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• How do you keep application logic separate from UI when UI components have built-in functionality?

  - by Al C

  I know it's important to keep user interface code separated from domain code--the application is easier to understand, maintain, change, and (sometimes) isolate bugs. But here's my mental block ... Delphi comes with components with methods that do what I want, e.g., a RichText Memo component lets me work with rich text. Other components, like TMS's string grid not only do what I want, but I paid extra for the functionality. These features put the R in RAD. It seems illogical to write my own classes to do things somebody else has already done for me. It's reinventing the wheel [ever tried working directly with rich text? :-) ] But if I use the functionality built into components like these, then I will end up with lots of intermingled UI and domain code--I'll have a form with most of my code built into its event handlers. How do you deal with this issue? ... Or, if I want to continue using the code others have already written for me, how would you suggest I deal with the issue?

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• How to display panels with component in frame

  - by terence6

  Why my JFrame 'frame' is diplaying empty window, when it should give me 3 menu buttons and my own painted JComponent below ? What am I missing here ? import java.awt.*; import javax.swing.*; public class Eyes extends JFrame { public static void main(String[] args) { final JFrame frame = new JFrame("Eyes"); frame.setPreferredSize(new Dimension(450, 300)); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel players = new JPanel(new GridLayout(1, 3)); players.add(new JButton("Eyes color")); players.add(new JButton("Eye pupil")); players.add(new JButton("Background color")); JPanel eyes = new JPanel(); eyes.add(new MyComponent()); JPanel content = new JPanel(); content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS)); content.add(players); content.add(eyes); frame.getContentPane(); frame.pack(); frame.setVisible(true); } } class MyComponent extends JComponent { public MyComponent(){ } @Override public void paint(Graphics g) { int height = 120; int width = 120; Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON); BasicStroke bs = new BasicStroke(3.0f); g2d.setStroke(bs); g2d.setColor(Color.yellow); g2d.fillOval(200, 200, height, width); g2d.setColor(Color.black); g2d.drawOval(60, 60, height, width); } }

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• Referencing not-yet-defined variables - Java

  - by user2537337

  Because I'm tired of solving math problems, I decided to try something more engaging with my very rusty (and even without the rust, very basic) Java skills. I landed on a super-simple people simulator, and thus far have been having a grand time working through the various steps of getting it to function. Currently, it generates an array of people-class objects and runs a for loop to cycle through a set of actions that alter the relationships between them, which I have stored in a 2d integer array. When it ends, I go look at how much they all hate each other. Fun stuff. Trouble has arisen, however, because I would like the program to clearly print what action is happening when it happens. I thought the best way to do this would be to add a string, description, to my "action" class (which stores variables for the actor, reactor, and the amount the relationship changes). This works to a degree, in that I can print a generic message ("A fight has occurred!") with no problem. However, ideally I would like it to be a little more specific ("Person A has thrown a rock at Person B's head!"). This latter goal is proving more difficult: attempting to construct an action with a description string that references actor and reactor gets me a big old error, "Cannot reference field before it is defined." Which makes perfect sense. I believe I'm not quite in programmer mode, because the only other way I can think to do this is an unwieldy switch statement that negates the need for each action to have its own nicely-packaged description. And there must be a neater way. I am not looking for examples of code, only a push in the direction of the right concept to handle this.

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• How do I create a simple Windows form to access a SQL Server database?

  - by NoCatharsis

  I believe this is a very novice question, and if I'm using the wrong forum to ask, please advise. I have a basic understanding of databasing with MS SQL Server, and programming with C++ and C#. I'm trying to teach myself more by setting up my own database with MS SQL Server Express 2008 R2 and accessing it via Windows forms created in C# Express 2010. At this point, I just want to keep it to free or Express dev tools (not necessarily Microsoft though). Anyway, I created a database using the instructions provided here and I set the data types appropriately for each column (no errors in setup at least). Now I'm designing the GUI in C# Express but I've kind of hit a wall as far as the database connection. Is there a simple way to access the database I created locally using C# Express? Can anyone suggest a guide that has all this spelled out already? I am a self-learner so I look forward to teaching myself how to use these applications, but any pointers to start me off in the right direction would be greatly appreciated.

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• With Maven2, how would I zip a directory in my resources?

