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From: dennison@romulus23.DAB.GE.COM (Ted Dennison)
Newsgroups: comp.lang.ada
Subject: Re: Posix.String_List question
Date: 5 Oct 1994 16:59:27 GMT
Organization: General Electric SCSD, Daytona Beach FL
Sender: dennison@romulus23 (Ted Dennison)
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References: <STEF.94Oct4234145@heron.cfmu.eurocontrol.be>
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Date: 1994-10-05T16:59:27+00:00
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In article <STEF.94Oct4234145@heron.cfmu.eurocontrol.be>, stef@heron.cfmu.eurocontrol.be (Stef Van Vlierberghe) writes:
|> 
|> I recently reported a "bug" (Alsys 5.5.2 on HP9000/700), but the actual
|> code is so aggressive that I'm not sure who really is to blame. I see a
|> choice of the appliction, the vendor, POSIX1003.5 definition, or Ada.
|> 
|> The relevant code is :
|> 
|>   BYPASS_COPY_BACK : exception;
|> 
|>   procedure TRY_BREAK_IT (  LIST : in out POSIX_STRING_LIST ) is
|>   begin
|>     MAKE_EMPTY(LIST);
|>     raise BYPASS_COPY_BACK;
|>     -- if LIST is by copy the caller won't see we emptied it
|>   end;
|> 
(rest of code deleted)
|> After quite a while this code gets the heap corrupted.
|> 
|> Evidently the relevant piece of LRM is 6.2(7) : The execution of a
|> program is erroneous if its effect depends on which mechanism is selected
|> by the implementation.
|> 

Also signifigant: LRM 6.2 (11-12):
"For parameters of array and record types, the parameter passing rules have
 these consequences:

  o  If the execution of a subprogram is abandoned as a result of an 
     exception, the final value of an acutal parameter of such a type can be
     either its value before the call or a value assigned to the formal 
     parameter during the execution of the subprogram."

Therefore this behavior is a bug in your code, NOT in the compiler.

To force a call by reference, simply pass TRY_BREAK_IT an object of type
"access POSIX_STRING_LIST". 

T.E.D.