Re: memory pool?

From:

peter koch <peter.koch.larsen@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 10 Nov 2008 04:21:48 -0800 (PST)

Message-ID:

<622c9b70-33f9-4377-bd23-c2180f5ebff7@a29g2000pra.googlegroups.com>

On 10 Nov., 12:49, Uli Kunkel <genija...@yahoo.com> wrote:

Juan Antonio Zaratiegui Vallecillo wrote:

Uli Kunkel escribi=F3:

I have a situation where I'm getting a picture from a camera in small
chunks.
So the photo is a few MBytes and I have a callback function that
returns 1KB until it finishes transfering the picture.
Any suggestions or examples how should I put a picture in one variable=

I heard something about using memory pools for this but I only need
something simple for this occasion.
Could I use CString?

Anyway thanks in advance for any suggestions.

Use a vector, taking advantage from its reserve() function.

#include <vector>

(...)

    std::vector<unsigned char> myPhoto;
    myPhoto.reserve(1024*1024);

    for (size_t part=0; part !=1024;++part) {
       <read image data into &myPhoto(part*1024) >
    }
(...)
    <you now have your photo in myPhoto.size() sequential bytes at
&myPhoto[0]

Just customize such piece for your exact needs, substsituting all magic
constants with nice real constants.
This code skeleton takes as granted that char size is one byte, you may
need to correct the code it it is otherwise

best regards,

Zara

Thanks for the answers.
I'm wondering if I could use reserve to allocate a few MB and then if
the size is not enough that the vector grows automatically?
I read that vector resizing is very costly so I presume that reserving
just 1KB is not enough.

std::vector resizes autmatically. As an alternative, you could also
use std::deque which memorywise is more optimal with regard to
reallocation but overall is slightly slower (does more allocations)
than a std::vector.

/Peter