Re: Concatenation and Characters

[Stuart Palin <stuart.palin@0.0>]

Jim Rogers wrote:
> 
> Programmer Dude wrote:
<snip>
> >
> > So, bottom line from the answers I've read is that Ada (the language)
> > allows uninitialized variables to be used which *may* (must?) require
> > a run-time exception.... but what if the random value in the variable
> > isn't a contraint violation?  Does that mean an uninitialized variable
> > *could* be taken seriously and never detected as having a random bit
> > pattern?
> >
> 
> If the compiler detects that you are attempting to use an uninitialized
> value it will issue a diagnostic message. It is never a good thing to
> release a program without first addressing and eliminating all compiler
> diagnostic messages.

It is my experience that compilers only tend to give such
warnings where the use of the uninitialized value is
unconditional.  Usually, where a variable may be
uninitialized under some conditions the compiler 'assumes'
the programmer knows what they are doing and does not give a
warning.

If you want the full set of warnings you need to consider
using tools such as SPARK (or possibly/probably) some of the
Abstract Interpretation analysis tools such as Polyspace
Verifier.

The matter of Initialization is one given considerable
attention in SPARK.

In response to Programmer Dude's comments: Ada is not a
'safe' language (whatever that may mean).  It does a number
of trade-offs between supporting 'safety enhancing' concepts
and reasonably efficient implementation.  Initialization of
variables is one of these trade-offs.

SPARK uses Ada as a basis, but takes the issues of
demonstrating safety-enhancing features (such as correctness
of data flow) much further.  But it is worth noting that it
can not (always) do this within the scope of the Ada
language; which is why, in addition to sub-setting the
language, it requires annotations to add information about
the [intended] behaviour of the software.

If you are unfamiliar with SPARK, check out
www.sparkada.com.

--
Stuart Palin
[usual disclaimers]