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  • XmlSerializer construction with same named extra types

    - by NoizWaves
    Hey, I am hitting trouble constructing an XmlSerializer where the extra types contains types with the same Name (but unique Fullname). Below is an example that illustrated my scenario. Type definitions in external assembly I cannot manipulate: public static class Wheel { public enum Status { Stopped, Spinning } } public static class Engine { public enum Status { Idle, Full } } Class I have written and have control over: public class Car { public Wheel.Status WheelStatus; public Engine.Status EngineStatus; public static string Serialize(Car car) { var xs = new XmlSerializer(typeof(Car), new[] {typeof(Wheel.Status),typeof(Engine.Status)}); var output = new StringBuilder(); using (var sw = new StringWriter(output)) xs.Serialize(sw, car); return output.ToString(); } } The XmlSerializer constructor throws a System.InvalidOperationException with Message "There was an error reflecting type 'Engine.Status'" This exception has an InnerException of type System.InvalidOperationException and with Message "Types 'Wheel.Status' and 'Engine.Status' both use the XML type name, 'Status', from namespace ''. Use XML attributes to specify a unique XML name and/or namespace for the type." Given that I am unable to alter the enum types, how can I construct an XmlSerializer that will serialize Car successfully?

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  • What is the best way to store static data in C# that will never change

    - by Luke101
    I have a class that stores data in asp.net c# application that never changes. I really don't want to put this data in the database - I would like it to stay in the application. Here is my way to store data in the application: public class PostVoteTypeFunctions { private List<PostVoteType> postVotes = new List<PostVoteType>(); public PostVoteTypeFunctions() { PostVoteType upvote = new PostVoteType(); upvote.ID = 0; upvote.Name = "UpVote"; upvote.PointValue = PostVotePointValue.UpVote; postVotes.Add(upvote); PostVoteType downvote = new PostVoteType(); downvote.ID = 1; downvote.Name = "DownVote"; downvote.PointValue = PostVotePointValue.DownVote; postVotes.Add(downvote); PostVoteType selectanswer = new PostVoteType(); selectanswer.ID = 2; selectanswer.Name = "SelectAnswer"; selectanswer.PointValue = PostVotePointValue.SelectAnswer; postVotes.Add(selectanswer); PostVoteType favorite = new PostVoteType(); favorite.ID = 3; favorite.Name = "Favorite"; favorite.PointValue = PostVotePointValue.Favorite; postVotes.Add(favorite); PostVoteType offensive = new PostVoteType(); offensive.ID = 4; offensive.Name = "Offensive"; offensive.PointValue = PostVotePointValue.Offensive; postVotes.Add(offensive); PostVoteType spam = new PostVoteType(); spam.ID = 0; spam.Name = "Spam"; spam.PointValue = PostVotePointValue.Spam; postVotes.Add(spam); } } When the constructor is called the code above is ran. I have some functions that can query the data above too. But is this the best way to store information in asp.net? if not what would you recommend?

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  • Dependencyproperty doesn't have value on load

