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  • What is the most efficient way to handle points / small vectors in JavaScript?

    - by Chris
    Currently I'm creating an web based (= JavaScript) application thata is using a lot of "points" (= small, fixed size vectors). There are basically two obvious ways of representing them: var pointA = [ xValue, yValue ]; and var pointB = { x: xValue, y: yValue }; So translating my point a bit would look like: var pointAtrans = [ pointA[0] + 3, pointA[1] + 4 ]; var pointBtrans = { x: pointB.x + 3, pointB.y + 4 }; Both are easy to handle from a programmer point of view (the object variant is a bit more readable, especially as I'm mostly dealing with 2D data, seldom with 3D and hardly with 4D - but never more. It'll allways fit into x,y,z and w) But my question is now: What is the most efficient way from the language perspective - theoretically and in real implementations? What are the memory requirements? What are the setup costs of an array vs. an object? ... My target browsers are FireFox and the Webkit based ones (Chromium, Safari), but it wouldn't hurt to have a great (= fast) experience under IE and Opera as well...

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  • How is covariance cooler than polymorphism...and not redundant?

    - by P.Brian.Mackey
    .NET 4 introduces covariance. I guess it is useful. After all, MS went through all the trouble of adding it to the C# language. But, why is Covariance more useful than good old polymorphism? I wrote this example to understand why I should implement Covariance, but I still don't get it. Please enlighten me. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace Sample { class Demo { public delegate void ContraAction<in T>(T a); public interface IContainer<out T> { T GetItem(); void Do(ContraAction<T> action); } public class Container<T> : IContainer<T> { private T item; public Container(T item) { this.item = item; } public T GetItem() { return item; } public void Do(ContraAction<T> action) { action(item); } } public class Shape { public void Draw() { Console.WriteLine("Shape Drawn"); } } public class Circle:Shape { public void DrawCircle() { Console.WriteLine("Circle Drawn"); } } public static void Main() { Circle circle = new Circle(); IContainer<Shape> container = new Container<Circle>(circle); container.Do(s => s.Draw());//calls shape //Old school polymorphism...how is this not the same thing? Shape shape = new Circle(); shape.Draw(); } } }

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  • How to check the correct radio button.

    - by MrW
    I have a Table containing some information that I need. All these rows also contains a column with a radio button in it so that the user is suppose to be able to check one of the rows as default. When I'm bringing the data back from the DB and want to select the one that's currentlly the default one. <% foreach (var item in (IEnumerable<Locale>) ViewData["Locales"]) { %> <tr> <td> <%= Html.Encode(item.Language.Name) %> </td> <td> <input type="radio" id="defaultLocale" name="defaultLocele" value="on" checked="<%= item.Default == false ? "false" : "true" %>" /> </td> I've also tried to do this: <input type="radio" id="defaultLocale" name="defaultLocele" value="on" checked="<%=item.Default == false ? "" : "checked" %>" /> but nothing seems to do the right thing. I always end up with having the last row in checked, which it isn't for sure.

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  • Why is Excel's 'Evaluate' method a general expression evaluator?

    - by jtolle
    A few questions have come up recently involving the Application.Evaluate method callable from Excel VBA. The old XLM macro language also exposes an EVALUATE() function. Both can be quite useful. Does anyone know why the evaluator that is exposed can handle general expressions, though? My own hunch is that Excel needed to give people a way to get ranges from string addresses, and to get the value of named formulas, and just opening a portal to the expression evaluator was the easiest way. (The help for the VBA version does say its purpose it to "convert a Microsoft Excel name to an object or a value".) But of course you don't need the ability to evaluate arbitrary expressions just to do that. (That is, Excel could provide a Name.Evaluate method or something instead.) Application.Evaluate seems kind of...unfinished. It's full behavior isn't very well documented, and there are quite a few quirks and limitations (as described by Charles Williams here: http://www.decisionmodels.com/calcsecretsh.htm) with what is exposed. I suppose the answer could be simply "why not expose it?", but I'd be interested to know what design decisions led to this feature taking the form that it does. Failing that, I'd be interested to hear other hunches.

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  • How to format dates in Jahia 6 CMS?

