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  • C# - Advantages/Disadvantages of different implementations for Comparing Objects

    - by Kevin Crowell
    This questions involves 2 different implementations of essentially the same code. First, using delegate to create a Comparison method that can be used as a parameter when sorting a collection of objects: class Foo { public static Comparison<Foo> BarComparison = delegate(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); }; } I use the above when I want to have a way of sorting a collection of Foo objects in a different way than my CompareTo function offers. For example: List<Foo> fooList = new List<Foo>(); fooList.Sort(BarComparison); Second, using IComparer: public class BarComparer : IComparer<Foo> { public int Compare(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); } } I use the above when I want to do a binary search for a Foo object in a collection of Foo objects. For example: BarComparer comparer = new BarComparer(); List<Foo> fooList = new List<Foo>(); Foo foo = new Foo(); int index = fooList.BinarySearch(foo, comparer); My questions are: What are the advantages and disadvantages of each of these implementations? What are some more ways to take advantage of each of these implementations? Is there a way to combine these implementations in such a way that I do not need to duplicate the code? Can I achieve both a binary search and an alternative collection sort using only 1 of these methods?

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  • What is the fastest way to do division in C for 8bit MCUs?

    - by Jordan S
    I am working on the firmware for a device that uses an 8bit mcu (8051 architecture). I am using SDCC (Small Device C Compiler). I have a function that I use to set the speed of a stepper motor that my circuit is driving. The speed is set by loading a desired value into the reload register for a timer. I have a variable, MotorSpeed that is in the range of 0 to 1200 which represents pulses per second to the motor. My function to convert MotorSpeed to the correct 16bit reload value is shown below. I know that float point operations are pretty slow and I am wondering if there is a faster way of doing this... void SetSpeed() { float t = MotorSpeed; unsigned int j = 0; t = 1/t ; t = t / 0.000001; j = MaxInt - t; TMR3RL = j; // Set reload register for desired freq return; }

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  • DDD and MVC Models hold ID of separate entity or the entity itself?

    - by Dr. Zim
    If you have an Order that references a customer, does the model include the ID of the customer or a copy of the customer object like a value object (thinking DDD)? I would like to do ths: public class Order { public int ID {get;set;} public Customer customer {get;set;} ... } right now I do this: public class Order { public int ID {get;set;} public int customerID {get;set;} ... } It would be more convenient to include the complete customer object rather than an ID to the View Model passed to the form. Otherwise, I need to figure out how to get the vendor information to the view that the order references by ID. This also implies that the repository understand how to deal with the customer object that it finds within the order object when they call save (if we select the first option). If we select the second option, we will need to know where in the view model to put it. It is certain they will select an existing customer. However, it is also certain they may want to change the information in-place on the display form. One could argue to have the controller extract the customer object, submit customer changes separately to the repository, then submit changes to the order, keeping the customerID in the order.

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  • ASP.NET Web Application: use 1 or multiple virtual directories

    - by tster
    I am working on a (largish) internal web application which has multiple modules (security, execution, features, reports, etc.). All the pages in the app share navigation, CSS, JS, controls, etc. I want to make a single "Web Application" project, which includes all the pages for the app, then references various projects which will have the database and business logic in them. However, some of the people on the project want to have separate projects for the pages of each module. To make this more clear, this is what I'm advocating to be the projects. /WebInterface* /SecurityLib /ExecutionLib etc... And here is what they are advocating: /SecurityInterface* /SecutiryLib /ExecutionInterface* /ExecutionLib etc... *project will be published to a virtual directory of IIS Basically What I'm looking for is the advantages of both approaches. Here is what I can think of so far: Single Virtual Directory Pros Modules can share a single MasterPage Modules can share UserControls (this will be common) Links to other modules are within the same Virtual directory, and thus don't need to be fully qualified. Less chance of having incompatible module versions together. Multiple Virtual Directories Pros Can publish a new version of a single module without disrupting other modules Module is more compartmentalized. Less likely that changes will break other modules. I don't buy those arguments though. First, using load balanced servers (which we will have) we should be able to publish new versions of the project with zero downtime assuming there are no breaking database changes. Second, If something "breaks" another module, then there is either an improper dependency or the break will show up eventually in the other module, when the developers copy over the latest version of the UserControl, MasterPage or dll. As a point of reference, there are about 10 developers on the project for about 50% of their time. The initial development will be about 9 months.

