[Boost-users] Re: Problems serializing via pointers

From: Jeffrey Holle (jeff.holle_at_[hidden])
Date: 2004-12-04 16:30:57

Following your instructions, I did get success dealing with pointers to 
std::string.  The attached file is what works for me.  The main 
additions involved making it a good C++ citizen.

Robert Ramey wrote:
> OK
> 
> Heres the short explanation using float as an example:
> 
> Its not a great idea to set the tracking trait for float to tracking because
> you'll end up tracking ALL the floats int the archive.
> 
> So you make a very small class that just contains a float.  That as  wrapper
> class.  This is to function just like a float except that it has a different
> class.  So it will have the default serialization trace assigned since its
> not a primitive.  This means it will be tracked by default.
> 
> struct tracked_float {
>     float m_float;     // the real data
>     template<class Archive>
>     void serialize(Archive &ar, unsigned int version){
>         ar & m_float;
>     }
>     // casting operators - not compiled
>     float operator float () const {
>         return m_float;
>     }
>     float & operator float() {
>         return m_float;
>     }
> };
> 
> Now just use tracked_float for those floats you want to serialize through a
> pointer and just float for other float variables.
> 
> This is more or less equivalent to using
> 
> BOOST_STRONG_TYPEDEF(tracked_float, float)
> 
> template<class Archive>
> void serialize(Archive &ar, tracked_float & tf){
>     ar & tf.m_float;
> }
> 
> I don't know if that helps - but there it is.
> 
> Robert Ramey
> 
> "Jeffrey Holle" <jeff.holle_at_[hidden]> wrote in message
> news:coqlem$mvg$1_at_sea.gmane.org...
> 
>>Just how am I supposed to use a BOOST_STRONG_TYPEDEF produced type?
>>If I make it the type of the class attribute, I get an error everywhere
>>that I use it.  Usage examples would be helpful.  For instance, what does:
>>   m_pByPointerPrefix = new char[strlen(src.m_pByPointerPrefix)+1];
>>need to be turned into when m_pByPointerPrefix goes from a "char" to
>>tracked_char"?
>>
>>If I only need to introduce tracked_char in the serialize methods, I
>>need examples of doing this too...
>>
>>
>>Robert Ramey wrote:
>>
>>>pointers to primitive objects are not serializable by default.  This is
>>>explained in the document which describes serialization traits.  The
> 
> reason
> 
>>>for this is
>>>
>>>a) suppose one place in the program I serialization a pointer to a
> 
> float.
> 
>>>Then addresses of ALLL the floats in the program would end up being
>>>seriailzed which is probably not what one wants.
>>>
>>>The solution is to make a wrapper so the the type has its own class
>>>
>>>BOOST_STRONG_TYPEDEF(float, tracked_float)
>>>
>>>Then use a tracked_float instead of a normal float where you want to
>>>serialize it through a pointer.
>>>
>>>Note that strings and characters are both considered primitive types in
> 
> this
> 
>>>context - I just used float as an example.
>>>
>>>This is the second time this question has come up so I guess we need to
>>>augment the manual and/or include another static assertion in the code.
>>>
>>>Good Luck - hope this his helpful
>>>
>>>Robert Ramey
>>>
>>>
>>>
>>>"Jeffrey Holle" <jeff.holle_at_[hidden]> wrote in message
>>>news:coqcn7$uhv$1_at_sea.gmane.org...
>>>
>>>
>>>>At this point, the last compilation problem in applying the
>>>>boost.serialization library to my application has to do with pointers.
>>>>
>>>>Specifically, its pointers to std::string and char member attributes.
>>>>
>>>>I have other pointer member attributes that compile successfully, but
>>>>this point to objects that have serialize methods.
>>>>
>>>>I have attempted use of register_type and am including
>>>>"serialization/string.hpp" in the modules that have pointer to string
>>>>attributes.  These actions were not affective.
>>>>
>>>>As an example of the type of compilation error, when I uncomment the
>>>>following attribute's archive attempt:
>>>>  char *m_pByPointerPrefix;
>>>>I get:
>>>>
>>>>/home/jholle/boost_1_32_0/boost/serialization/access.hpp: In static
>>>>member function `static void
>>>>boost::serialization::access::serialize(Archive&, T&, unsigned int)
>>>>[with Archive = boost::archive::binary_iarchive, T = char]':
>>>>/home/jholle/boost_1_32_0/boost/serialization/serialization.hpp:78:
>>>>instantiated from `void boost::serialization::serialize(Archive&, T&,
>>>>unsigned int) [with Archive = boost::archive::binary_iarchive, T =
> 
> char]'
> 
>>>>/home/jholle/boost_1_32_0/boost/serialization/serialization.hpp:121:
>>>>instantiated from `void boost::serialization::serialize_adl(Archive&,
>>>>T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T =
>>>>char]'
>>>>/home/jholle/boost_1_32_0/boost/archive/detail/iserializer.hpp:155:
>>>>instantiated from `void boost::archive::detail::iserializer<Archive,
>>>>T>::load_object_data(boost::archive::detail::basic_iarchive&, void*,
>>>>unsigned int) const [with Archive = boost::archive::binary_iarchive, T =
>>>>char]'
>>>>VariableName.cpp:102:   instantiated from here
>>>>/home/jholle/boost_1_32_0/boost/serialization/access.hpp:106: error:
>>>>request for member `serialize' in `t', which is of non-class type `char'
>>>>
>>>>
>>>>What is the solution to this?