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  • Jquery - binding click event to a variable

    - by Kayote
    All, I am really stuck/ confused at this point. I have an array with 6 items in it. Each item in the array is dynamically filled with elements using jquery '.html' method. However, I cannot seem to be able to attach/ bind an event to this dynamically created variable. As soon as the browser gets to the problem line (see the area labeled 'PROBLEM AREA'), I get a 'undefined' error, which is really confusing as all the previous code on the very same variable works just fine. var eCreditSystem = document.getElementById("creditSystem"); var i = 0; var eCreditT = new Array(6); // 6 members created which will be recycled function createCreditTransaction () // func called when a transaction occurs, at the mo, attached to onclick() { if (i < 6) { eCreditT[i] = undefined; // to delete the existing data in the index of array addElements (i); } else if (i > 5 || eCreditT[i] != undefined) { ... } } function addElements (arrayIndex) // func called from within the 'createCreditTransaction()' func { eCreditT[i] = $(document.createElement('div')).addClass("cCreditTransaction").appendTo(eCreditSystem); $(eCreditT[i]).attr ('id', ('trans' + i)); $(eCreditT[i]).html ('<div class="cCreditContainer"><span class="cCreditsNo">-50</span>&nbsp;<img class="cCurrency" src="" alt="" /></div><span class="cCloseMsg">Click box to close.</span><div class="dots"></div><div class="dots"></div><div class="dots"></div>'); creditTransactionSlideOut (eCreditT[i], 666); // calling slideOut animation console.log(eCreditT[i]); // this confirms that the variable is not undefined /* ***** THE PROBLEM AREA ***** */ $(eCreditT[i]).on ('click', function () // if user clicks on the transaction box { creditTransactionSlideBackIn (eCreditT[i], 150); // slide back in animation }); return i++; }

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  • Multiplication of 2 positive numbers giving a negative result

    - by krandiash
    My program is an implementation of a bloom filter. However, when I'm storing my hash function results in the bit array, the function (of the form f(i) = (a*i + b) % m where a,b,i,m are all positive integers) is giving me a negative result. The problem seems to be in the calculation of a*i which is coming out to be negative. Ignore the print statements in the code; those were for debugging. Basically, the value of temp in this block of code is coming out to be negative and so I'm getting an ArrayOutOfBoundsException. m is the bit array length, z is the number of hash functions being used, S is the set of values which are members of this bloom filter and H stores the values of a and b for the hash functions f1, f2, ..., fz. public static int[] makeBitArray(int m, int z, ArrayList<Integer> S, int[] H) { int[] C = new int[m]; for (int i = 0; i < z; i++) { for (int q = 0; q < S.size() ; q++) { System.out.println(H[2*i]); int temp = S.get(q)*(H[2*i]); System.out.println(temp); System.out.println(S.get(q)); System.out.println(H[2*i + 1]); System.out.println(m); int t = ((H[2*i]*S.get(q)) + H[2*i + 1])%m; System.out.println(t); C[t] = 1; } } return C; } Any help is appreciated.

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  • ASP.NET MVC: How do I validate a model wrapped in a ViewModel?

    - by Deniz Dogan
    For the login page of my website I would like to list the latest news for my site and also display a few fields to let the user log in. So I figured I should make a login view model - I call this LoginVM. LoginVM contains a Login model for the login fields and a List<NewsItem> for the news listing. This is the Login model: public class Login { [Required(ErrorMessage="Enter a username.")] [DisplayName("Username")] public string Username { get; set; } [Required(ErrorMessage="Enter a password.")] [DataType(DataType.Password)] [DisplayName("Password")] public string Password { get; set; } } This is the LoginVM view model: public class LoginVM { public Login login { get; set; } public List<NewsItem> newsItems { get; set; } } This is where I get stuck. In my login controller, I get passed a LoginVM. [HttpPost] public ActionResult Login(LoginVM model, FormCollection form) { if (ModelState.IsValid) { // What? In the code I'm checking whether ModelState is valid and this would work fine if the view model was actually the Login model, but now it's LoginVM which has no validation attributes at all. How do I make LoginVM "traverse" through its members to validate them all? Am I doing something fundamentally wrong using ModelState in this manner?

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  • How to detect whether there is a specific member variable in class?

