Re: [Boost-users] Segmentation fault when using std::string in stl::maps in shared memory

20 Oct 2008

      Hello All,

After a few search I found out that we cannot use std::string. Instead we
should try with interprocess::basic_string. Can anyone guide me through
this.

hamsinv wrote:
...
Hello All,
I have been trying boost library for sharing stl::maps using shared
memory. I am able to run the example code on sharing stl::maps
successfully. It uses int-float pair to store in map. I have to store
std::string-int pair. Writing into the map, works fine, yet reading the
same from a different process results in Segmentation fault.
Both the Process are as follows:
Process1.cpp
---------------------
//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2006-2007. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////
#include 
#include "boost/interprocess/detail/config_begin.hpp"
#include "boost/interprocess/detail/workaround.hpp"
//[doc_map
#include "boost/interprocess/managed_shared_memory.hpp"
#include "boost/interprocess/containers/map.hpp"
#include "boost/interprocess/allocators/allocator.hpp"
#include <functional>
#include <utility>
int main ()
{
   using namespace boost::interprocess;
   shared_memory_object::remove("MySharedMemory");
   try{
      managed_shared_memory segment
         (create_only
         ,"MySharedMemory" //segment name
         ,65536);          //segment size in bytes
typedef int    KeyType;
      typedef std::string  MappedType;
      typedef std::pair ValueType;
      typedef allocator
         ShmemAllocator;
      typedef map
MyMap;
     ShmemAllocator alloc_inst (segment.get_segment_manager());
 MyMap *mymap =
         segment.construct<MyMap>("MyMap")      //object name
                                    (std::less<int>() //first  ctor
parameter
                                    ,alloc_inst);     //second ctor
parameter
//Insert data in the map
      for(int i = 0; i < 10; ++i){
        cout<<"I value is: "<insert(std::pair(i,"Hello"));
      }
     mymap = segment.find<MyMap>("MyMap").first;
      cout<<"Shared memory map created"<< mymap<begin();it != mymap->end();++it)
        {
                 cout<<"key: "<<(*it).first<<"  Value:
"<<(*it).second<
Process2.cpp
--------------------
//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2006-2007. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////
#include 
#include "boost/interprocess/detail/config_begin.hpp"
#include "boost/interprocess/detail/workaround.hpp"
//[doc_map
#include "boost/interprocess/managed_shared_memory.hpp"
#include "boost/interprocess/containers/map.hpp"
#include "boost/interprocess/allocators/allocator.hpp"
#include <functional>
#include <utility>
int main ()
{
   using namespace boost::interprocess;
try{
      managed_shared_memory segment
         (open_only
         ,"MySharedMemory" //segment name
         );
      typedef int    KeyType;
      typedef std::string  MappedType;
      typedef std::pair ValueType;
     typedef allocator
         ShmemAllocator;
      typedef map
MyMap;
 MyMap *mymap =
         segment.find<MyMap>("MyMap").first;      //object name
     for( MyMap::iterator it = mymap->begin();it != mymap->end();++it)
        {
                 cout<<"key: "<<(*it).first<<"  Value:
"<<(*it).second<
Could anyone please tell me what's going wrong and how can i use
std::string as key and int as value.
Thank you.
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