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• Understanding Smarty and MVC Frameworks

  - by Korrupzion

  Hello there, I just created this thread to discuss with people who have adopted the smarty system, and how many time it took to you to understand it, because i just can't get the idea, instead of making every easier as everybody says i think it just make more complex to code. More than a problem with only smarty is with the whole MVC model, with CakePHP or KohanaPHP i experience the same problems, u need to do 3x lines of code and files for something that u can do with a few lines of simple php. Maybe u can tell how did u learned to code using MVC model :)

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• Need some help understanding this problem about maximizing graph connectivity

  - by Legend

  I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. I am not sure if this is a really a problem but I somehow have a feeling that there might exist more than one order in which case, it is required to choose the best order. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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• understanding this regex

  - by DarthVader

  I m trying to understand what the following does. ^([^=]+)(?:(?:\\=)(.+))?$ Any ideas? This is being used here. Obviously it s command line parser but i m trying to understand the syntax so i can actually run the program. This is from commandline-jmxclient , they have no documents on setting JMX properties but in their source code, there is such an option, so i just want to understand how i can invoke that method. Matcher m = Client.CMD_LINE_ARGS_PATTERN.matcher(command); if ((m == null) || (!m.matches())) { throw new ParseException("Failed parse of " + command, 0); } this.cmd = m.group(1); if ((m.group(2) != null) && (m.group(2).length() > 0)) this.args = m.group(2).split(","); else this.args = null;

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• Understanding an interesting array update/replace function

  - by dave

  I'm a PHP amateur. This array function is an adaption of a function I noticed while reading this article. I thought this was an interesting type of array function, but I have a question about the way it works. my_func( array( 'sky' => 'blue' ) ); function my_func( array $settings = array() ) { $settings = $settings + array( 'grass'=>'green','sky'=>'dark' ); print_r( $settings ) ; // outputs: Array ( [sky] => blue [grass] => green ) } but..................... my_func( array( 'sky' => 'blue' ) ); function my_func( array $settings = array() ) { $settings = array( 'clock'=>'time' ) ; $settings = $settings + array( 'grass'=>'green','sky'=>'dark' ); print_r( $settings ) ; // outputs: Array ( [clock] => time [grass] => green [sky] => dark ) } Why does [sky] not equal 'blue' in the second instance? Thanks.

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• Understanding SingleTableEntityPersister n QueryLoader

  - by Iapilgrim

  Hi, I have the Hibernate model @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Node extends StatefulEntity implements Inheritable, Cloneable { private Node _parent; private List<Node> _childNodes; .. } @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Page extends Node implements Defaultable, Securable { private RootZone _rootZone; ...... @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "root_zone_id", insertable = false, updatable = false) public RootZone getRootZone() { return _rootZone; } public void setRootZone(RootZone rootZone) { if (rootZone != null) { rootZone.setPageId(this.getId()); _rootZone = rootZone; } } I want to get all pages ( call getSiteTree), so I using this query String hpql = "SELECT n FROM Node n "; See the trace I find Page.setRootZone(RootZone) line: 155 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 BasicPropertyAccessor$BasicSetter.set(Object, Object, SessionFactoryImplementor) line: 66 PojoEntityTuplizer(AbstractEntityTuplizer).setPropertyValues(Object, Object[]) line: 352 PojoEntityTuplizer.setPropertyValues(Object, Object[]) line: 232 SingleTableEntityPersister(AbstractEntityPersister).setPropertyValues(Object, Object[], EntityMode) line: 3580 TwoPhaseLoad.initializeEntity(Object, boolean, SessionImplementor, PreLoadEvent, PostLoadEvent) line: 152 QueryLoader(Loader).initializeEntitiesAndCollections(List, Object, SessionImplementor, boolean) line: 877 QueryLoader(Loader).doQuery(SessionImplementor, QueryParameters, boolean) line: 752 QueryLoader(Loader).doQueryAndInitializeNonLazyCollections(SessionImplementor, QueryParameters, boolean) line: 259 QueryLoader(Loader).doList(SessionImplementor, QueryParameters) line: 2232 QueryLoader(Loader).listIgnoreQueryCache(SessionImplementor, QueryParameters) line: 2129 QueryLoader(Loader).list(SessionImplementor, QueryParameters, Set, Type[]) line: 2124 QueryLoader.list(SessionImplementor, QueryParameters) line: 401 QueryTranslatorImpl.list(SessionImplementor, QueryParameters) line: 363 HQLQueryPlan.performList(QueryParameters, SessionImplementor) line: 196 SessionImpl.list(String, QueryParameters) line: 1149 QueryImpl.list() line: 102 QueryImpl.getResultList() line: 67 NodeDaoImpl.getSiteTree(long) line: 358 PageNodeServiceImpl.getSiteTree(long) line: 797 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 AopUtils.invokeJoinpointUsingReflection(Object, Method, Object[]) line: 307 JdkDynamicAopProxy.invoke(Object, Method, Object[]) line: 198 $Proxy100.getSiteTree(long) line: not available the calling setRootZone in Page makes Hibernate issue a hit to database. I don't want this. So my question is + Why query String hpql = "SELECT n FROM Node n "; issues un-expected trace logs like above. Why the query String hpql = "SELECT n.nodename FROM Node n " not? What is the mechanism behind? Note: Im using hibernate caching level 2. In case I don't want to see that trace logs. I mean I just get Node data only. How to do ? Thanks for your help. Sorry for my bad english :( Van