    - by Jakob
    My problem is this, I have a UC called profile that contains another UC called FollowImageControl. In my Profile.xaml i declaretively bind a property of FollowImageControl called FollowerId to a CurrentUserId from Profile.xaml.cs. Problem is that I CurrentUserId is assigned in Profile.xaml.cs; the Profile.xaml code-behind. This means that I do not initially get the FollowerId. I have these methods in the FollowImageControl.xaml.cs: public static readonly DependencyProperty _followUserId = DependencyProperty.Register("FollowUserId", typeof(Guid), typeof(FollowImageControl), null); public Guid FollowUserId { get { return (Guid)GetValue(_followUserId); } set { SetValue(_followUserId, value); } } public FollowImageControl() { // Required to initialize variables InitializeComponent(); LoggedInUserId = WebContext.Current.User.UserId; var ctx = new NotesDomainContext(); if (ctx.IsFollowingUser(LoggedInUserId, FollowUserId).Value) SwitchToDelete.Begin(); } private void AddImg_MouseLeftButtonDown(object sender, MouseButtonEventArgs e) { if (LoggedInUserId != FollowUserId) { var ctx = new NotesDomainContext(); ctx.FollowUser(FollowUserId, LoggedInUserId); ctx.SubmitChanges(); } } THE WEIRD THING IS that when i insert breakpoints the FollowerUserId in FollowImageControl() is 0, but it has a value in AddImg_MouseLeftButtonDown, and there is no inbetween logic that sets the value of it. How is this??? Here's a little more code info: This is my binding from profile.xaml <internalCtrl:FollowImageControl FollowUserId="{Binding ElementName=ProfileCtrl, Path=CurrentUserId}" /> this is my constructor in profile.xaml.cs wherein the CurrentUserId is set public static readonly DependencyProperty _CurrentUserId = DependencyProperty.Register("CurrentUserId", typeof(Guid), typeof(Profile), null); public Guid CurrentUserId { get { return (Guid)GetValue(_CurrentUserId); } set { SetValue(_CurrentUserId, value); } } public Profile(Guid UserId) { CurrentUserId = UserId; InitializeComponent(); Loaded += new RoutedEventHandler(Profile_Loaded); } I'm seriously dumbfound that one minute the FollowerId has no value, and the next it holds the right, without me having changed the value in the code-behind.

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  • QProgressBar problem with uploading

    - by rolanddd
    Hey all! I show my code first, then I explain my problem: ... // somewhere in the constructor progressBar = new QProgressBar(this); progressBar-setMinimum(0); progressBar-setMaximum(100); ... connect(&http, SIGNAL(dataSendProgress(int, int)), this, SLOT(updateProgressBar(int, int))); ... void MainWindow::updateProgressBar(int bytesSent, int total) { progressBar-setMaximum(total); progressBar-setValue(bytesSent); } So this is how I try to make my progressBar being updated when I upload a file. The problem is, it won't do the job. When it starts uploading, I set the value of the progress bar to 0, then (thanks to this slot) it won't actually show the progress, but will jump to 100% immediately (even before it finished uploading). I already checked the HTTP Client example, and copied the progress bar part, it is for downloading, and more or less is the same as for uploading but it uses the dataReadProgress signal (needed for downloading) AND it works perfectly. Does anybody know how to solve this for uploading?

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  • efficient thread-safe singleton in C++

    - by user168715
    The usual pattern for a singleton class is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) inst = new Foo(...); return *inst; } However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread. One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) { pthread_mutex_lock(&mutex); if(inst == NULL) inst = new Foo(...); pthread_mutex_unlock(&mutex); } return *inst; } Is this the right way to do it, or are there any pitfalls I should be aware of? For instance, are there any static initialization order problems that might occur, i.e. is inst always guaranteed to be NULL the first time getInst is called?

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  • C# casting question: from IEnumerable to custom type

    - by Sarah Vessels
    I have a custom class called Rows that implements IEnumerable<Row>. I often use LINQ queries on Rows instances: Rows rows = new Rows { row1, row2, row3 }; IEnumerable<Row> particularRows = rows.Where<Row>(row => condition); What I would like is to be able to do the following: Rows rows = new Rows { row1, row2, row3 }; Rows particularRows = (Rows)rows.Where<Row>(row => condition); However, I get a "System.InvalidCastException: Unable to cast object of type 'WhereEnumerableIterator1[NS.Row]' to type 'NS.Rows'". I do have a Rows constructor taking IEnumerable<Row>, so I could do: Rows rows = new Rows { row1, row2, row3 }; Rows particularRows = new Rows(rows.Where<Row>(row => condition)); This seems bulky, however, and I would love to be able to cast an IEnumerable<Row> to be a Rows since Rows implements IEnumerable<Row>. Any ideas?

