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• Android Signal analysis + some filters.

  - by Profete162

  Hello, as the world cup is the main sport event and the Vuvuzelas are the most annoying sound in the world, I had an idea to remove them definitively by reading this new ( http://www.popsci.com/diy/article/2010-06/simple-software-can-filter-out-vuvuzela-whine) that told us that the sound has some frequencies at 233Hz + 466,932,1864Hz. I have already made a lot of Android application by myself but never touching the signal analysis and filtering part, so here are a few questions, I do not ask for precise answer but maybe links and tutorial to find something to work on. I guess that a new Android phone has the CPU and power to make real-time filtering. 1) How can I intercept the sound coming from the Jack microphone - Line-IN plug- ( I plan to link my TV to my phone with Jack to Jack plug). My question is totally software and coding, I have all the wires and adapters to plug a jack into my android phone Line IN. 2) Are there some Fourier analysis librairies, may I have a look to Java libraries on the web and import them to my Android project? I really apologize because my question seem not precise, but I think that would be something great. Thank you for your answers.

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• How can someone with no experience learn how to program?

  - by Mugatu

  A friend and I have been coming up with website ideas for a couple years, mostly just jotting them down whenever we come up with a good, useful idea when browsing the web. For the past 6 months we've hired a couple different programmers to make a couple of the sites for us, but have been disappointed with how it's gone. Been too slow and too many miscommunications for our liking. So like the saying goes if you want something done right do it yourself, we're going to do it ourselves. I know nothing about programming, I've never written a line of code in my life. I consider myself very good with math and about as logical as you can get, but I have zero real-life programming knowledge. The sites we want to make are all pretty 'Web 2.0'ish', meaning user-generated content, commenting on posts, pages that change on the fly, etc. So here are some of my questions for anyone who's been there before: Is there a language you'd recommend learning first? Something that is a good indicator how most other languages work? What web programming languages do you recommend learning first based on popularity both now and the future. I don't want to learn a language that's going to be outdated by the time I'm an expert at it. Any specific books you'd recommend? Any general advice you'd give to someone literally starting at square zero for coding who plans on being in it for the long haul?

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• Xlib.h and Xutil.h not found in Eclipse, how can I fix this?

  - by eclipseNoob

  Hi, I'm a newbie to Eclipse IDE for C/C++ development. I just installed MingW and set it up as my system's environment variable. I am trying to make an application that uses the X library but eclipse cant seem to find it. Eclipse works with any other simple standard library functions but it cant find the X library. Please Help! Here's a sample code snippet that's failing: #include <stdio.h> #include <X11/Xlib.h> // Can't find this #include <X11/Xutil.h> // Or this... int main() { printf("Hello"); return 0; } Do I have to download the X library from somewhere? If so then from where and where do I paste it to? Please tell me what to do in order for me to start coding using the Xlib in Eclipse. If you find any useful links, please dont hesitate to post. Thanks.

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• Get subdomain of XML page from XSL

  - by fudgey

  I am working with a guild hosting site that provides an XML/XSL transformation widget where all I need to do is enter the URL for the XML and XSL and it does the rest. I have written an XSL transform to display a World of Warcraft armory page: Here is an example XML page (view source to see it) of the group I'm trying to help now. So, the user is entering their own XML page url (which has an eu subdomain in this case, but it is not within the XML itself). So when I make links to the character url, I need to add the entire url <a target="_blank" href="http://eu.wowarmory.com/character-sheet.xml?{@url}"> <xsl:value-of select="@name"/> </a> But I can't just set the domain to eu since there are multiple regions. Here are the possibilities: us = www, europe = eu, korea = kr, china = cn and taiwan = tw. Here is a snippet of the XML which shows the url parameters: <character achPoints="4275" classId="3" genderId="0" level="80" name="Virtex" raceId="4" rank="2" url="r=Drek%27Thar&amp;cn=Virtex"/> I guess I could just have the user add a small bit of HTML with their region in another part of their page, something like <div id="region">eu</div>, but I'm trying to make this work without any extra coding on their part. Edit: Ok, my question explicitly stated: How do I get the URL subdomain using XSL?

