Re: Style Question

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 12 Dec 2007 23:59:45 -0500
Message-ID:
<umOB9TUPIHA.5140@TK2MSFTNGP05.phx.gbl>
"Tim Roberts" <timr@probo.com> wrote in message
news:r8d1m3p46ela7et3qtpakk3ac3br16ogje@4ax.com

I have an application where I need a queue of buffers whose size
changes relatively often. I was doing it with a "char *" with
separate Size and MaxSize members, but it seemed like a great
candidate for a std::vector<char>. After the size changes, I fill it
immediately, so the zero filling that vector::resize does is useless
to me, and it costs a fair amount.


You can reserve() instead, and push_back() or insert() new elements.

So, I derived a class from std::vector<char>, and overrode resize,
using knowledge of the VC++ STL implementation:

 class ByteVector
     : public std::vector<char>
 {
     ...
     void resize( size_t newSize, char init = -1 )
     {
         if( (init == -1) && (_Myfirst + newSize <= _Myend) )
             _Mylast = _Myfirst + newSize;
         else
             std::vector<char>::resize( newSize, init );
     }
 };

This solves my problem neatly, but is this considered very bad form?
It's certainly true that this won't work with another STL
implementation. Would you fire a programmer that did this to you?


I would seriously consider it, yes. The code will definitely not pass my
code review and won't be submitted as long as I have any say in the
matter. At the very least, the author would have to prove to me that a)
avoiding zero-initialization causes a measurable performance
improvement, and b) there's no other way to avoid it (and I have my
doubts on both points).
--
With best wishes,
    Igor Tandetnik

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