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• How to use interfaces in exception handling

  - by vikp

  Hi, I'm working on the exception handling layer for my application. I have read few articles on interfaces and generics. I have used inheritance before quite a lot and I'm comfortable with in that area. I have a very brief design that I'm going to implement: public interface IMyExceptionLogger { public void LogException(); // Helper methods for writing into files,db, xml } I'm slightly confused what I should be doing next. public class FooClass: IMyExceptionLogger { // Fields // Constructors } Should I implement LogException() method within FooClass? If yes, than I'm struggling to see how I'm better of using an interface instead of the concrete class... I have a variety of classes that will make a use of that interface, but I don't want to write an implementation of that interface within each class. In the same time If I implement an interface in one class, and then use that class in different layers of the application I will be still using concrete classes instead of interfaces, which is a bad OO design... I hope this makes sense. Any feedback and suggestions are welcome. Please notice that I'm not interested in using net4log or its competitors because I'm doing this to learn. Thank you Edit: Wrote some more code. So I will implement variety of loggers with this interface, i.e. DBExceptionLogger, CSVExceptionLogger, XMLExceptionLogger etc. Than I will still end up with concrete classes that I will have to use in different layers of my application.

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• WPF app startup problems

  - by Dave

  My brain is all over the map trying to fully understand Unity right now. So I decided to just dive in and start adding it in a branch to see where it takes me. Surprisingly enough (or maybe not), I am stuck just getting my darn Application to load properly. It seems like the right way to do this is to override OnStartup in App.cs. I've removed my StartupUri from App.xaml so it doesn't create my GUI XAML. My App.cs now looks something like this: public partial class App : Application { private IUnityContainer container { get; set; } protected override void OnStartup(StartupEventArgs e) { container = new UnityContainer(); GUI gui = new GUI(); gui.Show(); } protected override void OnExit(ExitEventArgs e) { container.Dispose(); base.OnExit(e); } } The problem is that nothing happens when I start the app! I put a breakpoint at the container assignment, and it never gets hit. What am I missing? App.xaml is currently set to ApplicationDefinition, but I'd expect this to work because some sample Unity + WPF code I'm looking at (from Codeplex) does the exact same thing, except that it works! I've also started the app by single-stepping, and it eventually hits the first line in App.xaml. When I step into this line, that's when the app just starts "running", but I don't see anything (and my breakpoint isn't hit). If I do the exact same thing in the sample application, stepping into App.xaml puts me right into OnStartup, which is what I'd expect to happen. Argh! Is it a Bad Thing to just put the Unity construction in my GUI's Window_Loaded event handler? Does it really need to be at the App level?

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• C++: inheritance problem

  - by Helltone

  It's quite hard to explain what I'm trying to do, I'll try: Imagine a base class A which contains some variables, and a set of classes deriving from A which all implement some method bool test() that operates on the variables inherited from A. class A { protected: int somevar; // ... }; class B : public A { public: bool test() { return (somevar == 42); } }; class C : public A { public: bool test() { return (somevar > 23); } }; // ... more classes deriving from A Now I have an instance of class A and I have set the value of somevar. int main(int, char* []) { A a; a.somevar = 42; Now, I need some kind of container that allows me to iterate over the elements i of this container, calling i::test() in the context of a... that is: std::vector<...> vec; // push B and C into vec, this is pseudo-code vec.push_back(&B); vec.push_back(&C); bool ret = true; for(i = vec.begin(); i != vec.end(); ++i) { // call B::test(), C::test(), setting *this to a ret &= ( a .* (&(*i)::test) )(); } return ret; } How can I do this? I've tried two methods: forcing a cast from B::* to A::*, adapting a pointer to call a method of a type on an object of a different type (works, but seems to be bad); using std::bind + the solution above, ugly hack; changing the signature of bool test() so that it takes an argument of type const A& instead of inheriting from A, I don't really like this solution because somevar must be public.

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• Is there unresizable space in latex? Pictures in good looking grid.