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• What's the next steps for moving from appengine to full django?

  - by tomcritchlow

  Hey guys, I'm super new to programming and I've been using appengine to help me learn python and general coding. I'm getting better quickly and I'm loving it all the way :) Appengine was awesome for allowing me to just dive into writing my app and getting something live that works (see http://www.7bks.com/). But I'm realising that the longer I continue to learn on appengine the more I'm constraining myself and locking myself into a single system. I'd like to move to developing on full django (since django looks super cool!). What are my next steps? To give you a feel for my level of knowledge: I'm not a unix user I'm not familiar with command line controls (I still use appengine/python completely via the appengine SDK) I've never programmed in anything other than python, anywhere other than appengine I know the word SQL, but don't know what MySQL is really or how to use it. So, specifically: What are the skills I need to learn to get up and running with full django/python? If I'm going to host somewhere else I suppose I'll need to learn some sysadmin type skills (maybe even unix?). Is there anywhere that offers easy hosting (like appengine) but that supports django? I hear such great things about heroku I'm considering switching to RoR and going there I appreciate that I'm likely not quite ready to move away from appengine just yet but I'm a fiercely passionate learner (http://www.7bks.com/blog/179001) and would love it if I knew all the steps I needed to learn so I could set about learning them. At the moment, I don't even know what the steps are I need to learn! Thank you very much. Sorry this isn't a specific programming question but I've looked around and haven't found a good how-to for someone of my level of experience and I think others would appreciate a good roadmap for the things we need to learn to get up and running. Thanks, Tom PS - if anyone is in London and fancies showing me the ropes in person that would be super awesome :)

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• Trouble with building up a string in Clojure

  - by Aki Iskandar

  Hi gang - [this may seem like my problem is with Compojure, but it isn't - it's with Clojure] I've been pulling my hair out on this seemingly simple issue - but am getting nowhere. I am playing with Compojure (a light web framework for Clojure) and I would just like to generate a web page showing showing my list of todos that are in a PostgreSQL database. The code snippets are below (left out the database connection, query, etc - but that part isn't needed because specific issue is that the resulting HTML shows nothing between the <body> and </body> tags). As a test, I tried hard-coding the string in the call to main-layout, like this: (html (main-layout "Aki's Todos" "Haircut<br>Study Clojure<br>Answer a question on Stackoverfolw")) - and it works fine. So the real issue is that I do not believe I know how to build up a string in Clojure. Not the idiomatic way, and not by calling out to Java's StringBuilder either - as I have attempted to do in the code below. A virtual beer, and a big upvote to whoever can solve it! Many thanks! ============================================================= ;The master template (a very simple POC for now, but can expand on it later) (defn main-layout "This is one of the html layouts for the pages assets - just like a master page" [title body] (html [:html [:head [:title title] (include-js "todos.js") (include-css "todos.css")] [:body body]])) (defn show-all-todos "This function will generate the todos HTML table and call the layout function" [] (let [rs (select-all-todos) sbHTML (new StringBuilder)] (for [rec rs] (.append sbHTML (str rec "<br><br>"))) (html (main-layout "Aki's Todos" (.toString sbHTML))))) ============================================================= Again, the result is a web page but with nothing between the body tags. If I replace the code in the for loop with println statements, and direct the code to the repl - forgetting about the web page stuff (ie. the call to main-layout), the resultset gets printed - BUT - the issue is with building up the string. Thanks again. ~Aki

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• c# Sending emails with authentication. standard approach not working

