Re: [Boost-users] [circular_buffer] About overwriting elements

Subject: Re: [Boost-users] [circular_buffer] About overwriting elements
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-04-16 10:49:42

AMDG

Daniele Barzotti wrote:
> in the introductory example I see this:
>
>   int a = cb[0];  // a == 1
>   int b = cb[1];  // b == 2
>   int c = cb[2];  // c == 3
>
>   // The buffer is full now, pushing subsequent
>   // elements will overwrite the front-most elements.
>
>   cb.push_back(4);  // Overwrite 1 with 4.
>   cb.push_back(5);  // Overwrite 2 with 5.
>
>   // The buffer now contains 3, 4 and 5.
>
>   a = cb[0];  // a == 3
>   b = cb[1];  // b == 4
>   c = cb[2];  // c == 5
>
> and I would ask why the 4 and 5 are in the 2nd and 3th position instead
> of 1st and 2nd respectively.
>
> I thought that it worked in the following way:
>
>  1  2  3                       1  2  3                      1  2  3
> [A][B][C]  -> push_back(D) -> [D][B][C] -> push_back(E) -> [D][E][C]
>
> I need a circular buffer for buffering network data and I need that the
> old data is replaced but doesn't change its position..
>   

What actually happens is something like this:

 1  2  3                       3  1  2                      2  3  1
[A][B][C]  -> push_back(D) -> [D][B][C] -> push_back(E) -> [D][E][C]

The indexes are adjusted, but the physical locations of the elements
don't change.

In Christ,
Steven Watanabe