  - by Benny

  I'm trying to upgrade my project from using Maven 1 to Maven 2, but I'm having a problem with one of the goals. I have the following Maven 1 goal in my maven.xml file: <goal name="jar:init"> <ant:delete file="${basedir}/src/installpack.zip"/> <ant:zip destfile="${basedir}/src/installpack.zip" basedir="${basedir}/src/installpack" /> <copy todir="${destination.location}"> <fileset dir="${source.location}"> <exclude name="installpack/**"/> </fileset> </copy> </goal> I'm unable to find a way to do this in Maven2, however. Right now, the installpack directory is in the resources directory of my standard Maven2 directory structure, which works well since it just gets copied over. I need it to be zipped though. I found this page on creating ant plugins: http://maven.apache.org/guides/plugin/guide-ant-plugin-development.html. It looks like I could create my own ant plugin to do what I need. I was just wondering if there was a way to do it using only Maven2. Any suggestions would be much appreciated. Thanks, B.J.

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• Atomic operations on several transactionless external systems

  - by simendsjo

  Say you have an application connecting 3 different external systems. You need to update something in all 3. In case of a failure, you need to roll back the operations. This is not a hard thing to implement, but say operation 3 fails, and when rolling back, the rollback for operation 1 fails! Now the first external system is in an invalid state... I'm thinking a possible solution is to shut down the application and forcing a manual fix of the external system, but then again... It might already have used this information (and perhaps that's why it failed), or we might not have sufficient access. Or it might not even be a good way to rollback the action! Are there some good ways of handling such cases? EDIT: Some application details.. It's a multi user web application. Most of the work is done with scheduled jobs (through Quartz.Net), so most operations is run in it's own thread. Some user actions should trigger jobs that update several systems though. The external systems are somewhat unstable. I Was thinking of changing the application to use the Command and Unit Of Work pattern

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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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• MySql "comments" parameter as descriptor?

  - by Nick

  So, I'm trying to learn a lot at once, and this place is really helpful! I'm making a little running log website for myself and maybe a few other people, and I have it so that the user can add workouts for each day. With each workout, I have a variety of information the user can fill out for the workout, such as running distance, time, quality of run, course, etc... I store this in a MySql database as a table with fields titled "distance", "time", "runquality", etc... Now, these field titles don't match up with what I want displayed on the running log, so I was thinking of using the "Comments" attribute for a field to store its human-readable title--thus the field "runquality" would have "Quality of run" as its comment, and then I would pull the comment with a SQL query and display it instead of the field name. Is this a good theoretical/practical way of going about it? And what sort of SQL would I use to pull the comment for the field anyway? Secondly, suppose I want to add the ability for the user to create their own workout descriptors. So say a user wants to add a "temperature" descriptor for their workout. Should I create a script that adds fields to my workout table, or should I create a separate table listing only workout descriptors and somehow link the descriptor table with the "contents" table? I haven't learned any theory about database design or anything so any help is appreciated!

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• How to use custom UITableViewCell from Interface Builder?

  - by Krumelur

  I want to be able to design my own UITableViewCell in IB. But I keep getting a null ref exception when trying to access the label I defined in IB. Here's what I'm doing: In Interface Builder: I removed the "View" and added a UITableViewCell instead. Changed the class of the UITableViewCell to "TestCellView". Added a UILabel to the cell. Added an outlet "oLblText" to TestCellView and connected the UILabel to it. Changed the identifier of the class to "TestCellView". Implement TestCellView.xib.cs public partial class TestCellView : UITableViewCell { public TestCellView(string sKey) : base(UITableViewCellStyle.Default, sKey) { } public TestCellView(IntPtr oHandle) : base(oHandle) { } public string TestText { get { return this.oLblText.Text; } set { // HERE I get the null ref exception! this.oLblText.Text = value; } } } ** The TestCellView.designer.cs** [MonoTouch.Foundation.Register("TestCellView")] public partial class TestCellView { private MonoTouch.UIKit.UILabel __mt_oLblText; #pragma warning disable 0169 [MonoTouch.Foundation.Connect("oLblText")] private MonoTouch.UIKit.UILabel oLblText { get { this.__mt_oLblText = ((MonoTouch.UIKit.UILabel)(this.GetNativeField("oLblText"))); return this.__mt_oLblText; } set { this.__mt_oLblText = value; this.SetNativeField("oLblText", value); } } } In my table's source: public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath) { TestCellView oCell = (TestCellView)tableView.DequeueReusableCell("myCell"); if(oCell == null) { // I suppose this is wrong but how to do it correctly? // this == my UITableViewSource. NSBundle.MainBundle.LoadNib("TestCellView", this, null); oCell = new TestCellView("myCell"); } oCell.TestText = "Cell " + indexPath.Row; return oCell; } Please note that I do NOT want a solution that involves a UIViewController for every cell. I have seen a couple of examples on the web doing this. I just think it is total overkill. What am I doing wrong?

