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• What's a good way of building up a String where you specific start and end locations?

  - by Michael Campbell

  (java 1.5) I have a need to build up a String, in pieces. I'm given a set of (sub)strings, each with a start and end point of where they belong in the final string. Was wondering if there were some canonical way of doing this. This isn't homework, and I can use any licensable OSS, such as jakarta commons-lang StringUtils etc. My company has a solution using a CharBuffer, and I'm content to leave it as is (and add some unit tests, of which there are none (?!)) but the code is fairly hideous and I would like something easier to read. As I said this isn't homework, and I don't need a complete solution, just some pointers to libraries or java classes that might give me some insight. The String.Format didn't seem QUITE right... I would have to honor inputs too long and too short, etc. Substrings would be overlaid in the order they appear (in case of overlap). As an example of input, I might have something like: String:start:end FO:0:3 (string shorter than field) BAR:4:5 (String larger than field) BLEH:5:9 (String overlays previous field) I'd want to end up with FO BBLEH 01234567890

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• What's a good way of building up a String given specific start and end locations?

  - by Michael Campbell

  (java 1.5) I have a need to build up a String, in pieces. I'm given a set of (sub)strings, each with a start and end point of where they belong in the final string. Was wondering if there were some canonical way of doing this. This isn't homework, and I can use any licensable OSS, such as jakarta commons-lang StringUtils etc. My company has a solution using a CharBuffer, and I'm content to leave it as is (and add some unit tests, of which there are none (?!)) but the code is fairly hideous and I would like something easier to read. As I said this isn't homework, and I don't need a complete solution, just some pointers to libraries or java classes that might give me some insight. The String.Format didn't seem QUITE right... I would have to honor inputs too long and too short, etc. Substrings would be overlaid in the order they appear (in case of overlap). As an example of input, I might have something like: String:start:end FO:0:3 (string shorter than field) BAR:4:5 (String larger than field) BLEH:5:9 (String overlays previous field) I'd want to end up with FO BBLEH 01234567890

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• PHP jQuery Long Polling Chat Application

  - by Tejas Jadhav

  I've made a simple PHP jQuery Chat Application with Short Polling (AJAX Refresh). Like, every 2 - 3 seconds it asks for new messages. But, I read that Long Polling is a better approach for Chat applications. So, I went through some Long Polling scripts. I made like this: Javascript: $("#submit").click(function(){ $.ajax({ url: 'chat-handler.php', dataType: 'json', data: {action : 'read', message : 'message'} }); }); var getNewMessage = function() { $.ajax({ url: 'chat-handler.php', dataType: 'json', data: {action : 'read', message : 'message'}, function(data){ alert(data); } }); getNewMessage(); } $(document).ready(getNewMessage); PHP <?php $time = time(); while ((time() - $time) < 25) { $data = $db->getNewMessage (); if (!empty ($data)) { echo json_encode ($data); break; } usleep(1000000); // 1 Second } ?> The problem is, once getNewMessage() starts, it executes unless it gets some response (from chat-handler.php). It executes recursively. But if someone wants to send a message in between, then actually that function ($("#submit").click()) never executes as getNewMessage() is still executing. So is there any workaround?

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• rapid application developement tools for very basic GUI apps

  - by Jurij

  I know there are many RAD platforms out there. Infact there are so many that I'm having a hard time finding out which one fits me best. What I want is a RAD tool that would allow me to define a database data model (make DB tables) and then create (view and edit) forms for the various tables. Data input, updating and various queries should be easy and GUI should generate automatically. I'd like to add some additional functionality by coding (such as various complex calculations on the data). I'm a programmer so I'm willing to learn to use a more complete, full-blown RAD solution if you can point me to it (NetBeans and RubyOnRails being the two such frameworks that I'd would probably be high on the list). I'm currently doing Windows Forms logistics apps in .NET. I've actually developed a very crude and basic version of what I need, but I just know that there are solutions out there that are much better and I'd benefit by knowing how to use them. So in short, the basic requirements: * database based data storage (SQLite if possible) * very automated GUI creation * desktop based (as in: not a web app) * extendable by coding * used for creating simple data entry, view & query apps. So basically something like Oracle Forms or DotNetMushroom Rapid Application Developer. But for .NET and SQLite if possible.

