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• Accessing subclass members from a superclass pointer C++

  - by Dr. Monkey

  I have an array of custom class Student objects. CourseStudent and ResearchStudent both inherit from Student, and all the instances of Student are one or the other of these. I have a function to go through the array, determine the subtype of each Student, then call subtype-specific member functions on them. The problem is, because these functions are not overloaded, they are not found in Student, so the compiler kicks up a fuss. If I have a pointer to Student, is there a way to get a pointer to the subtype of that Student? Would I need to make some sort of fake cast here to get around the compile-time error?

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• How to access Session values from layers beneath the web application layer.

  - by Matthew Vines

  We have many instances in our application where we would like to be able to access things like the currently logged in user id in our business domain and data access layer. On log we push this information to the session, so all of our front end code has access to it fairly easily of course. However, we are having huge issues getting at the data in lower layers of our application. We just can't seem to find a way to store a value in the business domain that has global scope just for the user (static classes and properties are of course shared by the application domain, which means all users in the session share just one copy of the object). We have considered passing in the session to our business classes, but then our domain is very tightly coupled to our web application. We want to keep the prospect of a winforms version of the application possible going forward. I find it hard to believe we are the first people to have this sort of issue. How are you handling this problem in your applications?

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• Is the C++ compiler optimizer allowed to break my destructor ability to be called multiple times?

  - by sharptooth

  We once had an interview with a very experienced C++ developer who couldn't answer the following question: is it necessary to call the base class destructor from the derived class destructor in C++? Obviously the answer is no, C++ will call the base class destructor automagically anyway. But what if we attempt to do the call? As I see it the result will depend on whether the base class destructor can be called twice without invoking erroneous behavior. For example in this case: class BaseSafe { public: ~BaseSafe() { } private: int data; }; class DerivedSafe { public: ~DerivedSafe() { BaseSafe::~BaseSafe(); } }; everything will be fine - the BaseSafe destructor can be called twice safely and the program will run allright. But in this case: class BaseUnsafe { public: BaseUnsafe() { buffer = new char[100]; } ~BaseUnsafe () { delete[] buffer; } private: char* buffer; }; class DerivedUnsafe { public: ~DerivedUnsafe () { BaseUnsafe::~BaseUnsafe(); } }; the explicic call will run fine, but then the implicit (automagic) call to the destructor will trigger double-delete and undefined behavior. Looks like it is easy to avoid the UB in the second case. Just set buffer to null pointer after delete[]. But will this help? I mean the destructor is expected to only be run once on a fully constructed object, so the optimizer could decide that setting buffer to null pointer makes no sense and eliminate that code exposing the program to double-delete. Is the compiler allowed to do that?

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• Does "delegate" mean a type or an object?

  - by Michal Czardybon

  Reading from MSDN: "A delegate is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method." Does then "delegate" mean a type or an object?! ...It cannot be both. It seems to me that the single word is used in two different meanings: a type containing a reference to a method of some specified signature, an object of that type, which can be actually called like a method. I would prefer a more precise vocabulary and use "delegate type" for the first case. I have been recently reading a lot about events and delegates and that ambiguity was making me confused many times. Some other uses of "delegate" word in MSDN in the first meaning: "Custom event delegates are needed only when an event generates event data" "A delegate declaration defines a class that is derived from the class System.Delegate" Some other uses of "delegate" word in MSDN in the second meaning: "specify a delegate that will be called upon the occurrence of some event" "Delegates are objects that refer to methods. They are sometimes described as type-safe function pointers" What do you think? Why did people from Microsoft introduced this ambiguity? Am I the only person to have conceptual problems with different notions being referenced with the same word.

