Boost serialization unable to restore saved objects - c++

Question

This is how my class looks:
#include <iostream>
#include <boost/dynamic_bitset/dynamic_bitset.hpp>
#include <vector>
#include <fstream>
// include headers that implement a archive in simple text format
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/vector.hpp>
using namespace std;
using namespace boost;
class outer{
friend class boost::serialization::access;
public:
int a;
class inner{
friend class boost::serialization::access;
public:
int a;
inner(int a){
this->a = a;
}
template<class Archive>
void serialize(Archive & ar,const unsigned int version){
ar & a;
}
inner(){
}
};
vector<inner> inners;
outer(int a){
this->a = a;
inners.push_back(inner(this->a+1));
}
outer(){
}
template<class Archive>
void serialize(Archive & ar,const unsigned int version){
ar & a;
ar & inners;
}
};
vector<outer> outers;
vector<outer> _outers;
BOOST_CLASS_EXPORT(outer);
int main(int, char*[]) {
int i;
std::ofstream ofs("filename.dat");
for(i=0;i<5;i++)
outers.push_back(outer(i));
boost::archive::text_oarchive oa(ofs);
oa << outers;
std::ifstream ifs("filename.dat");
boost::archive::text_iarchive ia(ifs);
// read class state from archive
ia >> _outers;
return EXIT_SUCCESS;
}
I create a vector of outer class instances and write it out to a text stream (which seems to work fine). But when I read it back, I get the error:
terminate called after throwing an instance of 'boost::archive::archive_exception'
what(): input stream error
The above is the entire self-contained code, compiled with:
g++ -I /path/to/boost test.cpp -lboost_serialization
How do I fix this, any ideas?

Answer 1

Missing:
#include <boost/serialization/export.hpp>
You need to close the output archive/stream before reading the file back:
int main() {
{
std::ofstream ofs("filename.dat");
std::vector<outer> outers(5);
std::iota(outers.begin(), outers.end(), 0u);
{
boost::archive::text_oarchive oa(ofs);
oa << outers;
}
}
{
// read class state from archive
std::vector<outer> _outers;
std::ifstream ifs("filename.dat");
boost::archive::text_iarchive ia(ifs);
ia >> _outers;
for(auto& outer : _outers) {
std::cout << "outer " << outer.a << "\n";
for (auto& inner: outer.inners)
std::cout << " inner " << inner.a << "\n";
}
}
}
Full Demo
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#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/export.hpp>
#include <boost/serialization/vector.hpp>
#include <iostream>
#include <fstream>
class outer {
friend class boost::serialization::access;
public:
int a;
class inner {
friend class boost::serialization::access;
public:
int a;
inner(int a) { this->a = a; }
template <class Archive> void serialize(Archive &ar, unsigned) { ar &a; }
inner() {}
};
std::vector<inner> inners;
outer(int a = 0) : a(a), inners {a+1} { }
template <class Archive> void serialize(Archive &ar, unsigned) {
ar &a;
ar &inners;
}
};
BOOST_CLASS_EXPORT(outer)
int main(int, char *[]) {
{
std::ofstream ofs("filename.dat");
std::vector<outer> outers(5);
std::iota(outers.begin(), outers.end(), 0u);
{
boost::archive::text_oarchive oa(ofs);
oa << outers;
}
}
{
// read class state from archive
std::vector<outer> _outers;
std::ifstream ifs("filename.dat");
boost::archive::text_iarchive ia(ifs);
ia >> _outers;
for(auto& outer : _outers) {
std::cout << "outer " << outer.a << "\n";
for (auto& inner: outer.inners)
std::cout << " inner " << inner.a << "\n";
}
}
}
Prints
outer 0
inner 1
outer 1
inner 2
outer 2
inner 3
outer 3
inner 4
outer 4
inner 5