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  • const pod and std::vector

    - by Baz
    To get this code to compile: std::vector<Foo> factory() { std::vector<Foo> data; return data; } I have to define my POD like this: struct Foo { const int i; const int j; Foo(const int _i, const int _j): i(_i), j(_j) {} Foo(Foo& foo): i(foo.i), j(foo.j){} Foo operator=(Foo& foo) { Foo f(foo.i, foo.j); return f; } }; Is this the correct approach for defining a pod where I'm not interested in changing the pod members after creation? Why am I forced to define a copy constructor and overload the assignment operator? Is this compatible for different platform implementations of std::vector? Is it wrong in your opinion to have const PODS like this? Should I just leave them as non-const?

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  • Dependency injection in C++

    - by Yorgos Pagles
    This is also a question that I asked in a comment in one of Miško Hevery's google talks that was dealing with dependency injection but it got buried in the comments. I wonder how can the factory / builder step of wiring the dependencies together can work in C++. I.e. we have a class A that depends on B. The builder will allocate B in the heap, pass a pointer to B in A's constructor while also allocating in the heap and return a pointer to A. Who cleans up afterwards? Is it good to let the builder clean up after it's done? It seems to be the correct method since in the talk it says that the builder should setup objects that are expected to have the same lifetime or at least the dependencies have longer lifetime (I also have a question on that). What I mean in code: class builder { public: builder() : m_ClassA(NULL),m_ClassB(NULL) { } ~builder() { if (m_ClassB) { delete m_ClassB; } if (m_ClassA) { delete m_ClassA; } } ClassA *build() { m_ClassB = new class B; m_ClassA = new class A(m_ClassB); return m_ClassA; } }; Now if there is a dependency that is expected to last longer than the lifetime of the object we are injecting it into (say ClassC is that dependency) I understand that we should change the build method to something like: ClassA *builder::build(ClassC *classC) { m_ClassB = new class B; m_ClassA = new class A(m_ClassB, classC); return m_ClassA; } What is your preferred approach?

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  • C# / this. and List<T>

    - by user3533030
    I am having trouble understanding how to initialize a List of objects and use it with methods inside of a class. I understand the mechanics of the List, but not how to initialize it inside a method and use it later. For example, I want to have a class that creates the List when it is constructed. Then, I want to use a method of that class to add elements to the list. The elements in the list are objects defined by the SolidWorks API. So, to construct the List, I used... public class ExportPoints : Exporter { public List<SldWorks.SketchPoint> listOfSketchPoints; public ExportPoints(SldWorks.SldWorks swApp, string nameSuffix) : base(swApp, nameSuffix) { List<SldWorks.SketchPoint> listOfSketchPoints = new List<SldWorks.SketchPoint>(); } public void createListOfFreePoints() { try { [imagine more code here] this.listOfSketchPoints.Add(pointTest); } catch (Exception e) { Debug.Print(e.ToString()); return; } } This fails during execution as if the listOfSketchPoints was never initialized as a List. So, I tried a hack and this worked: public ExportPoints(SldWorks.SldWorks swApp, string nameSuffix) : base(swApp, nameSuffix) { List<SldWorks.SketchPoint> listOfSketchPoints = new List<SldWorks.SketchPoint>(); this.listOfSketchPoints = listOfSketchPoints; } This approach creates the behavior that I want. However, it seems that I lack some understanding as to why this is necessary. Shouldn't it be possible to "initialize" a List that is a property of your object with a constructor? Why would you need to create the list, then assign the pointer of that new List to your property?

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  • C++ template and pointers

    - by Kary
    I have a problem with a template and pointers ( I think ). Below is the part of my code: /* ItemCollection.h */ #ifndef ITEMCOLLECTION_H #define ITEMCOLLECTION_H #include <cstddef> using namespace std; template <class T> class ItemCollection { public: // constructor //destructor void insertItem( const T ); private: struct Item { T price; Item* left; Item* right; }; Item* root; Item* insert( T, Item* ); }; #endif And the file with function defintion: /* ItemCollectionTemp.h-member functions defintion */ #include <iostream> #include <cstddef> #include "ItemCollection.h" template <class Type> Item* ItemCollection <T>::insert( T p, Item* ptr) { // function body } Here are the errors which are generated by this line of code: Item* ItemCollection <T>::insert( T p, Item* ptr) Errors: error C2143: syntax error : missing ';' before '*' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2065: 'Type' : undeclared identifier error C2065: 'Type' : undeclared identifier error C2146: syntax error : missing ')' before identifier 'p' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2470: 'ItemCollection::insert' : looks like a function definition, but there is no parameter list; skipping apparent body error C2072: 'ItemCollection::insert': initialization of a function error C2059: syntax error : ')' Any help is much appreciated.

