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• ApplicationDispatcher exception

  - by JFB

  Whenever I try to redirect to a certain page using this dispatch method that is called from my doGet method, I get the following exception. I have no idea why! account controller servlet protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); try { dispatcher.forward(request, response); } catch (java.lang.NullPointerException e) { System.out.println("NullPointerException: attribute expected in view"); } } Error msg java.lang.NullPointerException org.apache.jasper.JasperException: java.lang.NullPointerException org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:502) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:430) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) java.lang.NullPointerException org.apache.jsp.content.edit_jsp._jspService(edit_jsp.java:109) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

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• Visual Studio 2010 compile error with std::string?

  - by AJG85

  So this is possibly the strangest thing I've seen recently and was curious how this could happen. The compiler gave me an error saying that std::string is undefined when used as a return type but not when used as a parameter in methods of a class! #pragma once #include <string> #include <vector> // forward declarations class CLocalReference; class CResultSetHandle; class MyClass { public: MyClass() {} ~MyClass {} void Retrieve(const CLocalReference& id, CResultSetHandle& rsh, std::string& item); // this is fine const std::string Retrieve(const CLocalReference& id, CResultSetHandle& rsh); // this fails with std::string is undefined?!?! }; Doing a Rebuild All it still happened I had to choose clean solution and then Rebuild All again after for the universe to realign. While it's resolved for the moment I'd still like to know what could have caused this because I'm at a loss as to why when there should be no conflicts especially when I always use fully qualified names for STL.

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• Is std::move really needed on initialization list of constructor for heavy members passed by value?

  - by PiotrNycz

  Recently I read an example from cppreference.../vector/emplace_back: struct President { std::string name; std::string country; int year; President(std::string p_name, std::string p_country, int p_year) : name(std::move(p_name)), country(std::move(p_country)), year(p_year) { std::cout << "I am being constructed.\n"; } My question: is this std::move really needed? My point is that compiler sees that this p_name is not used in the body of constructor, so, maybe, there is some rule to use move semantics for it by default? That would be really annoying to add std::move on initialization list to every heavy member (like std::string, std::vector). Imagine hundreds of KLOC project written in C++03 - shall we add everywhere this std::move? This question: move-constructor-and-initialization-list answer says: As a golden rule, whenever you take something by rvalue reference, you need to use it inside std::move, and whenever you take something by universal reference (i.e. deduced templated type with &&), you need to use it inside std::forward But I am not sure: passing by value is rather not universal reference?

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• Need help with Django tutorial

  - by Nai

  I'm doing the Django tutorial here: http://docs.djangoproject.com/en/1.2/intro/tutorial03/ My TEMPLATE_DIRS in the settings.py looks like this: TEMPLATE_DIRS = ( "/webapp2/templates/" "/webapp2/templates/polls" # Put strings here, like "/home/html/django_templates" or "C:/www/django/templates". # Always use forward slashes, even on Windows. # Don't forget to use absolute paths, not relative paths. ) My urls.py looks like this: from django.conf.urls.defaults import * from django.contrib import admin admin.autodiscover() urlpatterns = patterns('', (r'^polls/$', 'polls.views.index'), (r'^polls/(?P<poll_id>\d+)/$', 'polls.views.detail'), (r'^polls/(?P<poll_id>\d+)/results/$', 'polls.views.results'), (r'^polls/(?P<poll_id>\d+)/vote/$', 'polls.views.vote'), (r'^admin/', include(admin.site.urls)), ) My views.py looks like this: from django.template import Context, loader from polls.models import Poll from django.http import HttpResponse def index(request): latest_poll_list = Poll.objects.all().order_by('-pub_date')[:5] t = loader.get_template('c:/webapp2/templates/polls/index.html') c = Context({ 'latest_poll_list': latest_poll_list, }) return HttpResponse(t.render(c)) I think I am getting the path of my template wrong because when I simplify the views.py code to something like this, I am able to load the page. from django.http import HttpResponse def index(request): return HttpResponse("Hello, world. You're at the poll index.") My index template file is located at C:/webapp2/templates/polls/index.html. What am I doing wrong?