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• JOIN (SELECT DISTINCT [..] substitute

  - by FRKT

  Hello, I'd like to find a substitute for using SELECT DISTINCT in a derived table. Let's say I have three tables: CREATE TABLE `trades` ( `tradeID` int(11) unsigned NOT NULL AUTO_INCREMENT, `employeeID` int(11) unsigned NOT NULL, `corporationID` int(11) unsigned NOT NULL, `profit` int(11) NOT NULL, KEY `tradeID` (`tradeID`), KEY `employeeID` (`employeeID`), KEY `corporationID` (`corporationID`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 CREATE TABLE `corporations` ( `corporationID` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, PRIMARY KEY (`corporationID`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 CREATE TABLE `employees` ( `employeeID` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, PRIMARY KEY (`employeeID`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 Let's say I'd like to find out how much profit a specific employee has generated. Simple: SELECT SUM(profit) FROM trades JOIN employees ON trades.employeeID = employees.employeeID AND employees.employeeID = 1; It gets trickier if I'd like to query how much revenue a specific corporation has, however. I cannot simply replicate the aforementioned query, because two or more employees from the same company might be involved in the same trade. This query should do the trick: SELECT SUM(profit) FROM trades JOIN (SELECT DISTINCT tradeID FROM trades WHERE trades.corporationID = 1) ... unfortunately, DISTINCT JOINs seem crazy ineffective. Is there any alternative I can use to determine how much revenue a corporation has, taking into account that a corporation might be listed several times with the same tradeID?

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• Are C++ exceptions sufficient to implement thread-local storage?

  - by Potatoswatter

  I was commenting on an answer that thread-local storage is nice and recalled another informative discussion about exceptions where I supposed The only special thing about the execution environment within the throw block is that the exception object is referenced by rethrow. Putting two and two together, wouldn't executing an entire thread inside a function-catch-block of its main function imbue it with thread-local storage? It seems to work fine: #include <iostream> #include <pthread.h> using namespace std; struct thlocal { string name; thlocal( string const &n ) : name(n) {} }; thlocal &get_thread() { try { throw; } catch( thlocal &local ) { return local; } } void print_thread() { cerr << get_thread().name << endl; } void *kid( void *local_v ) try { thlocal &local = * static_cast< thlocal * >( local_v ); throw local; } catch( thlocal & ) { print_thread(); return NULL; } int main() try { thlocal local( "main" ); throw local; } catch( thlocal & ) { print_thread(); pthread_t th; thlocal kid_local( "kid" ); pthread_create( &th, NULL, &kid, &kid_local ); pthread_join( th, NULL ); print_thread(); return 0; } Is this novel or well-characterized? Was my initial premise correct? What kind of overhead does get_thread incur in, say, GCC and VC++? It would require throwing only exceptions derived from struct thlocal, but altogether this doesn't feel like an unproductive insomnia-ridden Sunday morning…

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• Is an ArrayList automaticaly declared static in Java, if it is an instance variable?

  - by Alex

  I'm trying to do something like this: private class aClass { private ArrayList<String> idProd; aClass(ArrayList<String> prd) { this.idProd=new ArrayList<String>(prd); } public ArrayList<String> getIdProd() { return this.idProd; } } So if I have multiple instances of ArrayLIst<String> (st1 ,st2 ,st3) and I want to make new objects of aClass: { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); } Will all of the aClass objects return st3 if I access the method getIdProd() for each of them(obj1..obj3)? Is an ArrayList as an instance variable automatically declared static?

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• Is there a way to bring an application's GUI to the current desktop?

  - by Davy8

  Background: Started a fair amount of work before realizing that a Windows Service cannot start an app with a GUI that displays without potential problems. The proper solution of separating the GUI of the app to be started is non-trivial, so I'm trying to think of alternative solutions. There is a GUI to manage the service that is a separate executable, but the process to be launched (actually multiple instances of it) has its own GUI that needs to be shown. It doesn't need to be made visible by the service itself, but it needs to be at least able to be made visible by another process with a visible GUI. The Windows User that is running the service and that needs to see the GUI of the launched process is the same and known at install time. Is there some way to accomplish this or is it back to the drawing board? Also both the service and the app to launch are both our code and modifiable.