    - by Kirill V. Lyadvinsky
    For creating algorithm template function I need to know whether x or X (and y or Y) in class that is template argument. It may by useful when using my function for MFC CPoint class or GDI+ PointF class or some others. All of them use different x in them. My solution could be reduces to the following code: template<int> struct TT {typedef int type;}; template<class P> bool Check_x(P p, typename TT<sizeof(&P::x)>::type b = 0) { return true; } template<class P> bool Check_x(P p, typename TT<sizeof(&P::X)>::type b = 0) { return false; } struct P1 {int x; }; struct P2 {float X; }; // it also could be struct P3 {unknown_type X; }; int main() { P1 p1 = {1}; P2 p2 = {1}; Check_x(p1); // must return true Check_x(p2); // must return false return 0; } But it does not compile in Visual Studio, while compiling in the GNU C++. With Visual Studio I could use the following template: template<class P> bool Check_x(P p, typename TT<&P::x==&P::x>::type b = 0) { return true; } template<class P> bool Check_x(P p, typename TT<&P::X==&P::X>::type b = 0) { return false; } But it does not compile in GNU C++. Is there universal solution? UPD: Structures P1 and P2 here are only for example. There are could be any classes with unknown members.

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  • Mocking Autofac's "Resolve" extension method with TypeMock

    - by Lockshopr
    I'm trying to mock an Autofac resolve, such as: using System; using Autofac; using TypeMock.ArrangeActAssert; class Program { static void Main(string[] args) { var inst = Isolate.Fake.Instance<IContainer>(); Isolate.Fake.StaticMethods(typeof(ResolutionExtensions), Members.ReturnNulls); Isolate.WhenCalled(() => inst.Resolve<IRubber>()).WillReturn(new BubbleGum()); Console.Out.WriteLine(inst.Resolve<IRubber>()); } } public interface IRubber {} public class BubbleGum : IRubber {} Coming from Moq, the syntax and exceptions from TypeMock confuse me a great deal. Having initially run this in a TestMethod, I kept getting an exception resembling "WhenCalled cannot be run without a complementing behavior". I tried defining behaviors for everyone and their mothers, but to no avail. Then I debug stepped through the test run, and saw that an actual exception was fired from Autofac: IRubber has not been registered. So it's obvious that the static Resolve function isn't being faked, and I can't get it to be faked, no matter how I go about hooking it up. Isolate.WhenCalled(() => ResolutionExtensions.Resolve<IRubber>(null)).WillReturn(new BubbleGum()); ... throws an exception from Autofac complaining that the IComponentContext cannot be null. Feeding it the presumably faked IContainer (or faking an IComponentContext instead) gets me back to the "IRubber not registered" error.

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  • Partial Classes - are they bad design?

    - by dferraro
    Hello, I'm wondering why the 'partial class' concept even exists in .NET. I'm working on an application and we are reading a (actually very good) book relavant to the development platform we are implementing at work. In the book he provides a large code base /wrapper around the platform API and explains how he developed it as he teaches different topics about the platform development. Anyway, long story short - he uses partial classes, all over the place, as a way to fake multiple inheritence in C# (IMO). Why he didnt just split the classes up into multiple ones and use composition is beyond me. He will have 3 'partial class' files to make up his base class, each w/ 3-500 lines of code... And does this several times in his API. Do you find this justifiable? If it were me, I'd have followed the S.R.P. and created multiple classes to handle different required behaviors, then create a base class that has instances of these classes as members (e.g. composition). Why did MS even put partial class into the framework?? They removed the ability to expand/collapse all code at each scope level in C# (this was allowed in C++) because it was obviously just allowing bad habits - partial class is IMO the same thing. I guess my quetion is: Can you explain to me when there would be a legitimate reason to ever use a partial class? I do not mean this to be a rant / war thread. I'm honeslty looking to learn something here. Thanks

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  • Why can't I build this Javascript object?

    - by Alex Mcp
    I have an object I'm trying to populate from another object (that is, iterate over a return object to produce an object with only selected values from the original). My code looks like this: var collect = {}; function getHistoricalData(username){ $.getJSON("http://url/" + username + ".json?params", function(data){ for (var i=0; i < data.length; i++) { console.log(i); collect = { i : {text : data[i].text}}; $("#wrap").append("<span>" + data[i].text + "</span><br />"); }; console.log(collect); }); } So I'm using Firebug for debugging, and here's what I know: The JSON object is intact console.log(i); is showing the numbers 1-20 as expected When I log the collect object at the end, it's structure is this: var collect = { i : {text : "the last iteration's text"}}; So the incrementer is "applying" to the data[i].text and returning the text value, but it's not doing what I expected, which is create a new member of the collect object; it's just overwriting collect.i 20 times and leaving me with the last value. Is there a different syntax I need to be using for assigning object members? I tried collect.i.text = and collect[i].text = and the error was that whatever I tried was undefined. I'd love to know what's going on here, so the more in-depth an explanation the better. Thanks!

