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From: Ioannis Vranos <ivr@remove.this.grad.com>
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Tue, 22 Mar 2005 22:17:24 +0200
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Xref: g2news1.google.com comp.lang.ada:9754 comp.lang.c++:46725
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Date: 2005-03-22T22:17:24+02:00
List-Id: <comp.lang.ada>

fabio de francesco wrote:

> Ciao,
> 
> Ioannis wrote a C++ program that in his intentions would had operate
> like the Ada code that was provided as an example of language
> expressiveness.
> 
> Unfortunatelly that C++ code doesn't resembles the Ada one. Have a
> closer look at what Richard wrote:
> 
> type Index is range -800_000..12_000_000;
> type Decimal_Fraction is digits 12 range -473.0 .. 2_000.0;
> type Vector is array (Index range <>) of Decimal_Fraction;
> 
> V1 : Vector ( -47..600);   -- note the negative index range
> V2 : Vector (-1.. 10);       -- also a negative index range
> V3 : Vector (42..451);     -- index starts higher than zero;


It isn't difficult to implement a vector that accepts signed ranges too 
*with* range-checking, the default ones begin from 0 because this is the 
C++ natural feel. vector::at() performs range checked access.


#include <vector>
#include <exception>
#include <iostream>


int main() try
{
     std::vector<int> vec(10);

     vec.at(12)=4;


}

catch(std::exception &e)
{
     std::cerr<<e.what()<<"\n";
}


C:\c>temp
invalid vector<T> subscript

C:\c>



In other words it does not make much sense to have signed indexes. 
Otherwise it is easy and possible.



-- 
Ioannis Vranos

http://www23.brinkster.com/noicys