Unable to delete a list element in C++ - c++

I am working on a small game and came across a big problem with lists.
Here's my code:
void cCollisionManager::checkCollision(cPlayer * pPlayer, std::list<cAsteroid*> *asteroidList, std::list<cShot*> *ShotList)
{
sf::FloatRect PlayerBox = pPlayer->getSprite()->getGlobalBounds();
for (auto it : *asteroidList) {
for (auto es : *ShotList) {
sf::FloatRect asteroidboundingBox = it->getSprite()->getGlobalBounds();
sf::FloatRect ShotBox = es->getSprite().getGlobalBounds();
if (asteroidboundingBox.intersects(ShotBox)) {
it = asteroidList->erase(it);
*pPlayer->pPunkte += 1;
std::cout << *pPlayer->pPunkte << std::endl;
}
if (asteroidboundingBox.intersects(PlayerBox)) {
if (*pPlayer->phealth >= 0.f)
*pPlayer->phealth -= 0.5f;
}
}
}
}
I used SFML and basically everything works. But if I want to delete the colliding asteroid and the shot, the programs exits with an error. In the if loop I tried to erase the object, but the compiler also gives an error saying that the argument type is not the same as the object type I am giving to it.
EDIT
I had another look at the other question, you recommended to me, but still I haven't found out how to solve that problem. So if I changed my code to a while loop, the game couldn't handle it, because the Collision Manager is actually called in every single Call of the SFML main loop. So it would just get stuck in my collision loop. So I changed my code a bit, but still, things are not working.

Don't modify sequences that are being enumerated with range-for. Use
iterators and the appropriate result of an erase. – WhozCraig
This is actually the answer to it. I did the mistake - using a for loop and not a while loop and so I had some big issues and bad construction ideas for my code - luckily everything now works!
Here is my final code:
auto it = asteroidList->begin();
auto es = ShotList->begin();
while (it != asteroidList->end()) {
sf::FloatRect PlayerBox = pPlayer->getSprite()->getGlobalBounds();
sf::FloatRect asteroidboundingBox = (*it)->getSprite()->getGlobalBounds();
while (es != ShotList->end())
{
sf::FloatRect ShotBox = (*es)->getSprite().getGlobalBounds();
if (asteroidboundingBox.intersects(ShotBox)) {
it = asteroidList->erase(it);
es = ShotList->erase(es);
std::cout << "Asteroid destroyed" << std::endl;
*pPlayer->pPunkte += 1;
std::cout << *pPlayer->pPunkte << std::endl;
}
if (es != ShotList->end())
es++;
}
if (asteroidboundingBox.intersects(PlayerBox))
{
if (*pPlayer->phealth > 3.f) {
*pPlayer->phealth -= 5.f;
it = asteroidList->erase(it);
}
else
*pPlayer->pBStateAlive = false;
}
if (it != asteroidList->end()) {
it++;
es = ShotList->begin();
}
}
}

Related

list.remove_if() crashing the program

I'm working on a game and I'm trying to add collectables. I'm trying to remove the object from the list after the player has collided with it, but it ends up crashing and says:
Unhandled exception thrown: read access violation.
__that was 0xDDDDDDE9.
It says this on the for loop statement, but I think it has to do with the remove_if() function.
Here is my code:
for (sf::RectangleShape rect : world1.level1.brainFrag) {
collides = milo.sprite.getGlobalBounds().intersects(rect.getGlobalBounds());
if (collides == true) {
world1.level1.brainFrag.remove_if([rect](const sf::RectangleShape val) {
if (rect.getPosition() == val.getPosition()) {
return true;
}
else {
return false ;
}
});
brainFrag -= 1;
collides = false;
}
}
if (brainFrag == 0) {
milo.x = oldPos.x;
milo.y = oldPos.y;
brainFrag = -1;
}
I don't understand your approach, you loop the rects, then when you find the one you want to remove, you search for it again through list<T>::remove_if.
I think that you forgot about the fact that you can use iterators in addition to a range-based loop:
for (auto it = brainFrag.begin(); it != brainFrag.end(); /* do nothing */)
{
bool collides = ...;
if (collides)
it = world1.level1.brainFrag.erase(it);
else
++it;
}
This allows you to remove the elements while iterating the collection because erase will take care of returning a valid iterator to the element next to the one you removed.
Or even better you could move everything up directly:
brainFrag.remove_if([&milo] (const auto& rect) {
return milo.sprite.getGlobalBounds().intersects(rect.getGlobalBounds())
}
A side note: there's no need to use an if statement to return a boolean condition, so you don't need
if (a.getPosition() == b.getPosition()
return true;
else
return false;
You can simply
return a.getPosition() == b.getPosition();

