在C++中将对象传递给另一个类的构造函数时遇到问题

class A {
public:
    A(const std::string& name) : name_(name) {}
private:
    std::string name_;
};

class B {
public:
    B(const A& a) : a_(a) {}
private:
    A a_;
};

#include<memory>

class A {
public:
    A(const std::string& name) : name_(name) {}
private:
    std::string name_;
};

class B {
public:
    B(std::shared_ptr<A> a) : a_(a) {}
private:
    std::shared_ptr<A> a_;
};

class A {
public:
    A(const std::string& name) : name_(name) {}
    virtual ~A() = default;
private:
    std::string name_;
};

class B : public A {
public:
    B(const std::string& name) : A(name) {}
};

class C {
public:
    C(A* a) : a_(a) {}
private:
    A* a_;
};

template<typename T>
class C {
public:
    C(const T& t) : t_(t) {}
private:
    T t_;
};

class A {
public:
    A(const std::string& name) : name_(name) {}
private:
    std::string name_;
};

class B {
public:
    B(const std::string& name) : name_(name) {}
private:
    std::string name_;
};

int main() {
    A a("A");
    B b("B");
    C<A> c1(a);
    C<B> c2(b);
    return 0;
}