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• Represent multiple Null/Generic objects in an ActiveRecord association?

  - by slothbear

  I have a Casefile model that belongs_to a Doctor. In additional to all the "real" doctors, there are several generic Doctors: "self-treated", "not specified", and "removed" (it used to have a real doctor, but no longer does). I suspect there will be even more generic values in the future. I started with special "doctors" in the database, generated from seed. The generic Doctors only need to respond to the "name" and "real_doctor?" methods. This worked with one, was strained with two, and now feels completely broken. I want to change the behavior and can't figure out how to test it, a bad sign. Creating all the generic objects for testing is also trouble, including fake values to pass validation of the required Doctor attributes. The Null Object pattern works well for one generic object. The "name" method could check casefile.doctor.nil? and return "self-treated", as demonstrated by Craig Ambrose. What pattern should I use when there are multiple generic objects with very limited state?

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• Is it just me? I find LINQ to XML to be sort of cumbersome, compared to XPath.

  - by Cheeso

  I am a C# programmer, so I don't get to take advantage of the cool XML syntax in VB. Dim itemList1 = From item In rss.<rss>.<channel>.<item> _ Where item.<description>.Value.Contains("LINQ") Or _ item.<title>.Value.Contains("LINQ") Using C#, I find XPath to be easier to think about, easier to code, easier to understand, than performing a multi-nested select using LINQ to XML. Look at this syntax, it looks like Greek swearing: var waypoints = from waypoint in gpxDoc.Descendants(gpx + "wpt") select new { Latitude = waypoint.Attribute("lat").Value, Longitude = waypoint.Attribute("lon").Value, Elevation = waypoint.Element(gpx + "ele") != null ? waypoint.Element(gpx + "ele").Value : null, Name = waypoint.Element(gpx + "name") != null ? waypoint.Element(gpx + "name").Value : null, Dt = waypoint.Element(gpx + "cmt") != null ? waypoint.Element(gpx + "cmt").Value : null }; All the casting, the heavy syntax, the possibility for NullPointerExceptions. None of this happens with XPath. I like LINQ in general, and I use it on object collections and databases, but my first go-round with querying XML led me right back to XPath. Is it just me? Am I missing something? EDIT: someone voted to close this as "not a real question". But it is a real question, stated clearly. The question is: Am I misunderstanding something with LINQ to XML?

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• How do I programmatically create a bootable CD?

  - by Nicholas Flynt

  I'm using a barebones tutorial as the basis for an OS I'm working on, and it seems to be an older tutorial: it has be compiling the kernel down to a floppy image, and then loading it with GRUB. Basically, I still want to use GRUB, but I'd like to have my OS run from a CD instead. The main reason is that I don't actually have a real floppy drive available (I'm testing in VirtualBox currently) and I thus have no way to test my OS on real hardware. I've been poking around on the net, and I can find lots of utilities that create a bootable CD from a floppy image, but these all seem to require an actual floppy drive, plus it's not really what I'm looking for. I'd like to be able to end up with a bootable CD during my make step ideally, without needing to first place the image on a floppy, which seems rather pointless. I guess the easy way to answer this: How do I set up GRUB to read my kernel image from a CD? Will I need a special utility to do this from Windows? (The kernel can't compile itself yet, that's not for a looong while) Thanks!

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• How to overload operator<< for qDebug

  - by iyo

  Hi, I'm trying to create more useful debug messages for my class where store data. My code is looking something like this #include <QAbstractTableModel> #include <QDebug> /** * Model for storing data. */ class DataModel : public QAbstractTableModel { // for debugging purposes friend QDebug & operator<< (const QDebug &d, DataModel model); //other stuff }; /** * Overloading operator for debugging purposes */ QDebug & operator<< (QDebug &d, DataModel model) { d << "Hello world!"; return d; } I expect qDebug() << model will print "Hello world!". However, there is alway something like "QAbstractTableModel(0x1c7e520)" on the output. Do you have any idea what's wrong?