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• What is the best free cross-platform OpenGL GUI library for a video game?

  - by Jim Buck

  It must come with source. I've looked at these which look semi-promising: glgooey, guichan, and cegui. I've come across others that look more Windows-y than game-y, but that's not the direction I am looking to go in. I would like some simple functionality of typical controls (lists, dropdown box, etc.) but with support for graphical widgets that you would normally find in game frontends. Mouse clicking, dragging, dropping, etc. and sound effect hooks would be nice. (These libs often leave hooks for the external system to tell it when/where mouse events are occurring.) It would get rendered on top of what my own 3D engine is rendering for the game, so it must be able to play nicely with rendering code outside of the lib. The best criteria is whether or not a reasonable 2D game could be implemented just with the GUI library and minimal glue code. (By glue code, I mean init code, hooking up the mouse, and game logic.) I am creating a 3D game, but this criteria gives a pretty solid idea of what level of interactivity I would like in the GUI.

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• Artisan unable to access environment variables from $_ENV

  - by hansn

  Any artisan command I enter into the command line throws this error: $ php artisan <? return array( 'DB_HOSTNAME' => 'localhost', 'DB_USERNAME' => 'root', 'DB_NAME' => 'pc_booking', 'DB_PASSWORD' => 'secret', ); PHP Warning: Invalid argument supplied for foreach() in /home/martin/code/www/pc_backend/vendor/laravel/framework/src/Illuminate/Config/EnvironmentVariables.php on line 35 {"error":{"type":"ErrorException","message":"Undefined index: DB_HOSTNAME","file":"\/home\/martin\/code\/www\/pc_backend\/app\/config\/database.php","line":57}} This is only on my local development system, where I recently installed apache and php. On my production system on a shared host artisan commands work just fine. The prod system has it's own .env.php, but other than that the code should be identical. Relevant files: .env.local.php <? return array( 'DB_HOSTNAME' => 'localhost', 'DB_USERNAME' => 'root', 'DB_NAME' => 'pc_booking', 'DB_PASSWORD' => 'secret', ); app/config/database.php <?php return array( 'fetch' => PDO::FETCH_CLASS, 'default' => 'mysql', 'connections' => array( 'mysql' => array( 'driver' => 'mysql', 'host' => $_ENV['DB_HOSTNAME'], 'database' => $_ENV['DB_NAME'], 'username' => $_ENV['DB_USERNAME'], 'password' => $_ENV['DB_PASSWORD'], 'charset' => 'utf8', 'collation' => 'utf8_unicode_ci', 'prefix' => '', ), ), 'migrations' => 'migrations', ), ); The $_ENV array is populated as expected on the website - the problem appears to be with artisan only.

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• help on developing enterprise level software solutions

  - by wefwgeweg

  there is a specific niche which I would like to target by providing a complete enterprise level software solution.... the problem is, where do i begin ? meaning, i come from writing just desktop software on VB/ASP .net/PHP/mysql and suddenly unfamiliar terms popup like Oracle, SAP Business Information Warehouse, J2EE.... obviously, something is pointing towards Java, is it common for software suites, or solutions to be developed 100% on Java technology and standards? Are there any other platform to build enterprise level software on ? i am still lacking understanding what exactly is "Enterprise level" ? what is sufficient condition to call a software that sells for $199 and then suddenly it's $19,999 for "enterprise" package. I dont understand why there is such a huge discrepancy between "standard" and "enterprise" versions of software. Is it just attempting to bag large corporations on a spending spree ? so why does one choose to develop so called "enterprise" softwares ? is it because of the large inflated price tag you can justify with ? i would also like some more enterpreneural resources on starting your own enterprise software company in a niche.... Thank you for reading, i am still trying to find the right questions.

