[Gdal-dev] importFromWkt() problem

[Petteri Packalen]

Frank, list,

Once again, I struggled with the weird problem until I understood to look 
at the documentation... The problem was that, within importFromWkt(), the 
pointer was updated to pointer after the consumed text. However, I don't 
still understand why the first *corrected* solution does not work 
properly. I want to reset the geometry of an existing feature based on WKT 
representation. Below are two examples in which only the latter one works 
properly. An example 1 crashes due to illegal memory access. geo_trans is 
a buffer which stores WKT.

EXAMPLE 1
=========
OGRPolygon * poPoly = new OGRPolygon();
poPoly->importFromWkt( &geo_trans );
poDstFeature->SetGeometryDirectly( poPoly );
...
OGRFeature::DestroyFeature( poFeature );

EXAMPLE 2
=========
char* pszWkt = (char*) geo_trans;
OGRSpatialReference *ref = new OGRSpatialReference( NULL );
OGRGeometry *new_geom;
OGRErr err = OGRGeometryFactory::createFromWkt(&pszWkt, ref, &new_geom);
poDstFeature->SetGeometryDirectly( new_geom );
...
OGRFeature::DestroyFeature( poFeature );

In the comment within the ogrgeometryfactory.cpp it states that 
"createFromWkt() now updates pointer to text to indicate how much text was 
consumed". I understand that this can be useful in many occasions although 
I don't understand why it is implemented this way. Anyway, why the first 
solution does not work? In addition, in an example 1 the problem occurres 
only after very many (>million) calls to importFromWkt(). Something is 
happening in the background (related to reference counting etc.?) I don't 
understand.

Best regards,
Petteri

=========================================================================
Petteri Packalén 
University of Joensuu 
Faculty of Forestry 
P.O. Box 111 
80101 Joensuu
Finland 
e-mail: packalen at cs.joensuu.fi 
=========================================================================