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  • How can I determine PerlLogHandler performance impact?

    - by Timmy
    I want to create a custom Apache2 log handler, and the template that is found on the apache site is: #file:MyApache2/LogPerUser.pm #--------------------------- package MyApache2::LogPerUser; use strict; use warnings; use Apache2::RequestRec (); use Apache2::Connection (); use Fcntl qw(:flock); use File::Spec::Functions qw(catfile); use Apache2::Const -compile => qw(OK DECLINED); sub handler { my $r = shift; my ($username) = $r->uri =~ m|^/~([^/]+)|; return Apache2::Const::DECLINED unless defined $username; my $entry = sprintf qq(%s [%s] "%s" %d %d\n), $r->connection->remote_ip, scalar(localtime), $r->uri, $r->status, $r->bytes_sent; my $log_path = catfile Apache2::ServerUtil::server_root, "logs", "$username.log"; open my $fh, ">>$log_path" or die "can't open $log_path: $!"; flock $fh, LOCK_EX; print $fh $entry; close $fh; return Apache2::Const::OK; } 1; What is the performance cost of the flocks? Is this logging process done in parallel, or in serial with the HTTP request? In parallel the performance would not matter as much, but I wouldn't want the user to wait another split second to add something like this.

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  • How are you using C++0x today? [closed]

    - by Roger Pate
    This is a question in two parts, the first is the most important and concerns now: Are you following the design and evolution of C++0x? What blogs, newsgroups, committee papers, and other resources do you follow? Even where you're not using any new features, how have they affected your current choices? What new features are you using now, either in production or otherwise? The second part is a follow-up, concerning the new standard once it is final: Do you expect to use it immediately? What are you doing to prepare for C++0x, other than as listed for the previous questions? Obviously, compiler support must be there, but there's still co-workers, ancillary tools, and other factors to consider. What will most affect your adoption? Edit: The original really was too argumentative; however, I'm still interested in the underlying question, so I've tried to clean it up and hopefully make it acceptable. This seems a much better avenue than duplicating—even though some answers responded to the argumentative tone, they still apply to the extent that they addressed the questions, and all answers are community property to be cleaned up as appropriate, too.

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  • Java - Call to start method on thread : how does it route to Runnable interface's run () ?

    - by Bhaskar
    Ok , I know the two standard ways to create a new thread and run it in Java : 1 Implement Runnable in a class , define run method ,and pass an instance of the class to a new Thread. When the start method on the thread instance is called , the run method of the class instance will be invoked. 2 Let the class derive from Thread, so it can to override the method run() and then when a new instance's start method is called , the call is routed to overridden method. In both methods , basically a new Thread object is created and its start method invoked. However , while in the second method , the mechanism of the call being routed to the user defined run() method is very clear ,( its a simple runtime polymorphism in play ), I dont understand how the call to start method on the Thread object gets routed to run() method of the class implementing Runnable interface. Does the Thread class have an private field of Type Runnable which it checks first , and if it is set then invokes the run method if it set to an object ? that would be a strange mechanism IMO. How does the call to start() on a thread get routed to the run method of the Runnable interface implemented by the class whose object is passed as a parameter when contructing the thread ?

