220 13923 article Path: news.gmane.org!not-for-mail From: Bo Pesson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Shrink dynamic arrays with delete[] operator Date: Wed, 15 Oct 2014 20:45:10 +0200 Lines: 70 Approved: news@gmane.org Message-ID: References: <167019e1-7373-4688-b7ef-8da1a80acf07@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: ger.gmane.org 1413398735 17425 80.91.229.3 (15 Oct 2014 18:45:35 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 15 Oct 2014 18:45:35 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCZ6RLW3UIKBBR4B7OQQKGQEVOYVKRY@isocpp.org Wed Oct 15 20:45:31 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wi0-f198.google.com ([209.85.212.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XeTZh-0001Jb-UG for gclcip-std-proposals@m.gmane.org; Wed, 15 Oct 2014 20:45:29 +0200 Original-Received: by mail-wi0-f198.google.com with SMTP id hi2sf1184117wib.9 for ; Wed, 15 Oct 2014 11:45:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:user-agent:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=MFCfhl07pCSnLCJsT4FvH5GtfwH791kdGNKBeGc2LYU=; b=IpD+CEx03u8/7MrD9NSERcoObnw8zp5URZAtVRXXU/TzPMBaDwuwyipMJJjDWevozd rK5rWTa9DNHw1R+u+E5uPIEsvUGFOP0Wc41bqS5jm0y+pKLl2hJ8rfuphXx7OC1hfx3K DYBksnctItkgzgejI08egprZE4PpQWI26lA3fjTQysDTKiuO4Cra/KDdjF8KfHWiIlru G3787oAKCYyXinNflWGwLalI0SYyC1bTKL8WZFCNxDec2S2dyzBYyuWiz9pJuisqK0p2 Tf/o9yKW1u/Ywjif7AGorMfbopop5vLM7pO7Grg++BpbVSQ7ULeW4zeTOjPLIa9lM8AI iIXQ== X-Gm-Message-State: ALoCoQlAXDCJ8AlGfdeynBwiyYHrn+0SDDepmhEjMysfCt8e+xc2KGvGVTckmia3ZHYzAiSlfnOJ X-Received: by 10.180.93.35 with SMTP id cr3mr2417107wib.2.1413398729584; Wed, 15 Oct 2014 11:45:29 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.204.107 with SMTP id kx11ls91033lac.80.gmail; Wed, 15 Oct 2014 11:45:27 -0700 (PDT) X-Received: by 10.152.234.199 with SMTP id ug7mr14484116lac.26.1413398727627; Wed, 15 Oct 2014 11:45:27 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id z7si31809675lag.18.2014.10.15.11.45.27 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 15 Oct 2014 11:45:27 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1XeTZa-0001EQ-Ut for std-proposals@isocpp.org; Wed, 15 Oct 2014 20:45:22 +0200 Original-Received: from c193-14-6-157.cust.tele2.se ([193.14.6.157]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 15 Oct 2014 20:45:22 +0200 Original-Received: from bop by c193-14-6-157.cust.tele2.se with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 15 Oct 2014 20:45:22 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 61 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: c193-14-6-157.cust.tele2.se User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 In-Reply-To: <167019e1-7373-4688-b7ef-8da1a80acf07@isocpp.org> X-Original-Sender: gclcip-std-proposals@m.gmane.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:13923 Archived-At: On 2014-10-15 19:29, contact@ncomputers.org wrote: > > Shrink dynamic arrays on C++ > > > It is very useful to shrink arrays, which were created using the *new* > operator. > > *For example:* > > Your code requires a billion of objects of a class to find a solution to > a hard problem. As the code finds a new and better solution, some > objects will become useless. Due to complexity, the code starts to > require more time to process the useful data and find better solutions. > > As the code had a billion of useful objects in memory, it required only > a few seconds to find a solution to the problem, because they were > easier to find. When the code searches better solutions, it requires > less objects and more time. For example, when it searches a solution > with only one million of objects, it will delay a week to find a new and > better solution to the problem. > > It would be a waste of memory to have 999 millions of useless objects > for a whole week. Just imagine, if every object requires ten bytes, the > code will be wasting 9.99 billions of bytes for a whole week. > > Thanks to the community of stackoverflow.com > , cplusplus.com > and its contributors, we considered two possible solutions to shrink > arrays: > > * Allocate memory using the *std::malloc* function and shrink the > array using the *std::realloc* function. > * Create a *new* array, copy the useful objects and *delete* the old > arrays. > > Both are good solutions. > > But we desire a solution, which is oriented to objects, automatically > calls the destructors, is a C++ standard compatible with most memory > allocators and neither moves the useful data nor copies it, due to > performance. > > * To use the *std::malloc* and *std::realloc* functions is a solution, > which requires to overload the *new* and *delete* operators to make > it oriented to objects. > * To create a *new* array, copy the useful objects and *delete* the > old array is a solution, which would be very slow if we shrink the > array a billion of times. > * The performance offered by the *std::vector* when shrinking could be > overcome by other implementations or native arrays > . > I believe your calls to realloc(p, size-1) actually doesn't free up any memory, which of course would be faster than shrinking the vector. Bo Persson -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .