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  • Constructor Type Coercion in C++

    - by Robert Mason
    Take the following class: class mytype { double num; public: mytype(int a) { num = sqrt(a); } void print() { cout << num; } } Say there is a method which takes a mytype: void foo(mytype a) { a.print(); } Is it legal c++ (or is there a way to implement this) to call foo(4), which would (in theory) output 2? From what I can glean you can overload type casts from a user defined class, but not to. Can constructor do this in a standards-compliant manner (assuming, of course, the constructor is not explicit). Hopefully there is a way to in the end have this legal: int a; cin >> a; foo(a); Note: this is quite obviously not the actual issue, but just an example for posting purposes. I can't just overload the function because of inheritance and other program-specific issues.

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  • Unmanaged C++ instantiation question

    - by Jim Jones
    Want to verify that my understanding of how this works. Have an unmanaged C++ Class with one public instance variable: char* character_encoding; and whose only constructor is defined as: TF_StringList(const char* encoding = "cp_1252"); when I use this class in either managed or unmanaged C++, the first thing I do is declare a pointer to an object of this class: const TF_StringList * categories; Then later I instantiate it: categories = new TF_StringList(); this gives me a pointer to an object of type TF_StringList whose variable character_encoding is set to "cp_1252"; So, is all that logic valid? Jim

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  • Counting number of GC cleanups on an object

    - by tsps
    How do I keep a count of the number of times that objects of a specific class (type?) are getting disposed in the lifetime of my application. Imagine I have a class A, now, I want to count how many times the objects of A get collected by the GC. I hope I am phrasing this right because I was asked this in an interview today and the answer I gave did not satisfy the interviewer. And this is what I imagine he was trying to ask. What I said was that one could keep a static field called count in the class A and increment it in the Finalize() call of that object. The answer he was expecting was something called a static block. I've never heard of this in .NET/C#. Can someone explain what's this static block?

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  • C++ design with static methods

    - by user231536
    I would like to define as class X with a static method: class X { static string get_type () {return "X";} //other virtual methods } I would like to force classes which inherit from X to redefine the get_type() method and return strings different from "X" (I am happy if they just redefine get_type for now). How do I do this? I know that I cannot have virtual static methods. Edit: The question is not about the type_id, but in general about a static method that should be overriden. For example class X { static int getid() {return 1;} }

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  • Dynamically load a type from an external assembly

    - by Water Cooler v2
    From managed code, how do I load a managed type from another assembly at runtime, assuming the calling code does not have a static reference to the assembly? To clarify, let's say I have class Lib in Lib.cs compiled into Lib.dll. I want to write a class Foo in a separate assembly called Foo.dll, that does not have a reference to Lib.dll statically, but instead loads Lib.dll and then reflects on for the presence of the class Lib and then calls a method on it. Sorry for such an obvious question on Reflection. I figure it'll take much lesser time to get the answer on a forum that to read a few articles.

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  • Reading file data during form's clean method

    - by Dominic Rodger
    So, I'm working on implementing the answer to my previous question. Here's my model: class Talk(models.Model): title = models.CharField(max_length=200) mp3 = models.FileField(upload_to = u'talks/', max_length=200) Here's my form: class TalkForm(forms.ModelForm): def clean(self): super(TalkForm, self).clean() cleaned_data = self.cleaned_data if u'mp3' in self.files: from mutagen.mp3 import MP3 if hasattr(self.files['mp3'], 'temporary_file_path'): audio = MP3(self.files['mp3'].temporary_file_path()) else: # What goes here? audio = None # setting to None for now ... return cleaned_data class Meta: model = Talk Mutagen needs file-like objects - the first case (where the uploaded file is larger than the size of file handled in memory) works fine, but I don't know how to handle InMemoryUploadedFile that I get otherwise. I've tried: # TypeError (coercing to Unicode: need string or buffer, InMemoryUploadedFile found) audio = MP3(self.files['mp3']) # TypeError (coercing to Unicode: need string or buffer, cStringIO.StringO found) audio = MP3(self.files['mp3'].file) # Hangs seemingly indefinitely audio = MP3(self.files['mp3'].file.read()) Is there something wrong with mutagen, or am I doing it wrong?

