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• C++0x implementation guesstimates?

  - by dsimcha

  The C++0x standard is on its way to being complete. Until now, I've dabbled in C++, but avoided learning it thoroughly because it seems like it's missing a lot of modern features that I've been spoiled by in other languages. However, I'd be very interested in C++0x, which addresses a lot of my complaints. Any guesstimates, after the standard is ratified, as to how long it will take for major compiler vendors to provide reasonably complete, production-quality implementations? Will it happen soon enough to reverse the decline in C++'s popularity, or is it too little, too late? Do you believe that C++0x will become "the C++" within a few years, or do you believe that most people will stick to the earlier standard in practice and C++0x will be somewhat of a bastard stepchild, kind of like C99?

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• Why can I derived from a templated/generic class based on that type in C# / C++

  - by stusmith

  Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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• What workflow should I use for JavaScript editing?

  - by Patrick

  Warning: I have very little JavsScript experience. In my past programming experience, I usually have a standalone interpreter/compiler, a text editor and a command line to compile/run my software or my tests (I love test driven development). I really like it this way, since I have the feeling of being in complete control over the tools. However, editing JavaScript I need to put statements in a text file , open my web browser and click on reload. I don't feel comfortable with it, as I cannot really see what is going on (besides some alert boxes). Can you suggest me (I'm on a Mac) another workflow? Perhaps with a debugger? Is there a standalone JavaScript interpreter?

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• Java import from other directory

  - by heldopslippers

  Hi People! I am building a Enterprise Service Bus (ESB) with Java. I won't get into details But I have to build multiple servers who make use of the same classes. I have the following directory structure: /server1 -Main.java /server2 -Main.java /com -Database.java I want to import from the Main.java class for example the Database.class. But of course the following statements won't work: import com.Database; I am working with the javac compiler in the command line (so not eclipse stuff or whatever. just TextMate and the command line). And I found a (pretty stupid) solution by creating a symbolic link in the servers to the com directory. But that is not really an ideal solution. Does anybody have a better one?? THANXS in advanced!! :D

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• App Crashing Inspite of Being ARC Enabled

  - by proctr

  I have been working on an iOS App for sometime now and its almost ready to submit. However, when I gave it to few people for testing purposes (running iOS 5)..they reported cases where the app crashes and the home screen is displayed on the phone OR a frozen app screen appears with no response whatsoever The app is ARC enabled and Xcode shows no warnings. So, I'm relli tensed about what's going wrong. I have declared properties in the following fashion: @property (nonatomic) IBOutlet UILabel *devCountLabel; @property (nonatomic) IBOutlet UIView *splashView; Likewise other properties are declared. Could anyone provide a solution ASAP. It is mainly a network based app and thus, CoreData usage is minimum.. Anyway, I'm running out of time..So Please provide a fix asap..oh and thanks a ton for it. PS: The App doesn't crash in the simulator, so I'm guessing it has something related to memory. And the crashes are random. So, repeating a set of steps to reproduce the crash doesn't help either. For Eg. When I click a button, modalViewControllerAnimation results in normal case. Now this occurs as expected most of the time and freezes the app other times.

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• C++ assignment - stylish or performance?

  - by joejax

  Having been writing Java code for many years, I was amazed when I see this C++ statement: int a,b; int c = (a=1, b=a+2, b*3); My question is: Is this a choice of coding style, or it has real benefit? (looking for a practicle use case) I think the compiler will see it the same as following: int a=1, b=a+2; int c = b*3; (What's the offical name for this? I assume it's a standard C/C++ syntax.)

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• Whats the best to way convert a set of Java objects to another set of objects?

  - by HDave

  Basic Java question here from a real newbie. I have a set of Java objects (of class "MyClass") that implement a certain interface (Interface "MyIfc"). I have a set of these objects stored in a private variable in my class that is declared as follows: protected Set<MyClass> stuff = new HashSet<MyClass>(); I need to provide a public method that returns this set as a collection of objects of type "MyIfc". public Collection<MyIfc> getMyStuff() {...} How do I do the conversion? The following line gives me an error that it can't do the conversion. I would have guessed the compiler knew that objects of class MyClass implemented MyIfc and therefore would have handled it. Collection<MyIfc> newstuff = stuff; Any enlightenment is appreciated.

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• managedObjectContext question...

