Re: Teaching new tricks to an old dog (C++ -->Ada)

[Georg Bauhaus <bauhaus@futureapps.de>]

Ioannis Vranos wrote:
> Georg Bauhaus wrote:
>>
>> struct Test {    // compare random access to keyed access
>>

>>  for (int run = 0; run < R; ++run)
>>    t.arrays();

> I am not sure what you mean with the above, perhaps to use the 
> facilities of <ctime> to measure their performance? Of course vector is 
> faster than map.

You say "of course" now? I don't really understand then
why you asked me why my Ada _array_ code is faster than your
C++ std::_map_ code.

>> C# does provide fixing arrays.
> 
> 
> 
> You mean it can use signed indices?

Not at all. I mean that C# arrays can be dynamic or fixed size.
They always start at 0, IIRC.

>Look, just to be technically 
> accurate, C++ can also use negative indices,

Actually, there is no negative index in your example.
There are some offset computations, resulting in index
values no less than 0.
 By the same argument I could say that a 10-element
C-array can be indexed by the number 100000 by first
decrementing the pointer and then adding 100000 as an
offset. But you do not get the element number 100000,
because there is no such element. 

Index types are conceptually different from offsets from
the first element.

As a clever trick, this is nice though. I like the power
of assembly think.
 

>     vector<int>::iterator pi= vec.begin()+4;
> 
>     // Makes vec[2]== 4.
>     pi[-2]= 4;

>> OK. And lets see what happens when the C99 arrays will be adopted.
> 
> 
> Do you mean C99's built in Variable Length Arrays (VLAs)? I do not think 
> they will be adopted in C++.

Let's see.

Georg