    - by dpb
    I am helping a friend of mine put up a site for his business. I’ve read different posts and sites trying to find the ideal CMS tool, but people have different views of what is the best, so I finally just picked one of them at random. So I went for an evaluation of Jahia 6.0-CE. As you’ve probably guessed by now, I don’t have so much experience with CMS tools. I just want to setup the CMS, write the templates for the site and let my friend manage the content from there on. So I extracted the sources from SVN and went for a test drive. I managed to create some simple templates to get a hang of things but now I have an issue with a date format. In my definitions.cnd I declared the field like so: date myDateField (datetimepicker[format='dd.MM.yyyy']) This is formatted in the page and the selector also presents this in the dd.MM.yyyy format when inserting the content. But how about sites in other countries, countries that represent the date as MM.dd.yyyy for example? If I specify the format in the CND, hard coded, how can I change this later on so that it adapts based on the browser’s language? Do I extract the content from the repository and format it by hand in the JSP template based on a Locale, or is there a better way? Thank you.

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  • Concept: Information Into Memory Location.

    - by Richeve S. Bebedor
    I am having troubles conceptualizing an algorithm to be used to transform any information or data into a specific appropriate and reasonable memory location in any data structure that I will be devising. To give you an idea, I have a JPanel object instance and I created another Container type object instance of any subtype (note this is in Java because I love this language), then I collected those instances into a data structure not specifically just for those instances but also applicable to any type of object. Now my procedure for fetching those data again is to extract the object specific features similar in category to all object in that data structure and transform it into a integer data memory location (specifically as much as possible) or any type of data that will pertain to this transformation. And I can already access that memory location without further sorting or applications of O(n) time complex algorithms (which I think preferable but I wanted to do my own way XD). The data structure is of any type either binary tree, linked list, arrays or sets (and the like XD). What is important is I don't need to have successive comparing and analysis of data just to locate information in big structures. To give you a technical idea, I have to an array DS that contains JLabel object instance with a specific name "HelloWorld". But array DS contains other types of object (in multitude). Now this JLabel object has a location in the array at index [124324] (which is if you do any type of searching algorithm just to arrive at that location is conceivably slow because added to it the data structure used was an array *note please disregard the efficiency of the data structure to be used I just want to explain to you my concept XD). Now I want to equate "HelloWorld" to 124324 by using a conceptually made function applicable to all data types. So that I can do a direct search by doing this DS[extractLocation("HelloWorld")] just to get that JLabel instance. I know this may sound crazy but I want to test my concept of non-sorting feature extracting search algorithm for any data structure wherein my main problem is how to transform information to be stored into memory location of where it was stored.

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  • How can I write simulations in Erlang?

    - by rick
    Hi guys, I want to do some numerical stuff in Erlang like this: You've got an array with the following values: [2,3,4] In each iteration, you calculate 0.1 * [n-1] + 0.7 *[n] + 0.2 * [n+1] This becomes the new [n]. If n == 0 then [n-1] = 0. If [n] == length of array then [n] = 0. So I try an example: [2,3,4] calculations: 0.1 * 0 + 0.7 * 2 + 0.2 * 3 = 2 0.1 * 2 + 0.7 * 3 + 0.2 * 4 = 3.1 0.1 * 3 + 0.7 * 4 + 0.2 * 0 = 3.1 So [2,3,4] becomes to [2, 3.1, 3.1] after one iteration. I know how to write this in a non-functional language like C. But I have difficulties to imagine, how this could be done in Erlang. I found some tutorials on how you read a file to a list. So this is not the problem. How can I spawn different Erlang processes that each process has one element of the list? How can I do calculations by communicating with 'the neighbors', so that the neighbors know where their neigbors are generically, without specifying each? How can I collect the data into a list? Eventually, is it possible to solve that problem in Erlang at all? Thanks for your help.

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  • Why is T() = T() allowed?

    - by Rimo
    I believe the expression T() creates an rvalue (by the Standard). However, the following code compiles (at least on gcc4.0): class T {}; int main() { T() = T(); } I know technically this is possible because member functions can be invoked on temporaries and the above is just invoking the operator= on the rvalue temporary created from the first T(). But conceptually this is like assigning a new value to an rvalue. Is there a good reason why this is allowed? Edit: The reason I find this odd is it's strictly forbidden on built-in types yet allowed on user-defined types. For example, int(2) = int(3) won't compile because that is an "invalid lvalue in assignment". So I guess the real question is, was this somewhat inconsistent behavior built into the language for a reason? Or is it there for some historical reason? (E.g it would be conceptually more sound to allow only const member functions to be invoked on rvalue expressions, but that cannot be done because that might break some existing code.)

