C++ 当对虚拟基类使用boost序列化时,是什么原因导致C4250(类通过支配地位继承成员)?
VC++编译器警告“class1”的含义:通过支配地位继承“class2::member”,我很清楚。但请看一个解释 我目前的问题是,当使用boost::serialization 1.44.0序列化具有抽象基类的类层次结构时,会收到此警告 请注意,我的类不会形成任何可能导致此警告的菱形继承层次结构,但此警告是由序列化派生类实例时的boost::detail::is_virtual_base_of_impl实例化引起的。这似乎是使用Boost.TypeTraits 下面是在VisualStudio2005上重现警告的最小代码示例。请注意,代码应按原样放入一个cpp文件中,并进行编译 还要注意我在代码中用触发警告的注释标记的两点。如果未使用BOOST_CLASS_exportd,则不会触发警告,但更有趣的是,如果派生类未使用虚拟继承,则也不会触发警告!所以也许我根本不懂C4250C++ 当对虚拟基类使用boost序列化时,是什么原因导致C4250(类通过支配地位继承成员)?,c++,visual-c++,boost,boost-serialization,typetraits,C++,Visual C++,Boost,Boost Serialization,Typetraits,VC++编译器警告“class1”的含义:通过支配地位继承“class2::member”,我很清楚。但请看一个解释 我目前的问题是,当使用boost::serialization 1.44.0序列化具有抽象基类的类层次结构时,会收到此警告 请注意,我的类不会形成任何可能导致此警告的菱形继承层次结构,但此警告是由序列化派生类实例时的boost::detail::is_virtual_base_of_impl实例化引起的。这似乎是使用Boost.TypeTraits 下面是在VisualStudi
// -- std includes --
#include <iostream>
#include <sstream>
#include <string>
// -- boost serialization --
#define BOOST_SERIALIZATION_DYN_LINK
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/export.hpp>
// Base with serialization support
struct Base
{
virtual ~Base() {};
virtual void DoStuff() const {
std::cout << "Base@[" << static_cast<const void*>(this) << "]::DoStuff() called\n";
}
template<class Archive> // serialization support!
void serialize(Archive & ar, const unsigned int file_version) { /*empty*/ }
};
// (The only) Specific class with ser. support
struct Concrete2 : virtual/*!C4250!*/ public Base
{
virtual void DoStuff() const {
std::cout << "Concrete2@[" << static_cast<const void*>(this) << "]::DoStuff() called\n";
}
template<class Archive> // serialization support!
void serialize(Archive & ar, const unsigned int ver) {
ar & boost::serialization::base_object<Base>(*this);
// This is just a test - no members neccessary
std::cout << "Concrete2::serialize!" << typeid(ar).name() << "\n";
}
};
// Without guid export -> *no* C4250, even *with* virtual inheritance
// (however, can't be serialized via base class pointer anymore)
BOOST_CLASS_EXPORT(Concrete2);
BOOST_CLASS_TRACKING(Concrete2, boost::serialization::track_never);
int main() {
using namespace std;
Concrete2 obj1;
obj1.DoStuff();
// The following test code is not neccessary to generate the warning ...
// (but is neccessary to show if base-pointer serialization works at runtime)
Base* ref1 = &obj1;
ostringstream out_buf;
boost::archive::text_oarchive out_archive(out_buf);
out_archive << ref1;
const string buf = out_buf.str();
cout << "Serialized obj:\n~~~~\n";
cout << buf;
cout << "\n~~~~~\n";
std::istringstream in_buf(buf);
boost::archive::text_iarchive in_archive(in_buf);
// Concrete2 obj2;
Base* ref2;
in_archive >> ref2;
if(ref2)
ref2->DoStuff();
delete ref2;
}
下面是编译器警告:啊
1>...\boost_library-1_44_0\boost\type_traits\is_virtual_base_of.hpp(61) : warning C4250: 'boost::detail::is_virtual_base_of_impl<Base,Derived,tag>::X' : inherits 'Concrete2::Concrete2::DoStuff' via dominance
1> with
1> [
1> Base=type,
1> Derived=Concrete2,
1> tag=boost::mpl::bool_<true>
1> ]
1> ...\boostserializewarningtest\vbc.cpp(27) : see declaration of 'Concrete2::DoStuff'
...
1> ...\boost_library-1_44_0\boost\mpl\eval_if.hpp(40) : see reference to class template instantiation 'boost::mpl::if_<T1,T2,T3>' being compiled
1> with
1> [
1> T1=boost::is_virtual_base_of<type,Concrete2>,
1> T2=boost::mpl::identity<boost::serialization::void_cast_detail::void_caster_virtual_base<Concrete2,type>>,
1> T3=boost::mpl::identity<boost::serialization::void_cast_detail::void_caster_primitive<Concrete2,type>>
1> ]
1> ...\boost_library-1_44_0\boost\serialization\void_cast.hpp(279) : see reference to class template instantiation 'boost::mpl::eval_if<C,F1,F2>' being compiled
1> with
1> [
1> C=boost::is_virtual_base_of<type,Concrete2>,
1> F1=boost::mpl::identity<boost::serialization::void_cast_detail::void_caster_virtual_base<Concrete2,type>>,
1> F2=boost::mpl::identity<boost::serialization::void_cast_detail::void_caster_primitive<Concrete2,type>>
1> ]
1> ...\boost_library-1_44_0\boost\serialization\base_object.hpp(68) : see reference to function template instantiation 'const boost::serialization::void_cast_detail::void_caster &boost::serialization::void_cast_register<Derived,Base>(const Derived *,const Base *)' being compiled
1> with
1> [
1> Derived=Concrete2,
1> Base=type
1> ]
...
1> ...\boost_library-1_44_0\boost\serialization\export.hpp(128) : while compiling class template member function 'void boost::archive::detail::`anonymous-namespace'::guid_initializer<T>::export_guid(boost::mpl::false_) const'
1> with
1> [
1> T=Concrete2
1> ]
1> ...\boostserializewarningtest\vbc.cpp(40) : see reference to class template instantiation 'boost::archive::detail::`anonymous-namespace'::guid_initializer<T>' being compiled
1> with
1> [
1> T=Concrete2
1> ]
原因是事实上,这是来自助推类型特征的检查的虚拟基础。如果检查成功,此检查结构将生成警告C4250,如本例所示:
...
struct base {
virtual void mf() { };
};
struct derived_normal : public base {
virtual void mf() { };
};
struct derived_virt : virtual public base {
virtual void mf() { };
};
int main() {
using namespace std;
cout << "boost::is_virtual_base_of<base, derived_normal>::value reports: ";
// The following line DOES NOT cause C4250
cout << boost::is_virtual_base_of<base, derived_normal>::value << endl;
cout << "boost::is_virtual_base_of<base, derived_virt> reports: ";
// The following line causes C4250:
cout << boost::is_virtual_base_of<base, derived_virt>::value << endl;
...
#pragma warning( push )
#pragma warning( disable : 4250 ) // C4250 - 'class1' : inherits 'class2::member' via dominance
#include ...
#pragma warning( pop ) // C4250