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• C++ operator new, object versions, and the allocation sizes

  - by mizubasho

  Hi. I have a question about different versions of an object, their sizes, and allocation. The platform is Solaris 8 (and higher). Let's say we have programs A, B, and C that all link to a shared library D. Some class is defined in the library D, let's call it 'classD', and assume the size is 100 bytes. Now, we want to add a few members to classD for the next version of program A, without affecting existing binaries B or C. The new size will be, say, 120 bytes. We want program A to use the new definition of classD (120 bytes), while programs B and C continue to use the old definition of classD (100 bytes). A, B, and C all use the operator "new" to create instances of D. The question is, when does the operator "new" know the amount of memory to allocate? Compile time or run time? One thing I am afraid of is, programs B and C expect classD to be and alloate 100 bytes whereas the new shared library D requires 120 bytes for classD, and this inconsistency may cause memory corruption in programs B and C if I link them with the new library D. In other words, the area for extra 20 bytes that the new classD require may be allocated to some other variables by program B and C. Is this assumption correct? Thanks for your help.

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• SharePoint Item Event Receivers and Site Creation

  - by Michael Edwards

  I have created an Item Event Receiver for a document library and I have test that the logic works correctly and it all does. The next thing I wanted to do is automatically create the list when a site is created so I added the list to the ONET.xml file for the site: <Lists> <List Title="Documents" Description="Documents " url="MyDocumentLibrary" Type="10002" FeatureId="CFD8504D-70EB-4ba2-9CCB-52E38DB39E60" QuickLaunchUrl="Docs/AllItems.aspx" /> </Lists> And I ensure that the feature for this list is also activated be adding the feature to the <WebFeatures> <Feature ID="CFD8504D-70EB-4ba2-9CCB-52E38DB39E60" /> </WebFeatures> The problem occurs after I create the site, when I add a document to the list the Item Event Receiver does not run. However if I manually for to the web site features and deactivate and then reactivate the feature the Item Event Receiver does run. It seems that when creating a list through the ONET.xml and activating the feature it does not bind the Item Event Receiver to the list. What is the work around for this? Is this a bug?

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• Using same onmouseover function for multiple objects

  - by phpscriptcoder

  I'm creating a building game in JavaScript and PHP that involves a grid. Each square in the grid is a div, with an own onmouseover and onmousedown function: for(x=0; x < width; x++) { for(y=0; y < height; y++) { var div = document.createElement("div"); //... div.onmouseclick = function() {blockClick(x, y)} div.onmouseover = function() {blockMouseover(x, y)} game.appendChild(div); } } But, all of the squares seem to have the x and y of the last square that was added. I can sort of see why this is happening - it is making a pointer to x and y instead of cloning the variables - but how could I fix it? I even tried for(x=0; x < width; x++) { for(y=0; y < height; y++) { var div = document.createElement("div"); var myX = x; var myY = y; div.onmouseclick = function() {blockClick(myX, myY)} div.onmouseover = function() {blockMouseover(myX, myY)} game.appendChild(div); } } with the same result. I was using div.setAttribute("onmouseover", ...) which worked in Firefox, but not IE. Thanks!

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• Mmap and structure

  - by blid..pl

  I'm working some code including communication between processes, using semaphores. I made structure like this: typedef struct container { sem_t resource, mutex; int counter; } container; and use in that way (in main app and the same in subordinate processes) container *memory; shm_unlink("MYSHM"); //just in case fd = shm_open("MYSHM", O_RDWR|O_CREAT|O_EXCL, 0); if(fd == -1) { printf("Error"); exit(EXIT_FAILURE); } memory = mmap(NULL, sizeof(container), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); ftruncate(fd, sizeof(container)); Everything is fine when I use one of the sem_ functions, but when I try to do something like memory->counter = 5; It doesn't work. Probably I got something wrong with pointers, but I tried almost everything and nothing seems to work. Maybe there's a better way to share variables, structures etc between processes ? Unfortunately I'm not allowed to use boost or something similiar, the code is for educational purposes and I'm intentend to keep as simple as it's possible.

