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• Ask the Readers: How Do You Score Free Wi-Fi While Traveling?

  - by Jason Fitzpatrick

  The holiday season is in full swing and that means many of us will be traveling–and searching for Wi-Fi nodes in the process. Help your fellow readers out by sharing your best Wi-Fi finding tips and tricks. Internet access is a necessity for the modern traveler but finding it is a bit more difficult than simply plugging into your home Wi-Fi. This week we want to hear all about your tips, tricks, and methods for scoring free Wi-Fi service in your interstate (and even international) travels. How do you keep the bounty of the internet flowing to your laptops, netbooks, tablets, and smart phones as you traverse the world? Sound off in the comments with your best tips and then check back on Friday for the What You Said roundup. HTG Explains: Understanding Routers, Switches, and Network Hardware How to Use Offline Files in Windows to Cache Your Networked Files Offline How to See What Web Sites Your Computer is Secretly Connecting To

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• Upcoming Database Design Pre-Cons

  - by drsql

  In July and October, I will be doing my "How To Design a Relational Database" full day conference in two places. First on July 26 for the East Iowa SQL Saturday , and then for the big daddy SQLPASS Summit in Charlotte, NC on October 14. You can see the entire abstract here on the SQL PASS site. It is essentially the same concept as last year, but this year I am making a few big changes to really give the people what they have desired (and am truly glad to have a swing at it several months...(read more)

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• Looking for a real-world example illustrating that composition can be superior to inheritance

  - by Job

  I watched a bunch of lectures on Clojure and functional programming by Rich Hickey as well as some of the SICP lectures, and I am sold on many concepts of functional programming. I incorporated some of them into my C# code at a previous job, and luckily it was easy to write C# code in a more functional style. At my new job we use Python and multiple inheritance is all the rage. My co-workers are very smart but they have to produce code fast given the nature of the company. I am learning both the tools and the codebase, but the architecture itself slows me down as well. I have not written the existing class hierarchy (neither would I be able to remember everything about it), and so, when I started adding a fairly small feature, I realized that I had to read a lot of code in the process. At the surface the code is neatly organized and split into small functions/methods and not copy-paste-repetitive, but the flip side of being not repetitive is that there is some magic functionality hidden somewhere in the hierarchy chain that magically glues things together and does work on my behalf, but it is very hard to find and follow. I had to fire up a profiler and run it through several examples and plot the execution graph as well as step through a debugger a few times, search the code for some substring and just read pages at the time. I am pretty sure that once I am done, my resulting code will be short and neatly organized, and yet not very readable. What I write feels declarative, as if I was writing an XML file that drives some other magic engine, except that there is no clear documentation on what the XML should look like and what the engine does except for the existing examples that I can read as well as the source code for the 'engine'. There has got to be a better way. IMO using composition over inheritance can help quite a bit. That way the computation will be linear rather than jumping all over the hierarchy tree. Whenever the functionality does not quite fit into an inheritance model, it will need to be mangled to fit in, or the entire inheritance hierarchy will need to be refactored/rebalanced, sort of like an unbalanced binary tree needs reshuffling from time to time in order to improve the average seek time. As I mentioned before, my co-workers are very smart; they just have been doing things a certain way and probably have an ability to hold a lot of unrelated crap in their head at once. I want to convince them to give composition and functional as opposed to OOP approach a try. To do that, I need to find some very good material. I do not think that a SCIP lecture or one by Rich Hickey will do - I am afraid it will be flagged down as too academic. Then, simple examples of Dog and Frog and AddressBook classes do not really connivence one way or the other - they show how inheritance can be converted to composition but not why it is truly and objectively better. What I am looking for is some real-world example of code that has been written with a lot of inheritance, then hit a wall and re-written in a different style that uses composition. Perhaps there is a blog or a chapter. I am looking for something that can summarize and illustrate the sort of pain that I am going through. I already have been throwing the phrase "composition over inheritance" around, but it was not received as enthusiastically as I had hoped. I do not want to be perceived as a new guy who likes to complain and bash existing code while looking for a perfect approach while not contributing fast enough. At the same time, my gut is convinced that inheritance is often the instrument of evil and I want to show a better way in a near future. Have you stumbled upon any great resources that can help me?

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• Windows 7 Service Pack 1 is Released: But Should You Install It?