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• Difficulty in Understanding Slideshow script

  - by shining star

  I have taken slide show script from net. But There some functions i cannot understand here is script <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd" > <html lang="en"> <head> <title></title> <script> var interval = 1500; var random_display = 0; var imageDir = "my_images/"; var imageNum = 0; imageArray = new Array(); imageArray[imageNum++] = new imageItem(imageDir + "01.jpg"); imageArray[imageNum++] = new imageItem(imageDir + "02.jpg"); imageArray[imageNum++] = new imageItem(imageDir + "03.jpg"); imageArray[imageNum++] = new imageItem(imageDir + "04.jpg"); imageArray[imageNum++] = new imageItem(imageDir + "05.jpg"); var totalImages = imageArray.length; function imageItem(image_location) { this.image_item = new Image(); this.image_item.src = image_location; return this.image_item.src; } function get_ImageItemLocation(imageObj) { return(imageObj.image_item.src) } alert(imageArray[imageNum].image_item.src); function randNum(x, y) { var range = y - x + 1; return Math.floor(Math.random() * range) + x; } function getNextImage() { if (random_display) { imageNum = randNum(0, totalImages-1); } else { imageNum = (imageNum+1) % totalImages; } var new_image = get_ImageItemLocation(imageArray[imageNum]); //alert(new_image) return(new_image); } function getPrevImage() { imageNum = (imageNum-1) % totalImages; var new_image = get_ImageItemLocation(imageArray[imageNum]); return(new_image); } function prevImage(place) { var new_image = getPrevImage(); document[place].src = new_image; } function switchImage(place) { var new_image = getNextImage(); document[place].src = new_image; var recur_call = "switchImage('"+place+"')"; timerID = setTimeout(recur_call, interval); } </script> </head> <body onLoad="switchImage('slideImg')"> <img name="slideImg" src="27.jpg" width=500 height=375 border=0> <a href="#" onClick="switchImage('slideImg')">play slide show</a> <a href="#" onClick="clearTimeout(timerID)"> pause</a> <a href="#" onClick="prevImage('slideImg'); clearTimeout(timerID)"> previous</a> <a href="#" onClick="switchImage('slideImg'); clearTimeout(timerID)">next </a> </body> </html> here exactly i dont know what does acctually function of get_ImageItemLocation(imageObj) and imageItem(image_location) what does these two functions seperately? Thanks in advance for attention

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• Need help understanding _set_security_error_handler()

  - by Emil D

  So , I've been reading this article: http://msdn.microsoft.com/en-us/library/aa290051%28VS.71%29.aspx And I would like to define my custom handler.However, I'm not sure I understand the mechanics well.What happens after a call is made to the user-defined function ( e.g. the argument of _set_security_error_handler() ) ? Does the program still terminate afterward ? If that is the case, is it possible to terminate only the current thread(assuming that it is not the main thread of the application).AFAIK, each thread has its own stack , so if the stack of a thread gets corrupted, the rest of the application shouldn't be affected. Finally, if it is indeed possible to only terminate the current thread of execution, what potential problems could such an action cause? I'm trying to do all this inside an unmanaged C++ dll that I would like to use in my C# code.

