共享指针的多态行为

Question

我是shared_ptr struff的新手。所以这可能是一个愚蠢的问题，但我不知道我得到的错误。

#include<iostream>
#include<vector>
#include<memory>
#include<algorithm>
using namespace std;

class base
{
    public:
           base() { cout<<"  base::ctor "<<endl; }
           virtual void print() { cout<<"  base::print "<<endl; }
           virtual ~base() { cout<<"  base::dtor "<<endl; }
};

class derived : public base
{
    public:
           derived() { cout<<"  derived:ctor "<<endl; }
           void print() { cout<<"  derived::print "<<endl; }
           ~derived() { cout<<"  derived::dtor "<<endl; }
};

typedef shared_ptr<base> sPtr;

int main()
{
    vector<sPtr> v;
    v.push_back(make_shared<derived>());
    cout<<endl;
    v.push_back(make_shared<derived>());
    cout<<endl;
//    for_each(v.begin(), v.end(), [](sPtr sp) { sp.print(); });
    for(auto elem : v)
        elem.print();
    return 0;
}

错误：

sharedPtr.cpp: In function ‘int main()’:
sharedPtr.cpp:34:14: error: ‘class std::shared_ptr<base>’ has no member named ‘print’
         elem.print();
              ^

由于理解有限，elem应该是类型＆＃34; base＆＃34;的共享指针，应该调用派生类的打印，因为它是一个虚函数。

此代码有什么问题？