c++ Access violation reading location while erasing from list

Question

I have a following c++ code:

typedef std::list< Volume >::iterator   pVolume;
typedef std::list< pVolume >::iterator  ppVolume;
void Node::delVolume( pVolume _volume )
{
    for( ppVolume it = m_volumes.begin( ); it != m_volumes.end( ); )
        if( (*it) == _volume )
        {
            it = m_volumes.erase( it );
            break;
        }
        else
            it++;
}

it gets an error

Unhandled exception at 0x009a3c79 in Delone3D.exe: 0xC0000005: Access violation reading location 0xfeeefef2.

exactly when erasing. Debug shows that neither "it" nor "_volume" is null pointer.

What other reasons this may occur for?

Destructor of Volume is empty. All args in Volume are static. In this function I'm deleting only the pointer to Volume not the object itself. — Olzhas Turar, Oct 10 '15 at 09:34
Well, we cannot tell anything, if you're not showing the relevant code in context. — πάντα ῥεῖ, Oct 10 '15 at 09:36
@OlzhasTurar FYI: That loop can be replaced with this: `auto iter = std::find(m_volumes.begin(), m_volumes.end(), _volume); if ( iter != m_volumes.end()) m_volumes.erase( iter );` — PaulMcKenzie, Oct 10 '15 at 09:37
@OlzhasTurar You are mismanaging pointers elsewhere in your application. It is this code that finally shows the damage. — PaulMcKenzie, Oct 10 '15 at 09:40
I've replaced contents of the function to the proposed code and get the same error at the "erase" operator. — Olzhas Turar, Oct 10 '15 at 09:43
I'm using visual studio 2010 debugging and it shows that all the arguments evolved in this code have correct contents. List has only 4 elements and one of them is equal to the "_volume" object by [ptr] and other fields. — Olzhas Turar, Oct 10 '15 at 09:58
Debug then moves me to xutility file's line 177 and say that some _Iterator_base12 **_Pnext contain CXX0030: Error: expression cannot be evaluated — Olzhas Turar, Oct 10 '15 at 10:01

score 2 · Accepted Answer · edited May 23 '17 at 12:06

The code you show is correct, it seems like there's a problem elsewhere in your application. The memory pattern 0xfeeefef2 (a few addresses above 0xfeeefeee) indicates freed dynamic memory, see here.

You can massively simplify your code, by the way:

// for std::list, as in your example
m_volumes.remove(_volume);

// for std::vector and std::deque
auto itr = std::remove(m_volumes.begin(), m_volumes.end(), _volume);
m_volumes.erase(itr, m_volumes.end());

score -2 · Answer 2 · answered Oct 10 '15 at 11:00

I found the place generating the error. But I have no idea why.

Whole my code is implementing as heirs of abstract Event class

class Event
{
public:
    Event( ) { }
    ~Event( ) { }

    virtual void Implement( void ) abstract;
    virtual void ReturnColors( void );      
private:
};

There are deque of pointers to Events

std::deque< Event * >   m_triangulationEvents;

Which are used following way

void Delaunay3D::nextEvent( )
        {
            if( !m_triangulationEvents.empty( ) )
            {
                m_prevEvent->ReturnColors( );

                Event * cur = m_triangulationEvents.front( );
                m_triangulationEvents.pop_front( );
                cur->Implement( );

                delete m_prevEvent;
                m_prevEvent = cur;
            }
        }

The problem were at

delete m_prevEvent;

string. Commenting it or using

m_prevEvent.~Event( );

results in well working application. Thanks for everyone.

P.S. @TheOperator thanks for mentioning freed dynamic memory

-1 -- Your fix is not a fix. You are not supposed to call the destructor explicitly like that. The one glaring issue with your code is that your `Event` class lacks a virtual destructor. — PaulMcKenzie, Oct 10 '15 at 11:47

c++ Access violation reading location while erasing from list

2 Answers2