  - by The Geek

  Microsoft has just released the final version of Service Pack 1 for Windows 7, but should you drop everything and go through the process of installing it? Where can you get it? We’ve got the answers for you. If you’ve never installed a service pack before, it’s just a big collection of fixes and changes for your operating system, bundled into a big fat download to make it more convenient if you reinstall—if you’ve kept Windows updated, it should have most of the fixes already installed through Windows Update Latest Features How-To Geek ETC How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Ask How-To Geek: How Can I Monitor My Bandwidth Usage? Internet Explorer 9 RC Now Available: Here’s the Most Interesting New Stuff Never Call Me at Work [Humorous Star Wars Video] Add an Image Properties Listing to the Context Menu in Chrome and Iron Add an Easy to View Notification Badge to Tabs in Firefox SpellBook Parks Bookmarklets in Chrome’s Context Menu Drag2Up Brings Multi-Source Drag and Drop Uploading to Firefox Enchanted Swing in the Forest Wallpaper

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• Which DB should I use for my newbie program?

  - by knijo

  I'm really new to programming, and I need some advice. I'm currently working on a very simple program to maintain a list of users at a company, as well as their clock in and clock out info. I would like to make this application easy to distribute (on a cd probably), and I'm looking for advice on which database to use for storing my data. My application is implemented using java and swing. A friend recommended MySQL, but I don't want to go installing the db server on every computer the application is installed on. Another friend recommended Access. Any tips would be greatly appreciated

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• Which is the best non-java, dynamic, programming language to build attractive GUIs?

  - by VeeKay

  I am well acquainted with java and groovy but somehow I am not intrigued by the performance or looks of swing based applications that are developed on the same. So I want to learn and know about THE best alternate dynamic programming language (coz I am looking for little bit of luxury while writing code by not willing to fiddle with pointers, memory handling, static typing difficulties etc) to develop attractive cross platform GUIs. To be precise, when I say attractive I mean support for elegant translucent windows and nicer components (not the flashy adobe stuff). Can you please suggest me a programming language that manages to fit into this?

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• Leg animation not working

  - by Monacraft

  I am making a simple animation in XNA C# of a leg moving. This is the logic code for the thigh. It is meant to swing from 25' to 335'. However instead, it hits a point and then keeps on spinning in the other direction. Please help, here's the code: private void Thigh_method() { if (Legdata.Left == true) signvalue = -0.05f; else signvalue = 0.05f; if (Legdata.ToMid == true) Thighturn_ang += signvalue; if (Legdata.ToMid == false) Thighturn_ang -= signvalue; if (Thighturn_ang <= 25 || Thighturn_ang <= 335 && Thighturn_ang <= 180) Legdata.Left = true; if (Thighturn_ang >= 25 || Thighturn_ang >= 335 && Thighturn_ang >= 180) Legdata.Left = false; if (Thighturn_ang == 0) Legdata.ToMid = false; if (Math.Abs(Thighturn_ang) >= 25f) Legdata.ToMid = true; } Thanks in advance, Yours: Mona

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• Oracle Master Data Management at OOW 2012: A Look Back

  - by Mala Narasimharajan

  Oracle Master Data Management had a great showing at OOW 2012 ! Special thanks to our customers and partners for presenting with us, sharing their use cases and successes as well as co-sponsoring events.  Almost every session at the show featured a customer and the tremendous success or transformation Oracle MDM resulted in at their organization.  At the DemoGrounds, Oracle MDM saw tremendous interest with many individuals enquiring to see demos, and have their technical questions answered.  The demos provided a perfect opportunity to showcase technical enhancements as well as what features are on the horizon.The MDM customer appreciation dinner event was a smashing success as cusotmers and partners enjoyed a spectacular water view, fine dining and cocktails and one of San Francisco's finest restaurants - The Water Bar.  In a short while the planning for next year's OpenWorld will be under full swing and we can't wait to get started.  See you at OOW 2013!!    

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• Java graphic objects as in flashgames

  - by Ryu Kajiya

  How is it possible (with the standard Java2D engine) to use small sprites like graphic objects? For those who don't know what I mean, in all those Flash-games like on Facebook they put small sprites on the screen which react to mouse-over and clicks. I tried to do the same in Java but can't find a good method. Swing components always spread over the whole bitmap, but I only want to get a reaction from the object when the mouse is over a pixel that's not transparent. So basically checking every time if the object below the mouse contains a non-transparent pixel (which i believe could be pretty intense in a gameloop or repaint loop). I have no idea how to implement such a thing efficiently.

