On 28/02/2014 10:54, Even Rouault wrote:
Hi Vincent,
Hi,
OGRLayer::GetLayerDefn() doc says "The returned OGRFeatureDefn is owned by
the OGRLayer,
and should not be modified or freed by the application."
Yes, a OGRFeatureDefn created by a layer should not be modified outside of the
driver, otherwise chaos will happen.
But in alg/contour.cpp, in OGRContourWriter, the return value ofGetLayerDefn
is used to
create a feature that apparently takes ownership of the returned
OGRFeatureDefn. When this
feature is freed at the end ofOGRContourWriter, theOGRFeatureDefn is freed.
Am I missing something ?
OGRContourWriter is correct. If the OGRFeatureDefn is freed at the end of
OGRContourWriter, this is very likely because the ref count of the feature defn
passed to OGRContourWriter was 0, which is incorrect. Creating a feature
increases the ref count of the feature defn that is used to create it.
Destroying a feature decreases the ref count, and if 0 is reached, it destroys
the feature defn.
For info, my implementation ofGetLayerDefn is:
OGRFeatureDefn * OGRWAsPLayer::GetLayerDefn()
{
return &oLayerDefn;
}
withoLayerDefn a member ofOGRWAsPLayer:
classOGRWAsPLayer: public OGRLayer
{
...
OGRFeatureDefn oLayerDefn;
...
};
This is incorrect. Your OGRWAsPLayer should have a OGRFeatureDefn* pointer, and
do the following in its constructor :
poLayerDefn = new OGRFeatureDefn();
poLayerDefn->Reference();
and in its destructor
poLayerDefn->Release();
(look at
http://trac.osgeo.org/gdal/browser/trunk/gdal/ogr/ogrsf_frmts/pgdump/ogrpgdumplayer.cpp)
Thanks for that.
Note that the xls driver creates a new "dummy"OGRFeatureDefn in its
implementation
ofGetLayerDefn.
Why do you call it "dummy" ? This is perfectly valid. It is just a lazy/differed
instanciation of the layer defn (for performance reasons). But you likely don't
need that.
Sorry, I must have had a 'return new OGRFeatureDefn("dummy");' in my
code and mistakenly took that code for xls driver code (which I took as
a starting point before you mentionned pgdump). "Dummy" was referring to
that line of code (which was my code :-( ).
Even
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