  - by drasto

  I've created latex macro to typeset guitar chords diagrams(using picture environment). Now I want to make diagrams of different appear in good looking grid when typeset one next to each other as the picture shows: The picture. (on the picture: Labeled "First" bad layout of diagrams, labeled "Second" correct layout when equal number of diagrams in line) I'm using \hspace to make some skips between diagrams, otherwise they would be too near to each other. As you can see in second case when latex arrange pictures in so that there is same number of them in each line it works. However if there is less pictures in the last line they become "shifted" to the right. I don't want this. I guess is because latex makes the space between diagrams in first line a little longer for the line to exactly fit the page width. How do I tell latex not to resize spaces created by \hspace ? Or is there any other way ? I guess I cannot use tables because I don't know how many diagrams will fit in one line... This is current state of code: \newcommand{\spaceForChord}{1.7cm} \newcommnad{\chordChart}[1]{% %calculate dimensions xdim and ydim according to setings \begin{picture}(xdim, ydim){% %draw the diagram inside defined area }% \hspace*{\spaceForChord}% \hspace*{-\xdim}% }% %end preambule and begin document \begin{document} First:\\* \\* \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} \chordChart{...some arguments for to change diagram look...} %...above line is repeated 12 more times to produce result shown at the picture \end{document} Thanks for any help.

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• How to copy files without slowing down my app?

  - by Kevin Gebhardt

  I have a bunch of little files in my assets which need to be copied to the SD-card on the first start of my App. The copy code i got from here placed in an IntentService works like a charm. However, when I start to copy many litte files, the whole app gets increddible slow (I'm not really sure why by the way), which is a really bad experience for the user on first start. As I realised other apps running normal in that time, I tried to start a child process for the service, which didn't work, as I can't acess my assets from another process as far as I understood. Has anybody out there an idea how a) to copy the files without blocking my app b) to get through to my assets from a private process (process=":myOtherProcess" in Manifest) or c) solve the problem in a complete different way Edit: To make this clearer: The copying allready takes place in a seperate thread (started automaticaly by IntentService). The problem is not to separate the task of copying but that the copying in a dedicated thread somehow affects the rest of the app (e.g. blocking to many app-specific resources?) but not other apps (so it's not blocking the whole CPU or someting) Edit2: Problem solved, it turns out, there wasn't really a problem. See my answer below.

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• Is it possible to load an entire SQL Server CE database into RAM?

  - by DanM

  I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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• C++ private inheritance and static members/types

  - by WearyMonkey

  I am trying to stop a class from being able to convert its 'this' pointer into a pointer of one of its interfaces. I do this by using private inheritance via a middle proxy class. The problem is that I find private inheritance makes all public static members and types of the base class inaccessible to all classes under the inheriting class in the hierarchy. class Base { public: enum Enum { value }; }; class Middle : private Base { }; class Child : public Middle { public: void Method() { Base::Enum e = Base::value; // doesn't compile BAD! Base* base = this; // doesn't compile GOOD! } }; I've tried this in both VS2008 (the required version) and VS2010, neither work. Can anyone think of a workaround? Or a different approach to stopping the conversion? Also I am curios of the behavior, is it just a side effect of the compiler implementation, or is it by design? If by design, then why? I always thought of private inheritance to mean that nobody knows Middle inherits from Base. However, the exhibited behavior implies private inheritance means a lot more than that, in-fact Child has less access to Base than any namespace not in the class hierarchy!

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• What would be a better implementation of shared variable among subclass

  - by Churk

  So currently I have a spring unit testing application. And it requires me to get a session cookie from a foreign authentication source. Problem what that is, this authentication process is fairly expensive and time consuming, and I am trying to create a structure where I am authenticate once, by any subclass, and any subsequent subclass is created, it will reuse this session cookie without hitting the authentication process again. My problem right now is, the static cookie is null each time another subclass is created. And I been reading that using static as a global variable is a bad idea, but I couldn't think of another way to do this because of Spring framework setting things during run time and how I would set the cookie so that all other classes can use it. Another piece of information. The variable is being use, but is change able during run time. It is not a single user being signed in and used across the board. But more like a Sub1 would call login, and we have a cookie. Then multiple test will be using that login until SubX will come in and say, I am using different credential, so I need to login as something else. And repeats. Here is a outline of my code: public class Parent implements InitializingBean { protected static String BASE_URL; public static Cookie cookie; ... All default InitializingBean methods ... afterPropertiesSet() { cookie = // login process returns a cookie } } public class Sub1 extends Parent { @resource public String baseURL; @PostConstruct public void init() { // set parents with my baseURL; BASE_URL = baseURL; } public void doSomething() { // Do something with cookie, because it should have been set by parent class } } public class Sub2 extends Parent { @resource public String baseURL; @PostConstruct public void init() { // set parents with my baseURL; BASE_URL = baseURL; } public void doSomethingElse() { // Do something with cookie, because it should have been set by parent class } }