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  • Get the signed/unsigned variant of an integer template parameter without explicit traits

    - by Blair Holloway
    I am looking to define a template class whose template parameter will always be an integer type. The class will contain two members, one of type T, and the other as the unsigned variant of type T -- i.e. if T == int, then T_Unsigned == unsigned int. My first instinct was to do this: template <typename T> class Range { typedef unsigned T T_Unsigned; // does not compile public: Range(T min, T_Unsigned range); private: T m_min; T_Unsigned m_range; }; But it doesn't work. I then thought about using partial template specialization, like so: template <typename T> struct UnsignedType {}; // deliberately empty template <> struct UnsignedType<int> { typedef unsigned int Type; }; template <typename T> class Range { typedef UnsignedType<T>::Type T_Unsigned; /* ... */ }; This works, so long as you partially specialize UnsignedType for every integer type. It's a little bit of additional copy-paste work (slash judicious use of macros), but serviceable. However, I'm now curious - is there another way of determining the signed-ness of an integer type, and/or using the unsigned variant of a type, without having to manually define a Traits class per-type? Or is this the only way to do it?

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  • Hibernate Bi- Directional many to many mapping advice!

    - by Rob
    hi all, i woundered if anyone might be able to help me out. I am trying to work out what to google for (or any other ideas!!) basically i have a bidirectional many to many mapping between a user entity and a club entity (via a join table called userClubs) I now want to include a column in userClubs that represents the role so that when i call user.getClubs() I can also work out what level access they have. Is there a clever way to do this using hibernate or do i need to rethink the database structure? Thank you for any help (or just for reading this far!!) the user.hbm.xml looks a bit like <set name="clubs" table="userClubs" cascade="save-update"> <key column="user_ID"/> <many-to-many column="activity_ID" class="com.ActivityGB.client.domain.Activity"/> </set> the activity.hbm.xml part <set name="members" inverse="true" table="userClubs" cascade="save-update"> <key column="activity_ID"/> <many-to-many column="user_ID" class="com.ActivityGB.client.domain.User"/> </set> The current userClubs table contains the fields id | user_ID | activity_ID I would like to include in there id | user_ID | activity_ID | role and be able to access the role on both sides...

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  • Is it possible to store pointers in shared memory without using offsets?

    - by Joseph Garvin
    When using shared memory, each process may mmap the shared region into a different area of their address space. This means that when storing pointers within the shared region, you need to store them as offsets of the start of the shared region. Unfortunately, this complicates use of atomic instructions (e.g. if you're trying to write a lock free algorithm). For example, say you have a bunch of reference counted nodes in shared memory, created by a single writer. The writer periodically atomically updates a pointer 'p' to point to a valid node with positive reference count. Readers want to atomically write to 'p' because it points to the beginning of a node (a struct) whose first element is a reference count. Since p always points to a valid node, incrementing the ref count is safe, and makes it safe to dereference 'p' and access other members. However, this all only works when everything is in the same address space. If the nodes and the 'p' pointer are stored in shared memory, then clients suffer a race condition: x = read p y = x + offset Increment refcount at y During step 2, p may change and x may no longer point to a valid node. The only workaround I can think of is somehow forcing all processes to agree on where to map the shared memory, so that real pointers rather than offsets can be stored in the mmap'd region. Is there any way to do that? I see MAP_FIXED in the mmap documentation, but I don't know how I could pick an address that would be safe.