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  • PDO using singleton stored as class properity

    - by Misiur
    Hi again. OOP drives me crazy. I can't move PDO to work. Here's my DB class: class DB extends PDO { public function &instance($dsn, $username = null, $password = null, $driver_options = array()) { static $instance = null; if($instance === null) { try { $instance = new self($dsn, $username, $password, $driver_options); } catch(PDOException $e) { throw new DBException($e->getMessage()); } } return $instance; } } It's okay when i do something like this: try { $db = new DB(DB_TYPE.':host='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASS); } catch(DBException $e) { echo $e->getMessage(); } But this: try { $db = DB::instance(DB_TYPE.':host='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASS); } catch(DBException $e) { echo $e->getMessage(); } Does nothing. I mean, even when I use wrong password/username, I don't get any exception. Second thing - I have class which is "heart" of my site: class Core { static private $instance; public $db; public function __construct() { if(!self::$instance) { $this->db = DB::instance(DB_TYPE.':hpost='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASS); } return self::$instance; } private function __clone() { } } I've tried to use "new DB" inside class, but this: $r = $core->db->query("SELECT * FROM me_config"); print_r($r->fetch()); Return nothing. $sql = "SELECT * FROM me_config"; print_r($core->db->query($sql)); I get: PDOStatement Object ( [queryString] => SELECT * FROM me_config ) I'm really confused, what am I doing wrong?

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  • Overloading generic implicit conversions

    - by raichoo
    Hi I'm having a little scala (version 2.8.0RC1) problem with implicit conversions. Whenever importing more than one implicit conversion the first one gets shadowed. Here is the code where the problem shows up: // containers class Maybe[T] case class Nothing[T]() extends Maybe[T] case class Just[T](value: T) extends Maybe[T] case class Value[T](value: T) trait Monad[C[_]] { def >>=[A, B](a: C[A], f: A => C[B]): C[B] def pure[A](a: A): C[A] } // implicit converter trait Extender[C[_]] { class Wrapper[A](c: C[A]) { def >>=[B](f: A => C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, f) } def >>[B](b: C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, { (x: A) => b } ) } } implicit def extendToMonad[A](c: C[A]) = new Wrapper[A](c) } // instance maybe object maybemonad extends Extender[Maybe] { implicit object MaybeMonad extends Monad[Maybe] { override def >>=[A, B](a: Maybe[A], f: A => Maybe[B]): Maybe[B] = { a match { case Just(x) => f(x) case Nothing() => Nothing() } } override def pure[A](a: A): Maybe[A] = Just(a) } } // instance value object identitymonad extends Extender[Value] { implicit object IdentityMonad extends Monad[Value] { override def >>=[A, B](a: Value[A], f: A => Value[B]): Value[B] = { a match { case Value(x) => f(x) } } override def pure[A](a: A): Value[A] = Value(a) } } import maybemonad._ //import identitymonad._ object Main { def main(args: Array[String]): Unit = { println(Just(1) >>= { (x: Int) => MaybeMonad.pure(x) }) } } When uncommenting the second import statement everything goes wrong since the first "extendToMonad" is shadowed. However, this one works: object Main { implicit def foo(a: Int) = new { def foobar(): Unit = { println("Foobar") } } implicit def foo(a: String) = new { def foobar(): Unit = { println(a) } } def main(args: Array[String]): Unit = { 1 foobar() "bla" foobar() } } So, where is the catch? What am I missing? Regards, raichoo

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  • Linked List push()

    - by JKid314159
    The stack is initialized with a int MaxSize =3. Then I push one int onto the list. " Pushed:" is returned to the console. Program crashes here. I think my logic is flawed but unsure. Maybe an infinite loop or unmet condition? Thanks for your help. I'm trying to traverse the list to the last node in the second part of the full() method. I implemented this stack as array based so must implement this method full() as this method is inside of main class. while(!stacker.full()) { cout << "Enter number = "; cin >> intIn; stacker.push(intIn); cout << "Pushed: " << intIn << endl; }//while Call to LinkListStack.cpp to class LinkList full(). int LinkList::full() { if(head == NULL) { top = 0; } else { LinkNode * tmp1; LinkNode * tmp2; tmp1 = head; while(top != MaxSize) { if(tmp1->next != NULL){ tmp2 = tmp1->next; tmp1 = tmp2; ++top; }//if }//while }//else return (top + 1 == MaxSize); }

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  • Jquery selectors question