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• LINQ - Splitting up a string with maximum length, but not chopping words apart.

  - by Stacey

  I have a simple LINQ Extension Method... public static IEnumerable<string> SplitOnLength(this string input, int length) { int index = 0; while (index < input.Length) { if (index + length < input.Length) yield return input.Substring(index, length); else yield return input.Substring(index); index += length; } } This takes a string, and it chops it up into a collection of strings that do not exceed the given length. This works well - however I'd like to go further. It chops words in half. I don't need it to understand anything complicated, I just want it to be able to chop a string off 'early' if cutting it at the length would be cutting in the middle of text (basically anything that isn't whitespace). However I suck at LINQ, so I was wondering if anyone had an idea on how to go about this. I know what I am trying to do, but I'm not sure how to approach it. So let's say I have the following text. This is a sample block of text that I would pass through the string splitter. I call this method SplitOnLength(6) I would get the following. This i s a sa mple b lock o f text that I would pass t hrough the s tring splitt er. I would rather it be smart enough to stop and look more like .. This is a sample // bad example, since the single word exceeds maximum length, but the length would be larger numbers in real scenarios, closer to 200. Can anyone help me?

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• Centralizing Messagebox handling for application

  - by DRapp

  I'm wondering how others deal with trying to centralize MessageBox function calling. Instead of having long text embedded all over the place in code, in the past (non .net language), I would put system and application base "messagebox" type of messages into a database file which would be "burned" into the executable, much like a resource file in .Net. When a prompting condition would arise, I would just do call something like MBAnswer = MyApplication.CallMsgBox( IDUserCantDoThat ) then check the MBAnswer upon return, such as a yes/no/cancel or whatever. In the database table, I would have things like what the messagebox title would be, the buttons that would be shown, the actual message, a special flag that automatically tacked on a subsequent standard comment like "Please contact help desk if this happens.". The function would call the messagebox with all applicable settings and just return back the answer. The big benefits of this was, one location to have all the "context" of messages, and via constants, easier to read what message was going to be presented to the user. Does anyone have a similar system in .Net to do a similar approach, or is this just a bad idea in the .Net environment.

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• How to setup and teardown temporary django db for unit testing?

  - by blokeley

  I would like to have a python module containing some unit tests that I can pass to hg bisect --command. The unit tests are testing some functionality of a django app, but I don't think I can use hg bisect --command manage.py test mytestapp because mytestapp would have to be enabled in settings.py, and the edits to settings.py would be clobbered when hg bisect updates the working directory. Therefore, I would like to know if something like the following is the best way to go: import functools, os, sys, unittest sys.path.append(path_to_myproject) os.environ['DJANGO_SETTINGS_MODULE'] = 'myapp.settings' def with_test_db(func): """Decorator to setup and teardown test db.""" @functools.wraps def wrapper(*args, **kwargs): try: # Set up temporary django db func(*args, **kwargs) finally: # Tear down temporary django db class TestCase(unittest.TestCase): @with_test_db def test(self): # Do some tests using the temporary django db self.fail('Mark this revision as bad.') if '__main__' == __name__: unittest.main() I should be most grateful if you could advise either: If there is a simpler way, perhaps subclassing django.test.TestCase but not editing settings.py or, if not; What the lines above that say "Set up temporary django db" and "Tear down temporary django db" should be?