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  • questions about using svn

    - by ajsie
    i have set up a svn repository in a remote ubuntu server using webdav (http://ip/svn). but i have some questions: should i create one svn repository for each project folder? so i should use "svnadmin create" 5 times for 5 projects? or should i import them to seperate folders in the svn repository? should i after i have created a svn repo, import one project folder into it with "svn import" and then DELETE my original local folder thus only having it in the svn repo in the remote ubuntu server? is this safe or should i still have a local copy for some reason (cause i wont work in that one)? i use netbeans to check out projects from svn repo, then i edit the files and commit the changes. but how should i do to update the live web server content (in /var/www)? should i in my ubuntu server use "svn checkout" and check it out to /var/www or should i use netbeans to check out to a local folder and then upload the files to /var/www with ftp or webdav (and which one of them should i use)? so i got a svn repo and lets say 4 programmers are working with it, checking out and commiting. how do i check what is happening in the repo, which one made which changes, and all the changes from day 1 to day 213? does netbeans/eclipse letting me see this kind of information or do i download another application for it? i should have one svn user for each programmer in the ubuntu server? is this accomplished by using "htpasswd" 4 times for 4 programmers? how do i couple all these users to same group so that i could modify file access specific for the svn group and all its members?

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  • Precision of cos(atan2(y,x)) versus using complex <double>, C++

    - by Ivan
    Hi all, I'm writing some coordinate transformations (more specifically the Joukoswky Transform, Wikipedia Joukowsky Transform), and I'm interested in performance, but of course precision. I'm trying to do the coordinate transformations in two ways: 1) Calculating the real and complex parts in separate, using double precision, as below: double r2 = chi.x*chi.x + chi.y*chi.y; //double sq = pow(r2,-0.5*n) + pow(r2,0.5*n); //slow!!! double sq = sqrt(r2); //way faster! double co = cos(atan2(chi.y,chi.x)); double si = sin(atan2(chi.y,chi.x)); Z.x = 0.5*(co*sq + co/sq); Z.y = 0.5*si*sq; where chi and Z are simple structures with double x and y as members. 2) Using complex : Z = 0.5 * (chi + (1.0 / chi)); Where Z and chi are complex . There interesting part is that indeed the case 1) is faster (about 20%), but the precision is bad, giving error in the third decimal number after the comma after the inverse transform, while the complex gives back the exact number. So, the problem is on the cos(atan2), sin(atan2)? But if it is, how the complex handles that? Thanks!

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  • Modify static variables while debugging in Eclipse

    - by sleske
    As an extension the the question "Modify/view static variables while debugging in Eclipse", I'd like to be able to modify static variables while debugging in Eclipse. For instance and local variables, I can just choose the variable in the "Variables" view of Eclipse, and use the context menu "Change value..." to change the value. This is not possible for arbitrary static variables, because they do not appear in the "Variables" view. What I tried: If you choose "Java / Show static variables" from the triangle menu in the "Variables" view, you can see and modify static member variables of the variables listed in the "Variables view". However, I did not find how to access a static member of a class whose instance does not appear in the "Variables view". You can of course enter a static member as an expression into the "Expression view" (using fully qualified name). Then you can see the value, but the "Expression view" does not have an option to modify the value (it does allow to modify members of an expression, but not the expression itself, even if the expression is a field). So, if I have a static variable like a boolean MyClass.disableAllBugs, is there a way to change MyClass.disableAllBugs during debugging? As an aside: I realize that even having public mutable static fields (i.e. mutable global variables) is very bad style. But some codebases have it, and then it's sometimes useful to modify it while debugging.

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  • How to maintain base files for development environment central while allowing people to change their

    - by Ittai
    Hi, what I'd like to do is have files in a central location so that when I add people to my development team they can see the base version of these files but meanwhile have the ability for the rest of the team to work with their own local version. I know I can just put the files in source-control (we use Tortoiese-SVN) and have my team change the local versions but I'd rather not as the exclamation mark signaling the file has been changed and needs to be committed, quite frankly, irritates me greatly. I'll give two examples of what I mean: We use quite a few build.xml files which relate to a single properties files which contains many definitions. Some of them can be different between team-members (mainly temporary working directories) and I'd like a new team-member to have the ability to get the properties file with the base config but change it if they wish. Have the eclipse settings file in the SVN so that when a new team-member joins they can just retrieve the files from the server and have a base system running. If they wish they will be able to change some of these settings. Thanks, Ittai

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  • How do I model teams and gameplay in this scorekeeping application?