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• Use LaTeX Listings to correctly detect and syntax highlight embedded code of a different language in

  - by D W

  I have scripts that have one-liners or sort scripts from other languages within them. How can I have LaTeX listings detect this and change the syntax formating language withing the script? This would be especially useful for awk withing bash I believe. Bash #!/bin/bash ... # usage message to catch bad input without invoking R ... # any bash pre-processing of input ... # etc echo "hello world" R --vanilla << EOF # Data on motor octane ratings for various gasoline blends x <- c(88.5,87.7,83.4,86.7,87.5,91.5,88.6,100.3, 95.6,93.3,94.7,91.1,91.0,94.2,87.5,89.9, 88.3,87.6,84.3,86.7,88.2,90.8,88.3,98.8, 94.2,92.7,93.2,91.0,90.3,93.4,88.5,90.1, 89.2,88.3,85.3,87.9,88.6,90.9,89.0,96.1, 93.3,91.8,92.3,90.4,90.1,93.0,88.7,89.9, 89.8,89.6,87.4,88.9,91.2,89.3,94.4,92.7, 91.8,91.6,90.4,91.1,92.6,89.8,90.6,91.1, 90.4,89.3,89.7,90.3,91.6,90.5,93.7,92.7, 92.2,92.2,91.2,91.0,92.2,90.0,90.7) x length(x) mean(x);var(x) stem(x) EOF perl -n -e ' @t = split(/\t/); %t2 = map { $_ => 1 } split(/,/,$t[1]); $t[1] = join(",",keys %t2); print join("\t",@t); ' knownGeneFromUCSC.txt awk -F'\t' '{ n = split($2, t, ","); _2 = x split(x, _) # use delete _ if supported for (i = 0; ++i <= n;) _[t[i]]++ || _2 = _2 ? _2 "," t[i] : t[i] $2 = _2 }-3' OFS='\t' infile Python #!/usr/local/bin/python print "Hello World" os.system(""" VAR=even; sed -i "s/$VAR/odd/" testfile; for i in `cat testfile` ; do echo $i; done; echo "now the tr command is removing the vowels"; cat testfile |tr 'aeiou' ' ' """)

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• Prototype VS jQuery

  - by aSeptik

  Hi All guys! First of, thank's for your time; then i want go directly to the point by saying that, i don't want to open another "Yet Another Js VS Js" 3d , the web is almost busy of this! I want also make a premise, i have used both theese js frameworks and i love it and i know, that there are a lot of good js frameworks around, maybe better then this two; but, as you know we need to be perfomant and quickly by doing our works, so i want keep this two, that are the most famous and therefore have a great community support! now, if you are going to say me, that the choise depends on what i'm going to do!? then i can think, hey, in the end they are both javascript and they have almost the same methods and functions and for achieve a task they needs almost the same lines of code! So i want hear from you guys, from you that have really used one of theese, for a real Rich Internet Application what are the real points of force and what the weaknesses you find!? Regards.

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• Java remove HTML from String without regular expressions

  - by behrk2

  Hello, I am trying to remove all HTML elements from a String. Unfortunately, I cannot use regular expressions because I am developing on the Blackberry platform and regular expressions are not yet supported. Is there any other way that I can remove HTML from a string? I read somewhere that you can use a DOM Parser, but I couldn't find much on it. Text with HTML: <![CDATA[As a massive asteroid hurtles toward Earth, NASA head honcho Dan Truman (<a href="http://www.netflix.com/RoleDisplay/Billy_Bob_Thornton/20000303">Billy Bob Thornton</a>) hatches a plan to split the deadly rock in two before it annihilates the entire planet, calling on Harry Stamper (<a href="http://www.netflix.com/RoleDisplay/Bruce_Willis/99786">Bruce Willis</a>) -- the world's finest oil driller -- to head up the mission. With time rapidly running out, Stamper assembles a crack team and blasts off into space to attempt the treacherous task. <a href="http://www.netflix.com/RoleDisplay/Ben_Affleck/20000016">Ben Affleck</a> and <a href="http://www.netflix.com/RoleDisplay/Liv_Tyler/162745">Liv Tyler</a> co-star.]]> Text without HTML: As a massive asteroid hurtles toward Earth, NASA head honcho Dan Truman (Billy Bob Thornton) hatches a plan to split the deadly rock in two before it annihilates the entire planet, calling on Harry Stamper (Bruce Willis) -- the world's finest oil driller -- to head up the mission. With time rapidly running out, Stamper assembles a crack team and blasts off into space to attempt the treacherous task.Ben Affleck and Liv Tyler co-star. Thanks!

