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  • difference in using virtual and not using virtual

    - by numerical25
    In C++, whether you choose to use virtual or not, you can still override the base class function. The following compiles just fine... class Enemy { public: void SelectAnimation(); void RunAI(); void Interact() { cout<<"Hi I am a regular Enemy"; } private: int m_iHitPoints; }; class Boss : public Enemy { public: void Interact() { cout<<"Hi I am a evil Boss"; } }; So my question is what is the difference in using or not using the virtual function. And what is the disadvantage.

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  • c++ inheritance

    - by Meloun
    Hi, i am trouble with this.. Is there some solution or i have to keep exactly class types? //header file Class Car { public: Car(); virtual ~Car(); }; class Bmw:Car { public: Bmw(); virtual ~Bmw(); }; void Start(Car& mycar) {}; //cpp file Car::Car(){} Car::~Car() {} Bmw::Bmw() :Car::Car(){} Bmw::~Bmw() {} int main() { Car myCar; Bmw myBmw; Start(myCar); //works Start(myBmw); //!! doesnt work return 0; }

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  • Sharing base object with inheritance

    - by max
    I have class Base. I'd like to extend its functionality in a class Derived. I was planning to write: class Derived(Base): def __init__(self, base_arg1, base_arg2, derived_arg1, derived_arg2): super().__init__(base_arg1, base_arg2) # ... def derived_method1(self): # ... Sometimes I already have a Base instance, and I want to create a Derived instance based on it, i.e., a Derived instance that shares the Base object (doesn't re-create it from scratch). I thought I could write a static method to do that: b = Base(arg1, arg2) # very large object, expensive to create or copy d = Derived.from_base(b, derived_arg1, derived_arg2) # reuses existing b object but it seems impossible. Either I'm missing a way to make this work, or (more likely) I'm missing a very big reason why it can't be allowed to work. Can someone explain which one it is? [Of course, if I used composition rather than inheritance, this would all be easy to do. But I was hoping to avoid the delegation of all the Base methods to Derived through __getattr__.]

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  • Compiling C++ when two classes references one another

    - by Omry
    I am trying to write a simple wrapper around a connection pointer that will return it to the pool when the wrapper is destroyed. but it wont compile because the ConnectionPool and AutoConn need each other to be declared. I tried to use forward deceleration but it didn't work. how do I solve this? (using g++) class Connection {}; class ConnectionPool { Connection *m_c; public: AutoConn getConn() { return AutoConn(this, m_c); // by value } void releaseConnection(Connection *c) { } }; class AutoConn { ConnectionPool* m_pool; Connection *m_connection; public: AutoConn(ConnectionPool* pool, Connection *c) : m_pool(pool), m_connection(c) {} ~AutoConn() { m_pool->releaseConnection(m_connection); } };

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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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  • How/When/Where to Extend Gem Classes (via class_eval and Modules) in Rails 3?

    - by viatropos
    What is the recommended way to extend class behavior, via class_eval and modules (not by inheritance) if I want to extend a class buried in a Gem from a Rails 3 app? An example is this: I want to add the ability to create permalinks for tags and categories (through the ActsAsTaggableOn and ActsAsCategory gems). They have defined Tag and Category models. I want to basically do this: Category.class_eval do has_friendly_id :title end Tag.class_eval do has_friendly_id :title end Even if there are other ways of adding this functionality that might be specific to the gem, what is the recommended way to add behavior to classes in a Rails 3 application like this? I have a few other gems I've created that I want to do this to, such as a Configuration model and an Asset model. I would like to be able to add create an app/models/configuration.rb model class to my app, and it would act as if I just did class_eval. Anyways, how is this supposed to work? I can't find anything that covers this from any of the current Rails 3 blogs/docs/gists.

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  • PHP OOP: Unique method per argument type?

    - by sunwukung
    I'm writing a little homebrew ORM (academic interest). I'm trying to adhere to the TDD concept as a training exercise, and as part of that exercise I'm writing documentation for the API as I develop the class. Case in point - I'm working on a classic "getCollection" type mapper class. I want it to be able to retrieve collections of asset X (let's say blog posts) for a specific user, and also collections based on an arbitrary array of numeric values. So - you might have a method like any one of these $User = $UserMapper->load(1); $ArticleCollection = $ArticleMapper->getCollection(range(10,20)); $ArticleCollection = $ArticleMapper->getCollection($User); $ArticleCollection = $ArticleMapper->getCollection($User->getId()); So, in writing the documentation for the getCollection method - I want to declare the @param variable in the Docblock. Is it better to have a unique method for each argument type, or is it acceptable to have a method that delegates to the correct internal method/class based on argument type?