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• Objective-C - Unloading loaded view when it is swapped

  - by teepusink

  Hi, What is the best way to do view management in a multiview application? Right now I have this ViewSwitcher method/function that comes from a custom delegate I created. The code is a whole bunch of if else like this MyViewController *c = [[MyViewController alloc] initWithNibName:@"MyViewController" bundle:nil]; c.delegate = self; self.myViewController = c; [self.viewHolder insertSubview:c.view atIndex:0]; [c release]; That works fine, but when I visited the function a second time, is there going to be 2 instances of MyViewController now or just 1? How do I unload MyViewController when I switch to another view? Or is there a better way to manage my views? Thanks, Tee

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• MySQL - Join as zero if record Not IN

  - by Zurahn

  To explain by example, take two tables, A and B Table A id foo 1 x 2 y 3 z Table B id aid bar 1 3 50 2 1 100 An example join SELECT foo, bar FROM a, b WHERE a.id = b.aid; Garners a result of foo bar z 50 x 100 What I would like to do is get all values of foo and for any instances where there isn't a corresponding bar value, return 0 for that column. My best guess was something along the lines of SELECT foo, bar AS br FROM a, b WHERE a.id = b.aid OR a.id NOT IN (SELECT aid FROM b); But that returns duplicates and non-zero values for bar. Possible?

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• Purpose of Instance Methods vs. Class Methods in Objective-C

  - by qegal

  I have checked out all these questions... Difference Class and Instance Methods Difference between class methods and instance methods? Objective-C: Class vs Instance Methods? ...and all they explain is how instance methods are used on instances of a class and class methods are used with the class name, when a message is sent to a class object. This is helpful, but I'm curious to know why one would use a class method vs. an instance method. I'm fairly new to iOS application development, and usually use class methods, and I feel like I'm doing something wrong. Thanks in advanced!

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• Enable export to XML via HTTP on a large number of models with child relations

  - by Vasil

  I've a large number of models (120+) and I would like to let users of my application export all of the data from them in XML format. I looked at django-piston, but I would like to do this with minimum code. Basically I'd like to have something like this: GET /export/applabel/ModelName/ Would stream all instances of ModelName in applabel together with it's tree of related objects . I'd like to do this without writing code for each model. What would be the best way to do this?

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• How do I get certain code to execute before every single controller action in ASP.NET MVC 2?

  - by Chris

  I want to check some things about the state of the session, the user agent, etc, and possibly take action and return a special view BEFORE a controller method gets a chance to execute. For example: Most common: User requests Home/Index System checks to make sure x != 0. x does not equal zero, so the Home/Index controller executes like normal. But, sometimes: User requests Home/Index System checks to make sure x != 0. x DOES equal zero. The user must be notified and the requested controller action cannot be allowed to execute. I think this involves the use of ActionFilters. But I have read about them and I don't understand if I can preempt the controller method and return a view before it executes. I am sure I could execute code before the controller method runs, but how do I keep it from running in some instances and return a custom view, or direct to a different controller method?

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• LINQ .Cast() extension method fails but (type)object works.

  - by Ben Robinson

  To convert between some LINQ to SQL objects and DTOs we have created explicit cast operators on the DTOs. That way we can do the following: DTOType MyDTO = (LinqToSQLType)MyLinq2SQLObj; This works well. However when you try to cast using the LINQ .Cast() extension method it trows an invalid cast exception saying cannot cast type Linq2SQLType to type DTOType. i.e. the below does not work List<DTO.Name> Names = dbContact.tNames.Cast<DTO.Name>() .ToList(); But the below works fine: DAL.tName MyDalName = new DAL.tName(); DTO.Name MyDTOName = (DTO.Name)MyDalName; and the below also works fine List<DTO.Name> Names = dbContact.tNames.Select(name => (DTO.Name)name) .ToList(); Why does the .Cast() extension method throw an invalid cast exception? I have used the .Cast() extension method in this way many times in the past and when you are casting something like a base type to a derived type it works fine, but falls over when the object has an explicit cast operator.

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• Is an ArrayList automatically declared static in Java, if it is an instance variable?

  - by Alex

  I'm trying to do something like this: private class aClass { private ArrayList<String> idProd; aClass(ArrayList<String> prd) { this.idProd=new ArrayList<String>(prd); } public ArrayList<String> getIdProd() { return this.idProd; } } So if I have multiple instances of ArrayLIst<String> (st1 ,st2 ,st3) and I want to make new objects of aClass: { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); } Will all of the aClass objects return st3 if I access the method getIdProd() for each of them(obj1..obj3)? Is an ArrayList as an instance variable automatically declared static?

