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  • How to use the vtable to determine class type

    - by Alex Silverman
    I was recently on an interview for a position where C/C++ is the primary language and during one question I was told that it's possible to use the vtable to determine which class in a hierarchy a base pointer actually stores. So if, for example you have class A { public: A() {} virtual ~A() {} virtual void method1() {} }; class B : public A { public: B() {} virtual ~B() {} virtual void method1() {} }; and you instantiate A * pFoo = new B(), is it indeed possible to use the vtable to determine whether pFoo contains a pointer to an instance of A or B?

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  • Given an even number of vertices, how to find an optimum set of pairs based on proximity?

    - by Alex Z
    The problem: We have a set of n vertices in 3D euclidean space, and there is an even number of these vertices. We want to pair them up based on their proximity. In other words, we'd like to be able to find a set of vertex pairs, where the vertices in each pair are as close as possible together. We want to minimise sacrificing the proximity between the vertices of any other pairs as much as possible in doing this. I am not looking for the most optimal solution (if it even strictly exists/can be done), just a reasonable one that can be computed relatively quickly. A relatively awful brute force approach involves choosing a vertex and looping through the rest to find its nearest neighbor and then repeating until there are none left. Of course as we near the end of the list the closest vertex could be very far away, but it is the only choice, therefore this can fail badly on the third point above.

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  • The question about the basics of LINQ to SQL working

    - by Alex
    I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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  • Multiple Input From Keyboard C# WPF

    - by Alex
    I am writing a Tetris clone in WPF. If I hold down the right arrow key, the current piece shifts right. For playability, I want to allow the user to press another key (i.e. F-key) and rotate the moving piece without having to let go of the right arrow key first. Currently when I do this, the piece stops shifting. My first basic attempt at this was hooking into Window_PreviewKeyDown(object sender, KeyEventArgs e) and then sending a message to the controller layer. How do I structure my input-listening code to allow this? My current code Here

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  • Simple Scala syntax - trying to define "==" operator - what am I missing?

    - by Alex R
    While experimenting with some stuff on the REPL, I got to a point where I needed something like this: scala class A(x:Int) { println(x); def ==(a:A) : Boolean = { this.x == a.x; } } Just a simple class with an "==" operator. Why doesn't it work??? Here's the result: :10: error: type mismatch; found : A required: ?{val x: ?} Note that implicit conversions are not applicable because they are ambiguous: both method any2ArrowAssoc in object Predef of type [A](x: A)ArrowAssoc[A] and method any2Ensuring in object Predef of type [A](x: A)Ensuring[A] are possible conversion functions from A to ?{val x: ?} class A(x:Int) { println(x); def ==(a:A) : Boolean = { this.x == a.x; } } ^ This is scala 2.8 RC1. Thanks

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  • Using Time datatype in MySQL without seconds

    - by Alex
    I'm trying to store a 12/24hr (ie; 00:00) clock time in a MySQL database. At the moment I am using the time datatype. This works ok but it insists on adding the seconds to the column. So you enter 09:20 and it is stored as 09:20:00. Is there any way I can limit it in MySQL to just 00:00?

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  • Log information inside a JUnit Suite

    - by Alex Marinescu
    I'm currently trying to write inside a log file the total number of failed tests from a JUnite Suite. My testsuite is defined as follows: @RunWith(Suite.class) @SuiteClasses({Class1.class, Class2.class etc.}) public class SimpleTestSuite {} I tried to define a rule which would increase the total number of errors when a test fails, but apparently my rule is never called. @Rule public MethodRule logWatchRule = new TestWatchman() { public void failed(Throwable e, FrameworkMethod method) { errors += 1; } public void succeeded(FrameworkMethod method) { } }; Any ideas on what I should to do to achieve this behaviour?

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  • Is there an easier way to do Classic ASP "relative path"?

    - by Alex.Piechowski
    Right now, I'm having trouble. First of all I have a page, let's call it "http://blah.com/login". That obviously goes strait to "index.asp" A line of Main.asp: <!--#include file="resource/menu.asp"--> Page top includes all of what I need for my menu... so: Part of resource/menu.htm: <div id="colortab" class="ddcolortabs"> <ul> <li><a href="main.asp" title="Main" rel="dropmain"><span>Main</span></a></li> ... </ul> </div> <!--Main drop down menu --> <div id="dropmain" class="dropmenudiv_a"> <a href="main/announcements.asp">Announcements</a> <a href="main/contacts.asp">Contact Information</a> <a href="main/MeetingPlans.asp">Meeting Plan</a> <a href="main/photos.asp">Photo Gallery</a> <a href="main/events.asp">Upcoming Events</a> </div> Let's say I click on the "announcements" (http://blah.com/login/main/announcements.asp) link... Now I'm at the announcements page! But wait, I include the same menu file. Guess what happens: I get sent to "http://blah.com/login/main/main/announcements.asp Which doesn't exist... My solution: Make a menu_sub.asp include for any subpages. But wait a second... this WORKS, but it gets REALLY REALLY messy... What can I do to use just one main "menu.asp" instead of "menu_sub.asp"? using "/main/announcements.asp" WON'T be an option because this is a web application that will be on different directories per server. Any ideas? PLEASE

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  • in R, question about generate table

    - by alex
    a = matrix(1:25,5,5) B = capture.output(for (X in 1:5){ A = c(min(a[,X]),quantile(a[,X],0.25),median(a[,X]),quantile(a[,X],0.75),max(a[,X]),mean(a[,X]),sd(a[,X])/m^(1/2),var(a[,X])) cat(A,"\n") }) matrix(B,8,5) what i was trying to do is to generate a table which each column has those element in A and in that order. i try to use the matrix, but seems like it dont reli work here...can anyone help 1 2 3 4 5 min 1st quartile median SEM VAR THIS IS WHAT I WANT THE TABLE LOOKS LIKE ..

