I've attached the boost sample serialization code below. I see that they create an output archive and then write the class to the output archive. Then later, they create an input archive and read from the input archive into a new class instance. My question is, how does the input archive know which output archive its reading data from? For example, say I have multiple output archives. How does the input archive that is created know which output archive to read from? I'm not understanding how this is working. Thanks for your help!
#include <fstream>
// include headers that implement a archive in simple text format
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
/////////////////////////////////////////////////////////////
// gps coordinate
//
// illustrates serialization for a simple type
//
class gps_position
{
private:
friend class boost::serialization::access;
// When the class Archive corresponds to an output archive, the
// & operator is defined similar to <<. Likewise, when the class Archive
// is a type of input archive the & operator is defined similar to >>.
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
ar & degrees;
ar & minutes;
ar & seconds;
}
int degrees;
int minutes;
float seconds;
public:
gps_position(){};
gps_position(int d, int m, float s) :
degrees(d), minutes(m), seconds(s)
{}
};
int main() {
// create and open a character archive for output
std::ofstream ofs("filename");
// create class instance
const gps_position g(35, 59, 24.567f);
// save data to archive
{
boost::archive::text_oarchive oa(ofs);
// write class instance to archive
oa << g;
// archive and stream closed when destructors are called
}
// ... some time later restore the class instance to its orginal state
gps_position newg;
{
// create and open an archive for input
std::ifstream ifs("filename");
boost::archive::text_iarchive ia(ifs);
// read class state from archive
ia >> newg;
// archive and stream closed when destructors are called
}
return 0;
}
Example 2
void save_load_with_binary_archive()
{
// binary archive with stringstream
std::ostringstream oss;
boost::archive::binary_oarchive oa(oss);
Camera cam;
cam.id = 100;
cam.name = "new camera";
cam.pos = 99.88;
oa & (cam);
// get binary content
std::string str_data = oss.str();
std::istringstream iss(str_data);
boost::archive::binary_iarchive ia(iss);
Camera new_cam;
ia & (new_cam);
std::cout << new_cam << std::endl;
}