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• Testing fault tolerant code

  - by Robert

  I’m currently working on a server application were we have agreed to try and maintain a certain level of service. The level of service we want to guaranty is: if a request is accepted by the server and the server sends on an acknowledgement to the client we want to guaranty that the request will happen, even if the server crashes. As requests can be long running and the acknowledgement time needs be short we implement this by persisting the request, then sending an acknowledgement to the client, then carrying out the various actions to fulfill the request. As actions are carried out they too are persisted, so the server knows the state of a request on start up, and there’s also various reconciliation mechanisms with external systems to check the accuracy of our logs. This all seems to work fairly well, but we have difficult saying this with any conviction as we find it very difficult to test our fault tolerant code. So far we’ve come up with two strategies but neither is entirely satisfactory: Have an external process watch the server code and then try and kill it off at what the external process thinks is an appropriate point in the test Add code the application that will cause it to crash a certain know critical points My problem with the first strategy is the external process cannot know the exact state of the application, so we cannot be sure we’re hitting the most problematic points in the code. My problem with the second strategy, although it gives more control over were the fault takes, is I do not like have code to inject faults within my application, even with optional compilation etc. I fear it would be too easy to over look a fault injection point and have it slip into a production environment.

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• What is the best IDE setup for web development?

  - by Yuval A

  I am starting a little side project which consists of building a small-medium sized, django-based, website. However, last time I was actually in the business of websites, was a few good years ago. So while still technologically capable, I'm still rusted on the tools/IDE part of websites. I am looking for an IDE which can support the following: Basic HTML editing with syntax completion, highlighting, etc... Basic CSS editing with syntax completion, highlighting, etc... Python support for Django Support for the entire develop-debug-FTP upload cycle If all of this could happen inside my existing eclipse installation, it would be nothing short of perfection. So what's your recommendation on web development IDEs? EDIT: forgot to add that I'm running Win XP on my dev machine. EDIT after answers: thanks all you guys for the helpful advice. I think I'm going to go with Aptana as it fits in to eclipse which I already use. Also I will look into version control instead of simple FTP upload. Apparently I didn't know how much it is used even in web projects.

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• Code Golf: Morse code

  - by LiraNuna

  The challenge The shortest code by character count, that will input a string using only alphabetical characters (upper and lower case), numbers, commas, periods and question mark, and returns a representation of the string in Morse code. The Morse code output should consist of a dash (-, ascii 0x2D) for a long beep (aka 'dah') and a dot (., ascii 0x2E) for short beep (aka 'dit'). Each letter should be separated by a space (' ', ascii 0x20), and each word should be separated by a forward slash (/, ascii 0x2F). Morse code table: Test cases: Input: Hello world Output: .... . .-.. .-.. --- / .-- --- .-. .-.. -.. Input: Hello, Stackoverflow. Output: .... . .-.. .-.. --- --..-- / ... - .- -.-. -.- --- ...- . .-. ..-. .-.. --- .-- .-.-.- Code count includes input/output (i.e full program).

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• Mathematics for Computer Science Students

  - by Ender

  To cut a long story short, I am a CS student that has received no formal Post-16 Maths education for years. Right now even my Algebra is extremely rusty and I have a couple of months to shape up my skills. I've got a couple of video lectures in my bookmarks, consisting of: Pre-Calculus Algebra Calculus Probability Introduction to Statistics Differential Equations Linear Algebra My aim as of today is to be able to read the CLRS book Introduction to Algorithms and be able to follow the Mathematical notation in that, as well as being able to confidently read and back-up any arguments written in Mathematical notation. Aside from these video lectures, can anyone recommend any good books to help teach someone wishing to go from a low-foundation level to a more advanced level of Mathematics? Just as a note, I've taken a first-year module in Analytical Modelling, so I understand some of the basic concepts of Discrete Mathematics. EDIT: Just a note to those that are looking to learn Linear Algebra using the Video Lectures I have posted up. Peteris Krumins' Blog contains a run-through of these lecture notes as well as his own commentary and lecture notes, an invaluable resource for those looking to follow the lectures too.

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• How to install OpenCV 2.0 on win32

  - by Jive Dadson

  I need to install OpenCV on Win32. I do not have it installed currently. I downloaded OpenCV-2.0.0a-win32.exe and ran it. What the heck do I do now? There are no .lib's and whatnot. I found some instructions for building the release using cmake at http://opencv.willowgarage.com/wiki/InstallGuide . I downloaded the latest and greatest cmake, and tried to follow the instructions, but I was guessing. No joy. I specified VC++9 when I did the "configure," but cmake built a VC++ 6 dsw file. No vcproj. I converted the dsw into a vc++9 vcproj anyway, just to see if it would work. Nope. It compiled lots of files, but many failed because it could not find omp.h. Sure enough, it's not there, anywhere. The build log said, 'A tool returned an error code from "Performing Custom Build Step".' I am lost. Ideally, I would like to find a full installation with all the files pre-built for Win32 vc++ 2008. Failing that, I need instructions that even I can follow. Short sentences and small words, but lots of them. Please help! UPDATE: I tried to build just CXCORE. It complained, "cannot open file 'VCOMPD.lib'" There's that OMP again.