  - by Ready Cent

  I am trying to send an email using the following very standard code. However, I get the error that follow... MailMessage message = new MailMessage(); message.Sender = new MailAddress("[email protected]"); message.To.Add("[email protected]"); message.Subject = "test subject"; message.Body = "test body"; SmtpClient client = new SmtpClient(); client.Host = "mail.myhost.com"; //client.Port = 587; NetworkCredential cred = new NetworkCredential(); cred.UserName = "[email protected]"; cred.Password = "correct password"; cred.Domain = "mail.myhost.com"; client.Credentials = cred; client.UseDefaultCredentials = false; client.Send(message); Mailbox unavailable. The server response was: No such user here. This recipient email address definitely works. To make this account work I had to do some special steps in outlook. Specifically, I had to do change account settings - more settings - outgoing server - my outgoing server requires authentication & use same settings. I am wondering if there is some other strategy. I think the key here is that my host is Server Intellect and I know that some people on here use them so hopefully someone else has been able to get through this. I did talk to support but they said with coding issues I am on my own :o

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• How Would a Newborn Baby Learn Web Programming?

  - by Mugatu

  Hello all, I chose that title because I equate my knowledge of web programming and web development with that of a newborn. Here's the shortest version of my story and what I'm looking to do: A friend and I have been coming up with website ideas for a couple years, mostly just jotting them down whenever we come up with a good, useful idea when browsing the web. For the past 6 months we've hired a couple different programmers to make a couple of the sites for us, but have been disappointed with how it's gone. Been too slow and too many miscommunications for our liking. So like the saying goes if you want something done right do it yourself, we're going to do it ourselves. I know nothing about programming, I've never written a line of code in my life. I consider myself very good with math and about as logical as you can get, but I have zero real-life programming knowledge. The sites we want to make are all pretty 'Web 2.0'ish', meaning user-generated content, commenting on posts, pages that change on the fly, etc. So here are some of my questions for anyone who's been there before: Is there a language you'd recommend learning first? Something that is a good indicator how most other languages work? What web programming languages do you recommend learning first based on popularity both now and the future. I don't want to learn a language that's going to be outdated by the time I'm an expert at it. Any specific books you'd recommend? Any general advice you'd give to someone literally starting at square zero for coding who plans on being in it for the long haul? Thanks in advance for the help

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• Database for managing large volumes of (system) metrics

  - by symcbean

  Hi, I'm looking at building a system for managing and reporting stats on web page performance. I'll be collecting a lot more stats than are available in the standard log formats (approx 20 metrics) but compared to most types of database applications, the base data structure will be very simple. My problem is that I'll be accumulating a lot of data - in the region of 100,000 records (i.e. sets of metrics) per hour. Of course, resources are very limited! So that its possible to sensibly interact with the data, I'd need to consolidate each metric into one minute bins, broken down by URL, then for anything more than 1 day old, consolidated into 10 minute bins, then at 1 week, hourly bins. At the front end, I want to provide a view (prefereably as plots) of the last hour of data, with the facility for users to drill up/down through defined hierarchies of URLs (which do not always map directly to the hierarchy expressed in the path of the URL) and to view different time frames. Rather than coding all this myself and using a relational database, I was wondering if there were tools available which would facilitate both the management of the data and the reporting. I had a look at Mondrian however I can't see from the documentation I've looked at whether it's possible to drop the more granular information while maintaining the consolidated views of the data. RRDTool looks promising in terms of managing the data consolidation, but seems to be rather limited in terms of querying the dataset as a multi-dimensional/relational database. What else whould I be looking at?

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• php: autoload exception handling.

