I have a tree structure and I want to find all nodes matching a given criteria. Each time I call the find function, it returns next matching node. Children are searched by recursive function call.
For some reason a key comparison of pointers fails for this implementation. Please see the code below, I have pointed out the failing comparison.
HtmlTag* HtmlContent::FindTag(string tagName, string tagParameterContent)
{
if (tagName.empty() && tagParameterContent.empty())
return NULL;
if (this->startTag == NULL)
return NULL;
this->findContinue = this->FindChildren(this->startTag, &tagName, &tagParameterContent);
return this->findContinue;
}
HtmlTag* HtmlContent::FindChildren(HtmlTag* firstTag, string* tagName, string* tagParameterContent)
{
HtmlTag* currentTag = firstTag;
HtmlTag* childrenFound = NULL;
while (currentTag != NULL)
{
if (!tagName->empty() && *tagName == currentTag->tagName)
{
if (tagParameterContent->empty() || currentTag->tagParameters.find(*tagParameterContent, 0) != -1)
{
if (this->findContinue == NULL)
break; // break now when found
else if (this->findContinue == currentTag) // TODO why this fails?
this->findContinue == NULL; // break on next find
}
}
if (currentTag->pFirstChild != NULL)
{
childrenFound = this->FindChildren(currentTag->pFirstChild, tagName, tagParameterContent);
if (childrenFound != NULL)
{
currentTag = childrenFound;
break;
}
}
currentTag = currentTag->pNextSibling;
}
return currentTag;
}
VC++ compiler accepts this code but for some reason I can't put a breakpoint on this comparison. I guess this is optimized out, but why? Why this comparison fails?
I think that you shoud replace == with = in assignment after comparison. Compiler optimalized this whole section because it doesnt do anything useful.
Related
I am trying to implement a DFS algorithm to work in a maze. The maze has walls. The DFS gets stuck in a corner and does not backtrack therefore it results in an infinite loop. How should I rewrite my code to get it to backtrack. This is code for a space-search type of DFS.
Depth-First-Search Function
public List<Node<Point2D>> DFS(Problem p)
{
Node<Point2D> root = new Node<Point2D>() { Data = p.initial, Parent = null };
frontierStack.Push(root);
while (frontierStack.Count > 0 && explored.Count < 55)
{
Node<Point2D> currentNode = frontierStack.Pop();
explored.Add(currentNode.Data.ToString());
Console.WriteLine(currentNode);
//Debug.WriteLine(explored.Count);
foreach (string action in p.Action)
{
if (p.Result(currentNode.Data, action) != null)
{
Node<Point2D> adjacentNode
= new() { Data = p.Result(currentNode.Data, action), Parent = currentNode };
if (explored.Contains(adjacentNode.Data.ToString()) == false || frontierStack.Contains(adjacentNode) == false)
{
if (p.GoalTest(adjacentNode.Data) == true)
{
return GetNodes(adjacentNode);
}
}
frontierStack.Push(adjacentNode);
}
}
}
return null;
}
Here is Where it gets stuck:
The black line is the path it took, the blue 'X' are walls and the red 'X' is where it gets stuck at point (1,3) - (1,4). I have been trying to resolve this for a few hours now. Nothing seems to be working. I am still a beginner so sorry for asking something so trivial and thank you for your help in advance.
Solved it. Hope this is useful for other beginners out there.
Updated DFS Algorithm
foreach (string action in p.Action)
{
if (p.Result(currentNode.Data, action) != null)
{
Node<Point2D> adjacentNode = new() {
Data = p.Result(currentNode.Data, action),
Parent = currentNode
};
frontierStack.Push(adjacentNode);
if (explored.Contains(adjacentNode.Data.ToString()) == false || frontierStack.Contains(adjacentNode) == false)
{
if (p.GoalTest(adjacentNode.Data) == true)
{
return GetNodes(adjacentNode);
}
}
else if (explored.Contains(adjacentNode.Data.ToString()) == true && frontierStack.Contains(adjacentNode) == true)
{
frontierStack.Pop();
}
}
}
Add the else if to check if it is either visited/explored and still in the frontier.
I have this event handler in a modelless popup dialog tree control:
void CAssignHistoryDlg::OnTvnSelchangedTreeHistory(NMHDR *pNMHDR, LRESULT *pResult)
{
LPNMTREEVIEW pNMTreeView = reinterpret_cast<LPNMTREEVIEW>(pNMHDR);
if (!m_bBuildTreeMode)
{
if ((pNMTreeView->itemOld.hItem == nullptr && !m_bFirstSelChangeEvent) ||
pNMTreeView->itemOld.hItem != nullptr)
{
m_bFirstSelChangeEvent = true;
if (m_treeHistory.GetParentItem(pNMTreeView->itemNew.hItem) == nullptr)
{
// We must update the correct combo
// and associated string (in the SERVMEET_S structure)
if (m_pCombo != nullptr && m_pStrText != nullptr)
{
CString strExtractedName = ExtractName(pNMTreeView->itemNew.hItem);
m_pCombo->SetWindowText(strExtractedName);
*m_pStrText = strExtractedName;
}
GetParent()->PostMessage(UM_SM_EDITOR_SET_MODIFIED, (WPARAM)TRUE);
}
}
}
*pResult = 0;
}
What I don't understand is why once this event is triggered is that it goes in a continuous cycle.