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• MSMQ - Message Queue Abstraction and Pattern

  - by Maxim Gershkovich

  Hi All, Let me define the problem first and why a messagequeue has been chosen. I have a datalayer that will be transactional and EXTREMELY insert heavy and rather then attempt to deal with these issues when they occur I am hoping to implement my application from the ground up with this in mind. I have decided to tackle this problem by using the Microsoft Message Queue and perform inserts as time permits asynchronously. However I quickly ran into a problem. Certain inserts that I perform may need to be recalled (ie: retrieved) immediately (imagine this is for POS system and what happens if you need to recall the last transaction - one that still hasn’t been inserted). The way I decided to tackle this problem is by abstracting the MessageQueue and combining it in my data access layer thereby creating the illusion of a single set of data being returned to the user of the datalayer (I have considered the other issues that occur in such a scenario (ie: essentially dirty reads and such) and have concluded for my purposes I can control these issues). However this is where things get a little nasty... I’ve worked out how to get the messages back and such (trivial enough problem) but where I am stuck is; how do I create a generic (or at least somewhat generic) way of querying my message queue? One where I can minimize the duplication between the SQL queries and MessageQueue queries. I have considered using LINQ (but have very limited understanding of the technology) and have also attempted an implementation with Predicates which so far is pretty smelly. Are there any patterns for such a problem that I can utilize? Am I going about this the wrong way? Does anyone have an of their own ideas about how I can tackle this problem? Does anyone even understand what I am talking about? :-) Any and ALL input would be highly appreciated and seriously considered… Thanks again.

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• C# app running as either Windows Form or as Console Application

  - by Aeolien

  I am looking to have one of my Windows Forms applications be run programmatically—from the command line. In preparation, I have separated the logic in its own class from the Form. Now I am stuck trying to get the application to switch back and forth based on the presence of command line arguments. Here is the code for the main class: static class Program { /// <summary> /// The main entry point for the application. /// </summary> [STAThread] static void Main() { string[] args = Environment.GetCommandLineArgs(); if (args.Length > 1) // gets passed its path, by default { CommandLineWork(args); return; } Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } private static void CommandLineWork(string[] args) { Console.WriteLine("It works!"); Console.ReadLine(); } where Form1 is my form and the It works! string is just a placeholder for the actual logic. Right now, when running this from within Visual Studio (with command line arguments), the phrase It works! is printed to the Output. However, when running the /bin/Debug/Program.exe file (or /Release for that matter) the application crashes. Am I going about this the right way? Would it make more sense (i.e. take less developer time) to have my logic class be a DLL that gets loaded by two separate applications? Or is there something entirely different that I'm not aware of? Thanks in advance!

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• Web development tool that can comprehend the concept of more than one language in a file at once

  - by thecoshman

  I currently use notepad++ on windows or gedit on ubuntu. Both of them work great with code highlighting and hinting etc. But both of them suffer from a huge flaw. I am yet to find a code editor that can handle this concept: <?php // ooh, look I am doing some php ?><a onclick="alert('hay, some javascript in here now!')"> This link is HTML?!</a> <?PHP echo("NOW we have some php as well!"); ?> At the moment, I just have to settle for the one language. I want something that can think of a that text as a default as HTML, but notice when sections are PHP. I want those sections of PHP to have there own code hinting and highlighting. Even more, lets say in an 'if else' I exit PHP, write some HTML then back into PHP, I want it to work out how the braces ( '{' and '}' ) should match up and let me know if I have missed one. I want the sections of in-line JavaScript to be picked up as such. I want all of these languages to get checked for syntax! Damn it, I want to tool that understands more than one language at once!

