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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
 =?utf-8?Q?=29?=
 <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: best practice: error handling
Date: Sat, 11 Jun 2011 15:31:39 +0200
Organization: Ada @ Home
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Date: 2011-06-11T15:31:39+02:00
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Le Tue, 31 May 2011 16:01:19 +0200, milouz <a.michelizza@gmail.com> a  =

=C3=A9crit:

> Hi,
>
> I'm wondering about the best way to handle errors in Ada when calling
> a function/procedure that may fails.
>
> For example, when programming on Unix systems in C, the called
> functions usually return a zero or positive value on success and -1 on=

> failure, while setting a global variable (errno) to give some
> informations about the failure.
>
> What's the best way to deal with that kind of error in Ada ?
> Throwing an exception ? Returning some error code ? Passing a special
> parameter ?...
I would say : at least the =E2=80=9Cerrno=E2=80=9D strategy, is not conc=
urrency friendly.  =

if two threads of a same process commit errors, then you are in trouble =
 =

(one may overwrite the =E2=80=9Cerrno=E2=80=9D value of the other). Exce=
ptions would be  =

cleaner for such a case (providing your =E2=80=9Cerrno=E2=80=9D is not o=
wned by threads).

Also depends on whether or not the errors you have in mind are more or  =

less predictable. As two examples : a file write error is unpredictable,=
 a  =

user input error at the command line or at a use prompt, is on the  =

contrary, predictable and should be supposed to be likely to happen. For=
  =

the former, an exception would be the best in my opinion, and for the  =

latter, either an exception or a result property could be OK; while I  =

would personally be on favor of a result property, because a user error =
is  =

potentially a normal result of a user input.


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D  [Ep=
igrams on  =

Programming =E2=80=94 Alan J. =E2=80=94 P. Yale University]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [Idem]
=E2=80=9Cc++; /* this makes c bigger but returns the old value */=E2=80=9D=
 [Anonymous]