'iterator not dereferencable' C++ Stack

Question

No idea what is going on here. I have a std stack of Vector3D's (a 3-dimensional vector class give to me by my tutor). I have pushed two Vector3D's on to the stack but when I go to go the top one with vectorStack.top() I am treated to this very unhelpful error:

Debug Assertion Failed!

Expression: deque iterator not dereferenceble

I thought maybe there was something wrong with the Vector3D copy constructor but I've tried to make my own quick Vector3D struct (deleting the old one I was given) and that doesn't work either!

Here is the code:

D3Dapp.cpp
if (!lsys.initialised)
{
    LSystem::ReproductionRule r1;
    r1.from = 'F';
    r1.to = "F+F-[FFF]";
    lsys.rules.push_back(r1);

    LSystem::ReproductionRule r2;
    r2.from = 'F';
    r2.to = "FF";
    lsys.rules.push_back(r2);

    lsys.result = lsys.generateResult("F", 0, 5);
    lsys.currentPosition = Vector3D(0.0f,0.0f,0.0f);
    lsys.vectorStack.push(lsys.currentPosition);

    lsys.initialised = true;
}

  lsys.result = "[FF]+FF";

if (!lsys.complete)
{
    for (int i=0; i < lsys.result.length();i++)
    {
  // F move forward
        if (lsys.result[i] == 'F')
        {
            float cosAng = cos(lsys.angle);
            float sinAng = sin(lsys.angle);

    Vector3D currentPosition(lsys.vectorStack.top());

            Vector3D newPosition = Vector3D(
                currentPosition.x + (cosAng * 0.5f), 
                currentPosition.y + (sinAng * 0.5f), 
                currentPosition.z);

            //lsys.vectorStack.push(newPosition);

            Vertex s, e;
            s.x = currentPosition.x;
            s.y = currentPosition.y;
            s.z = currentPosition.z;
            e.x = newPosition.x;
            e.y = newPosition.y;
            e.z = newPosition.z;

            startList.push_back(s);
            endList.push_back(e);

            lsys.currentPosition = newPosition;

    // + turn right
        } else if (lsys.result[i] == '+')
        {
            float rdn = 3.141592f / 180.0f;
            lsys.angle = (lsys.angle + 20.0f);

    // - turn left
        } else if (lsys.result[i] == '-')
        {
            float rdn = 3.141592f / 180.0f;
            lsys.angle = (lsys.angle - 20.0f);

    // [ push stack
        } else if (lsys.result[i] == '[')
  {
    lsys.vectorStack.push(lsys.currentPosition);

    // ] pop stack
  } else if (lsys.result[i] == ']')
  {
    lsys.vectorStack.pop();
  }
    }

    lsys.currentPosition = Vector3D(0.0f,0.0f,0.0f);
}

lsys.complete = true;

The stack in lsystem is just stack<Vector3D> vectorStack;

I've tried a variety of ways of assigning vectorStack.top() to current position but nothing seems to be working.

For completeness, here are the constructors to Vector3D:

Vector3D.h
Vector3D() {
    x = y = z = 0;
}

Vector3D(double a, double b, double c) {
    x = a;
    y = b;
    z = c;
}

Vector3D(const Vector3D& v) {
    x = v.x;
    y = v.y;
    z = v.z;
}

EDIT: To prove there is something in the stack screenshot

This is the line in stack which throws the error screenshot2

If you're getting that message on a call to `top` your container is empty. — Mark Ransom, Dec 04 '12 at 21:27
I have breakpointed to the call and checked the stack myself it has 2 Vector3D's in it. Trust me! — BouncingCzech, Dec 04 '12 at 21:28
@BouncingCzech : If you were correct then you wouldn't have needed to post a question here. ;-] — ildjarn, Dec 04 '12 at 21:30
Here's a screenshot, you can see in the watch list below that there are two vectors in there: https://dl.dropbox.com/u/2577802/Hosted%20Images/stackfull.png — BouncingCzech, Dec 04 '12 at 21:33
I'm not sure, it's not part of my code I think it's some kind of generic container. — BouncingCzech, Dec 04 '12 at 22:16
c is the internal container in the implementation of std::stack - a std::deque. The type is visible in the watch window screenshot. — JasonD, Dec 04 '12 at 22:30

score 1 · Answer 1 · answered Dec 04 '12 at 22:35

There are only two two ways I can think of that would cause such a problem. The first is that you have a memory corruption somewhere in your program, which is possibly but we should only consider after eliminating our other options.

The second option is that the stack is, in fact, empty. Your screenshot doesn't show us the internal size of the stack, it only shows us that at some point it allocated memory for two items and pushed them on the stack. Most likely you have popped those items off and the stack is empty yet still pointing to seemingly valid memory. You can prove or disprove this by just putting some couts by the pushes and pops to your stack, as well as printing lsys.vectorStack.size() before calling top.

The VS debugger reports the current value of size for the deque - that's the number in []s in the screenshot. It certainly thinks there are actually two elements in the stack. — JasonD, Dec 04 '12 at 22:55
Thanks Mark I'll look in to that right now and let you guys know. — BouncingCzech, Dec 05 '12 at 00:24

score 0 · Accepted Answer · answered Dec 05 '12 at 12:50

It turns out the framework I'm using (being forced to use) is built with very strict memory requirements in mind, there are several calls to ZeroMemory which seem to allocate this amount of memory and this amount of memory only.

So when I start adding a load of dynamic memory structures like stacks and vectors everything goes to hell.

ZeroMemory( this, sizeof(D3dApp) )

After that removing the above I still had some issues but I followed Mark B's advice and now its up and running.

Many thanks.

'iterator not dereferencable' C++ Stack

2 Answers2