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From: Jerome Hugues <hugues@nephilimmmmm.enst.fr>
Newsgroups: comp.lang.ada
Subject: Re: This can't be done in Ada...or?
Date: Fri, 11 Feb 2005 17:08:04 +0000 (UTC)
Organization: ENST, France
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In article <1108139611.709714.36170@o13g2000cwo.googlegroups.com>, Per Lindquist wrote:

> My impression from reading some threads is that Ada DOES NOT offer a
> decent way to implement trace printouts (log messages), at least not
> with the features stated below.

Where did you read that ?

> We want to be able to output log messages, or traces as we call it,
> from an Ada program. There will be a few trace categories like Error,
> Warning, Note etc. The messages (strings) can be sent to a file or
> stdout or whatever (not important).
> 
> A call might look something like this:
> 
> Trace.Error(Package_Name, Subprogram_Name, "Woops, V=" &
> Some_Type'Image(V));
> 
> How do we write a tracing utility in Ada that:
> 1. has different behaviour on different target platforms

=> provide one body/target + GNAT project files

> 2. can disable some categories depending on target platform at
> compile-time.

=> build a spec-only package that looks like

package My_Flags is

  Feature_1 : constant Boolean := False;

end My_Flags

In the implementation of Trace.Error, use My_Flags.Feature_x to
disable code. Any decent (all ?) Ada compiler should remove all "if
False then .. end if;" blocks at compile-time

> 3. does *not* cause any execution overhead if disabled.

=> pragma Debug (Trace.Error  ..);

(GNAT specific)

> 4. does not need yucky "if Trace_Wanted then ... end if;" around all
> calls

=> pragma Debug ..

> 5. does not need preprocessing (some of you say it's never needed in
> Ada...)

=> My solution doesn't, yet it requires tweaking your compilation
process so that you can select the correct package depending on your
configuration.

> I say it can't be done in Ada. Please prove me wrong!

You can, but I confess my solution is in part vendor specific.

The only kludge is the one body/implementation, GNAT project files
should handle this easily.

> If we could get rid of those hardcoded constants
> 
>   Package_Name : constant String := "Some_Package";
>   ...
>   Subprogram_Name : constant String := "Some_Procedure1";
>   ...
>   Subprogram_Name : constant String := "Some_Procedure2";
> 
> it would be a great bonus, but I reckon it can't be done either..?

See GNAT.Source_Info

in your code, just try

Ada.Text_IO.Put_Line (GNAT.Source_Info (Source_Location));

and see the magic occurs. GNAT.Source_Info is the equivalent of
__FILE__, __LINE__ macros from C.

-- 
Jerome