Test of std::enable_shared_from_this

sharedPtrTest.c++

#include <memory>
#include <vector>
#include <iostream>

class Circle : public std::enable_shared_from_this<Circle> {
public:
    void setRadius(double r) {
        radius = r;
        if (radius < 1.0) {
            smallCircles.emplace_back(shared_from_this());
        }
    }

    static void printSmallCircles() {
        for (auto c: smallCircles) {
            std::cout << "radius=" << c->radius << std::endl;
        }
    }

private:
    double radius;

    static std::vector<std::shared_ptr<Circle>> smallCircles;
};
std::vector<std::shared_ptr<Circle>> Circle::smallCircles;

int main()
{
    auto a = std::make_shared<Circle>();
    a->setRadius(1.2);
    auto b = std::make_shared<Circle>();
    b->setRadius(0.9);
    auto c = std::make_shared<Circle>();
    c->setRadius(0.1);

    Circle::printSmallCircles();

    std::cout << "a.use_count=" << a.use_count() << std::endl;
    std::cout << "b.use_count=" << b.use_count() << std::endl;
    std::cout << "c.use_count=" << c.use_count() << std::endl;
}