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• Can I Always debug multiple instances of a same object that is of type thread with GDB?

  - by yan bellavance

  program runs fine. When I put a breakpoint a segmentation fault is generated. Is it me or GDB? At run time this never happens and if I instantiate only one object then no problems. Im using QtCreator on ubuntu x86_64 karmic koala. UPDATE1: I have made a small program containing a simplified version of that class. You can download it at: example program simply put a breakpoint on the first line of the function called drawChart() and step into to see the segfault happen UPDATE2: This is another small program but it is practically the same as the mandlebrot example and it is still happening. You can diff it with mandlebrot to see the small difference. almost the same as mandlebrot example program

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• C# Using singleton instead of a global static instance

  - by Farstucker

  I ran into a problem today and a friend recommended I use a global static instance or more elegantly a singleton pattern. I spent a few hours reading about singletons but a few things still escape me. Background: What Im trying to accomplish is creating an instance of an API and use this one instance in all my classes (as opposed to making a new connection, etc). There seems to be about 100 ways of creating a singleton but with some help from yoda I found some thread safe examples. ..so given the following code: public sealed class Singleton { public static Singleton Instance { get; private set; } static Singleton() { Instance = new Singleton(); } } How/Where would you instantiate the this new class and how should it be called from a separate class? Thanks for your help.

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• Autofac: Reference from a SingleInstance'd type to a HttpRequestScoped

  - by Michael Wagner

  I've got an application where a shared object needs a reference to a per-request object. Shared: Engine | Per Req: IExtensions() | Request If i try to inject the IExtensions directly into the constructor of Engine, even as Lazy(Of IExtension), I get a "No scope matching [Request] is visible from the scope in which the instance was requested." exception when it tries to instantiate each IExtension. How can I create a HttpRequestScoped instance and then inject it into a shared instance? Would it be considered good practice to set it in the Request's factory (and therefore inject Engine into RequestFactory)?

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• Java Spring 3.0 MVC Annotation vs COC. Whats the prefered method in the Java community?

  - by Athens

  I am using Spring's MVC framework for an application I'm hosting on Google's App Engine. So far, my controllers are registered via the @Controller annotation; however, prior to getting into Spring, I evaluated ASP.net MVC 2 which requires no configuration and is based on convention. Is convention over configuration (COC) the current and preferred method in the Java community to implement MVC with Spring. Also, this may be a result of my limited knowledge so far but i noticed that i could only instantiate my Controllers the required constuctor injection if i use the COC method via the ControllerClassNameHandlerMapping. For instance the following controller bean config will fail if i use the defaultannotationhandlermapping. My com.domain.TestController controller works fine if i use ControllerClassNameHandlerMapping/COC but it results in an error when i use defaultannotationhandlermapping/Annotations.

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• C++ overloading virtual = operator

  - by taz

  Hello, here is the code for my question: class ICommon { public: virtual ICommon& operator=(const ICommon & p)const=0; }; class CSpecial : public ICommon { public: CSpecial& operator=(const CSpecial & cs) { //custom operations return *this; } }; CSpecial obj; Basically: I want the interface ICommon to force it's descendants to implement = operator but don't want to have any typecasts in the implementation. The compiler says "can't instantiate an abstract class. Any help/advice will be appreciated.

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• How to track value of a variable in Eclipse Java Debugger

  - by aveschini

  I would like to track the value of a boolean (not Boolean) variable in the Eclips debugger. I need to know when it does change and, for this, i need to track it's value through all the execution; not only when it is in scope. More particularly i have a class (let's call it myClass) with a boolean member variable called isAvailable. My program instantiate 4 or 5 myClass objects. I am expecting that at the end of the execution the isAvailable value of all of my objects is set to true. Contrarily to my excpectation one of myClass objects has isAvailable set to false. I need to know which (in a lot of) methods is setting isAvailable to false.