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  • Can I do something like this?

    - by kumar
    <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IEnumerable<StudentInfo>>" %> <% int i = 0; %> <% foreach(var e in Model){%> <div> <% if(i==0) { %> <% Html.RenderAction("student", "home", new { @et = e}); %> <% break; } %> <div> <span> <% Html.RenderAction("studentDetails", "home", new { @et = e }); %> </span> </div> </div> <%i++; } %> here my intension was to execute Renderction Student only once.. and Studentdetails should be multiple times.. but int value is allways taking i =0 bec each time page is loading its considering 0 allways.. can anybody tell me how to do this? thanks

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  • Hide div based on url

    - by Ghetto Styles
    Sorry if this is another repost. I have been attempting to find a solution but nothing works that I have tried. I am using a blog which I have full html control over. I can usually find my way around basic html but when it comes to Java or CSS I am a complete newb. Sorry, I know absolutely nothing. Now that that is out of the way. I have two sidebar div's that I am trying to hide on one specific url to utilize more space for a content iframe. This is one of the coded I have tried to use which doesn't seem to work or I am missing something. <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <script language="text/javascript" <?php &#36;(function(){ if (window.location.search === "mywebsite/Videos.html") { &#36;('#navleft').hide(); } else { &#36;('#navleft').show(); } }); ?> </script> Please remember I do not know anything when it comes to php or java. I want to do this for both #navright and #navleft. Also this is in the CSS section. Thanks for any help!! #navright{ width: 200px; } #navleft{ width: 200px; } #content{ margin:0px; }

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  • dynamically insert new rows in the table (JavaScript) ?

    - by Karandeep Singh
    <script type="text/javascript" language="javascript"> function addNewRow() { var table = document.getElementById("table1"); var tr = table.insertRow(); var td = tr.insertCell(); td.innerHTML= "a"; td = tr.insertCell(); td.innerHTML= "b"; td = tr.insertCell(); td.innerHTML= "c"; td = tr.insertCell(); td.innerHTML= "d"; td = tr.insertCell(); td.innerHTML= "e"; } </script> <body> <table id="table1" border="1" cellpadding="0" cellspacing="0" width="100%"> <tr id="row1"> <td>1</td> <td>2</td> <td>3</td> <td>4</td> <td>5</td> </tr> </table> <input type="button" onClick="addNewRow()" value="Add New"/> </body> This example is for dynamically insert new row and cells in the table. But its behavior is different in all browsers. Internet Explorer = It add row in the last and new added cells are starts from first. Chrome/Safari = It add new row in the first and new added cells are starts from end. Mozilla Firefox = It is not working. Sir, I want new added row in the last and new added cells starts from first like(Interner Explorer) in all browsers. If you have any solution for same behavior please tell me. Thanks,

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  • Ajax post failing in asp

    - by Dave Kiss
    hey guys, this might be really stupid, but hopefully someone can help. I'm trying to post to an external script using ajax so i can mail the data, but for some reason my data is not making it to the script. $(document).ready(function() { $("#submitContactForm").click(function () { $('#loading').append('<img src="http://www.xxxxxxxx.com/demo/copyshop/images/loading.gif" alt="Currently Loading" id="loadingComment" />'); var name = $('#name').val(); var email = $('#email').val(); var comment = $('#comment').val(); var dataString = 'name='+ name + '&email=' + email + '&comment=' + comment; $.ajax({ url: 'http://www.xxxxx.com/demo/copyshop/php/sendmail.php', type: 'POST', data: '?name=Dave&[email protected]&comment=hiiii', success: function(result) { $('#loading').append('success'); } }); return false; }); }); the php script is simple (for now - just wanted to make sure it worked) <?php $name = $_POST['name']; $email = $_POST['email']; $comment = $_POST['comment']; $to = '[email protected]'; $subject = 'New Contact Inquiry'; $message = $comment; mail($to, $subject, $message); ?> the jquery is embedded in an .aspx page (a language i'm not familiar with) but is posting to a php script. i'm receiving emails properly but there is no data inside. am i missing something? i tried to bypass the variables in this example, but its still not working thanks

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  • Send string from java (or other platform) to application

