I have a class called Pixel where I only store the values (x,y). Then I created a std::vector to store the pixels in a patch and compute some disparity.
Surprisingly, after some Pixels are push_back() into the vector I get a NULL reference but I don't see why. Here's my code
std::vector<Pixel*> disparityPatches;
std::vector<Pixel*> patchPos;
//COMPUTE THE DISPARITY FOR EACH OF THE PIXEL COORDINATES IN THE PATCH
for (uint iPatchPos = 0; iPatchPos < patchPos.size(); iPatchPos++)
{
disparityPatches.push_back(new Pixel(patchPos[iPatchPos]->getX()+dispNodeX, patchPos[iPatchPos]->getY()+dispNodeY));
if( (disparityPatches[disparityPatches.size()-1]) == NULL)
{
std::cout << "WHAT!?" << std::endl;
}
}
Can you see why is this hapenning? I've checked that patchPoshas the correct data and dispNodeX and dispNodeY have the correct info too.
It's weird because the first three iterations (iPatchPos = [0,1,2,3]) work fine then i get the NULL reference.
EDIT
class Pixel
{
float _x;
float _y;
public:
Pixel();
Pixel::Pixel(float x, float y)
{
_x = x;
_y = y;
}
const float Pixel::getX()
{
return _x;
}
const float Pixel::getY()
{
return _y;
}
};
You used below code to add a pix into the vector:
disparityPatches.push_back(new Pixel(patchPos[iPatchPos]->getX()+dispNodeX, patchPos[iPatchPos]->getY()+dispNodeY));
maybe new Pixel(patchPos[iPatchPos]->getX()+dispNodeX, patchPos[iPatchPos]->getY()+dispNodeY) may return null when the constructor failed in someway, so NULL will be added, then you got your error.
Related
I'm making a small OpenGL program for my intro to C++ class in Uni. I have a program that is complete but I want to change it up a bit to make it more unique. I have a Cube class:
class Cube {
public:
Cube(Mesh* mesh, Texture2D* texture, float x, float y, float z);
~Cube();
void Draw();
void Update(float rSpeed);
Vector3 position;
private:
GLfloat rotationSpeed;
Vector3 rotationVector;
Mesh* _mesh;
Texture2D* _texture;
};
I then create an array of type Cube:
Cube* cubes[CUBE_AMOUNT];
I then fill each index of this array with data to draw the cube on screen later in the program:
for (int i = 0; i < CUBE_AMOUNT; i++) {
float x = ((rand() % 400) / 10.0f) - 20.0f;
float y = ((rand() % 200) / 10.0f) - 10.0f;
float z = -(rand() % 1000);
if (i % 2 == 1) {
cubes[i] = new Cube(cubeMesh, textureStars, x, y, z);
}
else {
cubes[i] = new Cube(cubeMesh, texturePenguins, x, y, z);
}
}
With this new thing I want to add to the program, I want to check whether an index of cubes[] has been filled with the data yet. However I keep getting exceptions when running. I have tried to check whether cubes[i] is equal to nullptr, and tried checking whether it is NULL too, but neither seem to match.
Sorry for any errors in terminology that I used. New to C++, and having come from only doing Python before this, it is confusing!
Solution:
When I create the array, I changed it to Cube* cubes[CUBE_AMOUNT] = { NULL }, and now when checking the array, cubes[i] == NULL!
If cubes is not a global variable, you can use:
Cube* cubes[CUBE_AMOUNT] = {};
to initialize all the elements to nullptr.
You can also use:
std::vector<std::unique_ptr<Cube>> cubes(CUBE_AMOUNT);
to remove the burden of having to deallocate dynamic memory in your code.
In either case, can use:
if ( cubes[index] )
{
// Got a valid pointer. Use it.
}
Your cubes variable is not automatically initialized with null_ptr's. Until you either fill it with null_ptr's or good pointers it initially points to random garbage.
