I have a mid-term assignment in which we conduct 3 sets of unit tests with documentation etc for a program from our course. The program I chose is a physics simulation.
Within this program, there are two classes, Thing and World. I am able to independently create these objects. I tried adding the Thing object to the World object by creating a std::vector<Thing> things, and then creating a function to add the Thing to the vector of things. However, when I do that, it seems as though the World object creates its own copy of the Thing, because when I change the Things position, the version of the Thing in the things vector remains the same.
Please provide some guidance on the matter, I feel my problem might be with how I use pointers in this situation.
void testBoundaryBounce()
{
//Create the world
World world{10.0f, 10.0f, 1.0f};
//Thing, 2 units away from boundary
Thing thing{8.0f, 5.0f, 1.0f};
//Add thing to world (adding it the the things vector)
world.addThing(&thing);
//Apply force that should trigger bounce back to x = 7
thing.applyForce(1.0f, 0.0f);
//Updating thing so that movement takes effect
thing.update();
//Running world update to account for collisions, bounces etc
world.update();
std::cout << "thing x : " << thing.getX() << std::endl;
CPPUNIT_ASSERT(thing.getX() == 7);
}
Thing::Thing(float x, float y, float radius)
: x{x}, y{y}, dX{0}, dY{0}, radius{radius}
{
}
World::World(float width, float height, float gravity)
: width{width}, height{height}, gravity{gravity}
{
std::vector<Thing> things;
}
void World::addThing(Thing* thing)
{
float thingX = thing->getX();
float thingY = thing->getY();
float thingRad = thing->getRad();
std::cout << "Radius : " << thingRad << std::endl;
if (thingX thingRad > width || thingX - thingRad <= 0 || thingY thingRad >
height|| thingY - thingRad <= 0)
{
std::cout << "Thing is out of bounds or is too large" << std::endl;
}
else {
std::cout << "Thing is good" << std::endl;
things.push_back(*thing);
}
}
void World::update()
{
for (Thing& thing : things)
{
thing.update();
float thingX = thing.getX();
float thingY = thing.getY();
float thingRad = thing.getRad();
float worldGrav = this->gravity;
std::cout << "thing x: " << thingX << std::endl;
std::cout << "thing rad: " << thingRad << std::endl;
//World Boundary Bounces
if (thingX thingRad >= width)
{
std::cout << "Bounce left" << std::endl;
thing.applyForce(-2.0f, 0.0f);
thing.update();
}
if (thingX thingRad <= 0)
{
thing.applyForce(2.0f, 0.0f);
thing.update();
std::cout << "Bounce right" << std::endl;
}
if (thingY thingRad >= height)
{
thing.applyForce(0.0f, -2.0f);
thing.update();
std::cout << "Bounce up" << std::endl;
}
if (thingY - thingRad <= 0)
{
thing.applyForce(0.0f, 2.0f);
thing.update();
std::cout << "Bounce down" << std::endl;
}
//Thing Collision Bounces
for (Thing& otherthing : things)
{
float thing2X = otherthing.getX();
float thing2Y = otherthing.getY();
float thing2Rad = otherthing.getRad();
if (thingX thingRad == thing2X thing2Rad && thingY thingRad ==
thing2Y thing2Rad)
{
thing.applyForce(-2.0f, -2.0f);
thing.update();
otherthing.applyForce(2.0f, 2.0f);
otherthing.update();
}
}
//Gravitational Pull
thing.applyForce(0.0f, worldGrav);
}
}
CodePudding user response：
Its right in the definition of void push_back (const value_type& val);...
Adds a new element at the end of the vector, after its current last element. The content of val is copied (or moved) to the new element.
so when you call things.push_back(*thing);, you are adding a new element to the 'things' vector which is a copy of the value pointed to by the thing pointer.
You want to change your vector to hold pointers to Thing types instead:
std::vector<Thing *> things;
and add the pointers instead of copies:
things.push_back(thing);
Note you will later have to access fields via -> instead of ., or you can create a reference to it such as:
for (Thing* pt: things)
{
Thing& thing = *pt;
thing.update();
//etc...
CodePudding user response：
Instead of constructing a Thing and copying it into world, you could have World construct the Things that it owns
void testBoundaryBounce()
{
//Create the world
World world{10.0f, 10.0f, 1.0f};
//Thing, 2 units away from boundary
Thing * thing = world.addThing(8.0f, 5.0f, 1.0f);
//Apply force that should trigger bounce back to x = 7
thing->applyForce(1.0f, 0.0f);
//Running world update to account for collisions, bounces etc
//Implies updating all the things
world.update();
std::cout << "thing x : " << thing.getX() << std::endl;
CPPUNIT_ASSERT(thing.getX() == 7);
}
Thing::Thing(float x, float y, float radius)
: x{x}, y{y}, dX{0}, dY{0}, radius{radius}
{
}
World::World(float width, float height, float gravity)
: width{width}, height{height}, gravity{gravity}
{
std::vector<Thing> things;
}
Thing * World::addThing(float x, float y, float radius)
{
std::cout << "Radius : " << radius << std::endl;
if ((x radius > width) || (x - radius <= 0) || (y radius >
height) || (y - radius <= 0))
{
std::cout << "Thing is out of bounds or is too large" << std::endl;
return nullptr;
}
else
{
std::cout << "Thing is good" << std::endl;
return &things.emplace_back(x, y, radius);
}
}
void World::update()
{
for (Thing& thing : things)
{
thing.update();
float thingX = thing.getX();
float thingY = thing.getY();
float thingRad = thing.getRad();
float worldGrav = this->gravity;
std::cout << "thing x: " << thingX << std::endl;
std::cout << "thing rad: " << thingRad << std::endl;
//World Boundary Bounces
if (thingX thingRad >= width)
{
std::cout << "Bounce left" << std::endl;
thing.applyForce(-2.0f, 0.0f);
thing.update();
}
if (thingX thingRad <= 0)
{
thing.applyForce(2.0f, 0.0f);
thing.update();
std::cout << "Bounce right" << std::endl;
}
if (thingY thingRad >= height)
{
thing.applyForce(0.0f, -2.0f);
thing.update();
std::cout << "Bounce up" << std::endl;
}
if (thingY - thingRad <= 0)
{
thing.applyForce(0.0f, 2.0f);
thing.update();
std::cout << "Bounce down" << std::endl;
}
//Thing Collision Bounces
for (Thing& otherthing : things)
{
float thing2X = otherthing.getX();
float thing2Y = otherthing.getY();
float thing2Rad = otherthing.getRad();
if (thingX thingRad == thing2X thing2Rad && thingY thingRad ==
thing2Y thing2Rad)
{
thing.applyForce(-2.0f, -2.0f);
thing.update();
otherthing.applyForce(2.0f, 2.0f);
otherthing.update();
}
}
//Gravitational Pull
thing.applyForce(0.0f, worldGrav);
}
}
As an aside, everything bounces off of itself every update