    - by Ben
    Hi all, I am not an expert at jquery but trying to get a menu to work. Basically, I have a menu made of up to 3 levels of nested lists. The first level has a little arrow has a background image that opens or close when opening the first level list. Any other nested lists don't need to have the background image. My script opens the menu when you click on it and is also supposed to switch the first level list from a class "inactive" to a class "active". Here is the script: $(document).ready(function(){ $("#left-navigation-holder ul.level1 li.inactive").toggle(function(){ $(this).addClass("active"); }, function () { $(this).removeClass("active"); }); $("#left-navigation-holder li a").click(function(){ menu = $(this).parent('li').children('ul'); menu.toggle(); }); }); The problem is that the toggle function also happens when clicking on second and third level lists causing the arrows to toggle even if the first level list isn't clicked on. I thought using $("#left-navigation-holder ul.level1 li.inactive").toggle would limit the function to the first level list with a class "inactive". Any help would be really appreciated. Ben

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  • Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (-1)

    - by user309670
    Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for concurrent connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR) suggests that ...'the connection was reset by peer', or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? Otherwise, use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. I cannot figure-out whatever is wrong even with Valgrind or GDB

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  • Java Executor: Small tasks or big ones?

    - by Arash Shahkar
    Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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  • How do the major C# DI/IoC frameworks compare?

    - by Slomojo
    At the risk of stepping into holy war territory, What are the strengths and weaknesses of these popular DI/IoC frameworks, and could one easily be considered the best? ..: Ninject Unity Castle.Windsor Autofac StructureMap Are there any other DI/IoC Frameworks for C# that I haven't listed here? In context of my use case, I'm building a client WPF app, and a WCF/SQL services infrastructure, ease of use (especially in terms of clear and concise syntax), consistent documentation, good community support and performance are all important factors in my choice. Update: The resources and duplicate questions cited appear to be out of date, can someone with knowledge of all these frameworks come forward and provide some real insight? I realise that most opinion on this subject is likely to be biased, but I am hoping that someone has taken the time to study all these frameworks and have at least a generally objective comparison. I am quite willing to make my own investigations if this hasn't been done before, but I assumed this was something at least a few people had done already. Second Update: If you do have experience with more than one DI/IoC container, please rank and summarise the pros and cons of those, thank you. This isn't an exercise in discovering all the obscure little containers that people have made, I'm looking for comparisons between the popular (and active) frameworks.

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  • Add xml-stylesheet and get standalone = yes.

    - by tumba25
    The code at the bottom is what I have. I removed the creation of all tags. At the top in the xml file I get.<?xml version="1.0" encoding="UTF-8" standalone="no"?> Note that standalone is no, even thou I have it set to yes. The first question: How do I get standalone = yes? I would like to add <?xml-stylesheet type="text/xsl" href="my.stylesheet.xsl"?> at line two in the xml file. Second question: How do I do that? Some useful links? Anything? DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance(); DocumentBuilder docBuilder = dbfac.newDocumentBuilder(); Document doc = docBuilder.newDocument(); <cut> TransformerFactory transfac = TransformerFactory.newInstance(); transfac.setAttribute("indent-number", new Integer(2)); Transformer trans = transfac.newTransformer(); trans.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); trans.setOutputProperty(OutputKeys.STANDALONE, "yes"); trans.setOutputProperty(OutputKeys.INDENT, "yes"); trans.setOutputProperty(OutputKeys.CDATA_SECTION_ELEMENTS, "name"); FileOutputStream fout = new FileOutputStream(filepath); BufferedOutputStream bout= new BufferedOutputStream(fout); trans.transform(new DOMSource(doc), new StreamResult(new OutputStreamWriter(bout, "utf-8")));

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  • Linq, should I join those two queries together?

