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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: How to bind this properly, C ** which is an array
Date: Fri, 1 Mar 2019 15:02:48 +0100
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Date: 2019-03-01T15:02:48+01:00
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On 2019-03-01 14:48, Lucretia wrote:
> Hi,
> 
> I'm trying to bind the following struct:
> 
> typedef struct mpc_ast_t {
>    char *tag;
>    char *contents;
>    mpc_state_t state;
>    int children_num;
>    struct mpc_ast_t** children;
> } mpc_ast_t;
> 
> I have this:
> 
>     type ASTs is
>     record
>        Tag                : C.Strings.chars_ptr;
>        Contents           : C.Strings.chars_ptr;
>        State              : States;
>        Number_Of_Children : C.int;
>        Children           : System.Address; --  Pointer to a pointer to an array of ASTs.
>     end record with
>       Convention => C;
> 
> Children needs to be accessed in code as a pointer to a pointer to an array of ASTs.
> 
> How do I best bind this thing? It's likely going to have to be converted from Address to a particular type using Unchecked_Conversion most likely.

I think you could do it without Unchecked_Conversion:

    -- Forward declaration
    type ASTs;
    type ASTs_Ptr is access all ASTs;
    pragma Convention (C, ASTs_Ptr);

    -- Flat array of pointers without bounds
    type ASTs_Ptr_Array is array (size_t) of ASTs_Ptr;
    pragma Convention (C, ASTs_Ptr_Array);
    type ASTs_Ptr_Array_Ptr is access all ASTs_Ptr_Array;
    pragma Convention (C, ASTs_Ptr_Array_Ptr);

    -- Now the type
    type ASTs is record
       Tag                : C.Strings.chars_ptr;
       Contents           : C.Strings.chars_ptr;
       State              : States;
       Number_Of_Children : C.int;
       Children           : ASTs_Ptr_Array_Ptr;
    end record;
    pragma Convention (C, ASTs);

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de