Re: [Boost-users] Compress to buffer

Subject: Re: [Boost-users] Compress to buffer
From: Kenneth Adam Miller (kennethadammiller_at_[hidden])
Date: 2014-01-14 20:46:44

On Tue, Jan 14, 2014 at 1:58 PM, Kenneth Adam Miller <
kennethadammiller_at_[hidden]> wrote:

> Thank you.
>
>
> On Tue, Jan 14, 2014 at 1:55 PM, Krzysztof Czainski <1czajnik_at_[hidden]>wrote:
>
>> 2014/1/14 Kenneth Adam Miller <kennethadammiller_at_[hidden]>
>>
>>> Ah ok. I apologize for posting too fast. I will be sure to go further in
>>> exhausting all resources before I post in the future. However, I did find
>>> some of the descriptions of the iostreams parts and how they compose
>>> (especially examples, that's what I was really looking for) vague, IMHO.
>>>
>>> No, I haven't measured performance.
>>>
>> [...]
>>
>>>  Those unnecessary allocation copies would, in the worst case, result in
>>> a 2-3x slowdown of the entire program
>>>
>>
>> How do you know?
>>
>>
>>>  due to the fact that it's literally pausing to repeat something that's
>>> unnecessary.
>>>
>>> But actually, if this appends my 30k string, I didn't know it. The
>>> back_insert_device<string> object wasn't something that I understood very
>>> well from the description at
>>> http://www.boost.org/doc/libs/1_45_0/libs/iostreams/doc/classes/back_inserter.html
>>>
>>> From what I had thought though, if my string was empty with 0's,
>>>
>>
>> Right here's your mistake. string(30000,0) creates a non empty string.
>> It's a string of 30k nulls.
>>
>>
>>> and I appended to it, then I would end up with precisely my compressed
>>> data. The idea of acquireStringFromPool is that it returns a large string
>>> that is always cleared out for the filtering_ostream to fill up as though
>>> it were a device. Is that incorrect? How can I get that functionality?
>>>
>>
>> Like I said, you want std::vector::reserve().
>>
>
Ok, so supposing I just use a vector; do I use vector<byte>? Is it more
efficient to use vector< word_size_of_computer > since any write to it
would obviously be faster or will the compiler catch this? Also, when I
grab all of the bytes from vector, does it automatically detect when the
end is? Like, one of the purposes of having 0's all through the string was
so that it was always terminated. In the case of vector, if I push_back 3
times, and then I output, will I get 3 bytes?

>
>> Perhaps, however, that reserve approach would be good. I apologize the
>>> email was so long lol.
>>>
>>
>> Btw, you're still top-posting. The idea is to leave the (minimal) context
>> above your reply message ;-)
>>
>> By top posting you meant just the position of my text. I thought you
> meant it to be me posting when I could have more fully investigated the
> issue. I will follow this convention.
>
>
>> Regards,
>> Kris
>>
>>
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>
>