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• What things need to be considered when redeveloping the whole UI for a web app?

  - by Robin

  I am the lead developer on a thick client web app (Java swing) which we're looking at recreating as a web app. We're part way through some initial work, have chosen a framework on the server and integrated with our previous backend code. We're just starting to get into the client side of things, looking at javascript frameworks etc. The previous system was pretty sensibly architected so the logic is already serverside. The challenge ahead of us is really about redeveloping the user interface rather than anything else. What would be the list of things to consider in redeveloping the entire user interface for any application? I'm trying to get an idea of how large a task might still be ahead of me and the team.

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• Quelles sont pour vous les plus belles applications de bureau développées en Java ? Partagez votre expérience

  Même si les applications Web prennent une part non négligeable dans le développement Java, de nombreuses applications de bureau sont encore très demandées. La plateforme Java via ses nombreuses bibliothèques graphiques (JavaFX, Swing, plateforme Eclipse, ...) permet de réaliser des applications de bureau très abouties. Nous vous invitons à partager les applications de bureau qui vous semblent les plus réussis et les plus à même de montrer la maturité de Java dans tous les domaines. Pour chaque application, merci de préciser un lien et un bref descriptif. A noter qu'un débat similaire avait été proposé il y a quelques années concernant

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• Overriding a function in an instance [on hold]

  - by MustSeeMelons

  Is it possible to override a function by instance? For example, A and B are both instances of MyClass. I have a function Action(), and I want to specify its implementation for each instance. To be more specific - the class is a Button, and the function is Clicked(). I don't want to derive a class 5 times to create 5 different button actions. Was thinking of something like it's handled in Java Swing: create a button, add code for the button press and use the button.

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• How to learn programming from very basic level to advanced level? [closed]

  - by user1022209

  I know many programming languages ,skills and concepts in very basic, such as PHP, Java, Object-oriented technology. Using PHP, I can build a simple website with CRUD, login function. Using Java, I can make an basic swing csv/plain text editor in which user can switch between 2 different views. In term of object-oriented Technology, I clearly understand what encapsulation, inheritance and Polymorphism are I want to know more about programming. Sometimes I "google" some of the topics I am interested at , the more I see on the internet, the more I feel I am a small potato in the world ( indeed I am ). The codings/concepts are difficult to understand. I lacks confidence right now so I am asking this question :( What is the best way to learn programming to advanced level? Just buy a book and read it page to page? Thanks for any helps

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• What is the worst programming language you ever worked with? [closed]

  - by Ludwig Weinzierl

  If you have an interesting story to share, please post an answer, but do not abuse this question for bashing a language. We are programmers, and our primary tool is the programming language we use. While there is a lot of discussion about the best one, I'd like to hear your stories about the worst programming languages you ever worked with and I'd like to know exactly what annoyed you. I'd like to collect this stories partly to avoid common pitfalls while designing a language (especially a DSL) and partly to avoid quirky languages in the future in general. This question is not subjective. If a language supports only single character identifiers (see my own answer) this is bad in a non-debatable way. EDIT Some people have raised concerns that this question attracts trolls. Wading through all your answers made one thing clear. The large majority of answers is appropriate, useful and well written. UPDATE 2009-07-01 19:15 GMT The language overview is now complete, covering 103 different languages from 102 answers. I decided to be lax about what counts as a programming language and included anything reasonable. Thank you David for your comments on this. Here are all programming languages covered so far (alphabetical order, linked with answer, new entries in bold): ABAP, all 20th century languages, all drag and drop languages, all proprietary languages, APF, APL (1), AS400, Authorware, Autohotkey, BancaStar, BASIC, Bourne Shell, Brainfuck, C++, Centura Team Developer, Cobol (1), Cold Fusion, Coldfusion, CRM114, Crystal Syntax, CSS, Dataflex 2.3, DB/c DX, dbase II, DCL, Delphi IDE, Doors DXL, DOS batch (1), Excel Macro language, FileMaker, FOCUS, Forth, FORTRAN, FORTRAN 77, HTML, Illustra web blade, Informix 4th Generation Language, Informix Universal Server web blade, INTERCAL, Java, JavaScript (1), JCL (1), karol, LabTalk, Labview, Lingo, LISP, Logo, LOLCODE, LotusScript, m4, Magic II, Makefiles, MapBasic, MaxScript, Meditech Magic, MEL, mIRC Script, MS Access, MUMPS, Oberon, object extensions to C, Objective-C, OPS5, Oz, Perl (1), PHP, PL/SQL, PowerDynamo, PROGRESS 4GL, prova, PS-FOCUS, Python, Regular Expressions, RPG, RPG II, Scheme, ScriptMaker, sendmail.conf, Smalltalk, Smalltalk , SNOBOL, SpeedScript, Sybase PowerBuilder, Symbian C++, System RPL, TCL, TECO, The Visual Software Environment, Tiny praat, TransCAD, troff, uBasic, VB6 (1), VBScript (1), VDF4, Vimscript, Visual Basic (1), Visual C++, Visual Foxpro, VSE, Webspeed, XSLT The answers covering 80386 assembler, VB6 and VBScript have been removed.