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• Understanding CUDA grid dimensions, block dimensions and threads organization (simple explanation)

  - by cibercitizen1

  How threads are organized to be executed by a GPU?

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• Trying to get a better understanding of SelectedValuePath and IsSynchronizedWithCurrentItem

  - by rasx

  The following XAML produces a run-time Binding error when I click on an item in the ListBox: <Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:sys="clr-namespace:System;assembly=mscorlib" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="WpfApplication1.MainWindow" x:Name="Window" Title="MainWindow" Width="640" Height="480"> <Window.Resources> <x:Array x:Key="strings" Type="{x:Type sys:String}"> <sys:String>one</sys:String> <sys:String>two</sys:String> <sys:String>three</sys:String> <sys:String>four</sys:String> </x:Array> </Window.Resources> <Grid> <ListBox DataContext="{StaticResource strings}" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding}" SelectedValuePath="{Binding /Length}"> <ListBox.ItemTemplate> <DataTemplate> <Grid> <Grid.Resources> <Style TargetType="{x:Type Label}"> <Setter Property="Background" Value="Yellow"/> <Setter Property="Margin" Value="0,0,4,0"/> <Setter Property="Padding" Value="0"/> </Style> </Grid.Resources> <Grid.ColumnDefinitions> <ColumnDefinition/> <ColumnDefinition/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition/> </Grid.RowDefinitions> <!-- Row 0 --> <Label Grid.Column="0" Grid.Row="0">String:</Label> <TextBlock Grid.Column="1" Grid.Row="0" Text="{Binding}"/> <!-- Row 1 --> <Label Grid.Column="0" Grid.Row="1">Length:</Label> <TextBlock Grid.Column="1" Grid.Row="1" Text="{Binding Length, Mode=Default}"/> </Grid> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </Grid> </Window> This is the run-time Binding error message: System.Windows.Data Error: 39 : BindingExpression path error: '3' property not found on 'object' ''String' (HashCode=1191344027)'. BindingExpression:Path=3; DataItem='String' (HashCode=1191344027); target element is 'ListBox' (Name=''); target property is 'NoTarget' (type 'Object') I would like the selected value of the ListBox to be the Length of the selected String object. What is wrong with my SelectedValuePath Binding syntax? Are there any related issues with IsSynchronizedWithCurrentItem?

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• Understanding addSubview: memoryLeak

  - by Leandros

  I don't really understand, why this code leaks. ParentViewController *parentController = [[ParentViewController alloc] init]; ChildViewController *childController = [[ChildViewController alloc] init]; [parentController containerAddChildViewController:childController]; [[self window] setRootViewController:parentController]; - (void)containerAddChildViewController:(UIViewController *)childViewController { [self addChildViewController:childViewController]; [self.view addSubview:childViewController.view]; // Instruments is telling me, the leak occurs here! [childViewController didMoveToParentViewController:self]; } According to Instruments, this line: [self.view addSubview:childViewController.view]; is leaking. The whole code is called once in application:didFinishLaunchingWithOptions:, but it is shown that this code is responsible for 30 leaks (approx. 1.12 kB).

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• Understanding pattern matching with cons operator

  - by Mathias

  In "Programming F#" I came across a pattern-matching like this one (I simplified a bit): let rec len list = match list with | [] -> 0 | [_] -> 1 | head :: tail -> 1 + len tail;; Practically, I understand that the last match recognizes the head and tail of the list. Conceptually, I don't get why it works. As far as I understand, :: is the cons operator, which appends a value in head position of a list, but it doesn't look to me like it is being used as an operator here. Should I understand this as a "special syntax" for lists, where :: is interpreted as an operator or a "match pattern" depending on context? Or can the same idea be extended for types other than lists, with other operators?

