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• Noob boost::bind member function callback question

  - by shaz

  #include <boost/bind.hpp> #include <iostream> using namespace std; using boost::bind; class A { public: void print(string &s) { cout << s.c_str() << endl; } }; typedef void (*callback)(); class B { public: void set_callback(callback cb) { m_cb = cb; } void do_callback() { m_cb(); } private: callback m_cb; }; void main() { A a; B b; string s("message"); b.set_callback(bind(A::print, &a, s)); b.do_callback(); } So what I'm trying to do is to have the print method of A stream "message" to cout when b's callback is activated. I'm getting an unexpected number of arguments error from msvc10. I'm sure this is super noob basic and I'm sorry in advance.

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• C# method generic params parameter bug?

  - by Mike M

  Hey, I appears to me as though there is a bug/inconsistency in the C# compiler. This works fine (first method gets called): public void SomeMethod(string message, object data); public void SomeMethod(string message, params object[] data); // .... SomeMethod("woohoo", item); Yet this causes "The call is ambiguous between the following methods" error: public void SomeMethod(string message, T data); public void SomeMethod(string message, params T[] data); // .... SomeMethod("woohoo", (T)item); I could just use the dump the first method entirely, but since this is a very performance sensitive library and the first method will be used about 75% of the time, I would rather not always wrap things in an array and instantiate an iterator to go over a foreach if there is only one item. Splitting into different named methods would be messy at best IMO. Thoughts?

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• Implementation/interface inheritance design question.

  - by Neil G

  I would like to get the stackoverflow community's opinion on the following three design patterns. The first is implementation inheritance; the second is interface inheritance; the third is a middle ground. My specific question is: Which is best? implementation inheritance: class Base { X x() const = 0; void UpdateX(A a) { y_ = g(a); } Y y_; } class Derived: Base { X x() const { return f(y_); } } interface inheritance: class Base { X x() const = 0; void UpdateX(A a) = 0; } class Derived: Base { X x() const { return x_; } void UpdateX(A a) { x_ = f(g(a)); } X x_; } middle ground: class Base { X x() const { return x_; } void UpdateX(A a) = 0; X x_; } class Derived: Base { void UpdateX(A a) { x_ = f(g(a)); } } I know that many people prefer interface inheritance to implementation inheritance. However, the advantage of the latter is that with a pointer to Base, x() can be inlined and the address of x_ can be statically calculated.

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• How can I make this client as a multithread client?

  - by Johanna

  Hi, I have read a lot about multithread client but for this one,I can not make it multithread! would you please help me? public class MainClient implements Runnable{ private static InformationClass info = new InformationClass(); private static Socket c; private static String text; public static String getText() { return text; } public static void setText(String text) { MainClient.text = text; } private static PrintWriter os; private static BufferedReader is; static boolean closed = false; /** * @param args the command line arguments */ public static void main(String[] args) { MainFrame farme = new MainFrame(); farme.setVisible(true); try { c = new Socket("localhost", 5050); os = new PrintWriter(c.getOutputStream(), true); is = new BufferedReader(new InputStreamReader(c.getInputStream())); } catch (UnknownHostException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } catch (IOException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } } public static void active() { String teXt = MainClient.getText(); System.out.println(teXt); os.println(teXt); try { String line = is.readLine(); System.out.println("Text received: " + line); os.flush(); is.close(); is.close(); c.close(); } catch (IOException ex) { Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex); } } } also active method will be called when the client write something on the text area and then clicks on the send button. 2) also i have a question that: in the other class I have this action performed for my send button,does it mean that client is multithread?? private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { new Thread(new Runnable() { @Override public void run() { // This gets run in a background thread String text = jTextArea1.getText(); jTextArea2.append(client.getCurrentName() + " : " + text + "\n"); MainClient.setText(client.getCurrentName() + " : " + text + "\n"); clear(); MainClient.active(); } }).start(); } Last EDIT: this is my active method: public static void active() { String teXt = MainClient.getText(); os.println(teXt); String line = is.readLine(); System.out.println("Text received: " + line); os.flush(); is.close(); is.close(); c.close(); }

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• How does the event dispatch thread work?

