c++构造器中成员函数初始化

#include <iostream>using namespace std;class Circle {    double radius;public:    Circle (double r) : radius (r) {}    double area () {return radius*radius*3.1415926;}};class Cylinder {    Circle base;    double height;public:    Cylinder (double r, double h) : base (r), height (h) {}    double volume () {return base.area() * height;}};int main(int argc, char const *argv[]){    Cylinder foo (10, 2);    cout << "foo's volume: " << foo.volume() << endl;    return 0;}