boost::stacktrace::frame::name() hangs

I am trying to retrieve a stack trace in my program, and store it for later use (debugging purposes). But the call to boost::stacktrace::frame::name() never returns, and I have no clue why. When I use this exact code in a simple project, it runs nicely. Any ideas?
boost::stacktrace::stacktrace stacktrace;
stringstream stacktraceText;
for (const auto& entry : stacktrace)
{
if (entry.empty() == false)
{
auto name = entry.name();
stacktraceText << name << "\n";
}
else
{
stacktraceText += L"<missing symbol info>\n";
}
}

Why does this function get wrong argument from iterator?

I'm writing a Space Invaders clone for IT project on uni. All the methods work, but I have a problem with deleting enemies.
I redone my code to use iterators. I store enemies in vector(horizontal) of vectors(vertical) of Enemy. The code works fine until i shoot more than 2 projectiles at a time when it gives me an error.
if (projectiles.size() != 0)
{
for (auto itr_columns = enemies.begin(); itr_columns != enemies.end(); itr_columns++)
{
for (auto itr_rows = itr_columns->begin(); itr_rows != itr_columns->end();)
{
if (projectiles.size() == 0)
{
break;
}
for (auto itr_projectiles = projectiles.begin(); itr_projectiles != projectiles.end();)
{
if (itr_projectiles->Collision(*itr_rows))
{
itr_projectiles = projectiles.erase(itr_projectiles);
itr_rows = itr_columns->erase(itr_rows);
}
else
{
itr_rows++;
itr_projectiles++;
}
}
}
}
}
That's the error i get:
line: if (itr_projectiles->Collision(*itr_rows))
Expression: can't dereference out of range vector iterator
Look at the instruction :
itr_rows = itr_columns->erase(itr_rows);
By doing that, you invalidate the iterators of itr_columns while you're are in the loop, which does use these iterators.
Never call functions invalidating iterators when you a are in a loop.

Unreal engine c++ write delegate OnScreenshotCaptured

I am new to C++. I've wrote code in C# and PHP.Since I am using Unreal engine I am trying to learn C++. For my project I need to make a screenshot in-game and show it immediately so I want to get it as a texture.
I made a blueprint node which calls this function i've made:
void UMyBlueprintFunctionLibrary::TakeScreenshot()
{
FScreenshotRequest::RequestScreenshot(true);
if (GEngine)
GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Red, "Tried to take screenshot");
}
When I hover my mouse above RequestScreenshot I see the following pop-up:
"Screenshot can be read from memory by subscribing to the viewsport OnScreenshopCaptured delegate"
So that is what I try to do but I have no idea how I looked up this:
https://docs.unrealengine.com/latest/INT/API/Runtime/Engine/Engine/UGameViewportClient/OnScreenshotCaptured/
Can someone tell me how to implement this and how you see/know how to implement it?
I have an alternative, no delegate, but FRenderTarget::ReadPixel() to some buffer you allocated, by implementing your own UGameViewportClient (inherit it), and overriding Draw() function.
I'll show the essential codes, but not complete.
void UMyGameViewportClient::Draw(FViewport* Viewport, FCanvas* SceneCanvas)
{
Super::Draw(Viewport, SceneCanvas);
if (any_condition_you_need) {
CaptureFrame();
}
}
void UMyGameViewportClient::CaptureFrame()
{
if (!Viewport) {
return;
}
if (ViewportSize.X == 0 || ViewportSize.Y == 0) {
return;
}
ColorBuffer.Empty(); // Declare this in header as TArray<FColor>
if (!Viewport->ReadPixels(ColorBuffer, FReadSurfaceDataFlags(),
FIntRect(0, 0, ViewportSize.X, ViewportSize.Y)))
{
return;
}
SaveThumbnailImage();
}
void UMyGameViewportClient::SaveThumbnailImage()
{
IImageWrapperModule& wrappermodule = FModuleManager::LoadModuleChecked<IImageWrapperModule>(FName("ImageWrapper"));
auto wrapper_ptr = wrappermodule.CreateImageWrapper(EImageFormat::PNG);
for (int i = 0; i < ColorBuffer.Num(); i++)
{
auto ptr = &ColorBuffer[i];
auto r = ptr->R;
auto b = ptr->B;
ptr->R = b;
ptr->B = r;
ptr->A = 255;
} // not necessary, if you like bgra, just change the following function argument to ERGBFormat::BGRA
wrapper_ptr->SetRaw(&ColorBuffer[0], ColorBuffer.Num() * 4,
ViewportSize.X, ViewportSize.Y, ERGBFormat::RGBA, 8);
FFileHelper::SaveArrayToFile(wrapper_ptr->GetCompressed(), *ThumbnailFile);
}