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  • [app-engine-java-groovy] One-to-Many relationship. Select objects from datastore.

    - by Olexandr
    Hi. I've omitted some code(package declarations, imports, other fields) for shortness. I have here simple One-to-Many relation. It worked fine till this moment. @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true") class Restaurant implements Serializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) Key id @Persistent(mappedBy = "restaurant") List<RestaurantAddress> addresses = new ArrayList<RestaurantAddress>() } //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true") class RestaurantAddress implements Serializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) Key id @Persistent Restaurant restaurant } Now i need to get(select) all the Restaurants from DB: def getRestaurantsToExport(final String dst, final int count) { String field = restaurantExportFields[dst] return transactionExecute() { PersistenceManager pm -> Query q = pm.newQuery(Restaurant.class) q.filter = "$field == null" q.setRange(0, count) return q.execute() } } But there are on problem - query gives me 12 restaurants(as in DB) but every Restaurant has 0 Address but in Datastore every Restaurant has minimum 2 addresses. Have anyone the same problem or knows the solution ?

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  • MVVM Binding To Property == Null

    - by LnDCobra
    I want to show some elements when a property is not null. What is the best way of achieving this? The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Company Company { get { return _company; } set { SetField(ref _company, value, () => Company); } } private Company _company; ...... } This is part of my View.xaml <GroupBox Visibility="{Binding Path=Trade.Company, Converter={StaticResource boolToVisConverter}}" /> I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?

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  • Constructors for C++ objects

    - by sasquatch
    I have class Person as following : class Person { char* name; int age; }; Now I need to add two contructors. One taking no arguments, that inserts field values to dynamically allocated resources. Second taking (char*, int) arguments initialized by initialization list. Last part is to define a destructor showing information about destroying objects and deallocating dynamically allocated resources. How to perform this task ? That's what I already have : class Person { char* name; int age; public: Person(){ this->name = new *char; this->age = new int; } Person(char* c, int i){ } };

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  • Inconsistent Behavior From Declared DLL Function

    - by Steven
    Why might my GetRawData declared function return a correct value when called from my VB.NET application, but return zero when called from my ASP.NET page? The code is exactly the same except for class type difference (Form / Page) and calling event handler (Form1_Load, Page_Load). Note: In the actual code, #DLL# and #RAWDATAFILE# are both absolute filenames to my DLL and raw data file respectively. Note: The DLL file was not created by Visual Studio. Form1.vb Public Class Form1 Declare Auto Function GetRawData Lib "#DLL#" (ByVal filename() As Byte, _ ByVal byteArray() As Byte, _ ByVal length As Int32) As Int32 Private Sub Form1_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load Dim buffer(10485760) As Byte Dim msg As String, length As Integer = 10485760 Dim filename As String = "#RAWDATAFILE#" length = GetRawData(Encoding.Default.GetBytes(filename), buffer, length) Default.aspx.vb Partial Public Class _Default Inherits System.Web.UI.Page Declare Auto Function GetRawData Lib "#DLL#" (ByVal filename() As Byte, _ ByVal byteArray() As Byte, _ ByVal length As Int32) As Int32 Protected Sub Page_Load(ByVal sender As Object, _ ByVal e As System.EventArgs) Handles Me.Load Dim buffer(10485760) As Byte Dim msg As String, length As Integer = 10485760 Dim filename As String = "#RAWDATAFILE#" length = GetRawData(Encoding.Default.GetBytes(filename), buffer, length)

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  • C# Why does this code not show a GUI properly?

    - by Tom
    class Program { static String ChannelName = null; static Form1 f; static void Main() { f = new Form1(); f.Show(); try { MY CODE WHICH CALLS INTO ANOTHER CLASS BUT CANNOT PASS THE GUI INSTANCE AS IT USES REMOTING } } } I know this isnt the best/normal way to do it, but i need to write data to the GUI from a class which has bo instance of the GUI so i was going to call Program.method() and use a function to write to the GUI in program. However when i run the above my GUI displays but with the windows hourglass? Could someone show me a quick fix so that i can still crudely show the GUI, let the application code run and then later write to the GUI?