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  • override the operator overloading in C++ ?

    - by stdnoit
    helo guys i have class call Complex I did operator overloading like such Complex c = a + b; // where a and b are object of Complex class which basically is operator+(Complex& that); but I dont know how to say for example double c = a + 10; //where a is object of Complex class but 10 is integer / double I did define typecasting for a to be double get my IDE says that there are too many operands + and it somehow complains for not being able to "understand" the + it has to be in this format though double c = a + 10; thanks

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  • maintain user login status in express.js

    - by chenliang
    when user login the app the username will be display in the header, this is my header.jade div#header_content input(type='text',name='search',id='globle_search') span#user_status if(req.isAuthenticated()) a(class='user_menu_btn',href='home', target='_blank' ) req.user.username a(class='user_menu_btn',href='logout') Logout else a(id='login_btn',href='login',class='user_status_btn') login run the app i get the error says ReferenceError: F:\shopping\views\includes\header.jade:4 req is not defined this is my index route: app.get('/',index.index); exports.index = function(req, res){ res.render('index', { title: 'Express' }); }; how to maintain login ststus in the heaedr? by the way am using passport to login user

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  • Does Qt support virtual pure slots ?

    - by ereOn
    Hi, My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget. Recently, I realized that all these classes share 2 commons slots (loadSettings() and saveSettings()). Regarding this, I have two questions: Does it make sense to write a intermediate base abstract class (lets name it BaseConfigurationPage) with these two slots as virtual pure methods ? (Every possible configuration page will always have these two methods, so I would say "yes") Before I do the heavy change in my code (if I have to) : does Qt support virtual pure slots ? Is there anything I should be aware of ? Here is a code example describing everything: class BaseConfigurationPage : public QWidget { // Some constructor and other methods, irrelevant here. public slots: virtual void loadSettings() = 0; virtual void saveSettings() = 0; }; class GeneralConfigurationPage : public BaseConfigurationPage { // Some constructor and other methods, irrelevant here. public slots: void loadSettings(); void saveSettings(); };

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  • test cases for testing a strtok-alike function [C++]

    - by Neeraj
    Consider the following class definition: class StrToTokens { StrToTokens(const char* str, const char* delimiters = "\t\r\n"); //constructor string getNextToken(); void reset(); bool empty(); } Can someone list some good testcases to test the above class. A few I could think of are: empty string, empty delimiters, repeated delimiters, consecutive delimiters, string with only delimiters. However, the interviewer expected some more(better ones). Can you help out. Thanks.

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  • bulk update/delete entities of different kind in db.run_in_transaction

    - by Ray Yun
    Here goes pseudo code of bulk update/delete entities of different kind in single transaction. Note that Album and Song entities have AlbumGroup as root entity. class AlbumGroup: pass class Album: group = db.ReferenceProperty(reference_class=AlbumGroup,collection_name="albums") class Song: album = db.ReferenceProperty(reference_class=Album,collection_name="songs") def bulk_update_album_group(album_group): updated = [album_group] deleted = [] for album in album_group.albums: updated.append(album) for song in album.songs: if song.is_updated: updated.append(song) if song.is_deleted: deleted.append(song) db.put(updated) db.delete(deleted) a = AlbumGroup.all().filter("...").get() # bulk update/delete album group. for simplicity, album cannot be deleted. db.run_in_transaction(bulk_update_album_group,a) But I met a famous "Only Ancestor Queries in Transactions" error at the iterating reference properties like album.songs or album_group.albums. I guess ancestor() filter does not help because those entities are modified in memory. Should I not to iterate reference property in transaction function and always provide them as function parameters like def bulk_update_album_group(updated,deleted): ??? Is there any good coding pattern for this situation?

