Serializing Non-Default-Constructible Classes with Cereal

I have a Weapon class that requires parameters in its constructor and doesn't have a default constructor. How can I serialize and deserialize objects of this class using cereal?

To serialize and deserialize objects of a class that doesn't have a default constructor using cereal, you can use the load_and_construct function. Here's how you can do it:

Step 1: Include the necessary cereal headers:

#include <cereal/access.hpp>
#include <cereal/types/string.hpp>

Step 2: In your Weapon class, define a load_and_construct function:

class Weapon {
 public:
  Weapon(const std::string& name, int damage)
    : name(name), damage(damage) {}

 private:
  friend class cereal::access;

  std::string name;
  int damage;

  template <class Archive>
  void save(Archive& ar) const {
    ar(name, damage);
  }

  template <class Archive>
  static void load_and_construct(
    Archive& ar,
    cereal::construct<Weapon>& construct
  ) {
    std::string name;
    int damage;
    ar(name, damage);
    construct(name, damage);
  }
};

In the load_and_construct function, you deserialize the necessary data members and then use the construct object to call the appropriate constructor of the Weapon class.

Step 3: Serialize and deserialize the Weapon object as usual:

#include <cereal/archives/binary.hpp>
#include <fstream>
#include <memory>

int main() {
  // Serialization
  auto weapon = std::make_unique<Weapon>(
    "Sword", 50);
  std::ofstream outputFile("weapon.dat");
  cereal::BinaryOutputArchive outputArchive(
    outputFile);
  outputArchive(weapon);

  // Deserialization
  std::unique_ptr<Weapon> deserializedWeapon;
  std::ifstream inputFile("weapon.dat");
  cereal::BinaryInputArchive inputArchive(
    inputFile);
  inputArchive(deserializedWeapon);
}

By using the load_and_construct function, cereal will be able to deserialize and reconstruct objects of your Weapon class even though it doesn't have a default constructor.

Note: Make sure to use smart pointers like std::unique_ptr or std::shared_ptr when serializing and deserializing objects that are dynamically allocated to ensure proper memory management.

A complete example is below:

// Suppress compilation warnings
#define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING

#include <cereal/archives/binary.hpp>
#include <cereal/types/string.hpp>
#include <cereal/types/memory.hpp>
#include <fstream>
#include <iostream>
#include <memory>

class Weapon {
 public:
  Weapon(const std::string& name, int damage)
    : name(name), damage(damage) {}

  std::string name;
  int damage;

 private:
  friend class cereal::access;
  template <class Archive>
  void save(Archive& ar) const {
    ar(name, damage);
  }

  template <class Archive>
  static void load_and_construct(Archive& ar,
    cereal::construct<Weapon>& construct) {
    std::string name;
    int damage;
    ar(name, damage);
    construct(name, damage);
  }
};

int main() {
  // Serialization
  auto weapon = std::make_unique<Weapon>(
    "Sword", 50);
  {
    std::ofstream outputFile("weapon.dat");
    cereal::BinaryOutputArchive outputArchive(
      outputFile);
    outputArchive(weapon);
  }

  // Deserialization
  std::unique_ptr<Weapon> deserializedWeapon;
  {
    std::ifstream inputFile("weapon.dat");
    cereal::BinaryInputArchive inputArchive(
      inputFile);
    inputArchive(deserializedWeapon);
  }

  std::cout << "Deserialized Weapon:\n";
  std::cout << "Name: "
    << deserializedWeapon->name << "\n";
  std::cout << "Damage: "
    << deserializedWeapon->damage << "\n";
}
Deserialized Weapon:
Name: Sword
Damage: 50

Binary Serialization using Cereal

A detailed and practical tutorial for binary serialization in modern C++ using the cereal library.

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Answers are generated by AI models and may not have been reviewed. Be mindful when running any code on your device.

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