Auto iteration iterates past the vectors end (I think) - c++

Question

I am currently trying to code a PacMan game with c++ and OpenGL. At the moment I am having some trouble when trying to delete a "Coin" pointer from a vector of "GameObject" pointers:
bool MovableObject::collisionHandling(std::vector<GameObject*>& v) {
bool deleteCoin = false;
int vectorIt;
for (auto it = begin(v); it != end(v); ++it) {
if (*it != this) {
// If there is a collision imminent:
if (collisionInt(this, *it)) {
// For PacMan:
if (this->classType == "PacMan") {
// Collision with coin:
if ((*it)->classType == "Coin") {
PacMan* ptr = static_cast<PacMan*>(this);
ptr->score += 10;
vectorIt = it - v.begin();
deleteCoin = true;
}
}
}
}
}
if (deleteCoin) {
Coin* ptr = static_cast<Coin*>(v[vectorIt]);
v.erase(v.begin() + vectorIt);
delete ptr;
}
return false;
}
This throws an exception in a vector file, which reads:
Exception thrown: read access violation.
_Mycont was nullptr. The exception is thrown on line 72, which has the following code:
_STL_VERIFY(_Ptr < _Mycont->_Mylast, "can't increment vector iterator past end")
It seems like the exception gets thrown between another for loop, where the collisionHandling function gets called from:
void GameLevel::update(GLFWwindow *window) {
std::string classType;
// Delta time:
float timeSinceStart = float(glfwGetTime());
deltaTime = timeSinceStart - oldTimeSinceStart;
oldTimeSinceStart = timeSinceStart;
if (!paused) {
std::cout << "Testing...";
// We don't need to update walls:
for (auto it = begin(objectsPtr); it != end(objectsPtr); ++it) {
classType = (*it)->classType;
if (classType == "Ghost") {
Ghost* ptr = static_cast<Ghost*>(*it);
ptr->deltaTime = deltaTime;
ptr->pickRandomOffDirection();
ptr->updateSpeed();
ptr->collisionHandling(objectsPtr);
ptr->move();
ptr->animate();
}
else if (classType == "PacMan") {
PacMan* ptr = static_cast<PacMan*>(*it);
ptr->deltaTime = deltaTime;
ptr->input(window);
ptr->updateSpeed();
paused = ptr->collisionHandling(objectsPtr);
ptr->move();
ptr->animate();
}
}
std::cout << "complete\n";
}
As I understand it, this shouldn't throw an exception. (Testing similar code with a vector of ints, where the last element was erased in the loop didn't fail.) This code also worked properly until I added the collision with coin part, so I know it has something to do with the vector loop. Additionally, this only fails when some specific coins should get deleted. Most of them get deleted without any problem.
I appreciate any feedback or attempt to help me.
Just in case you need more information, the collisionHandling function contains more code, but I don't think it has anything to do with the error. Here is the full code:
bool MovableObject::collisionHandling(std::vector<GameObject*>& v) {
bool deleteCoin = false;
int vectorIt;
for (auto it = begin(v); it != end(v); ++it) {
if (*it != this) {
// If there is a collision imminent:
if (collisionInt(this, *it)) {
// For PacMan:
if (this->classType == "PacMan") {
// Collision with wall:
if ((*it)->classType == "GameObject") {
bool xCollision = false, yCollision = false;
glm::vec2 oldSpeed = speed;
// Check x-axis:
speed.y = 0.f;
xCollision = collisionInt(this, *it);
// Check y-axis:
speed.y = oldSpeed.y;
speed.x = 0.f;
yCollision = collisionInt(this, *it);
speed = glm::vec2(!xCollision * oldSpeed.x, !yCollision * oldSpeed.y);
}
// Collision with ghost
if ((*it)->classType == "Ghost") {
std::cout << "GAME OVER\n";
return true;
}
// Collision with coin:
if ((*it)->classType == "Coin") {
PacMan* ptr = static_cast<PacMan*>(this);
ptr->score += 10;
vectorIt = it - v.begin();
deleteCoin = true;
}
}
// For Ghost:
else if (this->classType == "Ghost") {
// Collision with wall:
if ((*it)->classType == "GameObject") {
// Same as with PacMan:
bool xCollision = false, yCollision = false;
glm::vec2 oldSpeed = speed;
// Check x-axis:
speed.y = 0.f;
xCollision = collisionInt(this, *it);
// Check y-axis:
speed.y = oldSpeed.y;
speed.x = 0.f;
yCollision = collisionInt(this, *it);
speed = glm::vec2(!xCollision * oldSpeed.x, !yCollision * oldSpeed.y);
}
}
}
}
}
if (deleteCoin) {
Coin* ptr = static_cast<Coin*>(v[vectorIt]);
v.erase(v.begin() + vectorIt);
delete ptr;
}
return false;
}

Answer 1

Thanks to rafix07 for pointing out my mistake in a comment:
Undefined behaviour, it is invalidated in for loop inside update by collisionHandling. collisionHandling iterates over the same container, calling erase
I fixed this by deleting the desired object after the for loop inside the update method, instead of inside the collisionHandling method.