Memory leak with map

Question

I can't clear the map memory (I checked by Valgrind).

#include <map>

class testMap {
    public:
        testMap(){}
        ~testMap();

        void insert_map(int, int);

    private:
          std::map<int,int> _map;
};

void testMap::insert_map(int i, int j){
    _map.insert( pair<int, int>(i,j));
}

I tried _map.clear(), erase(), deleted _map->second manually but not still no luck.

---

Thanks for all replies. Actually map alone is not a problem but map with a singleton is causing a leak. What's wrong with the code below?

#include <iostream>
#include <string>
#include <map>
#include <algorithm>
#include "Object.h"

#include<boost/smart_ptr.hpp>

using namespace std;

class Singleton {
    public:

        // A wrapper around Object class
        class object
        {
            public:
                object() : _object(new Object())
                    {}
                Object get(void)
                    { return _object.get(); }
            private:
                boost::shared_ptr<Object> _object;
        };

        object insert_new(const std::string key)
        {
            _object_maps.insert( pair<string,object>( key, object() ));
            return _object_maps.find( key )->second;
            //_test_object = object();
            //return _test_object;  // Leak goes away if I don't use map.
        }

        static Singleton* Instance();
        void Print();

    protected:
        Singleton(){}
        ~Singleton();

    private:
        static Singleton* _instance;

        std::map<std::string, object > _object_maps;
        object _test_object;
};

Singleton* Singleton::_instance = 0;

Singleton* Singleton::Instance() {
    if( _instance ==0 )
    {
        _instance = new Singleton();
    }
    return _instance;
}

void Singleton::Print() {
    std::cout << " Hi I am a singleton object" << std::endl;
}

Singleton::~Singleton()
{
    _object_maps.clear();
}

From another code I was calling by

    Singleton::object _test_object(Singleton::Instance()->insert_new("TEST"));

Is there a problem? I am getting a Valgrind error, like

      ==19584== 17 bytes in 1 blocks are possibly lost in loss record 31,429 of 52,291
      ==19584==    at 0x69A1642: operator new(unsigned int) (vg_replace_malloc.c:255)
      ==19584==    by 0x772CB0A: std::string::_Rep::_S_create(unsigned int, unsigned int, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.8)
      ==19584==    by 0x772D904: ??? (in /usr/lib/libstdc++.so.6.0.8)
       ==19584==    by 0x772DB16: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, std::allocator<char> const&) (in /usr/lib/libstdc++.so.6.0.8)
       ==19584==    by 0xBF1BC17: test::test() (test.C:34)
       ==19584==    by 0xBF1DB66: G__testDict_143_0_1(G__value*, char const*, G__param*, int) (testDict.C:190)
       ==19584==    by 0x70EA4E5: Cint::G__ExceptionWrapper(int (*)(G__value*, char const*, G__param*, int), G__value*, char*, G__param*, int) (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71EF2E4: G__call_cppfunc (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71C0095: G__interpret_func (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71AF883: G__getfunction (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71D8CC1: G__new_operator (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x718D07F: G__getexpr (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x717724E: G__define_var (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71FDEC6: G__defined_type (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x7201A6D: G__exec_statement (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71BF6C8: G__interpret_func (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x71AF62F: G__getfunction (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x718437D: G__getitem (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x7189F12: G__getexpr (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)
       ==19584==    by 0x719713F: G__calc_internal (in /afs/rhic.bnl.gov/@sys/opt/phenix/root-5.17.01/lib/libCint.so)

Answer 1

Short answer:
you explicitly declared but not defined the destructor (forgot {}).

Long answer:

1. Your code does not even compile. Missing {} in class destructor and std:: in front of pair.

2. Corrected and completed with main:

   #include <map>
   
   class testMap {
     public:
       testMap() {}
       ~testMap() {};
   
       void insert_map(int, int);
   
     private:
       std::map<int,int> _map;
   };
   
   void testMap::insert_map(int i, int j) {
       _map.insert(std::pair<int, int>(i,j));
   }
   
   int main() {
       testMap t;
       t.insert_map(12, 34);
       return 0;
   }
   

3. Compiled on 32-bit Ubuntu 11.04:

   g++ leak.cpp -o leak
   

4. Run under valgrind supervision:

   valgrind ./leak
   ==20773== Memcheck, a memory error detector
   ==20773== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
   ==20773== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
   ==20773== Command: ./leak
   ==20773== 
   ==20773== 
   ==20773== HEAP SUMMARY:
   ==20773==     in use at exit: 0 bytes in 0 blocks
   ==20773==   total heap usage: 1 allocs, 1 frees, 24 bytes allocated
   ==20773== 
   ==20773== All heap blocks were freed -- no leaks are possible
   ==20773== 
   ==20773== For counts of detected and suppressed errors, rerun with: -v
   ==20773== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 17 from 6)
   

5. No memory leakage.

Probably your compiler auto-defines a completely empty class destructor (because of missing {}), not auto-calling anymore on exit the private member map destructor.

Hope it helps :)

Answer 2

Try:

{
    std::map<int,int> empty_map;
    empty_map.swap(_map);
}

(At least, this is the usual way to convince a standard library container actually to release its memory.)