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• Doing some downloading without blocking you app

  - by Code

  Hi guys, I'm working on my first app that's doing a few different web connections at once. My first screen is my Menu. And at the bottom of viewDidLoad of MenuViewController i call a method that gets and parses a .xml file that is located on my webserver. Also at the bottom of viewDidLoad i do FootballScores = [[FootBallScores alloc] init]; and FootballScores makes a connection to a html page which it loads into a string and then parses out data. Now since both of these are getting called at the bottom of viewDidLoad of the class thats is responsible for the main menu(first screen in the app) it means the app is kinda slow to load. What is the right way to do the above? Should i remove the 2 pieces of code from my viewDidLoad and replace with maybe dataGetterOne = [NSTimer scheduledTimerWithTimeInterval:1.000 target:self selector:@selector(xmlParser) userInfo:nil repeats:NO]; dataGetterTwo = [NSTimer scheduledTimerWithTimeInterval:2.000 target:self selector:@selector(htmlParser) userInfo:nil repeats:NO]; This would mean that the methods get called later on and the viewDidLoad gets to finish before the i try get the data from the web servers. Making 2 connections to we bservers a second apart to quick? Can the iphone handle having 2 connections open at once? I'm really unsure of anything bad/dangerous I am doing in regards to connections. Many Thanks -Code

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• Chicken and egg problem (restore database) when trying to write unit test against SQl Server 2008.

  - by Hamish Grubijan

  Ok, they are not unit tests but end-to-end tests. The setup is somewhat involved. Unit tests will use C#, ODBC connection. Every unit tests will try to clean up after itself, but every 20 tests or so (once per C# class) we would need to do a full database restore. I do not think I can do it over an ODBC connection, according to this document: http://www.sql-server-performance.com/articles/dba/Obtain_Exclusive_Access_to_Restore_SQL_Server_p1.aspx Msg 6104, Level 16, State 1, Line 1 Cannot use KILL to kill your own process. However, I would like to, so that 199 tests do not go amok because of a bad clean-up. Is there another way? Perhaps I can open a different "connection" such as use COM automation or something of that sort, and then kill all database connections from there? If so, how can I do that? Also, will the clients be able to re-connect automatically after a restore, or would I have to dismantle everything once every 20 tests or so? If you find this question confusing, please let me know what your questions are. Thanks!

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• Should .net comments start with a capital letter and end with a period?

  - by Hamish Grubijan

  Depending on the feedback I get, I might raise this "standard" with my colleagues. This might become a custom StyleCop rule. is there one written already? So, Stylecop already dictates this for summary, param, and return documentation tags. Do you think it makes sense to demand the same from comments? On related note: if a comment is already long, then should it be written as a proper sentence? For example (perhaps I tried too hard to illustrate a bad comment): //if exception quit vs. // If an exception occurred, then quit. If figured - most of the time, if one bothers to write a comment, then it might as well be informative. Consider these two samples: //if exception quit if (exc != null) { Application.Exit(-1); } and // If an exception occurred, then quit. if (exc != null) { Application.Exit(-1); } Arguably, one does not need a comment at all, but since one is provided, I would think that the second one is better. Please back up your opinion. Do you have a good reference for the art of commenting, particularly if it relates to .Net? Thanks.

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• How to avoid mouse move on Touch

  - by VirtualBlackFox

  I have a WPF application that is capable of being used both with a mouse and using Touch. I disable all windows "enhancements" to just have touch events : Stylus.IsPressAndHoldEnabled="False" Stylus.IsTapFeedbackEnabled="False" Stylus.IsTouchFeedbackEnabled="False" Stylus.IsFlicksEnabled="False" The result is that a click behave like I want except on two points : The small "touch" cursor (little white star) appears where clicked an when dragging. Completely useless as the user finger is already at this location no feedback is required (Except my element potentially changing color if actionable). Elements stay in the "Hover" state after the movement / Click ends. Both are the consequences of the fact that while windows transmit correctly touch events, he still move the mouse to the last main-touch-event. I don't want windows to move the mouse at all when I use touch inside my application. Is there a way to completely avoid that? Notes: Handling touch events change nothing to this. Using SetCursorPos to move the mouse away make the cursor blink and isn't really user-friendly. Disabling the touch panel to act as an input device completely disable all events (And I also prefer an application-local solution, not system wide). I don't care if the solution involve COM/PInvoke or is provided in C/C++ i'll translate. If it is necessary to patch/hook some windows dlls so be it, the software will run on a dedicated device anyway. I'm investigating the surface SDK but I doubt that it'll show any solution. As a surface is a pure-touch device there is no risk of bad interaction with the mouse.

