Re: Error-names.

[Martin Klaiber <martinkl@zedat.fu-berlin.de>]

David Marceau <davidmarceau@sympatico.ca> wrote:
> Martin Klaiber wrote:
>> David Marceau <davidmarceau@sympatico.ca> wrote:

>>> make sure when others is used it is logged somewhere.

>> Hm, sorry, I don't understand what you mean here.

> I just mean the reason you use "when others" in the first place is
> because it is an exception you never thought about when designing
> the component. 

This is true and it shows the dilemma.  When writing the code I don't
know which exceptions a real Ada-implementation might provide.  But I
also must ensure all exceptions are handled to give the C-program a
chance to avoid a crash.  So I use "when others" at last.

Is there a way to find out which exceptions an implementation provides?
Ok, I have the types mentioned in the ARM but the implementation could
add some more.

> You have to admit when this happens whatever happens in a "when
> others" you have to document and figure out in what context the
> situation occurred in order to go back and add more code and maybe a
> new exception type to raise :)

That's right.  Tracking down an error is more difficult then.

> The best way is to first catch it into a file in order to come back and
> read about it...hence logging the "when others" exception.  I think you
> already understand this kind of thing but I voiced it out anyways just
> in case.  A perfect application should not ever get into the part of
> the code inside "when others" at run-time.  That said "when others" has
> to exist to catch a real exception and log the real exception to enable
> us programmers to analyze what the problem is later to be able to fix
> it ASAP.  That's my opinion. Please correct me if I'm wrong.

No, you're right.  But I want to avoid to implement file-I/O to keep
the lib as platform- and compiler-independent as possible.  Perhaps I
implement a function, which allows the calling C-program to recall the
last error-message.  This could be used for a bug-report then.

> Ada Exceptions and C Exceptions don't seem to use the same default
> cleanup strategies so you have to be very careful.

What do you mean by C Exceptions?  Can C handle exceptions?

> As you stated in a C program returning a constant value for the error is
> standard "C" practice.
> From what I understand, returning nothing and placing valuable information in an
> "in out" parameter is more Ada95.
> The valuable information I talking about is an object holding a structure of a
> bunch of structures.

Ok, but complex types might give problems with the representation.
I also wanted to use records/structs for the interface first, instead
of the many set- and get-procedures/-functions.  But people told me
that a C-program compiled with a different compiler than the compiler
used for the Ada-lib doesn't necessarily represent the types in the
same way.  So I only use the C-types "int" and "long" now.  This makes
it more simple and hopefully more robust.

> Also notice one line for the opening brace/parentheses and another line for
> closing brace/parentheses.  Call me crazy but I think it is most legible this
> way.  It also helps you do focus on one problem at a time for each line.  I
> follow the same style for if statements and everything else.  Sure it takes a
> bit more time but in the long run it's better in my humble opinion.

It think this is very individual preferences and cannot be answered
generally.  So I wouldn't puzzle myself with it.  Preferences also
change with time.  I use more underscores now.  Before I found the
code without underscores more legible, now it's the other way round.

Martin