    - by Eric Hill
    I'm writing a scorekeeping application for card game that has a few possibly-interesting constraints. The application accepts user registrations for players, then lets them check-in to a particular game (modeled as Event). After the final player registers, the app should generate teams, singles or doubles, depending on the preference of the person running the game and some validations (can't do doubles if there's an odd number checked in). There are @event.teams.count rounds in the game. To sum up: An event consists of `@event.teams.count` rounds; Teams can have 1 or more players Events have n or n/2 teams (depending on whether it's singles or doubles) Users will be members of different teams at different events Currently I have a rat's nest of associations: class User < ActiveRecord::Base has_many :teams, :through => :players has_many :events, :through => :teams class Event < ActiveRecord::Base has_many :rounds has_many :teams has_many :players, :through => :teams class Player < ActiveRecord::Base belongs_to :user belongs_to :team end class Team < ActiveRecord::Base has_many :players belongs_to :event end class Round < ActiveRecord::Base belongs_to :event belongs_to :user end The sticky part is team generation. I have basically a "start game" button that should freeze the registrations and pair up teams either singly or doubly, and render to Round#new so that the first (and subsequent) matches can be scored. Currently I'm implementing this as a check on Round#new that calls Event#generate_teams and displays the view: # Event#generate_teams def generate_teams # User has_many :events, :through => :registrations # self.doubles is a boolean denoting 2 players per team registrations.in_groups_of(self.doubles ? 2 : 1, nil).each do |side| self.teams << Player.create(self,side) end end Which doesn't work. Should there maybe be a Game model that ties everything together rather than (my current method) defining the game as an abstraction via the relationships between Events, Users, and Rounds (and Teams and Players and etc.)? My head is swimming.

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  • Illegal Argument Exception in Google Wave App

    - by Yoenhofen
    I'm writing a Google Wave robot and I just messed something up. It was working just fine but now I'm getting an IllegalArgument exception on the line that includes query.execute. Am I doing something stupid? I've seen several code samples very similar to what I'm doing. I can include the code of the WaveUpdate class if necessary. The intent here is to select all WaveUpdate members that have an updateDateTime in the last hour. PersistenceManager pm = PMF.get().getPersistenceManager(); try { Query query = pm.newQuery(WaveUpdate.class); query.setFilter("emailAddress > '' && updateDateTime > referenceDateTime"); query.declareParameters("java.util.Date referenceDateTime"); Calendar referenceDateTime = Calendar.getInstance(); referenceDateTime.add(Calendar.HOUR_OF_DAY, -1); List<WaveUpdate> updates = (List<WaveUpdate>) query.execute(referenceDateTime.getTime());

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  • g++ linker can't find const member function

    - by Max
    I have a Point class (with integer members x and y) that has a member function withinBounds that is declared like so: bool withinBounds(const Point&, const Point&) const; and defined like this: bool Point::withinBounds(const Point& TL, const Point& BR) const { if(x < TL.getX()) return false; if(x > BR.getX()) return false; if(y < TL.getY()) return false; if(y > BR.getY()) return false; // Success return true; } and then in another file, I call withinBounds like this: Point pos = currentPlayer->getPosition(); if(pos.withinBounds(topleft, bottomright)) { // code block } This compiles fine, but it fails to link. g++ gives me this error: /home/max/Desktop/Development/YARL/yarl/src/GameData.cpp:61: undefined reference to 'yarl::utility::Point::withinBounds(yarl::utility::Point const&, yarl::utility::Point const&)' When I make the function not const, it links fine. Anyone know the reason why? The linker error looks like it's looking for a non-const version of the function, but I don't know why it would.

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  • Synchronizing Access to a member of the ASP.NET session

    - by Sam
    I'm building a Javascript application and eash user has an individual UserSession. The application makes a bunch of Ajax calls. Each Ajax call needs access to a single UserSession object for the user. Each Ajax call needs a UserSession object. Data in the UserSession object is unique to each user. Originally, during each Ajax call I would create a new UserSession object and it's data members were stored in the ASP.NET Session. However, I found that the UserSession object was being instantiated a lot. To minimize the construction of the UserSession object, I wrapped it in a Singleton pattern and sychronized access to it. I believe that the synchronization is happening application wide, however I only need it to happen per user. I saw a post here that says the ASP.NET cache is synchronized, however the time between creating the object and inserting it into the cache another Thread could start construction it's another object and insert it into the cache. Here is the way I'm currently synchronizing access to the object. Is there a better way than using "lock"... should be be locking on the HttpContext.Session object? private static object SessionLock = new object(); public static WebSession GetSession { get { lock (SessionLock) { try { var context = HttpContext.Current; WebSession result = null; if (context.Session["MySession"] == null) { result = new WebSession(context); context.Session["MySession"] = result; } else { result = (WebSession)context.Session["MySession"]; } return result; } catch (Exception ex) { ex.Handle(); return null; } } } }