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• Same Activity called twice... Issue with Multiple AsyncTasks?

  - by stormin986

  I have three simultaneous instances of an AsyncTask for download three files. When two particular ones finish, at the end of onPostExecute() I check a flag set by each, and if both are true, I call startActivity() for the next Activity. I am currently seeing the activity called twice, or something that resembles this type of behavior. Since the screen does that 'swipe left' kind of transition to the next activity, it sometimes does it twice (and when I hit back, it goes back to the same activity). It's obvious two versions of the activity that SHOULD only get called once are being put on the Activity stack. Could this be from both onPostExecute()s executing simultaneously and both checking the flags each other set at the exact same time? This seems extremely unlikely since two processes would have to be running line-by-line in parallel... *EDIT* A lot removed from this question since I was way off in what I thought was wrong. Nonetheless I found the answer here quite useful, so I have edited the question to reflect the useful parts.

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• How to access a website's url programmatically from within the page

  - by Jeff

  For work, I am working on a site that has a feature that lets users make custom instances of the site depending on who they want to show it to. So if they want to show their potential employer a little bit about themselves, they can send them a custom url, that has a uid on the end of it that tells the database what to show and what not to when the site is loaded up. Now, I need to be able to take the value that is on the end of the url, this unique uid that corresponds with their preferences in the db, accessable on run time. Meaning that when someone types in this custom url, I need to be able to show the name of the person whose portfolio is being viewed BEFORE password authentication takes place... If I could get the URL, I suppose I could parse through it to find the necessary UID...but how do I get the url? Maybe I am just missing something here, but if anyone has any thoughts or ideas, it would be appreciated!! Thanks

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• OpenGL and layouts

  - by Hnefi

  I'm using OpenGL to render a game view in my android application. The game is turn based and I wish to add some buttons to the interface. I'd prefer to use standard Android widgets, structured in an XML-generated layout (or, if I have to, a hardcoded layout) and put the OpenGL view in its own window as part of that layout. So in regards to this, I have 3 questions: 1: Is such a thing possible? I've done a few half-hearted tries, but have had no luck so far. 2: Is such a thing advisable? Does it carry a significant performance penalty, for example, over using OpenGL-based homebrew widgetry? 3: Is it possible to pass particular arguments to instances created in XML layouts? For example, my current OpenGL view has three arguments in its constructor; is it somehow possible for me to invoke that particular constructor with particular parameters when it's part of a layout?

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• How do you manage your sqlserver database projects for new builds and migrations?

  - by Rory

  How do you manage your sql server database build/deploy/migrate for visual studio projects? We have a product that includes a reasonable database part (~100 tables, ~500 procs/functions/views), so we need to be able to deploy new databases of the current version as well as upgrade older databases up to the current version. Currently we maintain separate scripts for creation of new databases and migration between versions. Clearly not ideal, but how is anyone else dealing with this? This is complicated for us by having many customers who each have their own db instance, rather than say just having dev/test/live instances on our own web servers, but the processes around managing dev/test/live for others must be similar.

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• Visual Studio - How to use an existing vsproj's project settings as a template for new project?

  - by Jakobud

  There is some software I want to write a plugin for. The software includes some sample plugins. I want to create a new fresh project but I want to use one of the sample plugin vsproj's project settings as a template. It doesn't seem very clear on how to do this. If I do "New Project From Existing Code" that only imports the cpp, h, etc files into the new project. Right now the only way I can see to copy a sample projects settings is to open two instances of VS2005 next to each other and simply mimic the settings... Surely there is a built in method of doing this?

