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• Grand Central Strategy for Opening Multiple Files

  - by user276632

  I have a working implementation using Grand Central dispatch queues that (1) opens a file and computes an OpenSSL DSA hash on "queue1", (2) writing out the hash to a new "side car" file for later verification on "queue2". I would like to open multiple files at the same time, but based on some logic that doesn't "choke" the OS by having 100s of files open and exceeding the hard drive's sustainable output. Photo browsing applications such as iPhoto or Aperture seem to open multiple files and display them, so I'm assuming this can be done. I'm assuming the biggest limitation will be disk I/O, as the application can (in theory) read and write multiple files simultaneously. Any suggestions? TIA

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• Best Practice - Validating Input In Simple GUI Application?

  - by Alex

  I'm writing a GUI app with wxwidgets in C++ for one of my programming classes. We have to validate input and throw custom exceptions if it doesn't meet certain conditions. My question is, what is best practice when it comes to this? Should I write a seperate function that checks for errors, and have my event handler's call that function? Or should I do my error-checking in my event handlers? Or does it really matter? Thanks!

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• ASP.NET HTTPHandler not throwing exception when one is expected

  - by josephj1989

  I have an HttpHandler class (implements IHttphandler) where the path defined for the handler in web.config is *.jpg. I am requesting a Jpg image in my page. Within the HTTP Handler I am writing to a file in the filesystem. By mistake I was trying to write to a non existant directory. This should have thrown an exception but the execution simply proceeds.Ofcourse no file is written. But if I give a proper directory the file is written correctly.Is there anything special about HttpHandler Exceptions. See part of the code public void ProcessRequest(HttpContext context){ File.WriteAllLines(context.Request.ApplicationPath+@"\"+"resul.log",new string[]{"Entered JPG Handler"}); If I put a breakpoint on the File.WriteAllLines statement and then step over it I can see an exception occurring.

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• Convert SelectedObjectCollection to Collection of Specific Type

  - by Jonathan Wood

  I have a WinForms multiselect listbox, and each item in the listbox is of type MyClass. I am also writing a method that needs to take a parameter that is a collection of MyClass. It could be of type MyClass[], List<MyClass>, IList<MyClass>, IEnumerable<MyClass>, etc. Any of those would work fine. Somehow, I need to pass the selected items in the listbox to my method. But how would I convert SelectedObjectCollection to any of the MyClass collection types described above?

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• .NET Database Apps: Your Preferred Setup

  - by mdvaldosta

  I'm struggling to settle into a pattern for developing typical database driven apps in C# and Visual Studio. There are so many ways to set them up, using drag/drop datasets and adapters or writing the queries manually in ADO.NET or Linq to SQL, Linq to Entities, to bind or not to data bind etc etc. Where to store the connection string, in app.config or in a method or both etc etc. So many tutorials and all of them are different. Everytime I write something I start hating the way it looks and works, so I scrap it and start over. It's getting a bit tedious. Maybe it's alittle of the OCD in me. Would any of you professional developers out there share your method of setting up and structuring your database logic and maybe some sample code? It's really how to go about organizing the code and the method(s) of interacting with SQL that I'm trying to get into a routine with, one that works and won't get me laughed at by someone reviewing it.

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• Naming convention for utility classes in Java

  - by Zarjay

  When writing utility classes in Java, what are some good guidelines to follow? Should packges be "util" or "utils"? Is it ClassUtil or ClassUtils? When is a class a "Helper" or a "Utility"? Utility or Utilities? Or do you use a mixture of them? The standard Java library uses both Utils and Utilities: javax.swing.Utilities javax.print.attribute.AttributeSetUtilities javax.swing.plaf.basic.BasicGraphicsUtils Apache uses a variety of Util and Utils, although mostly Utils: org.apache.commons.modeler.util.DomUtil org.apache.commons.modeler.util.IntrospectionUtils org.apache.commons.io.FileSystemUtils org.apache.lucene.wordnet.AnalyzerUtil org.apache.lucene.util.ArrayUtil org.apache.lucene.xmlparser.DOMUtils Spring uses a lot of Helper and Utils classes: org.springframework.web.util.UrlPathHelper org.springframework.core.ReflectiveVisitorHelper org.springframework.core.NestedExceptionUtils org.springframework.util.NumberUtils So, how do you name your utility classes?

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• How to simplify this Xpath expression ?

