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• static const double in c++

  - by Crystal

  Is this the proper way to use a static const variable? In my top level class (Shape) #ifndef SHAPE_H #define SHAPE_H class Shape { public: static const double pi; private: double originX; double originY; }; const double Shape::pi = 3.14159265; #endif And then later in a class that extends Shape, I use Shape::pi. I get a linker error. I moved the const double Shape::pi = 3.14... to the Shape.cpp file and my program then compiles. Why does that happen? thanks.

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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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• 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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• SQL returns non-array value in PHP

  - by DeadMG

  $request = 'SELECT * FROM flight WHERE Id = \''.$_SESSION['LFLightRadio'].'\''; $data = mysql_fetch_array(mysql_query($request, $SQL)); echo '<table class="table">'; foreach($data as $key => $value) { echo '<th class="head" align="center" height="19">'.$key.'</th>'; } echo '<tr>'; foreach($data as $key => $value) { echo '<td class="cell" align="center" height="19">'.$value.'</td>'; } echo '</tr></table>'; I know that the LFlightRadio value is set, and is a value returned by the Id value of a previously returned row from the flight database. So within "flight", a record definitely exists with this Id. But, this still gives me a non-array result, so that when I try to use foreach on it, it errors out. Suggestions?

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• PHP Object Oriented Web Application

  - by Sev

  I have a class called "Layout" for the layout of the page, another class called "User" for the user. Every page I create, I instantiate a new Layout. When a user logs in, there is a new User instantiated. How do I get an instance of the layout class to know about the instantiated user? I could also save the entire instance of the User in a session variable. I assume that's a bad idea though. What are the best practices for this?

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• syntax error, unexpected '.', expecting ')'

  - by Jonathan

  Hi, I've got a problem when I'm calling a static var from another class. I get this pretty syntax error where php is unexpected the '.' Here is where I'm calling it : private $aLien = array( "menu1" => array("Accueil","statique/".Variable_init::$langue."/accueil.html",0,0), //This line "menu2" => array("Infos Pratiques","statique/".Variable_init::$langue."/info.html",0,0), "menu3" => array("Faire une réservation","statique/".Variable_init::$langue."/reserver.html",0,0), "menu4" => array("Pour Nous Joindre","statique/".Variable_init::$langue."/nousJoindre.html",0,0), "menu5" => array("Plan du site","statique/".Variable_init::$langue."/plansite.html",0,0) ); And here is my static var declaration from another class: class Variable_init implements iVariable_init{ public static $langue; public static $id_choix; public static $id_contenu;

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• Can someone explain this java interface to me please?

  - by Karl Patrick

  I realize that the method run must be declared because its declared in the runnable interface. But my question comes when this class runs how is the Thread object allowed if there is no import call to a particular package? how does runnable know anything about Thread or its methods? does the runnable interface extend the thread class? Obviously i dont understand interfaces very well. thanks in advance. class PrimeFinder implements Runnable{ public long target; public long prime; public boolean finished = false; public Thread runner; PrimeFinder(long inTarget){ target = inTarget; if(runner == null){ runner = new Thread(this); runner.start() } } public void run(){ } }

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• C++ memory management of reference types

  - by Russel

  Hello, I'm still a fairly novice programmer and I have a question about c++ memory management with refence types. First of all, my understanding of reference types: A pointer is put on the stack and the actual data that the pointer points to is created and placed on the heap. Standard arrays and user defined classes are refence types. Is this correct? Second, my main question is do c and c++'s memory management mechanisms (malloc, free and new, delete) always handle this properly and free the memory that a class or array is pointing to? Does everything still work if those pointers get reassigned somehow to other objects of the same size/type on the heap? What if a class has a pointer member that points to another object? I am assuming that delete/freeing the class object doesn't free what it's member pointer points to, is that correct? Thanks all! -R

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• Program-wide data, C++

  - by bobobobo

  I'd like to make program-wide data in a C++ program. The easiest way to do it in C# is just public static members. C#: public static class DataContainer { public static Object data1 ; public static Object data2 ; } In C++ you can do the same thing C++ global data way#1: class DataContainer { public: static Object data1 ; static Object data2 ; } ; Object DataContainer::data1 ; Object DataContainer::data2 ; However there's also extern C++ global data way #2: class DataContainer { public: Object data1 ; Object data2 ; } ; extern DataContainer * dataContainer ; // instantiate in .cpp file Which is better, or possibly another way which I haven't thought about?