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  • Using unset member variables within a class or struct

    - by Doug Kavendek
    It's pretty nice to catch some really obvious errors when using unset local variables or when accessing a class or struct's members directly prior to initializing them. In visual studio 2008 you get an "uninitialized local variable used" warning at compile-time and get a run-time check failure at the point of access when debugging. However, if you access an uninitialized struct's member variable through one of its functions, you don't get any warnings or assertions. Obviously the easiest solution is don't do that, but nobody's perfect. For example: struct Test { float GetMember() const { return member; } float member; }; Test test; float f1 = test.member; // Raises warning, asserts in VS debugger at runtime float f2 = test.GetMember(); // No problem, just keeps on going This surprised me, but it makes some sense -- the compiler can't assume calling a function on an unused struct is an error, or how else would you initialize or construct it? And anything fancier just quickly brings up so many other complications that it makes sense that it wouldn't bother classifying which functions are ok to call and when, especially just as a debugging help. I know I can set up my own assertions or error checking within the class itself, but that can complicate some simpler structs. Still, it would seem like within the context of the function call, wouldn't it know insides GetMember() that member wasn't initialized yet? I'm assuming it's not only relying on static compile-time deduction, given the Run-Time Check Failure #3 it raises during execution, so based on my current understanding of it it would seem reasonable for the same checks to apply. Is this just a limitation of this specific compiler/debugger (Visual Studio 2008), or more tied to how C++ works?

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  • Programming Concepts: What should be done when an exception is thrown?

    - by Dooms101
    This does not really apply to any language specifically, but if it matters I am using VB.NET in Visual Studio 2008. I can't seem to find anything really that useful using Google about this topic, but I was wondering what is common practice when an exception is thrown and caught but since it has been thrown the application cannot continue operating. For example I have exceptions that are thrown by my FileLoader class when a file cannot be found or when a file is deemed corrupt. The exception is only thrown within the class and is not handled really. If the error is detected, then the exception is thrown and whatever function is was thrown is basically quits. So in the code trying to create that object or call one of its members I use a Try...Catch statement. However, I was wondering, what should even do when this exception is caught? My application needs these files to be intact, and if they are not, the application is almost useless. So far I just pop up a message box telling the user their is an error and to reinstall. What else can I do, or better, what's common practice in these situations?

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  • cast operator to base class within a thin wrapper derived class

    - by miked
    I have a derived class that's a very thin wrapper around a base class. Basically, I have a class that has two ways that it can be compared depending on how you interpret it so I created a new class that derives from the base class and only has new constructors (that just delegate to the base class) and a new operator==. What I'd like to do is overload the operator Base&() in the Derived class so in cases where I need to interpret it as the Base. For example: class Base { Base(stuff); Base(const Base& that); bool operator==(Base& rhs); //typical equality test }; class Derived : public Base { Derived(stuff) : Base(stuff) {}; Derived(const Base& that) : Base(that) {}; Derived(const Derived& that) : Base(that) {}; bool operator==(Derived& rhs); //special case equality test operator Base&() { return (Base&)*this; //Is this OK? It seems wrong to me. } }; If you want a simple example of what I'm trying to do, pretend I had a String class and String==String is the typical character by character comparison. But I created a new class CaseInsensitiveString that did a case insensitive compare on CaseInsensitiveString==CaseInsensitiveString but in all other cases just behaved like a String. it doesn't even have any new data members, just an overloaded operator==. (Please, don't tell me to use std::string, this is just an example!) Am I going about this right? Something seems fishy, but I can't put my finger on it.