  - by Stephan

  Hi , I have the following XML code : <root> <a><l_desc/></a> <b><l_desc>foo</l_desc></b> <c><l_desc>bar</l_desc></c> </root> I want to match the l_desc nodes with a or b nodes as parent. For now, i use this xpath expression : //a/l_desc/.. | //b/l_desc/.. I would prefer writing something like this : //(a|b)/l_desc/.. Unfortunately, this expression is invalid. Do you have any idea for reducing the first expression ? Stéphan

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• Does the chunk of the System.Collections.Concurrent.Partitioner need to be thread safe?

  - by Scott Chamberlain

  I am working with the Parallel libraries in .net 4 and I am creating a Partitioner and the example shown in the MSDN only has a chunk size of 1 (every time a new result is retrieved it hits the data source instead of the local cache. The version I am writing will pull 10000 SQL rows at a time then feed the rows from the cache until it is empty then pull another batch. Each partition in the Partitioner has its own chunk. I know every time I call to the IEnumerator in from the SQL data-source that needs to be thread safe but for use in a Parallel.ForEach do I need to make every call to the cache for the chunking thread safe?

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• Changing property type in class that implements interface with object type property.

  - by used2could

  I know the title is a bit confusing but bare with me. (I'm up for suggestions on a new title lol) I'm writing a TemplateEngine that will allow me to use my own markup in text based files. I'm wanting to add controls as plugins as the application matures. Currently i've got a structure like the following: interface IControl string Id object Value class Label : IControl string Id string Value class Repeater : IControl string Id List<IControl> Value Now you'll see the strange part right away in the Repeater class with the Value property. I was hoping that having the Value type as object in the interface would allow me the flexibility to expand the controls as i go along. The compiler doesn't like this and for good reason i guess. Does anyone have any suggestions how to accomplish this? Note: Please don't go into suggesting things like use Spark View Engine for templating. There is a reason i'm creating extra work for myself.

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• Humor in code

  - by pfranza

  When you are writing code or naming products, which sources of cultural references are you most likely to draw from? Which reference sources do you think are more likely to be universally understood? For example when findbugs sees that you've implemented equals() without overriding hashCode() it suggest that you implement it by returning 42 (a reference from HHGTTG) Or why we have big endian vs little endian encoding, referencing Gulliver's Travels Not that we should act unprofessionally with our code, but if you going to tell a person that they could only (watch/read/...) one (book/movie/show/...) which one would allow them to 'get' the most jokes?

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• Visual Studio Editor, MEF in-Depth

  - by NewProgrammer

  I have been having difficulty simply writing a Visual Studio Editor Extension with MEF (Managed Extensiblity Framework). I thank those who answered my previous question, as they helped me know that I need to work with MEF. I've been trying to learn MEF for the Visual Studio Editor from MSDN's page, Extending the Editor, but it appears that I have a hard time understanding it. Can anyone provide strong resource or tutorials in addressing problem such as using the right ContentTypeDefintion (IGlyphFactory, TextMarkTag, etc...), and what is a ITagger. I need to understand these things, as most of the walkthrough only extending the text, such as only using the "spans" functionality, while I need to use "selection" methods and use MouseEventHandlers. Does anyone know an example similiar to my example, or references can tell me something about MEF's for VS editor in-depth?

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• Are there any modern platforms with non-IEEE C/C++ float formats?

  - by Patrick Niedzielski

  Hi all, I am writing a video game, Humm and Strumm, which requires a network component in its game engine. I can deal with differences in endianness easily, but I have hit a wall in attempting to deal with possible float memory formats. I know that modern computers have all a standard integer format, but I have heard that they may not all use the IEEE standard for floating-point integers. Is this true? While certainly I could just output it as a character string into each packet, I would still have to convert to a "well-known format" of each client, regardless of the platform. The standard printf() and atod() would be inadequate. Please note, because this game is a Free/Open Source Software program that will run on GNU/Linux, *BSD, and Microsoft Windows, I cannot use any proprietary solutions, nor any single-platform solutions. Cheers, Patrick

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• Using set with values from a table

  - by gozzilli

  I'm writing a database of all DVDs I have at home. One of the fields, actors, I would like it to be a set of values from an other table, which is storing actors. So for every film I want to store a list of actors, all of which selected from a list of actors, taken from a different table. Is it possible? How do I do this? It would be a set of foreign keys basically. I'm using a MySQL database for a Django application (python), so any hint in SQL or Python would be much appreciated. I hope the question is clear, many thanks.

