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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Example Ada calling Gnu Scientific Library (GSL)
Date: Mon, 10 Apr 2017 18:43:22 +0100
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Content-Type: text/plain

hreba <f_hreba@yahoo.com.br> writes:

> On 04/10/2017 11:47 AM, Dmitry A. Kazakov wrote:
>>
>> You also seem confuse project to build and project to use a library.
>> They are not same! For a bindings library you need both.
>>
>
> I don't understand that.

If you're building a library project, you have to specify all sorts of
things - particularly the compiler options, but you might for example
have multiple source directories.

Once the project has been built, this sort of thing isn't needed, you
can use a different GPR to present just what's needed to use the
library. Indeed, you can write an externally-built library GPR for a
completely external library.

If you're going to install the built library, the tool gprinstall knows
what to do and will generate the necessary externally-built library GPR
for you.

But if you don't want to install the built library, your projects can
just use the GPR you used for building it.

I'm not quite sure what to do when using a two-layer library like your
GSL binding!

You can see a Makefile and GPR (complicated, I know) at
https://sourceforge.net/p/gnatutil/code/ci/default/tree/ . The resulting
installed GPR is


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Content-Type: text/plain
Content-Disposition: inline; filename=gnat_util.gpr
Content-Description: gnat_util.gpr

--  This project has been generated by GPRINSTALL Pro 17.0w (20150615) (x86_64-apple-darwin15)

library project Gnat_Util is
   type BUILD_KIND is ("static", "relocatable");
   BUILD : BUILD_KIND := external("LIBRARY_TYPE", "static");

   for Languages use ("Ada", "C");

   case BUILD is
      when "relocatable" =>
         for Source_Dirs use ("../../include/gnat_util/gnat_util.relocatable");
         for Library_Dir use "../gnat_util/gnat_util.relocatable";
         for Library_Kind use "relocatable";
      when "static" =>
         for Source_Dirs use ("../../include/gnat_util/gnat_util.static");
         for Library_Dir use "../gnat_util/gnat_util.static";
         for Library_Kind use "static";
   end case;

   for Library_Name use "gnat_util";

   package Naming is
      for dot_replacement use "-";
      for casing use "lowercase";
      
      case BUILD is
         when "relocatable" =>
            for body_suffix ("ada") use ".adb";
            for body_suffix ("c") use ".c";
            for spec_suffix ("ada") use ".ads";
            for spec_suffix ("c") use ".h";
         when "static" =>
            for body_suffix ("ada") use ".adb";
            for body_suffix ("c") use ".c";
            for spec_suffix ("ada") use ".ads";
            for spec_suffix ("c") use ".h";
      end case;
   end Naming;

   package Linker is
      case BUILD is
         when "relocatable" =>
            null;
         when "static" =>
            null;
      end case;
   end Linker;

   package Install is
      for Active use "False";
   end Install;

   for Externally_Built use "True";

   type Library_T is
     ("static", "relocatable");

   library_type : library_t := "static";
end Gnat_Util;

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