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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: GPS: Including C headers from paths which are not configured in
 Source_Dirs
Date: Thu, 08 Oct 2015 21:49:29 +0100
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Date: 2015-10-08T21:49:29+01:00
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"Rego, P." <pvrego@gmail.com> writes:

> On Thursday, October 8, 2015 at 12:29:32 PM UTC-3, Simon Wright wrote:
>>    package Compiler is
>>       for Switches ("C") use ("-I/your/include/dir");
>>    end Compiler;
>
> It did not work, maybe I did wrong. I built a test code to analyze better.
>
> --test.gpr
> project Test is 
>    for Languages use ("Ada", "C"); 
>    for Source_Dirs use ("."); 
>    for Main use ("ohmy.adb"); 
> 	
>    package Compiler is 
>       for Switches ("C") use ("-Ioutsiders"); 
>    end Compiler; 
>    
> end Test; 
>
> --ohmy.adb
> procedure Ohmy is
>    procedure Put_Ohmy;
>    pragma Import (C, Put_Ohmy, "putOhmy");
> begin
>    Put_Ohmy;
> end Ohmy;
>
> --bla.h
> void putOhmy(void);
>
> --bla.c
> #include <bla.h>
> #include "common/bla_other.h"
>
> void putOhmy (void) {
>     putOhmyOther();
> }

This clearly worked as intended, because bla.c got compiled.

> --outsiders/common/bla_other.h
> void putOhmyOther();
>
> --outsiders/common/bla_other.c
> #include <bla_other.h>
> #include <stdio.h>
>
> void putOhmyOther(){
>     printf("Ohmy");
> }

But ..

> In this case, the built returns the error message:
>> gprbuild -d -Ptest.gpr ohmy.adb
>> gcc ohmy.o -o ohmy.exe
>> libtest.a(bla.o):bla.c:(.text+0x7): undefined reference to `putOhmyOther'
>> collect2.exe: error: ld returned 1 exit status
>> gprbuild: link of ohmy.adb failed
>> [2015-10-08 13:38:54] process exited with status 4, 100% (2/2),
>> elapsed time: 03.94s

This is telling you that outsiders/common/bla_other.o never got included
in the link (probably never got compiled, either).

I take it that the outsiders directory corresponds to an
externally-built C library in your real application? Perhaps you could
represent it as a GPR of its own?

library project Outsiders is
   for Library_Name use "outsiders";
   for Library_Kind use "static";
   for Library_Dir use project'Project_Dir & "src";
   for Source_Dirs use project'Project_Dir & "include";
   for Externally_Built use "true";
end Outsiders;

and then your test.gpr might say

with Outsiders;
project Test is
   for Languages use ("Ada", "C");
   for Source_Dirs use (".");
   for Main use ("ohmy.adb");

   package Compiler is
      for Switches ("C") use ("-I" & Outsiders'Source_Dirs);
   end Compiler;
end Test;