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• Remove C# attribute of a property dynamically

  - by SysAdmin

  Hi, I have a class with a set of properties As given below. class ContactInfo { [ReadOnly(true)] [Category("Contact Info")] public string Mobile { get; set; } [Category("Contact Info")] public string Name{ get; set; } } The objects of this class is being assigned to a property grid, so that the users can update an existing contact. you can see that Mobile is marked as ReadOnly. But, when I want to add an entirely new Contact, I would want the users to be able to edit the contact Mobile also. For that I need to remove the Readonly property dynamically from the Type, before assigning the object to the property grid. Is it possible?

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• Use SQL query to populate property in nHibernate mapping file

  - by brainimus

  I have an object which contains a property that is the result of an SQL statement. How do I add the SQL statement to my nHibernate mapping file? Example Object: public class Library{ public int BookCount { get; set; } } Example Mapping File: <hibernate-mapping> <class name="Library" table="Libraries"> <property name="BookCount" type="int"> <- This is where I want the SQL query to populate the value. -> </class> </hibernate-mapping> Example SQL Query: SELECT COUNT(*) FROM BOOKS WHERE BOOKS.LIBRARY_ID = LIBRARIES.ID

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• Collectable<T> serialization, Root Namespaces on T in .xml files.

  - by Stacey

  I have a Repository Class with the following method... public T Single<T>(Predicate<T> expression) { using (var list = (Models.Collectable<T>)System.Xml.Serializer.Deserialize(typeof(Models.Collectable<T>), FileName)) { return list.Find(expression); } } Where Collectable is defined.. [Serializable] public class Collectable<T> : List<T>, IDisposable { public Collectable() { } public void Dispose() { } } And an Item that uses it is defined.. [Serializable] [System.Xml.Serialization.XmlRoot("Titles")] public partial class Titles : Collectable<Title> { } The problem is when I call the method, it expects "Collectable" to be the XmlRoot, but the XmlRoot is "Titles" (all of object Title). I have several classes that are collected in .xml files like this, but it seems pointless to rewrite the basic methods for loading each up when the generic accessors do it - but how can I enforce the proper root name for each file without hard coding methods for each one? The [System.Xml.Serialization.XmlRoot] seems to be ignored.

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• django form creation on init

  - by John

  Hi, How can I add a field in the form init function? e.g. in the code below I want to add a profile field. class StaffForm(forms.ModelForm): def __init__(self, user, *args, **kwargs): if user.pk == 1: self.fields['profile'] = forms.CharField(max_length=200) super(StaffForm, self).__init__(*args, **kwargs) class Meta: model = Staff I know I can add it just below the class StaffForm.... line but I want this to be dynamic depending on what user is passed in so can't do it this way. Thanks

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• Best way to map/join two autogenerated enums

  - by tomlip

  What is the best C++ (not C++11) way of joining two enums from autogenerated class similar to one presented below: namespace A { namespace B { ... class CarInfo { enum State { // basically same enums defined in different classes Running, Stopped, Broken } } class BikeInfo { enum State { // basically same enums defined in different classes Running, Stopped, Broken } } } } What is needed is unified enum State for both classes that is seen to outside world alongside with safe type conversion. The best and probably most straightforward way I came up with is to create external enum: enum State { Running, Stopped, Broken } together with conversion functions State stateEnumConv(A::B::CarInfo::State aState); State stateEnumConv(A::B::BikeInfo::State aState); A::B::CarInfo::State stateEnumConv(State aState); A::B::BikeInfo::State stateEnumConv(State aState); Direction into right approach is needed. Gosh coming from C I hate those long namespaces everywhere an I wish it could be only A::B level like in presented example. Four conversion functions seem redundant note that CarInfo::State and BikeInfo::State has same enum "members".

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• How do i get file path of my file in java enterprise application?

  - by Nitesh Panchal

  Hello, I created java enterprise application and it consists of ejb module and web application. I have plain old xml file in source packages folder in package "common" in my ejb module. I want to pass this file path in File() constructor for one class in ejb module. How do i do it? If i pass any of the below it doesn't work :- new File("abc.xml"); //this take file from glassfish/domains/domain1 :( new File("./abc.xml"); I don't want to pass hardcode path like /home/administrator/appname/module/etc.. I want the path relative from my ejb module. Please help me. I've tried all things. Actually when i created a class in same folder and then try classname.getResource("abc.xml").getPath() it works fine. But what if i don't have any class in that folder. Waiting for your replies

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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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• Optional parameters for interfaces

  - by bryanjonker

  Using c# 4.0 -- building an interface and a class that implements the interface. I want to declare an optional parameter in the interface and have it be reflected in the class. So, I have the following: public interface IFoo { void Bar(int i, int j=0); } public class Foo { void Bar(int i, int j=0) { // do stuff } } This compiles, but it doesn't look right. The interface needs to have the optional parameters, because otherwise it doesn't reflect correctly in the interface method signature. Should I skip the optional parameter and just use a nullable type? Or will this work as intended with no side effects or consequences?