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• stored as array understanding mongoid

  - by Gagan

  Hello frens, This is not a problem, but I just want to know stored as array of Mongoid better. I have following code in my model. class Company include Mongoid::Document include Mongoid::Timestamps references_many :people, :stored_as => :array, :inverse_of => :companies end class Person include Mongoid::Document include Sunspot::Mongoid references_many :companies, :stored_as => :array, :inverse_of => :people end Now in Company object we get person_ids as a result of stored_as array and company_ids in Person object. Now initially I inserted lots of person in company and the ids in person_ids fields is huge. Now I deleted most of person from company down to 8 people. Now I don't get why person_ids fields of Company object storing all the deleted ids of person. My console snapshot is follwing ruby-1.9.2-head Company.first.person_ids = [BSON::ObjectId('4d12d2907adf350695000025'), BSON::ObjectId('4d12d2907adf35069500002c'), BSON::ObjectId('4d12d2907adf350695000035'), BSON::ObjectId('4d12d2907adf35069500003f'), BSON::ObjectId('4d12d2907adf350695000048'), BSON::ObjectId('4d12d2907adf350695000052'), BSON::ObjectId('4d12d2907adf350695000059'), BSON::ObjectId('4d12d2907adf350695000062'), BSON::ObjectId('4d12d4017adf35069500008d'), BSON::ObjectId('4d12d4017adf350695000094'), BSON::ObjectId('4d12d4017adf35069500009d'), BSON::ObjectId('4d12d4017adf3506950000a7'), BSON::ObjectId('4d12d4017adf3506950000b0'), BSON::ObjectId('4d12d4017adf3506950000ba'), BSON::ObjectId('4d12d4017adf3506950000c1'), BSON::ObjectId('4d12d4017adf3506950000ca'), BSON::ObjectId('4d12d48a7adf3506950000f5'), BSON::ObjectId('4d12d48a7adf3506950000fc'), BSON::ObjectId('4d12d48a7adf350695000108'), BSON::ObjectId('4d12d48b7adf350695000115'), BSON::ObjectId('4d12d48b7adf350695000121'), BSON::ObjectId('4d12d48b7adf35069500012e'), BSON::ObjectId('4d12d48b7adf350695000135'), BSON::ObjectId('4d12d48b7adf350695000141'), BSON::ObjectId('4d12d53e7adf35069500016f'), BSON::ObjectId('4d12d53e7adf350695000176'), BSON::ObjectId('4d12d53e7adf350695000182'), BSON::ObjectId('4d12d53e7adf35069500018f'), BSON::ObjectId('4d12d53e7adf35069500019b'), BSON::ObjectId('4d12d53f7adf3506950001a8'), BSON::ObjectId('4d12d53f7adf3506950001af'), BSON::ObjectId('4d12d53f7adf3506950001bb'), BSON::ObjectId('4d12d8587adf3506950001e9'), BSON::ObjectId('4d12d8587adf3506950001f0'), BSON::ObjectId('4d12d8587adf3506950001ff'), BSON::ObjectId('4d12d8597adf35069500020f'), BSON::ObjectId('4d12d8597adf35069500021e'), BSON::ObjectId('4d12d8597adf35069500022e'), BSON::ObjectId('4d12d8597adf350695000235'), BSON::ObjectId('4d12d85a7adf350695000244'), BSON::ObjectId('4d12d9587adf35069500025b'), BSON::ObjectId('4d12db8b7adf35069500026a'), BSON::ObjectId('4d12de6f7adf3509c9000024'), BSON::ObjectId('4d12de6f7adf3509c900002b'), BSON::ObjectId('4d12de6f7adf3509c900003a'), BSON::ObjectId('4d12de707adf3509c900004a'), BSON::ObjectId('4d12de707adf3509c9000059'), BSON::ObjectId('4d12de707adf3509c9000069'), BSON::ObjectId('4d12de707adf3509c9000070'), BSON::ObjectId('4d12de717adf3509c900007f'), BSON::ObjectId('4d12e7f27adf350bd2000009'), BSON::ObjectId('4d12e81f7adf350bd2000015'), BSON::ObjectId('4d12e87f7adf350bd2000024'), BSON::ObjectId('4d12e8b87adf350bd200004c'), BSON::ObjectId('4d12e8b97adf350bd2000053'), BSON::ObjectId('4d12e8b97adf350bd200005c'), BSON::ObjectId('4d12e8b97adf350bd2000066'), BSON::ObjectId('4d12e8b97adf350bd200006f'), BSON::ObjectId('4d12e8b97adf350bd2000079'), BSON::ObjectId('4d12e8ba7adf350bd2000080'), BSON::ObjectId('4d12e8ba7adf350bd2000089'), BSON::ObjectId('4d12ee6b7adf350bd2000198'), BSON::ObjectId('4d12ee6b7adf350bd200019f'), BSON::ObjectId('4d12ee6c7adf350bd20001a5'), BSON::ObjectId('4d12ee6c7adf350bd20001ac'), BSON::ObjectId('4d12ee6c7adf350bd20001b2'), BSON::ObjectId('4d12ee6c7adf350bd20001b9'), BSON::ObjectId('4d12ee6c7adf350bd20001c0'), BSON::ObjectId('4d12ee6c7adf350bd20001c6'), BSON::ObjectId('4d141ca57adf35033e00006e'), BSON::ObjectId('4d141ca57adf35033e000075'), BSON::ObjectId('4d1420aa7adf350705000003'), BSON::ObjectId('4d1420aa7adf35070500000a'), BSON::ObjectId('4d1420f47adf350705000011'), BSON::ObjectId('4d1420f57adf350705000015'), BSON::ObjectId('4d1420f57adf350705000018'), BSON::ObjectId('4d1420f57adf35070500001c'), BSON::ObjectId('4d1420f57adf350705000023'), BSON::ObjectId('4d1420f57adf350705000026'), BSON::ObjectId('4d14215f7adf35070500004b'), BSON::ObjectId('4d14215f7adf350705000052'), BSON::ObjectId('4d14215f7adf350705000055'), BSON::ObjectId('4d14215f7adf350705000059'), BSON::ObjectId('4d14215f7adf35070500005c'), BSON::ObjectId('4d14215f7adf350705000060'), BSON::ObjectId('4d14215f7adf350705000067'), BSON::ObjectId('4d14215f7adf35070500006a')] Company.first.people.collect(&:id) = [BSON::ObjectId('4d14215f7adf35070500004b'), BSON::ObjectId('4d14215f7adf350705000052'), BSON::ObjectId('4d14215f7adf350705000055'), BSON::ObjectId('4d14215f7adf350705000059'), BSON::ObjectId('4d14215f7adf35070500005c'), BSON::ObjectId('4d14215f7adf350705000060'), BSON::ObjectId('4d14215f7adf350705000067'), BSON::ObjectId('4d14215f7adf35070500006a')] Isn't the Company.first.person_ids array be only storing the ids shown by Company.first.people.collect(&:id) It would be helpful if some one tell me when to best use stored_as = :array method. Do stored_as = :array increase querying performance? Thanks