  - by Roman

  With the help of people on stackoverflow I was able to get the following working code of the simples GUI countdown (it just displays a window counting down seconds). My main problem with this code is the invokeLater stuff. As far as I understand the invokeLater send a task to the event dispatching thread (EDT) and then the EDT execute this task whenever it "can" (whatever it means). Is it right? To my understanding the code works like that: In the main method we use invokeLater to show the window (showGUI method). In other words, the code displaying the window will be executed in the EDT. In the main method we also start the counter and the counter (by construction) is executed in another thread (so it is not in the event dispatching thread). Right? The counter is executed in a separate thread and periodically it calls updateGUI. The updateGUI is supposed to update GUI. And GUI is working in the EDT. So, updateGUI should also be executed in the EDT. It is why the code for the updateGUI is inclosed in the invokeLater. Is it right? What is not clear to me is why we call the counter from the EDT. Anyway it is not executed in the EDT. It starts immediately a new thread and the counter is executed there. So, why we cannot call the counter in the main method after the invokeLater block? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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• Is it good to subclass a class only to separate some functional parts?

  - by prostynick

  Suppose we have abstract class A (all examples in C#) public abstract class A { private Foo foo; public A() { } public void DoSomethingUsingFoo() { //stuff } public void DoSomethingElseUsingFoo() { //stuff } //a lot of other stuff... } But we are able to split it into two classes A and B: public abstract class A { public A() { } //a lot of stuff... } public abstract class B : A { private Foo foo; public B() : base() { } public void DoSomethingUsingFoo() { //stuff } public void DoSomethingElseUsingFoo() { //stuff } //nothing else or just some overrides of A stuff } That's good, but we are 99.99% sure, that no one will ever subclass A, because functionality in B is very important. Is it still good to have two separate classes only to split some code into two parts and to separate functional elements?

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• Replicating Java's DecimalFormat in C#

  - by Frank Krueger

  I am trying to replicate a subset of Java's DecimalFormat class. Below is what I've come up with. Does this look right to everyone? public class DecimalFormat : NumberFormat { int _maximumFractionDigits; int _minimumFractionDigits; string _format; void RebuildFormat () { _format = "{0:0."; _format += new string ('0', _minimumFractionDigits); if (_maximumFractionDigits > _minimumFractionDigits) { _format += new string ('#', _maximumFractionDigits - _minimumFractionDigits); } _format += "}"; } public override string format (object value) { return string.Format (_format, value); } public override void setMaximumFractionDigits (int n) { _maximumFractionDigits = n; RebuildFormat (); } public override void setMinimumFractionDigits (int n) { _minimumFractionDigits = n; RebuildFormat (); } public override void setGroupingUsed (bool g) { } public static NumberFormat getInstance () { return new DecimalFormat (); } }

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• Assemblies mysteriously loaded into new AppDomains

  - by Eric

  I'm testing some code that does work whenever assemblies are loaded into an appdomain. For unit testing (in VS2k8's built-in test host) I spin up a new, uniquely-named appdomain prior to each test with the idea that it should be "clean": [TestInitialize()] public void CalledBeforeEachTestMethod() { AppDomainSetup appSetup = new AppDomainSetup(); appSetup.ApplicationBase = @"G:\<ProjectDir>\bin\Debug"; Evidence baseEvidence = AppDomain.CurrentDomain.Evidence; Evidence evidence = new Evidence( baseEvidence ); _testAppDomain = AppDomain.CreateDomain( "myAppDomain" + _appDomainCounter++, evidence, appSetup ); } [TestMethod] public void MissingFactoryCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadMissingRegistrationAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } [TestMethod] public void InvalidFactoryMethodCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadInvalidFactoriesAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } public class SupportingClass : MarshalByRefObject { public void LoadMissingRegistrationAssembly() { MissingRegistration.Main(); } public void LoadInvalidFactoriesAssembly() { InvalidFactories.Main(); } } If every test is run individually I find that it works correctly; the appdomain is created and has only the few intended assemblies loaded. However, if multiple tests are run in succession then each _testAppDomain already has assemblies loaded from all previous tests. Oddly enough, the two tests get appdomains with different names. The test assemblies that define MissingRegistration and InvalidFactories (two different assemblies) are never loaded into the unit test's default appdomain. Can anyone explain this behavior?