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• Problem overridding virtual function

  - by William

  Okay, I'm writing a game that has a vector of a pairent class (enemy) that s going to be filled with children classes (goomba, koopa, boss1) and I need to make it so when I call update it calls the childclasses respective update. I have managed to create a example of my problem. #include <stdio.h> class A{ public: virtual void print(){printf("Hello from A");} }; class B : public A{ public: void print(){printf("Hello from B");} }; int main(){ A ab = B(); ab.print(); while(true){} } Output wanted: "Hello from B" Output got: "Hello from A" How do I get it to call B's print function?

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• What is the difference between declaring data attributes inside or outside __init__

  - by user1898540

  I'm trying to get my head around OOP in Python and I'm a bit confused when it comes to declare variables within a class. Should I declare them inside of the __init__ procedure or outside it? What's the difference? The following code works just fine: # Declaring variables within __init__ class MyClass: def __init__(self): country = "" city = "" def information(self): print "Hi! I'm from %s, (%s)"%(self.city,self.country) me = MyClass() me.country = "Spain" me.city = "Barcelona" me.information() But declaring the variables outside of the __init procedure also works: # Declaring variables outside of __init__ class MyClass: country = "" city = "" def information(self): print "Hi! I'm from %s, (%s)"%(self.city,self.country) me = MyClass() me.country = "Spain" me.city = "Barcelona" me.information()

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• Reuse C++ Header files

  - by Amrish

  Guys, I have a Visual C++ solution with 2 projects AlgorithmA & AlgorithmB and both share a common header file RunAlgo.h with the class declaration. Each project in the solution has its own unique implementation for the header file. I am trying to compile a DLL out of the common header file RunAlgo.h and add reference to this DLL in the projects AlgorithmA & AlgorithmB. I have then included separate RunAlgo.cpp definition file in both my projects. The problem is that I am getting linker errors while compiling the new DLL project which has only the header file. So, the question is Can a header file with only class declaration be compiled into a DLL (Similar to class library containing an Interface in C#)? For the above scenario, is there a better approach to reuse the common Header file among projects? Should the above method work (re-check my code?)

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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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• Breakpoint pointing out "objc_autoreleaseNoPool"

  - by Andrew

  So I'm debugging an app in preperation for its app so release, and I enabled a universal breakpoint for "All Exceptions". Since then, everytime I run the app, the console prints: Catchpoint 2 (throw)Pending breakpoint 1 - "objc_exception_throw" resolved objc[11765]: Object 0x8f18ff0 of class __NSCFLocale autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug objc[11765]: Object 0x8f190a0 of class __NSCFNumber autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug objc[11765]: Object 0x8f1fef0 of class __NSCFLocale autoreleased with no pool in place - just leaking - break on objc_autoreleaseNoPool() to debug Literally printed 3 times. I have no idea what this means but it looks bad. Any advice would be appreciated.

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• Map null column as 0 in a legacy database (JPA)

  - by Indrek

  Using Play! framework and it's JPASupport class I have run into a problem with a legacy database. I have the following class: @Entity @Table(name="product_catalog") public class ProductCatalog extends JPASupport { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) public Integer product_catalog; @OneToOne @JoinColumn(name="upper_catalog") public ProductCatalog upper_catalog; public String name; } Some product catalogs don't have an upper catalog, and this is referenced as 0 in a legacy database. If I supply the upper_catalog as NULL, then expectedly JPA inserts a NULL value to that database column. How could I force the null values to be 0 when writing to the database and the other way around when reading from the database?

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• How do I dynamically add and remove line items from an ASP.NET MVC view?

  - by Mike Roosa

  I have a PurchaseOrder model: public class PurchaseOrder { public string OrderNumber { get; set; } public string Customer { get; set; } public IList<LineItem> Lines { get; set; } } and a LineItem class: public class LineItem { public string PartNumber { get; set; } public int Quantity { get; set; } } What I want to do is on my view for the PurhcaseOrder Create action, I need a section for line items. The user should be able to add a new line, remove a line, then submit. One caveat is the PartNumber needs to be a dropdown list of valid parts. What can I do to accomplish what I'm looking for?

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