type_info 指针可以用来区分 C++ 中的类型吗？

发布于 2024-11-29 07:43:23 字数 724 浏览 7 评论 0原文

我有一组多态 C++ 类，它们都由同一模块（Windows DLL）实例化。现在有两个指向此类的指针并调用了 typeid：

SomeCommonBase* first = ...; //valid pointer
SomeCommonBase* second = ...; //valid pointer
const type_info& firstInfo = typeid( first );
const type_info& secondInfo = typeid( second );

我可以比较检索到的 type_info 地址

if( &firstInfo == &secondInfo ) {
   //objects are of the same class
} else {
   //objects are of different classes
}

或使用 ==

if( firstInfo == secondInfo ) {
   //objects are of the same class
} else {
   //objects are of different classes
}

来检测对象是否属于 (完全一样）同一类还是不同类？当从同一模块内实例化对象时，是否保证可以工作？

原文

I have a set of polymorphic C++ classes and they are all instantiated by the same module (Windows DLL). Now having two pointers to such classes and having called typeid:

SomeCommonBase* first = ...; //valid pointer
SomeCommonBase* second = ...; //valid pointer
const type_info& firstInfo = typeid( first );
const type_info& secondInfo = typeid( second );

can I compare retrieved type_info addresses

if( &firstInfo == &secondInfo ) {
   //objects are of the same class
} else {
   //objects are of different classes
}

or use ==

if( firstInfo == secondInfo ) {
   //objects are of the same class
} else {
   //objects are of different classes
}

to detect whether objects are of (exactly) the same class or of different classes? Is it guaranteed to work when objects are instantiated from within the same module?

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尽揽少女心 2024-12-06 07:43:23

当我写这篇文章时，您的代码

SomeCommonBase* first = ...; //valid pointer
SomeCommonBase* second = ...; //valid pointer
type_info& firstInfo = typeid( first );
type_info& secondInfo = typeid( second );

不应该编译，因为 typeid 返回对 const 的引用。

更糟糕的是，您需要有关指针的类型信息。两个指针的类型均为 SomeCommonBase*，因此可以保证它们具有相同的类型。相反，询问有关所指向对象的类型信息。

也就是说，正如 @DeadMg 所说，您还需要使用 operator== 来比较类型信息对象。

C++ 标准没有解决动态库的问题。但在任何给定的 Windows 模块中，您都应该是安全的。

干杯&呵呵，

As I'm writing this, your code is

SomeCommonBase* first = ...; //valid pointer
SomeCommonBase* second = ...; //valid pointer
type_info& firstInfo = typeid( first );
type_info& secondInfo = typeid( second );

It should not compile because typeid returns a reference to const.

Worse, you are asking for type info about the pointers. Both pointers are of type SomeCommonBase*, so you're guaranteed that they are of the same type. Ask instead for type info about the pointed to objects.

That said, as @DeadMg remarked, you also need to use operator== to compare type info objects.

The C++ standard does not address the issue of dynamic libraries. But within any given Windows module you should be safe.

Cheers & hth.,

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