  - by YuriKolovsky

  Hello again, I'm extending my previous question (Handling exceptions within exception handle) to address my bad coding practice. I'm trying to delegate autoload errors to a exception handler. <?php function __autoload($class_name) { $file = $class_name.'.php'; try { if (file_exists($file)) { include $file; }else{ throw new loadException("File $file is missing"); } if(!class_exists($class_name,false)){ throw new loadException("Class $class_name missing in $file"); } }catch(loadException $e){ header("HTTP/1.0 500 Internal Server Error"); $e->loadErrorPage('500'); exit; } return true; } class loadException extends Exception { public function __toString() { return get_class($this) . " in {$this->file}({$this->line})".PHP_EOL ."'{$this->message}'".PHP_EOL . "{$this->getTraceAsString()}"; } public function loadErrorPage($code){ try { $page = new pageClass(); echo $page->showPage($code); }catch(Exception $e){ echo 'fatal error: ', $code; } } } $test = new testClass(); ?> the above script is supposed to load a 404 page if the testClass.php file is missing, and it works fine, UNLESS the pageClass.php file is missing as well, in which case I see a "Fatal error: Class 'pageClass' not found in D:\xampp\htdocs\Test\PHP\errorhandle\index.php on line 29" instead of the "fatal error: 500" message I do not want to add a try/catch block to each and every class autoload (object creation), so i tried this. What is the proper way of handling this?

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• Using callback functions for error handling in C

  - by Earlz

  Hi, I have been thinking about the difficulty incurred with C error handling.. like who actually does if(printf("hello world")==-1){exit(1);} But you break common standards by not doing such verbose, and usually useless coding. Well what if you had a wrapper around the libc? like so you could do something like.. //main... error_catchall(my_errors); printf("hello world"); //this will automatically call my_errors on an error of printf ignore=1; //this makes it so the function will return like normal and we can check error values ourself if(fopen.... //we want to know if the file opened or not and handle it ourself. } int my_errors(){ if(ignore==0){ _exit(1); //exit if we aren't handling this error by flagging ignore } return 0; //this is called when there is an error anywhere in the libc } ... I am considering making such a wrapper as I am synthesizing my own BSD licensed libc(so I already have to touch the untouchable..), but I would like to know what people think about it.. would this actually work in real life and be more useful than returning -1?

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• Where can I find BLAS example code (in Fortran)?

  - by Feynman

  I have been searching for decent documentation on blas, and I have found some 315 pages of dense material that ctrl-f does not work on. It provides all the information regarding what input arguments the routines take, but there are a LOT of input arguments and I could really use some example code. I am unable to locate any. I know there has to be some or no one would be able to use these libraries! Specifically, I use ATLAS installed via macports on a mac osx 10.5.8 and I use gfortran from gcc 4.4 (also installed via macports). I am coding in Fortran 90. I am still quite new to Fortran, but I have a fair amount of experience with mathematica, matlab, perl, and shell scripting. I would like to be able to initialize and multiply a dense complex vector by a dense symmetric (but not hermitian) complex matrix. The elements of the matrix are defined through a mathematical function of the indices--call it f(i,j). Could anyone provide some code or a link to some code?

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• Ajax div can't access address bar variable

  - by Elaine Adams

  Can someone please advise me on how my Ajax div can get an address bar variable. The usual way just doesn't work. My address bar currently looks like this: http://localhost/social3/browse/?locationName=Cambridge Usually, I would use a little php and do this: $searchResult = $_POST['locationName']; echo $searchResult; But because I'm in an Ajax div, I can't seem to get to the variable. Do I need to add some JavaScript wizardry to my Ajax coding? (I have little knowledge of this) My Ajax: <script> window.onload = function () { var everyone = document.getElementById('everyone'), searching = document.getElementById('searching'), searchingSubmit = document.getElementById('searchingSubmit'); everyone.onclick = function() { loadXMLDoc('indexEveryone'); everyone.className = 'filterOptionActive'; searching.className = 'filterOption'; } searching.onclick = function() { loadXMLDoc('indexSearching'); searching.className = 'filterOptionActive'; everyone.className = 'filterOption'; } searchingSubmit.onclick = function() { loadXMLDoc('indexSearchingSubmit'); } function loadXMLDoc(pageName) { var xmlhttp; if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 && xmlhttp.status==200) { document.getElementById("leftCont").innerHTML=xmlhttp.responseText; } } function get_query(){ var url = location.href; var qs = url.substring(url.indexOf('?') + 1).split('&'); for(var i = 0, result = {}; i < qs.length; i++){ qs[i] = qs[i].split('='); result[qs[i][0]] = decodeURIComponent(qs[i][1]); } return result; } xmlhttp.open("GET","../browse/" + pageName + ".php?user=" + get_query()['user'],true); xmlhttp.send(); } } </script> <!-- ends ajax script -->