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• NSURL not instantiating properly

  - by taokakao

  Hi, I am new to IPhone developing. I have got very strange issue with NSURL which is driving me crazy. I want to instantiate NSURL object to use it in loading image. But instantiation never happens in proper way. It always says my url in invalid. Basically I use code like below: NSString *str = @"http://google.com"; NSURL *url = [NSURL URLWithString:str]; but I also have tried a lot of different modifications (with CFStringRef + CFURLCreateStringByAddingPercentEscapes and so on). All of them are not working for me. In debugger url is set to "Invalid". What it could be? I don't think this is algorithmic or environment issue. It could be about some settings? Have anyone any idea of what happens?

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• Asp.net error object not set to a reference

  - by Frank

  Hi all, Because I rush in development (a lot of whip cracking here) and declare my objects at the top of the function and instantiate inside my try-catch block, I get a lot of the good old "object not set to an instance of an object" errors while doing TDD, and later if I do miss a branch that object was used in (doing VB now, would prefer C#) or just in every day coding, object not set to an instance of an object is a bit vague. Sure the stack trace sends me to the line the error occured at, but it would be nice if I could modify my logging to either name the object or its type because sometimes I have multiple objects on the same line. It's not the end of the world, but in the end it would save me a few minutes each day. Any ideas on how I can pass the info on which object wasn't set? Thanks

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• Why element creation requires the document object in DOM?

  - by maayank

  As noted by others, in Java, with the default W3C DOM libraries, one is required to use the Document object a factory to elements, i.e.: import org.w3c.dom.Document; import org.w3c.dom.Element; Document d; Element e; e = d.createElement("tag"); Why is that necessary? Why conceptually a method can't create an XML element without knowing all of the target document? Why I can't just instantiate using 'new' or something to that effect?

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• Is There a Good Pattern for Creating a Unique Id based on a Type?

  - by Michael Kelley

  I have a template that creates a unique identifier for each type it is instanced. Here's a streamlined version of the template: template <typename T> class arType { static const arType Id; // this will be unique for every instantiation of arType<>. } // Address of Id is used for identification. #define PA_TYPE_TAG(T) (&arType<T >::Id) This works when you have an executable made purely of static libraries. Unfortunately we're moving to an executable made up of dlls. Each dlls could potentially have its own copy of Id for a type. One obvious solution is to explicitly instantiate all instances of arType. Unfortunately this is cumbersome, and I'd like to ask if anyone can propose a better solution?

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• C++ interface inheritance problem

  - by james t

  Hey, i'm trying to create a c++ stomp client, my client constructor is : Client(std::string &server, short port, std::string &login, std::string &pass, Listener &listener); it gets a listener object which when Listener is the following interface : class Listener { virtual void message(StmpMessage message) =0; }; now i attempt to instantiate a client in a test class : class test : public virtual Listener { public: void message(StmpMessage message) { message.prettyPrint(); } int main(int argc, char* argv[]) { Client client("127.0.0.1", 61613, *this); return 0; } }; i'm sending this to the client because this is a listener object, i get the following error : /Users/mzruya/Documents/STOMPCPP/main.cpp:18: error: no matching function for call to 'Client::Client(const char [10], int, test&)' /Users/mzruya/Documents/STOMPCPP/Client.h:43: note: candidates are: Client::Client(std::string&, short int, std::string&, std::string&, Listener&) /Users/mzruya/Documents/STOMPCPP/Client.h:37: note: Client::Client(const Client&)

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• Select a data template by item type programatically in WPF

  - by Michael Stoll

  Hi all, unfortunately the WPF ToolbarTray does not support binding to a collection of ToolbarViewModels (Correct me, if I'm wrong). Thus I want to create the Toolbars programmatically. So there are two tasks, which I don't know how to do: Select the data template based on the item type. Instantiate the data template as toolbar Both should do the same as WPF does, when we use ItemsControl with an enumerable content and empty template. I used reflector to anaylse what WPF does. Task 1 is done by FrameworkElement.FindTemplateResourceInternal, but this is internal, and I couldn't find any public methods to acomplish the task. Of course one could enumerate all resources and match the data template data type property, but this seems sub-optimal. Who know's how to acomplish these tasks?