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• Collision Detection (Ground & Slopes) in 2D Platform Game using Pygame Rects

  - by RedCap

  Hi, First off, I am not after any instructions on logic for collision detection; I get it. What I am trying to work out is the least complicated way to do this with Pygame using Sprites & Rects. I want to be able to check collisions for the Player against ground, walls & slopes. In theory it is quite straight forward, but I'm having difficulty because it seems like you cannot do this with one Rect. One Rect is simple enough to get you collisions in the X plane against walls. The same Rect could be used also be used in the Y plane against solids, but not with slopes - since with the collision routines in Pygame it checks the whole Rect (or mask), rather than perhaps just the bottom middle of the Rect. It seems in addition you need to have a number of "sprites" to check collisions with, that are 1x1 pixel in various places around the Player. What's the easiest way to do this, without having a bunch of 3, 4, or more separate "collision pixels" to check against slopes? Geoff

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• Checking servlet session attribute value in jsp file

  - by Marta

  I have a no framework java application. It consists of jsp files for view and servlets for the business logic. I must set the user session is the servlet with a firstName parameter. In the jsp file, I need to check if my firstName parameter has a value or not. If the firstName parameter is set, I need to display some html in the jsp file. If it is not set, I need to display different html in the jsp file. Servlet.java: HttpSession session = request.getSession(); session.setAttribute("firstName", customer.getFristName()); String url = "/index.jsp"; RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url); dispatcher.forward(request, response); header.jsp: // Between the <p> tags bellow I need to put some HTML with the following rules // If firstName exist: Hello ${firstName} <a href="logout.jsp">Log out</a> // Else: <a href="login.jsp">Login</a> or <a href="register.jsp">Register</a> <p class="credentials" id="cr"></p> What would be the best way to do this? Any help is much appreciated! Thank you in advance. -Marta

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• What are good examples of perfectly acceptable approaches to development that are NOT test driven development (TDD)?

  - by markbruns

  The TDD cycle is test, code, refactor, (repeat) and then ship. TDD implies development that is driven by testing, specifically that means understanding requirements and then writing tests first before developing or writing code. My natural inclination is a philosophical bias in favor of TDD; I would like to be convinced that there are other approaches that now work well or even better than TDD so I have asked this question. What are examples of perfectly acceptable approaches that NOT test driven development? I can think of plenty approaches that are not TDD but could be a lot more trouble than what they are worth ... it's not moral judgement, it's just that they are cost more than they are worth ... the following are simply examples of things that might be ok as learning exercises, but approaches I'd find to be NOT acceptable in serious production and NOT TDD might include: Inspecting quality into your product -- Focusing efforts on developing a proficiency in testing/QA can be problematic, especially if you don't work on the requirements and development side first ... symptom of this include bug triaging where the developers have so many different bugs to deal with it, it is necessary to employ a form of triage -- each development cycle gets worse and worse, programmers work more and more hours, sleep less and less, struggle to keep going in death march until they are consumed. Superstition ... believing in things that you don't understand -- this would involve borrowing code that you believe has been proven or tested from somewhere, e.g. legacy code, a magic code starter wizard or an open source project, and you go forward hacking up a storm of modifications, sliding FaceBook Connect into your the user interface, inventing some new magic features on the fly (e.g. a mashup using the Twitter API, GoogleMaps API and maybe Zappos API), showing off your cool new "product" to a few people and then writing up a simple "specification" and list of "test cases" and turning that over to Mechanical Turk for testing.

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• Servlets: forwarding to a resource in a different webapp

  - by skaffman

  I'm trying to construct a java web app along modular principles, with some common resources (JSPs, mainly) in one WAR, and some custom resources in another. This means JSPs scattered across different WARs. Now JavaEE frowns upon this sort of shenanigans, and wants you to put everything in one place. My current workaround to this is to have an Eclipse-triggered Ant script which copies the content of one WAR into the other, but this is not a pleasant solution (it's fragile and too IDE-dependent). Ideally, what I'd like to be able to do is for a servlet to forward to a JSP located in a different WAR to one in which it is itself deployed. This would allow greater freedom in how I assemble my WARs. However, the RequestDispatcher does not seem to support such things. Another possibility is to use <c:import>, which does allow resources to be imported from a different WAR (with some caveats). This would probably allow me to have a "hook" JSP in one WAR, which then drags in the required JSP from another. This is a bit clunky, though, and the fact that <c:import> permits it shows that the underlying servlet API does also. But how do I access that functionality via the RequestDispatcher in a servlet?

