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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Need a way to convert a constant to a variable
Date: Sat, 5 Aug 2017 21:37:41 +0200
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Xref: news.eternal-september.org comp.lang.ada:47619
Date: 2017-08-05T21:37:41+02:00
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On 2017-08-05 19:45, Victor Porton wrote:
> Dmitry A. Kazakov wrote:
> 
>> On 2017-08-05 17:11, Victor Porton wrote:
>>
>>> I do use char_array for interfacing with C.
>>
>> You should probably reconsider it. It works only for C functions that do
>> not expect null as a value, do not return strings allocated outside Ada,
>> do not deallocate strings passed into.
> 
> I use an indefinite holder with char_array inside to represent a C string
> (whose length size_t value ('Length in Ada) I pass separately to a C
> function), which may be either a real string (corresponding to char_array)
> or NULL (corresponding to empty indefinite handler).
> 
> Note that the above is NOT related to NUL-terminated strings.

Yes. What you do is not a good idea. Try this instead:

    type C_String is new Ada.Finalization.Limited_Controlled with record
       Data : chars_ptr := null_ptr;
    end record;
    procedure Set (X : in out C_String; Text : String) is
    begin
       Free (X.Data);
       X.Data := New_String (Text);
    end Set;
    procedure Finalize (X : in out C_String) is
    begin
       Free (X.Data);
    end Finalize;

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