[serialization] Difficulties with shared_ptr and export.hpp

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Deane Yang

23 Nov 2006 23 Nov '06

4:52 a.m.

First, I am trying to figure out how to use BOOST_CLASS_EXPORT. I am trying to do it using the following advice from the documentation: "As noted in the comments, this would work. But #include <.../export.hpp> can't be used without conflicting with other modules which use #include <.../*archive.hpp>. In this case we can move the export to an implementation file: // A.cpp #include "A.hpp" ... // export.hpp header should be last; #include ... BOOST_CLASS_EXPORT(A) ..." In fact, my implementation file contains *only* BOOST_CLASS_EXPORT statements. Code like this seems to compile only if I also include archive headers like: #include #include If these directives are omitted, then my code does not compile. Is this correct? (I didn't see anything about this in the documentation) But now if a class that is being exported contains a boost::shared_ptr<..> member (so I have to #include boost/serialization/shared_ptr.hpp), then I get the following compilation errors (in MSVC8.0express): ..\..\..\vendor\boost\boost/serialization/shared_ptr.hpp(134) : error C2039: 'reset' : is not a member of 'boost::archive::naked_xml_iarchive' ..\..\..\vendor\boost\boost/archive/xml_iarchive.hpp(91) : see declaration of 'boost::archive::naked_xml_iarchive' ..\..\..\vendor\boost\boost/serialization/split_free.hpp(58) : see reference to function template instantiation 'void boost::serialization::load(Archive &,boost::shared_ptr<T> &,const unsigned int)' being compiled Can someone tell from this what I'm doing wrong?

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Robert Ramey

23 Nov 23 Nov

7:20 a.m.

New subject: [serialization] Difficulties with shared_ptr andexport.hpp

Deane Yang wrote:

...

First, I am trying to figure out how to use BOOST_CLASS_EXPORT. I am trying to do it using the following advice from the documentation:

"As noted in the comments, this would work. But #include <.../export.hpp> can't be used without conflicting with other modules which use #include <.../*archive.hpp>. In this case we can move the export to an implementation file:

Where did you find this in the documentation? I know its in there but I can't find it when I look for it in the HEAD.

...

// A.cpp #include "A.hpp" ... // export.hpp header should be last; #include ... BOOST_CLASS_EXPORT(A) ..."

In fact, my implementation file contains *only* BOOST_CLASS_EXPORT statements.

Then no code will be instantiated - as you have indeed found.

...

Code like this seems to compile only if I also include archive headers like: #include #include

correct.

...

If these directives are omitted, then my code does not compile.

Hmmm - the required code to export class x to archive xml_?archive.hpp will not be instantiated. I would expect that to show up as a missing symbol during linking.

...

Is this correct? (I didn't see anything about this in the documentation)

In the section: Exporting Class Serialization ... "we have described BOOST_CLASS_EXPORT. This is used to make the serialization library aware that code should be instantiated for serialization of a given class even though the class hasn't been otherwise referred to by the program. This functionality is necessary to implement serialization of pointers through a virtual base class pointer. That is, a polymorphic pointer." maybe that explanation should be made more complete. The usage of BOOST_CLASS_EXPORT will ensure that appropriate code to serialize the indicated type is generated for all archive types (and only those archive types) included when BOOST_CLASS_EXPORT is used.

...

But now if a class that is being exported contains a boost::shared_ptr<..> member (so I have to #include boost/serialization/shared_ptr.hpp), then I get the following compilation errors (in MSVC8.0express):

...

..\..\..\vendor\boost\boost/serialization/shared_ptr.hpp(134) : error C2039: 'reset' : is not a member of 'boost::archive::naked_xml_iarchive' ..\..\..\vendor\boost\boost/archive/xml_iarchive.hpp(91) : see declaration of 'boost::archive::naked_xml_iarchive' ..\..\..\vendor\boost\boost/serialization/split_free.hpp(58) : see reference to function template instantiation 'void boost::serialization::load(Archive &,boost::shared_ptr<T> &,const unsigned int)' being compiled

Can someone tell from this what I'm doing wrong?

Send me a little code that reproduces the problem. Robert Ramey

Deane Yang

7:56 a.m.

New subject: [serialization] Difficulties with shared_ptr andexport.hpp

Robert Ramey wrote:

...

Deane Yang wrote:

...
First, I am trying to figure out how to use BOOST_CLASS_EXPORT. I am trying to do it using the following advice from the documentation:

"As noted in the comments, this would work. But #include <.../export.hpp> can't be used without conflicting with other modules which use #include <.../*archive.hpp>. In this case we can move the export to an implementation file:

Where did you find this in the documentation? I know its in there but I can't find it when I look for it in the HEAD.