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• Memory Bandwidth Performance for Modern Machines

  - by porgarmingduod

  I'm designing a real-time system that occasionally has to duplicate a large amount of memory. The memory consists of non-tiny regions, so I expect the copying performance will be fairly close to the maximum bandwidth the relevant components (CPU, RAM, MB) can do. This led me to wonder what kind of raw memory bandwidth modern commodity machine can muster? My aging Core2Duo gives me 1.5 GB/s if I use 1 thread to memcpy() (and understandably less if I memcpy() with both cores simultaneously.) While 1.5 GB is a fair amount of data, the real-time application I'm working on will have have something like 1/50th of a second, which means 30 MB. Basically, almost nothing. And perhaps worst of all, as I add multiple cores, I can process a lot more data without any increased performance for the needed duplication step. But a low-end Core2Due isn't exactly hot stuff these days. Are there any sites with information, such as actual benchmarks, on raw memory bandwidth on current and near-future hardware? Furthermore, for duplicating large amounts of data in memory, are there any shortcuts, or is memcpy() as good as it will get? Given a bunch of cores with nothing to do but duplicate as much memory as possible in a short amount of time, what's the best I can do?

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• How can I draw on JPanel using another quadrant for the coordinates?

  - by Sanoj

  I would like to draw some shapes on a JPanel by overriding paintComponent. I would like to be able to pan and zoom. Panning and zooming is easy to do with AffineTransform and the setTransform method on the Graphics2D object. After doing that I can easyli draw the shapes with g2.draw(myShape) The shapes are defined with the "world coordinates" so it works fine when panning and I have to translate them to the canvas/JPanel coordinates before drawing. Now I would like to change the quadrant of the coordinates. From the 4th quadrant that JPanel and computer often uses to the 1st quadrant that the users are most familiar with. The X is the same but the Y-axe should increase upwards instead of downwards. It is easy to redefine origo by new Point(origo.x, -origo.y); But How can I draw the shapes in this quadrant? I would like to keep the coordinates of the shapes (defined in the world coordinates) rather than have them in the canvas coordinates. So I need to transform them in some way, or transform the Graphics2D object, and I would like to do it efficiently. Can I do this with AffineTransform too?

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• Fun things you can do by mutating Java strings

  - by polygenelubricants

  So I've come around since I asked how to limit setAccessible to only “legitimate” uses and have come to embrace its power for fun. Enabled by its power, of course, is string mutation. import java.lang.reflect.Field; public class Mutator { static void mutate(Object obj, String field, Object newValue) { try { Field f = obj.getClass().getDeclaredField(field); f.setAccessible(true); f.set(obj, newValue); } catch (Exception e) { } } public static void mutate(String from, String to) { mutate(from, "value", to.toCharArray()); mutate(from, "count", to.length()); } public static void main(String args[]) { Mutator.mutate(System.getProperty("line.separator"), "<br/>\n"); System.out.println("Hello world!"); Mutator.mutate(Integer.toString(Integer.MIN_VALUE), "OMG!"); System.out.println(-2147483648); Mutator.mutate(String.valueOf((Object) null), "LOL!"); System.out.println(Arrays.toString(new int[3][])); Mutator.mutate(Arrays.toString(new int[0]), ":("); System.out.println(Arrays.toString(new byte[0])); } } Output (if no exception is thrown): Hello world!<br/> OMG!<br/> [LOL!, LOL!, LOL!]<br/> :(<br/> Let's see what other fun things we can come up with.

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• Are there any prototype-based languages with a whole development cycle?

  - by Kaveh Shahbazian

  Are there any real-world prototype-based programming languages with a whole development cycle? "A whole development cycle" like Ruby and Python: web frameworks, scripting/interacting with the system, tools for debugging, profiling, etc. Thank you A brief note on PBPLs: (let's call these languages PBPL : prototype-based programming language) There are some PBPLs out there. Some are being widely used like JavaScript (which Node.js may bring it into the field - or may not!). One other language is ActionScript which is also a PBPL but tightly bound to Flash VM (is it correct to say so?). From less known ones I can speak of Lua which has a strong reputation in game development (mostly spread by WOW) but never took off as a full language. Lua has a table concept which can provide you some sort of prototype based programming facility. There is also JScript (Windows scripting tool) which is already pointless by the newcomer PowerShell (I have used JScript to manipulate IIS but I never understood what is JScript!). Others can be named like io (indeed very very neat, you will fall in love with it; absolutely impossible to use) and REBOL (What is this all about? A proprietary scripting tool? You must be kidding!) and newLISP (Which is actually a full language, but no one ever heard about it). For sure there are much more to list here but either I do not remember or I did not understood them as a real world thing, like Self).