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• STL map containing references does not compile

  - by MTsoul

  The following: std::map<int, ClassA &> test; gives: error C2101: '&' on constant While the following std::map<ClassA &, int> test; gives error C2528: '_First' : pointer to reference is illegal The latter seems like map cannot contain a reference for the key value, since it needs to instantiate the class sometimes and a reference cannot be instantiated without an object. But why does the first case not work?

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• Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

  - by LoudNPossiblyRight

  Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

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• Checking lazy loaded properties have been instantiated

  - by PaulG

  In a class which has a lazy loaded property, such as: private Collection<int> someInts; public Collection<int> SomeInts { get { if (this.someInts == null) this.someInts = new Collection<int>(); return this.someInts; } } Is it worth also having a property such as: public bool SomeIntsExist { get { return (this.someInts != null && this.someInts.Count > 0); } } And then using that property.. eg: if (thatClass.SomeIntsExist) { // do something with thatClass.SomeInts collection } or is this premature optimisation. Its certainly easier to roll with something like below, but it will instantiate the collection needlessly: if (thatClass.SomeInts.Count > 0) { // do something with thatClass.SomeInts collection } Is the compiler smart enough to figure things like this out? Is there a better way?

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• Are we using IoC effectively?

  - by Juliet

  So my company uses Castle Windsor IoC container, but in a way that feels "off": All the data types are registered in code, not the config file. All data types are hard-coded to use one interface implementation. In fact, for nearly all given interfaces, there is and will only ever be one implementation. All registered data types have a default constructor, so Windsor doesn't instantiate an object graph for any registered types. The people who designed the system insist the IoC container makes the system better. We have 1200+ public classes, so its a big system, the kind where you'd expect to find a framework like Windsor. But I'm still skeptical. Is my company using IoC effectively? Is there an advantage to new'ing objects with Windsor than new'ing objects with the new keyword?

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• C# property in a form class only accessable after formload event

  - by Spooky2010

  using vs2008, c# Howdy, Im instantiating and calling Form B from Form A. FormB has some custom properties, to allow me to pass it things like sqlAdaptors and dataset instances. When i instantiate and show Form B from Form A as a dialog form with a Using statement, it all works fine, but i find the properties i pass are not available in Form B until after the form_load event has fired. I was under the impression the properties when passed to a instantiated class should be available from a constructor, but this is not the case. If it try to access the properties before the form load event i get a null reference exception. Is this correct behavior ? It is very annoying. thanks for any help

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• Error Instantiating an Inner Class in Parent's Constructor...

  - by stormin986

  In my application's main class (subclass of Application), I have a public inner class that simply contains 3 public string objects. In the parent class I declare an object of that inner class. public class MainApplication extends Application { public class Data { public String x; public String y; public String z; } private Data data; MainApplication() { data = new Data() data.x = "String"; } } After I instantiate the object in the constructor, I get a runtime error when I try to assign any of the inner class object's variables. Any idea what's up here??

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• Howto mix TDD and RAII

  - by f4

  I'm trying to make extensive tests for my new project but I have a problem. Basically I want to test MyClass. MyClass makes use of several other class which I don't need/want to do their job for the purpose of the test. So I created mocks (I use gtest and gmock for testing) But MyClass instantiate everything it needs in it's constructor and release it in the destructor. That's RAII I think. So I thought, I should create some kind of factory, which creates everything and gives it to MyClass's constructor. That factory could have it's fake for testing purposes. But's thats no longer RAII right? Then what's the good solution here?

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• how to get an instance of an XMLEventAllocator?

  - by kostja

  I am trying to follow the recommended way of parsing XML with StAX using sun's Cursor-to-Event Example for Java EE 5. You are supposed to traverse the XML via the Cursor API and allocate an XMLEventusing an XMLEventAllocator when necessary. Awkwardly, sun's own example does not compile (at least not with JDK 1.6, even with 1.5 code compliance). The example tries to instantiate an allocator via new, but the according implementation classes in the JDK are not accessible externally. After reading the JavaDocs and searching the web I have found literally nothing. One could implement the XMLEventAllocator interface from scratch, but it seems really wrong, when there are perfectly good implementations in the JDK, besides not being an expert in StAX makes it difficult to get it right.

