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<p>Abel Pau,</p>
<p>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<br>
</p>
<p>Typically ogr2ogr will never call CreateField() after
ICreateFeature()</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 02/10/2023 à 15:54, Abel Pau via
gdal-dev a écrit :<br>
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<p class="MsoNormal"><span lang="EN-US">Hi everybody,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">And every time a feature
is added the driver have to verify in which destination
field corresponds to the new one.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks a lot.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<o:p></o:p></span></p>
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