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• Scheme Homework Assignment

  - by user1704677

  In a course I am taking we recently had to learn the programming language Scheme. I get all of the basics, which is pretty much all that we have gone though. I'm just having trouble learning to think in the different way that Scheme consists of. I was given an assignment and really do not even know how to start. I have sat here for a few hours trying to figure out how to even get started, but I'm kind of stumped. For the record, I'm not asking for the code to solve this problem, but more of some thoughts to get me on the right track. Anyway, here is the gist of the assignment... We are given a list of ten numbers that represent a voter's votes. The numbers are -1, 0 or 1. Then we are given a list of lists of Candidates, with a name and then ten numbers corresponding to that candidate's votes. These numbers are also -1 0 and 1. So for example. '(0 0 0 -1 -1 1 0 1 0 -1) '(Adams 0 1 -1 0 1 1 0 -1 -1 0 0) We are asked to implement a function called best_candidates that will take in a list of numbers (Voter) and a list of lists of Candidates. Then we have to compare the votes of the voter against the list of each candidate and return a list of names with the most common votes. So far, I've come up with a few things. I'm just confused on how I will check the values and retain the name of the voter? I guess I'm still stuck in thinking C/Java and it's making this very tough. Any suggestions to help get me started?

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• FileInput Help/Advice

  - by user559142

  I have a fileinput class. It has a string parameter in the constructor to load the filename supplied. However it just exits if the file doesn't exist. I would like it to output a message if the file doesn't exist - but not sure how.... Here is the class: public class FileInput extends Input { /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final String fileName) { try { scanner = new Scanner(new FileInputStream(fileName)); } catch (FileNotFoundException e) { System.err.println("File " + fileName + " could not be found."); System.exit(1); } } /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final FileInputStream fileStream) { super(fileStream); } } And its implementation: private void loadFamilyTree() { out.print("Enter file name: "); String fileName = in.nextLine(); FileInput input = new FileInput(fileName); family.load(input); input.close(); }

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• NSTimer won't stop it only resets when invalidated & released

  - by J Fries

  When I press my stop button to stop the timer it just resets to the original time and begins counting down again. I have looked everywhere and all I have found is "invalidate" and it isn't working. I want the time to stop when I hit stop and the label to display the original time. I also turned off automatic counting so I could try releasing and it is giving me an error: 0x10e20a5: movl 16(%edx), %edx EXC_BAD_ACCESS (code=2, address=0x10) `NSTimer *rockettTimer; int rocketCount; @interface FirstViewController () @property (strong, nonatomic) IBOutlet UILabel *rocketTimer; - (IBAction)stopButton:(id)sender; - (IBAction)startButton:(id)sender; @end @implementation FirstViewController @synthesize rocketTimer; -(void) rocketTimerRun{ rocketCount = rocketCount - 1; int minuts = rocketCount / 60; int seconds = rocketCount - (minuts * 60); NSString *timerOutput = [NSString stringWithFormat:@"%d:%.2d", minuts, seconds]; rocketTimer.text = timerOutput; } - (IBAction)startButton:(id)sender { rocketCount = 180; rockettTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(rocketTimerRun) userInfo:nil repeats:YES]; - (IBAction)stopButton:(id)sender { [rockettTimer invalidate]; //[rockettTimer release]; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. } - (void)viewDidUnload { [self setRocketTimer:nil]; [super viewDidUnload]; // Release any retained subviews of the main view. } - (BOOL)shouldAutorotateToInterfaceOrientation: (UIInterfaceOrientation)interfaceOrientation { if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) { return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown); } else { return YES; } } @end`

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• Using overloaded operator== in a generic function

  - by Dimitri C.