Does anything jump out at you as wrong?
I don't know why the message seemed to be going in a continuous cycle. Maybe it was because I was inserting breakpoints or adding temporary popup message boxes to debug. Either way, I worked out the minor adjustment I needed:
void CAssignHistoryDlg::OnTvnSelchangedTreeHistory(NMHDR *pNMHDR, LRESULT *pResult)
{
LPNMTREEVIEW pNMTreeView = reinterpret_cast<LPNMTREEVIEW>(pNMHDR);
if (!m_bBuildTreeMode)
{
if ((pNMTreeView->itemOld.hItem == nullptr && !m_bFirstSelChangeEvent) ||
pNMTreeView->itemOld.hItem != nullptr)
{
m_bFirstSelChangeEvent = true;
if (m_treeHistory.GetParentItem(pNMTreeView->itemNew.hItem) == nullptr)
{
// We must update the correct combo
// and associated string (in the SERVMEET_S structure)
if (m_pCombo != nullptr && m_pStrText != nullptr)
{
CString strExtractedName = ExtractName(pNMTreeView->itemNew.hItem);
m_pCombo->SetWindowText(strExtractedName);
// Bug fix - Only set as modified if the name is different
if(*m_pStrText != strExtractedName)
GetParent()->PostMessage(UM_SM_EDITOR_SET_MODIFIED, (WPARAM)TRUE);
*m_pStrText = strExtractedName;
}
}
}
}
*pResult = 0;
}
As you can see, I have changed how and where I post the UM_SM_EDITOR_SET_MODIFIED message. This causes my application to work correctly. Previously it was always setting it as modified (multiple times). So even if you had just saved the file, it then was marked as modified again. This problem no longer happens.
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;
}
}
}
}
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.
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;
}
}
}
}
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
_bstr_t::wchar_t*, _bstr_t::char* operators return string of different types.
Do I need to delete or free them? using which function?
After stepping the implementation using debugger, my conclusion is that there is no need to manually delete/free the returned string. The lifetime of the returned string is managed by _bstr_t internally.
See the following snippets from the implementation:
// Extract a const char_t*
//
inline _bstr_t::operator const char*() const throw(_com_error)
{
return (m_Data != NULL) ? m_Data->GetString() : NULL;
}
inline const char* _bstr_t::Data_t::GetString() const throw(_com_error)
{
if (m_str == NULL) {
m_str = _com_util::ConvertBSTRToString(m_wstr);
if (m_str == NULL && m_wstr != NULL) {
_com_issue_error(E_OUTOFMEMORY);
}
}
return m_str;
}
inline void _bstr_t::Data_t::_Free() throw()
{
if (m_wstr != NULL) {
::SysFreeString(m_wstr);
}
if (m_str != NULL) {
delete [] m_str;
}
}
It is also okay to use unnamed _bstr_t as follows because _bstr_t instance is destroyed after the constructor of CString has finished.
CString abc((LPCTSTR)_bstr_t(OLESTR("ABC")));
AfxMessageBox(abc);
I have the following method where I want to test the event.status property only if status has been passed in:
def findEvent(String desc, String status = null, Collection events) {
return events.find {
it.description == desc && \\If status is not null: it.status == status
}
throw new Exception("Review Event Record Not Found: ${desc}")
}
I thought it could be done like this, but it doesn't seem to work:
def findEvent(String desc, String status = null, Collection events) {
return events.find {
it.description == desc && (status != null ?: {it.status == status})
}
throw new Exception("Review Event Record Not Found: ${desc}")
}
Is there any way this could be done? Or do I have to go back to something like this:
if (status != null) {
return events.find {
it.description == desc && it.status == status
}
} else if (status == null) {
return events.find {
it.description == desc
}
}
Is there some kind of best practice?
I don't believe the expression is sensical as it is.
Elvis means "if truthy, use the value, else use this other thing."
Your "other thing" is a closure, and the value is status != null, neither of which would seem to be what you want. If status is null, Elvis says true. If it's not, you get an extra layer of closure.
Why can't you just use:
(it.description == desc) && ((status == null) || (it.status == status))
Even if that didn't work, all you need is the closure to return the appropriate value, right? There's no need to create two separate find calls, just use an intermediate variable.