好的,所以我在使用谷歌(http://uscilab.github.io/cereal/)的C ++ 11中遇到了问题。
从抽象的意义上讲,我有一个大图,我用大量连接边和顶点的共享指针进行序列化。边(和顶点)也有附加属性。
现在,其中一个属性(基类)是一个帐户(子类)。帐户也继承自Idable,它也是可序列化的。现在这里有一些相关的代码片段,显示了我的一些谷类食用量。我会在这个背景下解释这个问题:
Attribute.hpp / CPP
class Attribute {
...
template<class Archive> void serialize(Archive&)
{
}
friend class cereal::access;
...
CEREAL_REGISTER_TYPE(mgraph::Attribute)
Idable.hpp / CPP
class Idable {
...
Id id;
template<class Archive> void serialize(Archive& archive)
{
archive(cereal::make_nvp("id", id));
}
template<class Archive> static void load_and_construct(Archive& ar, cereal::construct<mcommon::Idable>& construct)
{
mcommon::Id id;
ar(id);
construct(id);
}
friend class cereal::access;
...
CEREAL_REGISTER_TYPE(mcommon::Idable)
Position.hpp / CPP
class Position
: public mgraph::Attribute
, public mcommon::Displayable {
template<class Archive> void serialize(Archive& archive)
{
archive(cereal::make_nvp("Attribute",
cereal::base_class<mgraph::Attribute>(this)));
}
friend class cereal::access;
...
CEREAL_REGISTER_TYPE(mfin::Position)
Account.hpp / CPP
class Account
: public mcommon::Idable
, public Position {
...
Currency balance;
template<class Archive> void serialize(Archive& archive)
{
archive(cereal::make_nvp("Idable",
cereal::base_class<mcommon::Idable>(this)),
cereal::make_nvp("Position",
cereal::base_class<mfin::Position>(this)),
cereal::make_nvp("balance", balance));
}
template<class Archive> static void load_and_construct(Archive& ar, cereal::construct<Account>& construct)
{
mcommon::Id iden;
Currency::Code code;
ar(iden, code);
construct(iden, code);
}
friend class cereal::access;
...
CEREAL_REGISTER_TYPE(mfin::Account)
因此,当序列化mfin :: Account时会出现问题。 mfin :: Account属于std :: list&gt;。当我们进入Idable的序列化函数时,对象无效。
进入停止在段错误上的gdb我向这一行上面写了几个堆栈:/usr/include/cereal/types/polymorphic.hpp:341。这是:
(gdb) list
336
337 auto binding = bindingMap.find(std::type_index(ptrinfo));
338 if(binding == bindingMap.end())
339 UNREGISTERED_POLYMORPHIC_EXCEPTION(save, cereal::util::demangle(ptrinfo.name()))
340
341 binding->second.shared_ptr(&ar, ptr.get());
342 }
343
344 //! Loading std::shared_ptr for polymorphic types
345 template <class Archive, class T> inline
现在这就是ptr:
(gdb) print *((mfin::Account*)(ptr.get()))
$10 = {<mcommon::Idable> = {_vptr.Idable = 0x4f0d50 <vtable for mfin::Account+16>, id = "bank"}, <mfin::Position> = {<mgraph::Attribute> = {
_vptr.Attribute = 0x4f0d78 <vtable for mfin::Account+56>}, <mcommon::Displayable> = {_vptr.Displayable = 0x4f0da0 <vtable for mfin::Account+96>}, <No data fields>}, balance = {<mcommon::Displayable> = {
_vptr.Displayable = 0x4f0570 <vtable for mfin::Currency+16>}, amount = 0, code = mfin::Currency::USD}}
(gdb) print ptr
$11 = std::shared_ptr (count 3, weak 0) 0x758ad0
一切都很好看。但是当我把它投到虚空时注意*:
$11 = std::shared_ptr (count 3, weak 0) 0x758ad0
(gdb) print *((mfin::Account*)((void*)ptr.get()))
$12 = {<mcommon::Idable> = {_vptr.Idable = 0x4f0d78 <vtable for mfin::Account+56>,
id = "\363aL\000\000\000\000\000PbL\000\000\000\000\000\304\031L\000\000\000\000\000\021#L", '\000' <repeats 13 times>, " \232N", '\000' <repeats 21 times>, "P\251@\000\000\000\000\000\370\377\377\377\377\377\377\377 \232N", '\000' <repeats 21 times>, "\304\031L\000\000\000\000\000P\251@", '\000' <repeats 45 times>, "St19_Sp_counted_deleterIPN4mfin7AccountE"...}, <mfin::Position> = {<mgraph::Attribute> = {
_vptr.Attribute = 0x4f0570 <vtable for mfin::Currency+16>}, <mcommon::Displayable> = {_vptr.Displayable = 0x0}, <No data fields>}, balance = {<mcommon::Displayable> = {_vptr.Displayable = 0x0}, amount = 49,
code = (unknown: 7702648)}}
这当然是绑定中发生的事情 - &gt; second.shared_ptr(见下文),它取一个const void *。
(gdb) list
295 writeMetadata(ar);
296
297 #ifdef _MSC_VER
298 savePolymorphicSharedPtr( ar, dptr, ::cereal::traits::has_shared_from_this<T>::type() ); // MSVC doesn't like typename here
299 #else // not _MSC_VER
300 savePolymorphicSharedPtr( ar, dptr, typename ::cereal::traits::has_shared_from_this<T>::type() );
301 #endif // _MSC_VER
302 };
303
304 serializers.unique_ptr =
我使用麦片会导致什么问题?这是我得到的最后一个错误:
Program received signal SIGSEGV, Segmentation fault.
0x000000000040f7cd in rapidjson::Writer<rapidjson::GenericWriteStream, rapidjson::UTF8<char>, rapidjson::MemoryPoolAllocator<rapidjson::CrtAllocator> >::WriteString (this=0x7fffffffd358,
str=0x4f1ae0 <vtable for mfin::Account+96> "\363aL", length=4989722) at /usr/include/cereal/external/rapidjson/writer.h:276
276 if ((sizeof(Ch) == 1 || characterOk(*p)) && escape[(unsigned char)*p]) {
Missing separate debuginfos, use: debuginfo-install boost-date-time-1.55.0-8.fc21.x86_64 boost-filesystem-1.55.0-8.fc21.x86_64 boost-program-options-1.55.0-8.fc21.x86_64 boost-system-1.55.0-8.fc21.x86_64 boost-thread-1.55.0-8.fc21.x86_64 fcgi-2.4.0-24.fc21.x86_64 glog-0.3.3-3.128tech.x86_64 libgcc-4.9.2-1.fc21.x86_64 libstdc++-4.9.2-1.fc21.x86_64
答案 0 :(得分:2)
经过多次调查后,我相信我能解决问题。我相信这是图书馆的一个错误。在我与图书馆老板确认后,我会确保这是最新的结果。
我在下面制作了一个简单的程序来演示这个问题。该问题源于多重继承,多态和转换。在下面的程序中,我们创建了一个Derived对象。在内存中布局的Derived对象将具有大约。:
的格式Derived:
Base2::vtable
Base2::var
Base::vtable
考虑:
(gdb) print ptr
$2 = std::shared_ptr (count 1, weak 0) 0x63c580
(gdb) print *ptr
$3 = (Derived &) @0x63c580: {<Base2> = {_vptr.Base2 = 0x421f90 <vtable for Derived+16>, var = ""}, <Base> = {_vptr.Base = 0x421fa8 <vtable for Derived+40>}, <No data fields>}
现在当我们dynamic_pointer_cast它到Base时,我们有:
(gdb) print ptr
$8 = std::shared_ptr (count 2, weak 0) 0x63c590
(gdb) print *ptr
$9 = (Base &) @0x63c590: {_vptr.Base = 0x421fa8 <vtable for Derived+40>}
