Cereal serialization

I have a problem in C++11 with cereal (http://uscilab.github.io/cereal/).

I have a shared library, and I would like to serialize one of its classes using cereal library. Here is a part of the code of the library "I would like to serialize Object class":

"Object.hpp"

class ObjectPrivate;

class Object
{
 public:
    ...
    template <class Archive>
    void load(Archive& archive);

    template <class Archive>
    void save(Archive& archive) const;

 protected: 
    std::unique_ptr<ObjectPrivate> d_ptr;
};

template<>
void Object::load<cereal::BinaryInputArchive>(cereal::BinaryInputArchive& archive);

template<>
void Object::save<cereal::BinaryOutputArchive>(cereal::BinaryOutputArchive& archive) const;

"Object.cpp"

#include"Object_p.hpp"
template <class Archive>
void Object::load(Archive& archive)
{
    archive(d_ptr);
}

template <class Archive>
void Object::save(Archive& archive) const
{
    archive(d_ptr);
}

"Object_p.hpp"

#include"Object.hpp"

class ObjectPrivate
{
 public:
    int m_id;

    template<class Archive>
    void serialize(Archive & ar)
    {
        ar(m_id);
    }
};

but I got an error:

error: undefined reference to void GraphicalObject::save<cereal::BinaryOutputArchive>(cereal::BinaryOutputArchive&) const
error: undefined reference to void GraphicalObject::load<cereal::BinaryInputArchive>(cereal::BinaryInputArchive&)

Solution

CS Pei is right, I forgot the implementation of the functions:

template<>
void Object::load<cereal::BinaryInputArchive>(cereal::BinaryInputArchive& archive);

template<>
void Object::save<cereal::BinaryOutputArchive>(cereal::BinaryOutputArchive& archive) const;

The right implementation:

"Object.hpp"

class ObjectPrivate;

class Object
{
 public:
    ...
    template <class Archive>
    void load(Archive& archive);

    template <class Archive>
    void save(Archive& archive) const;

 protected: 
    std::unique_ptr<ObjectPrivate> d_ptr;
};

template<>
void Object::load<cereal::BinaryInputArchive>(cereal::BinaryInputArchive& archive);

template<>
void Object::save<cereal::BinaryOutputArchive>(cereal::BinaryOutputArchive& archive) const;

"Object.cpp"

#include"Object_p.hpp"
template <class Archive>
void Object::load(Archive& archive)
{
    archive(d_ptr->m_id);
}

template <class Archive>
void Object::save(Archive& archive) const
{
    archive(d_ptr->m_id);
}

template <>
void GraphicalObject::save<cereal::BinaryOutputArchive>(cereal::BinaryOutputArchive& archive) const
{
    archive(d_ptr->m_id);
}

template <>
void GraphicalObject::load<cereal::BinaryInputArchive>(cereal::BinaryInputArchive& archive)
{
    archive(d_ptr->m_id);
}

"Object_p.hpp"

#include"Object.hpp"

class ObjectPrivate
{
 public:
    int m_id;
};