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  • What is the benefits and drawbacks of using header files?

    - by vodkhang
    I had some experience on programming languages like Java, C#, Scala as well as some lower level programming language like C, C++, Objective - C. My observation is that low level languages separate out header files and implementation files while other higher level programming language never separate it out. They use some identifiers like public, private, protected to do the jobs of header files. I saw one benefit of using header file (in some book like Code Complete), they talk about that using header files, people can never look at our implementation file and it helps with encapsulation. A drawback is that it creates too many files for me. Sometimes, it looks like verbose. It is just my thought and I don't know if there are any other benefits and drawbacks that people ever see and work with header file This question may not relate directly to programming but I think that if I can understand better about programming to interface, design software.

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  • About the String#substring() method

    - by alain.janinm
    If we take a look at the String#substring method implementation : new String(offset + beginIndex, endIndex - beginIndex, value); We see that a new String is created with the same original content (parameter char [] value). So the workaround is to use new String(toto.substring(...)) to drop the reference to the original char[] value and make it eligible for GC (if no more references exist). I would like to know if there is a special reason that explain this implementation. Why the method doesn't create herself the new shorter String and why she keeps the full original value instead? The other related question is : should we always use new String(...) when dealing with substring?

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  • .NET - Retrieve attribute from controller context?

    - by ropstah
    I have a controller insert action: <AcceptVerbs(HttpVerbs.Post)> _ Function InsertObject(<Bind(Exclude:="Id")> <ModelBinder(GetType(CustomModelBinder))> ByVal object As SomeObject) As ActionResult End Function And i have a CustomModelBinder class with a BindModel implementation: Public Function BindModel( _ ByVal controllerContext As System.Web.Mvc.ControllerContext, _ ByVal bindingContext As System.Web.Mvc.ModelBindingContext) As Object Implements System.Web.Mvc.IModelBinder.BindModel For Each s In HttpContext.Current.Request.Form.Keys HttpContext.Current.Response.Write(s & ": " & HttpContext.Current.Request.Form(s) & "<br />") Next HttpContext.Current.Response.End() End Function As you can see I have a controllerContext and a ModelBindingContext available. How do I get the: <Bind(Exclude:="Id")> part inside the BindModel implementation?

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  • Objective C instance variables - Newbie

    - by Dwayne King
    OK - so I'm sure my confusion here is just a result of being stuck in a "Java mindset" and not understanding how Obj C differs in this case. In Java, I can declare a variable in a class, like this, and each instance of that class will have it's own: MyClass { String myVar; MyClass() { // constructor } } In Obj C I tried to do the same thing by declaring a variable only in the .m file like this: #import "MyClass.h" @implementation MyClass NSString *testVar; @end My expectation here was that this variable has a scope limited to this class. So I created a second class (identical): #import "MySecondClass.h" @implementation MySecondClass NSString *testVar; @end What I'm seeing (and has me baffled) is that changing the variable in one class, affects the value seen in the other class. In fact, if I set a breakpoint, and then "Jump to Definition" of the variable, it takes me to th I've created an extremely small XCode project that demonstrates the problem here Nothing more humbling than moving to a new language :) Thanks in advance.

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  • C# Why does calling an interface member from a class generate an error?

    - by Jack
    So I have an interface: interface IFoo { int Bar(); int this[int i] {get; set;} } And a class that derives from it class Foo : IFoo { public int IFoo.Bar() { //Implementation { public int IFoo.this[int i] { //Implementation } } Now, I try to do this: var fooey = new Foo(); int i = Fooey.Bar(); or this: int i = Fooey[4]; I would expect these to work properly. However, the compiler generates an error as if such members don't exist. Why is that? I am aware I can cast Foo as IFoo, but I am also aware that casting is costly to performance, which is often the reason to use interfaces in the first place. EDIT 1: These are the errors generated 'Foo' does not contain a definition for 'Bar' and no extension method 'Bar' accepting a first argument of type 'Foo' could be found (are you missing a using directive or an assembly reference?) "Cannot apply indexing to an expression of type 'Foo'"