Callback function confuses argument?

I have a sfml window container, and it appears to be working, however the glViewPorts are the wrong size, which I assume is because the wrong sf::Window is being passed.
Here is a function which adds to the window: It takes some information about the sfml window.
int WindowContainer::PushBack(WindowData& data)
{
if(data.WindowSettingsOK() && data.VideoModeOK()){
mWindowVector.resize(mWindowVector.size() + 1);
mDisplayFuncVector.resize(mWindowVector.size());
mInputFuncVector.resize(mWindowVector.size());
mWindowVector.at(mWindowVector.size() - 1) = new sf::Window();
mWindowVector.at(mWindowVector.size() - 1)->Create(data.VideoMode(), data.Title(), data.Style(), data.Settings());
mWindowVector.at(mWindowVector.size() - 1)->SetPosition(data.PositionX(), data.PositionY());
mDisplayFuncVector.at(mWindowVector.size() - 1) = nullptr;
mInputFuncVector.at(mWindowVector.size() - 1) = nullptr;
return 0;
}
else{
PrintError(ErrorMessageType::BadSettings);
return 1;
}
}
Alternatively, this function may be called to setup the display and input function callbacks:
int WindowContainer::PushBack(WindowData& data, function_p displayFunc, function_p inputFunc)
{
int return_val = PushBack(data);
mDisplayFuncVector.at(mWindowVector.size() - 1) = displayFunc;
mInputFuncVector.at(mWindowVector.size() - 1) = inputFunc;
return return_val;
}
Then, when the window needs .Display()'ing, this function is called:
void WindowContainer::ProcessDisplay()
{
for(unsigned int i = 0; i < mWindowVector.size(); i ++){
if(mDisplayFuncVector.at(i) != nullptr){
mDisplayFuncVector.at(i)(*mWindowVector.at(i), mClock, (const void*&)mExternalDrawingDataPointer);
}
mWindowVector.at(i)->Display();
}
}
... This is all good, until the result on the screen is that resizing one window affects the viewport of both windows. This suggests that calling the callback function: mDisplayFuncVector.at(i)(*mWindowVector.at(i), mClock, (const void*&)mExternalDrawingDataPointer); gives the argument of *mWindowVector.at(0) each time, instead of each window individually. (As in *mWindowVector.at(i))
Can anyone help with this problem?
The main loop contains this code:
while(container.Access(0)->IsOpened()){
container.ProcessInput();
container.ProcessDisplay();
}
Container.Access(int) is this function:
const sf::Window*& WindowContainer::Access(unsigned int index)
{
if(index > mWindowVector.size()){
PrintError(ErrorMessageType::IndexOutOfRange);
}
else{
return (const sf::Window*&)mWindowVector.at(index);
}
return (const sf::Window*&)mWindowVector.at(0);
}
Thanks again, I'm sure I have made a mistake somewhere but cannot spot it.
I have been thinking about this question and suspect openGL becomes confused with which window is it drawing to if more than one object is pushed back without a call to Display() to sync everything.
I am yet to test this and confirm.
EDIT The window container now works. It has nothing to do with the callback functions argument.