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• Chat Server with sockets in C

  - by Andrew

  I'm trying to write a chat server in C that allows communication between two clients using POSIX sockets. I'm not sure I have a good grasp on this concept or how I should set up the communication protocol between the clients and the server. I know I need one socket to bind() the server port to so I can accept incoming connections from clients, but in order to have two clients connected at the same time do I need to create a socket for each of these clients when I accept() or should I accept() a client and then fork() so I can have another client accept? I'm not worried about concurrent chatting yet, it's more of a ping-pong approach where the clients need to wait for a recv() after they send() before they can type a new message.

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• Sync data between a windows desktop app and windows mobile client app

  - by Chris W

  I need to knock up a very quick prototype/proof of concept application to demo to someone within the next couple of days so I've minimal time to research this as fully as I normally would. The set-up is a very simple database application running on a laptop - will only ever be a single user updating a couple of tables so I was thinking of knocking up a basic Win Forms app against SQL Compact. Visual Studio's auto generated data grid edit screens will be fine with a little customisation. The second aspect is to then add a windows mobile client application that can pull data from both tables stored on the laptop, edit some data and insert some extra rows before sending the changes back to the laptop copy of the database. I've not done any WinMo development so what's the best approach for me to look at. Is it easy enough to sync data between the two databases when the WinMo device is connected to the laptop with USB? Most of the samples I've looked at so far seem to be syncing SQL Compact with SQL Standard using IIS which seems a bit overkill. The volumes of data to be synced are so small that I can easily write some manual sync code if it's easy for me to query/update the Compact DB from the laptop application when the device is connected.

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• Why do I have to explicitly cast sometimes for varargs?

  - by Daniel Lew

  I've got a Class that uses reflection a lot, so I wrote a method to help out: private <T> T callMethod(String methodName, Class[] parameterTypes, Object[] args) { try { Class c = mVar.getClass(); Method m = c.getMethod(methodName, (Class[]) parameterTypes); return (T) m.invoke(mVar, args); } // Insert exception catching here [...] } This worked well for any method that had parameters, however I had to explicitly cast parameterTypes to Class[] in order for this to work for methods with no parameters (e.g., callMethod('funName', null, null);). I've been trying to figure out why this is the case. It seems to me that if parameterTypes, when null, had no concept of what type it is (Class[]), then I'd need to cast it for getMethod(). But if that's the case, why is getMethod() able to tell the difference between null, and (Class[]) null when the method is invoked?

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• Understanding reflection

  - by sdmiller

  I recently started work at a new company and a .net web application we have is built using reflection. I have only been out of school for a year and haven't worked with this concept. After studying the code... it looks like there is a single backend interface of type object that has about 20 classes that inherit from it. lots of generic gets and sets On the surface it looks like standard inheritance to me. I guess my question is, what makes this reflection? Is it because the interface is not strongly typed? Thanks

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• Ensure that my C# desktop application is making requests to my ASP .NET MVC action?

  - by Mathias Lykkegaard Lorenzen

  I've seen questions that are almost identical to this one, except minor but important differences that I would like to get detailed. Let's say that I have a controller and an action method in MVC which therefore accepts requests on the following URL: http://example.com/api/myapimethod?data=some-data-here. This URL is then being called regularly by 1000 clients or more spread out in the public. The reason for this is crowdsourcing. The clients around the globe help feed a global cache on my server, which makes it faster for the rest of the clients to fetch the data. Now, if I'm sneaky (and I am), I can go into Fiddler, Ethereal, Wireshark or any other packet sniffing tool and figure out which requests the program is making. By figuring that out, I can also replicate them, and fill the service with false corrupted data. What is the best approach to ensuring that the data received in my ASP .NET MVC action method is actually from the desktop client application, and not some falsely generated data that the user invented? Since it is all based on crowdsourcing, would it be a good idea for my users to be able to "vote" if some data is falsified, and then let an automatic cleanup commence if there are enough votes? I do not have access to a tool like SmartAssembly, so unfortunately my .NET program is fully decompilable. I realize this might be impossible to accomplish in an error-proof manner, but I would like to know where my best chances are.