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  • why this code not works?

    - by badgirl
    Hello. I want to create new node of BeanTreeView, and when I add some node in constructor, then run the app, and then I try to view the window with tree, it throws this error java.lang.AssertionError: Component cannot be created for {component=null, displayName=Exploirer, instanceCreate=AlwaysEnabledAction[Exploirer]} at org.openide.windows.OpenComponentAction.getTopComponent(OpenComponentAction.java:71) Why? And how to add node there? See the code. private ProjectsChildren projectsChildren; private ProjectNode projectNode = new ProjectNode(new MainProject("ggg"), projectsChildren); public ExploirerTopComponent() { initComponents(); setName(NbBundle.getMessage(ExploirerTopComponent.class, "CTL_ExploirerTopComponent")); setToolTipText(NbBundle.getMessage(ExploirerTopComponent.class, "HINT_ExploirerTopComponent")); // setIcon(ImageUtilities.loadImage(ICON_PATH, true)); //map.put("delete", ExplorerUtils.actionDelete(mgr, true)); associateLookup (ExplorerUtils.createLookup(mgr, getActionMap())); //projectsChildren.createProject("demence"); /* somewhere here is the problem*/ mgr.setRootContext(projectNode); ProjectNode[] pr = null; pr[0] = projectNode; mgr.getRootContext().getChildren().add(pr); }

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  • C++: Maybe you know this pitfall?

    - by Martijn Courteaux
    Hi, I'm developing a game. I have a header GameSystem (just methods like the game loop, no class) with two variables: int mouseX and int mouseY. These are updated in my game loop. Now I want to access them from Game.cpp file (a class built by a header-file and the source-file). So, I #include "GameSystem.h" in Game.h. After doing this I get a lot of compile errors. When I remove the include he says of course: Game.cpp:33: error: ‘mouseX’ was not declared in this scope Game.cpp:34: error: ‘mouseY’ was not declared in this scope Where I want to access mouseX and mouseY. All my .h files have Header Guards, generated by Eclipse. I'm using SDL and if I remove the lines that wants to access the variables, everything compiles and run perfectly (*). I hope you can help me... This is the error-log when I #include "GameSystem.h" (All the code he is refering to works, like explained by the (*)): In file included from ../trunk/source/domein/Game.h:14, from ../trunk/source/domein/Game.cpp:8: ../trunk/source/domein/GameSystem.h:30: error: expected constructor, destructor, or type conversion before ‘*’ token ../trunk/source/domein/GameSystem.h:46: error: variable or field ‘InitGame’ declared void ../trunk/source/domein/GameSystem.h:46: error: ‘Game’ was not declared in this scope ../trunk/source/domein/GameSystem.h:46: error: ‘g’ was not declared in this scope ../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘char’ ../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘bool’ ../trunk/source/domein/FPS.h:46: warning: ‘void FPS_SleepMilliseconds(int)’ defined but not used This is the code which try to access the two variables: SDL_Rect pointer; pointer.x = mouseX; pointer.y = mouseY; pointer.w = 3; pointer.h = 3; SDL_FillRect(buffer, &pointer, 0xFF0000);

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  • Delete on a very deep tree

    - by Kathoz
    I am building a suffix trie (unfortunately, no time to properly implement a suffix tree) for a 10 character set. The strings I wish to parse are going to be rather long (up to 1M characters). The tree is constructed without any problems, however, I run into some when I try to free the memory after being done with it. In particularly, if I set up my constructor and destructor to be as such (where CNode.child is a pointer to an array of 10 pointers to other CNodes, and count is a simple unsigned int): CNode::CNode(){ count = 0; child = new CNode* [10]; memset(child, 0, sizeof(CNode*) * 10); } CNode::~CNode(){ for (int i=0; i<10; i++) delete child[i]; } I get a stack overflow when trying to delete the root node. I might be wrong, but I am fairly certain that this is due to too many destructor calls (each destructor calls up to 10 other destructors). I know this is suboptimal both space, and time-wise, however, this is supposed to be a quick-and-dirty solution to a the repeated substring problem. tl;dr: how would one go about freeing the memory occupied by a very deep tree? Thank you for your time.

