Cereal seems to not properly serialize an std::string

Question

I am trying to serialize a class into a binary, to that effect I first started trying to serialize an std::string member within the class, I wrote this serialization method:

template<typename Archive>
void ShaderProgram::serialize(Archive& archive, ShaderProgram& program)
{
    archive(CEREAL_NVP(program.program_name));
}

Then I am trying to serialize and immediately read the class:

ShaderProgram program;
std::filesystem::create_directories(fs::path(cached_shader_path).parent_path());
std::ofstream os(cached_shader_path, std::ios::binary);
cereal::BinaryOutputArchive archive_out( os );
ShaderProgram::serialize(archive_out, program);

std::ifstream is(cached_shader_path, std::ios::binary);
cereal::BinaryInputArchive archive_in( is );
ShaderProgram::serialize(archive_in, program);

Which results in:

terminate called after throwing an instance of 'cereal::Exception'
  what():  Failed to read 8 bytes from input stream! Read 0

The class I am testing this with is trivial:

struct ShaderProgram
{
    std::string program_name = "name";

    template<typename Archive>
        static void serialize(Archive& archive, ShaderProgram& program);
};
template<typename Archive>
void ShaderProgram::serialize(Archive& archive, ShaderProgram& program)
{
    archive(CEREAL_NVP(program.program_name));
}

I don;t understand why this fails.

Answer 1

Here is an example. All is fine with cereal. In plain C++ remove Rcpp connections.

// [[Rcpp::depends(Rcereal)]]
#include <string>
#include <fstream>
#include <cereal/archives/binary.hpp>
#include <cereal/types/string.hpp>
#include <cereal/access.hpp>
#include <Rcpp.h>

struct ShaderProgram
{
  ShaderProgram(){};
  ShaderProgram(std::string program_name)
    : program_name{program_name}{};
  ~ShaderProgram() = default;
  
  std::string get_program_name() const {
    return program_name;
  }
  
private:
  std::string program_name{};
  
  friend class cereal::access;

  template<class Archive>
  void serialize(Archive& archive)
  {
    archive(program_name);
  }
  
};


// [[Rcpp::export]]
int main() {
  
  {
    ShaderProgram sp("King Kong 8");
    
    std::ofstream os("Backend/Serialize_StringProgram.bin", std::ios::binary);
    cereal::BinaryOutputArchive oarchive(os);
    oarchive(sp);
  }
  
  {
    ShaderProgram sp{};
    std::ifstream is("Backend/Serialize_StringProgram.bin", std::ios::binary);
    cereal::BinaryInputArchive iarchive(is);
    iarchive(sp);
    
    Rcpp::Rcout << sp.get_program_name() << std::endl;
  }

}