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• Nested bind expressions

  - by user328543

  This is a followup question to my previous question. #include <functional> int foo(void) {return 2;} class bar { public: int operator() (void) {return 3;}; int something(int a) {return a;}; }; template <class C> auto func(C&& c) -> decltype(c()) { return c(); } template <class C> int doit(C&& c) { return c();} template <class C> void func_wrapper(C&& c) { func( std::bind(doit<C>, std::forward<C>(c)) ); } int main(int argc, char* argv[]) { // call with a function pointer func(foo); func_wrapper(foo); // error // call with a member function bar b; func(b); func_wrapper(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); func_wrapper(std::bind(&bar::something, b, 42)); // error // call with a lambda expression func( [](void)->int {return 42;} ); func_wrapper( [](void)->int {return 42;} ); return 0; } I'm getting a compile errors deep in the C++ headers: functional:1137: error: invalid initialization of reference of type ‘int (&)()’ from expression of type ‘int (*)()’ functional:1137: error: conversion from ‘int’ to non-scalar type ‘std::_Bind(bar, int)’ requested func_wrapper(foo) is supposed to execute func(doit(foo)). In the real code it packages the function for a thread to execute. func would the function executed by the other thread, doit sits in between to check for unhandled exceptions and to clean up. But the additional bind in func_wrapper messes things up...

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• Java - Image encoding in XML

  - by Hoopla

  Hi everyone, I thought I would find a solution to this problem relatively easily, but here I am calling upon the help from ye gods to pull me out of this conundrum. So, I've got an image and I want to store it in an XML document using Java. I have previously achieved this in VisualBasic by saving the image to a stream, converting the stream to an array, and then VB's xml class was able to encode the array as a base64 string. But, after a couple of hours of scouring the net for an equivalent solution in Java, I've come back empty handed. The only success I have had has been by: import it.sauronsoftware.base64.*; import java.awt.image.BufferedImage; import org.w3c.dom.*; ... BufferedImage img; Element node; ... java.io.ByteArrayOutputStream os = new java.io.ByteArrayOutputStream(); ImageIO.write(img, "png", os); byte[] array = Base64.encode(os.toByteArray()); String ss = arrayToString(array, ","); node.setTextContent(ss); ... private static String arrayToString(byte[] a, String separator) { StringBuffer result = new StringBuffer(); if (a.length > 0) { result.append(a[0]); for (int i=1; i<a.length; i++) { result.append(separator); result.append(a[i]); } } return result.toString(); } Which is okay I guess, but reversing the process to get it back to an image when I load the XML file has proved impossible. If anyone has a better way to encode/decode an image in an XML file, please step forward, even if it's just a link to another thread that would be fine. Cheers in advance, Hoopla.

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• Trying to join two independent forms

  - by user248959

  Hi, i'm trying to join two independent forms (login and register) in the same page. My idea is (just looking at the signin form): Create an action that shows both forms (partials): public function executeLoginAndRegister(sfWebRequest $request){ $this->form_signin = $this->getUser()->getAttribute('form_signin'); } Each partial calls to its action: form action="php? echo url_for('@sf_guard_signin') ?" method="post" In the actions i write this code public function executeSignin($request) { //... $this->form = new $MyFormclass(); if ($this->form->isValid()) { //... }else{ // save the form to show the error messages. $this-&gt;getUser()-&gt;setAttribute('form_signin', $this-&gt;form); return $this-&gt;forward('sfGuardAuth', 'loginAndRegister'); } } It works, but, for example, if i execute LoginAndRegister and submit incorrectly the signin form and I go to another page and then return to LoginAndRegister, i will find the submiting error messages... If i execute LoginAndRegister and submit incorrectly the signin form and open another browser tab, i will find the submiting error messages in the signin form of the second tab... Any idea? any better approach?