    - by 5YrsLaterDBA
    I have a Logins table which records when user is login, logout or loginFailed and its timestamp. Now I want to get the list of loginFailed after last login and the loginFailed happened within 24 hrs. What I am doing now is get the last login timestamp first. then use second query to get the final list. do you think I should join those two queris together? why not? why yes? var lastLoginTime = (from inRecord in db.Logins where inRecord.Users.UserId == userId && inRecord.Action == "I" orderby inRecord.Timestamp descending select inRecord.Timestamp).Take(1); if (lastLoginTime.Count() == 1) { DateTime lastInTime = (DateTime)lastLoginTime.First(); DateTime since = DateTime.Now.AddHours(-24); String actionStr = "F"; var records = from record in db.Logins where record.Users.UserId == userId && record.Timestamp >= since && record.Action == actionStr && record.Timestamp > lastInTime orderby record.Timestamp select record; }

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  • What should i do for accomodating large scale data storage and retrieval?

    - by kailashbuki
    There's two columns in the table inside mysql database. First column contains the fingerprint while the second one contains the list of documents which have that fingerprint. It's much like an inverted index built by search engines. An instance of a record inside the table is shown below; 34 "doc1, doc2, doc45" The number of fingerprints is very large(can range up to trillions). There are basically following operations in the database: inserting/updating the record & retrieving the record accoring to the match in fingerprint. The table definition python snippet is: self.cursor.execute("CREATE TABLE IF NOT EXISTS `fingerprint` (fp BIGINT, documents TEXT)") And the snippet for insert/update operation is: if self.cursor.execute("UPDATE `fingerprint` SET documents=CONCAT(documents,%s) WHERE fp=%s",(","+newDocId, thisFP))== 0L: self.cursor.execute("INSERT INTO `fingerprint` VALUES (%s, %s)", (thisFP,newDocId)) The only bottleneck i have observed so far is the query time in mysql. My whole application is web based. So time is a critical factor. I have also thought of using cassandra but have less knowledge of it. Please suggest me a better way to tackle this problem.

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  • Unit testing, mocking - simple case: Service - Repository

    - by rafek
    Consider a following chunk of service: public class ProductService : IProductService { private IProductRepository _productRepository; // Some initlization stuff public Product GetProduct(int id) { try { return _productRepository.GetProduct(id); } catch (Exception e) { // log, wrap then throw } } } Let's consider a simple unit test: [Test] public void GetProduct_return_the_same_product_as_getProduct_on_productRepository() { var product = EntityGenerator.Product(); _productRepositoryMock.Setup(pr => pr.GetProduct(product.Id)).Returns(product); Product returnedProduct = _productService.GetProduct(product.Id); Assert.AreEqual(product, returnedProduct); _productRepositoryMock.VerifyAll(); } At first it seems that this test is ok. But let's change our service method a little bit: public Product GetProduct(int id) { try { var product = _productRepository.GetProduct(id); product.Owner = "totallyDifferentOwner"; return product; } catch (Exception e) { // log, wrap then throw } } How to rewrite a given test that it'd pass with the first service method and fail with a second one? How do you handle this kind of simple scenarios? HINT: A given test is bad coz product and returnedProduct is actually the same reference.

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  • Handling user interface in a multi-threaded application (or being forced to have a UI-only main thre

    - by Patrick
    In my application, I have a 'logging' window, which shows all the logging, warnings, errors of the application. Last year my application was still single-threaded so this worked [quite] good. Now I am introducing multithreading. I quickly noticed that it's not a good idea to update the logging window from different threads. Reading some articles on keeping the UI in the main thread, I made a communication buffer, in which the other threads are adding their logging messages, and from which the main thread takes the messages and shows them in the logging window (this is done in the message loop). Now, in a part of my application, the memory usage increases dramatically, because the separate threads are generating lots of logging messages, and the main thread cannot empty the communication buffer quickly enough. After the while the memory decreases again (if the other threads have finished their work and the main thread gradually empties the communication buffer). I solved this problem by having a maximum size on the communication buffer, but then I run into a problem in the following situation: the main thread has to perform a complex action the main thread takes some parts of the action and let's separate threads execute this while the seperate threads are executing their logic, the main thread processes the results from the other threads and continues with its work if the other threads are finished Problem is that in this situation, if the other threads perform logging, there is no UI-message loop, and so the communication buffer is filled, but not emptied. I see two solutions in solving this problem: require the main thread to do regular polling of the communication buffer only performing user interface logic in the main thread (no other logic) I think the second solution seems the best, but this may not that easy to introduce in a big application (in my case it performs mathematical simulations). Are there any other solutions or tips? Or is one of the two proposed the best, easiest, most-pragmatic solution? Thanks, Patrick

