如何打印shared_ptr类？

Question

如何打印shared_ptr？我必须通过“void print”打印 sp1 和 sp2，但我不知道该怎么做。这是代码

struct MediaAsset
{
    virtual ~MediaAsset() = default; // make it polymorphic
};

struct Song : public MediaAsset
{
    std::string artist;
    std::string title;
    Song(const std::string& artist_, const std::string& title_) :
        artist{ artist_ }, title{ title_ }
    {
        std::cout << "Song " << artist_ << " - " << title_ << " constructed\n";
    }

    ~Song()
    {
        std::cout << "~Song " << artist << " - " << title << " destructed\n";
    }

    void print()
    {
        //Complete to show information about the current object
    }
};
using namespace std;

void example1()
{
    auto sp1 = make_shared<Song>("poets","carnival");
    shared_ptr<Song> sp2(new Song("poets","late goodbye") );
    sp1.print();
    sp2.print();

}

我写了

 void print()
    {
        std::cout << "artist " << artist << " - " << "title" << title << " end\n";
    }

这是我运行程序时收到的消息

错误：“类 std::shared_ptr”没有名为“print”的成员

Answer 1

print()

不是

shared_ptr

的方法。您需要取消引用

shared_ptr

才能访问

Song

对象，例如：

auto sp1 = make_shared<Song>("poets","carnival");
shared_ptr<Song> sp2(new Song("poets","late goodbye") );
sp1->print();
sp2->print();

或者：

auto sp1 = make_shared<Song>("poets","carnival");
shared_ptr<Song> sp2(new Song("poets","late goodbye") );
(*sp1).print();
(*sp2).print();