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• A feeling that I'm not that good developer

  - by Karim

  Hi, Im having a strange feeling, but let me first introduce myself as a software developer. I started to program when I was still a kid, I had about 10 or 11 years. I really enjoy my work and never get bored from it. It's amazing how somebody could be paid for what he really likes to do and would be doing it anyway even for free. WHen I first started to program, I was feeling proud of what I was doing, each application I built was for me a success and after 2-3 year I had a feeling that I'm a coding guru. It was a nice feeling ;-) But the more I was in the field, the more types of software I started to develop I was starting to have a feeling that I'm completely wrong in that I'm guru. I felt that I'm not even a mediocre developer. Each new field I start to work on is giving me this feeling. Like when I once developed a device driver for a client, I saw how much I need to learn about device drivers. When I developed a video filter for an application, I saw how much do I still need to learn about DirectShow, Color Spaces, and all the theory behind that. The worst thing was when I started to learn algorithms. It was several years ago. I knew then the basic structures and algorithms like the sorting, some types of trees, some hashtables, strings etc.. and when I really wanted to learn a group of structures I learned about 5-6 new types and saw that in fact even this small group has several hundred subtypes of structures. It's depressing how little time people have in their lives to learn all this stuff. I'm now a software developer with about 10 years of experience and I still feel that I'm not a proficient developer when I think about things that others do in the industry. Is this normal what I'm experiencing or is it a sign of a destructive excessive ambition? Thanks in advance for any comments.

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• setup Qt and PyQt on mac osx so my app can also deployable on windows

  - by hk_programmer

  Hi, I've been coding with Python and C++ and now need to work on building a gui for data visualization purposes. I work on Mac Snow Leopard (intel), python 3.1 using gcc 4.2.1 (from Xcode 3.1) I wanted to first install Qt and then PyQt. And my goals are to be able to: - quickly prototype GUI and the accompanied logic that drives the GUI using PyQt and python - if I decided I need the speed, or if it's fairly easy to translate my GUI into C++ using the Qt tools, I have the options to translate my app into C++ - Be able to deploy my application onto Windows (both the python and c++ version of my app) Give the goals above, what are the correct steps I should take and what issues i should be aware of when setting up Qt and PyQt. Which other deployment tools do I need? From my readings so far, here's what I have: download the Qt source for mac and configure it with -platform macx-g++42 -arch x86_64 -no-framework (i've read somewhere that building as framework causes some trouble in deployment and/or debugging, can't find the article anymore) download latest SIP source and build download latest PyQt and build from source (any special options I should pay attention to?) For deployment, I've read that I would need to use py2exe/cx_freeze for windows, p2app for mac: http://arstechnica.com/open-source/guides/2009/03/how-to-deploying-pyqt-applications-on-windows-and-mac-os-x.ars but seems like what the article describe is deploying an app you build on windows on the windows platform and vice versa. How do you deploy to windows (is it even possible?) if you are writing your Qt app on a mac ? Really appreciate the help

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• Comparing two Objects which implement the same interface for equality / equivalence - Design help