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• Help understanding .NET delegates, events, and eventhandlers

  - by Seth Spearman

  Hello, In the last couple of days I asked a couple of questions about delegates HERE and HERE. I confess...I don't really understand delegates. And I REALLY REALLY REALLY want to understand and master them. (I can define them--type safe function pointers--but since I have little experience with C type languages it is not really helpful.) Can anyone recommend some online resource(s) that will explain delegates in a way that presumes nothing? This is one of those moments where I suspect that VB actually handicaps me because it does some wiring for me behind the scenes. The ideal resource would just explain what delegates are, without reference to anything else like (events and eventhandlers), would show me how all everything is wired up, explain (as I just learned) that delegates are types and what makes them unique as a type (perhaps using a little ildasm magic)). That foundation would then expand to explain how delegates are related to events and eventhandlers which would need a pretty good explanation in there own right. Finally this resource could tie it all together using real examples and explain what wiring DOES happen automatically by the compiler, how to use them, etc. And, oh yeah, when you should and should not use delegates, in other words, downsides and alternatives to using delegates. What say ye? Can any of you point me to resource(s) that can help me begin my journey to mastery? EDIT One last thing. The ideal resource will explain how you can and cannot use delegates in an interface declaration. That is something that really tripped me up. Thanks for your help. Seth

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• Understanding syntax in c#

  - by user279521

  I am hoping someone can help me understand what is going on in the code line below: Table t = (Table)Page.FindControl("Panel1").FindControl("tbl"); I understand Page.FindControl("Panel1").FindControl("tbl"); Why is there a (Table) before the Page.FindControl?