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• Hidden features of Perl?

  - by Adam Bellaire

  What are some really useful but esoteric language features in Perl that you've actually been able to employ to do useful work? Guidelines: Try to limit answers to the Perl core and not CPAN Please give an example and a short description Hidden Features also found in other languages' Hidden Features: (These are all from Corion's answer) C# Duff's Device Portability and Standardness Quotes for whitespace delimited lists and strings Aliasable namespaces Java Static Initalizers JavaScript Functions are First Class citizens Block scope and closure Calling methods and accessors indirectly through a variable Ruby Defining methods through code PHP Pervasive online documentation Magic methods Symbolic references Python One line value swapping Ability to replace even core functions with your own functionality Other Hidden Features: Operators: The bool quasi-operator The flip-flop operator Also used for list construction The ++ and unary - operators work on strings The repetition operator The spaceship operator The || operator (and // operator) to select from a set of choices The diamond operator Special cases of the m// operator The tilde-tilde "operator" Quoting constructs: The qw operator Letters can be used as quote delimiters in q{}-like constructs Quoting mechanisms Syntax and Names: There can be a space after a sigil You can give subs numeric names with symbolic references Legal trailing commas Grouped Integer Literals hash slices Populating keys of a hash from an array Modules, Pragmas, and command-line options: use strict and use warnings Taint checking Esoteric use of -n and -p CPAN overload::constant IO::Handle module Safe compartments Attributes Variables: Autovivification The $[ variable tie Dynamic Scoping Variable swapping with a single statement Loops and flow control: Magic goto for on a single variable continue clause Desperation mode Regular expressions: The \G anchor (?{}) and '(??{})` in regexes Other features: The debugger Special code blocks such as BEGIN, CHECK, and END The DATA block New Block Operations Source Filters Signal Hooks map (twice) Wrapping built-in functions The eof function The dbmopen function Turning warnings into errors Other tricks, and meta-answers: cat files, decompressing gzips if needed Perl Tips See Also: Hidden features of C Hidden features of C# Hidden features of C++ Hidden features of Java Hidden features of JavaScript Hidden features of Ruby Hidden features of PHP Hidden features of Python

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• Delegates in .NET: how are they constructed ?

  - by Saulius

  While inspecting delegates in C# and .NET in general, I noticed some interesting facts: Creating a delegate in C# creates a class derived from MulticastDelegate with a constructor: .method public hidebysig specialname rtspecialname instance void .ctor(object 'object', native int 'method') runtime managed { } Meaning that it expects the instance and a pointer to the method. Yet the syntax of constructing a delegate in C# suggests that it has a constructor new MyDelegate(int () target) where I can recognise int () as a function instance (int *target() would be a function pointer in C++). So obviously the C# compiler picks out the correct method from the method group defined by the function name and constructs the delegate. So the first question would be, where does the C# compiler (or Visual Studio, to be precise) pick this constructor signature from ? I did not notice any special attributes or something that would make a distinction. Is this some sort of compiler/visualstudio magic ? If not, is the T (args) target construction valid in C# ? I did not manage to get anything with it to compile, e.g.: int () target = MyMethod; is invalid, so is doing anything with MyMetod, e.g. calling .ToString() on it (well this does make some sense, since that is technically a method group, but I imagine it should be possible to explicitly pick out a method by casting, e.g. (int())MyFunction. So is all of this purely compiler magic ? Looking at the construction through reflector reveals yet another syntax: Func CS$1$0000 = new Func(null, (IntPtr) Foo); This is consistent with the disassembled constructor signature, yet this does not compile! One final interesting note is that the classes Delegate and MulticastDelegate have yet another sets of constructors: .method family hidebysig specialname rtspecialname instance void .ctor(class System.Type target, string 'method') cil managed Where does the transition from an instance and method pointer to a type and a string method name occur ? Can this be explained by the runtime managed keywords in the custom delegate constructor signature, i.e. does the runtime do it's job here ?