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• In Python, how to make sure database connection will always close before leaving a code block?

  - by Cawas

  I want to prevent database connection being open as much as possible, because this code will run on an intensive used server and people here already told me database connections should always be closed as soon as possible. def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # a lot more of workflow done here dbConnection.close() # even more stuff would come below I believe that leaves a database connection open when there is no row on the table, tho I'm still really not sure how it works. Anyway, maybe that is bad design in the sense that I could open and close a DB connection after each small block of execute. And sure, I could just add a close right before the return in that case... But how could I always properly close the DB without having to worry if I have that return, or a raise, or continue, or whatever in the middle? I'm thinking in something like a code block, similar to using try, like in the following suggestion, which obviously doesn't work: def do_something_that_needs_database (): dbConnection = MySQLdb.connect(host=args['database_host'], user=args['database_user'], passwd=args['database_pass'], db=args['database_tabl'], cursorclass=MySQLdb.cursors.DictCursor) try: dbCursor = dbConnection.cursor() dbCursor.execute('SELECT COUNT(*) total FROM table') row = dbCursor.fetchone() if row['total'] == 0: print 'error: table have no records' dbCursor.execute('UPDATE table SET field="%s"', whatever_value) return None print 'table is ok' dbCursor.execute('UPDATE table SET field="%s"', another_value) # again, that same lot of line codes done here except ExitingCodeBlock: closeDb(dbConnection) # still, that "even more stuff" from before would come below I don't think there is anything similar to ExitingCodeBlock for an exception, tho I know there is the try else, but I hope Python already have a similar feature... Or maybe someone can suggest me a paradigm move and tell me this is awful and highly advise me to never do that. Maybe this is just something to not worry about and let MySQLdb handle it, or is it?

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• Should I put actors in the Domain-Model/Class-Diagram?

  - by devoured elysium

  When designing both the domain-model and class-diagrams I am having some trouble understanding what to put in them. I'll give an example of what I mean: I am doing a vacations scheduler program, that has an Administrator and End-Users. The Administrator does a couple of things like registering End-Users in the program, changing their previleges, etc. The End-User can choose his vacations days, etc. I initially defined an Administrator and End-User as concepts in the domain-model, and later as classes in the class-diagram. In the class-diagram, both classes ended up having a couple of methods like Administrator.RegisterNewUser(); Administrator.UnregisterUser(int id); etc. Only after some time I realised that actually both Administrator and End-User are actors, and maybe I got this design totally wrong. Instead of filling Administrator and End-User classes with methods to do what my Use-Cases request, I could define other classes from the domain to do them, and have controllers handle the Use-Cases(actually, I decided to do one for each Use-Case). I could have a UserDatabase.RegisterNewUser() and UserDatabase.UnregisterUser(int id);, for example, instead of having those methods on the Administrator class. The idea would be to try to think of the whole vacation-scheduler as a "closed-program" that has a set of features and doesn't bother with things such as authentication, that should be internal/protected, being that the only public things I'd let the outside world see would be its controllers. Is this the right approach? Or am I getting this totally wrong? Is it generally bad idea to put Actors in the domain-model/class-diagrams? What are good rules of thumb for this? My lecturer is following Applying UML and Patterns, which I find awful, so I'd like to know where I could look up more info on this described actor-models situation. I'm still a bit confused about all of this, as this new approach is radically different from anything I've done before.