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  • Using a Loop to add objects to a list(python)

    - by Will
    Hey guys so im trying to use a while loop to add objects to a list. Heres bascially what i want to do: (ill paste actually go after) class x: blah blah choice = raw_input(pick what you want to do) while(choice!=0): if(choice==1): Enter in info for the class: append object to list (A) if(choice==2): print out length of list(A) if(choice==0): break ((((other options)))) as im doing this i can get the object to get added to the list, but i am stuck as to how to add multiple objects to the list in the loop. Here is my actual code i have so far... print "Welcome to the Student Management Program" class Student: def init (self, name, age, gender, favclass): self.name = name self.age = age self.gender = gender self.fac = favclass choice = int(raw_input("Make a Choice: " )) while (choice !=0): if (guess==1): print("STUDENT") namer = raw_input("Enter Name: ") ager = raw_input("Enter Age: ") sexer = raw_input("Enter Sex: ") faver = raw_input("Enter Fav: ") elif(guess==2): print "TESTING LINE" elif(guess==3): print(len(a)) guess=int(raw_input("Make a Choice: ")) s = Student(namer, ager, sexer, faver) a =[]; a.append(s) raw_input("Press enter to exit") any help would be greatly appreciated!

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  • Pattern for database-wrapper in java

    - by Space_C0wb0y
    I am currently writing a java-class that wraps an SQLite database. This class has two ways to be instantiated: Open an existing database. Create a new database. This is what I cam up with: public class SQLiteDatabaseWrapper { public static SQLiteDatabaseWrapper openExisting(File PathToDB) { return new SQLiteDatabaseWrapper(PathToDB); } public static SQLiteDatabaseWrapper createNew(File PathToDB) { CreateAndInitializeNewDatabase(PathToDB); return new SQLiteDatabaseWrapper(PathToDB); } private SQLiteDatabaseWrapper(File PathToDB) { // Open connection and setup wrapper } } Is this the way to go in Java, or is there any other best practice for this situation?

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  • Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

    - by Shane MacLaughlin
    Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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  • FindBugs and CheckForNull on classes vs. interfaces

    - by ndn
    Is there any way to let FindBugs check and warn me if a CheckForNull annotation is present on the implementation of a method in a class, but not on the declaration of the method in the interface? import javax.annotation.CheckForNull; interface Foo { public String getBar(); } class FooImpl implements Foo { @CheckForNull @Override public String getBar() { return null; } } public class FindBugsDemo { public static void main(String[] args) { Foo foo = new FooImpl(); System.out.println(foo.getBar().length()); } } I just discovered a bug in my application due to a missing null check that was not spotted by FindBugs because CheckForNull was only present on FooImpl, but not on Foo, and I don't want to spot all other locations of this problem manually.

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  • 0.20.2 API hadoop version with java 5

    - by abdeslam
    I have started a maven project trying to implement the MapReduce algorithm in java 1.5.0_14. I have chosen the 0.20.2 API hadoop version. In the pom.xml i'm using thus the following dependency: < dependency < groupId>org.apache.hadoop< /groupId> < artifactId>hadoop-core< /artifactId> < version>0.20.2< /version> < /dependency But when I'm using an import to the org.apache.hadoop classes, I get the following error: bad class file: ${HOME_DIR}\repository\org\apache\hadoop\hadoop-core\0.20.2\hadoop-core-0.20.2.jar(org/apache/hadoop/fs/Path.class) class file has wrong version 50.0, should be 49.0. Does someone know how can I solve this issue. Thanks.

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  • Can this be done with multiple inhertance?

    - by Milo
    Here is what I would like to do. Say I have Class Widget. I then create Button from Widget. I then create ModifiedWidget which re-implements certain functions of Widget. I then want Button to use ModifiedWidget rather than plain Widget. Is this possible to do some how? Thanks class Button : public Widget; class SuperButton : public Button, public ModifiedWidget; I'm just not sure if that would do what I want it to though.

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  • DJANGO complex modelling

    - by SledgehammerPL
    Hello. I have such model now: receipt contains components. component contain product. The difference between component and product is, that component has quantity and measure unit: eg. component is 100g sugar - sugar is a product. So I need to make lots of components to satisfy different recipes - 100g sugar is not equal 200g sugar I wonder if I can remodel it to kick off components - in pure sql it's rather easy, but I'm trying to USE django - not making workarounds. class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Component) class Component(models.Model): quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) product = models.ForeignKey(Product) class Product(models.Model): name = models.CharField(max_length = 128) TIA

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  • Jsf validation error (shown by h:message) while updating Model, why?

