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From: mab@dst17.wdl.loral.com (Mark A Biggar)
Subject: Re: C is 'better' than Ada because...
Date: 1996/07/16
Message-ID: <4sgakm$kcu@wdl1.wdl.lmco.com>#1/1
X-Deja-AN: 168510316
references: <31E4DC46.794BDF32@mailgw.sanders.lockheed.com>
 <31E57A6C.3F2E@csehp3.mdc.com> <nhafx022lu.fsf@paralysys>
organization: Loral Western Development Labs
newsgroups: comp.lang.ada
Date: 1996-07-16T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <nhafx022lu.fsf@paralysys> nasser@apldbio.com (Nasser Abbasi) writes:
>   What about the lack of any  boundary checking at all?  
>James make good points ofccourse, but I think the view that C++ 
>programmers would have is that some of the above could be fixed 
>by using classes instead of the primitive language data types. At least 
>to the point of boundary checking. As an example, one would use 
>an array class instantiated to the correct type and the size of the
>array, where this class would throw an exception (or do an assert) if 
>the index is out of bounds. SOmething like this:
>----------------------------------------------
>template< class type, int dimension>
>class array
>{
> ....
> type operator[] ( int index)
> {
>   if( index >= dimension || index < 0 )
>      throw ... some object as the exception
>   // or  assert ( index < dimension && index >=0); 
>   // all clear now , index is within range, get the index data
>   return data[index];
> }
> private:
>   type data[dimention];
>};
>--------------------------------------------
>and one would then create objects of this class as
>array<int,10> a;  // now a is array of int 0..9
>array<chat,100> b; // array of chars 0..99
>..
>now writing this
>   int i = a[11];   // should throw an exception
>So, in C++ it seems that one can say, if there is something not
>right in the core langauge, one can use the core language to fix
>this problem, as the example above show, one uses C++ to fix
>the fact that C++ do not have boundary range checking.
>The problem I see with this is that this addes a layer of
>software between the application/usr and the core langauge, in
>the above example, this layer is the array class software, so
>would would then use this class to make arrays instead of using
>the array construct avaliable in the core language.

In addition the above code make it almost impossible to optimize
out unnecessary checks.  The empirical evidence is that only about
10% of array bounds checks are really necessary, assuming that you
can declare index variables that are limited in range to the 
array bounds, but you can't so that either in C (you can in C++,
but that adds yet another layer of possible redundant checks
that you can't easily optimize away.)

--
Mark Biggar
mab@wdl.lmco.com