构造函数执行顺序

父类-> 类成员变量（按申明的前后顺序） -> 自己
析构相反。

class A1
{
public:
    A1(){
        cout<<"A1 construct"<<endl;
    }
    ~A1(){
        cout<<"A1 deconstruct"<<endl;
    }
};

class A2
{
public:
    A2(){
        cout<<"A2 construct"<<endl;
    }
    ~A2(){
        cout<<"A2 deconstruct"<<endl;
    }
};

class B
{
public:
    B(){
        cout<<"B construct"<<endl;
    }
    ~B(){
        cout<<"B deconstruct"<<endl;
    }
    A1 a1;
    A2 a2;
};

int main()
{
    B b;
    return 0;
}

输出：

A1 construct
A2 construct
B construct
B deconstruct
A2 deconstruct
A1 deconstruct

Process finished with exit code 0

可以利用这个特性对OpenGL与gl-Tools（比如glfw，EGL等）进行状态管理。