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• Using an element against an entire list in Haskell

  - by Snick

  I have an assignment and am currently caught in one section of what I'm trying to do. Without going in to specific detail here is the basic layout: I'm given a data element, f, that holds four different types inside (each with their own purpose): data F = F Float Int, Int a function: func :: F -> F-> Q Which takes two data elements and (by simple calculations) returns a type that is now an updated version of one of the types in the first f. I now have an entire list of these elements and need to run the given function using one data element and return the type's value (not the data element). My first analysis was to use a foldl function: myfunc :: F -> [F] -> Q myfunc y [] = func y y -- func deals with the same data element calls myfunc y (x:xs) = foldl func y (x:xs) however I keep getting the same error: "Couldn't match expected type 'F' against inferred type 'Q'. In the first argument of 'foldl', namely 'myfunc' In the expression: foldl func y (x:xs) I apologise for such an abstract analysis on my problem but could anyone give me an idea as to what I should do? Should I even use a fold function or is there recursion I'm not thinking about?

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• Handling close-to-impossible collisions on should-be-unique values

  - by balpha

  There are many systems that depend on the uniqueness of some particular value. Anything that uses GUIDs comes to mind (eg. the Windows registry or other databases), but also things that create a hash from an object to identify it and thus need this hash to be unique. A hash table usually doesn't mind if two objects have the same hash because the hashing is just used to break down the objects into categories, so that on lookup, not all objects in the table, but only those objects in the same category (bucket) have to be compared for identity to the searched object. Other implementations however (seem to) depend on the uniqueness. My example (that's what lead me to asking this) is Mercurial's revision IDs. An entry on the Mercurial mailing list correctly states The odds of the changeset hash colliding by accident in your first billion commits is basically zero. But we will notice if it happens. And you'll get to be famous as the guy who broke SHA1 by accident. But even the tiniest probability doesn't mean impossible. Now, I don't want an explanation of why it's totally okay to rely on the uniqueness (this has been discussed here for example). This is very clear to me. Rather, I'd like to know (maybe by means of examples from your own work): Are there any best practices as to covering these improbable cases anyway? Should they be ignored, because it's more likely that particularly strong solar winds lead to faulty hard disk reads? Should they at least be tested for, if only to fail with a "I give up, you have done the impossible" message to the user? Or should even these cases get handled gracefully? For me, especially the following are interesting, although they are somewhat touchy-feely: If you don't handle these cases, what do you do against gut feelings that don't listen to probabilities? If you do handle them, how do you justify this work (to yourself and others), considering there are more probable cases you don't handle, like a supernonva?

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• What database strategy to choose for a large web application

  - by Snoopy

  I have to rewrite a large database application, running on 32 servers. The hardware is up to date, each machine has two quad core Xeon and 32 GByte RAM. The database is multi-tenant, each customer has his own file, around 5 to 10 GByte each. I run around 50 databases on this hardware. The app is open to the web, so I have no control on the load. There are no really complex queries, so SQL is not required if there is a better solution. The databases get updated via FTP every day at midnight. The database is read-only. C# is my favourite language and I want to use ASP.NET MVC. I thought about the following options: Use two big SQL servers running SQL Server 2012 to serve the 32 servers with data. On the 32 servers running IIS hosting providing REST services. Denormalize the database and use Redis on each webserver. Use booksleeve as a Redis client. Use a combination of SQL Server and Redis Use SQL Server 2012 together with Hadoop Use Hadoop without SQL Server What is the best way for a read-only database, to get the best performance without loosing maintainability? Does Map-Reduce make sense at all in such a scenario? The reason for the rewrite is, the old app written in C++ with ISAM technology is too slow, the interfaces are old fashioned and not nice to use from an website, especially when using ajax. The app uses a relational datamodel with many tables, but it is possible to write one accerlerator table where all queries can be performed on, and all other information from the other tables are possible by a simple key lookup.

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• entity framework insert bug

