Array data is 'lost' after passing the array to another object - c++

Question

I'm having a problem where the objects in my array are lost when I pass the array through a constructor. My first guess was that I needed to change it to an array of pointers but that resulted in a segfault. My next guess was that I needed to copy the array data after passing it but that also didn't work. Here's the problem code:
Universe Object:
class Universe {
public:
Star stars[]; int starsLength;
Planet planets[]; int planetsLength;
public:
Universe(Star st[], int stl, Planet pl[], int pll) {
stars < st; starsLength = stl;
planets < pl; planetsLength = pll;
}
Universe() {
}
public:
void render() {
for(int i = 0;i < starsLength;i++) {
//std::cout << "STAR: " << stars[i].location.x << "," << stars[i].location.y << " " << stars[i].size << " " << stars[i].color.r << "," << stars[i].color.g << "," << stars[i].color.b << "\n";
renderCircle(stars[i].location, stars[i].size, stars[i].color);
}
for(int i = 0;i < planetsLength;i++) {
renderCircle(planets[i].location, planets[i].size, planets[i].color);
}
}
void renderCircle(Point location, float size, Color color) {
glBegin(GL_LINES);
glColor3f(color.r,color.g,color.b);
glVertex2f(location.x+size, location.y+size);
glVertex2f(location.x-size, location.y-size);
glVertex2f(location.x-size, location.y+size);
glVertex2f(location.x+size, location.y-size);
glEnd();
}
};
Method that creates the Universe and gives it the array:
Universe buildUniverse(int size, int seed) {
Point bounds = Point{static_cast <float> (size),static_cast <float> (size)}; //0,0 to size,size
int starCount = min(size/10,random(size/5));
int planetCount = min(size/3,random(size));
Star stars[starCount];
Planet planets[planetCount];
//std::cout << "-- Created " << starCount << " stars and " << planetCount << " planets...\n";
for(int i = 0;i < starCount;i++) {
Point location = {random(bounds.x),random(bounds.y)};
Point velocity = {random(bounds.x/100.0f),random(bounds.y/100.0f)};
float size = random(bounds.x/100.0f);
float mass = random(size*(random(1.0f)+0.5f));
Color color = {1.0f,1.0f,1.0f};
stars[i].setStar(location,velocity,size,mass,color);
}
for(int i = 0;i < planetCount;i++) {
Point location = {random(bounds.x),random(bounds.y)};
Point velocity = {random(bounds.x/100.0f),random(bounds.y/100.0f)};
float size = random(bounds.x/100.0f);
float mass = random(size*(random(1.0f)+0.5f));
Color color = {random(1.0f),random(1.0f),random(1.0f)};
planets[i].setPlanet(location,velocity,size,mass,color);
}
Universe uni = {stars, starCount, planets, planetCount};
std::cout << "Star in array: " << stars[0].location.x << "," << stars[0].location.y << " " << stars[0].size << " " << stars[0].color.r << "," << stars[0].color.g << "," << stars[0].color.b << "\n";
std::cout << "Star passed to uni in an array: " << uni.stars[0].location.x << "," << uni.stars[0].location.y << " " << uni.stars[0].size << " " << uni.stars[0].color.r << "," << uni.stars[0].color.g << "," << uni.stars[0].color.b << "\n";
return uni;
}
Output of of the program:
Building universe...
Star in array: 39.922,39.155 0.167611 1,1,8.85715e-39
Star passed to uni in an array: 7.00649e-45,2.24208e-44 0.0282954 5.90446e-39,1.4013e-45,1.4013e-45
Initializing threaded renderer...
Starting simulation...
What am I doing wrong?

Answer 1

First, your code is not valid C++. Declaring empty arrays using [] does not exist in C++.
So the first thing is to turn this into valid C++ that still preserves what you're trying to accomplish. One solution is to use std::vector:
#include <vector>
class Universe {
public:
std::vector<Star> stars;
std::vector<Planet> planets;
public:
Universe(const std::vector<Star>& st,
const std::vector<Planet>& pl) : stars(st), planets(pl) {}
};
Note the replacement of the non-C++ code with std::vector. Also note that we initialize the vectors using the initializer-list.
Last, note that we no longer need to keep the sizes as separate member variables. Why? Because a vector knows its size by calling the vector::size() member function. For example:
for(int i = 0;i < starsLength;i++) {
can be replaced with
for(int i = 0;i < stars.size();i++) {
In your buildUniverse function, use the following changes:
Universe buildUniverse(int size, int seed) {
Point bounds = Point{static_cast <float> (size),static_cast <float> (size)}; //0,0 to size,size
int starCount = min(size/10,random(size/5));
int planetCount = min(size/3,random(size));
std::vector<Star> stars(starCount);
std::vector<Planet> planets(planetCount);
//...
Universe uni(stars, planets);
The rest of the code stays the same. Now, if after the call to create the Universe, you see that the vectors didn't pass the correct information, then look further. The code above conforms to "normal" C++, such that we can go further and figure out the issue.