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• Trying to work with a multi-value array in LotusScript and sort of stuck

  - by rrumaner

  I have to find a way to store a series of variables - MonthYear (the key) and a counter. The purpose of this is to track the number of documents processed by Month & Year. I was thinking of a list but I am not sure how to save the data so that it is readable and able to be shown in a table at a later date. I thought about using a multi-dimensional array - someArray(1,0 to 1) and ReDim'ing it each time I start a new MonthYear and then save it back to a field on the document but am not sure how that is going to play out. Does anyone have an idea of how I can accomplish this? The first dimension will be the MonthYear (key) and the second will be a counter that is updated every time a new document is processed. The key will be based on a field on the document being processed. How can I make sure I am updating the right key/counter combination? How can I retrieve the existing counter from the field on the document, update the counter and then replace the value? I thought about just adding a new element (ReDim) every time a document is processed and than somehow adding up all the counters for each key and storing that in an array, but that just seems real messy. There has to be a good way to do this. Any and all ideas will be greatly appreciated

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• ListCtrl - wxPython / Python

  - by Francisco Aleixo

  Hello everyone. My question is if we can assign/bind some value to a certain item and hide that value(or if we can do the same thing in another way). Example: Lets say the columns on ListCtrl are "Name" and "Description": self.lc = wx.ListCtrl(self, -1, style=wx.LC_REPORT) self.lc.InsertColumn(0, 'Name') self.lc.InsertColumn(1, 'Description') And when I add a item I want them to show the Name parameter and the description: num_items = self.lc.GetItemCount() self.lc.InsertStringItem(num_items, "Randomname") self.lc.SetStringItem(num_items, 1, "Some description here") Now what I want to do is basically assign something to that item that is not shown so I can access later on the app. So I would like to add something that is not shown on the app but is on the item value like: hiddendescription = "Somerandomthing" Still didn't undestand? Well lets say I add a button to add a item with some other TextCtrls to set the parameters and the TextCtrls parameters are: "Name" "Description" "Hiddendescription" So then the user fills this textctrls out and clicks the button to create the item, and I basically want only to show the Name and Description and hide the "HiddenDescription" but to do it so I can use it later. Sorry for explaining more than 1 time on this post but I want to make sure you understand what I pretend to do.

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• C# Minimize all running windows when application runs

  - by Derek

  I am working on a C# windows form application. How can i edit my code in a way that when more than 2 faces is being detected by my webcam. More information: When "FaceDetectedLabel.Text = "Faces Detected : " + cam.facesdetected.ToString();" becomes Face Detected: 2 or more... How can i do the following: Minimize all program running except my application. Log out of my computer Here is my code: namespace PBD { public partial class MainPage : Form { //declaring global variables private Capture capture; //takes images from camera as image frames public MainPage() { InitializeComponent(); } private void ProcessFrame(object sender, EventArgs arg) { Wrapper cam = new Wrapper(); //show the image in the EmguCV ImageBox WebcamPictureBox.Image = cam.start_cam(capture).Resize(390, 243, Emgu.CV.CvEnum.INTER.CV_INTER_CUBIC).ToBitmap(); FaceDetectedLabel.Text = "Faces Detected : " + cam.facesdetected.ToString(); } private void MainPage_Load(object sender, EventArgs e) { #region if capture is not created, create it now if (capture == null) { try { capture = new Capture(); } catch (NullReferenceException excpt) { MessageBox.Show(excpt.Message); } } #endregion Application.Idle += ProcessFrame; }

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• C++ ofstream cannot write to file....

  - by user69514

  Hey I am trying to write some numbers to a file, but when I open the file it is empty. Can you help me out here? Thanks. /** main function **/ int main(){ /** variables **/ RandGen* random_generator = new RandGen; int random_numbers; string file_name; /** ask user for quantity of random number to produce **/ cout << "How many random number would you like to create?" << endl; cin >> random_numbers; /** ask user for the name of the file to store the numbers **/ cout << "Enter name of file to store random number" << endl; cin >> file_name; /** now create array to store the number **/ int random_array [random_numbers]; /** file the array with random integers **/ for(int i=0; i<random_numbers; i++){ random_array[i] = random_generator -> randInt(-20, 20); cout << random_array[i] << endl; } /** open file and write contents of random array **/ const char* file = file_name.c_str(); ofstream File(file); /** write contents to the file **/ for(int i=0; i<random_numbers; i++){ File << random_array[i] << endl; } /** close the file **/ File.close(); return 0; /** END OF PROGRAM **/ }

