C++ 为什么同一个变量的值不同？

Question

我有类 Sphere 和 Triangle，它们都是 Intersectable 的子类。 Intersectable 有一个公共(public)成员变量colour。考虑以下代码片段:

float t_min = 100000.0f;
pair<float, f3Vector> point_hit;
Intersectable * object_hit;
Triangle triangle;
Sphere sphere_trans;
bool hit = false;

//loop through triangles
for(unsigned int i = 0; i < mesh->tvi.size(); i++){
    ...

    triangle = Triangle((fRGB)mesh->color[mesh->tci[i].c0], va.toVector3(), vb.toVector3(), vc.toVector3());
    point_hit = triangle.intersect(orig, dir, c_near, c_far);

    if(point_hit.first != 0.0f && point_hit.first < t_min){
        object_hit = &triangle;
        std::cout << "color1 " << object_hit->color << std::endl;
hit = true;
        ...
    }
}

// loop through spheres
for(unsigned int j = 0; j < spheres.size(); j++){
    ...

    sphere_trans = Sphere(sphere.color, center3, sphere.getRadius());
    point_hit = sphere_trans.intersect(orig, dir, c_near, c_far);

    if(point_hit.first != 0 && point_hit.first < t_min){
        object_hit = &sphere_trans;
        std::cout << "color1 " << object_hit->color << std::endl;
hit = true;
        ...
    }
}

if(hit){
    std::cout << "color2 " << object_hit->color << std::endl;
}

我期望如果我有 color1 (1 0 0) 类型的输出，并且下一个输出是 color2 (...) 的值> 打印出来的颜色应该是一样的。但是，这不会发生。事实上，对于 color2 (...)，我总是得到相同的输出。你能告诉我我做错了什么吗？谢谢!

Answer 1

让我们把它瘦一点...

Intersectable * object_hit;
Sphere sphere_trans;

// loop through spheres
for(unsigned int j = 0; j < spheres.size(); j++)
{
    ...  
    sphere_trans = Sphere(sphere.color, center3, sphere.getRadius());

    if(some condition)
    {
        object_hit = &sphere_trans;
        ...    
    }
}

现在，当满足条件时，object_hit 指向 sphere_trans。但下一次循环时，sphere_trans 被分配了一个新对象。所以，当然，object_hit 现在也指向新对象，这可能不是您想要的。

最好的方法是让 object_hit 成为对象而不是指针。或者只是将索引保存到数组中。