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  • Thread-Safe lazy instantiating using MEF

    - by Xaqron
    // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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  • Storing C++ templated objects as same type

    - by JaredC
    I have a class that is a core component of a performance sensitive code path, so I am trying to optimize it as much as possible. The class used to be: class Widget { Widget(int n) : N(n) {} .... member functions that use the constant value N .... const int N; // just initialized, will never change } The arguments to the constructor are known at compile time, so I have changed this class to a template, so that N can be compiled into the functions: template<int N> class Widget { .... member functions that use N .... } I have another class with a method: Widget & GetWidget(int index); However, after templating Widget, each widget has a different type so I cannot define the function like this anymore. I considered different inheritance options, but I'm not sure that the performance gain from the template would outweigh the cost of inherited function invocations. SO, my question is this: I am pretty sure I want the best of both worlds (compile-time / run-time), and it may not be possible. But, is there a way to gain the performance of knowing N at compile time, but still being able to return Widgets as the same type? Thanks!

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  • Dependency Injection: How to pass DB around?

    - by Stephane
    Edit: This is a conceptual question first and foremost. I can make applications work without knowing this, but I'm trying to learn the concept. I've seen lots of videos with related classes and that makes sense, but when it comes to classes wrapping around other classes, I can't seem to grasp where things should be instantiated/passed around. =-=-=-=-=-=-= Question: Let's say I have a simple page that loads data from a table, manipulates the result and displays it. Simple. I'm going to use '=' for instantiating a class and '-' for passing a class in using constructor injection. It seems to me that the database has to be passed from one end of the application to the other which doesn't seem right. Here's how I would do it if I wanted to separate concerns: index =>Controller =>Model Layer =>Database =>DAO->Database I have this rule in my head that says I'm not supposed to create objects inside other objects. So what do I do with the Database? Or even the Model for that matter? I'm obviously missing something so basic about this. I would love a simplified example so that I can move forward in my code. I feel really hamstrung by this.

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  • Error while setting UserAcces permission for WebForms?

    - by ksg
    I've created a class named BaseClass.cs and I've written a function in its constructor. Here's how it looks public class BasePage:Page { public BasePage() { setUserPermission(); } private void setUserPermission() { String strPathAndQuery = HttpContext.Current.Request.Url.PathAndQuery; string strulr = strPathAndQuery.Replace("/SGERP/", "../"); Session["Url"] = strulr; GEN_FORMS clsForm = new GEN_FORMS(); clsForm.Form_Logical_Name = Session["Url"].ToString(); clsForm.User_ID = Convert.ToInt32(Session["User_ID"]); DataSet dsPermission = clsForm.RETREIVE_BUTTON_PERMISSIONS(); if (dsPermission.Tables.Count > 0) { if (dsPermission.Tables[1].Rows.Count > 0) { Can_Add = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Add"].ToString()); Can_Delete = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Delete"].ToString()); Can_Edit = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Edit"].ToString()); Can_Print = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Print"].ToString()); Can_View = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Print"].ToString()); } } } } I've inherited this class on my webform so that when the page loads, the setUserPermission function is executed. My webpage looks like this public partial class Setting_CompanyDetails : BasePage My problem is that I cannot access Session["Url"] in my BasePage. I'm getting the following error Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration. How can I solve this issue? Is this the right way to set UserPermission access?

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  • Determining an object's variable name dynamically?