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• Login Website, curious Cookie Problem

  - by Collin Peters

  Hello, Language: C# Development Environment: Visual Studio 2008 Sorry if the english is not perfect. I want to login to a Website and get some Data from there. My Problem is that the Cookies does not work. Everytime the Website says that I should activate Cookies but i activated the Cookies trough a Cookiecontainer. I sniffed the traffic serveral times for the login progress and I see no problem there. I tried different methods to login and I have searched if someone else have this Problem but no results... Login Page is: "www.uploaded.to", Here is my Code to Login in Short Form: private void login() { //Global CookieContainer for all the Cookies CookieContainer _cookieContainer = new CookieContainer(); //First Login to the Website HttpWebRequest _request1 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/login"); _request1.Method = "POST"; _request1.CookieContainer = _cookieContainer; string _postData = "email=XXXXX&password=XXXXX"; byte[] _byteArray = Encoding.UTF8.GetBytes(_postData); Stream _reqStream = _request1.GetRequestStream(); _reqStream.Write(_byteArray, 0, _byteArray.Length); _reqStream.Close(); HttpWebResponse _response1 = (HttpWebResponse)_request1.GetResponse(); _response1.Close(); //######################## //Follow the Link from Request1 HttpWebRequest _request2 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/login?coo=1"); _request2.Method = "GET"; _request2.CookieContainer = _cookieContainer; HttpWebResponse _response2 = (HttpWebResponse)_request2.GetResponse(); _response2.Close(); //####################### //Get the Data from the Page after Login HttpWebRequest _request3 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/home"); _request3.Method = "GET"; _request3.CookieContainer = _cookieContainer; HttpWebResponse _response3 = (HttpWebResponse)_request3.GetResponse(); _response3.Close(); } I'm stuck at this problem since many weeks and i found no solution that works, please help...

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• How to get around the event bubble using jQuery's: .live()

  - by Nick

  Hi there. Here is the code in question: $(".navItems>ul>li").live('click', function(){ var selectorID = $(this).attr('id'); $(".infoList").slideUp('fast', function(){ switchTabInfo(selectorID); }); function switchTabInfo(selectorID){ var actionID = selectorID.substring(4); actionID = "#" + actionID; $(actionID).slideDown(); } So in short i have a these .infoList classes with id names tied to back to the nav li id. That lists item's id might be nav_testsHistory for example. With all the content boxes hidden by class name this javascript makes a pleasing slide up, down effect. But the third content box flickers as will the second one after a third box push. It slides up and down a second unnecessary time. If I add an alert like this: $(".navItems>ul>li").live('click', function(){ var selectorID = $(this).attr('id'); $(".infoList").slideUp('fast', function(){ switchTabInfo(selectorID); alert('bubble'); }); The alert fires 3 times?! So my research took to reading about the event bubble. What I cannot find is how to check if it has been fired. I have not tried setting an input val and doing a tf test around the nested slider action. Cause that's crude. More info, all the code above is in a function, which is in an init() function, which is called on document ready. That's the only js file besides jquery 1.3.2. What do you guys think?

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• Is there a way to do 'correct' arithmetical rounding in .NET? / C#

