我可以将一个派生类转换为私有基类，使用C风格的转换吗？ [英] Can I cast a derived class to a private base class, using C-style cast?

问题描述

我可以这样做吗？

  class A {...} 
 
 class B：private A 
 {
 const A& foo（）const 
 {
 return *（（const A *）this）; 
} 
}; 
  

我可以从子类继承一个子类，并将其转换为它的公共版本基类？我可以在没有虚拟方法的情况下这样做吗？

我的猜测是肯定的，但我想确保它是安全的/可移植的。

<是的，您可以：§5.4/ 7的标准：

...下面的static_cast和reinterpret_cast操作
（可选地后跟一个const_cast操作）可以使用
执行显式类型转换的转换符号，即使基类
类型不可访问：

指向派生类类型的对象的指针或派生的
类型的左值可以被显式地转换为指针或对$ b $的引用分别为b明确的基类类型;

但是，请尝试不要，因为它违背了私人继承的目的。

Can I do this?

class A { ... };

class B : private A
{
    const A &foo() const
    {
        return *((const A *)this);
    }
};

Can I take a subclass that inherits privately from a base class and cast it to a public version of its base class? Can I do this without it having virtual methods?

My guess is yes, but I wanted to make sure it's safe / portable.

解决方案

Yes you can: §5.4/7 of the standard:

... the following static_cast and reinterpret_cast operations (optionally followed by a const_cast operation) may be performed using the cast notation of explicit type conversion, even if the base class type is not accessible:

a pointer to an object of derived class type or an lvalue of derived class type may be explicitly converted to a pointer or reference to an unambiguous base class type, respectively;

But try not to as it defeats the purpose of private inheritance.

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