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• Can I perform some processing on the POST data before ASP.NET MVC UpdateModel happens?

  - by Domenic

  I would like to strip out non-numeric elements from the POST data before using UpdateModel to update the copy in the database. Is there a way to do this? // TODO: it appears I don't even use the parameter given at all, and all the magic // happens via UpdateModel and the "controller's current value provider"? [HttpPost] public ActionResult Index([Bind(Include="X1, X2")] Team model) // TODO: stupid magic strings { if (this.ModelState.IsValid) { TeamContainer context = new TeamContainer(); Team thisTeam = context.Teams.Single(t => t.TeamId == this.CurrentTeamId); // TODO HERE: apply StripWhitespace() to the data before using UpdateModel. // The data is currently somewhere in the "current value provider"? this.UpdateModel(thisTeam); context.SaveChanges(); this.RedirectToAction(c => c.Index()); } else { this.ModelState.AddModelError("", "Please enter two valid Xs."); } // If we got this far, something failed; redisplay the form. return this.View(model); } Sorry for the terseness, up all night working on this; hopefully my question is clear enough? Also sorry since this is kind of a newbie question that I might be able to get with a few hours of documentation-trawling, but I'm time-pressured... bleh.

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• Send already generated MHTML using CDOSYS through C#?

  - by mutex

  I have a ready generated MHTML as a byte array (from Aspose.Words) and would like to send it as an email. I'm trying to do this through CDOSYS, though am open to other suggestions. For now though I have the following: CDO.Message oMsg = new CDO.Message(); CDO.IConfiguration iConfg = oMsg.Configuration; Fields oFields = iConfg.Fields; // Set configuration. Field oField = oFields["http://schemas.microsoft.com/cdo/configuration/sendusing"]; oField.Value = CDO.CdoSendUsing.cdoSendUsingPort; oField = oFields["http://schemas.microsoft.com/cdo/configuration/smtpserver"]; oField.Value = SmtpClient.Host; oField = oFields["http://schemas.microsoft.com/cdo/configuration/smtpserverport"]; oField.Value = SmtpClient.Port; oFields.Update(); //oMsg.CreateMHTMLBody("http://www.microsoft.com", CDO.CdoMHTMLFlags.cdoSuppressNone, "", ""); // NEED MAGIC HERE :) oMsg.Subject = warning.Subject; // string oMsg.From = "[email protected]"; oMsg.To = warning.EmailAddress; oMsg.Send(); In this snippet, the warning variable has a Body property which is a byte[]. Where it says "NEED MAGIC HERE" in the code above I want to use this byte[] to set the body of the CDO Message. I have tried the following, which unsurprisingly doesn't work: oMsg.HTMLBody = System.Text.Encoding.ASCII.GetString(warning.Body); Anybody have any ideas how I can achieve what I want with CDOSYS or something else?

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• Is it possible to use boost::bind to effectively concatenate functions?

  - by Catskul

  Assume that I have a boost::function of with an arbitrary signature called type CallbackType. Is it possible to use boost::bind to compose a function that takes the same arguments as the CallbackType but calls the two functors in succession? Hypothetical example using a magic template: Template<typename CallbackType> class MyClass { public: CallbackType doBoth; MyClass( CallbackType callback ) { doBoth = bind( magic<CallbackType>, protect( bind(&MyClass::alert, this) ), protect( callback ) ); } void alert() { cout << "It has been called\n"; } }; void doIt( int a, int b, int c) { cout << "Doing it!" << a << b << c << "\n"; } int main() { typedef boost::function<void (int, int, int)> CallbackType; MyClass<CallbackType> object( boost::bind(doIt) ); object.doBoth(); return 0; }

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• I installed XAMPP in a virtual drive and now I can't run its services. Why?