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• servlet and jsp sending query result following MVC framework

  - by kawtousse

  Hi every one, in order to separate java code and html code and be more faithful to MVC framework i am coding like that; in the servlet i put the following: net.sf.hibernate.Session s = null; net.sf.hibernate.Transaction tx; try { s= HibernateUtil.currentSession(); tx=s.beginTransaction(); Query query = s.createQuery("select opcemployees.Nom,opcemployees.Prenom,dailytimesheet.TrackingDate,dailytimesheet.Activity," + "dailytimesheet.ProjectCode,dailytimesheet.WAName,dailytimesheet.TaskCode," + "dailytimesheet.TimeSpent,dailytimesheet.PercentTaskComplete from Opcemployees opcemployees,Dailytimesheet dailytimesheet " + "where opcemployees.Matricule=dailytimesheet.Matricule and dailytimesheet.Etat=3 " + "group by opcemployees.Nom,opcemployees.Prenom" ); for(Iterator it=query.iterate();it.hasNext();) { if(it.hasNext()){ Object[] row = (Object[]) it.next(); request.setAttribute("items", row); }} } catch (HibernateException e){ e.printStackTrace(); } request.getRequestDispatcher("EspaceValidation.jsp").forward(request, response); and in jsp i start like that: <table> <c:forEach items="${items}" var="item"> <tr> <td>? </td> <td>?</td> </tr> </c:forEach> in this case what should i put exactly to obtain my result.a table fulled with the right value from the request

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• Best loose way to get objects with common base class

  - by Michael Teper

  I struggled to come up with a good title for this question, so suggestions are welcome. Let's say we have an abstract base class ActionBase that looks something like this: public abstract class ActionBase { public abstract string Name { get; } public abstract string Description { get; } // rest of declaration follows } And we have a bunch of different actions defined, like a MoveFileAction, WriteToRegistryAction, etc. These actions get attached to Worker objects: public class Worker { private IList<ActionBase> _actions = new List<ActionBase>(); public IList<ActionBase> Actions { get { return _actions; } } // worker stuff ... } So far, pretty straight-forward. Now, I'd like to have a UI for setting up Workers, assigning Actions, setting properties, and so on. In this UI, I want to present a list of all available actions, along with their properties, and for that I'd want to first gather up all the names and descriptions of available actions (plus the type) into a collection of the following type of item: public class ActionDescriptor { public string Name { get; } public string Description { get; } poblic Type Type { get; } } Certainly, I can use reflection to do this, but is there a better way? Having Name and Description be instance properties of ActionBase (as opposed to statics on derived classes) smells a bit, but there isn't an abstract static in C#. Thank you!

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• A question of long-running and disruptive branches

  - by Matt Enright

  We are about to begin prototyping a new application that will share some existing infrastructure assemblies with an existing application, and also involve a significant subset of the existing domain model. Parts of the domain model will likely undergo some serious changes for this new application, and the endgame for all of this, once the new application has been fully specified and is launch-ready is that we would like to re-unify the models of the two applications (as well as share a database, link functionality, etc.), but for the duration of development, prototyping, etc, we will be using a separate database so that we can change things without worrying about impact to development or use of the existing application. Since it is a prototype, there will be a pretty long window during which serious changes or rearchitecturing can occur as product management experiments with different workflows, different customer bases are surveyed, and we try and keep up. We have already made a Subversion branch, so as to not impact concurrent development on the mature application, and are toying with 2 potential ways of moving forward with this: Use the svn branch as the sole mechanism of separation. Make our changes to the existing domain models, and evaluate their impact on the existing application (and make requisite changes to ProjectA) when we have established that our long-running side branch is stable enough for re-entry to trunk. "Fork" the shared code (temporarily): Copy ProjectA.Entities to NewProject.Entities, and treat all of the NewProject code as self-contained. When all of the perturbations around the model have died down and we feel satisfied, manually re-integrate the changes (as granular or sweeping as warranted) back into ProjectA.Entities, updating ProjectA to use the improved models at each step (this can take place either before or after the subversion merge has occurred). The subversion merge will then not handle recombination of any of the heavy changes here. Note: the "fork" method only applies to the code we see significant changes in store for, and whose modification will break ProjectA - shared infrastructure stuff for example, we would just modify in place (on our branch) and let the merge sort out. Development is hard, go shopping. Naturally, after not coming to an agreement, we're turning it over to the oracle of power that is SO. Any experience with any of these methods, pain points to watch out for, something new entirely?

