From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 123192 invoked by alias); 12 Jan 2017 12:00:35 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 103034 invoked by uid 89); 12 Jan 2017 12:00:30 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-5.1 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=philipp, *string, Philipp, Rudo X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 12 Jan 2017 12:00:29 +0000 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6425EC04B926; Thu, 12 Jan 2017 12:00:29 +0000 (UTC) Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.phx2.redhat.com [10.5.9.4]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v0CC0NbE031934; Thu, 12 Jan 2017 07:00:27 -0500 Subject: Re: [RFC 2/7] Add libiberty/concat styled concat_path function To: Philipp Rudo , gdb-patches@sourceware.org References: <20170112113217.48852-1-prudo@linux.vnet.ibm.com> <20170112113217.48852-3-prudo@linux.vnet.ibm.com> Cc: peter.griffin@linaro.org, yao.qi@arm.com, arnez@linux.vnet.ibm.com From: Pedro Alves Message-ID: Date: Thu, 12 Jan 2017 12:00:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20170112113217.48852-3-prudo@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-SW-Source: 2017-01/txt/msg00216.txt.bz2 On 01/12/2017 11:32 AM, Philipp Rudo wrote: > static inline int > -startswith (const char *string, const char *pattern) > +startswith (std::string str, std::string pattern) NAK. This is passing by copy, so will force unnecessary deep string copies all over the place. > { > - return strncmp (string, pattern, strlen (pattern)) == 0; > + return (str.find (pattern) == 0); > +} > + I.e., before, this caused 0 copies: startswith ("foo, "f"); After, you force a deep string copy for "foo", and another for "f". It's as if you wrote: startswith (xstrdup ("foo), xstrdup ("f")); Also, this function is a static inline in a header so that the compiler can see when "pattern" is a string literal, and thus strlen can be optimized to a plain 'sizeof (pattern) - 1', which is very frequent. If you want to add overloads that can take "const std::string &" for convenience, to avoid str.c_str(), that's maybe fine, but you'd have to add all the combinations of 'const char *' x 'const std::string &' in the parameters, I suppose. Thanks, Pedro Alves