Reference -> Special Considerations -> Exporting Class Serialization (at the very end)

...

...
In fact, my implementation file contains *only* BOOST_CLASS_EXPORT statements.

Then no code will be instantiated - as you have indeed found.

What else is supposed to be in this file? Do I need to put in the code that loads and saves archives in this file?

...

...
Code like this seems to compile only if I also include archive headers like: #include #include

correct.

...
If these directives are omitted, then my code does not compile.

Hmmm - the required code to export class x to archive xml_?archive.hpp will not be instantiated. I would expect that to show up as a missing symbol during linking.

No, I get something like: ..\..\..\..\vendor\boost\boost/serialization/type_info_implementation.hpp(48) : error C2027: use of undefined type 'boost::serialization::extended_type_info_impl<T>' with [ T=Input::Bond ] ..\..\..\..\vendor\boost\boost/serialization/export.hpp(75) : see reference to class template instantiation 'boost::serialization::type_info_implementation<T>' being compiled with [ T=Input::Bond ]

...

Send me a little code that reproduces the problem.

I'll see if I can reproduce my error with a simple example. Thanks! Deane

Robert Ramey

5:04 p.m.

New subject: [serialization] Difficulties with shared_ptrandexport.hpp

The real question here is:

...

What else is supposed to be in this file? Do I need to put in the code that loads and saves archives in this file?

And here is the answer. I expect that BOOST_CLASS_EXPORT will be specified in the same header file as the class declaration to which it corresponds. That is, BOOST_CLASS_EXPORT(T) is a "trait" of the class. This trait is the "external name" used to identify the class and is needed when serializing polymorphic types through a base class pointer. I expect that one's program will generally look like: #include .... #include "my_class.hpp" // which has BOOST_CLASS_EXPORT inside In boost 1.35 (aka HEAD) these headers can be in any order. In 1.34 and earlier, the archive headers have to go before any headers which contain BOOST_CLASS_EXPORT This will instantiate any code required to serialize types specified by BOOST_CLASS_EXPORT for each archive included. (note that the code is instantiated regardless of whether or not it is actually invoked.) If no archive headers are included - no code should be instantiated. This will permit BOOST_CLASS_EXPORT to be a permanent part of the my_class declaration. (Right now this provokes an error message. I'll rectify that.) I hope this clarifies things. Robert Ramey Deane Yang wrote:

...

Robert Ramey wrote:

...
...
In fact, my implementation file contains *only* BOOST_CLASS_EXPORT statements.

Then no code will be instantiated - as you have indeed found.

...

...
...
Code like this seems to compile only if I also include archive headers like: #include #include

correct.

...
If these directives are omitted, then my code does not compile.

Hmmm - the required code to export class x to archive xml_?archive.hpp will not be instantiated. I would expect that to show up as a missing symbol during linking.

No, I get something like:

..\..\..\..\vendor\boost\boost/serialization/type_info_implementation.hpp(48)

...
error C2027: use of undefined type 'boost::serialization::extended_type_info_impl<T>' with [ T=Input::Bond ] ..\..\..\..\vendor\boost\boost/serialization/export.hpp(75) : see reference to class template instantiation 'boost::serialization::type_info_implementation<T>' being compiled with [ T=Input::Bond ]

OK - I believe that is misleading. I'm changing my local copy to #include so that this error doesn't appear.

Deane Yang

6:26 p.m.

New subject: [serialization] Difficulties with shared_ptrandexport.hpp

Robert Ramey wrote:

...

The real question here is:

...
What else is supposed to be in this file? Do I need to put in the code that loads and saves archives in this file?

And here is the answer.

I expect that BOOST_CLASS_EXPORT will be specified in the same header file as the class declaration to which it corresponds. That is, BOOST_CLASS_EXPORT(T) is a "trait" of the class. This trait is the "external name" used to identify the class and is needed when serializing polymorphic types through a base class pointer.

