Question

Suppose I have two classes:

class1 {
 int m_i;
 std::string m_s;
};

class2 {
 int m_i2;
 class1 *m_ptr;
};

Now, I want to send a class2 variable over network, and want to use any of the libraries that does serialization.(Protocol-buffers, Thrift, MessagePack..)

Which one can I use?(note the class1* m_ptr)

Answer 1

Using google protocol buffers, you would need a .proto file (say test.proto) like:

package serialisation;  // puts this in namespace serialisation

message class1 {
  required int32 m_i = 1;
  required bytes m_s = 2;
}

message class2 {
  required int32 m_i2 = 1;
  optional class1 m_ptr = 2;
}

Using C++, once you run the protoc compiler against this, you end up with test.pb.cc and test.pb.h

You can then use these like:

#include <string>
#include "test.pb.h"

struct class1 {
  int m_i;
  std::string m_s;
};

struct class2 {
  int m_i2;
  class1 *m_ptr;
};

int main() {
  class2 second_class;
  second_class.m_i2 = 2;
  second_class.m_ptr = new class1;
  second_class.m_ptr->m_i = 1;
  second_class.m_ptr->m_s = "one";

  // Serialise class 2
  serialisation::class2 serialisable_second_class;
  serialisable_second_class.set_m_i2(second_class.m_i2);
  if (second_class.m_ptr) {
    serialisation::class1* serialisable_first_class = serialisable_second_class.mutable_m_ptr();
    serialisable_first_class->set_m_i(second_class.m_ptr->m_i);
    serialisable_first_class->set_m_s(second_class.m_ptr->m_s);
  }
  std::string serialised(serialisable_second_class.SerializeAsString());

  // Parse class 2
  serialisation::class2 parsed_second_class;
  parsed_second_class.ParseFromString(serialised);
  class2 retrieved_second_class;
  retrieved_second_class.m_i2 = parsed_second_class.m_i2();
  if (parsed_second_class.has_m_ptr()) {
    retrieved_second_class.m_ptr = new class1;
    retrieved_second_class.m_ptr->m_i = parsed_second_class.m_ptr().m_i();
    retrieved_second_class.m_ptr->m_s = parsed_second_class.m_ptr().m_s();
  } else {
    retrieved_second_class.m_ptr = nullptr;
  }

  return 0;
}

Note, for the sake of brevity I’m not doing any error checking or exception handling here – this would be needed in production code. I’m also not managing the lifetime of the class1 pointer.