vcList<T>& fays)
{
//might not be completely necessary, but we're not hurting anything by making sure
clear();
//check the import list's root entry
cur = fays.root;
//if the list containing the values we are importing is empty, we're done, move along
if(cur==NULL)
return;//just return, constructors don't get return types
//otherwise, make a new node - it's our new root
vcListNode<T> *newEntry = new vcListNode<T>;
newEntry->data = fays.root->data;
newEntry->prev = NULL;
newEntry->next = NULL;
//set root/end to the new entry
root = newEntry;
end = newEntry;
//update our count
count=1;
//fire through the import-list's entries
//cur starts at root
while(cur->next!=NULL)//(count<fays.count)
{
//move to next entry
cur=cur->next;
//add it to our list, push_back should update the location of 'end' for us
push_back(cur->data);
}
//we should be done here, so go ahead and return everything
//return *this;
}
#endif