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  • Is extending a base class with non-virtual destructor dangerous in C++

    - by Akusete
    Take the following code class A { }; class B : public A { }; class C : public A { int x; }; int main (int argc, char** argv) { A* b = new B(); A* c = new C(); //in both cases, only ~A() is called, not ~B() or ~C() delete b; //is this ok? delete c; //does this line leak memory? return 0; } when calling delete on a class with a non-virtual destructor with member functions (like class C), can the memory allocator tell what the proper size of the object is? If not, is memory leaked? Secondly, if the class has no member functions, and no explicit destructor behaviour (like class B), is everything ok? I ask this because I wanted to create a class to extend std::string, (which I know is not recommended, but for the sake of the discussion just bear with it), and overload the +=,+ operator. -Weffc++ gives me a warning because std::string has a non virtual destructor, but does it matter if the sub-class has no members and does not need to do anything in its destructor? -- FYI the += overload was to do proper file path formatting, so the path class could be used like class path : public std::string { //... overload, +=, + //... add last_path_component, remove_path_component, ext, etc... }; path foo = "/some/file/path"; foo = foo + "filename.txt"; //and so on... I just wanted to make sure someone doing this path* foo = new path(); std::string* bar = foo; delete bar; would not cause any problems with memory allocation

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  • Extension methods for encapsulation and reusability

    - by tzaman
    In C++ programming, it's generally considered good practice to "prefer non-member non-friend functions" instead of instance methods. This has been recommended by Scott Meyers in this classic Dr. Dobbs article, and repeated by Herb Sutter and Andrei Alexandrescu in C++ Coding Standards (item 44); the general argument being that if a function can do its job solely by relying on the public interface exposed by the class, it actually increases encapsulation to have it be external. While this confuses the "packaging" of the class to some extent, the benefits are generally considered worth it. Now, ever since I've started programming in C#, I've had a feeling that here is the ultimate expression of the concept that they're trying to achieve with "non-member, non-friend functions that are part of a class interface". C# adds two crucial components to the mix - the first being interfaces, and the second extension methods: Interfaces allow a class to formally specify their public contract, the methods and properties that they're exposing to the world. Any other class can choose to implement the same interface and fulfill that same contract. Extension methods can be defined on an interface, providing any functionality that can be implemented via the interface to all implementers automatically. And best of all, because of the "instance syntax" sugar and IDE support, they can be called the same way as any other instance method, eliminating the cognitive overhead! So you get the encapsulation benefits of "non-member, non-friend" functions with the convenience of members. Seems like the best of both worlds to me; the .NET library itself providing a shining example in LINQ. However, everywhere I look I see people warning against extension method overuse; even the MSDN page itself states: In general, we recommend that you implement extension methods sparingly and only when you have to. So what's the verdict? Are extension methods the acme of encapsulation and code reuse, or am I just deluding myself?

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  • Algorithm for count-down timer that can add on time

    - by Person
    I'm making a general timer that has functionality to count up from 0 or count down from a certain number. I also want it to allow the user to add and subtract time. Everything is simple to implement except for the case in which the timer is counting down from some number, and the user adds or subtracts time from it. For example: (m_clock is an instance of SFML's Clock) float Timer::GetElapsedTime() { if ( m_forward ) { m_elapsedTime += m_clock.GetElapsedTime() - m_elapsedTime; } else { m_elapsedTime -= m_elapsedTime - m_startingTime + m_clock.GetElapsedTime(); } return m_elapsedTime; } To be a bit more clear, imagine that the timer starts at 100 counting down. After 10 seconds, the above function would look like 100 -= 100 - 100 + 10 which equals 90. If it was called after 20 more seconds it would look like 90 -= 90 - 100 + 30 which equals 70. This works for normal counting, but if the user calls AddTime() ( just m_elapsedTime += arg ) then the algorithm for backwards counting fails miserably. I know that I can do this using more members and keeping track of previous times, etc. but I'm wondering whether I'm missing some implementation that is extremely obvious. I'd prefer to keep it as simple as possible in that single operation.

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  • Problem with LINQ in C#

    - by David Bonnici
    I am encountering a problem when using LINQ in C#, I am constantly getting "Specified cast is not valid". This is what I am trying to do. I create a class in which I declare all the columns of the table. [Table(Name="tbl_Aff")] public class Affiliate { [Column] public string name; [Column] public string firstname; [Column] public string surname; [Column] public string title; } I then declare a strongly typed DataContext in which I declare all Table collections as members of the context. public partial class Database : DataContext { public Table affiliate; public Database() : base(Settings.getConnectionString()) { } //This method gets the connection string by reading from an XML file. } public partial class Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { Database database = new Database(); try { var q = from a in database.affiliate select a; foreach (var aff in q) // Here I get the error "Specified cast is not valid" { lblMessage.InnerHtml += aff.name + ""; } } catch (Exception ex) { System.Console.WriteLine(ex.Message); } } }

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