From -3198315301171772003 X-Google-Thread: 7894ca11fe,191c67e7ffa6c8e7 X-Google-Attributes: gid7894ca11fe,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news2.google.com!news1.google.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Wed, 27 Oct 2010 01:30:02 -0500 Return-Path: X-Hash: SCt|4e067be5e2a2bb10f67dc17eaabd661f4998c925|9b4d6473cf396727ec79bcc87eb51039 X-Countries: United States X-SMTP-From: accepted assassin.cs.rpi.edu [128.113.126.17] (assassin.cs.rpi.edu) {United States} DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=cs.rpi.edu; h=date :to:sender:message-id:from:subject:references:content-type; s= default; i=128.113.126.17@cs.rpi.edu; t=1288160552; x= 1288765352; l=3357; bh=zVnsv1MDBYGjITTxzj7wExcZz9Q=; b=UCLQz7tMy 3EGsEdgtJBNm0/Ecb2YmfFx/TyusE+gaCTbuOl+N3WFFHDaJebXGgQ68zNzkkgr/ d5mage6YBL28n5fmabmW4cFQe+iAExCogOJQ1HYJiVQhSm0e9qADvQazd5fYsA1a HGUdegsXL2231PzpUsGXAmJ4/GP6XOqlX4= DomainKey-Signature: a=rsa-sha1; c=nofws; d=cs.rpi.edu; h=date:to:sender :message-id:from:subject:references:content-type; q=dns; s= default; b=V253kBjI+qpNiSYbTIHnqDXXJG/e4csrpEDCn+B12YubryTF0O/wE keE25YkG8fCptyEtsHssrxFatWjwN05xYbMzgXgNPTtI7nyZPP1jgo8Pd+9FgsJt BnDl3VAbVH43W9QETIWbaMPUjHyNHQtD8Df92SlQKoj8mreXdngPqQ= X-Spam-Report: Spam Report from cliffclavin.cs.rpi.edu (SA:3.2.5): -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP 3.4 HEADER_SPAM Bulk email fingerprint (header-based) found -0.9 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.2 SARE_HEAD_HDR_APPROV Message headers used which identify spam 0.0 AWL AWL: From: address is in the auto white-list X-Spam-Info: 0.9, local; ALL_TRUSTED,AWL,BAYES_00,HEADER_SPAM,SARE_HEAD_HDR_APPROV X-Spam-Scanned-By: cliffclavin.cs.rpi.edu using SpamAssassin 3.2.5 X-Virus-Scanned-By: cliffclavin.cs.rpi.edu To: (Usenet) Sender: std-c++-request@ruralroute.cs.rpi.edu Approved: james.dennett@gmail.com Message-ID: Newsgroups: comp.std.c++ From: James Kanze Subject: Re: reinterpret_cast(&some_int) Organization: http://groups.google.com References: <402768.38178.qm@web110410.mail.gq1.yahoo.com> <1bb08f2a-854d-4d6c-b686-42a84dd8c2c2@t13g2000yqm.googlegroups.com> <842870f3-3d2f-46aa-9b4e-b463ac5b4af0@l14g2000yqb.googlegroups.com> Content-Type: text/plain; charset=ISO-8859-1 X-Original-Date: Mon, 25 Oct 2010 12:04:27 -0700 (PDT) X-Submission-Address: std-c++@netlab.cs.rpi.edu X-Scanned-By: MIMEDefang 2.67 on 128.113.126.25 Date: Wed, 27 Oct 2010 01:22:32 CST Lines: 85 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-XPxH3hnYVVODsAMQMNl9vOhiZ/G/0LfjLUYX6DSRVjyAm06jiHtt4co6hSxIPW2FWoMfK7QzhNmmqJ9!iYh0QSbMUwOL5IFQ4LXCzysMY1IWtCq2bpdUeYmYsAceDTWF+j9fvaPh4bxvg+Q716YtOWMXgdhh!ACBjdwQt3xqPZCopfYaeuJviXHY= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 6555 Xref: g2news1.google.com comp.std.c++:3056 On Oct 23, 9:06 am, Trigve wrote: > Thank you for the reply, > On 21. Okt, 00:14 h., James Kanze > wrote:> On Oct 13, 6:52 pm, Trigve Siver > wrote: > > > On 12. Okt, 02:06 h., James Kanze wrote: > > > > It is and it isn't. About all you can say is that you're more > > > > or less guaranted to pass the address of the int into > > > > input.read. Since this function expects the address of a char > > > > buffer, and will write it as such, just about anything can > > > > happen after that. > > > Is there ANY portable way to read binary data of PODs from file? > > Unless you know the format of the data in the file, there's no > > way to read it, portable or not. If you know the format, you > > read the bytes, and assemble them as the format requires. > Ok, the last example :): > > std::fstream file("temp.bin", std::ios_base::in | std::ios_base::out | > std::ios_base::binary | std::ios_base::trunc); > char buffer[4]; > std::int32_t value_write = 1234; > std::int32_t value_read = 0; > std::memcpy(buffer, &value_write, sizeof(value_write)); > file.write(buffer, 4); > file.flush(); > std::memset(buffer, 0, 4); > file.seekg(0, std::ios_base::beg); > file.read(buffer, 4); > std::memcpy(&value_read, buffer, sizeof(value_read)); > assert(value_write == value_read); > Is the code above portable in following circumstances: > 1 - using the code on the same platform > 2 - using the code across multiple platform with same endianess > 3 - using the code across multiple platform The code, as written, is perfectly portable, since you're reading the data from the same process (the same compiled image) that wrote it. Beyond that, you should be able to read the data from a different process if the two processes were compiled with the "same" compiler: same version, same compilation flats, running on the same hardware, under the same OS (although the standard doesn't even make this guarantee). Beyond that, all bets are off. > > > Only method I can think of is using "char *" buffer and then > > > "std::memcpy()" to target of POD type (3.9/2). > > Which will be about the same as using reinterpret_cast. You > > will get just about anything. > Do you mean that the following code is as much portable as the code > above?: > std::fstream file("temp.bin", std::ios_base::in | std::ios_base::out | > std::ios_base::binary | std::ios_base::trunc); > std::int32_t value_write = 1234; > std::int32_t value_read = 0; > file.write(reinterpret_cast(&value_write), > sizeof(value_write)); > file.flush(); > file.seekg(0, std::ios_base::beg); > file.read(reinterpret_cast(&value_read), sizeof(&value_read)); > assert(value_write == value_read); Yep. The two versions are, in practice, pretty much equivalent. In practice, such hacks are fine for temporarily spilling data to disk, to be reread later by the same process. For anything else, however, you need to define a format, and write it. -- James Kanze -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. 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