  Consider the following code: class CustomClass { public CustomClass(string value) { m_value = value; } public static bool operator==(CustomClass a, CustomClass b) { return a.m_value == b.m_value; } public static bool operator!=(CustomClass a, CustomClass b) { return a.m_value != b.m_value; } public override bool Equals(object o) { return m_value == (o as CustomClass).m_value; } public override int GetHashCode() { return 0; /* not needed */ } string m_value; } class G { public static bool enericFunction1<T>(T a1, T a2) where T : class { return a1.Equals(a2); } public static bool enericFunction2<T>(T a1, T a2) where T : class { return a1==a2; } } Now when I call both generic functions, one succeeds and one fails: var a = new CustomClass("same value"); var b = new CustomClass("same value"); Debug.Assert(G.enericFunction1(a, b)); // Succeeds Debug.Assert(G.enericFunction2(a, b)); // Fails Apparently, G.enericFunction2 executes the default operator== implementation instead of my override. Can anybody explain why this happens?

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• Multisite Enabling a Table

  - by Joe Fitzgibbons

  I am creating a table (table A) that will have a number of columns(of course) and there will be another table (table B) that holds metadata associated to rows in table A. I am working with a multi site implementation that has one database for the whole shabang. Rows in table A could belong to any number of sites but must belong to at least one. The problem I have is I am not sure what the best practice is for defining what site each row in table A belongs to. I want performance and scalability. There is no finite number of sites going forward. Rows in table A could belong to any number of sites in the future. Right now there are only 3. My initial thoughts are to have a primary site ID in Table A and then metadata in table B will have rows defining additional sites as needed. Another thought is to have a column in Table A for each site and it is a boolean as to wether it belongs to that site. Lastly I have thought about having another table to map rows in Table A to each site. What is the best way to associate rows in a table with any number of sites with performance and scalability in mind?

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• implementing user tracking (logging) in Rails 3

  - by seth.vargo

  Hi, I'm creating a Rails application in which logging individual user actions is vital. Every time a user clicks a url, I want to log the action along with all parameters. Here is my current implementation: class CreateActivityLogs < ActiveRecord::Migration create_table :activity_logs do |t| t.references :user t.string :ip_address t.string :referring_url t.string :current_url t.text :params t.text :action t.timestamps end end   class ActivityLog < ActiveRecord::Base belongs_to :user end In a controller, I'd like to be able to do something like the following: ... ActivityLog::log @user.id, params, 'did foo with bar' ... I'd like to have the ActivityLog::log method automatically get the IP address, referring url, and current url (I know how to do this already) and create a new record in the table. So, my questions are: How do I do this? How do I use ActivityLog without having to create an instance everytime I want to log? Is this the best way? Some people have argued for a flat-file log for this kind of logging - however, I want admins to be able to see a user's activity in the backend as well, so I thought a database solution may be better?

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• Fade in and out a div contains video embedHTML in jquery

  - by Ahmy

  I have a div and three links when a link is clicked the div is set its innerHTML with an embedHTML of video and i need to cause some effects when the current div video is changed on clicking the link Example : <a id="Link1" onClick="ChangeVideo(1)">Link1</a> <a id="Link2" onClick="ChangeVideo(2)">Link2</a> <a id="Link3" onClick="ChangeVideo(3)">Link3</a> <div id="CurrVideo"></div> <script type="text/javascript" language="javascript"> //The ArrEmbed is an array that is set on the load of the page:: var ArrEmbed = new Array(); function ChangeVideo(index) { $('#CurrVideo).fadeTo(1000,0.25,function(){ document.getElementById("CurrVideo").innerHTML = ArrEmbed[index-1]; }); $('#CurrVideo).fadeTo(500,1.25); } </script> The effect is not noticeable and fading with opacity diminshing is not noticed even if the duration time is increased (e.g. 'slow') and when i replace the EmbedHTML with image this code is applicable and the effect of fading is noticed but with the video it is not noticeable so how can i solve this problem ? Thanks in advance for any try Note: The embedHTML differ as it may come from youtube or any server or from my JWPlayer.