  - by tmfkmoney

  I found a previous question which seemed related but there's no resolution and it's 5 months old so I've opened my own version. http://stackoverflow.com/questions/1545583/entity-framework-inserting-new-entity-via-objectcontext-does-not-use-existing-e When I insert records into my database with the following it works fine for a while and then eventually it starts inserting null values in the referenced field. This typically happens after I do an update on my model from the database although not always after I do an update. I'm using a MySQL database for this. I have debugged the code and the values are being set properly before the save event. They're just not getting inserted properly. I can always fix this issue by re-creating the model without touching any of my code. I have to recreate the entire model, though. I can't just dump the relevant tables and re-add them. This makes me think it doesn't have anything to do with my code but something with the entity framework. Does anyone else have this problem and/or solved it? using (var db = new MyModel()) { var stocks = from record in query let ticker = record.Ticker select new { company = db.Companies.FirstOrDefault(c => c.ticker == ticker), price = Convert.ToDecimal(record.Price), date_stamp = Convert.ToDateTime(record.DateTime) }; foreach (var stock in stocks) { if (stock.company != null) { var price = new StockPrice { Company = stock.company, price = stock.price, date_stamp = stock.date_stamp }; db.AddToStockPrices(price); } } db.SaveChanges(); }

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• Creating collaborative whiteboard drawing application

  - by Steven Sproat

  I have my own drawing program in place, with a variety of "drawing tools" such as Pen, Eraser, Rectangle, Circle, Select, Text etc. It's made with Python and wxPython. Each tool mentioned above is a class, which all have polymorphic methods, such as left_down(), mouse_motion(), hit_test() etc. The program manages a list of all drawn shapes -- when a user has drawn a shape, it's added to the list. This is used to manage undo/redo operations too. So, I have a decent codebase that I can hook collaborative drawing into. Each shape could be changed to know its owner -- the user who drew it, and to only allow delete/move/rescale operations to be performed on shapes owned by one person. I'm just wondering the best way to develop this. One person in the "session" will have to act as the server, I have no money to offer free central servers. Somehow users will need a way to connect to servers, meaning some kind of "discover servers" browser...or something. How do I broadcast changes made to the application? Drawing in realtime and broadcasting a message on each mouse motion event would be costly in terms of performance and things get worse the more users there are at a given time. Any ideas are welcome, I'm not too sure where to begin with developing this (or even how to test it)

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• Exercise for exam about comparing string on file

  - by Telmo Vaz

  I'm trying to do this exercise for my exam tomorrow. I need to compare a string of my own input and see if that string is appearing on the file. This needs to be done directly on the file, so I cannot extract the string to my program and compare them "indirectly". I found this way but I'm not getting it right, and I don't know why. The algorithm sounds good to me. Any help, please? I really need to focus on this one. Thanks in advance, guys. #include<stdio.h> void comp(); int main(void) { comp(); return 0; } void comp() { FILE *file = fopen("e1.txt", "r+"); if(!file) { printf("Not possible to open the file"); return; } char src[50], ch; short i, len; fprintf(stdout, "What are you looking for? \nwrite: "); fgets(src, 200, stdin); len = strlen(src); while((ch = fgetc(file)) != EOF) { i = 0; while(ch == src[i]) { if(i <= len) { printf("%c - %c", ch, src[i]); fseek(file, 0, SEEK_CUR + 1); i++; } else break; } } }

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• Efficiency of manually written loops vs operator overloads (C++)

  - by Sagekilla

  Hi all, in the program I'm working on I have 3-element arrays, which I use as mathematical vectors for all intents and purposes. Through the course of writing my code, I was tempted to just roll my own Vector class with simple +, -, *, /, etc overloads so I can simplify statements like: for (int i = 0; i < 3; i++) r[i] = r1[i] - r2[i]; // becomes: r = r1 - r2; Which should be more or less identical in generated code. But when it comes to more complicated things, could this really impact my performance heavily? One example that I have in my code is this: Manually written version: for (int j = 0; j < 3; j++) { p.vel[j] = p.oldVel[j] + (p.oldAcc[j] + p.acc[j]) * dt2 + (p.oldJerk[j] - p.jerk[j]) * dt12; p.pos[j] = p.oldPos[j] + (p.oldVel[j] + p.vel[j]) * dt2 + (p.oldAcc[j] - p.acc[j]) * dt12; } Using a Vector class with operator overloads: p.vel = p.oldVel + (p.oldAcc + p.acc) * dt2 + (p.oldJerk - p.jerk) * dt12; p.pos = p.oldPos + (p.oldVel + p.vel) * dt2 + (p.oldAcc - p.acc) * dt12; I am compiling my code for maximum possible speed, as it's extremely important that this code runs quickly and calculates accurately. So will me relying on my Vector's for these sorts of things really affect me? For those curious, this is part of some numerical integration code which is not trivial to run in my program. Any insight would be appreciated, as would any idioms or tricks I'm unaware of.

