From: "Alejandro R. Mosteo" <alejandro@mosteo.com>
Subject: Re: Interfaces.C.Strings chars_ptr memory management strategy
Date: Wed, 30 May 2018 15:10:23 +0200
Date: 2018-05-30T15:10:23+02:00 [thread overview]
Message-ID: <pem7s0$go4$1@dont-email.me> (raw)
In-Reply-To: <6ff31dc6-31e7-4755-bda0-1b53fa02f31f@googlegroups.com>
On 26/05/2018 00:22, NiGHTS wrote:
> I am creating a binding to a C library that requires me to repeat the same function but with a string parameter that changes on each call. I don't want to have to keep creating and destroying string memory for all of these function calls. I would like to create the memory for the string once, allocate enough space so it doesn't need to grow, and reuse that memory for the function call every time I need to pass a new string to it.
I'm currently using this:
https://github.com/mosteo/cstrings
which is not what you want since it allocates on every instance (although
on the stack). Still, it might give you some ideas.
I'm still unsure if that's 100% guaranteed to be safe; for the experts
out here, the question is, in a call to a C function like this:
Call_To_C_Function
(Function_That_Returns_A_Limited_Tagged_Type (...)
.Subprogram_That_Returns_A_C_Pointer_To_Data_In_The_Tagged_Type);
Is the in-place built limited tagged type guaranteed to live during the
call to the C function? (In other words, is the pointer safe (as long as
the C side does not make a copy, of course)?
My suspicion is that once the subprogram returns the pointer, the limited
type can be optimized away before the call to the C side. It's not what
I'm seeing now, but I don't want to depend on an erroneous assumption.
Alex.
>
> The trick here is that whatever strategy I use must be compatible with C, so for instance using a storage pool would not be directly compatible with the C binding.
>
> Here is just a quick and sloppy idea I had on how to tackle my problem.
>
> str : chars_ptr := New_String (" ");
> ...
> Update (Item => str, Offset => 0, Str => "Some Param");
> ...
> Update (Item => str, Offset => 0, Str => "Some Other Param");
> ...
> Free (str);
>
> I find the first line quite ugly. I'm sure there is an easier way to create a large empty string but I can't seem to come up with an elegant way to do it.
>
> As far as the Update commands, will it act like strcpy() in C? If so I'd guess that this is an efficient technique.
>
> Thanks for your help!
>
next prev parent reply other threads:[~2018-05-30 13:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-25 22:22 Interfaces.C.Strings chars_ptr memory management strategy NiGHTS
2018-05-26 2:52 ` Shark8
2018-05-26 12:44 ` NiGHTS
2018-05-26 13:56 ` Shark8
2018-05-30 13:10 ` Alejandro R. Mosteo [this message]
2018-05-30 19:56 ` Randy Brukardt
2018-05-31 10:34 ` Alejandro R. Mosteo
2018-05-31 22:25 ` Randy Brukardt
2018-06-05 12:42 ` Alejandro R. Mosteo
2018-06-03 18:31 ` ytomino
2018-06-03 19:33 ` Dmitry A. Kazakov
2018-06-03 20:03 ` ytomino
2018-06-04 7:06 ` Dmitry A. Kazakov
2018-06-04 7:47 ` ytomino
2018-06-03 20:37 ` ytomino
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