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• Is this a valid pattern for raising events in C#?

  - by Will Vousden

  Update: For the benefit of anyone reading this, since .NET 4, the lock is unnecessary due to changes in synchronization of auto-generated events, so I just use this now: public static void Raise<T>(this EventHandler<T> handler, object sender, T e) where T : EventArgs { if (handler != null) { handlerCopy(sender, e); } } And to raise it: SomeEvent.Raise(this, new FooEventArgs()); Having been reading one of Jon Skeet's articles on multithreading, I've tried to encapsulate the approach he advocates to raising an event in an extension method like so (with a similar generic version): public static void Raise(this EventHandler handler, object @lock, object sender, EventArgs e) { EventHandler handlerCopy; lock (@lock) { handlerCopy = handler; } if (handlerCopy != null) { handlerCopy(sender, e); } } This can then be called like so: protected virtual void OnSomeEvent(EventArgs e) { this.someEvent.Raise(this.eventLock, this, e); } Are there any problems with doing this? Also, I'm a little confused about the necessity of the lock in the first place. As I understand it, the delegate is copied in the example in the article to avoid the possibility of it changing (and becoming null) between the null check and the delegate call. However, I was under the impression that access/assignment of this kind is atomic, so why is the lock necessary? Update: With regards to Mark Simpson's comment below, I threw together a test: static class Program { private static Action foo; private static Action bar; private static Action test; static void Main(string[] args) { foo = () => Console.WriteLine("Foo"); bar = () => Console.WriteLine("Bar"); test += foo; test += bar; test.Test(); Console.ReadKey(true); } public static void Test(this Action action) { action(); test -= foo; Console.WriteLine(); action(); } } This outputs: Foo Bar Foo Bar This illustrates that the delegate parameter to the method (action) does not mirror the argument that was passed into it (test), which is kind of expected, I guess. My question is will this affect the validity of the lock in the context of my Raise extension method? Update: Here is the code I'm now using. It's not quite as elegant as I'd have liked, but it seems to work: public static void Raise<T>(this object sender, ref EventHandler<T> handler, object eventLock, T e) where T : EventArgs { EventHandler<T> copy; lock (eventLock) { copy = handler; } if (copy != null) { copy(sender, e); } }

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• Call to pop failing in my java code.

  - by Antony Kelt

  public void CardToPile() { waste.push(reserve.pop); }

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• Using a c# .net object in an Excel VBA form

  - by Mark O'G

  Hi I have a .net object that I want to use in Excel. I have an existing VBA script that i need to alter to call this the object from. I have then converted the object to a TLB. I've not really touched on this area before so any help will be appreciated. I have created an interface [Guid("0F700B48-E0CA-446b-B87E-555BCC317D74"),InterfaceType(ComInterfaceType.InterfaceIsDual)] public interface IOfficeCOMInterface { [DispId(1)] void ResetOrder(); [DispId(2)] void SetDeliveryAddress(string PostalName, string AddressLine1, string AddressLine2, string AddressLine3, string AddressLine4, string PostCode, string CountryCode, string TelephoneNo, string FaxNo, string EmailAddress); } I have also created an class that inherits that object. [ClassInterface(ClassInterfaceType.None), ProgId("NAMESPACE.OfficeCOMInterface"), Guid("9D9723F9-8CF1-4834-BE69-C3FEAAAAB530"), ComVisible(true)] public class OfficeCOMInterface : IOfficeCOMInterface, IDisposable { public void ResetSOPOrder() { } public void SetDeliveryAddress(string PostalName, string AddressLine1, string AddressLine2, string AddressLine3, string AddressLine4, string PostCode, string CountryCode, string TelephoneNo, string FaxNo, string EmailAddress) { try { SalesOrder.AmendDeliveryAddress(PostalName, AddressLine1, AddressLine2, AddressLine3, AddressLine4, PostCode); MessageBox.Show("Delivery address set"); } catch (Exception ex) { throw ex; } } }

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• Inject runtime exception to pthread sometime fails. How to fix that?