  - by Haris

  Hi, The description is quite long. Please spend some time to read it. ^:)^ I have an old PHP application and I'm trying to test and debug it. Unfortunately, the application uses important data so I can't just click this and that. Now, what I'm trying to do is create a copy of the application in a different computer. From now on, I will call the computer running my original PHP application as 'Computer A' and the computer which I'm going to use to run the copy of the application as 'Computer B'. To prevent missing link problems since the application contains static paths, such in images or tags, I have to copy all files and folder related to my PHP application from Computer A to the same path in Computer B. Unfortunately, Computer B only has drive C while Computer A has drive D and the files of my PHP application is located in 'D:\xampp\htdocs' in Computer A. OK, now I have to create drive D in computer B. At first, I tried to create a second partition in Computer B by using PowerQuest Partition Magic 8, but somehow Partition Magic doesn't run in Computer B. I have tried to reinstall it but it still doesn't run. So, another alternative is to create a virtual drive. That is what I did. I created a virtual drive by running the 'subst' command in Command Prompt. The virtual drive is D and it refers to a directory, which is 'C:\Virtual'. After I have drive D in Computer B, I installed XAMPP there. The installation was successful. Now, I also have 'D:\xampp\htdocs' in Computer B. However, when I ran the Apache, MySQL, or Filezilla service, I receive an error message "Error 3: The system cannot find the file specified.". In Computer B, there is no IIS or process using the port 80. What should I do? Please help me. Many thanks in advance, Haris

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• Where is the errnos defined? Example linux c/c++ program for i2c.

  - by Johan

  Hi When something goes wrong in a classic linux c/c++ software we have the magic variable errno that gives us a clue on what just went wrong. But where is those errors defined? Let's take a example (it's actually a piece from a Qt app, therefore the qDebug()). if (ioctl(file, I2C_SLAVE, address) < 0) { int err = errno; qDebug() << __FILE__ << __FUNCTION__ << __LINE__ << "Can't set address:" << address << "Errno:" << err << strerror(err); .... The next step is to look at what that errno was so we can decide if we just quit or try to do something about the problem. So we maybe add a if or switch at this point. if (err == 9) { // do something... } else { //do someting else } And my question is where to find the errors that "9" represents? I don't like that kind of magic numbers in my code. /Thanks

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• Apples, oranges, and pointers to the most derived c++ class

  - by Matthew Lowe

  Suppose I have a bunch of fruit: class Fruit { ... }; class Apple : public Fruit { ... }; class Orange: public Fruit { ... }; And some polymorphic functions that operate on said fruit: void Eat(Fruit* f, Pesticide* p) { } void Eat(Apple* f, Pesticide* p) { ingest(f,p); } void Eat(Orange* f, Pesticide* p) { peel(f,p); ingest(f,p); } OK, wait. Stop right there. Note at this point that any sane person would make Eat() a virtual member function of the Fruit classes. But that's not an option, because I am not a sane person. Also, I don't want that Pesticide* in the header file for my fruit class. Sadly, what I want to be able to do next is exactly what member functions and dynamic binding allow: typedef list<Fruit*> Fruits; Fruits fs; ... for(Fruits::iterator i=fs.begin(), e=fs.end(); i!=e; ++i) Eat(*i); And obviously, the problem here is that the pointer we pass to Eat() will be a Fruit*, not an Apple* or an Orange*, therefore nothing will get eaten and we will all be very hungry. So what I really want to be able to do instead of this: Eat(*i); is this: Eat(MAGIC_CAST_TO_MOST_DERIVED_CLASS(*i)); But to my limited knowledge, such magic does not exist, except possibly in the form of a big nasty if-statement full of calls to dynamic_cast. So is there some run-time magic of which I am not aware? Or should I implement and maintain a big nasty if-statement full of dynamic_casts? Or should I suck it up, quit thinking about how I would implement this in Ruby, and allow a little Pesticide to make its way into my fruit header?

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• Scala: Correcting type inference of representation type over if statement