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• Best strategies for reading J code

  - by estanford

  I've been using J for a few months now, and I find that reading unfamiliar code (e.g. that I didn't write myself) is one of the most challenging aspects of the language, particularly when it's in tacit. After a while, I came up with this strategy: 1) Copy the code segment into a word document 2) Take each operator from (1) and place it on a separate line, so that it reads vertically 3) Replace each operator with its verbal description in the Vocabulary page 4) Do a rough translation from J syntax into English grammar 5) Use the translation to identify conceptually related components and separate them with line breaks 6) Write a description of what each component from (5) is supposed to do, in plain English prose 7) Write a description of what the whole program is supposed to do, based on (6) 8) Write an explanation of why the code from (1) can be said to represent the design concept from (7). Although I learn a lot from this process, I find it to be rather arduous and time-consuming -- especially if someone designed their program using a concept I never encountered before. So I wonder: do other people in the J community have favorite ways to figure out obscure code? If so, what are the advantages and disadvantages of these methods?

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• Which way of declaring a variable is fastest?

  - by ADB

  For a variable used in a function that is called very often and for implementation in J2ME on a blackberry (if that changed something, can you explain)? class X { int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { static int i; public void someFunc(int j) { i = 0; while( i < j ){ [...] i++; } } } or class X { public void someFunc(int j) { int i = 0; while( i < j ){ [...] i++; } } } I know there is a difference how a static versus non-static class variable is accessed, but I don't know it would affect the speed. I also remember reading somewhere that in-function variables may be accessed faster, but I don't know why and where I read that. Background on the question: some painting function in games are called excessively often and even small difference in access time can affect the overall performance when a variable is used in a largish loop.

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• QMetaMethods for regular methods missing?

  - by oleks

  Hi, I'm new in QT, and I'm just testing out the MOC. For a given class: class Counter : public QObject { Q_OBJECT int m_value; public: Counter() {m_value = 0;} ~Counter() {} int value() {return m_value;} public slots: void setValue(int value); signals: void valueChanged(int newValue); }; I want to get a list of all methods in a class, but seem to only be getting a list of signals and slots, although the documentation says it should be all methods? Here's my code: #include <QCoreApplication> #include <QObject> #include <QMetaMethod> #include <iostream> using std::cout; using std::endl; int main(int argc, char *argv[]) { QCoreApplication app(argc, argv); const QMetaObject cntmo = Counter::staticMetaObject; for(int i = 0; i != cntmo.methodCount(); ++i) { QMetaMethod qmm(cntmo.method(i)); cout << qmm.signature() << endl; } return app.exec(); } Please beware this is my best c/p, perhaps I forgot to include some headers. My output: destroyed(QObject*) destroyed() deleteLater() _q_reregisterTimers(void*) valueChanged(int) setValue(int) Does anyone know why this is happening? Does qt not recognise int value() {return m_value;} as a valid method? If so, is there a macro I've forgotten or something like that? P.S. I'm using 4.6.2 UPDATE I forgot the implementation of the setValue method, not that it makes too much a difference to my actual question. void Counter::setValue(int value) { if(value != m_value) { m_value = value; emit valueChanged(value); } }

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• 2 basic but interesting questions about .NET

  - by b-gen-jack-o-neill

  Hi, when I first saw C#, I thought this must be some joke. I was starting with programming in C. But in C# you could just drag and drop objects, and just write event code to them. It was so simple. Now, I still like C the most, becouse I am very attracted to the basic low level operations, and C is just next level of assembler, with few basic routines, so I like it very much. Even more becouse I write little apps for microcontrollers. But yeasterday I wrote very simple control program for my microcontroller based LED cube in asm, and I needed some way to simply create animation sequences to the Cube. So, I remembered C#. I have practically NO C# skills, but still I created simple program to make animation sequences in about hour with GUI, just with help of google and help of the embeded function descriptions in C#. So, to get to the point, is there some other reason then top speed, to use any other language than C#? I mean, it is so effective. I know that Java is a bit of similiar, but I expect C# to be more Windows effective since its directly from Microsoft. The second question is, what is the advantage of compiling into CIL, and than run by CLR, than directly compile it into machine code? I know that portability is one, but since C# is mainly for Windows, wouldn´t it be more powerfull to just compile it directly? Thanks.

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• How do you get and set a class property across multiple functions in Objective-C?

  - by editor

  Following up on this question about sharing objects between classes, I now need to figure out how to share the objects across various functions in a class. First, the setup: In my App Delegate I load menu information from JSON into a NSMutableDictionary and message that through to a view controller using a function called initWithData. I need to use this dictionary to populate a new Table View, which has methods like numberOfRowsInSection and cellForRowAtIndexPath. I'd like to use the dictionary count to return numberOfRowsInSection and info in the dictionary to populate each cell. Unfortunately, my code never gets beyond the init stage and the dictionary is empty so numberOfRowsInSection always returns zero. I thought I could create a class property, synthesize it and then set it. But it doesn't seem to want to retain the property's value. What am I doing wrong here? In the header .h: @interface FirstViewController:UIViewController <UITableViewDataSource, UITableViewDelegate, UITabBarControllerDelegate> { NSMutableDictionary *sectorDictionary; NSInteger sectorCount; } @property (nonatomic, retain) NSMutableDictionary *sectorDictionary; - (id)initWithData:(NSMutableDictionary*)data; @end in the implementation .m: - (id) testFunction:(NSMutableDictionary*)dictionary { NSLog(@"Count #1: %d", [dictionary count]); return nil; } - (id)initWithData:(NSMutableDictionary *)data { if (!(self=[super init])) { return nil; } [self testFunction:data]; // this is where I'd like to set a retained property self.sectorDictionary = data; return nil; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { NSLog(@"Count #2: %d", [self.sectorDictionary count]); return [self.sectorDictionary count]; } Output from NSLog: 2010-05-04 23:00:06.255 JSONApp[15890:207] Count #1: 9 2010-05-04 23:00:06.259 JSONApp[15890:207] Count #2: 0

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• How to use scrollTop in jQuery when scrolling within a div?

  - by sharataka

  I am trying to get the scrollTop using jQuery to work when the content I am trying to scroll to is located in within a div. The current implementation doesn't do anything javascript <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script> <script> $(document).ready(function (){ //$(this).animate(function(){ $('html, body').animate({ scrollTop: $("#test4").offset().top }, 2000); //}); }); </script> html <div class="row"> <div class = "span12"> <div class = "row"> <div class = "span2"> <div style="height:480px;font:12px Georgia, Garamond, Serif;overflow:auto;"> <div id = "test1">Test1</div> <div id = "test2">Test2</div> <div id = "test3">Test3</div> <div id = "test4">Test4</div> </div> </div> <div class = "row"> <div class = "span8"> Other content on the page </div> </div> </div> </div> </div>

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• Radio button is not funtioning

  - by user3614421

  I'm having problem with my radio button in my gridview. I want to select any row one by one so that I can perform UPDATE, DELETE, and DISPLAY the row. When I select the button, the page will be refreshed and the button I selected before is not selected anymore. So I can't click any menu to update, delete or display the row. I noticed this is happening when I set the Autopostback = "True". How can I solve it? Any idea? Below are my codes: Page: <script language="javascript" type="text/javascript"> function radiobtn(id) { var rdBtn = document.getElementById(id); var List = document.getElementsByTagName("input"); for (i = 0; i < List.length; i++) { if (List[i].type == "radio" && List[i].id != rdBtn.id) { List[i].checked = false; } } } </script> <asp:RadioButton ID="CheckDel" runat="server" onclick="javascript:radiobtn(this.id)" OnCheckedChanged="CheckDel_CheckedChanged" AutoPostBack="True" /> server end: protected void CheckDel_CheckedChanged(object sender, EventArgs e) { CheckBox chkStatus = (CheckBox)sender; GridViewRow row = (GridViewRow)chkStatus.NamingContainer; Session["datestart"] = row.Cells[1].Text; Session["empid"] = row.Cells[2].Text; Session["empname"] = row.Cells[3].Text; Session["days"] = row.Cells[4].Text; Session["leavetype"] = row.Cells[5].Text; Session["leavestatus"] = row.Cells[6].Text; bool status = chkStatus.Checked; } Please help

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• C++ bit shifting

  - by JB_SO

  Hi, I am new to working with bits & bytes in C++ and I'm looking at some previously developed code and I need some help in understanding what is going on with the code. There is a byte array and populating it with some data and I noticed that the data was being '&' with a 0x0F (Please see code snipped below). I don't really understand what is going on there....if somebody could please explain that, it would be greatly apperciated. Thanks! //Message Definition /* Byte 1: Bit(s) 3:0 = Unused; set to zero Bit(s) 7:4 = Message ID; set to 10 */ /* Byte 2: Bit(s) 3:0 = Unused; set to zero Bit(s) 7:4 = Acknowledge Message ID; set to 11 */ //Implementation BYTE Msg_Arry[2]; int Msg_Id = 10; int AckMsg_Id = 11; Msg_Arry[0] = Msg_Id & 0x0F; //MsgID & Unused Msg_Arry[1] = AckMsg_Id & 0x0F; //AckMsgID & Unused

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• Initializing ExportFactory using MEF

  - by Riz

  Scenario Application has multiple parts. Each part is in separate dll and implements interface IFoo All such dlls are present in same directory (plugins) The application can instantiate multiple instances of each part Below is the code snippet for the interfaces, part(export) and the import. The problem I am running into is, the "factories" object is initialized with empty list. However, if I try container.Resolve(typeof(IEnumerable< IFoo )) I do get object with the part. But that doesn't serve my purpose (point 4). Can anyone point what I am doing wrong here? public interface IFoo { string Name { get; } } public interface IFooMeta { string CompType { get; } } Implementation of IFoo in separate Dll [ExportMetadata("CompType", "Foo1")] [Export(typeof(IFoo), RequiredCreationPolicy = CreationPolicy.NonShared))] public class Foo1 : IFoo { public string Name { get { return this.GetType().ToString(); } } } Main application that loads all the parts and instantiate them as needed class PartsManager { [ImportMany] private IEnumerable<ExportFactory<IFoo, IFooMeta>> factories; public PartsManager() { IContainer container = ConstructContainer(); factories = (IEnumerable<ExportFactory<IFoo, IFooMeta>>) container.Resolve(typeof(IEnumerable<ExportFactory<IFoo, IFooMeta>>)); } private static IContainer ConstructContainer() { var catalog = new DirectoryCatalog(@"C:\plugins\"); var builder = new ContainerBuilder(); builder.RegisterComposablePartCatalog(catalog); return builder.Build(); } public IFoo GetPart(string compType) { var matchingFactory = factories.FirstOrDefault( x => x.Metadata.CompType == compType); if (factories == null) { return null; } else { IFoo foo = matchingFactory.CreateExport().Value; return foo; } } }

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• Main purpose of this task is to calculate volumes and surface areas of three dimensional geometric shapes like, cylinders, cones.

  - by Csc_Girl_Geek

  In Java Language Design your classes as below introducing: an Interface named “GeometricShapes” an abstract class named “ThreeDShapes” two child classes of ThreeDShapes: Cylinders and Cones. One test class names “TestShapes” Get the output for volumes and surface areas of cylinders and cones along with respective values of their appropriate input variables. Try to use toString() method and array. Your classes should be designed with methods that are required for Object-Oriented programming. So Far I Have: package Assignment2; public interface GeometricShapes { public void render(); public int[] getPosition(); public void setPosition(int x, int y); } package Assignment2; public abstract class ThreeDShapes implements GeometricShapes { public int[] position; public int[] size; public ThreeDShapes() { } public int[] getPosition() { return position; } public void setPosition(int x, int y) { position[0] = x; position[1] = y; } } package Assignment2; public class Cylinders extends ThreeDShapes { public Cylinder() { } public void render() { } } I don't think this is right and I do not know how to fix it. :( Please help.

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• How duplicate an object in a list and update property of duplicated objects ?

  - by user359706

  Hello What would be the best way to duplicate an object placed in a list of items and change a property of duplicated objects ? I thought proceed in the following manner: - get object in the list by "ref" + "article" - Cloned the found object as many times as desired (n times) - Remove the object found - Add the clones in the list What do you think? A concrete example: Private List<Product> listProduct; listProduct= new List<Product>(); Product objProduit_1 = new Produit; objProduct_1.ref = "001"; objProduct_1.article = "G900"; objProduct_1.quantity = 30; listProducts.Add(objProduct_1); ProductobjProduit_2 = new Product; objProduct_2.ref = "002"; objProduct_2.article = "G900"; objProduct_2.quantity = 35; listProduits.Add(objProduct_2); desired method: public void updateProductsList(List<Product> paramListProducts,Produit objProductToUpdate, int32 nbrDuplication, int32 newQuantity){ ... } Calling method example: updateProductsList(listProducts,objProduct_1,2,15); Waiting result: Replace follow object : ref = "001"; article = "G900"; quantite = 30; By: ref = "001"; article = "G900"; quantite = 15; ref = "001"; article = "G900"; quantite = 15; The Algorithm is correct? Would you have an idea of the method implementation "updateProductsList" Thank you in advance for your help.

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• (Java) Is there a type of object that can handle anything from primitives to arrays?

  - by Michael

  I'm pretty new to Java, so I'm hoping one of you guys knows how to do this. I'm having the user specify both the type and value of arguments, in any XML-like way, to be passed to methods that are external to my application. Example: javac myAppsName externalJavaClass methodofExternalClass [parameters] Of course, to find the proper method, we have to have the proper parameter types as the method may be overloaded and that's the only way to tell the difference between the different versions. Parameters are currently formatted in this manner: (type)value(/type), e.g. (int)71(/int) (string)This is my string that I'm passing as a parameter!(/string) I parse them, getting the constructor for whatever type is indicated, then execute that constructor by running its method, newInstance(<String value>), loading the new instance into an Object. This works fine and dandy, but as we all know, some methods take arrays, or even multi-dimensional arrays. I could handle the argument formatting like so: (array)(array)(int)0(/int)(int)1(/int)(/array)(array)(int)2(/int)(int)3(/int)(/array)(/array)... or perhaps even better... {{(int)0(/int)(int)1(/int)}{(int)2(/int)(int)3(/int)}}. The question is, how can this be implemented? Do I have to start wrapping everything in an Object[] array so I can handle primitives, etc. as argObj[0], but load an array as I normally would? (Unfortunately, I would have to make it an Object[][] array if I wanted to support two-dimensional arrays. This implementation wouldn't be very pretty.)

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• Is it possible to exclude some elements from parsing when using regular expression and .replace()?

  - by Fletus Mefitis

  <script language="javascript"> $("div.post-content , .parsedsig").each(function(){ if($(this).html().indexOf("[/tabulaScriptum]") != -1) { pattern = /\[tabulaScriptum=(.*?)\]([^\[]*)\[\/tabulaScriptum\]/gi $(this).html($(this).html().replace(pattern, "<div class='tabulaScriptum'><div class='tabulaNomen'>$1</div><div class='tabulaImpleo'>$2</div></div>")) } }); </script> This script is working perfectly, except for one thing... I need not to replace [tabulaScriptum=][/tabulaScriptum] in certain elements. For example, I don't want to replace those "tags" in element that has class .code-box. Is it possible? Clarification: element .code-box is located within .post-content. Clarification #2: this script creates simple division spoiler. .tabulaScriptum is spoier's body, .tabulaNomen is spoiler's name and button which, in turn, reveals(or hides) .tabulaImpleo on click. Reveal\hide script is located in some other place, and I didn't post it here since it doesn't really matter. Clarification #3: http://jsfiddle.net/PRtsw/1/ fiddle.

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• Checking if a function has C-linkage at compile-time [unsolvable]

  - by scjohnno

  Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Is there a possible implementation of is_c_linkage that would throw a compiler error for the second function, but not the first? I'm not sure that it's possible (though it may exist as a compiler extension, which I'd still like to know of). Thanks.

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• Template function overloading with identical signatures, why does this work?

  - by user1843978

  Minimal program: #include <stdio.h> #include <type_traits> template<typename S, typename T> int foo(typename T::type s) { return 1; } template<typename S, typename T> int foo(S s) { return 2; } int main(int argc, char* argv[]) { int x = 3; printf("%d\n", foo<int, std::enable_if<true, int>>(x)); return 0; } output: 1 Why doesn't this give a compile error? When the template code is generated, wouldn't the functions int foo(typename T::type search) and int foo(S& search) have the same signature? If you change the template function signatures a little bit, it still works (as I would expect given the example above): template<typename S, typename T> void foo(typename T::type s) { printf("a\n"); } template<typename S, typename T> void foo(S s) { printf("b\n"); } Yet this doesn't and yet the only difference is that one has an int signature and the other is defined by the first template parameter. template<typename T> void foo(typename T::type s) { printf("a\n"); } template<typename T> void foo(int s) { printf("b\n"); } I'm using code similar to this for a project I'm working on and I'm afraid that there's a subtly to the language that I'm not understanding that will cause some undefined behavior in certain cases. I should also mention that it does compile on both Clang and in VS11 so I don't think it's just a compiler bug.

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• Graph not following orientation

  - by user1214037

  so I am trying to draw some grid lines that in landscape go all the way down to the bottom, however when I switch to landscape the the graph doesn't follow and the grid lines go smaller. I have set the - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { // Return YES for supported orientations return YES; } However it still doesn't work, here is my code. Can anyone spot the problem? this is the custom view file, the view controller is the default apart from the code above that returns yes. .h file #import <UIKit/UIKit.h> #define kGraphHeight 300 #define kDefaultGraphWidth 900 #define kOffsetX 10 #define kStepX 50 #define kGraphBottom 300 #define kGraphTop 0 @interface GraphView : UIView @end And here is the implementation - (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetLineWidth(context, 0.6); CGContextSetStrokeColorWithColor(context, [[UIColor lightGrayColor] CGColor]); // How many lines? int howMany = (kDefaultGraphWidth - kOffsetX) / kStepX; // Here the lines go for (int i = 0; i < howMany; i++) { CGContextMoveToPoint(context, kOffsetX + i * kStepX, kGraphTop); CGContextAddLineToPoint(context, kOffsetX + i * kStepX, kGraphBottom); } CGContextStrokePath(context); } Any help would be appreciated btw I am following this tutorial http://buildmobile.com/creating-a-graph-with-quartz-2d/#fbid=YDPLqDHZ_9X

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• Implement two functions with the same name but different, non-covariant return types due to multiple abstract base classes

  - by user1508167

  If I have two abstract classes defining a pure virtual function with the same name, but different, non-covariant return types, how can I derive from these and define an implementation for both their functions? #include <iostream> class ITestA { public: virtual ~ITestA() {}; virtual float test() =0; }; class ITestB { public: virtual ~ITestB() {}; virtual bool test() =0; }; class C : public ITestA, public ITestB { public: /* Somehow implement ITestA::test and ITestB::test */ }; int main() { ITestA *a = new C(); std::cout << a->test() << std::endl; // should print a float, like "3.14" ITestB *b = dynamic_cast<ITestB *>(a); if (b) { std::cout << b->test() << std::endl; // should print "1" or "0" } delete(a); return 0; } As long as I don't call C::test() directly there's nothing ambiguous, so I think that it should work somehow and I guess I just didn't find the right notation yet. Or is this impossible, if so: Why?

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• recvfrom() return values in Stop-and-Wait UDP?

  - by mavErick

  I am trying to implement a Stop-and-Wait UDP client-server socket program in C. As known, there are basically three possible scenarios for Stop-and-Wait flow control. i.e., After transmitting a packet, the sender receives a correct ACK and thus starts transmitting the next packet; the sender receives an incorrect ACK and thus retransmits this packet; the sender receives no ACK within a TIMEOUT and thus retransmits this packet. My idea is to differentiate these three scenarios with the return value of recvfrom() on the sender side. For scenario 1&2: recvfrom() just returns the length of the received ACK. Since in my implementation the incorrect ACK is of the same length of the correct one, so I will have to go deeper and check the contents of the ACK. It's not a big deal. I know how to do. Problems come when I am trying to recognize scenario 3 where no ACK is received. What confuses me is that my recvfrom() is within a while loop, so the recvfrom() will be called constantly. What will it return when the receiver is not actually sending the sender ACK? Is it 0 or 1?

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