    - by MrSnowflake
    I want to send a barcode, read with my cellphone, to my computer. My computer has a simple server running, which listens to barcodes. When a barcode arrives, the server app should be able to input the value of the received barcode into the active application (I don't really care which application is going to get the input, the user should be able to select gedit, a terminal window or the browser if they choose to). My language at the moment is Java on GNU/Linux (Ubuntu), so I know about the Robot class. But the Robot class emulates a keyboard, which means: when you send VK_1 on a US keyboard layout, the output is '1' indeed, but when you send VK_1 on another layout (like belgian, which I use), which requires shift for the '1' key, the output is '&' (this is the character on the '1' key, when you don't hold shift). I also found xsendkeys, but this application too requires you to specify whether you need to hold shift. So it will be able to send an 'a' but for an 'A' (thus capital) you need to specify you want to hold shift with your 'a'. Isn't there an easy way to do this, for GNU/Linux and Windows, just using strings. I want to be able to send "12a68dd" to the active application. And I also would like to be able to send UTF-8 characters to the active application. I have been looking for a solution, but most require the breakdown in multiple keystrokes, which are often dependent on the keyboard layout.

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  • UTF-8 support in java application

    - by jacekn
    I'm having trouble with UTF-8. common.jsp <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> typical.jsp <%@ include file="common.jsp" %> Page Head <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> Form <form id="screenObject" accept-charset="UTF-8" action="/SiteAdmin/articleHeaderEdit?articleId=15" method="post"> I enter non latin1 characters into a text field and click Save. Validator complains about another field and stops the submission. This never gets to the database, so database ability to handle UTF-8 is not in this picture. The page redisplays with appropriate error but the text that had been entered is all messed up. All non latin1 characters are converted to some gibberish. I'm using Spring 3 MVC, in case that matters... Attempts Adding this to my view resolver didn't help: <property name="contentType" value="text/html;charset=UTF-8" />

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  • JavaScript Load New Page Question

    - by Michael
    What I am looking to do is if a user complete a form it will provide access to a new location. <script language="JavaScript" type="text/javascript"> <!-- function validateForm(theForm) { var firstname = theForm.firstname.value; var lastname = theForm.lastname.value; var email = theForm.email.value; if (firstname == "") { alert("Please fill in your First Name."); theForm.firstname.focus(); return false; } if (lastname == "") { alert("Please fill in your Last Name."); theForm.lastname.focus(); return false; } if (email == "") { alert("Please fill in your email address."); theForm.email.focus(); return false; } return true; } I know this part is wrong but I have no idea how to go about doing it. any help would be nice.. if lastname="" if firstname="" if email="" load('www.google.com');

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  • How do I access a value of a nested Perl hash?

    - by st
    I am new to Perl and I have a problem that's very simple but I cannot find the answer when consulting my Perl book. When printing the result of Dumper($request); I get the following result: $VAR1 = bless( { '_protocol' => 'HTTP/1.1', '_content' => '', '_uri' => bless( do{\(my $o = 'http://myawesomeserver.org:8081/counter/')}, 'URI::http' ), '_headers' => bless( { 'user-agent' => 'Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.4) Gecko/20080528 Epiphany/2.22 Firefox/3.0', 'connection' => 'keep-alive', 'cache-control' => 'max-age=0', 'keep-alive' => '300', 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'accept-language' => 'en-us,en;q=0.5', 'accept-encoding' => 'gzip,deflate', 'host' => 'localhost:8081', 'accept-charset' => 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' }, 'HTTP::Headers' ), '_method' => 'GET', '_handle' => bless( \*Symbol::GEN0, 'FileHandle' ) }, 'HTTP::Server::Simple::Dispatched::Request' ); How can I access the values of '_method' ('GET') or of 'host' ('localhost:8081'). I know that's an easy question, but Perl is somewhat cryptic at the beginning.

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  • Javascript get image height works in all browsers but firefox...please help?

    - by Calvin
    So I am fairly new to Javascript (a lot of experience in PHP), but I have this basic script that checks a link that redirects to a URL to see what the image height is. If it is a certain height then it adds one to a variable, otherwise nothing. I would easily do this in PHP but the images are on other servers and not my own so it doesn't work. Anyways, ehre is the script. Let me know if you have any tips. Works well and tested in Chrome, Safari, Opera, and IE. <script language='JavaScript'> window.onload = function() { var nstar = 0, urls = []; urls[0] = "http://optout.imiclk.com/cgi/nai_status.cgi?nocache="; urls[1] = "http://www.adbrite.com/mb/nai_optout_check.php?nocache="; urls[2] = "http://events.adchemy.com/visitor/auuid/nai-status?nocache="; function getImgSize(imgSrc){ var newImg = new Image(); newImg.src = imgSrc; return{height:newImg.height, width:newImg.width} } for(i=0,length=urls.length;i<length;i++){ if(getImgSize(urls[i]).height==43){nstar++;} } document.getElementById('tracknum').innerHTML = "<b>" + nstar + "</b>"; } </script>

