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  • Comparing objects and inheritance

    - by ereOn
    Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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  • Purpose of singletons in programming

    - by thecoshman
    This is admittedly a rather loose question. My current understanding of singletons is that they are a class that you set up in such a way that only one instance is ever created. This sounds a lot like a static class to me. The main differnce being that with a static class you don't / can't instance it, you just use it such as Math.pi(). With a singletong class, you would still need to do something like singleton mySingleton = new singleton(); mysingleton.set_name("foo"); singleton otherSingleton = new singleton(); // correct me if i am wrong, but mysingleton == othersingleton right now, yes? // this the following should happen? otherSingleston.set_name("bar"); mysingleton.report_name(); // will output "bar" won't it? Please note, I am asking this language independently, more about the concept. So I am not so worried about actually how to coed such a class, but more why you would wan't to and what thing you would need to consider.

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  • Generics and anonymous type

    - by nettguy
    I understood,normally generics is for compile time safe and allow us to keep strongly typed collection.Then how do generic allow us to store anonymous types like List<object> TestList = new List<object>(); TestList.Add(new { id = 7, Name = "JonSkeet" }); TestList.Add(new { id = 11, Name = "Marc Gravell" }); TestList.Add(new { id = 31, Name = "Jason" });

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  • Graph Tour with Uniform Cost Search in Java

    - by user324817
    Hi. I'm new to this site, so hopefully you guys don't mind helping a nub. Anyway, I've been asked to write code to find the shortest cost of a graph tour on a particular graph, whose details are read in from file. The graph is shown below: http://img339.imageshack.us/img339/8907/graphr.jpg This is for an Artificial Intelligence class, so I'm expected to use a decent enough search method (brute force has been allowed, but not for full marks). I've been reading, and I think that what I'm looking for is an A* search with constant heuristic value, which I believe is a uniform cost search. I'm having trouble wrapping my head around how to apply this in Java. Basically, here's what I have: Vertex class - ArrayList<Edge> adjacencies; String name; int costToThis; Edge class - final Vertex target; public final int weight; Now at the moment, I'm struggling to work out how to apply the uniform cost notion to my desired goal path. Basically I have to start on a particular node, visit all other nodes, and end on that same node, with the lowest cost. As I understand it, I could use a PriorityQueue to store all of my travelled paths, but I can't wrap my head around how I show the goal state as the starting node with all other nodes visited. Here's what I have so far, which is pretty far off the mark: public static void visitNode(Vertex vertex) { ArrayList<Edge> firstEdges = vertex.getAdjacencies(); for(Edge e : firstEdges) { e.target.costToThis = e.weight + vertex.costToThis; queue.add(e.target); } Vertex next = queue.remove(); visitNode(next); } Initially this takes the starting node, then recursively visits the first node in the PriorityQueue (the path with the next lowest cost). My problem is basically, how do I stop my program from following a path specified in the queue if that path is at the goal state? The queue currently stores Vertex objects, but in my mind this isn't going to work as I can't store whether other vertices have been visited inside a Vertex object. Help is much appreciated! Josh

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  • Rapid Opening and Closing System.IO.StreamWriter in C#

    - by ccomet
    Suppose you have a file that you are programmatically logging information into with regards to a process. Kinda like your typical debug Console.WriteLine, but due to the nature of the code you're testing, you don't have a console to write onto so you have to write it somewhere like a file. My current program uses System.IO.StreamWriter for this task. My question is about the approach to using the StreamWriter. Is it better to open just one StreamWriter instance, do all of the writes, and close it when the entire process is done? Or is it a better idea to open a new StreamWriter instance to write a line into the file, then immediately close it, and do this for every time something needs to be written in? In the latter approach, this would probably be facilitated by a method that would do just that for a given message, rather than bloating the main process code with excessive amounts of lines. But having a method to aid in that implementation doesn't necessarily make it the better choice. Are there significant advantages to picking one approach or the other? Or are they functionally equivalent, leaving the choice on the shoulders of the programmer?

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  • How to provide metadata tags,keywords to Windows and fill properties page for a custom file format?

