Abel Pau,
no you can't know the number of fields at the moment of creating the
layer. A number of drivers only accept the CreateField() method to be
called until the first call to ICreateFeature(). Cf the
"bFeaturesWritten" variable in ogr/ogrsf_frmts/jml/ogrjmlwriterlayer.cpp
Typically ogr2ogr will never call CreateField() after ICreateFeature()
Even
Le 02/10/2023 à 15:54, Abel Pau via gdal-dev a écrit :
Hi everybody,
do anyone know if a driver can know the number of fields (and it’s
names, etc) of a layer BEFORE starting fetch features? So in the
moment of create the layer.
I mean, when a driver is creating the own layer it could probably be
interested in creating all fields before starting and not in the
middle of translation. It could be caused because the output format
requires that in terms of efficiency.
For instance, first feature have 3 fields, second feature have four,
etc... Until the last feature driver is not sure of all fields are
definitive.
And every time a feature is added the driver have to verify in which
destination field corresponds to the new one.
So, I accepted that it happens with the number of features (Even can
remember my concerns that time) and I am wondering if I have to accept
that for the number of fields.
Thanks a lot.
*Abel Pau Garcia*
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