Hi Even,
then I understand that CreateField() is the only thing that can create the 
fields and that call to this function stablish the number of fields for ALL 
EXISTING features at the moment of being called?

Thanks for the explanations. I’ll thing if it’s easy to support that or it’s 
better to error out this.
Abel

De: Even Rouault <even.roua...@spatialys.com>
Enviado el: dilluns, 2 d’octubre de 2023 17:36
Para: Abel Pau <a....@creaf.uab.cat>; gdal dev <gdal-dev@lists.osgeo.org>
Asunto: Re: [gdal-dev] Number of fields when creating layer?



Le 02/10/2023 à 17:23, Abel Pau a écrit :
Thanks Even,

that it’s not so bad. I can “wait” until ICreateFeature and if it’s the first 
feature create the number of fields it has.

But, then, what happens with other fields that can appear after in next 
features? I might ignore them, but... it’s not a good thing.
Just look at existing drivers, like the JML one I pointed. They will error out 
when attempting to call CreateField() once a feature has been written, and they 
will stop advertizing the OLCCreateField capability as well.


Can they appear later or not? I haven’t understood it at complete.

Calling CreateField() at any time is a possibility of the OGR API. That doesn't 
mean that all drivers have to support it. Most writers will generally create 
all needed fields before writing features, if they can, to be compatible with 
as many output drivers as possible.



--

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