    - by Mode
    Hi, My application uses its own file format (compressed SQLite databases) to store user created data. 1) I would like to know how to provide keywords, tags to Windows so that Vista search function can include my file format when indexing. 2) I would like to provide a properties page like you see when you right click a Microsoft Word document and select properties. Kindly point me in the right direction. Thank you.

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  • need some tips about distributed c# desktop application

    - by amipax
    Hi , my doubt is the following, I have a network with 5 pcs, each machine has XP installed, I don't know much about distributed desktop applications, so what i want is to create a C# application using sql server 2005 database and visual studio 2008. I want that each pc can have access to create/update/delete data on the one XP machine that will store the database files. Do i need WServer2003 or any special network technology?? thanks in advance

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  • Variable type for Application on Time Events [on hold]

    - by user2931226
    Been Trying to figure out how to go about setting a Variable for some Application On Time events, But still not confident to do it. These events (Macro's) get called by another Macro then they wait for 10 - 20 minutes, then they don't Run. So have read that (EarliestTime argument) should be assigned to a variable to store it other wise it looses it when other things are running Help appreciated Thanks Sub settimers() Application.OnTime TimeValue(Range("$X$9").Text), "StartBlink" Application.OnTime TimeValue(Range("$W$11").Text), "StopBlink" End Sub

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  • help for splitting a string in javascript

    - by Hero
    Hi everyone... I'd asked a question about the splitting the a string like below: Input string: "a=aa| b=b||b | c=cc" and the output: a=aa b=b||b c=cc Kobi's answer was: var matches = "a=aa|b=b||b|c=cc".match(/(?:[^|]|\|\|)+/g) his answer was correct. But I need to use "split" method and save store the outputs in a array. so I can't use the Match Method. So please help me...

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  • Custom URL for the Birdhouse app

    - by bryanjclark
    I'd like to figure out the custom URL scheme for the Birdhouse iPhone app, but there doesn't seem to be any documentation. Birdhouse is an app to store drafts for Twitter. I'd like to send it a string of text, and I know that it's possible: Birdhouse responds to the URL birdhouse:/// The Twitter app sends drafts to Birdhouse if it's installed on your phone. I've figured out the birdhouse:/// part, but how do I send the text?

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  • Does NSClassFromString affect performance?

    - by Tomen
    I want to create a controller that depends on the class of a given instance of a model -(BaseController *)getControllerForModel:(Model *)model { BaseController *controller = nil; Class controllerClass = [BaseController class]; //the default value //find the right controller if ([model isMemberOfClass:[ModelClass1 class]]) controllerClass = [ConcreteController1 class]; else if ([model isMemberOfClass:[ModelClass2 class]]) controllerClass = [ConcreteController2 class]; else if ([model isMemberOfClass:[ModelClass3 class]]) controllerClass = [ConcreteController3 class]; ... else if ([model isMemberOfClass:[ModelClassX class]]) controllerClass = [ConcreteControllerX class]; else Trace(TRACELEVEL_WARNING, @"Unrecognized model type: %@", NSStringFromClass([model class])); //Now instantiate it with the model controller = [[[controllerClass alloc] initWithModel:model] autorelease]; return slotController; } I want to find a more flexible solution to this and thought of having a dictionary, which maps Model-Classes to Controller-Classes and then NSClassFromString could give me the right instance. My question is this: Is NSClassFromString using much of my applications performance if i use it several times (say, 100 times at once)? Or would it be about as fast as the above approach?

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  • Validation - Data Integrity

    - by Thomas
    A table can only store 10 records in a particular state, 10 users over 30 years for example, the others must be less than 30 years. It is a business rule and as such should be respected. How to ensure that state? Think: multiple users accessing this table.

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  • Free SVN repo server without requiring a project

    - by Nathan Campos
    I want to know if there are any free Subversion repository hosting servers where you don't need to have a 'project' to host your C++ files in. I don't have a actual project, but I want to store my C++ in an SVN repository. I am looking for something like OpenSVN where you can upload your C++ files, but it requires you to have a project. Can you recommend a Subversion hosting service where you can upload your files to an account, rather than a project. Something like: http://www.test-svn.com/~nathanpc/

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  • Stored Queries?