  - by gav

  Hi All, I have an interface and two objects implementing that interface, massively simplied; public interface MyInterface { public int getId(); public int getName(); ... } public class A implements MyInterface { ... } public class B implements MyInterface { ... } We are migrating from using one implementation to the other but I need to check that the objects of type B that are generated are equivalent to those of type A. Specifically I mean that for all of the interface methods an object of Type A and Type B will return the same value (I'm just checking my code for generating this objects is correct). How would you go about this? Map<String, MyInterface> oldGeneratedObjects = getOldGeneratedObjects(); Map<String, MyInterface> newGeneratedObjects = getNewGeneratedObjects(); // TODO: Establish that for each Key the Values in the two maps return equivalent values. I'm looking for good coding practices and style here. I appreciate that I could just iterate through one key set pulling out both objects which should be equivalent and then just call all the methods and compare, I'm just thinking there may be a cleaner, more extensible way and I'm interested to learn what options there might be. Would it be appropriate / possible / advised to override equals or implement Comparable? Thanks in advance, Gavin

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• How to reference an embedded JCA resource adapater

  - by cg

  For our current J2EE project based on JBoss, we need to interface with a remote system using message driven beans and a JCA resource adapter provided as a RAR file by a third party. I would like to package and deploy the entire project as an EAR file to our JBoss server. Most notably, the RAR file should be embedded within the EAR file and not be deployed globally. All of this is working fine so far, but I'm not particularly happy with the way the RAR file is referenced. The jboss.xml packaged with the MDB for example, currently looks like this: <jboss> <enterprise-beans> <message-driven> <ejb-name>testBean1</ejb-name> <resource-adapter-name>test1.ear#thirdparty-1.0.rar</resource-adapter-name> </message-driven> </enterprise-beans> </jboss> While this is generally working fine, it will break when the EAR file is renamed to "test2.ear". Is there a way to reference the embedded RAR file without hard-coding the containing archive's name?

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• Objective C code to handle large amount of data processing in iPhone

  - by user167662

  I had the following code that takes in 14 mb or more of image data encoded in base4 string and converts them to jpeg before writing to a file in iphone. It crashes my program giving the following error : Program received signal: “0”. warning: check_safe_call: could not restore current frame I tweak my program and it can process a few more images before the error appear again. My coding is as follows: // parameters is an array where the fourth element contains a list of images in base64 >encoded string NSMutableArray *imageStrList = (NSMutableArray*) [parameters objectAtIndex:5]; while (imageStrList.count != 0) { NSString *imgString = [imageStrList objectAtIndex:0]; // Create a file name using my own Utility class NSString *fileName = [Utility generateFileNName]; NSData *restoredImg = [NSData decodeWebSafeBase64ForString:imgString]; UIImage *img = [UIImage imageWithData: restoredImg]; NSData *imgJPEG = UIImageJPEGRepresentation(img, 0.4f); [imgJPEG writeToFile:fileName atomically:YES]; [imageStrList removeObjectAtIndex:0]; } I tried playing around with UIImageJPEGRepresentation and found out that the lower the value, the more image it can processed but this should not be the way. I am wondering if there is anyway to free up memory of the imageStrList immediately after processing each image so that it can be used by the next one in the line.

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• Flex vs GWT again

  - by CK Lee

  Hi all, I am working on a customized web ontology editor (something like http://webprotege.stanford.edu/ which is built by GWT). My backend will be Java+Spring+Hibernate and domain models are in Java. My frontend will be something like WebProtege which requires extensive RPC call. It is quite clear that I should use GWT as I can refer to the open source code. However, due to company policy, I shall consider Flex as well. I understand Flex can remotely invoke Java backend methods via BlazeDS using AMF (Is there a Flex equivalent of GWT-RPC?). I have read discussion on GWT vs Flex vs ?. If I can make full decision sure I will go with GWT. GWT strengths like support right to left characters, support iPhone/iPad, smaller size, support JSON out of the box, support printing are not important considerations for my project. Besides GWT supports Java generic, enum; domain objects can be shared with both GWT client and server; coding are more seamlessly... anyone can suggest other strong reasons that I should only go with GWT? FYI, I have plenty of Java experience but both GWT and Flex are new to me. Thanks.