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• Multiple ajax request and progress bar

  - by hunt

  Hi, In a following piece of code i am create a progress bar and showing its progress as the ajax request get processed. i am faking the progress shown here just by adding 5 in to cnt counter variable after that i made a check when counter reach to 90. at this point if the request is not executed successfully then i will pause/disable the progress bar and whenever response come i will complete the whole progress bar with 100. now the problem is i want to add multiple progress bar as i am firing multiple ajax request. so following is the code to implement only for one request and one progress bar but i want it for more than one. as global variables are used over here for checking response and timer id so i don't know how well i can handle it for multiple request var cnt=0; var res=null; function getProgress(data){ res=data; } var i =0; $('#start').click(function(){ i = setInterval(function() { if(res!=null) { clearInterval(i); $("#pb1").progressbar( "option", "value", cnt=cnt+100 ); } var value = $("#pb1").progressbar("option", "value"); if(value >=90 && res==null){ $("#pb1").progressbar("option", "disable"); } else{ $("#pb1").progressbar( "option", "value", cnt=cnt+5 ); } },2500); $.ajax({ url: 'http://localhost/beta/demo.php', success: getProgress }); }); $("#pb1").progressbar({ value: 0 , change: function(event, ui) { if(res!=null) clearInterval(i); } });

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• Change classloader

  - by Chris

  I'm trying to switch the class loader at runtime: public class Test { public static void main(String[] args) throws Exception { final InjectingClassLoader classLoader = new InjectingClassLoader(); Thread.currentThread().setContextClassLoader(classLoader); Thread thread = new Thread("test") { public void run() { System.out.println("running..."); // approach 1 ClassLoader cl = TestProxy.class.getClassLoader(); try { Class c = classLoader.loadClass("classloader.TestProxy"); Object o = c.newInstance(); c.getMethod("test", new Class[] {}).invoke(o); } catch (Exception e) { e.printStackTrace(); } // approach 2 new TestProxy().test(); }; }; thread.setContextClassLoader(classLoader); thread.start(); } } and: public class TestProxy { public void test() { ClassLoader tcl = Thread.currentThread().getContextClassLoader(); ClassLoader ccl = ClassToLoad.class.getClassLoader(); ClassToLoad classToLoad = new ClassToLoad(); } } (it is not relevant what the InjectingClassLoader is) I'd like to make the result of "approach 1" and "approach 2" exactly same, but it looks like thread.setContextClassLoader(classLoader) does nothing and the "approach 2" always uses the system classloader (can be determined by comparing tcl and ccl variables while debugging). Is it possible to make all classes loaded by new thread use given classloader?

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• FFMEPG permission problem, is there any alternative solution instead of FFMPEG?

  - by caglaror

  We have some kind of permenant permission problem on FFMPEG.exe to write JPEG file on to HDD. We are using IIS and try all permission methods to ffmepg.exe, its including folder,folders, cmd.exe and any executable file, related folder, file. Also we tried many many command examples. But never went beyond the "permission denied" error messages. We give up. Do you know another alternative solution to pick images from flv, f4v movie files? Or %100 quaranteed method to achive this permission control on IIS? Thank you. ---last code we try variables etc. aren't shown here. jpegYapKomutu = videoEditorKlasoru &"\ffmpeg.exe -i " & videoEditorKlasoru & "\deneme.flv" &" -s 480×360 -ss 00:00:"&saniyesi&" -vframes 1 -f mjpeg "& "C:\Webhome\normworks\caglarorhan\deneme.jpg" WScript.Run "%COMSPEC% /C dir" & jpegYapKomutu

