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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Detecting the OS type before clearing screen
Date: 26 Mar 2003 20:36:41 +0000
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Date: 2003-03-26T20:36:41+00:00
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sk <noname@myob.com> writes:

> Using make files ? Then either you somehow get "make" to
> detect which version you require or edit the makefile
> to set a variable.

The new GNAT Project feature lets you do this based on envirnment
variables or gnatmake switches.

   project Foo is

      type Target_Type is ("host", "target");

      Target : Target_Type := external ("TARGET", "host");

      case Target is

         when "host" =>
            for Source_Dirs use (".", "./host");

         when "target" =>
            for Source_Dirs use (".", "./target");

      end case;

   end Foo;

means you put the spec inthe same directory as the project file, the
target (eg VxWorks) body in ./target and the host (eg Linux) body in
./host. The default is the host version; select the other by either

   TARGET=target gnatmake -PFoo

or 

   gnatmake -PFoo -XTARGET=target

See http://gcc.gnu.org/onlinedocs/gnat_ug_unx/GNAT-Project-Manager.html#GNAT%20Project%20Manager

-S