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• How to make use of Grails Dependencies in your IDE

  - by raoulsson

  Hi All, So I finally got my dependencies working with Grails. Now, how can my IDE, eg IntelliJ or Eclipse, take advantage of it? Or do I really have to manually manage what classes my IDE knows about at "development time"? If the BuildConfig.groovy script is setup right (see here), you will be able to code away with vi or your favorite editor without any troubles, then run grails compile which will resolve and download the dependencies into the Ivy cache and off you go... If, however, you are using an IDE like Eclipse or IntelliJ, you will need the dependencies at hand while coding. Obviously - as these animals will need them for the "real time" error detection/compilation process. Now, while it is certainly possible to code with all the classes shining up in bright red all over the place that are unknown to your IDE, it is certainly not much fun... The Maven support or whatever it is officially called lives happily with the pom file, no extra "jar directory" pointers needed, at least in IntelliJ. I would like to be able to do the same with Grails dependencies. Currently I am defining them in the BuildConfig.groovy and additionally I copy/paste the current jars around on my local disk and let the IDE point to it. Not very satisfactory, as I am working in a highly volatile project module environment with respect to code change. And this situation ports me directly into "jar hell", as my "develop- and build-dependencies" easily get out of sync and I have to manage manually, that is, with my brain... And my brain should be busy with other stuff... Thanks! Raoul P.S: I'm currently using Grails 1.2M4 and IntelliJ 92.105. But feel free to add answers on future versions of Grails and different, future IDEs, as the come in...

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• python crc32 woes

  - by lazyr

  I'm writing a python program to extract data from the middle of a 6 GB bz2 file. A bzip2 file is made up of independently decryptable blocks of data, so I only need to find a block (they are delimited by magic bits), then create a temporary one-block bzip2 file from it in memory, and finally pass that to the bz2.decompress function. Easy, no? The bzip2 format has a crc32 checksum for the file at the end. No problem, binascii.crc32 to the rescue. But wait. The data to be checksummed does not necessarily end on a byte boundary, and the crc32 function operates on a whole number of bytes. My plan: use the binascii.crc32 function on all but the last byte, and then a function of my own to update the computed crc with the last 1-7 bits. But hours of coding and testing has left me bewildered, and my puzzlement can be boiled down to this question: how come crc32("\x00") is not 0x00000000? Shouldn't it be, according to the wikipedia article? You start with 0b00000000 and pad with 32 0's, then do polynomial division with 0x04C11DB7 until there are no ones left in the first 8 bits, which is immediately. Your last 32 bits is the checksum, and how can that not be all zeroes? I've searched google for answers and looked at the code of several crc32 implementations without finding any clue to why this is so.

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• java : how to handle the design when template methods throw exception when overrided method not throw

  - by jiafu

  when coding. try to solve the puzzle: how to design the class/methods when InputStreamDigestComputor throw IOException? It seems we can't use this degisn structure due to the template method throw exception but overrided method not throw it. but if change the overrided method to throw it, will cause other subclass both throw it. So can any good suggestion for this case? abstract class DigestComputor{ String compute(DigestAlgorithm algorithm){ MessageDigest instance; try { instance = MessageDigest.getInstance(algorithm.toString()); updateMessageDigest(instance); return hex(instance.digest()); } catch (NoSuchAlgorithmException e) { LOG.error(e.getMessage(), e); throw new UnsupportedOperationException(e.getMessage(), e); } } abstract void updateMessageDigest(MessageDigest instance); } class ByteBufferDigestComputor extends DigestComputor{ private final ByteBuffer byteBuffer; public ByteBufferDigestComputor(ByteBuffer byteBuffer) { super(); this.byteBuffer = byteBuffer; } @Override void updateMessageDigest(MessageDigest instance) { instance.update(byteBuffer); } } class InputStreamDigestComputor extends DigestComputor{ // this place has error. due to exception. if I change the overrided method to throw it. evey caller will handle the exception. but @Override void updateMessageDigest(MessageDigest instance) { throw new IOException(); } }

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• Design question for windows application, best approach?