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  • Getting meaningful error messages from fstream's in C++

    - by Hassan Syed
    What is the best way to get meaningful file access error messages, in a portable way from std::fstreams ? The primitiveness of badbits and failbits is getting to be bit annoying. I have written my own exception hierarchies against win32 and POSIX before, and that was far more flexible than the way the STL does it. I am getting "basic::ios_clear" as an error message from the what method of a downcasted catch (std::exception) of a fstream which has exceptions enabled. This doesn't mean much to me, although I do know what the problem is I'd like my program to be a tad more informative so that when I start deployment a few months later my life will be easier. Is there anything in Boost to extract meaningful messages out of the ofstream's implementation cross platform and cross STL implementation ?

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  • unrecognized selector sent to instance while trying to add an object to a mutable array

    - by madpoet
    I'm following the "Your Second iOS App" and I decided to play with the code to understand Objective C well... What I'm trying to do is simply adding an object to a mutable array in a class. Here are the classes: BirdSighting.h #import <Foundation/Foundation.h> @interface BirdSighting : NSObject @property (nonatomic, copy) NSString *name; @property (nonatomic, copy) NSString *location; @property (nonatomic, copy) NSDate *date; -(id) initWithName: (NSString *) name location:(NSString *) location date:(NSDate *) date; @end BirdSighting.m #import "BirdSighting.h" @implementation BirdSighting -(id) initWithName:(NSString *)name location:(NSString *)location date:(NSDate *)date { self = [super init]; if(self) { _name = name; _location = location; _date = date; return self; } return nil; } @end BirdSightingDataController.h #import <Foundation/Foundation.h> @class BirdSighting; @interface BirdSightingDataController : NSObject @property (nonatomic, copy) NSMutableArray *masterBirdSightingList; - (NSUInteger) countOfList; - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex; - (void) addBirdSightingWithSighting: (BirdSighting *) sighting; @end BirdSightingDataController.m #import "BirdSightingDataController.h" @implementation BirdSightingDataController - (id) init { if(self = [super init]) { NSMutableArray *sightingList = [[NSMutableArray alloc] init]; self.masterBirdSightingList = sightingList; return self; } return nil; } -(NSUInteger) countOfList { return [self.masterBirdSightingList count]; } - (BirdSighting *) objectInListAtIndex: (NSUInteger) theIndex { return [self.masterBirdSightingList objectAtIndex:theIndex]; } - (void) addBirdSightingWithSighting: (BirdSighting *) sighting { [self.masterBirdSightingList addObject:sighting]; } @end And this is where I'm trying to add a BirdSighting instance to the mutable array: #import "BirdsMasterViewController.h" #import "BirdsDetailViewController.h" #import "BirdSightingDataController.h" #import "BirdSighting.h" @implementation BirdsMasterViewController - (void)awakeFromNib { [super awakeFromNib]; BirdSightingDataController *dataController = [[BirdSightingDataController alloc] init]; NSDate *date = [NSDate date]; BirdSighting *sighting = [[[BirdSighting alloc] init] initWithName:@"Ebabil" location:@"Ankara" date: date]; [dataController addBirdSightingWithSighting: sighting]; NSLog(@"dataController: %@", dataController.masterBirdSightingList); self.dataController = dataController; } .......... @end It throws NSInvalidArgumentException in BirdSightingDataController addBirdSightingWithSighting method... What am I doing wrong?

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  • Separation of domain and ui layer in a composite

    - by hansmaad
    Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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  • What does "static" mean in the context of declaring global template functions?

