Segfault when trying to access a boolean inside of a class - c++

Question

const int PIXEL_WIDTH = 10;
const int PIXEL_HEIGHT = 10;
const int WORLD_X = 64; //WORLD_X * PIXEL WIDTH = SCREEN_WIDTH if you want the world to be the same size as the screen
const int WORLD_Y = 64;
enum Pixel_Types {
AIR,
WALL,
DIRT,
STONE
};
class Pixel
{
int x, y;
bool affected_by_gravity;
Pixel_Types type;
public:
Pixel() : affected_by_gravity(false), type(AIR), x(0), y(0) {}
Pixel(int temp_x, int temp_y) : affected_by_gravity(false), type(AIR), x(temp_x), y(temp_y) {}
int getX() { return x; } //x is 0-63, scales up in the rendering code
int getY() { return y; } //y is 0-63, scales up in the rendering code
int getScreenX() { return x*PIXEL_WIDTH; } //x is 0-63, scales up in the rendering code
int getScreenY() { return y*PIXEL_HEIGHT; } //y is 0-63, scales up in the rendering code
bool setDeltaX(int temp_delta_x);
bool setDeltaY(int temp_delta_y);
void setAffectedByGravity(bool yesorno) { affected_by_gravity = yesorno; }
bool getAffectedByGravity() { return affected_by_gravity; }
Pixel_Types getType() { return type; }
void setType(Pixel_Types what_type) { type = what_type; }//if (type == DIRT or type == STONE) { affected_by_gravity = true; } }
};
std::vector<Pixel> world; //the world is a dynamically allocated thing
Pixel* getPixelFromCoordinates(int x, int y)
{
if (x > 63) x = 63;
else if (x < 0) x = 0;
if (y > 63) y = 63;
else if (y < 0) y = 0;
for (int pixel_index = 0; pixel_index < world.size(); pixel_index++) {
if (world.at(pixel_index).getX() == x && world.at(pixel_index).getY() == y) {
return &world.at(pixel_index);
}
}
return NULL;
}
bool Pixel::setDeltaX(int temp_delta_x) {
if (x+temp_delta_x > SCREEN_WIDTH/PIXEL_WIDTH or x+temp_delta_x < 0) {
return false;
}
if (getPixelFromCoordinates(x+temp_delta_x, y)->type == AIR) {
x += temp_delta_x;
return true;
}
return false;
}
bool Pixel::setDeltaY(int temp_delta_y) {
if (y+temp_delta_y > SCREEN_HEIGHT/PIXEL_HEIGHT or y+temp_delta_y < 0) {
return false;
}
if (getPixelFromCoordinates(x, y+temp_delta_y)->type == AIR) {
y += temp_delta_y;
return true;
}
return false;
}
void generateWorld()
{
for (int world_generation_index = 0; world_generation_index < 4096; world_generation_index++) {
int x = world_generation_index % WORLD_X; //the world is 64 pixels left and right, and 64 up and down. this math is pretty easy and just extrapolates that. also each pixel is 10 pixels across, times 64 pixels = 640 (the resolution)
int y = floor(world_generation_index / WORLD_Y); //both x and y start at 0
world.push_back(Pixel(x, y));
if (x == 0 || x == 63) {
world.at(world_generation_index).setType(WALL);
}
if (y == 1) {
world.at(world_generation_index).setType(WALL);
}
}
std::cout << "World size: " << world.size() << std::endl;
}
void createPixel(int x, int y, Pixel_Types type)
{
std::cout << x << std::endl;
std::cout << y << std::endl << std::endl;
y = (SCREEN_HEIGHT / PIXEL_HEIGHT) - y; //compensate for the stupid inverted y in opengl
//if (getPixelFromCoordinates(x, y)->getType() == AIR) {
getPixelFromCoordinates(x, y)->setType(type);
//}
}
void physicsOneStep()
{
for (int pixel_index = 0; pixel_index < world.size(); pixel_index++) {
if (world.at(pixel_index).getType() == DIRT or world.at(pixel_index).getType() == STONE) {//if (world.at(pixel_index).getAffectedByGravity()) {
world.at(pixel_index).setDeltaY(-1);
//std::cout << world.at(pixel_index).getX() << std::endl;
//std::cout << world.at(pixel_index).getY() << std::endl << std::endl;
}
}
}
So when I try to run this code (part of a larger project) it occasionally gives me a Segfault on calling setType(DIRT) from within createPixel(). I know that the values provided to createPixel() are within the range that they are allowed to be (0 to 64). It seems to segfault if you click (which calls createPixel()) in the same spot twice. The line that the debugger says segfaults is
void setType(Pixel_Types what_type) { type = what_type; }
though, I've verified that the values that I have supplied to this are correct.

Answer 1

Since there is no dynamic allocation inside the class, having a segfault on such an allocation most certainly occur because the this pointer itself is incorrect (NULL or badly allocated). You should get up the traceback when it segfaulted to see how the object on which you called setType was allocated. For example, shouldn't the line
world.push_back(Pixel(x, y));
be
world.push_back(new Pixel(x,y));
?