从 'B *' 到 'std::shared_ptr<A>' 的函数式转换没有匹配的转换

No matching conversion for functional-style cast from 'B *' to 'std::shared_ptr<A>'

我有一个尝试初始化共享指针的简单应用程序。

#include <iostream>
#include <memory>
#include <algorithm>

class A {
public:
    A(){
        std::cout << "default ctor for A" << std::endl;
    }
    ~A(){
        std::cout << "default dtor for A" << std::endl;
    }
};

class B : A{
    B(){
        std::cout << "default ctor for B" << std::endl;
    }
    ~B(){
        std::cout << "default dtor for B" << std::endl;
    }
};



int main()
{

    auto ap = std::shared_ptr<A>(new B());
    
    return 0;
}

我遇到了错误

No matching conversion for functional-style cast from 'B *' to 'std::shared_ptr<A>'

在这一行 自动 ap = std::shared_ptr(新 B());

我做错了什么?

Class B 应该声明为

class B : public A{
public:
    B(){
        std::cout << "default ctor for B" << std::endl;
    }
    ~B(){
        std::cout << "default dtor for B" << std::endl;
    }
};