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  • Reinstantiating a GUI (JFrame) object

    - by Alex
    Hi guys, basically I want my JFrame to become a completely new JFrame object when an event is triggered. I have some code that basically calls [CODE]GUI gui = new GUI(x, y)[/CODE] the only problem I'm having is that as well as creating the new GUI object, it is not deleting the old window. Can anyone tell me how to get rid of the old window. Thanks.

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  • In MS Access is there a way to allow forms to update while maintaning Read Only

    - by Alex
    I have several forms linked tables via queries. The form pull data such as sales and ratios by selecting a product from the main's form's combo box. I am however having to issues: 1- I would ultimately prefer the combo box to be a free entry; however by just entering in the box and hitting enter (not a button called “enter on a screen” which would initiate recalcs, just normal enter), while it does bring the new information in sub-forms it also changes the information in the original table. If I make the table read only that it just doesn't allow the form to work by saying that the table is read only. 2- The same Read only issue occurs when another user with read only rights tries to use the database. I understand that ready only is functioning as intended, however I am wondering if there is way to make some functions work while disallowing the updating. I am unfortunately learning on the go, so go easy plz. Thank you

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  • C# Get Keys from a Dictionary<string, Stream>

    - by alex
    Suppose I have a Dictionary like so: Dictionary<string, Stream> How can I get a list (or IEnumerable or whatever) of JUST the Keys from this dictionary? Is this possible? I could enumerate the dictionary, and extract the keys one by one, but I was hoping to avoid this. In my instance, the Dictionary contains a list of filenames (file1.doc, filex.bmp etc...) and the stream content of the file from another part of the application.

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  • How do I find where an exception was thrown in C++?

    - by Alex
    I have a program that throws an uncaught exception somewhere. All I get is a report of an exception being thrown, and no information as to where it was thrown. It seems illogical for a program compiled to contain debug symbols not to notify me of where in my code an exception was generated. Is there any way to tell where my exceptions are coming from short of setting 'catch throw' in gdb and calling a backtrace for every single thrown exception?

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  • Deployment of SQL Server: installing a second instance?

    - by Workshop Alex
    Simple problem. I'm working on a Delphi 2007/WIN32 application which now uses MS Access as simple data store. I have to modify it to support SQL Server Express, which is easy. These modifications are working so the application can be deployed using either SQL Server or MS Access. (Whatever the user prefers.) I did consider deploying the whole application together with the SQL Compact but this is not practicak. Using SQL Server Express 2008 instead of 2005 is an option, but also has a few nasty side-effects which we don't want to resolve for now. The problem is deploying the whole project. The installation with SQL Server would need a quiet installation so the user won't notice it. SQL Server is mentioned in the documentation so they know it's there. We just don't want to bother them with technical issues. In most cases, such an installation will go just fine. But what if the user already has an SQL Server (2005) installation which is used for something else? Personally, I would prefer to just install a second instance of SQL Server on their system so it won't conflict with the other installation. (Thus, if they uninstall the other app, the SQL instance will just stay installed.) While SQL Server 2005 and 2008 can be installed on the same system simply by using two different names for the instance, I wonder if it's also possible to install SQL Server 2005 twice on a single system to get two instances. And if possible, how?

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  • How to cancel a touch sequence

    - by Alex
    I have an UIImage view that responds to touch events. I want to cancel the touch sequence if the touch goes outside of certain bounds. How can I do that? I know that I can inspect the coordinates of the touch object, what I don't know is how to cancel the sequence. I don't see any event in the API that allows for that.

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  • mysql replace matching but not changing

    - by alex
    I've used mysql's update replace function before, but even though I think I'm following the same syntax, I can't get this to work-it matches the rows, but doesn't replace. Here's what I'm trying to do: mysql> update contained_widgets set preference_values = replace(preference_values, '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li>', '<li><a_href="/enewsletter"><span class="not-tc">eNewsletter</span></a></li> <li> <a_href="/projects"><span class="not-tc">Projects</span></a></li>'); Query OK, 0 rows affected (0.00 sec) Rows matched: 77 Changed: 0 Warnings: 0 I don't see what I'm missing. Any help is appreciated. I edited "a " to "a_" because the site thinks I'm posting spam links otherwise.

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  • ASP.NET MVC Route based on Web Browser/Device (e.g. iPhone)

    - by Alex
    Is it possible, from within ASP.NET MVC, to route to different controllers or actions based on the accessing device/browser? I'm thinking of setting up alternative actions and views for some parts of my website in case it is accessed from the iPhone, to optimize display and functionality of it. I don't want to create a completely separate project for the iPhone though as the majority of the site is fine on any device. Any idea on how to do this?

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  • Save phone calls data in a DB?

    - by Alex
    How would you save this data on a database: An user can make phone calls (id, date, hour, duration, outcome). The "outcome" can be, for example, to recall the client on another day (so I have to save the date, the hour, etc of this "future" call). How would you manage this data on a db? At the moment i have only a "Call" table.

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