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From: ncohen@watson.ibm.com (Norman H. Cohen)
Subject: Re: Side-effect arithmetic again [was: Ada ... in embedded systems]
Date: 1996/03/25
Message-ID: <4j6d12$lbn@watnews1.watson.ibm.com>#1/1
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distribution: world
references: <dewar.827599280@schonberg> <Dot06M.Asu.0.-s@inmet.camb.inmet.com>
organization: IBM T.J. Watson Research Center
reply-to: ncohen@watson.ibm.com
newsgroups: comp.lang.ada
Date: 1996-03-25T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <Dot06M.Asu.0.-s@inmet.camb.inmet.com>,
stt@henning.camb.inmet.com (Tucker Taft) writes: 

|> As a small anecdote here relating to the "op=" operations of C,
|> my most recent "favorite" bug in C code I was writing was in the following: 
|>
|>   if (a /= b) {
|>     ...
|>   }
|>
|> The GCC compiler nicely warns you if you write "if (a = b) {" and
|> suggests an extra level of parentheses to emphasize that you really
|> want an assignment, not an equality, operator.  Unfortunately, it
|> isn't so helpful with the "op=" operators, and presumes that if
|> you use one of those, you know what you are doing.  Alas, after
|> writing a lot of Ada, I didn't in this case.  Of course what I meant
|> was "if (a != b) {".  Instead, I divided A by B, and tested the result
|> for non-zero-ness.  Groink!

Yes, I've done the same thing.  It's one of a group of C pitfalls to
which Ada programmers are especially susceptible.  Another is to leave
the empty parentheses off a parameterless function call in a context
in which C is willing to accept a pointer-valued expression.  There are
far too many such contexts.  When I wrote

   if ( some_predicate ) {
      ...
   }

instead of

   if ( some_predicate() ) {
      ...
   }

C obediently coerced some_predicate to a pointer to the function and
tested whether that pointer was null.  As Tuck so eloquently put it,
Groink!

|> At this point Dave Emery comes on and asks me why in the world
|> I am writing any code in C... ;-}

So we don't start to take Ada for granted, of course. ;-)

--
Norman H. Cohen    ncohen@watson.ibm.com