  - by lionbest

  I try to inject the exception to thread using signals, but some times the exception is not get caught. For example the following code: void _sigthrow(int sig) { throw runtime_error(strsignal(sig)); } struct sigaction sigthrow = {{&_sigthrow}}; void* thread1(void*) { sigaction(SIGINT,&sigthrow,NULL); try { while(1) usleep(1); } catch(exception &e) { cerr << "Thread1 catched " << e.what() << endl; } }; void* thread2(void*) { sigaction(SIGINT,&sigthrow,NULL); try { while(1); } catch(exception &e) { cerr << "Thread2 catched " << e.what() << endl; //never goes here } }; If I try to execute like: int main() { pthread_t p1,p2; pthread_create( &p1, NULL, &thread1, NULL ); pthread_create( &p2, NULL, &thread2, NULL ); sleep(1); pthread_kill( p1, SIGINT); pthread_kill( p2, SIGINT); sleep(1); return EXIT_SUCCESS; } I get the following output: Thread1 catched Interrupt terminate called after throwing an instance of 'std::runtime_error' what(): Interrupt Aborted How can I make second threat catch exception? Is there better idea about injecting exceptions?

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• Custom Memory Allocator for STL map

  - by Prasoon Tiwari

  This question is about construction of instances of custom allocator during insertion into a std::map. Here is a custom allocator for std::map<int,int> along with a small program that uses it: #include <stddef.h> #include <stdio.h> #include <map> #include <typeinfo> class MyPool { public: void * GetNext() { return malloc(24); } void Free(void *ptr) { free(ptr); } }; template<typename T> class MyPoolAlloc { public: static MyPool *pMyPool; typedef size_t size_type; typedef ptrdiff_t difference_type; typedef T* pointer; typedef const T* const_pointer; typedef T& reference; typedef const T& const_reference; typedef T value_type; template<typename X> struct rebind { typedef MyPoolAlloc<X> other; }; MyPoolAlloc() throw() { printf("-------Alloc--CONSTRUCTOR--------%08x %32s\n", this, typeid(T).name()); } MyPoolAlloc(const MyPoolAlloc&) throw() { printf(" Copy Constructor ---------------%08x %32s\n", this, typeid(T).name()); } template<typename X> MyPoolAlloc(const MyPoolAlloc<X>&) throw() { printf(" Construct T Alloc from X Alloc--%08x %32s %32s\n", this, typeid(T).name(), typeid(X).name()); } ~MyPoolAlloc() throw() { printf(" Destructor ---------------------%08x %32s\n", this, typeid(T).name()); }; pointer address(reference __x) const { return &__x; } const_pointer address(const_reference __x) const { return &__x; } pointer allocate(size_type __n, const void * hint = 0) { if (__n != 1) perror("MyPoolAlloc::allocate: __n is not 1.\n"); if (NULL == pMyPool) { pMyPool = new MyPool(); printf("======>Creating a new pool object.\n"); } return reinterpret_cast<T*>(pMyPool->GetNext()); } //__p is not permitted to be a null pointer void deallocate(pointer __p, size_type __n) { pMyPool->Free(reinterpret_cast<void *>(__p)); } size_type max_size() const throw() { return size_t(-1) / sizeof(T); } void construct(pointer __p, const T& __val) { printf("+++++++ %08x %s.\n", __p, typeid(T).name()); ::new(__p) T(__val); } void destroy(pointer __p) { printf("-+-+-+- %08x.\n", __p); __p->~T(); } }; template<typename T> inline bool operator==(const MyPoolAlloc<T>&, const MyPoolAlloc<T>&) { return true; } template<typename T> inline bool operator!