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• Getting empty update rectangle in OnPaint after calling InvalidateRect on a layered window

  - by Shawn

  I'm trying to figure out why I've been getting an empty update rectangle when I call InvalidateRect on a transparent window. The idea is that I've drawn something on the window (it gets temporarily switched to have an alpha of 1/255 for the drawing), and then I switch it to full transparent mode (i.e. alpha of 0) in order to interact with the desktop & to be able to move the drawing around the screen on top of the desktop. When I try to move the drawing, I get its bounding rectangle & use it to call InvalidateRect, as such: InvalidateRect(m_hTarget, &winRect, FALSE); I've confirmed that the winRect is indeed correct, and that m_hTarget is the correct window & that its rectangle fully encompasses winRect. I get into the OnPaint handler in the class corresponding to m_hTarget, which is derived from a CWnd. In there, I create a CPaintDC, but when I try to access the update rectangle (dcPaint.m_ps.rcPaint) it's always empty. This rectangle gets passed to a function that determines if we need to update the screen (by using UpdateLayeredWindow in the case of a transparent window). If I hard-code a non-empty rectangle in here, the remaining code works correctly & I am able to move the drawing around the screen. I tried changing the 'FALSE' parameter to 'TRUE' in InvalidateRect, with no effect. I also tried using a standard CDC, and then using BeginPaint/EndPaint method in my OnPaint handler, just to ensure that CPaintDC wasn't doing something odd ... but I got the same results. The code that I'm using was originally designed for opaque windows. If m_hTarget corresponds to an opaque window, the same set of function calls results in the correct (i.e. non-empty) rectangle being passed to OnPaint. Once the window is layered, though, it doesn't seem to work right.

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• Checking when two headers are included at the same time.

  - by fortran

  Hi, I need to do an assertion based on two related macro preprocessor #define's declared in different header files... The codebase is huge and it would be nice if I could find a place to put the assertion where the two headers are already included, to avoid polluting namespaces unnecessarily. Checking just that a file includes both explicitly might not suffice, as one (or both) of them might be included in an upper level of a nesting include's hierarchy. I know it wouldn't be too hard to write an script to check that, but if there's already a tool that does the job, the better. Example: file foo.h #define FOO 0xf file bar.h #define BAR 0x1e I need to put somewhere (it doesn't matter a lot where) something like this: #if (2*FOO) != BAR #error "foo is not twice bar" #endif Yes, I know the example is silly, as they could be replaced so one is derived from the other, but let's say that the includes can be generated from different places not under my control and I just need to check that they match at compile time... And I don't want to just add one include after the other, as it might conflict with previous code that I haven't written, so that's why I would like to find a file where both are already present. In brief: how can I find a file that includes (direct or indirectly) two other files? Thanks!

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• Howto check if a object is connected to another in hibernate

  - by codevourer

  Imagine two domain object classes, A and B. A has a bidirectional one-to-many relationship to B. A is related to thousands of B. The relations must be unique, it's not possible to have a duplicate. To check if an instance of B is already connected to a given instance of A, we could perform an easy INNER JOIN but this will only ensure the already persisted relations. What about the current transient relations? class A { @OneToMany private List<B> listOfB; } If we access the listOfB and perform a check of contains() this will fetch all the connected instances of B lazy from the datasource. I only want to validate them by their primary-key. Is there an easy solution where I can do things like "Does this instance of A is connected with this instance of B?" Without loading all these data into memory and perform a based on collections?

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• How to make a daemon which will accept arbitrary commands

  - by Jono

  Right now the program can be launched in a linux terminal. Once running you can type various commands and the program will do stuff on the machine until the user quits. I would like to make the program into a service that the user runs and it goes to the background. Then the user should be able to make commands to it. Like start and stop, and write something to a log and whatever else my program does. Note that I need to send it arbitrary commands that my program will handle, not just start and stop. Maybe this means it is no longer a daemon - I dont know. How do I do this? Also, if this is not too hard, I would like to be able to run multiple instances of this service. But it is not essential.

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• define method for instance of class

  - by aharon

  Let there be class Example defined as: class Example def initialize(test='hey') self.class.send(:define_method, :say_hello, lambda { test }) end end On calling Example.new; Example.new I get a warning: method redefined; discarding old say_hello. This, I conclude, must be because it defines a method in the actual class (which makes sense, from the syntax). And that, of course, would prove disastrous should there be multiple instances of Example with different values in their methods. Is there a way to create methods just for the instance of a class from inside that instance? Thanks so much.

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