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• Web-based game in Python + Django and client browser polling

  - by ty

  I am creating a text-based game that implements a basic model in which multiple (10+) players interact with data and one moderator watches them and sets certain environmental statistics that affect gameplay. Recently I have begun to familiarize myself with Django. It seems to me that it would be an excellent tool for creating a game quickly, particularly because the nature of my game depends largely on sets of data (which lends itself quite well to a database). I am wondering how to "push" changes made by the game moderator to the players (for example, the moderator can decide to display an image to all players). The game is turn-based, not real-time, but certain messages need to be pushed out in roughly real-time. My thoughts: I could have each player's browser poll a status periodically (say, every 30 seconds) to see if there is a message from a moderator. But this forces a lag and means different players might receive it at different times. And reducing this interval to <10 seems like a bad idea for the server. Is there a better way to inform clients of changes? Would you suggest something other than using a web framework like Django? Thanks!

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• Which Project Management Software is adequate for Software & Non-Software Projects?

  - by cusack

  PMS = (Project Management Software) I used trac for software development some time ago. Right now I'm searching for a new more powerful (scheduling, gantt charts, ...) free solution (as in free beer ;-) and free to install on my server) for my current software project. Besides the current software project, abstract project management features like issue-tracking & scheduling would be great for coordinating a group of volunteers for real-life projects as well. I would want one solution for both purposes, so that I have the hassle of installation, getting used to the system and administration only once. So I tried redmine but the problem is it seems to be designed for software projects only. I can't suggest such a solution for the volunteer-group if tickets/issues would have to be of type bug, feature, ... I shortlisted the following six PMS from the wikipedia comparison http://en.wikipedia.org/wiki/List_of_project_management_software Project.net Project-Open Redmine Trac Endeavour Software Project Management eGroupWare I guess they are all more or less fine for software development but would you consider any of these to be good for the non-software project as well? Cliff Notes: I would want a start page situation like in trac. The start-page is a wiki presenting the project and not the PMS. But you can log into the PMS from there. Feature-wish list: wiki, Issue tracking, revision control, scheduling & gantt charts, forums (least important) (Btw: I'm very aware that I can't expect everything to be perfect ;-) 1.)Do you know a suitable solution for software and real-life projects or a highly customizable PMS where I can easily remove sth. like "browse source"(trac) and rename things like ticket/issue-types "bug", "feature"? 2.)Any experience good/bad with the above mentioned six PMS? I would personally guess that "Redmine" and "Endeavour Software Project Management" are too focused on software projects.

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• F# Async problem.

  - by chrisdew

  Hi, I've written a dummy http server as an exercise in F#. I'm using Mono 2.4.4 on Ubuntu 10.04 x86_64, with MonoDevelop. The following code fails to compile with the error: Error FS0039: The field, constructor or member 'Spawn' is not defined (FS0039) Could someone try this in VisualStudio please, I don't know whether this is a Mono problem, or my problem. I have tried several Async examples from the F# book, and they also all produce similar messages about Async.* methods. Thanks, Chris. #light open System open System.IO open System.Threading open System.Net open System.Net.Sockets open Microsoft.FSharp.Control.CommonExtensions printfn "%s" "Hello World!" let headers = System.Text.Encoding.ASCII.GetBytes("HTTP/1.0 200 OK\r\nContent-Type: text/html; charset=UTF-8\r\nContent-Length: 37\r\nDate: Sun, 13 Jun 2010 05:30:00 GMT\r\nServer: FSC/0.0.1\r\n\r\n") let content = System.Text.Encoding.ASCII.GetBytes("<html><body>Hello World</body></html>") let serveAsync (client : TcpClient) = async { let out = client.GetStream() do! out.AsyncWrite(headers) do! Async.Sleep 3000 do! out.AsyncWrite(content) do out.Close() } let http_server (ip, port) = let server = new TcpListener(IPAddress.Parse(ip),port) server.Start() while true do let client = server.AcceptTcpClient() printfn "new client" Async.Spawn (serveAsync client) http_server ("0.0.0.0", 1234)

