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From: Martin Klaiber <martinkl@zedat.fu-berlin.de>
Newsgroups: comp.lang.ada
Subject: Re: Error-names.
Date: Sun, 29 Feb 2004 21:33:35 +0100
Organization: Freie Universitaet Berlin
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Jeffrey Carter <spam@spam.com> wrote:
> tmoran@acm.org wrote:

>>   subtype Exception_Codes is Interfaces.C.Int range -10 .. 1;

>>   Coded_Exception_List : constant array(Exception_Codes)
>>     := (Constraint_Error'Identity,
>>         Program_Error'Identity,
>>         Storage_Error'Identity,
>>         Tasking_Error'Identity,
>>         Ada.IO_Exceptions.Status_Error'Identity,
>>         Ada.IO_Exceptions.Mode_Error'Identity,
>>         Ada.IO_Exceptions.Name_Error'Identity,
>>         ...

>>   function Error_Code_Of(E : Ada.Exceptions.Exception_Occurrence)
>>   return Exception_Codes is
>>     use Ada.Exceptions;
>>   begin
>>     for i in Coded_Exception_List'range loop
>>       if Exception_Identity(E) = Coded_Exception_List(i) then
>>         return i;
>>       end if;
>>     end loop;
>>     raise; -- we have no code for this exception!  re-raise it
>>   end Error_Code_Of;

> This is pretty much what I would have suggested if Moran hadn't beat me 
> to it. However, I think you can't use "raise" here without an exception 
> name, since we're not necessarily in an exception handler. You could use 
> Ada.Exceptions.Raise_Exception (E), but I suspect what is really wanted, 
> based on the OP's earlier messages, is to return General_Error_Code.

Yes, General_Error_Code shall be a fallback in case there is no special
handler for a certain exception.  I implemented it like this:

    function Get_Error_Code (E : Exception_Occurrence) return C_Integer is
    begin
        if Exception_Identity (E) = Program_Error'Identity then
            return Program_Error_Code;
        elsif Exception_Identity (E) = Constraint_Error'Identity then
            return Constraint_Error_Code;
        elsif ...
            ...
        else
            return General_Error_Code;
        end if;
    end Get_Error_Code;

Not as elegant as Toms(?) code with the array but it works ok.

It's a pity that I can't use "case" instead of "if".  The compiler
moans that Exception_Id is not a discrete type.

Martin