Access violation, cannot read memory xxxxxxx

Hi, I recently encountered an access violation problem. In VC++, if I run it, the error code is "cannot read memory xxxxxxx"; in the debug mode, it will show "xxxxxxxx: access violation".

I found out that this exception happened when a function was called to a number of times -- I am not sure if it happened at the same number. But the function works and this only happens after a number of calls, which frustrates me. Please help me!

Here is the functions. drawSurface() is to generate a set of x and y coordinates, and for each set, use surfacePoint() to calculate the z value of that point, and draw it in drawSurface().

void CBSplineView::drawSurface()
{
      MyPoint* s=new MyPoint();
      glColor3f(1.0,1.0,0.0);
      std::vector<MyPoint*> stor,cal;
      int i,j;
      double u,v;
      u=0.0;
      for (i=0;i<cal.size();i++) delete cal[i];
      cal.clear();
      for (j=0;j<=NUMBER; j++)
      {
            v=(double)j/fNUMBER*n;
            s=new MyPoint();
            surfacePoint(u,v,1,s);
            cal.push_back(s);
      }
      for (i=1; i<=NUMBER; i++)  
      {
            u=(double)i/fNUMBER*m;
            for (int k=0;k<stor.size();k++) delete stor[k];
            stor.clear();
            stor=cal;
            v=0.0;
            cal.clear();
            s=new MyPoint();
            surfacePoint(u,v,1,s);
            cal.push_back(s);
            for (j=1; j<=NUMBER; j++)
            {
                  v=(double)j/fNUMBER*n;
                  
                  glBegin(GL_POLYGON);
                        glVertex3f(stor[j-1]->x,stor[j-1]->y,stor[j-1]->z);
                        glVertex3f(stor[j]->x,stor[j]->y,stor[j]->z);
                        s=new MyPoint();
                        surfacePoint(u,v,1,s);
                        cal.push_back(s);
                        glVertex3f(cal[j]->x,cal[j]->y,cal[j]->z);
                        glVertex3f(cal[j-1]->x,cal[j-1]->y,cal[j-1]->z);
                  glEnd();
            }
      }
      
      for (i=0;i<cal.size();i++) delete cal[i];
      for (int k=0;k<stor.size();k++) delete stor[k];

}

void CBSplineView::surfacePoint(double u, double v, int h, MyPoint* S)
{
      int i,j,k,l;
      double s,t,temp;

      i=floor(u*h);
      j=floor(v*h);
      s=(u-floor(u))*h;
      t=(v-floor(v))*h;

      temp=0.0;

      for (k=0;k<=m_p;k++)
      {
            for (l=0;l<=m_q;l++)
            {
                  temp=temp+B(k,m_p,s)*B(l,m_q,t)*points[(i+k)*(n*h+m_q)+j+l]->z; // WHEN AN ERROR OCCURS, THE PROGRAM STOPS AT THIS LINE.
            }
      }

      S->x=u;
      S->y=v;
      S->z=temp;
      
}
applebiboAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

AlexFMCommented:
I guess some index is out of range. Replace this line with number of lines by the following way:

int i1 = B(k,m_p,s);
int i2 = B(l,m_q,t);
int i3= (i+k)*(n*h+m_q)+j+l;   // this is index, possibly out of range
MyPoint* p1 = mypoints[i3];
...
temp = i1 * i2 ...;

This can give more information what happens. When exception occurs, enter debugger and see variable values.


Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
mahesh1402IT ProfessionalCommented:
temp=temp+B(k,m_p,s)*B(l,m_q,t)*points[(i+k)*(n*h+m_q)+j+l]->z; <== whats values of m_p and m_q ? have you crosschecked them at run time ?

How you want to evaluate above expression ? Do close it with proper parenthesis.

MAHESH
applebiboAuthor Commented:
Thanks! i3 is out of range at a very special point. Other variables are OK.
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
System Programming

From novice to tech pro — start learning today.