[gdal-dev] argument default value in the C API to GDALAlgorithmArg

[Even Rouault]

Hi Chris,

This was indeed missing in the C API. Queued for 3.12 in 
https://github.com/OSGeo/gdal/pull/12853

If you need this in 3.11, you can define the following implementation 
detail in your code

struct GDALAlgorithmArgHS
{
     GDALAlgorithmArg *ptr = nullptr;

     explicit GDALAlgorithmArgHS(GDALAlgorithmArg *arg) : ptr(arg)
     {
     }
};

but better conditionalize it to 3.11 only, so that to avoid issues in 
later version if we would change the definition of struct GDALAlgorithmArgHS

and then do things like

GDALAlgorithmArgH hArg;

hArg->ptr->GetDefault<std::string>();

Even


Le 04/08/2025 à 03:46, Chris Toney via gdal-dev a écrit :
> Hi,
> In the C API there is GDALAlgorithmArgHasDefaultValue(), but no
> interface to the GetDefault() class method to access the value itself
> when there is one (nor in the Python bindings, AFAICS).
>
> I don't believe there is a fromHandle() method on GDALAlgorithmArg to
> get to the C++ object.
>
> Is there possibly a workaround for that when working through the C API?
>
> Chris
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