    - by smf68
    I know what static means in the context of declaring global non-template functions (see e.g. What is a "static" function?), which is useful if you write a helper function in a header that is included from several different locations and want to avoid "duplicate definition" errors. So my question is: What does static mean in the context of declaring global template functions? Please note that I'm specifically asking about global, non-member template functions that do not belong to a class. In other words, what is the difference between the following two: template <typename T> void foo(T t) { /* implementation of foo here */ } template <typename T> static void bar(T t) { /* implementation of bar here */ }

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  • Returnimng collection of interfaces

    - by apoorv020
    I have created the following interface public interface ISolutionSpace { public boolean isFeasible(); public boolean isSolution(); public Set<ISolutionSpace> generateChildren(); } However, in the implementation of ISolutionSpace in a class called EightQueenSolutionSpace, I am going to return a set of EightQueenSolutionSpace instances, like the following stub: @Override public Set<ISolutionSpace> generateChildren() { return new HashSet<EightQueenSolutionSpace>(); } However this stub wont compile. What changes do I need to make? EDIT: I tried 'HashSet' as well and had tried using the extends keyword. However since 'ISolutionSpace' is an interface and EightQueenSolutionSpace is an implementation(and not a subclass) of 'ISolutionSpace', it is still not working.

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  • Qt: any way to automatically generate QSharedData-based structures?

    - by Eye of Hell
    Hello. Qt has a build-in supprt for creating objects with integrated reference counting via QSharedData and QSharedDataPointer. All wordks great, but for each such object i need to write a lot of code: QSharedData-based implementation class with constructor and copy constructor, object class itsef with accessor methods for each filed. For a simple structures with 5-10 fields this requires really lot of near same code. Is it some ways to automate such classes generation? Maybe it's some generators exists that take a short description and automatically generates implementation class and object class with all accessors?

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  • Is there a way to localize input type="date" in HTML5

    - by lambacck
    I know that at the time of this writing only Opera supports a browser UI for <input type="date" name="mydate"> and maybe my attempts to localize this field have been met with frustration because niceties like localization have not yet been included in their implementation, but I don't even see mention of it in the HTML5 spec. Is there a way that localization should be specified? Should I do lang="fr" on a parent element? Some notes on the implementation of the site in question: Localization (language) is explicitly picked by the user because they are managing data in multiple languages and it is not reasonable to expect that the user's browser chrome is in the language being viewed or that the browser is providing desired language request headers. I want to be sure that if the page is rendered in French that the date picker provided by browser chrome shows options that make sense for French language. The plan is to fall back to jQueryUI for browsers that do not support type="date", I will use the detection mechanism provided in Dive into HTML 5

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  • I want to use Google Map API for my Desktop application

    - by Nubkadiya
    i want to use google map api for my desktop application. the application will be totally connected to internet. while i was searching some research notes about this implementation. i found a ideal site with the configurations. but it has some java files to be downloaded. but when i tried that website its not loading. which is swinglabs.org http://today.java.net/pub/a/today/2007/10/30/building-maps-into-swing-app-with-jxmapviewer.html any other options of doing this api implementation to my desktop application. and one more thing. i tried downloading the google api. even it ask a url. we have to provide a url then only we get a key to download it. and the api should run in that specific url. otherwise its not working. how this appears to a desktop application any ideas welcome..

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  • How to convince a colleague that code duplication is bad?

    - by vitaut
    A colleague of mine was implementing a new feature in a project we work on together and he did it by taking a file containing the implementation of a similar feature from the same project, creating a copy of it renaming all the global declarations and slightly modifying the implementation. So we ended up with two large files that are almost identical apart from renaming. I tried to explain that it makes our project more difficult to maintain but he doesn't want to change anything saying that it is easier for him to program in such way and that there is no reason to fix the code if it "ain't broke". How can I convince him that such code duplication is a bad thing? It is related to this questions, but I am more interested in the answers targeted to a technical person (another programmer), for example a reference to an authoritative source like a book would be great. I have already tried simple arguments and haven't succeeded.

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  • C# - Why can't I enforce derived classes to have parameterless constructors?

    - by FrisbeeBen
    I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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  • Allocation Target of std::aligned_storage (stack or heap?)

    - by Zenikoder
    I've been trying to get my head around the TR1 addition known as aligned_storage. Whilst reading the following documents N2165, N3190 and N2140 I can't for the life of me see a statement where it clearly describes stack or heap nature of the memory being used. I've had a look at the implementation provided by msvc2010, boost and gcc they all provide a stack based solution centered around the use of a union. In short: Is the memory type (stack or heap) used by aligned_storage implementation defined or is it always meant to be stack based? and, What the is the specific document that defines/determines that?

