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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: How can one record component be local and another not?
Date: Tue, 5 May 2020 22:08:36 +0300
Organization: Tidorum Ltd
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Date: 2020-05-05T22:08:36+03:00
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On 2020-05-05 20:17, hreba wrote:
> On 5/5/20 5:45 PM, Jeffrey R. Carter wrote:
>> On 5/5/20 1:04 PM, hreba wrote:
>>>
>>> (The reason for the above construction is the need to pass a pointer 
>>> to a C library function.)
>>
>> Most likely you do not need to pass a pointer to your C function. For 
>> example, given the C function
>>
>> void f (int* i);
>>
>> You can do
>>
>> procedure F (I : in out Interfaces.C.int) with Import, Convention => 
>> C, ...;
>>
>> and the compiler will call the C function correctly.
>>
> 
> It is more complicated, unfortunately. I got
> 
>     type gsl_odeiv2_system is record
>        c_function : access function
>             (arg1 : double;
>              arg2 : access double;
>              arg3 : access double;
>              arg4 : System.Address) return int;  -- 
> /usr/include/gsl/gsl_odeiv2.h:58
>        jacobian : access function
>             (arg1 : double;
>              arg2 : access double;
>              arg3 : access double;
>              arg4 : access double;
>              arg5 : System.Address) return int;  -- 
> /usr/include/gsl/gsl_odeiv2.h:60
>        dimension : aliased size_t;  -- /usr/include/gsl/gsl_odeiv2.h:61
>        params : System.Address;  -- /usr/include/gsl/gsl_odeiv2.h:62
>     end record;
>     pragma Convention (C_Pass_By_Copy, gsl_odeiv2_system);  -- 
> /usr/include/gsl/gsl_odeiv2.h:64
> 
> and I have to pass a variable
>     sys: access gsl_odeiv2_system
> to the initialization function of that C library, and the
> 
>    params: System.Address;
> 
> component in the record, which internally is then passed to c_function() 
> and jacobian(), posed the problem.

I don't understand -- System.Address is not an access type; why do you 
need to use an access type to produce this parameter? Do you need a 
pointer to the "params" component?

Perhaps you can show a bit more of the actual code that has the problem?

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .