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Articles indexed Thursday April 29 2010

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  • Pointer to auto_ptr instead of a classical double pointer

    - by Pin
    Hello. I'm quite new to smart pointers and was trying to refactor some existing code to use auto_ptr. The question I have is about double pointers and their auto_ptr equivalent, if that makes sense. I have a function that accepts a double pointer as its parameter and the function allocates resources for it: void foo ( Image** img ) { ... *img = new Image(); ...} This function is then used like this: Image* img = NULL; foo ( &img ); ... delete img; I want to use auto_ptr to avoid having to call delete explicitly. Is the following correct? void foo ( auto_ptr<Image>* img ); and then auto_ptr<Image> img = NULL; foo ( &img ); Thanks.

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  • .NET: will Random.Random operate differently inside a static method

    - by Craig Johnston
    I am having difficulty with the following code which is inside a static method of a non-static class. int iRand; int rand; rand = new Random((int)DateTime.Now.Ticks); iRand = rand.Next(50000); The iRand number, along with some other values, are being inserted into a new row of an Access MDB table via OLEDB. The iRand number is being inserted into a field that is part of the primary key, and the insert attempt is throwing the following exception even though the iRand number is supposed to be random: System.Data.OleDb.OleDbException: The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again. Could the fact the method is static be making the iRand number stay the same, for some reason?

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  • Should I use custom exceptions to control the flow of application?

    - by bonefisher
    Is it a good practise to use custom business exceptions (e.g. BusinessRuleViolationException) to control the flow of user-errors/user-incorrect-inputs??? The classic approach: I have a web service, where I have 2 methods, one is the 'checker' (UsernameAlreadyExists()) and the other one is 'creator' (CreateUsername())... So if I want to create a username, I have to do 2 roundtrips to webservice, 1.check, 2.if check is OK, create. What about using UsernameAlreadyExistsException? So I call only the 2. web service method (CrateUsername()), which contains the check and if not successfull, it throws the UsernameAlreadyExistsException. So the end goal is to have only one round trip to web service and the checking can be contained also in other web service methods (so I avoid calling the UsernameAlreadyExists() all the times..). Furthermore I can use this kind of business error handling with other web service calls completely avoiding the checking prior the call.

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  • Thread testing for time

    - by DanielFH
    Hi there :) I'm making a thread for my application that's going to do an exit operation at a given time (only hours and minutes, day/month doesn't matter). Is this the right way to do it, and also the right way to test for time? I'm testing for a 24 hour clock by the way, not AM / PM. I'm then in another class going to call this something like new Thread(new ExitThread()).start(); public class ExitThread implements Runnable { @Override public void run() { Date date = new Date(System.currentTimeMillis()); String time = new SimpleDateFormat("HHmmss").format(date); int currentTime = Integer.parseInt(time); int exitTime = 233000; while(true) { try { Thread.sleep(10000); } catch (InterruptedException e) { e.printStackTrace(); } if(currentTime >= exitTime ) { // do exit operation here } } } Thanks. //D

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  • Time calculations with MySQL TIMEDIFF

    - by Oli
    Hi there, I have the following table: mysql> SELECT id,start1,stop1,start2,stop2 FROM times; +----+---------------------+---------------------+---------------------+---------------------+ | id | start1 | stop1 | start2 | stop2 | +----+---------------------+---------------------+---------------------+---------------------+ | 4 | 2010-04-23 08:05:00 | 2010-04-23 12:15:00 | 2010-04-23 12:45:00 | 2010-04-23 16:50:00 | | 2 | 2010-04-26 09:30:00 | 2010-04-26 12:10:00 | 2010-04-26 12:50:00 | 2010-04-26 16:50:00 | | 7 | 2010-04-28 08:45:00 | 2010-04-28 11:45:00 | 2010-04-28 13:10:00 | 2010-04-28 17:29:00 | | 6 | 2010-04-27 09:30:00 | 2010-04-27 12:15:00 | 2010-04-27 12:55:00 | 2010-04-27 18:44:00 | +----+---------------------+---------------------+---------------------+---------------------+ I want to sum total worktime and the difference to the "needed work hours". It works pretty well with the statement below, but for unknown reasons it doesn't work for id 6. start*/stop* fields are in format datetime. SELECT *, TIME_FORMAT(TIMEDIFF(totaltime,'08:24'),'%H:%i') AS diff, totaltime > '08:24' AS redorgreen FROM ( SELECT DATE_FORMAT(start1,'%a %e. %M %Y') AS date, TIME_FORMAT(SUM(TIMEDIFF(stop1,start1) + TIMEDIFF(stop2,start2)),'%H:%i') AS totaltime, TIME_FORMAT(start1,'%H:%i') AS start1, TIME_FORMAT(stop1,'%H:%i') AS stop1, TIME_FORMAT(start2,'%H:%i') AS start2, TIME_FORMAT(stop2,'%H:%i') AS stop2, id as id FROM times GROUP BY id ASC ) AS somethingwedontneed; This is the result: select id, TIME_FORMAT(SUM(TIMEDIFF(stop1,start1) + TIMEDIFF(stop2,start2)),'%H:%i') AS totaltime from times group by id; +----+-----------+ | id | totaltime | +----+-----------+ | 2 | 06:40 | | 4 | 08:15 | | 6 | NULL | | 7 | 07:19 | +----+-----------+ Thanks in advance for every hint.

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  • What is the equivalent of .NET events in Ruby?

    - by Gishu
    The problem is very simple. An object needs to notify some events that might be of interest to observers. When I sat to validate a design that I cooked up now in Ruby just to validate it.. I find myself stumped as to how to implement the object events. In .Net this would be a one-liner.. .Net also does handler method signature verification,etc. e.g. // Object with events public delegate void HandlerSignature(int a); public event HandlerSignature MyEvent; public event HandlerSignature AnotherCriticalEvent; // Client MyObject.MyEvent += new HandlerSignature(MyHandlerMethod); // MyHandlerMethod has same signature as delegate Is there an EventDispatcher module or something that I am missing that I can strap on to a Ruby class ? Hoping for an answer that plays along with Ruby's principle of least surprise. An event would be the name of the event plus a queue of [observer, methodName] objects that need to be invoked when the event takes place.

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  • In PHP + MySQL, How do I join many tables with conditions

    - by Moe
    Hi, I'm trying to get the users full activity throughout the website. I need to Join many tables throughout the database, with that condition that it is one user. What I currently have written is: SELECT * FROM comments AS c JOIN rphotos AS r ON c.userID = r.userID AND c.userID = '$defineUserID'; But What it is returning is everything about the user, but it repeats rows. For instance, for one user he has 6 photos and 5 comments So I expect the join to return 11 rows. Instead it returns 30 results like so: PhotoID = 1; CommentID = 1; PhotoID = 1; CommentID = 2; PhotoID = 1; CommentID = 3; and so on... What am i doing wrong?

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  • Cycles/byte calculations

    - by matskn
    Hi ! In Crypto communities it is common to measure algorithm performance in cycles/byte. My question is, which parameters in the CPU architecture are affecting this number? Except the clockspeed ofcourse :)

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  • Where to put constants in Rails

    - by Sam
    I have a few constants which are arrays that I don't want to create db's for but I don't know where to store the constants without getting errors. For example CONTAINER_SIZES = [["20 foot"],["40 foot"]] Where can I store this so all models and controller have access to this?

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  • Why do browsers allow switching off Javascript?

    - by gath
    Am curious why modern browsers allow switching off Javascript. It's so clear now that to do any substantial modern web application you need to integrate some high level of Javascript, why cant javascript be made an integral part of the browser? It becomes even more annoying especially when this option is OFF by default (IE!!) My opinion is, it should be made a standard for all the browsers to have javascript option enabled by default. What do you guys think?

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  • Casting class to interface and back

    - by Thomas
    I have the following: public interface ICartItem { string Name { get; set; } } public class CartItem : ICartItem { public string Name { get; set; } } I then create a List and cast it to an interface: IList<CartItem> items = new List<CartItem>() { new CartItem() { Name = "MyItem" } }; IList<ICartItem> cartItems = items.Cast<ICartItem>().ToList(); Is there a way to cast it back again like illustrated below? IList<CartItem> newList = cartItems as IList<CartItem>;

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  • Is it necessarily bad style to ignore the return value of a method

    - by Jono
    Let's say I have a C# method public void CheckXYZ(int xyz) { // do some operation with side effects } Elsewhere in the same class is another method public int GetCheckedXYZ(int xyz) { int abc; // functionally equivalent operation to CheckXYZ, // with additional side effect of assigning a value to abc return abc; // this value is calculated during the check above } Is it necessarily bad style to refactor this by removing the CheckXYZ method, and replacing all existing CheckXYZ() calls with GetCheckedXYZ(), ignoring the return value? The returned type isn't IDisposable in this case. Does it come down to discretion?

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