I think this would work
//This bit should check if theres anything stored currently.
cout << "\nWhich Slot would you like to store the informaton in ?(1-10)";
cin >> i;
i--;
if (information[i] != NULL){
// Already written
cout << "THERES SOMETHING HERE";
}
else{
cout << "\nEMPTY!!!!!!!!!";
}
I'm having some problems with polymorphism I have a superclass of CEntity, and a subclass of unit type, I am dynamic casting and removing and emplacing a new entity of the dynamic casts type at its place, I have the opposite problem of my previous question.
Problem is the values being set are not changing, it remains with default values, it appeared to work before but now it has stopped working, I'm not sure what has caused the issue.
specifically buildsetup, sets the x-y-z values of the unit subclass's x,y,z, but when I look inside the vector the values remain unchanged, this is strange because it does actually manage to change the values for whether the unit is alive or not.
void builder(int no, string in , int top, int bot, CTeam &team, string owner, string original)
{
for (int i = top; i <= bot; i++)
{
EntityUnit* a;
a = dynamic_cast<EntityUnit*>(AWorld.EntitiesVector[i]);
a->unit_alive;
if (a->unit_alive == false)
{
float x = Player.returncity_add().cit_ret_X();
float y = Player.returncity_add().cit_ret_Y();
float z = Player.returncity_add().cit_ret_Z();
cout << "X:" << x;
cout << "Y:" << y;
cout << "Z:" << z;
float cost = MainAB.UnitTemplates[no]->UDRetCost();
float health = MainAB.UnitTemplates[no]->UDRetMaxHealth();
float damage = MainAB.UnitTemplates[no]->UDRetStrength();
float speed = MainAB.UnitTemplates[no]->UDRetSpeed();
float buildtime = MainAB.UnitTemplates[no]->UDRetBuildTime();
int popcost = MainAB.UnitTemplates[no]->UDRetPop();
a->set_owner(owner);
setmodel(i, x, y, z); // takes an xyz by ref and sets the model
to them then changes the model's localz by -10
Units[i]->SetSkin(setskin(owner, original));
a->BuildSetup(x, y, z, health, damage, speed, buildtime, cost, popcost);
team.inc_popcount(a->UDRetPop());
a->set_unit_alive(true);
sBuildUnit.play();
AWorld.EntitiesVector.erase(AWorld.EntitiesVector.begin() + i);
AWorld.EntitiesVector.emplace(AWorld.EntitiesVector.begin() + i, new EntityUnit(a));
AWorld.EntitiesVector[i]->set_x(x);
AWorld.EntitiesVector[i]->set_y(y);
AWorld.EntitiesVector[i]->set_z(z);
break;
}
}
Entity build setup
void EntityUnit::BuildSetup(float x, float y, float z,float _health, float _damage, float _speed, float _buildtime, float _cost, int _popcost)
{
unit_x = x;
unit_y = y;
unit_z = z;
unit_health[0] = _health;
unit_health[1] = _health;
unit_damage = _damage;
speed = _speed;
buildtime = _buildtime;
cost = _cost;
CUnitType = NA;
pop_req = _popcost;
}
After static debugging it, it most definately emplaces a new unit with the updated -is_alive, and while a's values change at the point of unitbuild, when its emplaced all x,y,z's return to 9999, which was what it was when they were pushed on the vector.
When you call
AWorld.EntitiesVector.erase(AWorld.EntitiesVector.begin() + i);
you destroy the object pointed to by a. The subsequent reference to it on the next line is Undefined Behavior, and anything is possible.
I'm not sure why you erase the entity, then try to put a new one in the same place. If you structure your code right you should be able to just reuse the existing entity (pointed to by a) without the erase and emplace calls.
Ok, Apparently the problem was it was totally unnecessary to erase/emplace, as I get what you mean now returning a pointer, it edited the value... odd it didn't work last time.
