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The Kraken's questions

Martin Hope
The Kraken
Asked: 2024-10-07 18:45:04 +0800 CST
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我想要一个具有公共只读访问权限并可在私有上下文中编辑的类变量。在之前的 Stackoverflow问题中，它被描述为使用 const 引用。然而对我来说，这会导致奇怪的行为。

    class Vec3 {
    public:
        double x, y, z;
        Vec3(double x, double y, double z) : x(x), y(y), z(z) {}
        Vec3() : x(0), y(0), z(0) {}
    };
    
    std::ostream& operator<<(std::ostream& os, const Vec3& a) {
        os << "(" << a.x << ", " << a.y << ", " << a.z << ")";
        return os;
    }
    
    class Triangle3 {
    private:
        Vec3 _a, _b, _c;
    public:
        Triangle3(const Vec3& a, const Vec3& b, const Vec3& c) : _a(a), _b(b), _c(c) {}
        Triangle3() : _a(Vec3()), _b(Vec3()), _c(Vec3()) {}
    
        const Vec3& a = _a;
        const Vec3& b = _b;
        const Vec3& c = _c;
    };
    
    std::ostream& operator<<(std::ostream& os, const Triangle3& a) {
        os << "(" << a.a.x << ", " << a.a.y << ", " << a.a.z << "), ";
        os << "(" << a.b.x << ", " << a.b.y << ", " << a.b.z << "), ";
        os << "(" << a.c.x << ", " << a.c.y << ", " << a.c.z << ")";
        return os;
    }

    class Mesh {
    public:
        std::vector<Triangle3> triangles;
        Mesh(std::vector<Triangle3> triangles) : triangles(triangles) {}
        Mesh() {}
    };

    int main (int argc, char** argv) {
        std::vector<Triangle3> triangles;
        int N = 10;
        for (int i = 0; i < N; i++) {
                triangles.push_back(Triangle3(Vec3(i, i, i), Vec3(i, i, i), Vec3(i, i, i)));
        }
        std::cout << "Triangle 0: " << triangles[0] << std::endl;
        Mesh mesh(triangles);
        std::cout << "Triangle 0: " << mesh.triangles[0] << std::endl;
    }

该程序输出：

Triangle 0: (9, 9, 9), (9, 9, 9), (9, 9, 9)
Triangle 0: (4.03359e-316, 4.03364e-316, 4.03364e-316), (9, 9, 9), (9, 9, 9)

valgrind --leak-check=full -s 返回时没有错误或警告。

然后重写 Triangle3 类以不使用 const 引用：

class Triangle3 {
private:
public:
    Vec3 a, b, c;
    Triangle3(const Vec3& a, const Vec3& b, const Vec3& c) : a(a), b(b), c(c) {}
    Triangle3() : a(Vec3()), b(Vec3()), c(Vec3()) {}
};

这将返回正确的结果：

Triangle 0: (0, 0, 0), (0, 0, 0), (0, 0, 0)
Triangle 0: (0, 0, 0), (0, 0, 0), (0, 0, 0)

有人知道是什么原因造成的吗？我严重怀疑 const 引用没有像宣传的那样工作，但为什么呢？

c++