=(const MyPoolAlloc<T>&, const MyPoolAlloc<T>&) { return false; } template<typename T> MyPool* MyPoolAlloc<T>::pMyPool = NULL; int main(int argc, char *argv[]) { std::map<int, int, std::less<int>, MyPoolAlloc<std::pair<const int,int> > > m; //random insertions in the map m.insert(std::pair<int,int>(1,2)); m[5] = 7; m[8] = 11; printf("======>End of map insertions.\n"); return 0; } Here is the output of this program: -------Alloc--CONSTRUCTOR--------bffcdaa6 St4pairIKiiE Construct T Alloc from X Alloc--bffcda77 St13_Rb_tree_nodeISt4pairIKiiEE St4pairIKiiE Copy Constructor ---------------bffcdad8 St13_Rb_tree_nodeISt4pairIKiiEE Destructor ---------------------bffcda77 St13_Rb_tree_nodeISt4pairIKiiEE Destructor ---------------------bffcdaa6 St4pairIKiiE ======Creating a new pool object. Construct T Alloc from X Alloc--bffcd9df St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE +++++++ 0985d028 St4pairIKiiE. Destructor ---------------------bffcd9df St4pairIKiiE Construct T Alloc from X Alloc--bffcd95f St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE +++++++ 0985d048 St4pairIKiiE. Destructor ---------------------bffcd95f St4pairIKiiE Construct T Alloc from X Alloc--bffcd95f St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE +++++++ 0985d068 St4pairIKiiE. Destructor ---------------------bffcd95f St4pairIKiiE ======End of map insertions. Construct T Alloc from X Alloc--bffcda23 St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE -+-+-+- 0985d068. Destructor ---------------------bffcda23 St4pairIKiiE Construct T Alloc from X Alloc--bffcda43 St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE -+-+-+- 0985d048. Destructor ---------------------bffcda43 St4pairIKiiE Construct T Alloc from X Alloc--bffcda43 St4pairIKiiE St13_Rb_tree_nodeISt4pairIKiiEE -+-+-+- 0985d028. Destructor ---------------------bffcda43 St4pairIKiiE Destructor ---------------------bffcdad8 St13_Rb_tree_nodeISt4pairIKiiEE Last two columns of the output show that an allocator for std::pair<const int, int> is constructed everytime there is a insertion into the map. Why is this necessary? Is there a way to suppress this? Thanks! Edit: This code tested on x86 machine with g++ version 4.1.2. If you wish to run it on a 64-bit machine, you'll have to change at least the line return malloc(24). Changing to return malloc(48) should work.

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• how do call a polymorphic function from an agnostic function?

  - by sds

  I have a method foo void foo (String x) { ... } void foo (Integer x) { ... } and I want to call it from a method which does not care about the argument: void bar (Iterable i) { ... for (Object x : i) foo(x); // this is the only time i is used ... } the code above complains that that foo(Object) is not defined and when I add void foo (Object x) { throw new Exception; } then bar(Iterable<String>) calls that instead of foo(String) and throws the exception. How do I avoid having two textually identical definitions of bar(Iterable<String>) and bar(Iterable<Integer>)? I thought I would be able to get away with something like <T> void bar (Iterable<T> i) { ... for (T x : i) foo(x); // this is the only time i is used ... } but then I get cannot find foo(T) error.

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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• c# multi inheritance