  - by treasure

  Hello, I have an app which is a UITabBarController, I have defined two subviews Both tabs have their Class attribute in the Identity Inspector set to UINavigationController. Now i have managed to get this far with my coding after VERY LONG trials. - (void)viewDidLoad { [super viewDidLoad]; myAppDelegate *appDelegate = (myAppDelegate *)[[UIApplication sharedApplication] delegate]; self.managedObjectContext = appDelegate.managedObjectContext; { NSError *error = nil; NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; [fetchRequest setEntity:[NSEntityDescription entityForName:@"User" inManagedObjectContext:self.managedObjectContext]]; NSArray *fetchedItems = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; NSEntityDescription *entityDesc = [NSEntityDescription entityForName:@"User" inManagedObjectContext:self.managedObjectContext]; // replace the old data with new. this DOESNT WORK if (fetchedItems.count > 0) { Usr *newUsr; for (newUsr in fetchedItems) { if ([newUsr.name isEqualToString:@"Line One"]) { newUsr.uName = @"Line One (new)"; } } } //add a new default data. THIS ADDS DATA TO MY TABLEVIEW BUT IT DOESNT SAVE THEM TO THE SQLITE User *addedDefaultdata = nil; addedDefaultdata = [[User alloc] initWithEntity:entityDesc insertIntoManagedObjectContext:self.managedObjectContext]; addedDefaultdata.name = @"Added new 1"; [addedDefaultdata release]; } NSError *error = nil; if (![[self fetchedResultsController] performFetch:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } } and my appdelegate looks like this: - (void)applicationDidFinishLaunching:(UIApplication *)application { [application setStatusBarStyle:UIStatusBarStyleBlackOpaque]; [window addSubview:navigationController.view]; [window makeKeyAndVisible]; } now I cannot quire the "User" at all! although i get no errors or warnings! Any suggestions would be much appreciated! Thanks

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• const member functions can call const member functions only?

  - by Abhi

  Hi all. Do const member functions call only const member functions? class Transmitter{ const static string msg; mutable int size; public: void xmit() const{ size = compute(); cout<<msg; } private: int compute() const{return 5;} }; string const Transmitter::msg = "beep"; int main(){ Transmitter t; t.xmit(); return EXIT_SUCCESS; } If i dont make compute() a const, then the compiler complains. Is it because since a const member function is not allowed to modify members, it wont allow any calls to non-consts since it would mean that the const member function would be 'indirectly' modifying the data members?

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• C++ template overloading - wrong function called

  - by DeadMG

  template<typename T> T* Push(T* ptr); template<typename T> T* Push(T& ref); template<typename T, typename T1> T* Push(T1&& ref); I have int i = 0; Push<int>(i); But the compiler calls it ambiguous. How is that ambiguous? The second function is clearly the preferred match since it's more specialized. Especially since the T1&& won't bind to an lvalue unless I explicitly forward/move it. Sorry - i is an int. Otherwise, the question would make no sense, and I thought people would infer it since it's normally the loop iterator.

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• modified closure warning in ReSharper

  - by Sarah Vessels

  I was hoping someone could explain to me what bad thing could happen in this code, which causes ReSharper to give an 'Access to modified closure' warning: bool result = true; foreach (string key in keys.TakeWhile(key => result)) { result = result && ContainsKey(key); } return result; Even if the code above seems safe, what bad things could happen in other 'modified closure' instances? I often see this warning as a result of using LINQ queries, and I tend to ignore it because I don't know what could go wrong. ReSharper tries to fix the problem by making a second variable that seems pointless to me, e.g. it changes the foreach line above to: bool result1 = result; foreach (string key in keys.TakeWhile(key => result1)) Update: on a side note, apparently that whole chunk of code can be converted to the following statement, which causes no modified closure warnings: return keys.Aggregate( true, (current, key) => current && ContainsKey(key) );

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• Why does C++ linking use virtually no CPU? (updated)

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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• Why Java cannot find my constructor?

  - by Roman

  Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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• How do you keep Cocoa controllers from getting too big?

  - by zoul

  Hello! Do you have some tricks or techniques to break Cocoa controller classes into smaller chunks? I find that whatever I do the controllers end up being one of the more complicated classes in my design. The basic stuff is simple, but once I have several pop-overs or action sheets running, things get uncomfortably complex. It's not that bad, but still I would like to refactor the code into several standalone chunks. I thought about categories, but the code is not that independent (a lot of times it needs to tap into viewWillAppear, for example) and I find that I spend a long time fighting the compiler. I also thought about adding functionality in layers using inheritance, but that feels like a hack.