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• How can I create a generic constructor? (ie. BaseClass.FromXml(<param>)

  - by SofaKng

  I'm not sure how to describe this but I'm trying to create a base class that contains a shared (factory) function called FromXml. I want this function to instantiate an object of the proper type and then fill it via an XmlDocument. For example, let's say I have something like this: Public Class XmlObject Public Shared Function FromXml(ByVal source as XmlDocument) As XmlObject // <need code to create SPECIFIC TYPE of object and return it End Function End Class Public Class CustomObject Inherits XmlObject End Class I'd like to be able to do something like this: Dim myObject As CustomObject = CustomObject.FromXml(source) Is this possible?

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• Multi-Threaded Application - Help with some pseudo code!!

  - by HonorGod

  I am working on a multi-threaded application and need help with some pseudo-code. To make it simpler for implementation I will try to explain that in simple terms / test case. Here is the scenario - I have an array list of strings (say 100 strings) I have a Reader Class that reads the strings and passes them to a Writer Class that prints the strings to the console. Right now this runs in a Single Thread Model. I wanted to make this multi-threaded but with the following features - Ability to set MAX_READERS Ability to set MAX_WRITERS Ability to set BATCH_SIZE So basically the code should instantiate those many Readers and Writers and do the work in parallel. Any pseudo code will really be helpful to keep me going!

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• Plugin methods are missing in Firefox 3.6

  - by splintor

  Hi, We have a plugin that we use to enable printing and saving from our app. We instantiate it using tag with all needed attributes, and then call Save() or Print() method on the document.embeds[0] object. This used to work perfectly on Firefox 3.5 and earlier, but it no longer works in Firefox 3.6. In 3.6, document.embeds[0].Save is null, that is our custom methods are not defined on this object. Any idea why this happens, and what has changed in Firefox 3.6 that causes it? Any idea on how to debug it and find the cause? And most important, any idea of a workaround that will allow us to access this methods? Thanks, splintor

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• Why does C++ mandate that complex only be instantiated for float, double, or long double?

  - by templatetypedef

  According to the C++ ISO spec, §26.2/2: The effect of instantiating the template complex for any type other than float, double or long double is unspecified. Why would the standard authors explicitly add this restriction? This makes it unspecified, for example, what happens if you make complex<int> or a complex<MyCustomFixedPointType> and seems like an artificial restriction. Is there a reason for this limitation? Is there a workaround if you want to instantiate complex with your own custom type? I'm primarily asking this question because of this earlier question, in which the OP was confused as to why abs was giving bizarre outputs for complex<int>. That said, this still doesn't quite make sense given that we also might want to make complex numbers out of fixed-points types, higher-precision real numbers, etc. Thanks!

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• C Class Instance from Void Pointer using Ctypes

  - by g.d.d.c

  I've got a C DLL that exposes a handful of methods that return void pointers to a Class like so: void *GetLicense() { static AppLicenseImpl ipds_; return (void *) &ipds_; } In C++, after loading the DLL, I'd do this to work with it: typedef void *(* FPGetLicense)(); GetLicense_ = (FPGetLicense)GetAddress("GetLicense"); license_ = (AppLicense *) GetLicense_(); license_->GetApplicationStatus(); // Load data so that other calls don't fail I can't figure out how to parallel that in Python. This gets me the pointer: d = ctypes.cdll.LoadLibrary('license.dll') d.GetLicense.restype = ctypes.c_void_p p = d.GetLicense() # returns ptr loc, something like 8791433660848L But I obviously can't call p.GetApplicationStatus() in Python. Does anyone have a suggestion on how I'd instantiate that Class the rest of the way in Python so that I can call GetApplicationStatus()?

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