  - by user326839

  So ive got a base class which requires a Socket: class Sock { public Socket s; public Sock(Socket s) { this.s = s; } public virtual void Process(byte[] data) { } ... } then ive got another class. if a new socket gets accepted a new instance of this class will be created: class Game : Sock { public Random Random = new Random(); public Timerr Timers; public Test Test; public Game(Socket s) : base(s) { } public static void ReceiveNewSocket(object s) { Game Client = new Game((Socket)s); Client.Start(); } public override void Process(byte[] buf) { Timers = new Timerr(s); Test = new Test(s); Test.T(); } } in the Sock class ive got a virtual function that gets overwritten by the Game class.(Process function) in this function im calling a function from the Test Class(Test+ Timerr Class: class Test : Game { public Test(Socket s) : base(s) { } public void T() { Console.WriteLine(Random.Next(0, 10)); Timers.Start(); } } class Timerr : Game { public Timerr(Socket s) : base(s) { } public void Start() { Console.WriteLine("test"); } } ) So in the Process function im calling a function in Test. And in this function(T) i need to call a function from the Timerr Class.But the problem is its always NULL , although the constructor is called in Process. And e.g. the Random Class can be called, i guess its because its defined with the constructor.: public Random Random = new Random(); and thats why the other classes(without a constructor): public Timerr Timers; public Test Test; are always null in the inherited class Test.But its essentiel that i call other Methods of other classes in this function.How could i solve that?

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• 47 memory leaks. STL pointers.

  - by icelated

  I have a major amount of memory leaks. I know that the Sets have pointers and i cannot change that! I cannot change anything, but clean up the mess i have... I am creating memory with new in just about every function to add information to the sets. I have a Cd/ DVD/book: super classes of ITEM class and a library class.. In the library class i have 2 functions for cleaning up the sets.. Also, the CD, DVD, book destructors are not being called.. here is my potential leaks.. library.h #pragma once #include <ostream> #include <map> #include <set> #include <string> #include "Item.h" using namespace std; typedef set<Item*> ItemSet; typedef map<string,Item*> ItemMap; typedef map<string,ItemSet*> ItemSetMap; class Library { public: // general functions void addKeywordForItem(const Item* const item, const string& keyword); const ItemSet* itemsForKeyword(const string& keyword) const; void printItem(ostream& out, const Item* const item) const; // book-related functions const Item* addBook(const string& title, const string& author, int const nPages); const ItemSet* booksByAuthor(const string& author) const; const ItemSet* books() const; // music-related functions const Item* addMusicCD(const string& title, const string& band, const int nSongs); void addBandMember(const Item* const musicCD, const string& member); const ItemSet* musicByBand(const string& band) const; const ItemSet* musicByMusician(const string& musician) const; const ItemSet* musicCDs() const; // movie-related functions const Item* addMovieDVD(const string& title, const string& director, const int nScenes); void addCastMember(const Item* const movie, const string& member); const ItemSet* moviesByDirector(const string& director) const; const ItemSet* moviesByActor(const string& actor) const; const ItemSet* movies() const; ~Library(); void Purge(ItemSet &set); void Purge(ItemSetMap &map); }; here is some functions for adding info using new in library. Keep in mind i am cutting out alot of code to keep this post short. library.cpp #include "Library.h" #include "book.h" #include "cd.h" #include "dvd.h" #include <iostream> // general functions ItemSet allBooks; ItemSet allCDS; ItemSet allDVDs; ItemSetMap allBooksByAuthor; ItemSetMap allmoviesByDirector; ItemSetMap allmoviesByActor; ItemSetMap allMusicByBand; ItemSetMap allMusicByMusician; const ItemSet* Library::itemsForKeyword(const string& keyword) const { const StringSet* kw; ItemSet* obj = new ItemSet(); return obj; const Item* Library::addBook(const string& title, const string& author, const int nPages) { ItemSet* obj = new ItemSet(); Book* item = new Book(title,author,nPages); allBooks.insert(item); // add to set of all books obj->insert(item); return item; const Item* Library::addMusicCD(const string& title, const string& band, const int nSongs) { ItemSet* obj = new ItemSet(); CD* item = new CD(title,band,nSongs); return item; void Library::addBandMember(const Item* musicCD, const string& member) { ItemSet* obj = new ItemSet(); (((CD*) musicCD)->addBandMember(member)); obj->insert((CD*) musicCD); here is the library destructor..... Library::~Library() { Purge(allBooks); Purge(allCDS); Purge(allDVDs); Purge(allBooksByAuthor); Purge(allmoviesByDirector); Purge(allmoviesByActor); Purge(allMusicByBand); Purge(allMusicByMusician); } void Library::Purge(ItemSet &set) { for (ItemSet::iterator it = set.begin(); it != set.end(); ++it) delete *it; set.clear(); } void Library::Purge(ItemSetMap &map) { for (ItemSetMap::iterator it = map.begin(); it != map.end(); ++it) delete it->second; map.clear(); } so, basically item, cd, dvd class all have a set like this: typedef set<string> StringSet; class CD : public Item StringSet* music; and i am deleting it like: but those superclasses are not being called.. Item destructor is. CD::~CD() { delete music; } Do, i need a copy constructor? and how do i delete those objects i am creating in the library class? and how can i get the cd,dvd, destructor called? would the addbandmember function located in the library.cpp cause me to have a copy constructor? Any real help you can provide me to help me clean up this mess instead of telling me not to use pointers in my sets i would really appreciate. How can i delete the memory i am creating in those functions? I cannot delete them in the function!!