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• Anchor tags are blank

  - by ryanday

  I'm having a problem where the my anchor tags sometimes aren't displaying their links. This is happening on Mobile Safari on multiple iPhones, and in the iPhone simulator. I'm using jQtouch r147, PhoneGap, and jQuery 1.4.2. I'm generating the data from a database call, and adding anchor tags to a list like this: for(var i=0;i<data.rows.length;i++) { var item = $('<li></li>'); var name = data.rows.item(i).name; var anchor = $('<a href="#lpage">'+name+'</a>'); item.addClass('arrow'); // This line always displays the name, even when I can't see // the name in the browser debug.log('The name: ' + name); (function(info) { anchor.bind('tap', function(e) { debug.log('Touch start ' + info.id); }); })(data.rows.item(i)); item.append(anchor); if( anchor.html() == null ) { debug.log('html is blank'); } $('#myUL').append(item); } Sometimes my list of names shows fine(http://imagebin.org/101462), and sometimes it is just blank(http://imagebin.org/101464). When the list is blank, I see the debug.log() line show me 'html is blank', and I also see the log line show me that the variable 'name' does, in fact, contain a valid name. When I check for anchor.html() == null, I've also tried to .remove() the anchor tag, and re-create it. But it always comes back without the name displayed. This happens on the mobile device and in the simulator, but I've never seen it happen in Safari or in Chrome. Has anyone seen something like this? I can't find the cause, and I can't get it to stop. Thank you for any ideas or suggestions!

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• Struts2 Converting Enum Array fills array with single null value

  - by Kyle Partridge

  For a simple action class with these member variables: ... private TestConverterEnum test; private TestConverterEnum[] tests; private List<TestConverterEnum> tList; ... And a simple enum: public enum TestConverterEnum { A, B, C; } Using the default struts2 enum conversion, when I send the request like so: TestConterter.action?test=&tests=&tList=&b=asdf For test I get a null value, which is expected. For the Array and List, however, I get and Array (or list) with one null element. Is this what is expected? Is there a way to prevent this. We recently upgraded our struts2 version, and we had our own converters, which also don't work in this case, so I was hoping to use the default conversion method. We already have code that is validating these arrays for null and length, and I don't want to have to add another condition to these branches. Is there a way to prevent this bevavior?

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• diffuculty in appending images dynamically in an Custom List View

  - by ganesh

  Hi I have written an custom List view which binds images according to the result from a feed @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder; if (convertView == null) { convertView = mInflater.inflate(R.layout.row_for_stopnames, null); holder = new ViewHolder(); holder.name = (TextView)convertView.findViewById(R.id.stop_name); holder.dis = (TextView)convertView.findViewById(R.id.distance); holder.route_one=(ImageView)convertView.findViewById(R.id.one); holder.route_two=(ImageView)convertView.findViewById(R.id.two); holder.route_three=(ImageView)convertView.findViewById(R.id.three); convertView.setTag(holder); } else { holder = (ViewHolder) convertView.getTag(); } holder.name.setText(elements.get(position).get("stop_name")); holder.dis.setText(elements.get(position).get("distance")); String[] route_txt=elements.get(position).get("route_name").split(","); for(int i=0;i<route_txt.length;i++) { if(i==0) { holder.route_one.setBackgroundResource(Utils.getRouteImage().get(stop_txt[0])); } else if(i==1) { holder.route_two.setBackgroundResource(Utils.getRouteImage().get(stop_txt[1])); } else if(i==2) { holder.route_three.setBackgroundResource(Utils.getRouteImage().get(stop_txt[2])); } } convertView.setOnClickListener(new OnItemClickListener(position,elements)); return convertView; } class ViewHolder { TextView name; TextView dis; ImageView route_one; ImageView route_two; ImageView route_three; } for every stop name there may be route_names, maximum of three routes.I have to bind images according to the number of route names.This is what I tried to do by the above code .This works fine until I start scrolling up and down .When I do so the route images gets displayed where it does not want to be,this behaviour is unpredictable.I will be glad if someone explain me why this happens,and the best way to do this.The getRouteImage method of Utils class returns HashMap with key String and value a drawable

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• memcache is not storing data accross requests