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• What's a good way to provide additional decoration/metadata for Python function parameters?

  - by Will Dean

  We're considering using Python (IronPython, but I don't think that's relevant) to provide a sort of 'macro' support for another application, which controls a piece of equipment. We'd like to write fairly simple functions in Python, which take a few arguments - these would be things like times and temperatures and positions. Different functions would take different arguments, and the main application would contain user interface (something like a property grid) which allows the users to provide values for the Python function arguments. So, for example function1 might take a time and a temperature, and function2 might take a position and a couple of times. We'd like to be able to dynamically build the user interface from the Python code. Things which are easy to do are to find a list of functions in a module, and (using inspect.getargspec) to get a list of arguments to each function. However, just a list of argument names is not really enough - ideally we'd like to be able to include some more information about each argument - for instance, it's 'type' (high-level type - time, temperature, etc, not language-level type), and perhaps a 'friendly name' or description. So, the question is, what are good 'pythonic' ways of adding this sort of information to a function. The two possibilities I have thought of are: Use a strict naming convention for arguments, and then infer stuff about them from their names (fetched using getargspec) Invent our own docstring meta-language (could be little more than CSV) and use the docstring for our metadata. Because Python seems pretty popular for building scripting into large apps, I imagine this is a solved problem with some common conventions, but I haven't been able to find them.

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• Using group_by with fields_for and accepts_nested_attributes_for

  - by Derek

  I have a the following rails models: class Release < ActiveRecord::Base has_many :release_questionnaires, :dependent => :destroy accepts_nested_attributes_for :release_questionnaires ... end class class ReleaseQuestionnaire < ActiveRecord::Base belongs_to :release belongs_to :milestone ... end class In my view code, I have the following form. <% form_for @release, ... do |f| %> ... <table class="questionnaires"> <% f.fields_for :release_questionnaires, @release.release_questionnaires.sort_by{|ra| ra.questionnaire.name} do |builder| %> ... <% end %> </table> <% end %> This works and allows me to view and edit the questionnaires as desired. However, I have an additional requirement to break the questionnaires out into their own tables grouped by the milestone they are associated to, rather than in a single table. It appears as though the group_by method is design to accomplish this, but I cannot get it to work as desired inside the tag. It may be that I'm missing something obvious, as I am a beginner... Any help is appreciated.

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• How to get address the object of an related entity with CoreData ?

  - by eemceebee

  Hi Ok, after I ran into a dead end modifieing an existing Apple example for CoreData, I started completely new creating my own project and that worked fine,..... until I tried to access a related entity. So here is what I did. I created 2 entities, where one is just the detail information of the other one, so there is a one-2-one relationship. Entity #1, Stocks: name value details -- relationship to Entity #2 Entity #2, StockDetails: bank published stock -- relationship to Entity #1 Now, I created the "Managed Object Class" for both of the Entities. Then I created a few lines to put some data into it NSManagedObjectContext *context = [self managedObjectContext]; Stocks *stockinfo= [NSEntityDescription insertNewObjectForEntityForName:@"Stocks" inManagedObjectContext:context]; stockinfo.name = @"Apple"; stockinfo.value = [NSNumber numberWithInt:200]; StockDetails *thestockdetails = [NSEntityDescription insertNewObjectForEntityForName:@"StockDetails" inManagedObjectContext:context]; thestockdetails.bank = @"Bank of America"; thestockdetails.published = [NSDate date]; thestockdetails.stock = stocks_; stockinfo.details = thestockdetails ; NSError *error; if (![context save:&error]) { NSLog(@"A Problem occured, couldn't save: %@", [error localizedDescription]); } Just want to mention here, that I do not get an error with this. Next I put everything into a UITableViewController for a preview and another for a detail view. The preview just shows infos form Entity #1 (Stocks) and when selected it shows the detail view. Now here I also display the infos form Entity #1 (Stocks) but I want to show the Entity #2 (StockDetails) aswell. This is how I try to access the data : StockDetails *details_ = [stockinfo details]; And this gives me a EXC_BAD_ACCESS. So any idea what I am doing wrong here ? Thanks

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