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• How to organise a many to many relationship in MongoDB

  - by Gareth Elms

  I have two tables/collections; Users and Groups. A user can be a member of any number of groups and a user can also be an owner of any number of groups. In a relational database I'd probably have a third table called UserGroups with a UserID column, a GroupID column and an IsOwner column. I'm using MongoDB and I'm sure there is a different approach for this kind of relationship in a document database. Should I embed the list of groups and groups-as-owner inside the Users table as two arrays of ObjectIDs? Should I also store the list of members and owners in the Groups table as two arrays, effectively mirroring the relationship causing a duplication of relationship information? Or is a bridging UserGroups table a legitimate concept in document databases for many to many relationships? Thanks

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• Inconsistent Routing Results in MVC

  - by HapiDjus

  Seems I'm still missing something to the MVC routing concept. I have a route that follows nearly the same pattern as another route in an area but for what ever reason I get a 404 every time I attempt to run it. I've tried to use Phil Haack's Route Tester DLL and according to that it hits the correct route (matched route comes out to common/itemhistory/{contentid}). When I try to run it for real, it blows up. I'm trying to map a call to a JsonResult by passing a Guid. I've had success with other routes working fine (common is an area in my site). What could I be doing wrong? context.MapRoute( "ItemHistory", "common/itemhistory/{contentid}", new { controller = "common", action = "GetItemHistory" }, new { contentid = @"^(\{){0,1}[0-9a-fA-F]{8}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{4}\-[0-9a-fA-F]{12}(\}){0,1}$" } ); context.MapRoute( "Common_default", "common/{action}", new { controller="common", action = "Index" } );

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• Are there any Visual Studio add-ins for true 'smart tabs'?

  - by Eye of Hell

  Hello. 'Smart Tabs' concept allows to automatically insert tab character for block indentation and space characters for in-block formatting. It's described here. Unfortunately, Visual Studio's 'smart tabs' option in text editor settings just indents text on enter press. Same name, completely different and near useless thing :). So, maybe someone knows of a visual studio addin that can change how 'tab' key work so it will insert tab characters and space characters according to rules mentioned above? Any hints are welcome. Update: I need it for C++. According to comments, ReSharper can do something like this, but only for Basic and C#.

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• How to start coding the "Dining Philosophers" simulation?

  - by GrizzlyGuru

  I'm not a beginner at C# but I really need to increase my understanding, so I've picked a classic deadlock problem to code to help teach myself some of the more advanced concepts of C#. The Dining Philosophers Problem seems like a good one, but I need a little help to get started. I know I need to approach the "diners" as objects, but to simulate the random delays between eating, should I look to threading with each diner in a separate thread? Do I need some kind of "master" to monitor all the actions? Any general design concept advice is welcome, but I'd like to do the grunt programming as an exercise. Thanks!

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• Is there an equivalent to C++'s "friend class" in Java?

  - by Ricket

  In C++ there is a concept of a "friend", which has access to a class's private variables and functions. So if you have: class Foo { friend class Bar; private: int x; } then any instance of the class Bar can modify any Foo instance's x member, despite it being private, because Bar is a friend of Foo. Now I have a situation in Java where this functionality would come in handy. There are three classes: Database, Modifier, Viewer. The Database is just a collection of variables (like a struct). Modifier should be "friends" with Database; that is, it should be able to read and write its variables directly. But Viewer should only be able to read Database's variables. How is this best implemented? Is there a good way to enforce Viewer's read-only access of Database?

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• Is it a good idea to apply some basic macros to simplify code in a large project?

  - by DoctorT

  I've been working on a foundational c++ library for some time now, and there are a variety of ideas I've had that could really simplify the code writing and managing process. One of these is the concept of introducing some macros to help simplify statements that appear very often, but are a bit more complicated than should be necessary. For example, I've come up with this basic macro to simplify the most common type of for loop: #define loop(v,n) for(unsigned long v=0; v<n; ++v) This would enable you to replace those clunky for loops you see so much of: for (int i = 0, i < max_things; i++) With something much easier to write, and even slightly more efficient: loop (i, max_things) Is it a good idea to use conventions like this? Are there any problems you might run into with different types of compilers? Would it just be too confusing for someone unfamiliar with the macro(s)?

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• Does thread pool size keep growing for scheduledthreadpoolexecutor?

  - by Sourajit Basak

  Imagine a situation where tasks are being added to scheduledthreadpoolexecutor. Each of these tasks will keep on running at different periodic intervals. Although all such tasks will not be running at the same time because each is set at different intervals, there may be a situation where a high number of threads are competing for execution. Is there any restriction on total number of threads ? It seems there is a restriction on the total number of idle threads. And does this concept of idle thread imply that long running tasks (thread) may be destroyed and recreated when needed ?

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• Reading Matrices in MATLAB and assigning coordinates to the entries

  - by Michael Schofield

  Hi, I'm a bit new to MATLAB. Basically, I have a 25x25 Matrix, complete with various random entries ranging from 0 to 3. I need to write a program that reads this matrix, and assigns x-y coordinates to the entries, so that when I ask for an input of a particular x-y coordinate which has, say an entry of 3, then it will result in an error. I'm a bit overwhelmed - but I understand the general concept of what I'm supposed to be finding. I'm wondering if I should use a plot instead to help me.