I have a Rectangle class shown below:
Header:
class Rectangle: public Polygon {
private:
float _width, _height;
public:
Rectangle(float width, float height);
float getWidth(float* width) const;
float getHeight(float* height) const;
bool isCollidingWith(Rectangle* other) const;
};
Selected Implementation:
Rectangle::Rectangle(float width, float height) : Polygon(explodeRect(width, height, new struct vertex[4]), 4) {
printf("creating rect %f x %f\n", width, height);
_width = width;
_height = height;
printf("set _width to %f\n", _width);
}
float Rectangle::getWidth(float* width) const {
printf("_w: %f\n", _width);
*width = _width;
return *width;
//return (*width = _width);
}
float Rectangle::getHeight(float* height) const {
return (*height = _height);
}
I initialize an instance of the Rectangle class, and the output indicates that the _width variable is being correctly assigned. However, when I later try to read the variable using the getWidth method, I get an EXC_BAD_ACCESS error on the line:
printf("_w: %f\n", _width);
Why can I no longer read this variable? I get the same problem with the _height variable as well.
EDIT: I would also like to note that if I skip reading the width, I get an error trying to read public variables directly from the object, e.g. when I try to read its x position with obj->x.
EDIT 2: Could this be from the fact that the object is an instance of a subclass of Rectangle, and this subclass is defined in a different file than Rectangle is? I am also reading the values from a third file.
EDIT 3: More code below.
I am trying to re-create Tetris with OpenGL. In my display method, I have this code to draw the rectangles:
if(fallingBlock != nullptr) {
printf("drawing falling block at (%f, %f)\n", fallingBlock->x, fallingBlock->y);
draw(fallingBlock);
}
fallingBlock is defined as a global variable at the top of my file:
Block* fallingBlock;
From my main, I call an initVars method that subsequently calls a startDroppingBlock method. Here it is:
void startDroppingBlock() {
Block* block = availableBlocks[random() % numAvailableBlocks].copy();
block->x = 0.5;
block->y = SCREEN_TOP;
block->dy = -0.01f;
//printf("copied block is at (%f, %f)\n", block->x, block->y);
fallingBlock = block;
}
And here is my block drawing method:
void draw(Block* obj) {
bool shape[3][3];
obj->getShape(shape);
//printf("got shape: {%d, %d, %d}, {%d, %d, %d}, {%d, %d, %d}\n", shape[0][0], shape[0][1], shape[0][2], shape[1][0], shape[1][1], shape[1][2], shape[2][0], shape[2][1], shape[2][2]);
/*float pieceWidth;
obj->getWidth(&pieceWidth);
pieceWidth /= 3.0f;*/
float pieceWidth = obj->getWidth();
for(unsigned int i=0; i<3; i++) {
for(unsigned int j=0; j<3; j++) {
if(shape[i][j]) {
Square rect = Square(pieceWidth);
rect.x = obj->x + pieceWidth * j;
rect.y = obj->y + pieceWidth * i;
rect.color = obj->color;
draw(&rect);
}
}
}
}
I get an EXC_BAD_ACCESS error on the line [...]. Why can I no longer read this variable? I get the same problem with the _height variable as well. [later...] I have tried both float pieceWidth; obj->getWidth(&pieceWidth); and obj->getWidth(new float) - the actual error is on the line where I read _width, before I even use the passed in pointer. [later...] I modified the getWidth and getHeight methods to just simply return _width and _height. Now I just get an error on return _width;
In this case I see you are using a Rectangle* pointer as obj->getWidth which can as well lead to a bad access error if obj is not a valid pointer.
It is to note that I don't quite understand your getter method at all. A simplified (and possibly standard) version of it might be:
float Rectangle::getWidth() const {
return _width;
}
With the only difference that when you used:
// float a;
// float b;
a = rect.getWidth(&b);
you can now do:
// float a;
// float b;
a = b = rect.getWidth();
which is possibly cleaner and will surely don't cause such an error. A good rule of thumb is never to use pointers when possible. If you need to modify a variable inside a function just use a reference.
I add one double value from a file to a variable and push it into a vector, with format "338620.3478" , then after that I get the value from the vector, it just gets "338620", as it could not get all the double value.