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• Help understanding linux/tcp.h

  - by Chris

  I'm learning to use raw sockets, and im trying to prase out the tcp header data, but i can't seem to figure out what res1, ece, and cwr are. Through my networking book and google i know what the rest stand for, but can't seem to find anything on those three. Below is the tcphdr struct in my includes area. Ive commented the parts a bit as i was figureing out what they stood for. struct tcphdr { __be16 source; __be16 dest; __be32 seq; __be32 ack_seq; #if defined(__LITTLE_ENDIAN_BITFIELD) _u16 res1:4, doff:4,//tcp header length fin:1,//final syn:1,//synchronization rst:1,//reset psh:1,//push ack:1,//ack urg:1,// urge ece:1, cwr:1; #elif defined(_BIG_ENDIAN_BITFIELD) __u16 doff:4,//tcp header length res1:4, cwr:1, ece:1, urg:1,//urge ack:1,//ack psh:1,//push rst:1,//reset syn:1,//synchronization fin:1;//final #else #error "Adjust your defines" #endif __be16 window; __sum16 check; __be16 urg_ptr; };

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• understanding silverlight resource file format

  - by Quincy

  I'm trying to understand the format of silverlight resource files. There are 4 bytes of the data comes after PAD. I'd like to know what these values are, and how they are generated. here is the hex dump of a .g.resources file. Here is what I know: there is 0xbeefcace at the beginning, then there is dependancies, then padding. after that is the great unknown (but I really like to know). After 4 null bytes, are the file name and size of the resource. and After that is content of the said file. I'm not that familiar with .Net and silverlight resource management. would someone please tell me what the mystical 4 bytes are, or point me the url to the specification doc or something. Any help would be appreciated!

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• Understanding the Unix file system and ruby installs without Sudo

  - by JZ

  I'm trying to comprehend the Unix file system on my OSX. I'm following wikipedia Filesystem Hierarchy Standard. I understand when I install ruby gems I must use the command sudo gem install but if I omit sudo, problems may occur. Where are gems installed within the file system when I omit sudo? How can I delete these gems? A Fun side question: When I enter cd ~/.gem my terminal is directed to .gem user$, When I enter cd ~/ and list folders using the ls command I can't find a .gem folder. Where is the .gem folder? How does this fit into the Filesystem?

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• Help on understanding multiple columns on an index?

  - by Xaisoft

  Assume I have a table called "table" and I have 3 columns, a, b, and c. What does it mean to have a non-clustered index on columns a,b? Is a nonclustered index on columns a,b the same as a nonclustered index on columns b,a? (Note the order). Also, Is a nonclustered index on column a the same as a nonclustered index on a,c? I was looking at the website sqlserver performance and they had these dmv scripts where it would tell you if you had overlapping indexes and I believe it was saying that having an index on a is the same as a,b, so it is redundant. Is this true about indexes? One last question is why is the clustered index put on the primary key. Most of the time the primary key is not queried against, so shouldn't the clustered index be on the most queried column. I am probably missing something here like having it on the primary key speeds up joins? Great explanations. Should I turn this into a wiki and change the title index explanation?

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• Help on understanding JS

  - by Anonymous

  I have thos piece of code: Math&&Math.random?Math.floor(Math.random()*10000000000000):Date.getTime(); And as far as i know && is logic operator for AND, so im trying to convert this into PHP and this is where i got: intval(floor(time()/10800000)%10+(rand()?floor(rand()*10000000000000):time())) The problem is that i can't understand the first part Math&& Can anyone help with this one cause i always get negative result, when i should get positive (probably the logic rand-time is not working in my php example)

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• Understanding Domain Driven Design

