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Newsgroups: comp.lang.ada
Date: Thu, 31 May 2018 05:18:01 -0700 (PDT)
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Subject: Re: Header-only Ada libraries...
From: joakimds@kth.se
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Xref: reader02.eternal-september.org comp.lang.ada:52805
Date: 2018-05-31T05:18:01-07:00
List-Id: <comp.lang.ada>

Den torsdag 31 maj 2018 kl. 13:14:13 UTC+2 skrev Alejandro R. Mosteo:
> A while ago I commented on how I unexpectedly found myself writing more=
=20
> and more expression functions... today I realized that this tiny project=
=20
> to interact with C subprograms is header-only:
>=20
> https://github.com/mosteo/cstrings/tree/master/src
>=20
> What it does isn't important, but I couldn't but think of the trend in=20
> the C++ world to go for header-only libraries.
>=20
> https://en.wikipedia.org/wiki/Header-only
>=20
> Anyway, just a curiosity... and something to worry about? ;)
>=20
> Alex.

A trick that is GNAT specific that I use in the Ada binding to Wayland (htt=
ps://github.com/joakim-strandberg/wayland_ada_binding) on Linux (and which =
might work on other platforms too when using GNAT) is using the standard St=
ring type where the input argument is char*. In the C code the function wl_=
display_connect has the following signature:

struct wl_display * wl_display_connect(const char *name);

To import it into Ada:

function wl_display_connect (Name : in C_String) return Display_Ptr with
           Convention    =3D> C,
           Import        =3D> True,
           External_Name =3D> "wl_display_connect";

where C_String is defined as:

Nul : constant Character :=3D Character'Val (0);
type C_String is new String with
  Dynamic_Predicate =3D> C_String'Length > 0
  and then C_String (C_String'Last) =3D Nul;

For convience I added the following conversion routines between standard St=
ring types and C_String types in the Posix package:


function "-" (Text : C_String) return String;
-- Removes the last 'Nul' character and returns a normal String.

function "+" (Text : String) return C_String;
-- Appends a 'Nul' character to a standard String and returns a C_String.

Not sure how well known this trick is so just mentioning it :)