  - by drhagen

  This is a follow-up to two questions on representation types, which are type parameters of a trait designed to represent the type underlying a bounded type member (or something like that). I've had success creating instances of classes, e.g ConcreteGarage, that have instances cars of bounded type members CarType. trait Garage { type CarType <: Car[CarType] def cars: Seq[CarType] def copy(cars: Seq[CarType]): Garage def refuel(car: CarType, fuel: CarType#FuelType): Garage = copy( cars.map { case `car` => car.refuel(fuel) case other => other }) } class ConcreteGarage[C <: Car[C]](val cars: Seq[C]) extends Garage { type CarType = C def copy(cars: Seq[C]) = new ConcreteGarage(cars) } trait Car[C <: Car[C]] { type FuelType <: Fuel def fuel: FuelType def copy(fuel: C#FuelType): C def refuel(fuel: C#FuelType): C = copy(fuel) } class Ferrari(val fuel: Benzin) extends Car[Ferrari] { type FuelType = Benzin def copy(fuel: Benzin) = new Ferrari(fuel) } class Mustang(val fuel: Benzin) extends Car[Mustang] { type FuelType = Benzin def copy(fuel: Benzin) = new Mustang(fuel) } trait Fuel case class Benzin() extends Fuel I can easily create instances of Cars like Ferraris and Mustangs and put them into a ConcreteGarage, as long as it's simple: val newFerrari = new Ferrari(Benzin()) val newMustang = new Mustang(Benzin()) val ferrariGarage = new ConcreteGarage(Seq(newFerrari)) val mustangGarage = new ConcreteGarage(Seq(newMustang)) However, if I merely return one or the other, based on a flag, and try to put the result into a garage, it fails: val likesFord = true val new_car = if (likesFord) newFerrari else newMustang val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here The switch alone works fine, it is the call to ConcreteGarage constructor that fails with the rather mystical error: error: inferred type arguments [this.Car[_ >: this.Ferrari with this.Mustang <: this.Car[_ >: this.Ferrari with this.Mustang <: ScalaObject]{def fuel: this.Benzin; type FuelType<: this.Benzin}]{def fuel: this.Benzin; type FuelType<: this.Benzin}] do not conform to class ConcreteGarage's type parameter bounds [C <: this.Car[C]] val switchedGarage = new ConcreteGarage(Seq(new_car)) // Fails here ^ I have tried putting those magic [C <: Car[C]] representation type parameters everywhere, but without success in finding the magic spot.

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• Template trick to optimize out allocations

  - by anon

  I have: struct DoubleVec { std::vector<double> data; }; DoubleVec operator+(const DoubleVec& lhs, const DoubleVec& rhs) { DoubleVec ans(lhs.size()); for(int i = 0; i < lhs.size(); ++i) { ans[i] = lhs[i]] + rhs[i]; // assume lhs.size() == rhs.size() } return ans; } DoubleVec someFunc(DoubleVec a, DoubleVec b, DoubleVec c, DoubleVec d) { DoubleVec ans = a + b + c + d; } Now, in the above, the "a + b + c + d" will cause the creation of 3 temporary DoubleVec's -- is there a way to optimize this away with some type of template magic ... i.e. to optimize it down to something equivalent to: DoubleVec ans(a.size()); for(int i = 0; i < ans.size(); i++) ans[i] = a[i] + b[i] + c[i] + d[i]; You can assume all DoubleVec's have the same # of elements. The high level idea is to have do some type of templateied magic on "+", which "delays the computation" until the =, at which point it looks into itself, goes hmm ... I'm just adding thes numbers, and syntheizes a[i] + b[i] + c[i] + d[i] ... instead of all the temporaries. Thanks!

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• How to handle window closed in the middle of a long running operation gracefully?

  - by Marek

  We have the following method called directly from the UI thread: void DoLengthyProcessing() { DoStuff(); var items = DoMoreStuff(); //do even more stuff - 200 lines of code trimmed this.someControl.PrepareForBigThing(); //someControl is a big user control //additional 100 lines of code that access this.someControl this.someControl.Finish(items); } Many of the called methods call Application.DoEvents() (and they do so many times) (do not ask me why, this is black magic written by black magic programmers and it can not be changed because everyone is scared what the impact would be) and there is also an operation running on a background thread involved in the processing. As a result, the window is not fully nonresponsive and can be closed manually during the processing. The Dispose method of the form "releases" the someControl variable by setting it to null. As a result, in case the user closes the window during the lengthy process, a null reference exception is thrown. How to handle this gracefully without just catching and logging the exception caused by disposal? Assigning the someControl instance to a temporary variable in the beginning of the method - but the control contains many subcontrols with similar disposal scheme - sets them to null and this causes null reference exceptions in other place put if (this.IsDisposed) return; calls before every access of the someControl variable. - making the already nasty long method even longer and unreadable. in Closing event, just indicate that we should close and only hide the window. Dispose it at the end of the lengthy operation. This is not very viable because there are many other methods involved (think 20K LOC for a single control) that would need to handle this mechanism as well. How to most effectively handle window disposal (by user action) in the middle of this kind of processing?

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