Deletion of std::list causing Access violation - c++

Question

For a school project, my group is using OpenCV to capture video. From these (top-down) images, positions of objects are extracted and turned into a list of Points. Those Points then get triangulated using http://code.google.com/p/poly2tri/ (to overcome the problem of possible non-convex objects). Then, using the coordinates of the triangulated ground pane, we draw the objects in 3D using freeglut. (Side and Top panes are calculated using the ground pane coordinates). The problem we have is that when we delete our old list of Points, the application randomly crashes. Sometimes after 1 second, sometimes after 30 seconds, sometimes after a few minutes. The error we get is "Access violation writing location 0xCCCCCCCC"
Our code:
void WorldLayoutBuilder::update()
{
pointList.clear();
// Capture image
<code to capture image and get countours>
for(size_t i = 0; i < contours.size(); i++)
{
if(contours[i].size() > 50)
{
approxPolyDP(contours[i], approxShape, cv::arcLength(cv::Mat(contours[i]), true)*0.04, true);
drawContours(drawing, contours, i, cv::Scalar(255, 0, 0), 0);
std::vector<Point> newObject;
for(size_t j = 0; j < contours[i].size(); j++)
{
cv::Point newPoint = contours[i][j];
newObject.push_back(Point((float) newPoint.x / 100, 0.0f,(float) newPoint.y / 100));
}
pointList.push_back(newObject);
}
}
ObjectCreator3D::createObjects(&pointList);
contours.clear();
<code to release images, etc>
}
This captures an image, retrieves coordinates of objects, and then calls ObjectCreator3D::createObjects():
void ObjectCreator3D::createObjects(std::list<std::vector<Point>>* inputList)
{
std::list<WorldObject>* tempObjects = new std::list<WorldObject>;
for(std::vector<Point>&pointObject : *inputList)
{
WorldObject worldObject(&pointObject);
tempObjects->push_back(worldObject);
}
DataStorage::getInstance()->setObjects(tempObjects);
}
All objects are turned into WorldObjects:
#include <list>
#include <iostream>
#include <GL/glut.h>
#include <GL/freeglut.h>
#include <time.h>
#include "WorldObject.h"
#include "Point.h"
//Constant height - adjustable/randomized solution is partially implemented in the constructor.
const float WorldObject::HEIGHT = 5.0f;
template <class C> void FreeClear(C & cntr)
{
for(typename C::iterator it = cntr.begin(); it != cntr.end(); ++it)
{
delete * it;
}
cntr.clear();
}
WorldObject::WorldObject(std::vector<Point>* pointList)
{
//TODO, when we have time. Seems difficult because height will change each update...
/*srand (time(NULL));
float fGeneratedY = (rand() % 20 + 2) / 2.0f;*/
cdt = nullptr;
for (Point &point : *pointList)
//point.setY(fGeneratedY);
point.setY(HEIGHT);
this->pointList = pointList;
}
WorldObject::~WorldObject()
{
//Cleanup
delete cdt;
FreeClear(polyPoints);
}
/*
Author Tim Cocu & Bas Rops
Function for drawing the WorldObject
*/
void WorldObject::draw()
{
glPushMatrix();
glColor3f(0.8f, 0.8f, 0.8f);
//Calculate our bottom pane
calculateTriangles();
//BOTTOM PANE
for (unsigned int i = 0; i < calculatedTriangles.size(); i++)
{
p2t::Triangle& t = *calculatedTriangles[i];
p2t::Point& a = *t.GetPoint(0);
p2t::Point& b = *t.GetPoint(1);
p2t::Point& c = *t.GetPoint(2);
glBegin(GL_TRIANGLES);
glNormal3f(0, -1, 0);
glVertex3f((GLfloat)a.x, (GLfloat)0.0f, (GLfloat)a.y);
glVertex3f((GLfloat)b.x, (GLfloat)0.0f, (GLfloat)b.y);
glVertex3f((GLfloat)c.x, (GLfloat)0.0f, (GLfloat)c.y);
glEnd();
}
//TOP PANE
for (unsigned int i = 0; i < calculatedTriangles.size(); i++)
{
p2t::Triangle& t = *calculatedTriangles[i];
p2t::Point& a = *t.GetPoint(0);
p2t::Point& b = *t.GetPoint(1);
p2t::Point& c = *t.GetPoint(2);
glBegin(GL_TRIANGLES);
glNormal3f(0, 1, 0);
glVertex3f((GLfloat)a.x, (GLfloat)HEIGHT, (GLfloat)a.y);
glVertex3f((GLfloat)b.x, (GLfloat)HEIGHT, (GLfloat)b.y);
glVertex3f((GLfloat)c.x, (GLfloat)HEIGHT, (GLfloat)c.y);
glEnd();
}
glColor3f(1.0f, 1.0f, 1.0f);
//SIDE PANES
for(std::size_t iPaneCounter = 0; iPaneCounter < pointList->size(); iPaneCounter++)
