C ++：使用typeinfo测试类继承 [英] C++: using typeinfo to test class inheritance

问题描述

我有一个指向多态类型的指针， p 。我也有一个 type_info 在同一层次中的某个类， ti 。

I have a pointer to a polymorphic type, p. I also have a type_info for a class somewhere in the same hierarchy, ti.

如果我只是比较 typeid（* p）== ti ，那么我可以在运行时测试指针是否指向一个直接实例。

If I just compare the typeid(*p) == ti, then I can test at runtime whether the pointer is pointing to a direct instance of that class.

是否有类似的方法使用C ++的RTTI来测试 * p inherits

Is there a similar way to use C++'s RTTI to test whether *p inherits from that class?

推荐答案

在标准C ++中没有办法做到这一点。如果您使用的实施包含 Itanium C ++ ABI ¹ ，你可以这样做，例如：

There's no way to do this in standard C++ alone. If you're using an implementation that has the Itanium C++ ABI¹ you can do this though, for example:

#include <iostream>
#include <typeinfo>
#include <cxxabi.h>
#include <memory>

class base {
protected:
  base() {
  }
public:
  static bool check(const std::type_info& p) {
    // Find the real type_info for single inheritance non virtual 
    const __cxxabiv1::__si_class_type_info* test = dynamic_cast<const __cxxabiv1::__si_class_type_info*>(&p);
    return test ? typeid(base) == *test->__base_type : false;
  }

  virtual ~base() {}
};

class der : public base {
};

class foo {};

int main() {
  der d;
  foo f;

  std::cout << base::check(typeid(d)) << "\n";
  std::cout << base::check(typeid(f)) << "\n";
}

在这里，这是因为类型有一个单一的非精确继承的基。你可以支持更多的情况，但要小心和类似 dynamic_casts 。

Here this works because the type has a single, non-virtuallly inherited base. You can support more cases though with care and similar dynamic_casts.

虽然这是可能的，你解决了错误的问题虽然 - 基于 std :: map 的解决方案是更便携，避免依赖于这样的实现细节。

Whilst this is possible under these certain circumstances I think you're solving the wrong problem though - a solution based around a std::map is more portable and avoids relying on implementation details like this.

¹ 混淆地命名，它是一个惊人的大型编译器/体系结构列表，而不仅仅是Itanium

¹ confusingly named, it's a surprisingly large compiler/architecture list, not just Itanium

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