    - by phpeffedup
    Is it considered crazy to store common SQL queries for my web app in a database for use in execution? Or is that common practice? Or is it impossible? My thinking is, this way, I avoid hard-coding SQL into my application files, and add another level of abstraction. Is this crazy? Is this what a stored procedure is? Or is that something else?

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  • Authenticating users in iPhone app

    - by Myron
    I'm developing an HTTP api for our web application. Initially, the primary consumer of the API will be an iPhone app we're developing, but I'm designing this with future uses in mind (such as mobile apps for other platforms). I'm trying to decide on the best way to authenticate users so they can access their accounts from the iPhone. I've got a design that I think works well, but I'm no security expert, so I figured it would be good to ask for feedback here. The design of the user authentication has 3 primary goals: Good user experience: We want to allow users to enter their credentials once, and remain logged in indefinitely, until they explicitly log out. I would have considered OAuth if not for the fact that the experience from an iPhone app is pretty awful, from what I've heard (i.e. it launches the login form in Safari, then tells the user to return to the app when authentication succeeds). No need to store the user creds with the app: I always hate the idea of having the user's password stored in either plain text or symmetrically encrypted anywhere, so I don't want the app to have to store the password to pass it to the API for future API requests. Security: We definitely don't need the intense security of a banking app, but I'd obviously like this to be secure. Overall, the API is REST-inspired (i.e. treating URLs as resources, and using the HTTP methods and status codes semantically). Each request to the API must include two custom HTTP headers: an API Key (unique to each client app) and a unique device ID. The API requires all requests to be made using HTTPS, so that the headers and body are encrypted. My plan is to have an api_sessions table in my database. It has a unique constraint on the API key and unique device ID (so that a device may only be logged into a single user account through a given app) as well as a foreign key to the users table. The API will have a login endpoint, which receives the username/password and, if they match an account, logs the user in, creating an api_sessions record for the given API key and device id. Future API requests will look up the api_session using the API key and device id, and, if a record is found, treat the request as being logged in under the user account referenced by the api_session record. There will also be a logout API endpoint, which deletes the record from the api_sessions table. Does anyone see any obvious security holes in this?

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  • Specify .doc file encoding when creating with php?

    - by arma
    Hey, Currently i try to create some of my database export work more automated and i decided to go with exporting data from MySql database to .doc file in php. So im doing some database work and store complete html to a $str variable and then write/make new file: $fp = fopen($file, 'w+'); fwrite($fp,$str); fclose($fp); The problem here is not creating .doc file, but when i download and view that .doc file it's not in UTF-8 it's in unicode.

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  • Microphone question in iPhone SDK

    - by Henry D'Andrea
    I am trying to do an app, to where when it launches, it will detect audio, and then play it back automatically. NO BUTTONS, NOthing to press. Just a picture of something then, it listens for audio, then plays it back. Similar to the Talking Carl app in the App Store. Any ideas/help? Would appreciate it, if i could use the code with IB.

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  • Access is refusing to run an query with linked table?

    - by Mahmoud
    Hey all i have 3 tables each as follow cash_credit Bank_Name-------in_date-------Com_Id---Amount America Bank 15/05/2010 1 200 HSBC 17/05/2010 3 500 Cheque_credit Bank_Name-----Cheque_Number-----in_date-------Com_Id---Amount America Bank 74835435-5435 15/05/2010 2 600 HSBC 41415454-2851 17/05/2010 5 100 Companies com_id----Com_Name 1 Ebay 2 Google 3 Facebook 4 Amazon Companies table is a linked table when i tried to create an query as follow SELECT cash_credit.Amount, Companies.Com_Name, cheque_credit.Amount FROM cheque_credit INNER JOIN (cash_credit INNER JOIN Companies ON cash_credit.com_id = Companies.com_id) ON cheque_credit.com_id = Companies.com_id; I get an error saying that my inner Join is incorrectly, this query was created using Access 2007 query design the error is Type mismatch in expression then i thought it might be the inner join so i tried Left Join and i get an error that this method is not used JOIN expression is not supported I am confused on where is the problem that is causing all this

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