So how can I get a full double value like the original format?
The Code:
struct Point {
double x, y;
bool operator <(const Point &p) const {
return x < p.x || (x == p.x && y < p.y);
}
};
ifstream iFile("griddata.dat"); //read a file (grid)
string line;
Point Grid; /
while(getline(iFile,line))
{
unsigned pos = line.find(",");//the symbol is used to separate X and Y
std::string strs = line.substr(0,pos); // get X
std::string strs2 = line.substr(pos+1); // get Y
Grid.x = atof(strs.c_str()); // get the first cooordinate X
Grid.y = atof(strs2.c_str()); // get the second cooordinate Y
// A list of coordinates of grid is stored into the vector gridPoints
gridPoints.push_back(Grid); // adding the points of grid to vector
}
int j;
for(j=0;j<gridPoints.size();j++)
{
//here i cannot get the full double value for gridPoints[j].x;
//....it just gets "338620"
}
The format of file (griddata.dat):
338620.3478,6196150.566
Thank you!
Assuming that your Point class is in the windows framework, I'm pretty sure it's members are int types.
Either way, your values are being cast to a type that isn't floating point and is being truncated.
I think your problem is retrieving the values (maybe with cout?? -->then you can use: cout.precision(15))
see: How do I print a double value with full precision using cout?
I've implemented a 3D strange attractor explorer which gives float XYZ outputs in the range 0-100, I now want to implement a colouring function for it based upon the displacement between two successive outputs.
I'm not sure of the data structure to use to store the colour values for each point, using a 3D array I'm limited to rounding to the nearest int which gives a very coarse colour scheme.
I'm vaguely aware of octtrees, are they suitable in this siutation?
EDIT: A little more explanation:
to generate the points i'm repeatedly running this:
(a,b,c,d are random floats in the range -3 to 3)
x = x2;
y = y2;
z = z2;
x2 = sin(a * y) - z * cos(b * x);
y2 = z2 * sin(c * x) - cos(d * y);
z2 = sin(x);
parr[i][0]=x;
parr[i][1]=y;
parr[i][2]=z;
which generates new positions for each axis each run, to colour the render I need to take the distance between two successive results, if I just do this with a distance calculation between each run then the colours fade back and forth in equilibrium so I need to take running average for each point and store it, using a 3dimenrsionl array is too coarse a colouring and I'm looking for advice on how to store the values at much smaller increments.
Maybe you could drop the 2-dim array off and use an 1-dim array of
struct ColoredPoint {
int x;
int y;
int z;
float color;
};
so that the code would look like
...
parr[i].x = x;
parr[i].y = y;
parr[i].z = z;
parr[i].color = some_computed_color;
(you may also wish to encapsulate the fields and use class ColoredPoint with access methods)
I'd probably think bout some kind of 3-d binary search tree.
template <class KEY, class VALUE>
class BinaryTree
{
// some implementation, probably available in libraries
public:
VALUE* Find(const KEY& key) const
{
// real implementation is needed here
return NULL;
}
};
// this tree nodes wil actually hold color
class BinaryTree1 : public BinaryTree<double, int>
{
};
class BinaryTree2 : public BinaryTree<double, BinaryTree1>
{
};
class BinaryTree3 : public BinaryTree<double, BinaryTree2>
{
};
And you function to retreive the color from this tree would look like that
bool GetColor(const BinaryTree3& tree, double dX, double dY, double& dZ, int& color)
{
BinaryTree2* pYTree = tree.Find(dX);
if( NULL == pYTree )
return false;
BinaryTree1* pZTree = pYTree->Find(dY);
if( NULL == pZTree )
return false;
int* pCol = pZTree->Find(dZ);
if( NULL == pCol )
return false;
color = *pCol;
return true;
}
Af course you will need to write the function that would add color to this tree, provided 3 coordinates X, Y and Z.
std::map appears to be a good candidate for base class.