[Boost-users] Re: Problems serializing via pointers

4 Dec 2004


      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"  wrote in message
news:coqlem$mvg$1@sea.gmane.org...
...
Just how am I supposed to use a BOOST_STRONG_TYPEDEF produced type?
If I make it the type of the class attribute, I get an error everywhere
that I use it.  Usage examples would be helpful.  For instance, what does:
  m_pByPointerPrefix = new char[strlen(src.m_pByPointerPrefix)+1];
need to be turned into when m_pByPointerPrefix goes from a "char" to
tracked_char"?
If I only need to introduce tracked_char in the serialize methods, I
need examples of doing this too...
Robert Ramey wrote:
...
pointers to primitive objects are not serializable by default.  This is
explained in the document which describes serialization traits.  The
reason
...
...
for this is
a) suppose one place in the program I serialization a pointer to a
float.
...
...
Then addresses of ALLL the floats in the program would end up being
seriailzed which is probably not what one wants.
The solution is to make a wrapper so the the type has its own class
BOOST_STRONG_TYPEDEF(float, tracked_float)
Then use a tracked_float instead of a normal float where you want to
serialize it through a pointer.
Note that strings and characters are both considered primitive types in
this
...
...
context - I just used float as an example.
This is the second time this question has come up so I guess we need to
augment the manual and/or include another static assertion in the code.
Good Luck - hope this his helpful
Robert Ramey
"Jeffrey Holle"  wrote in message
news:coqcn7$uhv$1@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::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?