  - by Markus

  I'm trying to round a number to it's first decimal place and, considering the different MidpointRounding options, that seems to work well. A problem arises though when that number has sunsequent decimal places that would arithmetically affect the rounding. An example: With 0.1, 0.11..0.19 and 0.141..0.44 it works: Math.Round(0.1, 1) == 0.1 Math.Round(0.11, 1) == 0.1 Math.Round(0.14, 1) == 0.1 Math.Round(0.15, 1) == 0.2 Math.Round(0.141, 1) == 0.1 But with 0.141..0.149 it always returns 0.1, although 0.146..0.149 should round to 0.2: Math.Round(0.145, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.ToEven) == 0.1 Math.Round(0.146M, 1, MidpointRounding.ToEven) == 0.1M Math.Round(0.146M, 1, MidpointRounding.AwayFromZero) == 0.1M I tried to come up with a function that addresses this problem, and it works well for this case, but of course it glamorously fails if you try to round i.e. 0.144449 to it's first decimal digit (which should be 0.2, but results 0.1.) (That doesn't work with Math.Round() either.) private double round(double value, int digit) { // basically the old "add 0.5, then truncate to integer" trick double fix = 0.5D/( Math.Pow(10D, digit+1) )*( value = 0 ? 1D : -1D ); double fixedValue = value + fix; // 'truncate to integer' - shift left, round, shift right return Math.Round(fixedValue * Math.Pow(10D, digit)) / Math.Pow(10D, digit); } I assume a solution would be to enumerate all digits, find the first value larger than 4 and then round up, or else round down. Problem 1: That seems idiotic, Problem 2: I have no idea how to enumerate the digits without a gazillion of multiplications and subtractios. Long story short: What is the best way to do that?

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• What should every developer know about databases?

  - by Aaronaught

  Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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• Editing a User's Likes on Facebook

  - by Ed Marty

  I've been looking at the Facebook API to find some way to edit a user's Likes (that is, add or remove items from https://graph.facebook.com/me/likes/). The API doesn't say anything about it specifically, but does say this: You can publish to the Facebook graph by issuing HTTP POST requests to the appropriate connection URLs above. Where above, one of the connection URLs is the aforementioned https://graph.facebook.com/me/likes link. However, there's no documentation for the PROFILE_ID/likes post, and whenever I try to post it returns the error "invalid post_id". I assume this is because to like something, you post a request to POST_ID/likes. It's a bit inconsistent. What I'm trying to do is get the user's profile to add a Page to their likes (by posting using the page's id as an "id" parameter in the post body). However, it seems like there's just no way to edit user's likes. At the end of the day, I just want to allow a user to click a button in my application (mobile device application, not a web app) and have them add our Facebook page into their list of pages, and I've found no way of doing that short of presenting our page to them and making them click on the "Like" button manually. Many other things are supported without showing the Facebook website, like posting to their wall or making albums, but I can't find anything to do this. Any ideas?

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• Avoiding GC thrashing with WSE 3.0 MTOM service

  - by Leon Breedt

  For historical reasons, I have some WSE 3.0 web services that I cannot upgrade to WCF on the server side yet (it is also a substantial amount of work to do so). These web services are being used for file transfers from client to server, using MTOM encoding. This can also not be changed in the short term, for reasons of compatibility. Secondly, they are being called from both Java and .NET, and therefore need to be cross-platform, hence MTOM. How it works is that an "upload" WebMethod is called by the client, sending up a chunk of data at a time, since files being transferred could potentially be gigabytes in size. However, due to not being able to control parts of the stack before the WebMethod is invoked, I cannot control the memory usage patterns of the web service. The problem I am running into is for file sizes from 50MB or so onwards, performance is absolutely killed because of GC, since it appears that WSE 3.0 buffers each chunk received from the client in a new byte[] array, and by the time we've done 50MB we're spending 20-30% of time doing GC. I've played with various chunk sizes, from 16k to 2MB, with no real great difference in results. Smaller chunks are killed by the latency involved with round-tripping, and larger chunks just postpone the slowdown until GC kicks in. Any bright ideas on cutting down on the garbage created by WSE? Can I plug into the pipeline somehow and jury-rig something that has access to the client's request stream and streams it to the WebMethod? I'm aware that it is possible to "stream" responses to the client using WSE (albeit very ugly), but this problem is with requests from the client.

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• More than 100 connection to sql server 2008 in "sleeping" status - Solved

  - by Allende

  I have a big trouble here, well at my server. I have an ASP .net web (framework 4.x) running on muy server, all the transactions/select/update/insert are made with ADO.NET. Well my problem is that after being using for a while (a couple of updates/selects/inserts) sometimes I got more than 100 connections on "sleeping" status when check for the connections on sql server with this query: SELECT spid, a.status, hostname, program_name, cmd, cpu, physical_io, blocked, b.name, loginame FROM master.dbo.sysprocesses a INNER JOIN master.dbo.sysdatabases b ON a.dbid = b.dbid where program_name like '%TMS%' ORDER BY spid I've been checking my code and closing every time I make a connection, I'm gonna test the new class, but I'm afraid the problem doesn't be fixed. It suppose that the connection pooling, keep the connections to re-use them, but until I see don't re-use them always. Any idea besides check for close all the connections open after use them? SOLVED(now I have just one and beautiful connection on "sleeping" status): Besides the anwser of David Stratton, I would like to share this link that help explain really well how the connection pool it works: http://dinesql.blogspot.com/2010/07/sql-server-sleeping-status-and.html Just to be short, you need to close every connection (sql connection objects) in order that the connection pool can re-use the connection and use the same connectinos string, to ensure this is highly recommended use one of the webConfig. Be careful with dataReaders you sould close its connection to (that was what make got out of my mind for while).