    - by ZenBlender
    Let's say I have some objects: ArrayList<SomeObject> list = new ArrayList<SomeObject>(); SomeObject A = new SomeObject(); SomeObject B = new SomeObject(); SomeObject C = new SomeObject(); SomeObject D = new SomeObject(); These constructors automatically add each object to the ArrayList so I can iterate over them but still maintain the variable names for direct access: public SomeObject(){ // init stuff here list.add(this); } But then, let's say I want to output some debug info, and iterate through list and print out the NAME of each object? How can I do that? Essentially, when "SomeObject A = new SomeObject();" is executed, I want to use reflection (if possible) to determine that this variable's name is "A" (a String) and either store that in the object when the constructor executes, or determine it dynamically through reflection when referencing this object with the variable named "A". Does that make sense? How can I do this? Thanks!

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  • Can't see anything wrong with simple code

    - by melee
    Here is my implementation file: using namespace std; #include <iostream> #include <iomanip> #include <string> #include <stack> //line 5 #include "proj05.canvas.h" //----------------Constructor----------------// Canvas::Canvas() //line 10 { Title = ""; Nrow = 0; Ncol = 0; image[][]; // line 15 PixelCoordinates.r = 0; PixelCoordinates.c = 0; } //-------------------Paint------------------// line 20 void Canvas::Paint(int R, int C, char Color) { cout << "Paint to be implemented" << endl; } The errors I'm getting are these: proj05.canvas.cpp: In function 'std::istream& operator>>(std::istream&, Canvas&)': proj05.canvas.cpp:11: error: expected `;' before '{' token proj05.canvas.cpp:22: error: a function-definition is not allowed here before '{' token proj05.canvas.cpp:24: error: expected `}' at end of input proj05.canvas.cpp:24: error: expected `}' at end of input These seem like simple syntax errors, but I am not sure what's wrong. Could someone decode these for me? I'd really appreciate it, thanks for your time!

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  • C# XNA: What can cause SpriteBatch.End() to throw a NPE?

    - by Rosarch
    I don't understand what I'm doing wrong here: public void Draw(GameTime gameTime) // in ScreenManager { SpriteBatch.Begin(SpriteBlendMode.AlphaBlend); for (int i = 0; i < Screens.Count; i++) { if (Screens[i].State == Screen.ScreenState.HIDDEN) continue; Screens[i].Draw(gameTime); } SpriteBatch.End(); // null ref exception } SpriteBatch itself is not null. Some more context: public class MasterEngine : Microsoft.Xna.Framework.Game { public MasterEngine() { graphicsDeviceManager = new GraphicsDeviceManager(this); Components.Add(new GamerServicesComponent(this)); // ... spriteBatch = new SpriteBatch(graphicsDeviceManager.GraphicsDevice); screenManager = new ScreenManager(assets, gameEngine, graphicsDeviceManager.GraphicsDevice, spriteBatch); } //... protected override void Draw(GameTime gameTime) { screenManager.Draw(gameTime); // calls the problematic method base.Draw(gameTime); } } Am I failing to initialize something properly? UPDATE: As an experiment, I tried this to the constructor of MasterEngine: spriteBatch = new SpriteBatch(graphicsDeviceManager.GraphicsDevice); spriteBatch.Begin(); spriteBatch.DrawString(assets.GetAsset<SpriteFont>("calibri"), "ftw", new Vector2(), Color.White); spriteBatch.End(); This does not cause a NRE. hmm....

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  • Difference between std::result_of and decltype

    - by Luc Touraille
    I have some trouble understanding the need for std::result_of in C++0x. If I understood correctly, result_of is used to obtain the resulting type of invoking a function object with certain types of parameters. For example: template <typename F, typename Arg> typename std::result_of<F(Arg)> invoke(F f, Arg a) { return f(a); } I don't really see the difference with the following code: template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(f(a)) //uses the f parameter { return f(a); } or template <typename F, typename Arg> auto invoke(F f, Arg a) -> decltype(F()(a)); //"constructs" an F { return f(a); } The only problem I can see with these two solutions is that we need to either: have an instance of the functor to use it in the expression passed to decltype. know a defined constructor for the functor. Am I right in thinking that the only difference between decltype and result_of is that the first one needs an expression whereas the second does not?