I expect that one's program will generally look like:

#include .... #include "my_class.hpp" // which has BOOST_CLASS_EXPORT inside

In boost 1.35 (aka HEAD) these headers can be in any order. In 1.34 and earlier, the archive headers have to go before any headers which contain BOOST_CLASS_EXPORT

Robert, First, thank you very much for taking the time to answer my clueless questions. Second, I'm not sure what I get when I check out the boost files using CVS, as instructed in the "Getting Started" section of the web site. Do I have "HEAD" this way? If not, how do I get it? Third, here is some code that reproduces my error. I'm sorry if it's a bit overly complicated; I just don't know what exactly is causing the error. #include #include #include #include <fstream> template <class ObjectType> void save(const ObjectType& object, const char* filename) { std::ofstream ofs(filename); assert(ofs.good()); boost::archive::xml_oarchive oa(ofs); oa << BOOST_SERIALIZATION_NVP(object); } template <class ObjectType> void load(ObjectType& object, const char* filename) { std::ifstream ifs(filename); assert(ifs.good()); boost::archive::xml_iarchive ia(ifs); ia >> BOOST_SERIALIZATION_NVP(object); } namespace A { namespace B { namespace C { struct Base { int type; virtual ~Base() {} }; struct Point :Base { double x; }; } } } #include namespace boost { namespace serialization { using namespace A::B; template<class Archive> void serialize(Archive& ar, C::Base& x, const unsigned int version) { ar & BOOST_SERIALIZATION_NVP(x.type); } template<class Archive> void serialize(Archive& ar, C::Point& x, const unsigned int version) { ar & make_nvp("Base", base_object(x)); ar & BOOST_SERIALIZATION_NVP(x.x); } } } namespace A { namespace B { namespace C { BOOST_CLASS_EXPORT(Point); } } } #include #include <list> namespace A { namespace B { namespace C { struct Line :Base { struct Item { bool flop; boost::shared_ptr<Base> ptr; }; double slope; double intercept; std::list<Item> items; }; } struct Object { struct Item { bool flip; boost::shared_ptr ptr; }; std::list<Item> items; }; } } #include #include #include namespace boost { namespace serialization { using namespace A::B; template<class Archive> void serialize(Archive& ar, C::Line::Item& x, const unsigned int version) { ar & BOOST_SERIALIZATION_NVP(x.flop); ar & BOOST_SERIALIZATION_NVP(x.ptr); } template<class Archive> void serialize(Archive& ar, C::Line& x, const unsigned int version) { ar & make_nvp("Security", base_object(x)); ar & BOOST_SERIALIZATION_NVP(x.items); } template<class Archive> void serialize(Archive& ar, Object::Item& x, const unsigned int version) { ar & BOOST_SERIALIZATION_NVP(x.flip); ar & BOOST_SERIALIZATION_NVP(x.ptr); } template<class Archive> void serialize(Archive& ar, Object& x, const unsigned int version) { ar & BOOST_SERIALIZATION_NVP(x.items); } } } namespace A { namespace B { namespace C { BOOST_CLASS_EXPORT(Line) } } } namespace A { namespace B { void Load(Object& object, const char* filename); void Save(const Object& object, const char* filename); void Load(Object& object, const char* filename) { load(object, filename); } void Save(const Object& object, const char* filename) { save(object, filename); } } }

Robert Ramey

8:35 p.m.

New subject: [serialization] Difficulties withshared_ptrandexport.hpp

Deane Yang wrote:

...

Second, I'm not sure what I get when I check out the boost files using CVS, as instructed in the "Getting Started" section of the web site. Do I have "HEAD" this way? If not, how do I get it?

Its clear to me that you have the "HEAD". This error only appears in the HEAD branch of the cvs tree. You should make sure that HEAD is what you want. The head is where the development code is - RC_1_34 is where the next release versionis and the "normal" current one for users is Boost 1.33. By using the HEAD, you're helping debug the libraries and its much appreciated. But you should know that that is what you're doing. So I traced your error to and error in a recent enhancement that I've checked in to the HEAD branch. I'll check in a correction is a few days. Robert Ramey

Deane Yang

24 Nov 24 Nov

3:32 a.m.

New subject: [serialization] Difficulties withshared_ptrandexport.hpp

Robert Ramey wrote:

...

Deane Yang wrote:

...
Second, I'm not sure what I get when I check out the boost files using CVS, as instructed in the "Getting Started" section of the web site. Do I have "HEAD" this way? If not, how do I get it?

Its clear to me that you have the "HEAD". This error only appears in the HEAD branch of the cvs tree. You should make sure that HEAD is what you want. The head is where the development code is - RC_1_34 is where the next release versionis and the "normal" current one for users is Boost 1.33. By using the HEAD, you're helping debug the libraries and its much appreciated. But you should know that that is what you're doing.

Thanks for the advice! I guess I'm living dangerously. I'll have to figure out how to check out the RC_1_34 code instead.

...

So I traced your error to and error in a recent enhancement that I've checked in to the HEAD branch. I'll check in a correction is a few days.

Ach. I was sure I was doing something dumb. Thanks very much for your help with this! Deane

...

Robert Ramey

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