C++ serialization of static array of struct using Cereal - c++

Question

I am using Cereal library for serialization of structured data, to send them over MPI and later on process them on GPU using CUDA. Due to the latter, I cannot use std::vector, because CUDA has problems with dynamic objects. Therefore I am using static arrays of structures.
GOAL
To do binary serialization & deserialization on objects with nested static array of objects.
OBJECTS TO BE SERIALIZED
//==========================================================//
// ELEMENT DEFINITION //
//==========================================================//
class element{
public:
//==========================//
// CONTENT //
//==========================//
int grid_id;
int NN_id;
int debug;
//==========================//
// SERIALIZATION //
//==========================//
// function required by cereal library
template<class Archive>
void serialize(Archive & ar){
ar( grid_id );
ar( NN_id );
ar( debug );
}
};
//==========================================================//
// CONTAINER DEFINITION //
//==========================================================//
class GPU_in_grid : public Managed{
public:
//==========================//
// CONTENT //
//==========================//
int gpu_id;
element element[GRID_SIZE]; <------ static array of structures
int debug;
//==========================//
// SERIALIZATION //
//==========================//
template<class Archive>
void serialize(Archive & ar){
ar( gpu_id );
ar( debug );
ar( element );
}
};
SERIALIZATION FUNCTIONS
// cereal serialization
#include <cereal/archives/binary.hpp>
#include <cereal/archives/portable_binary.hpp>
//#include <cereal/archives/xml.hpp>
template<typename data_type>
int Process::serialize(data_type * data, char *serial_data, int *size){
// serialize the data
std::ostringstream oss(std::ios::binary);
cereal::BinaryOutputArchive ar(oss);
//cereal::XMLOutputArchive ar(std::cout);
ar(*data);
std::string s=oss.str();
*size = s.length();
strncpy(serial_data, s.c_str(), s.length());
std::cout << "buffer["<< s.length() << "] >> " << s << std::endl;
s.clear();
return _SUCCESS_;
};
template<typename data_type>
int Process::deserialize(data_type * data, char *serial_data, int size){
// create temporary buffer to store the received data
char * buf=new char[size];
strncpy(buf, serial_data, size);
std::istringstream iss(std::string(serial_data, size), std::ios::binary);
cereal::BinaryInputArchive arin(iss);
arin(*data);
// clean buffer
delete[] buf;
return _SUCCESS_;
};
DEBUGGING OUTPUT
cpu_mem BEFORE serialization
cpu_mem.debug = -1
cpu_mem.gpu_id = -5
cpu_mem.element[0].NN_id = 1
cpu_mem.element[0].debug = 2
buffer[248] >> �������� <------ binary format
cpu_mem AFTER deserialization
cpu_mem.debug = -1 <----- CORRECT
cpu_mem.gpu_id = -5 <----- CORRECT
cpu_mem.element[0].NN_id = 0 <----- INCORRECT
cpu_mem.element[0].debug = 0 <----- INCORRECT
If I play around a bit with the streams, I can print out the serialized object as XML, to check whether the serialization is successful.
<?xml version="1.0" encoding="utf-8"?>
<cereal>
<value0>
<gpu_id>-5</gpu_id> <----- CORRECT
<debug>-1</debug> <----- CORRECT
<element>
<value0>
<grid_id>0</grid_id>
<NN_id>1</NN_id> <----- CORRECT
<debug>2</debug> <----- CORRECT
</value0>
<value1>
<grid_id>32522</grid_id>
<NN_id>2</NN_id>
<debug>4612412</debug>
</value1>
</element>
</value0>
</cereal>
PROBLEM
The above outputs shows, that deserialization correctly recognizes variables in the container (class GPU_in_grid) but cannot deserialize the lower levels of my structure, namely static array of structures -> element[].

Answer 1

For some unknown reason to me, the strncpy() malfunctions. The content of the string differs from the content of the array, EVEN if I keep eye on '\0', which need to be appended at the end of the char array, shown here http://www.cplusplus.com/reference/string/string/copy/ .
I have ended up using std::string.copy() instead, which performs as expected, as long as you add '\0' at the end of the char array.
the above code works then just fine.