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• Efficient mapping of game entity positions in Java

  - by byte

  In Java (Swing), say I've got a 2D game where I have various types of entities on the screen, such as a player, bad guys, powerups, etc. When the player moves across the screen, in order to do efficient checking of what is in the immediate vicinity of the player, I would think I'd want indexed access to the things that are near the character based on their position. For example, if player 'P' steps onto element 'E' in the following example... | | | | | | | | | |P| | | | |E| | | | | | | | | ... would be to do something like: if(player.getPosition().x == entity.getPosition().x && entity.getPosition.y == thing.getPosition().y) { //do something } And thats fine, but that implies that the entities hold their positions, and therefor if I had MANY entities on the screen I would have to loop through all possible entities available and check each ones position against the player position. This seems really inefficient especially if you start getting tons of entities. So, I would suspect I'd want some sort of map like Map<Point, Entity> map = new HashMap<Point, Entity>(); And store my point information there, so that I could access these entities in constant time. The only problem with that approach is that, if I want to move an entity to a different point on the screen, I'd have to search through the values of the HashMap for the entity I want to move (inefficient since I dont know its Point position ahead of time), and then once I've found it remove it from the HashMap, and re-insert it with the new position information. Any suggestions or advice on what sort of data structure / storage format I ought to be using here in order to have efficient access to Entities based on their position, as well as Position's based on the Entity?

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• Is it advisable to have an interface as the return type?

  - by wb

  I have a set of classes with the same functions but with different logic. However, each class function can return a number of objects. It is safe to set the return type as the interface? Each class (all using the same interface) is doing this with different business logic. protected IMessage validateReturnType; <-- This is in an abstract class public bool IsValid() <-- This is in an abstract class { return (validateReturnType.GetType() == typeof(Success)); } public IMessage Validate() { if (name.Length < 5) { validateReturnType = new Error("Name must be 5 characters or greater."); } else { validateReturnType = new Success("Name is valid."); } return validateReturnType; } Are there any pitfalls with unit testing the return type of an function? Also, is it considered bad design to have functions needing to be run in order for them to succeed? In this example, Validate() would have to be run before IsValid() or else IsValid() would always return false. Thank you.

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• What are the javascript performance tradeoffs in adding id's to dom elements?

  - by Blinky

  For example, I have a website which has a dynamically-generated segment of its dom which looks roughly like this: <div id="master"> <div class="child"> ... </div> <div class="child"> ... </div> <div class="child"> ... </div> ... <div class="child"> ... </div> </div> There might be hundreds of child elements in this manner, and they, too, might have yet more children. At present, none of them have id's except for the master. Javascript manipulates them via dom-walking. It's a little scary. I'd like to add id's, e.g.: <div id="master"> <div id="child1" class="child"> ... </div> <div id="child2" class="child"> ... </div> <div id="child3" class="child"> ... </div> ... <div id="childN" class="child"> ... </div> </div> What are the tradeoffs in adding id's to these divs? Certainly, jQuery must maintain a hash of id's, so there's going to be some sort of performance hit. Any general guidelines in when adding additional id's is a bad idea? Is jQuery so awesome that, in practice, it doesn't matter?

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• How to write curiously recurring templates with more than 2 layers of inheritance?

  - by Kyle

  All the material I've read on Curiously Recurring Template Pattern seems to one layer of inheritance, ie Base and Derived : Base<Derived>. What if I want to take it one step further? #include <iostream> using std::cout; template<typename LowestDerivedClass> class A { public: LowestDerivedClass& get() { return *static_cast<LowestDerivedClass*>(this); } void print() { cout << "A\n"; } }; template<typename LowestDerivedClass> class B : public A<LowestDerivedClass> { public: void print() { cout << "B\n"; } }; class C : public B<C> { public: void print() { cout << "C\n"; } }; int main() { C c; c.get().print(); // B b; // Intentionally bad syntax, // b.get().print(); // to demonstrate what I'm trying to accomplish return 0; } How can I rewrite this code to compile without errors (and output "C\nB\n")?

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• Error in Android's clearCheck() for RadioGroup?

