从构造函数初始化列表传递 [英] passing this from constructor initializer list

问题描述

在以下代码中将this传递给初始化器列表中的另一个对象时，是否有任何问题？

Are there any issues when passing 'this' to another object in the initializer list in the following code?

class Callback { public: virtual void DoCallback() = 0; }; 

class B
{
    Callback& cb;
public:
    B(Callback& callback) : cb(callback) {}
    void StartThread();

    static void Thread() 
    {
        while (!Shutdown())
        {
            WaitForSomething();
            cb.DoCallback();
        }
     }
};

class A : public Callback
{
    B b;
public:
    A() : b(*this) {b.StartThread();}
    void DoCallback() {} 
};

如果这样做不安全，最好的选择是什么？

If it is unsafe to do that, what's the best alternative?

推荐答案

如果你非常小心，这将工作正常。如果你开始调用虚方法或使用依赖于类型中其他对象的方法，你会遇到很多麻烦。但是如果你只是设置一个引用，这应该工作正常。

If you are extremely careful this will work fine. You will get into a lot of trouble if you start calling virtual methods or using methods which depend on other objects in the type. But if you're just setting a reference this should work fine.

一个更安全（但不完全安全）的替代方法是一旦构造函数完成后再设置b。这不会消除vtable问题，但会消除在构建之前访问其他成员变量的问题。

A safer (but not completely safe) alternative is to set b later on once the constructor is completed. This won't eliminate vtable issues but will remove problems like accessing other member variables before they are constructed.

class A : public Callback {
  std::auto_ptr<B> spB;
public:
  A() {
    spB.reset(new B(this));
    spB->StartThread();
  }
};

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