  - by morpheous

  I am new to using memcache, so I may be doing something wrong. I have written a wrapper class around memcache. The wrapper class has only static methods, so is a quasi singleton. The class looks something like this: class myCache { private static $memcache = null; private static $initialized = false; public static function init() { if (self::$initialized) return; self::$memcache = new Memcache(); if (self::configure()) //connects to daemon { self::store('foo', 'bar'); } else throw ConnectionError('I barfed'); } public static function store($key, $data, $flag=MEMCACHE_COMPRESSED, $timeout=86400) { if (self::$memcache->get($key)!== false) return self::$memcache->replace($key, $data, $flag, $timeout); return self::$memcache->set($key, $data, $flag, $timeout); } public static function fetch($key) { return self::$memcache->get($key); } } //in my index.php file, I use the class like this require_once('myCache.php'); myCache::init(); echo 'Stored value is: '. myCache::fetch('foo'); The problem is that the myCache::init() method is being executed in full everytime a page is requested. I then remembered that static variables do not maintain state accross page requests. So I decided instead, to store the flag that indicates whether the server contains the start up data (for our purposes, the variable 'foo', with value 'bar') in memcache itself. Once the status flag is stored in memcache itself, It solves the problem of the initialisation data being loaded for every page request (which quite frankly, defeats the purpose of memcache). However, having solved that problem, when I come to fetch the data in memcache, it is empty. I dont understand whats going on. Can anyone clarify how I can store my data once and retrieve it accross page requests? BTW, (just to clarify), the get/set is working correctly, and if I allow memcache to load the initialisation data for each page request, (which is silly), then the data is available in memcache.

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• Creating has_many :through records 2x times

  - by antiarchitect

  I have models class Question < ActiveRecord::Base WEIGHTS = %w(medium hard easy) belongs_to :test has_many :answers, :dependent => :destroy has_many :testing_questions end class Testing < ActiveRecord::Base belongs_to :student, :foreign_key => 'user_id' belongs_to :subtest has_many :testing_questions, :dependent => :destroy has_many :questions, :through => :testing_questions end So when I try to bind questions to testing on it's creation: >> questions = Question.all ... >> questions.count => 3 >> testing = Testing.create(:user_id => 3, :subtest_id => 1, :questions => questions) Testing Columns (0.9ms) SHOW FIELDS FROM `testings` SQL (0.1ms) BEGIN SQL (0.1ms) COMMIT SQL (0.1ms) BEGIN Testing Create (0.3ms) INSERT INTO `testings` (`created_at`, `updated_at`, `user_id`, `subtest_id`) VALUES('2010-05-18 00:53:05', '2010-05-18 00:53:05', 3, 1) TestingQuestion Columns (0.9ms) SHOW FIELDS FROM `testing_questions` TestingQuestion Create (0.3ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(1, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) TestingQuestion Create (0.4ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(2, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) TestingQuestion Create (0.3ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(3, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) TestingQuestion Create (0.3ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(1, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) TestingQuestion Create (0.3ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(2, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) TestingQuestion Create (0.3ms) INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(3, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31) SQL (90.2ms) COMMIT => #<Testing id: 31, subtest_id: 1, user_id: 3, created_at: "2010-05-18 00:53:05", updated_at: "2010-05-18 00:53:05"> There is 6 SQL queries and 6 records in testing_questions are created. Why?

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• Effective Method to Manage and Search Through 100,000+ Objects Instantly? (C#)

  - by Kirk

  I'm writing a media player for enthusiasts with large collections (over 100,000 tracks) and one of my main goals is speed in search. I would like to allow the user to perform a Google-esque search of their entire music collection based on these factors: Song Path and File Name Items in ID3 Tag (Title, Artist, Album, etc.) Lyrics What is the best way for me to store this data and search through it? Currently I am storing each track in an object and iterating over an array of these objects checking each of their variables for string matches based on given search text. I've run into problems though where my search is not effective because it is always a phrase search and I'm not sure how to make it more fuzzy. Would an internal DB like SQLlite be faster than this? Any ideas on how I should structure this system? I also need playlist persistence, so that when they close the app and open the app their same playlist loads immediately. How should I store the playlist information so it can load quickly when the application starts? Currently I am JSON encoding the entire playlist, storing it in a text file, and reading it into the ListView at runtime, but it is getting sluggish over 20,000 tracks. Thanks!

