Boost c++ serializing a char *

Question

I have a class and I am trying to serialize a shared_ptr but the normal method of serializing an object is not working:

class Object {
public:
    Object();
    ~Object();

    shared_ptr<char>objectone;

    friend class boost::serialization::access;
    template <typename Archive>
    void serialize(Archive &ar, const unsigned int version)
    {
        ar & objectone;
    }
};

I've even attempted it in this way but it still doesn't work:

    void serialize(Archive &ar, const unsigned int version)
    {
        for (int i = 0; i < (strlen(objectone.get())); i++)
             ar & objectone.get()[i];
    }

Any ideas how to approach this? Thanks.

Some extra information:

I've already included both shared_ptr header files:

#include <boost/serialization/shared_ptr.hpp>
#include <boost/serialization/shared_ptr_132.hpp>

I've attempted to convert to a string and serialize it in that way but it produces the following error: boost::archive::archive_exception' what(): stream error

friend class boost::serialization::access;
template <typename Archive>
void serialize(Archive &ar, const unsigned int version)
{
    if (objectone.get()) {
        string temp(objectone.get());
        ar & temp;
    }
    ar & objectone;
}

shared_ptr<char> doesn't do what you seem to think it does. You can't treat it like a string because it is not a string. It is a smart pointer to a single character. — Alan
– Alan, Commented Feb 23, 2011 at 20:42

Edward Strange · Accepted Answer · 2011-02-23 18:21:50Z

4

There's more than just one problem with your code.

First, shared_ptr is not meant to hold arrays. Stop doing that.

Second, the serialization library doesn't save C-style strings that I know of. It would be pretty hard to implement and basically pointless since you can save vector or string, which is what you should be using anyway.

If you really insist on keeping a char* string then you need to convert it into a vector/string, and save it. Then upon reading you need to read that vector/string back, get the size, allocate the memory, stick it in...etc... Pointer tracking is not going to work so if you're relying on that you'll have to implement it yourself. Have fun.

New code edit:

You're doing the save bit in a function that covers both save and load. It of course doesn't work very well wrt loading. You need to split your serialization. if (Archive::is_saving) won't work either. The boost documentation explains how to correctly split the serialization routine.

edited Feb 23, 2011 at 18:21

answered Feb 23, 2011 at 17:55

Edward Strange

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1 Comment

user459811 Over a year ago

I dont have the flexibility of changing my member variables to strings but I attempted a string conversion which produced an error. Can someone point me in the right direction? Question has been edited to include code above. Thanks.

tallganglyguy · Accepted Answer · 2011-02-23 19:04:20Z

4

Keep in mind what Crazy Eddie said about shared_ptr not being the right tool for the job. Since you don't have the flexibility to change the class definition here is a work around.

boost::serialization provides a wrapper make_array that takes a pointer and wraps it up as an array for the serialization. This requires the array size to be known prior to serialization.

You could then do something like:

void serialize(Archive &ar, const unsigned int version)
{
    ar & array_size; // Figure out how to determine this (perhaps strlen(objectone.get())

    if (ar::is_loading)
    {
        objectone.reset(new char[array_size]); // allocate the array before we load it
    }

    if (objectone.get() != NULL)
    {
        ar & make_array(objectone.get(), array_size);
    }
}

That code sample is pretty rudimentary but conveys the concept.

edited Feb 23, 2011 at 19:04

answered Feb 23, 2011 at 18:56

tallganglyguy

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2 Comments

David Doria Over a year ago

I am trying this with archive & boost::serialization::make_array but getting "make_array is not a member of boost::serialization". What else do I need to include other than #include <boost/serialization/serialization.hpp> ?

tallganglyguy Over a year ago

@DavidDoria I believe you need to include <boost/serialization/array.hpp> to get boost::serialization::make_array.

Andrew T Finnell · Accepted Answer · 2011-02-23 18:39:33Z

2

You are missing some key concepts. You don't need a share_ptr anymore if you use a std::string.

You can do

class Object {
public:
    Object();
    ~Object();

    std::string name;

    template <typename Archive>
    void serialize(Archive &ar, const unsigned int version)
    {
        ar & name;
    }
};

and you are done.

Addition

Given your requirements this is what you have to do

class test
{
public:

friend class boost::serialization::access;

test() 
{       
}

template<class Archive>
void save(Archive & ar, const unsigned int version) const
{
    int len = strlen(data.get());
    ar  & len;
    for (int index = 0; index < len; ++index)
        ar & data[index];       
}
template<class Archive>
void load(Archive & ar, const unsigned int version)
{
    int len = 0;
    ar  & len;
    data = boost::shared_array<char>(new char[len+1]);
    for (int index = 0; index < len; ++index)
        ar & data[index];
    data[len] = 0;
}
BOOST_SERIALIZATION_SPLIT_MEMBER()

boost::shared_array<char> data;
};

edited Feb 23, 2011 at 18:39

answered Feb 23, 2011 at 18:19

Andrew T Finnell

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1 Comment

user459811 Over a year ago

Thank you for the code stub. :) As I mentioned in crazy's comment. I dont have the flexibility of changing my member variables to strings but I attempted a string conversion in my serialize method which produced an error. Not sure if that was the right approach since this is my first experience with boost. A point in the right direction will be much appreciated. Thanks.

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