    - by Ignacio
    List.xhtml: <h:selectOneMenu value="#{produtosController.selected.codigo}"> <f:selectItems value="#{produtosController.itemsAvailableSelectOne}"/> </h:selectOneMenu> <h:commandButton action="#{produtosController.createByCodigos}" value="Buscar" /> Controller Class method: public String createByCodigos(){ items = new ListDataModel(ejbFacade.findByCodigos(current.getCodigo())); updateCurrentItem(); return "List"; } Facade Class method: public List<Produtos> findByCodigos(Integer codigo){ Query q = em.createNamedQuery("Produtos.findByCodigo"); q.setParameter("codigo", codigo); return q.getResultList(); } Bean Class query: @NamedQuery(name = "Produtos.findByCodigo", query = "SELECT p FROM Produtos p WHERE p.codigo = :codigo") @Column(name = "codigo") private Integer codigo;

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  • C# where keyword

    - by Carra
    Our Indian overseas developers have written the following piece of code (C# 2.0): public abstract class ObjectMapperBase<T> where T : new() { internal abstract bool UpdateObject(T plainObjectOrginal, T plainObjectNew, WebMethod fwm, IDbTransaction transaction); } Inheritor example: public abstract class OracleObjectMapperBase<T> : ObjectMapperBase<T> where T : new() { internal override bool UpdateObject(T plainObjectOrginal, T plainObjectNew, WebMethod fwm, IDbTransaction transaction) { //Fancy Reflection code } } I've never seen the where keyword before after the class name. What does this do?

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  • .replace method in jquery

    - by amit
    i want to replace class me to old when user clicks on a tag, i want to do that only with .replace function. My purpose to learn how replace method work. But the function which i have made not working. <head> <script type="text/javascript" src="jquery-1.7.2.js"></script> <script type="text/javascript"> $(function(){ $('a').click(function(){ $(this).attr('class').replace('me','old') }) }) </script> </head> <body> <a href="#" class="me">click</a> </body>

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  • how to use multiple $_name using extends Zend_Db_Table_Abstract in zend frame work.

    - by karthik
    we tried to give our tables(users,messages) like this in two different abstract classes but it is not working. This is included in a file childconnect1.php ,is there any relation between the file name(childconnect1.php) and the class(Application_Model_childconnect1). class Application_Model_childconnect1 extends Zend_Db_Table_Abstract { protected $_name = 'users'; public function loginvalidation($username,$pwd) { $row = $this->fetchRow('UserName = \'' . $username . '\'and UserPW = \''. $pwd . '\''); if (!$row) { $msg="invalid"; return $msg; } else { return $row->toArray(); } } } class Application_Model_childconnect2 extends Zend_Db_Table_Abstract { protected $_name = 'messages'; public function replymessage($message) { $data=array( 'MessageText'=>$message ); $this->insert($data); } }

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  • Constructor with non-instance variable assistant?

    - by Robert Fischer
    I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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  • manage date fields when are int in the db

    - by Luca Romagnoli
    Hi in my db there is a field "date_start" type integer. This is the part of form for this field <div class="editor-label"> <%: Html.LabelFor(model => model.date_start) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.date_start, new { @class = "calendar" })%> <%: Html.ValidationMessageFor(model => model.date_start) %> </div> In the form i want that the field's format is date type. and memorize it in int type after calling a my function for the convertion. How can i manage it? thanks

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  • Forbid public Add and Delete for a List<T>

    - by aaginor
    Hi folks, in my C#-project, I have a class which contains a List public class MyClass { public MyClass parent; public List<MyClass> children; ... } I want to prevent the user of the class from Adding (and Deleting) an Element to the children-List, but he shall still be able to parse its elements. I want to handle the Adding and Deleting within MyClass, providing an AddChild(MyClass item) and DeleteChild(MyClass item) to ensure that, when an item is added to the child list, the parent of that item will be set properly. Any idea how to do this besides implementing my own IList? Thanks in advance, Frank

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