这就是问题的开始。现在在/usr/include/cereal/types/polymorphic.hpp,第341行。我们有这个ptr到Base。我们在这里:
binding->second.shared_ptr(&ar, ptr.get());
最终成为const void *的演员。稍后根据类型信息,我们将此类型从已注册的多态类型转换为类型。由于shared_ptr指向Derived类型的对象,因此这意味着Derived *。如下所示:
272 static inline void savePolymorphicSharedPtr( Archive & ar, void const * dptr, std::false_type /* has_shared_from_this */ )
273 {
274 PolymorphicSharedPointerWrapper psptr( dptr );
275 ar( CEREAL_NVP_("ptr_wrapper", memory_detail::make_ptr_wrapper( psptr() ) ) );
276 }
现在这意味着堆栈ptr是一个Base *被转换为void *然后转换为Derived *。因此,转换链导致无效对象。如下所示,ptr现在无效:
(gdb) print *ptr
$7 = (const Derived &) @0x63c590: {<Base2> = {_vptr.Base2 = 0x421fa8 <vtable for Derived+40>, var = <error reading variable: Cannot access memory at address 0x49>}, <Base> = {_vptr.Base = 0x0}, <No data fields>}
指针指向Base的vtable而不是Derived / Base2,因为它应该是程序崩溃:
{
"ptr": {
"polymorphic_id": 2147483649,
"polymorphic_name": "Derived",
"ptr_wrapper": {
"id": 2147483649,
"data": {
"Base2": {
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b8e9e3 in std::string::size() const () from /lib64/libstdc++.so.6
下面是一个重现这个的示例程序:
// g++ test.cpp -std=c++11 -ggdb -o test && gdb ./test
#include <cereal/archives/json.hpp>
#include <cereal/types/polymorphic.hpp>
#include <iostream>
struct Base {
virtual void foo() { }
template<class Archive> void serialize(Archive& archive) { }
};
struct Base2 {
virtual void foo() { }
std::string var;
template<class Archive> void serialize(Archive& archive) {
archive(cereal::make_nvp("var", var));
}
};
struct Derived : public Base2, public Base {
template<class Archive> void serialize(Archive& archive) {
archive(cereal::make_nvp("Base2",
cereal::base_class<Base2>(this)),
cereal::make_nvp("Base",
cereal::base_class<Base>(this)));
}
};
CEREAL_REGISTER_TYPE(Base);
CEREAL_REGISTER_TYPE(Base2);
CEREAL_REGISTER_TYPE(Derived);
int main() {
auto ptr = std::make_shared<Derived>();
cereal::JSONOutputArchive ar(std::cout);
ar(cereal::make_nvp("ptr", std::dynamic_pointer_cast<Base>(ptr)));
return 0;
}
答案 1 :(得分:0)
我想我遇到了类似的问题。一些静力学无法在谷物中正确初始化。最后,通过将此代码放在实例化输入存档的源文件中,我能够找到解决方案。
#define SC_REGISTER_INPUT_ARCHIVE(Archive) \
namespace cereal \
{ \
namespace detail \
{ \
template StaticObject<InputBindingCreator<Archive, first_polymorphic_class>>; \
template StaticObject<InputBindingCreator<Archive, second_polymorphic_class>>; \
... /* repeat for all polymorphic serialized types */
} \
}
SC_REGISTER_INPUT_ARCHIVE(XMLInputArchive);
SC_REGISTER_INPUT_ARCHIVE(BinaryInputArchive);
答案 2 :(得分:0)
这不是您特定问题的答案,但是非常相似。我正在尝试使用外部序列化功能序列化结构,但是却收到关于我的派生结构无法转换为基本结构类型的错误。诀窍是我没有传递指针。
所以
ar(cereal::base_class<Base>(derived_instance), derived_instance.y)
成为
ar(cereal::base_class<Base>(&derived_instance), derived_instance.y)
任何编译正常!