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  • Couldn't I just pass an copied string to an Core Data property?

    - by dontWatchMyProfile
    The docs say: The default implementation does not copy attribute values. If the attribute value may be mutable and implements the NSCopying protocol (as is the case with NSString, for example), you can copy the value in a custom accessor to help preserve encapsulation (for example, in the case where an instance of NSMutableString is passed as a value). So instead of getting into trouble and inconvenience with overwriting accessors in my NSManagedObject subclass, couldn't I simply do something like this? myManagedObject.firstName = [[firstNameMutableStr copy] autorelease]; This would have the exact same effect, or not? The dynamic implementation would retain that anyways ... so.... why not the easy way?

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  • How to use the variable declared in one class in another class in Obj C.

    - by srikanth rongali
    I have a NSDate *date1 in class1 implementation file(I initialized it as Global variable). I have NSDate *date2 in class 2 implementation file (initialized it as Global variable). I need to calculate the NSTimeInterval between the two dates in class 2. But I could not do it. I could not access date1 in this class. It is giving error as (date2 undeclared). Please give me help in how to call other class variables in this class. Thank you.

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  • C++ Singleton design pattern

    - by Artem Barger
    Recently I've bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real life example): // a lot of methods are omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that the instance field is initiated on the heap. That means there is a memory allocation. What is completely unclear for me is when exactly the memory is going to be deallocated? Or is there a bug and memory leak? It seems like there is a problem in the implementation. My main question is, how do I implement it in the right way?

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  • How to calculate median of a Map<Int,Int>?

    - by Chris
    For a map where the key represents a number of a sequence and the value the count how often this number appeared in the squence, how would an implementation of an algorithm in java look like to calculate the median? For example: 1,1,2,2,2,2,3,3,3,4,5,6,6,6,7,7 in a map: Map<Int,Int> map = ... map.put(1,2) map.put(2,4) map.put(3,3) map.put(4,1) map.put(5,1) map.put(6,3) map.put(7,2) double median = calculateMedian(map); print(median); would result in: > print(median); 3 > So what i am looking for is a java implementation of calculateMedian.

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  • iphone memory management: alloc and retain properties.

    - by Jonathan
    According to the docs, you do one release per alloc or retain (etc) However what about when using retain propertys? eg: HEADER @property(retain)UIView *someView; IMPLEMENTATION /*in some method*/ UIView *tempView = [[UIView alloc] init]; //<<<<<ALLOC - retain count = +1 [tempView setBackgroundColor:[UIColor redColor]]; self.someView = tempView; ///<<<<<RETAIN - retain count = +2 [tempView release]; ///should I do this? or a different version of the IMPLEMENTATION self.someView = [[UIView alloc] init]; //<<<<<ALLOC & RETAIN - retain count = +2 //now what??? [self.someView release]; ???? EDIT: I didn't make it clear, but I meant what to do in both circumstances, not just the first.

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  • Counting bits set in a .Net BitArray Class

    - by Sam
    I am implementing a library where I am extensively using the .Net BitArray class and need an equivalent to the Java BitSet.Cardinality() method, i.e. a method which returns the number of bits set. I was thinking of implementing it as an extension method for the BitArray class. The trivial implementation is to iterate and count the bits set (like below), but I wanted a faster implementation as I would be performing thousands of set operations and counting the answer. Is there a faster way than the example below? count = 0; for (int i = 0; i < mybitarray.Length; i++) { if (mybitarray [i]) count++; }

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  • Unexpected result from reduce function

    - by StackedCrooked
    I would like to get the smallest element from a vector. For this I use combine the reduce and min functions. However, when providing my own implementation of min I get unexpected results: user=> (reduce (fn [x y] (< x y) x y) [1 2 3 2 1 0 1 2]) 2 user=> (reduce min [1 2 3 2 1 0 1 2 3]) 0 The reduce with standard min returns 0 as expected. However, when I provide my own implementation it returns 2. What am I doing wrong?

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