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• Technically why is processes in Erlang more efficient than OS threads?

  - by Jonas

  Spawning processes seam to be much more efficient in Erlang than starting new threads using the OS (i.e. by using Java or C). Erlang spawns thousands and millions of processes in a short period of time. I know that they are different since Erlang do per process GC and processes in Erlang are implemented the same way on all platforms which isn't the case with OS threads. But I don't fully understand technically why Erlang processes are so much more efficient and has much smaller memory footprint per process. Both the OS and Erlang VM has to do scheduling, context switches and keep track of the values in the registers and so on... Simply why isn't OS threads implemented in the same way as processes in Erlang? Does it have to support something more? and why does it need a bigger memory footprint? Technically why is processes in Erlang more efficient than OS threads? And why can't threads in the OS be implemented and managed in the same efficient way?

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• Outputing value of TrueClass / FalseClass to integer or string/

  - by Nick Gorbikoff

  Hello. I'm trying to figure out if there is an easy way to do the following short of adding to_i method to TrueClass/FalseClass. Here is a dilemma: I have a boolean field in my rails app - that is obviously stored as Tinyint in mysql. However - I need to generate xml based of the data in mysql and send it to customer - there SOAP service requires the field in question to have 0 or 1 as the value of this field. So at the time of the xml generation I need to convert my False to 0 and my True to 1 ( which is how they are stored in the DB). Since True & False lack to_i method I could write some if statement that generate either 1 or 0 depending on true/false state. However I have about 10 of these indicators and creating and if/else for each is not very DRY. So what you recommend I do? Or I could add a to_i method to the True / False class. But I'm not sure where should I scope it in my rails app? Just inside this particular model or somewhere else?

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• Ideas for a rudimentary software licensing implementation

  - by Ross

  I'm trying to decide how to implement a very basic licensing solution for some software I wrote. The software will run on my (hypothetical) clients' machines, with the idea being that the software will immediately quit (with a friendly message) if the client is running it on greater-than-n machines (n being the number of licenses they have purchased). Additionally, the clients are non-tech-savvy to the point where "basic" is good enough. Here is my current design, but given that I have little to no experience in the topic, I wanted to ask SO before I started any development on it: A remote server hosts a MySQL database with a table containing two columns: client-key and license quantity The client-side application connects to the MySQL database on startup, offering it's client-key that I've put into a properties file packaged into the distribution (I would create a new distribution for each new client) Chances are, I'll need a second table to store validation history, so that with some short logic, the software can decide if it can be run on a given machine (maybe a sliding window of n machines using the software per 24 hours) If the software cannot establish a connection to the MySQL database, or decides that it's over the n allowed machines per day, it closes The connection info for the remote server hosting the MySQL database should be hard-coded into the app? (That sounds like a bad idea, but otherwise they could point it to some other always-validates-to-success server) I think that about covers my initial design. The intent being that while it certainly isn't full-proof, I think I've made it at least somewhat difficult to create an easily-sharable cracking solution. Also, I can easily adjust the license amount for a given client/key pair. I gotta figure this has been done a million times before, so tell me about a better solution that's just as simple to implement and provides the same (low) amount of security. In the event that external libraries are used, I prefer Java, as that's what the software has been written in.

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• Effective java hashcode implementation

  - by Scobal

  I was wondering if someone could explain in detail what (int)(l ^ (l >>> 32)); does in the following hashcode implementation (generated by eclipse, but the same as Effective Java): private int i; private char c; private boolean b; private short s; private long l; private double d; private float f; @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + i; result = prime * result + s; result = prime * result + (b ? 1231 : 1237); result = prime * result + c; long t = Double.doubleToLongBits(d); result = prime * result + (int) (t ^ (t >>> 32)); result = prime * result + Float.floatToIntBits(f); result = prime * result + (int) (l ^ (l >>> 32)); return result; } Thanks!

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• What headaches should I expect from using Trac?

