[gdal-dev] A question of eficiency

[Even Rouault]

Abel,

At the minimum for the reading side of a vector driver, you need to 
implement GetNextFeature().

If there is an efficient way of knowing the number of features without 
iterating over the whole file (typically a field in a header giving that 
number), you may implement GetFeatureCount(). If you don't implement it, 
and code using your driver needs the feature count, the generic 
implementation of OGRLayer::GetFeatureCount() will call GetNextFeature() 
repeatdly until it returns NULL.

Not totally sure to understand your question about multielements. If you 
have an instance of OGRGeometryCollection or any deriving class, there's 
a getNumGeometries() method to get the number of parts

Even

Le 07/07/2023 à 11:33, Abel Pau a écrit :
>
> Hi,
>
> I would like to know if when we use the code of GDAL to program a 
> driver (or whatever) in vectors (so, ogr) we can assume that we can 
> know the number of elements we are going to import in any way or it 
> would be possible not knowing that until NextFeature is empty (or 
> something like that). So, there is any way to obtain this number of 
> elements without doing a while? And in case of multielements its 
> possible to know how many parts are there in total?
>
> I need that to write my format (I don’t explain the details cause I 
> don’t get you bored :) )
>
> If anyone know that I’d appreciate an answer. Thanks in advance.
>
> Abel.
>
>
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