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• What else I must do allow my method to handle any type of objects

  - by NewHelpNeeder

  So to allow any type object I must use generics in my code. I have rewrote this method to do so, but then when I create an object, for example Milk, it won't let me pass it to my method. Ether there's something wrong with my generic revision, or Milk object I created is not good. How should I pass my object correctly and add it to linked list? This is a method that causes error when I insert an item: public void insertFirst(T dd) // insert at front of list { Link newLink = new Link(dd); // make new link if( isEmpty() ) // if empty list, last = newLink; // newLink <-- last else first.previous = newLink; // newLink <-- old first newLink.next = first; // newLink --> old first first = newLink; // first --> newLink } This is my class I try to insert into linked list: class Milk { String brand; double size; double price; Milk(String a, double b, double c) { brand = a; size = b; price = c; } } This is test method to insert the data: public static void main(String[] args) { // make a new list DoublyLinkedList theList = new DoublyLinkedList(); // this causes: // The method insertFirst(Comparable) in the type DoublyLinkedList is not applicable for the arguments (Milk) theList.insertFirst(new Milk("brand", 1, 2)); // insert at front theList.displayForward(); // display list forward theList.displayBackward(); // display list backward } // end main() } // end class DoublyLinkedApp Declarations: class Link<T extends Comparable<T>> {} class DoublyLinkedList<T extends Comparable<T>> {}

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• How can I work out if a date is on or before today?

  - by Yvonne

  My web application consists of library type system where books have due dates. I have the current date displayed on my page, simply by using this: date_default_timezone_set('Europe/London'); $date = date; print $date("d/m/Y"); I have set 'date' as a variable because I'm not sure if it makes a difference when I use it in the IF statement you're about see, on my library books page. On this page, I am simply outputting the due dates of the books, many have dates which have not yet reached todays date, and others which have dates greater than todays date. Basically, all I want is the due date to appear bold (or strong), if it has passed todays date (the system displayed date). This is what I have and thought would work: <? if ($duedate < $date) { echo '<td><strong>'; } else { echo '<td>'; } ?> <?php echo $date('d/m/Y', $timestamp);?></strong></td> I have declared $timestamp as a var which converts the date of default MySQL format to a UK version. Can anyone help me out? I thought this would've been very straight forward!

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• Turn based synchronization between threads

  - by Amarus

  I'm trying to find a way to synchronize multiple threads having the following conditions: * There are two types of threads: 1. A single "cyclic" thread executing an infinite loop to do cyclic calculations 2. Multiple short-lived threads not started by the main thread * The cyclic thread has a sleep duration between each cycle/loop iteration * The other threads are allowed execute during the inter-cycle sleep of the cyclic thread: - Any other thread that attempts to execute during an active cycle should be blocked - The cyclic thread will wait until all other threads that are already executing to be finished Here's a basic example of what I was thinking of doing: // Somewhere in the code: ManualResetEvent manualResetEvent = new ManualResetEvent(true); // Allow Externally call CountdownEvent countdownEvent = new CountdownEvent(1); // Can't AddCount a CountdownEvent with CurrentCount = 0 void ExternallyCalled() { manualResetEvent.WaitOne(); // Wait until CyclicCalculations is having its beauty sleep countdownEvent.AddCount(); // Notify CyclicCalculations that it should wait for this method call to finish before starting the next cycle Thread.Sleep(1000); // TODO: Replace with actual method logic countdownEvent.Signal(); // Notify CyclicCalculations that this call is finished } void CyclicCalculations() { while (!stopCyclicCalculations) { manualResetEvent.Reset(); // Block all incoming calls to ExternallyCalled from this point forward countdownEvent.Signal(); // Dirty workaround for the issue with AddCount and CurrentCount = 0 countdownEvent.Wait(); // Wait until all of the already executing calls to ExternallyCalled are finished countdownEvent.Reset(); // Reset the CountdownEvent for next cycle. Thread.Sleep(2000); // TODO: Replace with actual method logic manualResetEvent.Set(); // Unblock all threads executing ExternallyCalled Thread.Sleep(1000); // Inter-cycles delay } } Obviously, this doesn't work. There's no guarantee that there won't be any threads executing ExternallyCalled that are in between manualResetEvent.WaitOne(); and countdownEvent.AddCount(); at the time the main thread gets released by the CountdownEvent. I can't figure out a simple way of doing what I'm after, and almost everything that I've found after a lengthy search is related to producer/consumer synchronization which I can't apply here.

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• Which DVCS would work best on Windows for my scenario?

