[Boost-users] Boost.Interprocess accessing an unordered_map in shared memory.

Subject: [Boost-users] Boost.Interprocess accessing an unordered_map in shared memory.
From: lazylabs_at_[hidden]
Date: 2013-03-11 08:20:45

Hi,

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;

In the main reader program, I create a map in the shared memory and I
insert an object in this map:

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));
}

However, when I am trying to access the map in the reader program, 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?

Thanks.