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  • Adding new records in Access without wrecking the form

    - by Matt Parker
    I'm working on a simple Access 2003 application to keep track of things that need to be done for clients for some colleagues. Each colleague has a set of clients, and each client has a set of actions that need to be taken by a certain date. I've set up a form that consists of a combobox for client ID (indexed), a drop-down for the person who is handling that client's case, and a button for adding new clients (a standard Access-created Add Record button). The actions are listed in a subform below these three elements. The problem I've run into is that the first person I tested this on clicked the button to add a new record, then didn't fill it out and tried to select another client from the drop-down list. Access interprets this as an attempt to set the selected Client ID as the ID for the new record and rightfully throws an error for duplicate primary keys. I can think of a couple of ways around this problem, but I'd much rather hear your elegant solutions than kludge together some junk in a language I don't know. Let me know if you have any questions. Thank you.

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  • How do I import facebook friends from another website

    - by Jim Zimmerman
    I am looking for a way to connect to facebook by allowing the user to enter in their username and password and have our app connect to their account and get their contacts so that they can invite them to join their group on our site. I have written a facebook app before, but this is not an app as much as it is a connector so that they can invite all their friends or just some to the site we are working on. I have seen several other sites do this and also connect to Yahoo, Gmail and Hotmail contacts. I dont think they are using Facebook Connect to do this since it is so new, but they may be. Any solution in any language is fine as I can port whatever example to use C#. I cannot find anything specifically on Google or Facebook to address this specific problem. Any help is appreciated. I saw a first answer get removed that had suggested i might need to scrape the friends page. The more I look around, this might be what i need to do. Any other way i think will require the person to add it as an app. I am wondering how a answer can get removed, maybe that user deleted it.

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  • Passing data to a jQuery click() function

    - by jakenoble
    Hi I have a simple span like so <span class="action removeAction">Remove</span> This span is within a table, each row has a remove span. And then I call a URL using AJAX when that span is clicked. The AJAX event needs to know the ID of the object for that row? What is the best way of getting that ID into the click function? I thought I could do something like this <span class="action removeAction" id="1">Remove</span> But an ID should not start with a number? Right? Then I thought I could do <span class="action removeAction" id="my1">Remove</span> Then just strip the 'my' part from the ID, but that just seems Yuk! Below is my click event and where my AJAX event is. <script type="text/javascript" language="text/javascript"> $(document).ready(function() { $(".removeAction").click(function() { //AJAX here that needs to know the ID } }); </script> I am sure there is a nice way of doing this? Thanks. Jake.

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  • selecting text by ignoring inner Elements of div tag javascript

    - by sugar
    <html> <body> <script language="javascript"> function getSelectionHTML() { var div = document.getElementById("myDiv").childNodes; if (document.createRange) { var textNode=div.firstChild; var rangeObj=document.createRange(); rangeObj.setStart(textNode,0); rangeObj.setEnd(textNode,10); selRange.collapse(true); var elem = document.getElementById('myDiv') elem .innerHTML = elem .innerHTML.replace(rangeObj.toString(), '<span style="background-color: lime">'+rangeObj.toString()+'</span>') } } </script> <div id="myDiv"> asdf as<b>dfas df asf asdf sdfjk dvh a sjkh jhcdjkv</b> iof scjahjkv ahsjv hdjk biud fcsvjksdhf k </div> <form name="aform"> <input type="button" value="Get selection" onclick="getSelectionHTML()"> </body> </html> Ok. Let me explain - getSelectionHTML() method is for selection of characters from 0 to 10. I am getting the values by "myDiv" id. but inner bold, italic & other tags are putting me in trouble. In simple words, I just want to make selection of first ten characters (& apply them span tag) which are in "myDiv" tag. What exactly I am missing ? Can anyone help me ? Thanks in advance for sharing your knowledge. Sagar.

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  • Alignment for image display on hover works only in IE7?