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• Cross-domain REST proxy with Javascript, HTML5

  - by Bosh

  I'm writing a service (say, service.com) that provides a REST API to external apps running inside of IFrames. (These apps are hosted from domains outside the service.com). I'm planning a javascript client library for the apps to make pure-javascript requests to the service.com REST API -- basically using postMessage and some ad-hoc encapsulation of my API calls to get messages back and forth across frames (from the outside-app.com IFrame -- service.com REST API, and back to the IFrame with a response). My question: is there any robust, general-purpose javascript library to accomplish the kind of cross-domain REST request proxying I need, or should I just hack it from scratch?

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• How to create a backup from SqlAlchemy?

  - by swilliams

  I'm writing a Pylons app, and am trying to create a simple backup system where every table is serialized and tarred up into a single file for an administrator to download, and use to restore the app should something bad happen. I can serialize my table data just fine using the SqlAlchemy serializer, and I can deserialize it fine as well, but I can't figure out how to commit those changes back to the database. In order to serialize my data I am doing this: from myproject.model.meta import Session from sqlalchemy.ext.serializer import loads, dumps q = Session.query(MyTable) serialized_data = dumps(q.all()) In order to test things out, I go ahead and truncation MyTable, and then attempt to restore using serialized_data: from myproject.model import meta restore_q = loads(serialized_data, meta.metadata, Session) This doesn't seem to do anything... I've tried calling a Session.commit after the fact, individually walking through all the objects in restore_q and adding them, but nothing seems to work. What am I missing? Or is there a better way to do what I'm aiming for? I don't want to shell out and directly touch the database, since SqlAlchemy supports different database engines.

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• php send mail code not working

  - by anand

  php $to = "[email protected]"; $subject = "Hi!"; $body = "Hi,\n\nHow are you?"; if (mail($to, $subject, $body)) { echo("pMessage successfully sent!/p"); } else { echo("pMessage delivery failed.../p"); } wrote a basic php sendmail code that but it gives me the following error Warning: mail() [function.mail]: "sendmail_from" not set in php.ini or custom "From:" header missing in C:\xampp\htdocs\mail.php on line 5 Message delivery failed... i changed the php.ini file and put [email protected] but still the problem persists... writing the mail script for the first time Am i doing something wrong? is there a better code or way to go thru this? Any help will be appreciated Thank you

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• Putting WPF Control (ComboBox) into canvas with Visuals

  - by Mikhail

  I am writing a WPF chart and use Visuals for performance. The code looks like: public class DrawingCanvas2 : Canvas { private List<Visual> _visuals = new List<Visual>(); protected override Visual GetVisualChild( int index ) { return _visuals[index]; } protected override int VisualChildrenCount { get { return _visuals.Count; } } public void AddVisual( Visual visual ) { _visuals.Add( visual ); base.AddVisualChild( visual ); base.AddLogicalChild( visual ); } } Beside DrawingVisual elements (line, text) I need a ComboBox in the chart. So I tried this: public DrawingCanvas2() { ComboBox box = new ComboBox(); AddVisual( box ); box.Width = 100; box.Height = 30; Canvas.SetLeft( box, 10 ); Canvas.SetTop( box, 10 ); } but it does not work, there is no ComboBox displayed. What I am missing?

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• MIDI on Android: Java and/or AIR libraries

  - by yar

  I've been contemplating (re)building an app on iPad for some time, where I would use objective-C and DSMI to send MIDI signals to a host computer. This is not bad (I mean, except for actually writing the app). Now I'm contemplating perhaps developing the app for Android tablets (TBA). In Java, what options are available for MIDI message communication? I'm quite familiar with javax.sound.midi, but then I would need a virtual MIDI port to send messages to the host. On the other hand, if the app were done in Adobe AIR, what options would I have available for communicating with MIDI? Obviously another option is to send/receive messages over a TCP/IP socket to a Java host, and talk that way, but it sounds a tad cumbersome... or perhaps not? DSMI does use a host program, after all.

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• Creating an SQL Compact file: Template or script?