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• I write barely functional scripts that tend to not be resuable and make the baby jesus cry. Please h

  - by maxxpower

  I received a request to add around 100 users to a linux box the users are already in ldap so I can't just use newusers and point it at a text file. Another admin is taking care of the ldap piece so all I have to do is create all the home directories and chown them to the correct user once he adds the users to the box. creating the directories isn't a problem, but I'd like a more elegant script for chowning them to the correct user. what I have currently basically looks like chown -R testuser1 testgroup1 /home/tetsuser1; chown -R testuser2 testgroup2 /home/testgroup2; chown -R testsuser3 testgroup1 /home/testuser3 bascially I took the request that the user name and group name popped it into excel added a column of "chown -R" to the front, then added a column of "/", copied and pasted the username column after it and then added a column of ";" and dragged it down to the second to last row. Popped it into notepad ran some quick find and replaces and in less than a minute I have a completed request and a sad empty feeling. I know this was a really ghetto method and I'm trying to get away from using excel to avoid learning new scripting techniques so here's my real question. tl;dr I made 100 home directories and chowned them to the correct users, but it was ugly. Actual question below. You have a file named idlist that looks like this (only with say 1000 users and real usernames and groups) testuser1 testgroup1 testuser2 testgroup2 testuser3 testgroup1 write a script that creates home directories for all the users and chowns the created directories to the correct user and group. To make the directories I used the following(feel free to flame/correct me on this as well. ) var= 'cut -f1 -d" " idlist' (I used backticks not apostrophes around the cut command) mkdir $var

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• jquery google link

  - by Val

  Has anyone got any idea how this google code works? i got the following: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>My Google AJAX Search API Application</title> <script src="http://www.google.com/jsapi?key=blahblahblah" type="text/javascript"></script> <script language="Javascript" type="text/javascript"> google.load("jquery", "1"); google.load("jqueryui", "1"); </script> </head> <body> <div class="ui-state-highlight"> hello world </div> </body> </html> However the <div></div> should display the error box with hello world. but it doesn't show the red background therefor the ui is not working ... What have i done wrong here?

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• How to design Models the correct way: Object-oriented or "Package"-oriented?

  - by ajsie

  I know that in OOP you want every object (from a class) to be a "thing", eg. user, validator etc. I know the basics about MVC, how they different parts interact with each other. However, i wonder if the models in MVC should be designed according to the traditional OOP design, that is to say, should every model be a database/table/row (solution 2)? Or is the intention more like to collect methods that are affecting the same table or a bunch of related tables (solution 1). example for an Address book module in CodeIgniter, where i want be able to "CRUD" a Contact and add/remove it to/from a CRUD-able Contact Group. Models solution 1: bunching all related methods together (not real object, rather a "package") class Contacts extends Model { function create_contact() {) function read_contact() {} function update_contact() {} function delete_contact() {} function add_contact_to_group() {} function delete_contact_from_group() {} function create_group() {} function read_group() {} function update_group() {} function delete_group() {} } Models solution 2: the OOP way (one class per file) class Contact extends Model { private $name = ''; private $id = ''; function create_contact() {) function read_contact() {} function update_contact() {} function delete_contact() {} } class ContactGroup extends Model { private $name = ''; private $id = ''; function add_contact_to_group() {} function delete_contact_from_group() {} function create_group() {} function read_group() {} function update_group() {} function delete_group() {} } i dont know how to think when i want to create the models. and the above examples are my real tasks for creating an Address book. Should i just bunch all functions together in one class. then the class contains different logic (contact and group), so it can not hold properties that are specific for either one of them. the solution 2 works according to the OOP. but i dont know why i should make such a dividing. what would the benefits be to have a Contact object for example. Its surely not a User object, so why should a Contact "live" with its own state (properties and methods). you experienced guys with OOP/MVC, please shed a light on how one should think here in this very concrete task.

