SFML Sprite moving violently down on 2nd tick - c++

Question

I am working on an SFML game and for some reason after spawning the player, the player gets teleported down. On the first tick he is correctly positioned, but after wards, he is moved down. Any idea on how to diagnose this problem? I set up breakpoints in the move mechanism, the only place where the player's co-ordinates change, and it seems to happen right after the function ends. This is the main function:
int main(){
App.ShowMouseCursor(false);
mainch.mainchinventory.read();
while (App.IsOpened())
{
sf::Event Event;
while (App.GetEvent(Event))
{
if (Event.Type == sf::Event::Closed)
App.Close();
}
float time = App.GetFrameTime();
mainch.move(time);
App.Clear();
drawall();
App.Display();
}
return EXIT_SUCCESS;
}
Mainch.move(t):
void cmainchar::move(float t){
if (App.GetInput().IsKeyDown(sf::Key::S)) mainchinventory.save();
if (App.GetInput().IsKeyDown(sf::Key::R)) mainchinventory.read();
if (App.GetInput().IsKeyDown(sf::Key::A)) A = true;
else A = false;
if (App.GetInput().IsKeyDown(sf::Key::D)) D = true;
else D = false;
if(grounded)
if (App.GetInput().IsKeyDown(sf::Key::W)) first = true;
if ((App.GetInput().IsKeyDown(sf::Key::I)) && (keyreleased)){
if (mainchinventory.drawmain){
mainchinventory.drawmain = false;
mainchinventory.press(mainchinventory.selectionx, 3);
}
else{
mainchinventory.drawmain = true;
}
keyreleased = false;
}
else if (!App.GetInput().IsKeyDown(sf::Key::I))
keyreleased = true;
if(!mainchinventory.drawmain){
if(App.GetInput().IsKeyDown(sf::Key::Num1)) mainchinventory.press(0, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num2)) mainchinventory.press(1, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num3)) mainchinventory.press(2, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num4)) mainchinventory.press(3, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num5)) mainchinventory.press(4, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num6)) mainchinventory.press(5, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num7)) mainchinventory.press(6, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num8)) mainchinventory.press(7, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num9)) mainchinventory.press(8, 3);
else if(App.GetInput().IsKeyDown(sf::Key::Num0)) mainchinventory.press(9, 3);
if(App.GetInput().IsMouseButtonDown(sf::Mouse::Button::Left)){
mainchinventory.dockitems[mainchinventory.selectionx].use();
spells.push_back(cspell());
}
}
else if ((App.GetInput().IsMouseButtonDown(sf::Mouse::Button::Left)) && (mainchinventory.drawmain) && (buttonreleased)){
mainchinventory.checkmouse();
buttonreleased = false;
}
else if (!App.GetInput().IsMouseButtonDown(sf::Mouse::Button::Left))
buttonreleased = true;
int xmap = (View.GetCenter().x - 320) / 40;
int ymap = (View.GetCenter().y - 240) / 40;
if ((xmap != xmapold) || (ymap != ymapold))
maps.read();
xmapold = xmap;
ymapold = ymap;
collisions();
for(std::list<cspell>::iterator i = mainch.spells.begin(); i != mainch.spells.end(); i++)
if (i->move(t))
spells.erase(i);
if (A && left){
animate(2, t);
you.Move(-160 * t, 0);
}
if (D && right){
animate(1, t);
you.Move(160 * t, 0);
}
if (!D && !A)
animate(0, t);
if (up){
if(grounded && first){
jump = 1.25;
first = false;
}
if (jump > 0){
you.Move (0,-250 * t * jump);
jump = jump - 1 * t;
}
if (jump <= 0){
jump = 0.f;
}
}
else{
first = false;
jump = 0.f;
}
if (down){
fall = fall + 10 * t;
you.Move(0, 25 * fall * t);
grounded = false;
}
else{
fall = 0.f;
grounded = true;
}
if(teleport){
mainchinventory.spawn = true;
fall = 0.f;
jump = 0.f;
maps.changemap(maps.nxtmap);
teleport = false;
}
moveview();
}

Answer 1

You don't show the code where you're manipulating the sf::Sprite object, so I (or anyone else, really) can't say for certain, but...that said, I have a strong guess as to what's happening.
I've been familiarizing myself with SFML recently, too, and I encountered this issue myself. What I think is happening is you're calling sf::Sprite::Move(x,y) to move the sprite to position (x,y). This is incorrect; what you should be calling is sf::Sprite::SetPosition(x,y). (Both these functions take will take a 2d vector as an argument instead, btw).
I'm operating under the assumption you're using SFML 1.6, yes? Looks that way...version 2.0 changes the API somewhat, so in case you're using that Sprite::Move() becomes Sprite::move() and Sprite::SetPosition() becomes Sprite::setPosition().
Anyways, to wrap this up: the difference between Move(x,y) and SetPosition(x,y) is that Move adjusts the sprite's position relative to its current position, whereas SetPosition moves the sprite to a new position regardless of where it was before.
Again, this is a blind guess since the relevant code was not included...so was my shot in the dark correct?

Answer 2

Unfortunately, you haven't provided enough code for a straightforward diagnosis. With what you provided however, my best guess is that your fall variable hasn't been initialized. If it hasn't been initialized, its values can be completely random, likely being much larger than expected. This would explain your 'teleporting' behavior.