  - by Manuel R. Ciosici

  I'm having an issue with RadioGroup's clearChecked(). I'm displaying a multiple choice question to the user and after the user selects an answer I check the answer, give him some feedback and then move to the next question. In the process of moving to the next question I clearCheck on the RadioGroup. Can anyone explain to me why the onCheckedChanged method is called 3 times? Once when the change actually occurs (with the user changes), once when I clearCheck(with -1 as the selected id) and once in between (with the user changes again)? As far as I could tell the second trigger is provoked by clearCheck. Code below: private void checkAnswer(RadioGroup group, int checkedId){ // this makes sure it doesn't blow up when the check is cleared // also we don't check the answer when there is no answer if (checkedId == -1) return; if (group.getCheckedRadioButtonId() == -1) return; // check if correct answer if (checkedId == validAnswerId){ score++; this.giveFeedBack(feedBackType.GOOD); } else { this.giveFeedBack(feedBackType.BAD); } // allow for user to see feedback and move to next question h.postDelayed(this, 800); } private void changeToQuestion(int questionNumber){ if (questionNumber >= this.questionSet.size()){ // means we are past the question set // we're going to the score activity this.goToScoreActivity(); return; } //clearing the check gr.clearCheck(); // give change the feedback back to question imgFeedback.setImageResource(R.drawable.question_mark); //OTHER CODE HERE } and the run method looks like this public void run() { questionNumber++; changeToQuestion(questionNumber); }

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• SQL - table alias scope.

  - by Support - multilanguage SO

  I've just learned ( yesterday ) to use "exists" instead of "in". BAD select * from table where nameid in ( select nameid from othertable where otherdesc = 'SomeDesc' ) GOOD select * from table t where exists ( select nameid from othertable o where t.nameid = o.nameid and otherdesc = 'SomeDesc' ) And I have some questions about this: 1) The explanation as I understood was: "The reason why this is better is because only the matching values will be returned instead of building a massive list of possible results". Does that mean that while the first subquery might return 900 results the second will return only 1 ( yes or no )? 2) In the past I have had the RDBMS complainin: "only the first 1000 rows might be retrieved", this second approach would solve that problem? 3) What is the scope of the alias in the second subquery?... does the alias only lives in the parenthesis? for example select * from table t where exists ( select nameid from othertable o where t.nameid = o.nameid and otherdesc = 'SomeDesc' ) AND select nameid from othertable o where t.nameid = o.nameid and otherdesc = 'SomeOtherDesc' ) That is, if I use the same alias ( o for table othertable ) In the second "exist" will it present any problem with the first exists? or are they totally independent? Is this something Oracle only related or it is valid for most RDBMS? Thanks a lot

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• Type-safe generic data structures in plain-old C?

  - by Bradford Larsen

  I have done far more C++ programming than "plain old C" programming. One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates. For sake of concreteness, consider a generic singly linked list. In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need. In C, I can think of a few ways of implementing a generic singly linked list: Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures. Use a more sophisticated, stand-alone tool to generate the code for the types you need. I don't like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation. Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type. Option 2 doesn't require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly. Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros). However, this option is the most heavyweight, a sort of "poor-man's templates". I have used this approach before, using a simple sed script to specialize a "templated" version of some C code. I would like to program my future "low-level" projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type. What experience do people have with this issue? Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

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• Why Can't Businesses Upgrade their Browsers from IE6/IE7?

  - by viatropos

  I have read lots these past few weeks on IE6, seeing if it was really that bad to make it look right. I have just learned HTML and CSS this past year so I've been spoiled to start with basically CSS3 and HTML5, and I can do some really cool stuff super fast. I'm no IE6 master and I don't have years of experience with IE. So I thought it'd take a little time to figure out all the hacks to IE6/7 discovered and just implement them. But it's way harder than that (or maybe just way too much work). I'd have to either completely rebuild my design using "Internet Explorer 'Principles'", or cut out a lot of the neat things I could do using more recent technologies. For a million and one other reasons, everyone who builds things online seems to think IE should die. My question is, why can't businesses upgrade their browsers? When I work with businesses, they almost always resist the first time I ask, but 5 seconds later I'll show them what it looks like on my computer and talk about how great the latest stuff is (how much more secure later browser are, all the famous IE security cases, how much smoother and faster they new browsers are, how the IE team has basically missed the boat entirely, how much smoother business processes run, etc.), and they get excited! And within a few seconds they're up and running with Chrome or something. So can businesses not upgrade for some reasons? What are the reasons a business cannot upgrade? The main reason I think of is because they have an old version of windows. But a) wasn't there a legal case against this? and b) somebody must have figured out how to install Chrome or Firefox on ancient versions of Windows by now.

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