  - by Jamie Keeling

  Hello, I am in the process of designing an application that will allow you to find pictures (screen shots) made from certain programs. I will provide the locations of a few of the program in the application itself to get the user started. I was wondering how I should go about adding new locations as the time goes on, my first thought was simply hard coding it into the application but this will mean the user has to reinstall it to make the changes take affect. My second idea was to use an XML file to contain all the locations as well as other data, such as the name of the application. This also means the user can add their own locations if they wish as well as sharing them over the internet. The second option seemed the best approach but then I had to think how would it be managed on the users computer. Ideally I'd like just a single .exe without the reliance on any external files such as the XML but this would bring me back to point one. Would it be best to simply use the ClickOnce deployment to create an entry in the start menu and create a folder containing the .exe and the file names? Thanks for the feedback, I don't want to start implementing the application until the design is nailed.

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• Building static (but complicated) lookup table using templates.

  - by MarkD

  I am currently in the process of optimizing a numerical analysis code. Within the code, there is a 200x150 element lookup table (currently a static std::vector < std::vector < double ) that is constructed at the beginning of every run. The construction of the lookup table is actually quite complex- the values in the lookup table are constructed using an iterative secant method on a complicated set of equations. Currently, for a simulation, the construction of the lookup table is 20% of the run time (run times are on the order of 25 second, lookup table construction takes 5 seconds). While 5-seconds might not seem to be a lot, when running our MC simulations, where we are running 50k+ simulations, it suddenly becomes a big chunk of time. Along with some other ideas, one thing that has been floated- can we construct this lookup table using templates at compile time? The table itself never changes. Hard-coding a large array isn't a maintainable solution (the equations that go into generating the table are constantly being tweaked), but it seems that if the table can be generated at compile time, it would give us the best of both worlds (easily maintainable, no overhead during runtime). So, I propose the following (much simplified) scenario. Lets say you wanted to generate a static array (use whatever container suits you best- 2D c array, vector of vectors, etc..) at compile time. You have a function defined- double f(int row, int col); where the return value is the entry in the table, row is the lookup table row, and col is the lookup table column. Is it possible to generate this static array at compile time using templates, and how?

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• Clever Next and Previous Buttons in jQuery

  - by matt

  I have created a webpage which when you press 'down' automatically scrolls down to the next ID (a section which isn't visible due to overflow: hidden) When you press 'up' it scrolls back up. At the moment each arrow simply tells the webpage to go to a specific div e.g. the 'down arrow' says <a class="tab" href="#page2">Down</a> This is ok for just two pages however as I will be having more pages what I would like is to be able to specify the amount of pages and for the arrows to automatically change which link it needs to go to next. For example, on page 1 the 'up arrow' is not visible and when you press the 'down arrow' it scrolls to #page2 whereupon the 'up arrow' is then visible. If you now press the down arrow again it will take you to #page3 whereupon it then becomes hidden as page 3 is the last page. I'm guessing I need to create a 'var' which specifies the amount of pages and that to make the arrows invisible it will change the css property 'display' to none yet I don't know how to do this nor to make the links work out which number to go to next! edit: Just botched together some code which hides the arrows based on the page number however still need to work out how to update the variables and change the links the arrows go to. (please exclude the coding, it's my first time trying to write script as opposed to just editing plugins!) var PageNumber = 1; var PageAmount = 2; function getPageNumber() { } function hideUpArrow() { if(PageNumber==1) { $("#up_arrow").css({ "display": "none" }); } } function hideDownArrow() { if(PageNumber==PageAmount) { $("#down_arrow").css({ "display": "none" }); } } $(document).ready(function(){ hideUpArrow(); });

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