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• How would one call std::forward on all arguments in a variadic function?

  - by Noah Roberts

  I was just writing a generic object factory and using the boost preprocessor meta-library to make a variadic template (using 2010 and it doesn't support them). My function uses rval references and std::forward to do perfect forwarding and it got me thinking...when C++0X comes out and I had a standard compiler I would do this with real variadic templates. How though, would I call std::forward on the arguments? template < typename ... Params void f(Params ... params) // how do I say these are rvalue reference? { y(std::forward(...params)); //? - I doubt this would work. } Only way I can think of would require manual unpacking of ...params and I'm not quite there yet either. Is there a quicker syntax that would work?

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• boost variant static_visitor problem picking correct function

  - by Steve

  I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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• How to understand the programming of an operating system

  - by piemesons

  Hello, I want to learn the operating system. How it works. I don't want to make my own operating system. I just want to learn how it works. As I can find out source code of any open source OS. But how to start. Like starting from the first elementary kernel (whatever it is). Somebody suggested I try to implement Linux from scratch etc. Please guide me in a proper way. I want to know about the proper path to follow. I am ready to invest three to four years just to understand the basics. I have good fundamentals of C, C++, PHP, OOP and compiler design.

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• typedef fixed length array

  - by Rajorshi

  Hi, I have to define a 24-bit data type.I am using char[3] to represent the type. Can I typedef char[3] to type24? I tried it in a code sample. I put typedef char[3] type42; in my header file. The compiler did not complain about it. But when I defined a function void foo(type24 val) {} in my C file, it did complain. I would like to be able to define functions like type24_to_int32(type24 val) instead of type24_to_int32(char value[3]).

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• Are C++ Templates just Macros in disguise?

  - by Roddy

  I've been programming in C++ for a few years, and I've used STL quite a bit and have created my own template classes a few times to see how it's done. Now I'm trying to integrate templates deeper into my OO design, and a nagging thought keeps coming back to me: They're just a macros, really... You could implement (rather UGLY) auto_ptrs using #defines, if you really wanted to. This way of thinking about templates helps me understand how my code will actually work, but I feel that I must be missing the point somehow. Macros are meant evil incarnate, yet "template metaprogramming" is all the rage. So, what ARE the real distinctions? and how can templates avoid the dangers that #define leads you into, like Inscrutable compiler errors in places where you don't expect them? Code bloat? Difficulty in tracing code? Setting Debugger Breakpoints?

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• In C#: How to declare a generic Dictionary whose key and value types have a common constraint type?

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: private IDictionary<T, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• How do XAML files associate with cs files?

  - by LLS

  It seems that XAML files should have corresponding .cs files in a C# project. I know Visual Studio does all the things for us. I'm just curious how they are linked together? I mean, are they specified in the project file, or just because they have the same names? And also, App.xaml file specifies the startup file, but how does the compiler know? Is it possible to appoint another file other than App.xaml to do the same things as App.xaml does?

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• Determine an object's class returned by a factory method (Error: function does not take 1 arguments

  - by tzippy

  I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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• how to access child instances in a vector in c++

  - by tsubasa

  I have a parent class and child class (inherited from parent). In the child class, I have a member function named function_blah(); I used vector<parent*> A to store 5 parent instances, 3 child instances. So the total number of elements in the vector is 8. I can easily access to member functions of element A[0] to A[4], which are parent instances. But whenever I try to have access to member functions of element A[5] to A[7], the compiler complains that class parent has no member named 'function_blah' The way I access to elements is using index. e.x A[i] with i = 0..7. Is it correct? if not, how?

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• Why is there "data" and "newtype" in Haskell?

  - by martingw

  To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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• STL: how to overload operator= for <vector> ?

  - by MBes

  There's simple example: #include <vector> int main() { vector<int> veci; vector<double> vecd; for(int i = 0;i<10;++i){ veci.push_back(i); vecd.push_back(i); } vecd = veci; // <- THE PROBLEM } The thing I need to know is how to overload operator = so that I could make assignment like this: vector<double> = vector<int>; I've just tried a lot of ways, but always compiler has been returning errors... Is there any option to make this code work without changing it? I can write some additional lines, but can't edit or delete the existing ones. Ty.

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