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  • Compatibility jquery with IE - click function and fade

    - by Julien Fotnaine
    Here my script : http://jsfiddle.net/3XwZv/153/ HTML <div id="box1" class="choice" style="background:blue;"> <div class="selection ordinateur"> <div class="choix1"><a class="link1" href="#"></a></div> </div> </div> <div id="box2" class="choice" style="display:none;background:red;"> <div class="selection ordinateur"> <div class="choix1"><a class="link2" href="#"></a></div> </div> </div> <div id="box3" class="choice" style="display:none;background:green;"> <div class="selection ordinateur"> <div class="choix1"><a href="#"></a></div> </div> </div> JS $(".link1").click(function() { $('#box1').fadeOut("slow", function(){ $('#box2').css("display","block"); $('#box2').replaceWith(div); $('#box1').fadeIn("slow"); }); $('.link1').fadeOut("slow"); return false; }); $(".link2").click(function() { $('#box2').fadeOut("slow", function(){ $('#box3').css("display","block"); $('#box3').replaceWith(div); $('#box2').fadeIn("slow"); }); $('.link2').fadeOut("slow"); return false; }); The main goal is that when you click on the giant square, I have three differents action. However, in Internet Explorer I block to the second. (the red square does not go to the green square). Please I need your help guys!

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  • algorithim for simple colision detection in Java

    - by Bob Twinkles
    I'm not very experienced with Java, just started a couple weeks ago, but I have a simple applet that has two user controlled balls, drawn through java.awt and I need a way to detect a collision with between them. I have an algorithm for detecting collision with the walls: while (true){ if (xPositon > (300 - radius)){ xSpeed = -xSpeed; } else if (xPositon < radius){ xSpeed = -xSpeed; } else if (yPositon > (300 - radius)) { ySpeed = -ySpeed; } else if (yPositon < radius){ ySpeed = -ySpeed; } xPositon += xSpeed; yPositon += ySpeed; and for the second ball if (xPositon2 > (300 - radius)){ xSpeed2 = -xSpeed2; } else if (xPositon2 < radius){ xSpeed2 = -xSpeed2; } else if (yPositon2 > (300 - radius)) { ySpeed2 = -ySpeed2; } else if (yPositon2 < radius){ ySpeed2 = -ySpeed2; } xPositon2 += xSpeed2; yPositon2 += ySpeed2; the applet is 300 pixels by 300 pixels radius stores the radius of the circles xPositon and xPositon2 store the x cordanents for the two balls yPositon and yPositon store the y cordanents for the two balls xSpeed and xSpeed2 store the x velocities for the two balls ySpeed and ySpeed2 store the y velocities for the two balls I've only taken algebra 1 so please no advanced math or physics.

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  • How safe and reliable are C++ String Literals?

    - by DoctorT
    So, I'm wanting to get a better grasp on how string literals in C++ work. I'm mostly concerned with situations where you're assigning the address of a string literal to a pointer, and passing it around. For example: char* advice = "Don't stick your hands in the toaster."; Now lets say I just pass this string around by copying pointers for the duration of the program. Sure, it's probably not a good idea, but I'm curious what would actually be going on behind the scenes. For another example, let's say we make a function that returns a string literal: char* foo() { // function does does stuff return "Yikes!"; // somebody's feeble attempt at an error message } Now lets say this function is called very often, and the string literal is only used about half the time it's called: // situation #1: it's just randomly called without heed to the return value foo(); // situation #2: the returned string is kept and used for who knows how long char* retVal = foo(); In the first situation, what's actually happening? Is the string just created but not used, and never deallocated? In the second situation, is the string going to be maintained as long as the user finds need for it? What happens when it isn't needed anymore... will that memory be freed up then (assuming nothing points to that space anymore)? Don't get me wrong, I'm not planning on using string literals like this. I'm planning on using a container to keep my strings in check (probably std::string). I'm mostly just wanting to know if these situations could cause problems either for memory management or corrupted data.

