[Gdal-dev] OGR:GetNextFeature() throws exception in WINXP

[Mateusz Łoskot]

Vidhiyadharan Nadarajah wrote:
> You can down load the shape files from the following link
> http://vdharan.741.com/india_ds.dbf
> http://vdharan.741.com/india_ds.shp
> http://vdharan.741.com/india_ds.shx
> 

Hi,
I think I've found the problem.
Your code also gave me exceptions and your program crashed.
I tested with GDAL 1.3.0, compiled using VC++ 2005.

Simply, you've used OGR API incorrectly.
So, here is working version with my fixes, please read big comments 
marked with my nickname "mloskot".


//////////////////////////////////////////////////////////////////////////////
#include <ogrsf_frmts.h>

int main()
{

     OGRRegisterAll();
     OGRDataSource* poDS = NULL;
     poDS = 
OGRSFDriverRegistrar::Open("D:\\download\\india\\india_ds.shp", FALSE);
     if( poDS == NULL )
     {
     	printf( "Open failed.\n%s" );
     	exit( 1 );
     }

     OGRLayer* poLayer = NULL;
     poLayer = poDS->GetLayerByName( "india_ds" );
     OGRFeature *poFeature;
     poLayer->ResetReading();
     if (NULL == poLayer)
     {
     	printf("Layer not found\n");
     	OGRDataSource::DestroyDataSource(poDS);
     	return -1;
     }

     while( (poFeature = poLayer->GetNextFeature()) != NULL )
     {
         long fid = poFeature->GetFID();
	printf("==================================\n");
	printf("FID: %d\n", fid);		

	OGRFeatureDefn *poFDefn = poLayer->GetLayerDefn();
	if (NULL == poFDefn)
	{
	    // mloskot: HANDLE THIS ERROR AS YOU WISH
	    printf("\nEEERRROOORRR!\n");
	    return 0;
	}

	for(int iField = 0; iField < poFDefn->GetFieldCount(); iField++)
	{
	    OGRFieldDefn *poFieldDefn = poFDefn->GetFieldDefn( iField );
	    if( poFieldDefn->GetType() == OFTInteger )
		printf( "%d,", poFeature->GetFieldAsInteger( iField ) );
	    else if( poFieldDefn->GetType() == OFTReal )
		printf( "%.3f,", poFeature->GetFieldAsDouble(iField) );
	    else if( poFieldDefn->GetType() == OFTString )
		printf( "%s,", poFeature->GetFieldAsString(iField) );
	    else
		printf( "%s,", poFeature->GetFieldAsString(iField) );
	}

	OGRGeometry *poGeometry = NULL;
     	poGeometry = poFeature->GetGeometryRef();
	if( poGeometry == NULL)
	{
	   printf("NULL GEOMETRY!!!\n");
	}
	else
	{
	    if (wkbFlatten(poGeometry->getGeometryType()) == wkbPolygon)
	    {
		// mloskot: I'D CHECK THOSE POINTERS AGAINST NULL
		OGRPolygon *poPolygon = (OGRPolygon *)poGeometry ;
		OGRLinearRing *poLinearRing = poPolygon->getExteriorRing();
		
		// mloskot:
		// WHAT IS THIS CAST FOR???
		// This line causes your problems
		//OGRPoint *poPoint = (OGRPoint *) poGeometry;

		for(int pi = 0; pi < poLinearRing->getNumPoints(); pi++)
		{
		    // mloskot:
		    OGRPoint point; // CAN NOT BE NULL
		    // getPoint expects allocated OGRPoint objec to will with coordinates
		    poLinearRing->getPoint(pi, &point);
		    printf( "%.3f,%.3f\n", point.getX(), point.getY() );
		}
	    }
	    else
	    {
		printf( "no polygon geometry\n" );
	    }
	}
     }
     printf("\n\n");

     OGRFeature::DestroyFeature( poFeature );
     OGRDataSource::DestroyDataSource( poDS );
     return 0;
}
//////////////////////////////////////////////////////////////////////////////

Good Luck!
-- 
Mateusz Łoskot
http://mateusz.loskot.net