{
Point firstPoint = (*pointList)[iPaneCounter];
Point secondPoint (0.0f, 0.0f, 0.0f);
if(iPaneCounter + 1 < pointList->size())
secondPoint.set((*pointList)[iPaneCounter + 1].getX(), (*pointList)[iPaneCounter + 1].getY(), (*pointList)[iPaneCounter + 1].getZ() );
else
secondPoint.set((*pointList)[0].getX(), (*pointList)[0].getY(), (*pointList)[0].getZ());
glBegin(GL_POLYGON);
float fNormalX = (firstPoint.getY() * secondPoint.getZ()) - (firstPoint.getZ() * secondPoint.getY());
float fNormalY = -((secondPoint.getZ() * firstPoint.getX()) - (secondPoint.getX() * firstPoint.getZ()));
float fNormalZ = (firstPoint.getX() * secondPoint.getY()) - (firstPoint.getY() * secondPoint.getX());
glNormal3f(fNormalX, fNormalY, fNormalZ);
glVertex3f(firstPoint.getX(), 0.0f, firstPoint.getZ());
glVertex3f(secondPoint.getX(), 0.0f, secondPoint.getZ());
glVertex3f(secondPoint.getX(), secondPoint.getY(), secondPoint.getZ());
glVertex3f(firstPoint.getX(), firstPoint.getY(), firstPoint.getZ());
glEnd();
}
}
/*
Calculates triangles that make a ground or top pane. Used for calculating possible non-convex objects
*/
void WorldObject::calculateTriangles()
{
//Empty the polyPoints list
if(polyPoints.size() > 0)
FreeClear(polyPoints);
//Convert our Points to p2t::Points
for(std::size_t iBottomIndex = 0; iBottomIndex < pointList->size(); iBottomIndex++)
polyPoints.push_back(new p2t::Point((*pointList)[iBottomIndex].getX(), (*pointList)[iBottomIndex].getZ()));
if(cdt == nullptr)
//Create CDT (Constrained Delaunay Triangulation) and add primary polyPoints
//NOTE: polyPoints must be a simple polygon. The polyPoints' points constitute constrained edges. No repeating points are allowed!
cdt = new p2t::CDT(polyPoints);
//Turn our polyPoints into p2t::Triangles
cdt->Triangulate();
//Set the triangles to use for drawing
calculatedTriangles = cdt->GetTriangles();
}
/*
Retrieve a pointer to a list of Points
*/
std::vector<Point>* WorldObject::getPoints()
{
return pointList;
}
/*
Retrieve a pointer to a list of p2t::Triangles
*/
std::vector<p2t::Triangle*> WorldObject::getCalculatedTriangles()
{
return calculatedTriangles;
}
When all WorldObjects are created, they are stored in DataStorage, DataStorage::getInstance()->setObjects() is called:
void DataStorage::setObjects(std::list<WorldObject>* objectList)
{
delete this->objectList;
this->objectList = objectList;
}
The application seems to crash on delete this->objectList; in setObjects(), so we think the application is trying to delete things he can't delete.
Any help would be greatly appreciated, we've been on this for a few days already

Answer 1

Here, you pass a pointer to an object owned by the list to the constructor of WorldObject:
for(std::vector<Point>&pointObject : *inputList)
{
WorldObject worldObject(&pointObject);
tempObjects->push_back(worldObject);
}
In WorldObject you store the pointer:
//Default Constructor
WorldObject::WorldObject(std::vector<Point>* pointList)
{
float fGeneratedY = (rand() % 20 + 2) / 2.0f;*/
cdt = nullptr;
for (Point &point : *pointList)
point.setY(HEIGHT);
this->pointList = pointList;
}
Which means WorldObject::pointList is only valid so long as the std::list which you constructed your WorldObjects from is still around. (After that, the result is undefined -- it could work, it could crash, it could format your hard drive and leak your identity to Texas).
If you insist on working with raw pointers, you as programmer are responsible for checking and keeping track of the lifetime of every single pointer. This is error prone and will cause random crashes that you will find difficult to track down.
Stop using raw pointers. Instead, if an object owns a resource, store it in a std::unique_ptr<>. If you want the same resource to be shared by multiple objects, use std::shared_ptr and std::weak_ptr, unless the lifetime of all but one of these objects is much, much shorter than the others in a guaranteed way.