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  • FileInput Help/Advice

    - by user559142
    I have a fileinput class. It has a string parameter in the constructor to load the filename supplied. However it just exits if the file doesn't exist. I would like it to output a message if the file doesn't exist - but not sure how.... Here is the class: public class FileInput extends Input { /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final String fileName) { try { scanner = new Scanner(new FileInputStream(fileName)); } catch (FileNotFoundException e) { System.err.println("File " + fileName + " could not be found."); System.exit(1); } } /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final FileInputStream fileStream) { super(fileStream); } } And its implementation: private void loadFamilyTree() { out.print("Enter file name: "); String fileName = in.nextLine(); FileInput input = new FileInput(fileName); family.load(input); input.close(); }

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  • Is it okay to violate the principle that collection properties should be readonly for performance?

    - by uriDium
    I used FxCop to analyze some code I had written. I had exposed a collection via a setter. I understand why this is not good. Changing the backing store when I don't expect it is a very bad idea. Here is my problem though. I retrieve a list of business objects from a Data Access Object. I then need to add that collection to another business class and I was doing it with the setter method. The reason I did this was that it is going to be faster to make an assignment than to insert hundreds of thousands of objects one at a time to the collection again via another addElement method. Is it okay to have a getter for a collection in some scenarios? I though of rather having a constructor which takes a collection? I thought maybe I could pass the object in to the Dao and let the Dao populate it directly? Are there any other better ideas?

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  • NHibernate Performance Optimization | Suggestions invited!!!

    - by user336749
    Hi, I’m facing an issue with NHibernate performance and can you please suggest me some optimizations? Below mentioned is a small summary of my application architecture I have a windows service which is listening to a messaging bus. On receiving a message the service creates an object out of which a property is the received xml snippet and saves the message to the DB (uses NH). There is a WPF UI with a readonly connection to the DB, and on refresh of the UI it displays the objects on the screen. While the UI does a refresh, it retrieves the xml and deserializes it , from which the object’s properties are derived and binded to the screen. For example assume an xml XXX is received by the service, it deserializes the xml , creates the book object and save it to the DB and a property/column is SCHEMA which contains the xml snippet. The UI while refreshed searches all book objects by ID and creates the book objects out of the xml which is being saved (yes, the xml is the constructor param). Now my issue is that the refresh takes more than 2 minutes to display say 50 book objects. I analyzed it using the NHibernate profiler, and found that the time spend within the DB is negligible, however time spent to create the entities is proportionally huge(10ms:1990 ms).I guess it’s due to the fairly huge size of xml snippet and it’s deserialization. My question is, how can I improve the performance. I dispose sessions after every refresh and is not lazy loading (please note that the time spend in DB is negligible). On every refresh it’s possible that all objects are updated by some downstream systems or maybe one of them are updated.Can I implement some sort of caching mechanism in this case? Thanks in advance for any suggestions. Regards, -Mike

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  • What to throw in a C++ class wrapping a C library ?

    - by ereOn
    I have to create a set of wrapping C++ classes around an existing C library. For many objects of the C library, the construction is done by calling something like britney_spears* create_britney_spears() and the opposite function void free_britney_spears(britney_spears* brit). If the allocation of a britney_spears fails, create_britney_spears() returns NULL. This is, as far as I know, a very common pattern. Now I want to wrap this inside a C++ class. //britney_spears.hpp class BritneySpears { public: BritneySpears(); private: boost::shared_ptr<britney_spears> m_britney_spears; }; And here is the implementation: // britney_spears.cpp BritneySpears::BritneySpears() : m_britney_spears(create_britney_spears(), free_britney_spears) { if (!m_britney_spears) { // Here I should throw something to abort the construction, but what ??! } } So the question is in the code sample: What should I throw to abort the constructor ? I know I can throw almost anything, but I want to know what is usually done. I have no other information about why the allocation failed. Should I create my own exception class ? Is there a std exception for such cases ? Many thanks.

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