boost interprocess unordered_map string

Question

I am trying to create a unordered_map in shared memory using Boost Interprocess library. Here, is the code, which I'm trying to use (taking examples from Boost Interprocess documentation):

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <functional>
#include <boost/functional/hash.hpp>
#include <boost/unordered_map.hpp>
#include <iostream>
#include <string>
#include <boost/interprocess/containers/string.hpp>

namespace bipc = boost::interprocess;

typedef bipc::allocator<char, bipc::managed_shared_memory::segment_manager> CharAllocator;
typedef bipc::basic_string<char, std::char_traits<char>, CharAllocator> ShmemString;


struct Person
{
  int age;
  ShmemString name;
  double salary;

  Person(int i,
     double sal,
     const char* s,
     const char_allocator& a)
    : age(i),
      name(s, a),
      salary(sal)
    {
    }
  void print() {}
}

typedef ShmemString KeyType;
typedef Person MappedType;

typedef std::pair< KeyType, MappedType > MapPersonType;


typedef bipc::allocator< MapPersonType,
                     bipc::managed_shared_memory::segment_manager >
ShMemAllocator;

typedef boost::unordered_map< KeyType,
                          MappedType,
                          boost::hash<KeyType>,
                          std::equal_to<KeyType>,
                          ShMemAllocator >
PersonMap;

This is what I'm trying to do in the main program:

int main() 
{
bipc::managed_shared_memory segment(bipc::create_only, "MySharedMemory", 65536);

PersonMap *persons = segment.construct<PersonMap>("MyHashMap")
    ( 3, boost::hash<ShmemString>(), std::equal_to<ShmemString>()
        , segment.get_allocator<MapPersonType>());

char_allocator alloc(segment.get_allocator<char>());

Person p1(20, 10000, "ABC", alloc);
persons->insert(MapPersonType(ShmemString("Person1", alloc), p1));
}

Using the above code, I'm able to create an unordered_map in shared memory. However, when I am trying to access the map, I need to use a syntax like

persons->at(ShmemString("H", segment.get_allocator<char>())).print();

However, I would prefer to do this with a std::string, which results in compilation errors:

persons->at(std::string("H")).print();

Is it possible to write the above statement, i.e. accessing the map allocated in shared memory with std::string?

Answer 1

I posted this on boost-users mailing list. And, got an answer from Boost.Interprocess author that this cannot be done.