    - by Ram
    Hello, I tried to display a image when a mouseover on text occurs. It works fine. And the alignment of the image should be shown such that the end of the image should be at the container. It works fine with the code shown below, Only in IE7. In everything, it gets chopped off.. What is wrong here? <td valign="middle" class="table_td td" style="width: 347px"> <span class="feature_text" style="cursor:pointer" onmouseover="ShowPicture('Style16',1)" onmouseout="ShowPicture('Style16',0)" id="a16"> Storefront Window Decal</span> <div id="Style16" style="position:relative;height:0px;left:50%;bottom:700%; visibility:hidden; border:solid 0px #CCC; padding:5px"> <img src="images/window-decal-image.gif"></div> <script language="javascript" type="text/javascript"> function ShowPicture(id,Source) { var vis, elem; if (1 == Source) { vis = "visible"; } else if (0 == Source) { vis = "hidden"; } else { throw new RangeError("Unknown Flag"); } if (elem = document.getElementById(id)) { elem.style.visibility = vis; } else { throw new TypeError("Element with id '"+id+"' does not exist."); } return vis; } </script> Can someone help me out. Thanks in advance!!

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  • What is better for a student programming in C++ to learn for writing GUI: C# vs QT?

    - by flashnik
    I'm a teacher(instructor) of CS in the university. The course is based on Cormen and Knuth and students program algorithms in C++. But sometimes it is good to show how an algorithm works or just a result of task through GUI. Also in my opinion it's very imporant to be able to write full programs. They will have courses concerning GUI but a three years, later, in fact, before graduatuion. I think that they should be able to write simple GUI applications earlier. So I want to teach them it. How do you think, what is more useful for them to learn: programming GUI with QT or writing GUI in C# and calling unmanaged C++ library? Update. For developing C++ applications students use MS Visual studio, so C# is already installed. But QT AFAIK also can be integrated into VS. I have following pros of C# (some were suggested there in answers): The need to make an additional layer. It's more work, but it forces you explicitly specify contract between GUI and processing data. The border between GUI and algorithms becomes very clear. It's more popular among employers. At least, in Russia where we live. It's rather common to write performance-critical algorithms in C++ and PInvoke them from well-looking C# application/ASP.Net website. Maybe it is not so widespread in the rest of the world but in Russia Windows is very popular, especially in companies and corporations due to some reasons, so most of b2b applications are Windows applications. Rapid development. It's much quicker to code in .Net then in C++ due to many reasons. And the con is that it's a new language with own specific for students. And the mess with invoking calls to library.

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  • Is it not possible to make a C++ application "Crash Proof"?

    - by Enno Shioji
    Let's say we have an SDK in C++ that accepts some binary data (like a picture) and does something. Is it not possible to make this SDK "crash-proof"? By crash I primarily mean forceful termination by the OS upon memory access violation, due to invalid input passed by the user (like an abnormally short junk data). I have no experience with C++, but when I googled, I found several means that sounded like a solution (use a vector instead of an array, configure the compiler so that automatic bounds check is performed, etc.). When I presented this to the developer, he said it is still not possible.. Not that I don't believe him, but if so, how is language like Java handling this? I thought the JVM performs everytime a bounds check. If so, why can't one do the same thing in C++ manually? UPDATE By "Crash proof" I don't mean that the application does not terminate. I mean it should not abruptly terminate without information of what happened (I mean it will dump core etc., but is it not possible to display a message like "Argument x was not valid" etc.?)

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  • Does using functional languages help against computing values repeatedly?

    - by sharptooth
    Consider a function f(x,y): f(x,0) = x*x; f(0,y) = y*(y + 1); f(x,y) = f(x,y-1) + f(x-1,y); If one tries to implement that recursively in some language like C++ he will encounter a problem. Suppose the function is first called with x = x0 and y = y0. Then for any pair (x,y) where 0 <= x < x0 and 0 <= y < y0 the intermediate values will be computed multiple times - recursive calls will form a huge tree in which multiple leaves will in fact contain the same pairs (x,y). For pairs (x,y) where x and y are both close to 0 values will be computed numerous times. For instance, I tested a similar function implemented in C++ - for x=20 and y=20 its computation takes about 4 hours (yes, four Earth hours!). Obviously the implementation can be rewritten in such way that repeated computation doesn't occur - either iteratively or with a cache table. The question is: will functional languages perform any better and avoid repeated computations when implementing a function like above recursively?

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