将数组传递给另一个对象后，数组数据“丢失”

Question

我遇到一个问题，当我通过构造函数传递数组时，数组中的对象会丢失。我的第一个猜测是我需要将其更改为一个指针数组，但导致了段错误。我的下一个猜测是，我需要复制数组数据后通过它，但也没有工作。这里的问题代码：

Universe对象：

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(); 
    } 
}; 

方法，创造宇宙，并赋予它的数组：

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; 
} 

方案的输出：

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... 

我究竟做错了什么？

Answer 1

首先，你的代码是无效的C++。在C++中不存在使用[]声明空数组。

所以第一件事就是把它变成有效的C++，它仍然保留你想要完成的事情。一个解决方案是使用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) {} 
}; 

注更换非C++代码与std::vector。另请注意，我们使用initializer-list初始化矢量。

最后，请注意，我们不再需要将大小保持为单独的成员变量。为什么？因为矢量通过调用vector::size()成员函数来知道它的大小。例如：

for(int i = 0;i < starsLength;i++) { 

可以

for(int i = 0;i < stars.size();i++) { 

---

更换在你buildUniverse功能，请使用以下的变化：

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); 

代码的其余部分保持不变。现在，如果在创建Universe的呼叫之后，您看到矢量没有传递正确的信息，那么请进一步查看。上面的代码符合“正常”的C++，这样我们可以进一步找出问题。