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• Running an application from an USB device...

  - by Workshop Alex

  I'm working on a proof-of-concept application, containing a WCF service with console host and client, both on a single USB device. On the same device I will also have the client application which will connect to this service. The service uses the entity framework to connect to the database, which in this POC will just return a list of names. If it works, it will be used for a larger project. Creating the client and service was easy and this works well from USB. But getting the service to connect to the database isn't. I've found this site, suggesting that I should modify machine.config but that stops the XCopy deployment. This project cannot change any setting of the PC, so this suggestion is bad. I cannot create a deployment setup either. The whole thing just needs to run from USB disk. So, how do I get it to run? (The service just selects a list of names from the database, which it returns to the client. If this POC works, it will do far more complex things!)

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• using helper methods in a view in rails 3

  - by Frida777

  Hello everyone, there is something that is disturbing me a bit about rails 3. i am trying to upgrade my application from rails 2 to rails 3. i followed all the steps necessary to do and things were working well for me till now except one thing: i have a helper method that is defined differently in different helpers, for example it is defined in the application_helper in one way and the same method defined in a different way in the homepage_helper, and defined differently in another helper, let's say video_helper, in addition to that, it is used in a shared view that is used throughout the application, now if i am in the homepage, i want this function to get called from the homepage_helper and if i am in the video page, the function must be called from the video_helper, based on the concept of convention in rails, this worked perfectly in rails 2 but in rails 3, the function is always called from the last helper, alphabetically ordered, that is in the example, video_helper. How can i fix this? Kindly advice. Appreciate all the help.

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• Open Source PHP search engine

  - by Ravi Gupta

  I am looking for an open source search engine plugin written in php for my website(eCommerce). Before anybody answer that I have a doubt regarding the search engine. Usually search engine crawl web pages, create indexes and then use them while looking for contents. But will the same model work for eCommerce websites? Yeah, it can crawl products pages, index them but don't you think it would be better if it crawls the database directly and index the products stored in the database? And when a user search for any product, it will simply give us the rows of the table which matches the user query? May be what I am asking is a stupid question but I am new to web development, so kindly help me to understand the concept. I have looked at a search engine called Sphider but didn't get what all I have to do to make it work with an eCommerce website.

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• How would you code this: Grid-breaking shapes

  - by BeachRunnerJoe

  I'm a person that learns best from example. Currently, I'm diving into the field of Web Development after fifteen years of developing desktop apps. I'm still getting used to all the web technologies used for developing modern web sites and everywhere I look, I see cool little UI elements and question how they're implemented. So I thought I'd ask you, the web experts...the wexperts :) What are some straight forward or creative ways you could code this grid-breaking arrow... The basic layout for this page looks like... What would the html/css code look like? Would you split the image into multiple images or could you use a single image? I'm sure this is a really simple concept and it completely boggles me. I'm sorry if this is a strange question, remember I'm a noob! :) Thanks in advance for all your help! Here's a link to the original tutorial where I found these images

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• Can I transform this asynchronous java network API into a monadic representation (or something else

  - by AlecZorab

  I've been given a java api for connecting to and communicating over a proprietary bus using a callback based style. I'm currently implementing a proof-of-concept application in scala, and I'm trying to work out how I might produce a slightly more idiomatic scala interface. A typical (simplified) application might look something like this in Java: DataType type = new DataType(); BusConnector con = new BusConnector(); con.waitForData(type.getClass()).addListener(new IListener<DataType>() { public void onEvent(DataType t) { //some stuff happens in here, and then we need some more data con.waitForData(anotherType.getClass()).addListener(new IListener<anotherType>() { public void onEvent(anotherType t) { //we do more stuff in here, and so on } }); } }); //now we've got the behaviours set up we call con.start(); In scala I can obviously define an implicit conversion from (T = Unit) into an IListener, which certainly makes things a bit simpler to read: implicit def func2Ilistener[T](f: (T => Unit)) : IListener[T] = new IListener[T]{ def onEvent(t:T) = f } val con = new BusConnector con.waitForData(DataType.getClass).addListener( (d:DataType) => { //some stuff, then another wait for stuff con.waitForData(OtherType.getClass).addListener( (o:OtherType) => { //etc }) }) Looking at this reminded me of both scalaz promises and f# async workflows. My question is this: Can I convert this into either a for comprehension or something similarly idiomatic (I feel like this should map to actors reasonably well too) Ideally I'd like to see something like: for( d <- con.waitForData(DataType.getClass); val _ = doSomethingWith(d); o <- con.waitForData(OtherType.getClass) //etc )

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• How to Delete Duplicate Rows in SQL 2000?