  - by PoorLuzer

  At work I use ClearCase and SourceSafe, but have found some time to do some time to code for myself enroute thanks to a disposable laptop. However, I wish I had a lightweight VCS on my system using which I would be able to make changes to my code during the commute and then push/grab them from my Linux systems. I use git on my home system, but I can't really get it working on Windows. I don't want all that cygwin hack. If it does not run natively on Windows, it just won't do. What have you guys tried on your Windows system? Something that YOU use. The big player at the moment seems to be Mercurial? What would be best for a one (or maybe two) man team? I just need to maintain : Versioned copies of source code. Checking in and out should be as less obtrusive as possible. I am looking forward to a multiple Undo kind of feature (like that in an EMacs buffer) but persistent. I really like the way git keeps track of lines moving between files in a source code set I should be able to move part(s)/sub tree(s) of the source tree (each sub tree implies a module/plugin to my the main software I am building) to an archival system either completly or partially and restore them back from the archive as and when required and the system should track any changes to this tree as well. I actually want to experiment with my code as much as possible without me manually keeping track of what I modified and what I need to undo once I try out some idea, so that I am back to where I want to continue from. Notes : A similar topic came up a year ago : http://stackoverflow.com/questions/4670/dvcs-choices-whats-good-for-windows I hope things have changed, and I really want people to share their own, real life experiences. Not something they recommend without using it or they think will work.

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• How do I call C++/CLI (.NET) DLLs from standard, unmanaged non-.NET applications?

  - by tronjohnson

  In the unmanaged world, I was able to write a __declspec(dllexport) or, alternatively, use a .DEF file to expose a function to be able to call a DLL. (Because of name mangling in C++ for the __stdcall, I put aliases into the .DEF file so certain applications could re-use certain exported DLL functions.) Now, I am interested in being able to expose a single entry-point function from a .NET assembly, in unmanaged-fashion, but have it enter into .NET-style functions within the DLL. Is this possible, in a simple and straight-forward fashion? What I have is a third-party program that I have extended through DLLs (plugins) that implement some complex mathematics. However, the third-party program has no means for me to visualize the calculations. I want to somehow take these pre-written math functions, compile them into a separate DLL (but using C++/CLI in .NET), but then add hooks to the functions so I can render what's going on under the hood in a .NET user control. I'm not sure how to blend the .NET stuff with the unmanaged stuff, or what to Google to accomplish this task. Specific suggestions with regard to the managed/unmanaged bridge, or alternative methods to accomplish the rendering in the manner I have described would be helpful. Thank you.

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• Cant get JavaScipt to check for null objects

  - by CountMurphy

  I really don't know what the issue is here. Far as I can see, the code is simple and should work fine. var Prices=""; for (var PriceCount = 1; PriceCount <= 120; PriceCount++) { var CurrentPrice = "Price" + PriceCount; if (prevDoc.getElementById(CurrentPrice).value != null) { if (Prices == "") { Prices = prevDoc.getElementById(CurrentPrice).value; } else { Prices += "," + prevDoc.getElementById(CurrentPrice).value; } } else { break; } } There could be up to 120 hidden inputs on the form. The moment we check for an input that doesn't exist the loop should break. My test page has two input elements that get pulled. On the third (the null) I get this error in firebug: prevDoc.getElementById(CurrentPrice) is null if (prevDoc.getElementById(CurrentPrice).value != null) { Yes it is null...that's what the check is for ?_? Does any one know what I'm doing wrong? This seems like it should be really straight forward. EDIT: for clarity's sake, prevDoc=window.opener.document

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• Is there a way to identify that a file has been modified and moved?

  - by Eric

  I'm writing an application that catalogs files, and attributes them with extra meta data through separate "side-car" files. If changes to the files are made through my program then it is able to keep everything in sync between them and their corresponding meta data files. However, I'm trying to figure out a way to deal with someone modifying the files manually while my program is not running. When my program starts up it scans the file system and compares the files it finds to it's previous record of what files it remembers being there. It's fairly straight forward to update after a file has been deleted or added. However, if a file was moved or renamed then my program sees that as the old file being deleted, and the new file being added. Yet I don't want to loose the association between the file and its metadata. I was thinking I could store a hash from each file so I could check to see if newly found files were really previously known files that had been moved or renamed. However, if the file is both moved/renamed and modified then the hash would not match either. So is there some other unique identifier of a file that I can track which stays with it even after it is renamed, moved, or modified?