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• Nested asynchronous calls do not seem to execute as expected

  - by Kristof Van Landschoot

  While trying out jQuery, I have a question that is probably a newbie mistake, but I cannot seem to find the solution. This is the code: $.get("index.html", function() { var i = 0; for (; i < 3; i++) { var lDiv = document.createElement('div'); lDiv.id = 'body-' + i; document.getElementById('body').appendChild(lDiv); $.get('index.html', function(data) { lDiv.innerHTML = "<p>Hello World " + i + "</p>"; }); } }); The output seems to be <div id='body-0'></div> <div id='body-1'></div> <div id='body-2'> <p>Hello World 3</p> </div> I expected the lDiv.innerHTML= code to be executed for each i, but apparently it is only executed for the last i? What am I overlooking?

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• jquery ajax html response change 1.3.2 vs 1.4.2 (aka where is my script tag?)

  - by cmroanirgo

  I've been using jquery 1.3.2 to pull snippets of html (including script) from a server. A typical response might be: <div id="content"<div id="inner"... <script type=... alert("hello world");</script <pHello World</p </div</div I've been using the query .get function: $.get($(this).attr("href"), function(response) { $("#inner").replaceWith($("#inner", response)); }); And everything is fine and works as expected: the returned html snippets get loaded into the DOM and the scripts run. When I use 1.4.2 however, I notice that the script tags have been removed and no longer run. Stepping into the newer jquery codebase yields the lines of code (line 4498) : ret.splice.apply( ret, [i + 1, 0].concat(jQuery.makeArray(ret[i].getElementsByTagName("script"))) ); which seems to be the culprit 'removing' the script from its happy resting place as part of the selector process. But it doesn't help me in injecting exactly what i want into the DOM. Any idea why jquery is doing this? More importantly, how can I go about fixing this so that my scripts run?

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• How do I read text from a serial port?

  - by user2164

  I am trying to read data off of a Windows serial port through Java. I have the javax.comm libraries and am able to get some data but not correct data. When I read the port into a byte array and convert it to text I get a series of characters but no real text string. I have tried to specify the byte array as being both "UTF-8" and "US-ASCII". Does anyone know how to get real text out of this? Here is my code: while (inputStream.available() > 0) { int numBytes = inputStream.read(readBuffer); System.out.println("Reading from " + portId.getName() + ": "); System.out.println("Read " + numBytes + " bytes"); } System.out.println(new String(readBuffer)); System.out.println(new String(readBuffer, "UTF-8")); System.out.println(new String(readBuffer, "US-ASCII")); the output of the first three lines will not let me copy and paste (I assume because they are not normal characters). Here is the output of the Hex: 78786000e67e9e60061e8606781e66e0869e98e086f89898861878809e1e9880 I am reading from a Hollux GPS device which does output in string format. I know this for sure because I did it through C#. The settings that I am using for communication which I know are right from the work in the C# app are: Baud Rate: 9600 Databits: 8 Stop bit: 1 parity: none

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• i386 assembly question: why do I need to meddle with the stack pointer?

  - by zneak

  Hello everyone, I decided it would be fun to learn x86 assembly during the summer break. So I started with a very simple hello world program, borrowing on free examples gcc -S could give me. I ended up with this: HELLO: .ascii "Hello, world!\12\0" .text .globl _main _main: pushl %ebp # 1. puts the base stack address on the stack movl %esp, %ebp # 2. puts the base stack address in the stack address register subl $20, %esp # 3. ??? pushl $HELLO # 4. push HELLO's address on the stack call _puts # 5. call puts xorl %eax, %eax # 6. zero %eax, probably not necessary since we didn't do anything with it leave # 7. clean up ret # 8. return # PROFIT! It compiles and even works! And I think I understand most of it. Though, magic happens at step 3. Would I remove this line, my program would die between the call to puts and the xor from a misaligned stack error. And would I change $20 to another value, it'd crash too. So I came to the conclusion that this value is very important. Problem is, I don't know what it does and why it's needed. Can anyone explain me? (I'm on Mac OS, would it ever matter.)

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• Scala programming language for beginners, is it a legend?