  - by David Veeneman

  I am writing an application that writes to SQL Compact files that have a specific schema, and I am now implementing the New File use case. The simplest approach seems to be to use a Template pattern: first, create a template file that lives in the application directory. Then, when the user selects New File, the template is copied to the name and destination specified by the user in a New File dialog. The alternative is a scripted approach: Use the same New File dialog, but dispense with the template file. Instead, create an empty SQL Compact file using the name/destination specified by the user, and then execute a T-SQL script on it from managed code. At this point, I am leaning toward the Template approach, because it is simpler. Is there any reason I should not use that approach? Thanks for your help.

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• What's wrong with my logic here?

  - by stu

  In java they say don't concatenate Strings, instead you should make a stringbuffer and keep adding to that and then when you're all done, use toString() to get a String object out of it. Here's what I don't get. They say do this for performance reasons, because concatenating strings makes lots of temporary objects. But if the goal was performance, then you'd use a language like C/C++ or assembly. The argument for using java is that it is a lot cheaper to buy a faster processor than it is to pay a senior programmer to write fast efficient code. So on the one hand, you're supposed let the hardware take care of the inefficiencies, but on the other hand, you're supposed to use stringbuffers to make java more efficient. While I see that you can do both, use java and stringbuffers, my question is where is the flaw in the logic that you either use a faster chip or you spent extra time writing more efficient software.

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• C# Proxy using Sockets, how should I do this?

  - by Kin

  I'm writing a proxy using .NET and C#. I haven't done much Socket programming, and I am not sure the best way to go about it. What would be the best way to implement this? Should I use Synchronous Sockets, Asynchronous sockets? Please help! It must... Accept Connections from the client on two different ports, and be able to receive data on both ports at the same time. Connect to the server on two different ports, and be able to send data on both ports as the same time. Immediately connect to the server and start forwarding packets as soon as a client connection is made. Forward packets in the same order they were received. Be as low latency as possible. I don't need the ability for multiple clients to connect to the proxy, but it would be a nice feature if its easy to implement. Client --------- Proxy ------- Server ---|-----------------|----------------| Port <-------- Port <------- Port Port <-------- Port <------- Port

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• Transactional isolation level needed for safely incrementing ids

  - by Knut Arne Vedaa

  I'm writing a small piece of software that is to insert records into a database used by a commercial application. The unique primary keys (ids) in the relevant table(s) are sequential, but does not seem to be set to "auto increment". Thus, I assume, I will have to find the largest id, increment it and use that value for the record I'm inserting. In pseudo-code for brevity: id = select max(id) from some_table id++ insert into some_table values(id, othervalues...) Now, if another thread started the same transaction before the first one finished its insert, you would get two identical ids and a failure when trying to insert the last one. You could check for that failure and retry, but a simpler solution might be setting an isolation level on the transaction. For this, would I need SERIALIZABLE or a lower level? Additionally, is this, generally, a sound way of solving the problem? Are the any other ways of doing it?

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• How to reset the value of NSInterval ?

  - by srikanth rongali

  I am writing a small game. After the completion of the game we get the previous screen. So, we can play again. But problem is that the time interval (NSTime Interval)started first time while running game is still continuing. For example the time interval of my touch when I first started game is 3.0 seconds. When again I played (not quitting the application) the time interval is 3.0 seconds + interval till the present touch ? Hoe can I make it work ? Please help me with solution for my problem.

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• Xcode & 64 bit & 32 bit Question

  - by I00I

  Hello All, I have a 32bit iMac that I am writing an iPhone app in Xcode with, and I was wondering if I saved my project to a flash drive and dropped it on my MacBookPro which is 64 bit and continued to code the iPhone project on my laptop in Xcode would this cause a problem? I don't see how it would since the target is not for either of those computers, but I thought I would ask since I would like to work on the project when I am not always around my iMac. Are there any gottcha's with doing this that I should look out for? Thanks, I00I

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• Loop through hex variable in C

  - by Jud Stephenson

  I have the following code in a project that write's the ascii representation of packet to a unix tty: int written = 0; int start_of_data = 3; //write data to fifo while (length) { if ((written = write(fifo_fd, &packet[start_of_data], length)) == -1) { printf("Error writing to FIFO\n"); } else { length -= written; } } I just want to take the data that would have been written to the socket and put it in a variable. to debug, I have just been trying to printf the first letter/digit. I have tried numerous ways to get it to print out, but I keep getting hex forms (I think). The expected output is: 13176 and the hex value is: 31 33 31 37 36 0D 0A (if that is even hex) Obviously my C skills are not the sharpest tools in the shed. Any help would be appreciated.

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