  - by Dolph Mathews

  No tool is perfect, and I'm about to start several long-term projects using Trac, and wanted a heads up of the kinds of problems I may or may not experience with it. In other words, Trac meets my needs in the short term, and I've already made the decision to use it, but I want to know what to expect down the road. I am not looking for: "Use product X instead of Trac because..." answers. "Trac is great because..." answers. A comparison to any other specific system. "Trac doesn't support Feature X" answers. I can read the feature list too, thank you very much. I am looking for: "Feature X does not behave as expected..." "Trac behaves oddly when..." "Trac doesn't fully support..." "Trac itself has a known bug that will likely never be fixed..." And especially "Trac can't handle..." etc So, what Trac-induced headaches do I have to look forward to? For future reference, this question was asked while Trac v0.11 was the latest stable release.

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• Is it possible to alternate between two types in an XML Schema

  - by lief79

  I'm wondering if I am missing something obvious. I have a list of numbers, possibly including ranges (think of the print page option of a print dialog). Ideally I'd like to have the final XML output look like this, with page and pageRange in an order. <pages> <page> 1</page> <pageRange><start>3</start><end>6</end></pageRange> <page> 34</page> </pages> What would I have to put into a schema to allow this? From what I saw: Sequence with multiple page and page Range allowed doesn't permit alternation. Choice only allows one or the other. I tried messing with all, but I wasn't getting it to validate properly. My short term solution is to have a sequence of ranges, and to force single numbers into the range, but it seems potentially cumbersome. So am I missing something?

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• Building a News-feed that comprises posts "created by user's connections" && "on the topics user is following"

  - by aklin81

  I am working on a project of Questions & Answers website that allows a user to follow questions on certain topics from his network. A user's news-feed wall comprises of only those questions that have been posted by his connections and tagged on the topics that he is following(his expertise topics). I am confused what database's datamodel would be most fitting for such an application. The project needs to consider the future provisions for scalability and high performance issues. I have been looking at Cassandra and MySQL solutions as of now. After my study of Cassandra I realized that Simple news-feed design that shows all the posts from network would be easy to design using Cassandra by executing fast writes to all followers of a user about the post from user. But for my kind of application where there is an additional filter of 'followed topics', (ie, the user receives posts "created by his network" && "on topics user is following"), I could not convince myself with a good schema design in Cassandra. I hope if I missed something because of my short understanding of cassandra, perhaps, can you please help me out with your suggestions of how this news-feed could be implemented in Cassandra ? Looking for a great project with Cassandra ! Edit: There are going to be maximum 5 tags allowed for tagging the question (ie, max 5 topics can be tagged on a question).

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• ASP.net dynamic controls issue when trying to reverse them

  - by Mattias Sandsäter

  I add some DropDownList dynamically to my form. It seems to work as it should when I use ...Controls.Add(dropdownlist), but in an attempt to turn them around and show them in reversed order I have tried to use ....Controls.AddAt(0, dropdownlist) However, this causes some strange behaviour. Before we dig in to the code, is there something I should know about dynamic adding, and more specific the AddAt()-method that usually causes trouble? Short description about what I do I start with a DropDownList (level1), when I choose something there, a new list should be added (level2) and so on. You can say you go your way down in a menu structure. Whenever you want you can change your choice at whatever level you want (of course not on later levels that you dont see yet). So lets say you are down to level 4 (You then have four boxes) and change your choice at level1, when the page reloads you are back to two boxes. http://forums.asp.net/p/885886/927411.aspx It seems that my problem was discussed here, but I didn´t see any solution about how I can acheive my intended behaviour.

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• How to minimize total cost of shortest path tree

  - by Michael

  I have a directed acyclic graph with positive edge-weights. It has a single source and a set of targets (vertices furthest from the source). I find the shortest paths from the source to each target. Some of these paths overlap. What I want is a shortest path tree which minimizes the total sum of weights over all edges. For example, consider two of the targets. Given all edge weights equal, if they share a single shortest path for most of their length, then that is preferable to two mostly non-overlapping shortest paths (fewer edges in the tree equals lower overall cost). Another example: two paths are non-overlapping for a small part of their length, with high cost for the non-overlapping paths, but low cost for the long shared path (low combined cost). On the other hand, two paths are non-overlapping for most of their length, with low costs for the non-overlapping paths, but high cost for the short shared path (also, low combined cost). There are many combinations. I want to find solutions with the lowest overall cost, given all the shortest paths from source to target. Does this ring any bells with anyone? Can anyone point me to relevant algorithms or analogous applications? Cheers!

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