C++11 Cereal: load_and_allocate not loading correctly - c++

Question

I am using cereal, a C++11 serialization library. I am uncertain if this is a bug with the library or an issue with how I am using it and I would like some assistance.
Given the following minimal repro which is representative (but not reliant) on my own code I am getting an exception thrown from JSONInputArchive::search as invocated by the line next to my comment in the code sample below (//breaks here.)
I'm currently on commit 436a0a275cda007f137876f37b4fc8783e615352 in this github repro (at the time of writing, the tip of their develop branch.)
#include <iostream>
#include <sstream>
#include <string>
#include <map>
#include "cereal/cereal.hpp"
#include "cereal/types/map.hpp"
#include "cereal/types/vector.hpp"
#include "cereal/types/memory.hpp"
#include "cereal/types/string.hpp"
#include "cereal/types/base_class.hpp"
#include "cereal/archives/json.hpp"
#include <cereal/types/polymorphic.hpp>
class BaseClass : public std::enable_shared_from_this<BaseClass> {
public:
virtual ~BaseClass(){}
template <class Archive>
void serialize(Archive & archive){
archive(CEREAL_NVP(name), CEREAL_NVP(baseMember));
}
protected:
BaseClass(const std::string &a_name):
name(a_name){
}
std::string name;
int baseMember; //let this have random junk so we can see if it saves right.
};
class DerivedClass : public BaseClass {
friend cereal::access;
public:
static std::shared_ptr<DerivedClass> make(const std::string &a_name, int a_derivedMember){
return std::shared_ptr<DerivedClass>(new DerivedClass(a_name, a_derivedMember));
}
template <class Archive>
void serialize(Archive & archive){
archive(CEREAL_NVP(derivedMember), cereal::make_nvp("base", cereal::base_class<BaseClass>(this)));
}
private:
DerivedClass(const std::string &a_name, int a_derivedMember):
BaseClass(a_name),
derivedMember(a_derivedMember){
}
template <class Archive>
static DerivedClass * load_and_allocate(Archive &archive){
int derivedMember;
archive(CEREAL_NVP(derivedMember)); //breaks here.
DerivedClass* object = new DerivedClass("", derivedMember);
archive(cereal::make_nvp("base", cereal::base_class<BaseClass>(object)));
return object;
}
int derivedMember;
};
CEREAL_REGISTER_TYPE(DerivedClass);
void saveTest(){
std::stringstream stream;
{
cereal::JSONOutputArchive archive(stream);
auto testSave = DerivedClass::make("TestName", 4);
archive(cereal::make_nvp("test", testSave));
}
std::cout << stream.str() << std::endl;
std::shared_ptr<DerivedClass> loaded;
{
cereal::JSONInputArchive archive(stream);
archive(cereal::make_nvp("test", loaded));
}
std::stringstream stream2;
{
cereal::JSONOutputArchive archive(stream2);
archive(cereal::make_nvp("test", loaded));
}
std::cout << stream2.str() << std::endl;
std::cout << "TA-DA!" << std::endl;
}
int main(){
saveTest();
}
The sample output I get from the above (before the exception) is:
{
"test": {
"id": 1073741824,
"ptr_wrapper": {
"id": 2147483649,
"data": {
"derivedMember": 4,
"base": {
"name": "TestName",
"baseMember": -1163005939
}
}
}
}
}
I've modified the throwing method (in cereal/archive/json.hpp) to print what it is searching for and each of the values it is looking through in an effort to debug the problem. Here is my modified version:
//! Adjust our position such that we are at the node with the given name
/*! #throws Exception if no such named node exists */
inline void search( const char * searchName )//, GenericValue const & parent )
{
size_t index = 0;
std::cout << "_____" << std::endl;
for( auto it = itsMemberItBegin; it != itsMemberItEnd; ++it, ++index )
if( std::strcmp( searchName, it->name.GetString() ) == 0 )
{
itsIndex = index;
return;
} else{
//I added this part here
std::cout << "!" << searchName << " == " << it->name.GetString() << std::endl;
}
throw Exception("JSON Parsing failed - provided NVP not found");
}
Output for the above method before it excepts:
!derivedMember == id
!derivedMember == data
The output I get from this seems to indicate that search is looking through the members of "test.ptr_wrapper" instead of "test.ptr_wrapper.data".
My question is this: am I doing something wrong? Or is there an issue with cereal?

Answer 1

https://github.com/USCiLab/cereal/issues/42
It seems like this is indeed a bug with Cereal. My temporary work-around is as follows:
For now, to work around the issue I added a line 144 in memory.hpp (as
it appears on line 168 in the case of no load_and_allocate which means
that there is a default constructor.)
ar( *ptr );
I will simply avoid using the load_and_allocate archive
directly and will use my serialization functions. In my
load_and_allocate method I will construct an object with "default"
like information.
When this is fixed I should be able to correctly load in the parameters required to construct the object properly.
*edit: this has been fixed on the develop branch.