Accidently deleting entire linked list when trying to delete the head - visual-c++

Question

I'm working on a checker's simulation game for my C++ class. My issue is with the linked list that holds the checkers. I can delete any checker perfectly with the exception of the head of the list. I've looked around here and other websites and I believe there's a memory leak somewhere. I'm fairly new to C++ so I'm not sure what to really do other than playing around with things (which will probably just create a bigger problem). I've never posted here before, so excuse me if the formatting is slightly off or too messy. I'll try to make it brief. First, here's a snippet of the node class for the linked list.
class CheckerpieceNode
{
private:
Checkerpiece *Node;
CheckerpieceNode *Next;
public:
CheckerpieceNode(); // sets Node and Next to NULL in .cpp file
void setNode(Checkerpiece *node);
void setNext(CheckerpieceNode *next);
Checkerpiece* getNode();
CheckerpieceNode* getNext();
};
And the functions are set up pretty much as you would expect in a Checkerpiece.cpp class.
Here's how the code is used. Its called by a Checkerboard object in my main class.
theCheckerboard.removeChecker(theCheckerboard.findChecker(selector->getCurrentX() + 0, selector->getCurrentY() - VERTICAL_SHIFT, listHead), listHead);
The VERTICAL_SHIFT simply has to do with the way my checkerboard graphic is on the console. Since it works perfectly for all other nodes (excluding the head) I've ruled it out as a source of error. Selector is a checkerpiece object but its not part of the list.
Here's the actual findChecker and removeChecker code from Checkerboard class.
Checkerpiece* findChecker(int x, int y, CheckerpieceNode* list_head)
{
if(list_head== NULL) return NULL; // do nothing
else
{
CheckerpieceNode* node = new CheckerpieceNode;
node = list_head;
while(node != NULL && node->getNode() != NULL)
{
if()// comparison check here, but removed for space
{
return node->getNode();
delete node;
node = NULL;
}
else // traversing
node = node->getNext();
}
return NULL;
}
}
void removeChecker(Checkerpiece* d_checker, CheckerpieceNode* list_head)
{
if(list_head== NULL) // throw exception
else
{
CheckerpieceNode *temp = NULL, *previous = NULL;
Checkerpiece* c_checker= new Checkerpiece;
temp = list_head;
while(temp != NULL && temp->getNode() != NULL)
{
c_checker= temp->getNode();
if(d_checker!= c_checker)
{
previous = temp;
temp = temp->getNext();
}
else
{
if(temp != list_head)
{
previous->setNext(temp->getNext());
delete temp;
temp = NULL;
}
else if(temp == list_head) // this is where head should get deleted
{
temp = list_head;
list_head= list_head->getNext();
delete temp;
temp = NULL;
}
return;
}
}
}
}

Answer 1

Oh my, you're complicating it. Lots of redundant checks, assignments and unnecessary variables (like c_checker which leaks memory too).
// Write down the various scenarios you can expect first:
// (a) null inputs
// (b) can't find d_checker
// (c) d_checker is in head
// (d) d_checker is elsewhere in the list
void removeChecker(Checkerpiece* d_checker, CheckerpieceNode* list_head) {
// first sanitize your inputs
if (d_checker == nullptr || list_head == nullptr) // use nullptr instead of NULL. its a keyword literal of type nullptr_t
throw exception;
// You understand that there is a special case for deleting head. Good.
// Just take care of it once and for all so that you don't check every time in the loop.
CheckerpieceNode *curr = list_head;
// take care of deleting head before traversal
if (d_checker == curr->getNode()) {
list_head = list_head->next; // update list head
delete curr; // delete previous head
return; // we're done
}
CheckerpieceNode *prev = curr;
curr = curr->next;
// traverse through the list - keep track of previous
while (curr != nullptr) {
if (d_checker == curr->getNode()) {
prev->next = curr->next;
delete curr;
break; // we're done!
}
prev = curr;
curr = curr->next;
}
}
I hope that helps. Take the time to break down the problem into smaller pieces, figure out the scenarios possible, how you'll handle them and only then start writing code.

Answer 2

Based on this edit by the question author, the solution he used was to:
I modified the code to show the address passing in the checker delete
function.
void delete_checker(Checker* d_checker, CheckerNode* &list_head) // pass by address
{
if(list_head== NULL) // throw exception
else
{
CheckerNode*temp = NULL, *previous = NULL;
Checker* c_checker= new Checker;
temp = list_head;
while(temp != NULL && temp->node!= NULL)
{
c_checker= temp->node;
if(d_checker!= c_checker)
{
previous = temp;
temp = temp->next;
}
else
{
if(temp != list_head)
{
previous->next = temp->next;
delete temp;
temp = NULL;
}
else if(temp == list_head) // this is where head should get deleted
{
temp = list_head;
list_head= list_head->next;
delete temp;
temp = NULL;
}
delete c_checker;
c_checker = nullptr;
return;
}
}
}
}

Answer 3

removeChecker cannot modify the value of list_head as it is past by value. The method signature should be:
void removeChecker(Checkerpiece* d_checker, CheckerpieceNode** list_head)
// You will need to call this function with &list_head
or
void removeChecker(Checkerpiece* d_checker, CheckerpieceNode* &list_head)
// Calling code does not need to change