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• How to retrieve checkboxlist values in the controller in asp.net mvc

  - by sukumar

  I am having a form in a view page that looks as below: <form runat="server" id="dcrsubmit"> <asp:CheckBoxList ID="CheckBoxList1" runat="server"> <asp:ListItem>test1</asp:ListItem> <asp:ListItem>test2</asp:ListItem> <asp:ListItem>test3</asp:ListItem> <asp:ListItem>test4</asp:ListItem> <asp:ListItem>test5</asp:ListItem> <asp:ListItem>test6</asp:ListItem> </asp:CheckBoxList> ....other controls </form> Now when the form is posted, I am trying to retrieve the values submitted in the controller as below: [AcceptVerbs(HttpVerbs.Post)] public ActionResult testmethod(FormCollection formValues) { string s = formvalues.get("CheckBoxList1"); . . /* other code */ . } The string value shows null when I submit the form by checking some checkboxes. Is this the way to retrieve the values or am I doing something wrong? And I cannot use html control because all other controls on the form are server controls and I am not sure if I can only make this control a html control. And I am not sure how can I bind the values to it?

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• InvalidCastException when getting Text from a Label referenced by dynamicaly built String, Fix?

  - by Chris

  NET Version: 3.5 Ok, I recieve an error (System.InvalidCastException was unhandled. Message="Unable to cast object of type 'System.Windows.Forms.Control[]' to type 'System.Windows.Forms.Label'.") when trying to get Text from a Label referenced by a dynamicly built string. Here's my situation; I have an array of 250 labels named l1 - l250. What I want to do is loop through them using this while statement: int c = 1; while (c < 251) { string k = "l" + c.ToString(); //dynamic name of Control(Label) object ka = Controls.Find(k, true); string ct = ((Label)ka).Text; //<<Error Occurs Here build = build + ct; c++; } and get the text value of each to build a string named build. I don't get any build errors, just this while debuging. While debuging I can go down to view my local variables. When looking through these, I can view the contents of object ka; it does contain the correct Text value of the correct Label I want to "access". I just don't understand how to get there. The text value is listed under "[0]" which is the only subcatagory for "ka".

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• Is there really such a thing as a char or short in modern programming?

  - by Dean P

  Howdy all, I've been learning to program for a Mac over the past few months (I have experience in other languages). Obviously that has meant learning the Objective C language and thus the plainer C it is predicated on. So I have stumbles on this quote, which refers to the C/C++ language in general, not just the Mac platform. With C and C++ prefer use of int over char and short. The main reason behind this is that C and C++ perform arithmetic operations and parameter passing at integer level, If you have an integer value that can fit in a byte, you should still consider using an int to hold the number. If you use a char, the compiler will first convert the values into integer, perform the operations and then convert back the result to char. So my question, is this the case in the Mac Desktop and IPhone OS environments? I understand when talking about theses environments we're actually talking about 3-4 different architectures (PPC, i386, Arm and the A4 Arm variant) so there may not be a single answer. Nevertheless does the general principle hold that in modern 32 bit / 64 bit systems using 1-2 byte variables that don't align with the machine's natural 4 byte words doesn't provide much of the efficiency we may expect. For instance, a plain old C-Array of 100,000 chars is smaller than the same 100,000 ints by a factor of four, but if during an enumeration, reading out each index involves a cast/boxing/unboxing of sorts, will we see overall lower 'performance' despite the saved memory overhead?

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• C++0x rvalue references and temporaries

  - by Doug

  (I asked a variation of this question on comp.std.c++ but didn't get an answer.) Why does the call to f(arg) in this code call the const ref overload of f? void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { f(arg); } My intuition says that the f(string &&) overload should be chosen, because arg needs to be converted to a temporary no matter what, and the temporary matches the rvalue reference better than the lvalue reference. This is not what happens in GCC and MSVC. In at least G++ and MSVC, any lvalue does not bind to an rvalue reference argument, even if there is an intermediate temporary created. Indeed, if the const ref overload isn't present, the compilers diagnose an error. However, writing f(arg + 0) or f(std::string(arg)) does choose the rvalue reference overload as you would expect. From my reading of the C++0x standard, it seems like the implicit conversion of a const char * to a string should be considered when considering if f(string &&) is viable, just as when passing a const lvalue ref arguments. Section 13.3 (overload resolution) doesn't differentiate between rvalue refs and const references in too many places. Also, it seems that the rule that prevents lvalues from binding to rvalue references (13.3.3.1.4/3) shouldn't apply if there's an intermediate temporary - after all, it's perfectly safe to move from the temporary. Is this: Me misreading/misunderstand the standard, where the implemented behavior is the intended behavior, and there's some good reason why my example should behave the way it does? A mistake that the compiler vendors have somehow all made? Or a mistake based on common implementation strategies? Or a mistake in e.g. GCC (where this lvalue/rvalue reference binding rule was first implemented), that was copied by other vendors? A defect in the standard, or an unintended consequence, or something that should be clarified?