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• Architecture of finding movable geotagged objects

  - by itsme

  I currently have a Postgres DB filled with approx. 300.000 data-sets of moving vehicles all over the world. My very frequently repeated query is: Give me all vehicles in a 5/10/20mile radius. Currently I spend around 600 to 1200 ms in the DB to prepare the set of located vehicle-objects. I am looking to vastly improve this time by ideally one or two orders of magnitude if possible. I am working in a Ruby on Rails 3.0beta environment if this is relevant. Any ideas how to architect the whole system to accelerate this query? Any NoSQL database able to deliver this kind of geolocation performance? I know of MongoDB working on an extension to facilitate this scenario but haven't tried it yet. Any intelligent use of Redis to achieve this? One problem with SQL-DBs here seems to be that I can't possibly use indexes because my vehicles are mostly moving around, meaning I had to constantly created DB indexes which, by itself, is probably more expensive than just doing the searching without index. Looking forward to your thoughs, Thanks!

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• iPhone app developed with SDK 4.2, requires backward compatibility with iOS 3.1.3 .. easy way?

  - by mrd3650

  I have built an iPhone app with SDK 4.2 however I know also want to make it compatible with iOS 3.1.3. First step was to set the Deployment Target to 3.1.3. It runs fine on the 3.2 Simulator but the app crashes at times since I'm using some methods which are not available in this early SDK. So my qestion is, is there a straight forward way to locate the offending methods/classes I'm using in my project which are not available in 3.1.3 ? (without manually going through each method call and consult with the docs for the SDK availability?) Thanks. UPDATE: I have executed the app on 3.1.3 and attempted to manually test each execution path with the hope of locating all exceptions. This was completed with some level of success. However, what if the application is huge? and there are lots of execution paths? There must be some tool for this scenario. Any thoughts are much appreciated.

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• Sharing class member data between sub components

  - by Tim Gradwell

  I have an aggregate 'main' class which contains some data which I wish to share. The main class also has other class members. I want to share the data with these other class members. What is the correct / neatest way to do this? The specific example I have is as follows. The main class is a .net Form. I have some controls (actually controls within controls) on the main form which need access to the shared data. Main Form - DataX - DataY - Control1 -- Subcontrol1 - Control2 -- SubControl2 SubControls 1 and 2 both wish to access DataX and DataY. The trouble is, I feel like better practice (to reduce coupling), would be that either subcontrols should not know about Main Form, or Main Form should not know about subcontrols - probably the former. For subcontrols not to know about Main Form, would probably mean Main Form passing references to both Controls 1 and 2, which in turn would pass the references on to SubControls 1 and 2. Lots of lines of code which just forward the references. If I later added DataZ and DataW, and Controls 3 and 4 and SubControls 3 and 4, I'd have to add lots more reference forwarding code. It seems simpler to me to give SubControls 1 and 2 member references to Main Form. That way, any sub control could just ask for MainForm.DataX or MainForm.DataY and if I ever added new data, I could just access it directly from the sub controls with no hassle. But it still involves setting the 'MainForm' member references every time I add a new Control or Subcontrol. And it gives me a gut feeling of 'wrong'. As you might be able to tell I'm not happy with either of my solutions. Is there a better way? Thanks

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• How to handle exceptions from an image-generating Servlet?

  - by ssahmed555

  I have a simple (Servlet, JSP, and JSTL) web app whose main functionality is displaying images retrieved from a back-end server. The controller servlet forwards the user to a JSP that in turn uses another Servlet to display the resulting image on that same JSP. Further down, the JSP has a line similar to: <a href="<c:out value='${imageURL}'/>"><img src="<c:out value='${imageURL}'/>" alt="image view" border="1"></a> which invokes a GET request on the image-generating servlet causing it to generate the image. My question is: how do I handle Exceptions thrown by this image-generating servlet? I already have an error page defined (in web.xml) to handle ServletException within my web app but this doesn't work for this image-generating Servlet, and results in the following errors showing up in my Tomcat server logs: SEVERE: Exception Processing ErrorPage[exceptionType=javax.servlet.ServletException, location=/WEB-INF/ExceptionPage.jsp] java.lang.IllegalStateException: Cannot reset buffer after response has been committed What's my recourse in this situation? I'd like to be able to handle Exceptions thrown from this image-generating Servlet, and display some error on the main UI or forward the user to another error page.

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