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  • How to filter Many2Many / Generic Relations properly with Q?

    - by HWM-Rocker
    Hi, I have 3 Models, the TaggedObject has a GenericRelation with the ObjectTagBridge. And the ObjectTagBridge has a ForeignKey to the Tag Model. class TaggedObject(models.Model): """ class that represent a tagged object """ tags = generic.GenericRelation('ObjectTagBridge', blank=True, null=True) class ObjectTagBridge(models.Model): """ Help to connect a generic object to a Tag. """ # pylint: disable-msg=W0232,R0903 content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey('content_type', 'object_id') tag = models.ForeignKey('Tag') class Tag(models.Model): ... when I am attaching a Tag to an Object, I am creating a new ObjectTagBridge and set its ForeignKey tag to the Tag I want to attach. That is working fine, and I can get all Tags that I attached to my Object very easy. But when I want to get (filter) all Objects that have Tag1 and Tag2 I tried to something like this: query = Q(tags__tag=Tag1) & Q(tags__tag=Tag2) object_list = TaggedObjects.filter(query) but now my object_list is empty, because it is looking for TaggedObjects that have one ObjectTagBridge with 2 tag objects, the first with Tag1 and the second with Tag2. I my application will be more complex Q queries than this one, so I think I need a solution with this Q object. In fact any combination of binary conjunctions, like: (...) and ( (...) or not(...)) How can I filter this correctly? Every answer is welcome, maybe there is also a different way do achieve this. thx for your help!!!

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  • Where do I put the logic of my MFC program?

    - by Matthew
    I created an application core, in C++, that I've compiled into a static library in Visual Studio. I am now at the process of writing a GUI for it. I am using MFC to do this. I figured out how to map button presses to execute certain methods of my application core's main class (i.e. buttons to have it start and stop). The core class however, should always be sampling data from an external source every second or two. The GUI should then populate some fields after each sample is taken. I can't seem to find a spot in my MFC objects like CDialog that I can constantly check to see if my class has grabbed the data.. then if it has put that data into some of the text boxes. A friend suggested that I create a thread on the OnInit() routine that would take care of this, but that solution isn't really working for me. Is there no spot where I can put an if statement that keeps being called until the program quits? i.e. if( coreapp.dataSampleReady() ) { // put coreapp.dataItem1() in TextBox1 // set progress bar to coreapp.dataItem2() // etc. // reset dataSampleReady }

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  • horizontal uiview's controls unresponsive.. or how to foul up a view hierarchy

    - by Oldmicah
    Hello all, I'm working on an app that has two sections, a config section and a results section. My config section needs to be 2 separate views (horizontal and vert, and yes, I can hear the intake of breath from here), with one rotatable view for the results. b/c of layout restraints and a lot of pain around rotation, I'm not using a navigation controller. I've been experiencing the joys of rotation experimentation and have settled upon keeping my views contained as subviews of my view controller. i.e. view controller.view.subviews = configH, configV, and results. I then use the controller.view bringSubviewToFront to bring the either the configH, configV, or the result view to the front. Rotation works-queue(humor intended) the angelic choirs... almost. What's happening is that my configV button's are responsive, but when the device (or simulator) is rotated, my configH controls are not. (configV is the second subview added, but the first one to be brought to the front because app comes up in portrait mode) The controls on the results view also work. Plan B was to assign the controller.view to configH, configV, or results. All of my controls now work, but rotation is now fouled up. Question 1: Is there a better way to do this? (a horizontal and vertical config view and a rotatable results view) Question 2: Does the above suggest a design issue, or is it more likely that my addled brain is just missing something in my own code. (nothing from the peanut gallery please) many thanks!

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