Run-time error : Access violation writing loacation while deleting a pointer in dynamic memory allocation

Question

I have written this code in order to show line shapefiles in an opengl window.
In fact it's the code Rendering Shapefile in OpenGL here in code-project, but I'm making some changes on it in order to read the shapes with the OGR library not shapelib.

#include "ogrsf_frmts.h" 
//#include "shapelib\shapefil.h"

void OpenShapeFile(char* filename)
{
   int i = 0;
   int j = 0;
   OGRErr error;
   OGRDataSource *poDataSource;
   poDataSource = OGRSFDriverRegistrar::Open(filename,false);
   OGRLayer *poLayer;
   poLayer = poDataSource ->GetLayer(0);
   OGREnvelope *poEnvelope = new OGREnvelope();
   error = poLayer ->GetExtent(poEnvelope,true);
   sBoundingBox.fMaxX = poEnvelope ->MaxX;
   sBoundingBox.fMaxY = poEnvelope ->MaxY;
   sBoundingBox.fMinX = poEnvelope ->MinX;
   sBoundingBox.fMinY = poEnvelope ->MinY;
   delete poEnvelope;
   OGRwkbGeometryType GeometryType = poLayer ->GetGeomType();
   int NumberOfFeatures = poLayer ->GetFeatureCount(true);
   poLayer ->ResetReading();

   //Line Shapefile
   if ( wkbFlatten ( GeometryType ) == wkbLineString )
   {
       OGRFeature *poFeature;
       MyLineString2D lineString;

       //temporary pointer in order to store coordinates of individual line vertexes
       OGRPoint *poPointTemp = new OGRPoint();
       for ( i = 0; i < NumberOfFeatures; i++ )
       {
           poFeature = poLayer ->GetNextFeature();
           OGRGeometry *poGeometry;
           poGeometry = poFeature ->GetGeometryRef();
           if ( poGeometry != NULL )
           {
               OGRLineString *poLineString = (OGRLineString *)poGeometry;
               int NumberOfVertexes = poLineString ->getNumPoints();
               lineString.vPointList.resize(NumberOfVertexes);
               for ( j = 0; j < NumberOfVertexes ; j++ )
               {
                   poLineString ->getPoint(j,poPointTemp);
                   MyPoint2D ptTemp;
                   ptTemp.dX = poPointTemp ->getX();
                   ptTemp.dY = poPointTemp ->getY();
                   lineString.vPointList.at(j) = ptTemp;
               }
               vLines.push_back(lineString);
           }
           OGRFeature::DestroyFeature( poFeature );
       }
   delete poPointTemp;
   } 
}  

void initializeGL()
{
    //glClearColor (0.0, 0.0, 0.0, 0.0);
    glClearColor (1.0, 1.0, 1.0, 1.0);  

int main(int argc, char** argv)
{
//OpenShapeFile("Shapefiles\\poi.shp");//Point Shapefile
OpenShapeFile("Shapefiles\\strassen.shp");//Line Shapefile
//OpenShapeFile("Shapefiles\\gruenflaechen.shp");//Polygon Shapefile

when I comment the line:

delete poPointTemp;  

there's no error and the shape is drawn on an OpenGL window properly. But as you know it's kind of memory leaking so when I don't need poPointTemp I should delete it.
But at the line:

delete poPointTemp;  

I get the run-time error:

I have debugged my code and the address and contents of poPointTemp before running this line is as follows:

poPointTemp 0x00503a90 {x=3435936.3300000001 y=5790327.5999999996 z=0.00000000000000000 }  

I mean poPointTemp is not a NULL pointer and also the address of where we don't have access to is not the same as the poPointTemp's address!!!

what do you think is the problem of my code?

I have tried to minimize the code as much as I can. So if you want to debug the code yourself you can download it in code-project and then just make changes to it according to the code that I have written above.

• please use my OpenShapeFile method instead of the code's corresponding method and do other changes to the code.
  Also I have uploaded my code here in 4shared, you can take it here and just link GDAL Library and run it.

---

Of course with the help of john's answer my problem got fixed. But I'll still appreciate someone who tells me what's the problem of the above code?

Answer 1

I had the same problem. Your code is correct.

In my case the problem was other gdal.dll in the PATH. Be sure that your executable load the right library.

(There's a lot off application that comes with gdal.dll, and add their folder to the PATH. Like QGis or GeoConcept...)

Answer 2

This is not really an answer but it might help and it's a bit too long to put in a comment. Also bear in mind that I don't know this library so my advice might not be correct.

Undoubtedly this error is masking the real error which is somewhere else in your code. As you say you should delete the memory at this point. However it does seem to me that you are unnecessarily allocating memory. For instance this

OGREnvelope *poEnvelope = new OGREnvelope();
error = poLayer ->GetExtent(poEnvelope,true);
sBoundingBox.fMaxX = poEnvelope ->MaxX;
sBoundingBox.fMaxY = poEnvelope ->MaxY;
sBoundingBox.fMinX = poEnvelope ->MinX;
sBoundingBox.fMinY = poEnvelope ->MinY;
delete poEnvelope;

could be rewritten without any memory allocation like this

OGREnvelope poEnvelope;
error = poLayer ->GetExtent(&poEnvelope,true);
sBoundingBox.fMaxX = poEnvelope.MaxX;
sBoundingBox.fMaxY = poEnvelope.MaxY;
sBoundingBox.fMinX = poEnvelope.MinX;
sBoundingBox.fMinY = poEnvelope.MinY;

A similar change could be made for poPointTemp. In general if you find yourself allocating memory for an object and then deleting it in the same scope it's an indication that you don't really need to allocate the memory at all.

None of this will fix the error which is still hidden, but the point is by simplifying your code and allocating less memory you will get closer to the real error, which is undoubtedly some kind of memory corruption.