将shared_ptr与多继承类一起使用

Question

我有一个继承两个接口的类:

class Multi : public IFoo, public IBar {
public:
  virtual ~Multi();

  // Foo part
  virtual void fooMethod();
  // ...

  // Bar part
  virtual void barMethod();
  // ...
};

不幸的是,这个类不能在每个接口的两个单独的类中分解.事实上,在类实现中,这些实体(Foo和Bar)紧密耦合,但将来它们可能会分开.

另一个类想要使用Multi类,有一个指向IFoo和IBar的指针:

class ClientClass {
    public:
       ClientClass(); // constructor
       // smth
    private:
       std::shared_ptr<IFoo> foo_;
       std::shared_ptr<IBar> bar_;
};

在构造函数中,我做了类似的事情:

ClientClass::ClientClass(){
    auto pMulti = new Multi;
    foo_ = std::shared_ptr<IFoo>(pMulti);
    bar_= std::shared_ptr<IBar>(pMulti);  
}

但是每个共享指针都有单独的引用计数器,它会导致在类破坏时删除已经删除的指针,对不对？

1. 我该怎么对待它？
2. 这种情况的最佳实践是什么？

Answer 1

ClientClass::ClientClass()
{
    auto pMulti = std::make_shared<Multi>();
    foo_ = pMulti;
    bar_ = pMulti;  
}

将确保他们有相同的参考计数器.你可以自己看看:

#include <iostream>
#include <memory>

class Base1{};
class Base2{};
class Derived : public Base1, public Base2 {};

int main()
{
    auto derived = std::make_shared<Derived>();
    std::shared_ptr<Base1> base1 = derived;
    std::shared_ptr<Base2> base2 = derived;

    std::cout << "base1 usecount = " << base1.use_count() << '\n';
    std::cout << "base2 usecount = " << base2.use_count() << '\n';
    std::cout << "derived usecount = " << derived.use_count() << '\n';

    return 0;
}

生产:

base1 usecount = 3
base2 usecount = 3
derived usecount = 3