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• Why would this Lua optimization hack help?

  - by Ian Boyd

  i'm looking over a document that describes various techniques to improve performance of Lua script code, and i'm shocked that such tricks would be required. (Although i'm quoting Lua, i've seen similar hacks in Javascript). Why would this optimization be required: For instance, the code for i = 1, 1000000 do local x = math.sin(i) end runs 30% slower than this one: local sin = math.sin for i = 1, 1000000 do local x = sin(i) end They're re-declaring sin function locally. Why would this be helpful? It's the job of the compiler to do that anyway. Why is the programmer having to do the compiler's job? i've seen similar things in Javascript; and so obviously there must be a very good reason why the interpreting compiler isn't doing its job. What is it? i see it repeatedly in the Lua environment i'm fiddling in; people redeclaring variables as local: local strfind = strfind local strlen = strlen local gsub = gsub local pairs = pairs local ipairs = ipairs local type = type local tinsert = tinsert local tremove = tremove local unpack = unpack local max = max local min = min local floor = floor local ceil = ceil local loadstring = loadstring local tostring = tostring local setmetatable = setmetatable local getmetatable = getmetatable local format = format local sin = math.sin What is going on here that people have to do the work of the compiler? Is the compiler confused by how to find format? Why is this an issue that a programmer has to deal with? Why would this not have been taken care of in 1993? i also seem to have hit a logical paradox: Optimizatin should not be done without profiling Lua has no ability to be profiled Lua should not be optimized

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• How do you refactor a large messy codebase?

  - by Ricket

  I have a big mess of code. Admittedly, I wrote it myself - a year ago. It's not well commented but it's not very complicated either, so I can understand it -- just not well enough to know where to start as far as refactoring it. I violated every rule that I have read about over the past year. There are classes with multiple responsibilities, there are indirect accesses (I forget the technical term - something like foo.bar.doSomething()), and like I said it is not well commented. On top of that, it's the beginnings of a game, so the graphics is coupled with the data, or the places where I tried to decouple graphics and data, I made the data public in order for the graphics to be able to access the data it needs... It's a huge mess! Where do I start? How would you start on something like this? My current approach is to take variables and switch them to private and then refactor the pieces that break, but that doesn't seem to be enough. Please suggest other strategies for wading through this mess and turning it into something clean so that I can continue where I left off!

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• Interface vs Abstract Class (general OO)

  - by Kave

  Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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• How does Backbone.js connect View to Model

  - by William Sham

  I am trying to learn backbone.js through the following example. Then I got stuck at the point ItemView = Backbone.View.extend why you can use this.model.get? I thought this is referring to the instance of ItemView that would be created. Then why would ItemView has a model property at all?!! (function($){ var Item = Backbone.Model.extend({ defaults: { part1: 'hello', part2: 'world' } }); var List = Backbone.Collection.extend({ model: Item }); var ItemView = Backbone.View.extend({ tagName: 'li', initialize: function(){ _.bindAll(this, 'render'); }, render: function(){ $(this.el).html('<span>'+this.model.get('part1')+' '+this.model.get('part2')+'</span>'); return this; } }); var ListView = Backbone.View.extend({ el: $('body'), events: { 'click button#add': 'addItem' }, initialize: function(){ _.bindAll(this, 'render', 'addItem', 'appendItem'); this.collection = new List(); this.collection.bind('add', this.appendItem); this.counter = 0; this.render(); }, render: function(){ $(this.el).append("<button id='add'>Add list item</button>"); $(this.el).append("<ul></ul>"); _(this.collection.models).each(function(item){ appendItem(item); }, this); }, addItem: function(){ this.counter++; var item = new Item(); item.set({ part2: item.get('part2') + this.counter }); this.collection.add(item); }, appendItem: function(item){ var itemView = new ItemView({ model: item }); $('ul', this.el).append(itemView.render().el); } }); var listView = new ListView(); })(jQuery);

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