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  • Rails 3 loading all models on startup

    - by janechii
    Hi all, I have a class method mixed in to all my models. the method gets called when the model class is evaluated. unfortunately (for me), this seems to be on-demand, whenever the model is needed in development env. how can have rails load all the models at start up? is this even advisable? class Foo < ActiveRecord::Base include Acl register_acl # i need this to be called for all models at start up end thank you!

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  • Hibernate - join un related objects

    - by CuriousMind
    I have a requirement, wherein I have to join two unrelated objects using Hibernate HQL. Here is the sample POJO class class Product{ int product_id; String name; String description; } and Class Item{ int item_id; String name; String description; int quantity; int product_id; //Note that there is no composed product object. } Now I want to perform a query like select * from Product p left outer join Item i on p.product_id = i.item_id I want a multidimensional array as an output of this query so that I can have separate instances of Product and Item, instead of one composed in another. Is there any way to do this in Hibernate?

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  • This javascript works in every browser EXCEPT for internet explorer!

    - by user309641
    The webpage is here: http://develop.macmee.com/testdev/ I'm talking about when you click the ? on the left, it is supposed to open up a box with more content in it. It does that in every browser except IE! function question() { $('.rulesMiddle').load('faq.php?faq=rules_main',function(){//load page into .rulesMiddle var rulesa = document.getElementById('rulesMiddle').innerHTML; var rules = rulesa.split('<div class="blockbody">');//split to chop off the top above rules var rulesT = rules[1].split('<form class="block');//split to chop off below rules rulesT[0] = rulesT[0].replace('class=','vbclass');//get rid of those nasty vbulletin defined classes document.getElementById('rulesMiddle').innerHTML = rulesT[0];//readd the content back into the DIV $('.rulesMain').slideToggle();//display the DIV $('.rulesMain').center();//center DIV $('.rulesMain').css('top','20px');//align with top }); }

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  • Django Forms: TimeField Validation

    - by Tom
    I feel like I'm missing something obvious here. I have a Django form with a TimeField on it. I want to be able to allow times like "10:30AM", but I cannot get it to accept that input format or to use the "%P" format (which has a note attached saying it's a "Proprietary extension", but doesn't say where it comes from). Here's the gist of my form code: calendar_widget = forms.widgets.DateInput(attrs={'class': 'date-pick'}, format='%m/%d/%Y') time_widget = forms.widgets.TimeInput(attrs={'class': 'time-pick'}) valid_time_formats = ['%P', '%H:%M%A', '%H:%M %A', '%H:%M%a', '%H:%M %a'] class EventForm(forms.ModelForm): start_date = forms.DateField(widget=calendar_widget) start_time = forms.TimeField(required=False, widget=time_widget, help_text='ex: 10:30AM', input_formats=valid_time_formats) end_date = forms.DateField(required=False, widget=calendar_widget) end_time = forms.TimeField(required=False, widget=time_widget, help_text='ex: 10:30AM', input_formats=valid_time_formats) description = forms.CharField(widget=forms.Textarea) Any time I submit "10:30AM", I get a validation error. The underlying model has two fields, event_start and event_end, no time fields, so I don't think the problem is in there. What stupid thing am I missing?

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  • Implementing N-tire structure in .net

    - by pravakar
    Hi friends, my requirement is suppose i have three classes namely Employee, Customer and Department where Employee contains attributes i.e. id,name,dept and Customer class contains Id,name and Department class contains i.e. id and name. Now all these three class has common function i.e. create, update and delete. This functions i want to implement using interface. So can any one suugest me to perform these things in n-tier architecture.

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  • Hibernate - One design problem

    - by Yatendra Goel
    I am learning Hibernate from the tutorial on JBoss website. I have a confusion in a code example located here. There is a Cat class code at 4.1. A simple POJO example. This Cat class has a reference to his mother as private Cat mother; Q1. If the class has an identifier property as id, then wouldn't it be better to store the cat's mother's id instead of cat's mother object. means instead of private Cat mother; wouldn't it be better to have private long motherId; `

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  • Rails: Creating subfolders in model?

    - by keruilin
    I'm going to have a ton of subclasses, so want to organize them under a subfolder called stream. I added the following line to the environment.rb so that all classes in the subfolder would be loaded: Rails::Initializer.run do |config| ... config.load_paths += Dir["#{RAILS_ROOT}/app/models/*"].find_all { |f| File.stat(f).directory? } ... end I thought this would solve the issue in which by convention the model class is namespaced into an according module. However, when I try to call one of the classes called stream in the stream folder, I get the following error: NoMethodError: undefined method `new' for Stream:Module from (irb):28 from /usr/local/bin/irb:12:in `<main>' Here's the model for the parent and one child: class Stream end class EventStream < Stream end Any idea what the issue is?