  - by ali

  Hi every one, I am Ali from Saudi Arabia. undoubtedly, Scala is one of the best programming language for any programmer to learn, but there is "good" problems that is faced especially by beginners, and what seems frustrating that these problems won't solve soon, so as a beginner and on behalf of beginners let me raise these "objective" questions: 1- why scala has no effective and stable development platform, in fact, it suffers many problems with Eclipse, Netbeat, and Intellij. 2- although I have looked for a clear,easy, and understandable explanation of how to get started with Scala, but fortunately, there was no article or guide that deserves to spend the time I have spent to read it. nobody could tell you clear steps that fit you as a beginner who wants to start his"HELLO WORLD" with Scala, while all other languages have its "HELLO WORLD" guides and books. thank you for your time, be sure that you read notes below. 1- I have no experience in programming language before. 2- don't tell me "not to begin with scala", simply, because I will do. 3- OS is windows vista home premium. 4- I hate excuses, such as Scala is new language......etc

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• Java problem: Could not find main class HelloWorld

  - by Newbie

  I am new to java(a real novice). I installed Java 1.7.0 in the following folder C:\Program Files\Java The environment variable which I set are CLASSPATH : C:\Program Files\Java\jdk1.7.0\jre\lib\rt.jar; Path : C:\Program Files\Java\jdk1.7.0\bin; JAVA_HOME : C:\Program Files\Java; I have presented here the class names which are in my system. Next I wrote a program(HelloWorld.java) import java.io.*; class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } } When I am compiling using javac HelloWorld.java it is compiling fine. But after I issue java HelloWorld I am encountering the below error Error: Could not find main class HelloWorld Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:198) Caused by: java.lang.ClassNotFoundException: HelloWorld at java.net.URLClassLoader$1.run(URLClassLoader.java:299) at java.net.URLClassLoader$1.run(URLClassLoader.java:288) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:287) at java.lang.ClassLoader.loadClass(ClassLoader.java:422) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325) at java.lang.ClassLoader.loadClass(ClassLoader.java:355) at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:195) After a bit of google search I found that may be something wrong in the environment variable. I tried to play with that but no luck. I know that it may be a very simple thing for the real java developers(actually basic) but for me as of now no luck! I even RESTARTED the machine and then again I tried to run but with same fate. OS: Windows XP(Version 2002) with Service pack 3 Help needed . Thanks .

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• check whether mmap'ed address is correct

  - by reddot

  I'm writing a high-loaded daemon that should be run on the FreeBSD 8.0 and on Linux as well. The main purpose of daemon is to pass files that are requested by their identifier. Identifier is converted into local filename/file size via request to db. And then I use sequential mmap() calls to pass file blocks with send(). However sometimes there are mismatch of filesize in db and filesize on filesystem (realsize < size in db). In this situation I've sent all real data blocks and when next data block is mapped -- mmap returns no errors, just usual address (I've checked errno variable also, it's equal to zero after mmap). And when daemon tries to send this block it gets Segmentation Fault. (This behaviour is guarantedly issued on FreeBSD 8.0 amd64) I was using safe check before open to ensure size with stat() call. However real life shows to me that segfault still can be raised in rare situtaions. So, my question is there a way to check whether pointer is accessible before dereferencing it? When I've opened core in gdb, gdb says that given address is out of bound. Probably there is another solution somebody can propose.

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• Using diff and patch to force one local code base to look like another

  - by Dave Aaron Smith

  I've noticed this strange behavior of diff and patch when I've used them to force one code base to be identical to another. Let's say I want to update update_me to look identical to leave_unchanged. I go to update_me. I run a diff from leave_unchanged to update_me. Then I patch the diff into update_me. If there are new files in leave_unchanged, patch asks me if my patch was reversed! If I answer yes, it deletes the new files in leave_unchanged. Then, if I simply re-run the patch, it correctly patches update_me. Why does patch try to modify both leave_unchanged and update_me? What's the proper way to do this? I found a hacky way which is to replace all +++ lines with nonsense paths so patch can't find leave_unchanged. Then it works fine. It's such an ugly solution though. $ mkdir copyfrom $ mkdir copyto $ echo "Hello world" > copyfrom/myFile.txt $ cd copyto $ diff -Naur . ../copyfrom > my.diff $ less my.diff diff -Naur ./myFile.txt ../copyfrom/myFile.txt --- ./myFile.txt 1969-12-31 19:00:00.000000000 -0500 +++ ../copyfrom/myFile.txt 2010-03-15 17:21:22.000000000 -0400 @@ -0,0 +1 @@ +Hello world $ patch -p0 < my.diff The next patch would create the file ../copyfrom/myFile.txt, which already exists! Assume -R? [n] yes patching file ../copyfrom/myFile.txt $ patch -p0 < my.diff patching file ./myFile.txt

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