  - by Nihilist

  Hi I have been trying to understand DDD for few weeks now. Its very confusing. I dont understand how I organise my projects. I have lot of questions on UnitOfWork, Repository, Associations and the list goes on... Lets take a simple example. Album and Tracks. Album: AlbumId, Name, ListOf Tracks Tracks: TrackId, Name Question1: Should i expose Tracks as a IList/IEnumerabe property on Album ? If that how do i add an album ? OR should i expose a ReadOnlyCollection of Tracks and expose a AddTrack method? Question2: How do i load Tracks for Album [assuming lazy loading]? should the getter check for null and then use a repository to load the tracks if need be? Question3: How do we organise the assemblies. Like what does each assembly have? Model.dll - does it only have the domain entities? Where do the repositories go? Interfaces and implementations both. Can i define IAlbumRepository in Model.dll? Infrastructure.dll : what shold this have? Question4: Where is unit of work defined? How do repository and unit of work communicate? [ or should they ] for example. if i need to add multiple tracks to album, again should this be defined as AddTrack on Album OR should there a method in the repository? Regardless of where the method is, how do I implement unit of work here? Question5: Should the UI use Infrastructure..dll or should there be ServiceLayer? Do my quesitons make sense? Regards

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• Understanding the workings of equals and hashCode in a HashMap

  - by andandandand

  I have this test code: import java.util.*; class MapEQ { public static void main(String[] args) { Map<ToDos, String> m = new HashMap<ToDos, String>(); ToDos t1 = new ToDos("Monday"); ToDos t2 = new ToDos("Monday"); ToDos t3 = new ToDos("Tuesday"); m.put(t1, "doLaundry"); m.put(t2, "payBills"); m.put(t3, "cleanAttic"); System.out.println(m.size()); } } class ToDos{ String day; ToDos(String d) { day = d; } public boolean equals(Object o) { return ((ToDos)o).day == this.day; } // public int hashCode() { return 9; } } When // public int hashCode() { return 9; } is uncommented m.size() returns 2, when it's left commented it returns three. Why?

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• Understanding Ruby class vs instance methods

  - by randombits

  I have the following code: #!/usr/bin/ruby class Person def self.speak p = self.new puts "Hello" p.chatter end private def chatter puts "Chattering" end end p = Person.new Person.speak I'd like to make chatter private, accessible only within p.. but I want p to be able to access it within the class method. Is there a better way to design this so chatter isn't available to the public, but a "factory" method like self.speak can call chatter?

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• Need some help understanding the MATLAB `cat` command in high dimensions

  - by Runner

  The commands a = magic(3); b = pascal(3); c = cat(4,a,b); produce a 3-by-3-by-1-by-2 array. Why is the result 3-3-1-2 when the dimension is 4?

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• Understanding Symbols In Ruby

  - by Kezzer

  Despite reading this article, I'm still confused as to the representation of the data in memory when it comes to using symbols. If a symbol, two of them contained in different objects, exist in the same memory location, then how is it that they contain different values? I'd have expected the same memory location to contain the same value. As a quote from the link: Unlike strings, symbols of the same name are initialized and exist in memory only once during a session of ruby I just don't understand how it manages to differentiate the values contained in the same memory location. EDIT So let's consider the example: patient1 = { :ruby => "red" } patient2 = { :ruby => "programming" } patient1.each_key {|key| puts key.object_id.to_s} 3918094 patient2.each_key {|key| puts key.object_id.to_s} 3918094 patient1 and patient2 are both hashes, that's fine. :ruby however is a symbol. If we were to output the following: patient1.each_key {|key| puts key.to_s} Then what will be output? "red", or "programming"? FURTHER EDIT I'm still really quite confused. I'm thinking a symbol is a pointer to a value. Let's forget hashes for a second. The questions I have are; can you assign a value to a symbol? Is a symbol just a pointer to a variable with a value in it? If symbols are global, does that mean a symbol always points to one thing?

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• Need help in understanding the mapping of user-space send, sendto, sendmsg to kernel-space sendmsg

  - by bala1486

  Hello, I am trying to implement my own transport layer protocol in Linux for an experiment. I am going to use socket interface and add my protocol using sock_register. For the proto_ops i can see that the parameters for the sendmsg and recvmsg are (struct kiocb *iocb, struct socket *sock, struct msghdr *msg, size_t len, int flags). But there are three types of user api's send, sendto, sendmsg. Of these three only sendmsg contains a parameter for msghdr. I find that the other two api's are incompatible with the parameters supplied by the kernel to my kernel-space sendmsg function. So what happens when we use send and sendto user-space api's? Hope i am clear.. Thanks, Bala

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