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  • Django ForeignKey _set on an inherited model

    - by neolaser
    I have two models Category and Entry. There is another model ExtEntry that inherits from Entry class Category(models.Model): title = models.CharField('title', max_length=255) description = models.TextField('description', blank=True) ... class Entry(models.Model): title = models.CharField('title', max_length=255) categories = models.ManyToManyField(Category) ... class ExtEntry(Entry): groups= models.CharField('title', max_length=255) value= models.CharField('title', max_length=255) ... I am able to use the Category.entry_set but I want to be able to do Category.blogentry_set but it is not available. If this is not available,then I need another method to get all ExtEntryrelated to one particular Category Thanks

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  • How to avoid double construction of proxy with DynamicProxy::CreateClassProxyWithTarget?

    - by Belvasis
    I am decorating an existing object using the CreateClassProxyWithTarget method. However, the constructor and therefore, initialization code, is being called twice. I already have a "constructed" instance (the target). I understand why this happens, but is there a way to avoid it, other than using an empty constructor? Edit: Here is some code: First the proxy creation: public static T Create<T>(T i_pEntity) where T : class { object pResult = m_pGenerator.CreateClassProxyWithTarget(typeof(T), new[] { typeof(IEditableObject), typeof(INotifyPropertyChanged) , typeof(IMarkerInterface), typeof(IDataErrorInfo) }, i_pEntity, ProxyGenerationOptions.Default, new BindingEntityInterceptor<T>(i_pEntity)); return (T)pResult; } I use this for example with an object of the following class: public class KatalogBase : AuditableBaseEntity { public KatalogBase() { Values = new HashedSet<Values>(); Attributes = new HashedSet<Attributes>(); } ... } If i now call BindingFactory.Create(someKatalogBaseObject); the Values and Attributes properties are beeing initialized again.

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  • Split file with PHP and generate contents

    - by user201140
    How do I split the content below into separate files without the placeholder tags. I'd also like to take the text inside the placeholder tags and place them inside a new contents file. <div class='placeholder'>The First Chapter</div> This is some text. <div class='placeholder'>The Second Chapter</div> This is some more text. <div class='placeholder'>Last Chapter</div> The last chapter. Thanks.

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  • what is serialization and how it works

    - by Rozer
    I know the serialization process but have't implemented it. In my application i have seen there are various classes that has been implemented serilizable interface. consider following class public class DBAccessRequest implements Serializable { private ActiveRequest request = null; private Connection connection = null; private static Log log = LogFactory.getLog(DBAccessRequest.class); public DBAccessRequest(ActiveRequest request,Connection connection) { this.request = request; this.connection = connection; } /** * @return Returns the DB Connection object. */ public Connection getConnection() { return connection; } /** * @return Returns the active request object for the db connection. */ public ActiveRequest getRequest() { return request; } } just setting request and connection in constructor and having getter setter for them. so what is the use of serilizable implementation over here...

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  • Writing Strings to files in python

    - by Leif Andersen
    I'm getting the following error when trying to write a string to a file in pythion: Traceback (most recent call last): File "export_off.py", line 264, in execute save_off(self.properties.path, context) File "export_off.py", line 244, in save_off primary.write(file) File "export_off.py", line 181, in write variable.write(file) File "export_off.py", line 118, in write file.write(self.value) TypeError: must be bytes or buffer, not str I basically have a string class, which contains a string: class _off_str(object): __slots__ = 'value' def __init__(self, val=""): self.value=val def get_size(self): return SZ_SHORT def write(self,file): file.write(self.value) def __str__(self): return str(self.value) Furthermore, I'm calling that class like this: def write(self, file): for variable in self.variables: variable.write(file) I have no idea what is going on. I've seen other python programs writing strings to files, so why can't this one? Thank you very much for your help.

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  • cygwin permissions for executing .bat files

    - by TomD
    Hey guys, I have a .bat file, which contains the following contents ... jar cfm myjar.jar manifest.txt *.class ... Which executes well under windows command prompt, but when executed under cygwin, I get the following C:\cygwin\home\user\path\to\folderjar cfm myjar.jar manifest.txt *.class Access is denied. I tried starting cygwin as administrator, but it does not help Would appreciate any suggestions Thanks

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