  - by Mikecancook

  I thought I had this figured out but it turns out I'm just deleting the first record. The following returns the duplicate rows. All have a count of 2. I just want to delete the first one for each duplicate record. select scorestudentid, scoreadvisor, scorecorrect, count(*) from scores where scoretestid = 3284 group by scorestudentid, scoreadvisor, scorecorrect having count(scorestudentid) > 1 Which returns: scorestudentid scoreadvisor scorecorrect no column name 13033719 28059 3.0 2 13033777 28086 3.0 2 13033826 28147 3.0 2 13033960 28023 3.0 2 So I put this together thinking it would work: set rowcount 1 delete from scores where scoretestid = 3284 and scorestudentid in ( select scorestudentid from scores where scoretestid = 3284 group by scorestudentid having count(scorestudentid) > 1) It really seems like it should be a simple concept but I'm not getting it.

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• Is there a .NET class that represents operator types?

  - by user323774

  I would like to do the following: *OperatorType* o = *OperatorType*.GreaterThan; int i = 50; int increment = -1; int l = 0; for(i; i o l; i = i + increment) { //code } this concept can be kludged in javascript using an eval()... but this idea is to have a loop that can go forward or backward based on values set at runtime. is this possible? Thanks

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• NHibernate lazy properties behavior?

  - by GeReV

  I've been trying to get NHibernate into development for a project I'm working on at my workplace. Since I have to put a strong emphasis on performance, I've been running a proof-of-concept stress test on an existing project's table with thousands of records, all of which contain a large text column. However, when selecting a collection of these records, the select statement takes a relatively long time to execute; apparently due to the aforementioned column. The first solution that comes to mind is setting this property as lazy: <property name="Content" lazy="true"/> But there seems to be no difference in the SQL generated by NHibernate. My question is, how do lazy properties behave in NHibernate? Is there some kind of type limitations I could be missing? Should I take a different approach altogether? Using HQL's new Class(column1, column2) approach works, but lazy properties sounds like a simpler solution. It's perhaps worth mentioning I'm using NHibernate 2.1.2GA with the Castle DynamicProxy. Thanks!

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• Does Core Data automatically validate new values when they are set?

  - by mystify

  In this question, someone asked how to write a validation method for Core Data. I did that, and it looks cool. But one thing doesn't happen: The validation. I can easily set any "bad" value and this method doesn't get called automatically. What's the concept behind this? Must I always first call the validation method before setting any value? So would I write setter methods which call the appropriate validation method first? And if yes, what's the point of following a strict convention in how to write the validation method signature? I guess there's also some automatic way of validation, then. How to activate this?

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• In TDD, should tests be written by the person who implemented the feature under test?

  - by martin

  We run a project in which we want to solve with test driven development. I thought about some questions that came up when initiating the project. One question was: Who should write the unit-test for a feature? Should the unit-test be written by the feature-implementing programmer? Or should the unit test be written by another programmer, who defines what a method should do and the feature-implementing programmer implements the method until the tests runs? If I understand the concept of TDD in the right way, the feature-implementing programmer has to write the test by himself, because TDD is procedure with mini-iterations. So it would be too complex to have the tests written by another programmer? What would you say? Should the tests in TDD be written by the programmer himself or should another programmer write the tests that describes what a method can do?

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• How to play a set of jpeg files as a movie?

  - by RJ

  I have a set of jpeg images where eacg image has an associated description. e.g. im1.jpg - suspect enters bank im7.jpg - suspect hands teller a note imj41.jpg - teller gives suspect a bag ... ... It's trivial to view these images individually and see the description but how do I play this as a movie? I need to play the images and when I encounter one with a description, display the description in a status pane. Do I need to convert the images into a movie, if so how? How do I get the player to notify me when the description frame is encountered? I'm using Windows. language doesn't matter, I just need the concept right now.

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• Formal name of Magento’s Class Override Design Pattern?

  - by Alan Storm

  Magento is a newish (past 5 years) PHP based Ecommerce system with an architecture that's similar to the Java Spring framework (or so I've been told) One of the features of the Framework is certain classes are not directly instantiated. Rather than do something like $model = new Mage_Foo_Model_Name(); you pass an identifier into a static method on a global application object $model = Mage::getModel('foo/name'); and this instantiates the class for you. One of the wins with this approach is getModel checks a global configuration system for the foo/name identifier, and instantiates the class name it finds in the configuration system. This allows you to change the behavior of a Model system wide with a single configuration change. Is there a formal, Gang of Four or otherwise, name that describes this system/design pattern? The instantiation itself looks like a classic Factory pattern, but I'm specifically interested in the whole "override a class in the system via configuration" aspect. Is there a name/concept that covers this, or is it contained within the worldview of a Factory?

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