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• C++ 'ClassName Not Declared' Error

  - by Arjun Nayini

  I have this cpp file. dsets.cpp: #ifndef DSETS_CPP #define DSET_CPP //Adds elements to the DisjointSet data structure. This function adds //x unconnected roots to the end of the array. void DisjointSets::addelements(int x){ } //Given an int this function finds the root associated with that node. int DisjointSets::find(int x){ return 0; } //This function reorders the uptree in order to represent the union of two //subtrees void DisjointSets::setunion(int x, int y){ } #endif and this header file dsets.h: #ifndef DSETS_H #define DSET_H #include <iostream> #include <vector> using namespace std; class DisjointSets { public: void addelements(int x); int find(int x); void setunion(int x, int y); private: vector<int> x; }; #include "dsets.cpp" #endif And I keep getting an error that is saying that "DisjointSets has no been declared" ~ ~

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• breakpoint inside QComboBox subclass not working

  - by yan bellavance

  I have subclassed QComboBox to customize it for special needs. The subclass is used to promote QComboBoxes in a ui file from QtDesigner. Everything works except that when I put a break point in a slot, the program does not stop at the breakpoint. I do however know that it is being called from the result it generates. I checked other slots in my program and they work fine with breakpoints. Doing a clean and rebuild all did not fix it. What could be causing this and is there anything I can do about it? The slot in question is the only one in the subclass and is called "do_indexChanged()". You can find the slot on line 37 of the class header below and the signal-slot connection on line 10 of the class source file. CLASS HEADER: #ifndef WVQCOMBOBOX_H #define WVQCOMBOBOX_H #include <QWidget> #include <QObject> #include <QComboBox> #include <QVariant> class wvQComboBox : public QComboBox { Q_OBJECT //Q_PROPERTY(bool writeEnable READ writeEnable WRITE setWriteEnable) public: explicit wvQComboBox(QWidget *parent = 0); bool writeEnable() { return this->property("writeEnable").toBool(); } void setWriteEnable(const bool & writeEnable){ this->setProperty("writeEnable",writeEnable); } bool newValReady() { return this->property("newValReady").toBool(); } void setNewValReady(const bool & newValReady){ this->setProperty("newValReady",newValReady); } QString getNewVal(); int getNewValIndex(); int oldVal; //comboBox Index before user edit began private slots: void do_indexChanged(){ this->setWriteEnable(true); if(oldVal!=currentIndex()){ this->setNewValReady(true); oldVal=currentIndex(); } } protected: void focusInEvent ( QFocusEvent * event ); //void focusOutEvent ( QFocusEvent * event );//dont need because of currentIndexChanged(int) }; #endif // WVQCOMBOBOX_H #include "wvqcombobox.h" wvQComboBox::wvQComboBox(QWidget *parent) : QComboBox(parent) { this->setWriteEnable(true); this->setNewValReady(false); oldVal=this->currentIndex(); connect(this,SIGNAL(currentIndexChanged(int)),this,SLOT(do_indexChanged())); } void wvQComboBox::focusInEvent ( QFocusEvent * event ) { this->setWriteEnable(false); oldVal=this->currentIndex(); } QString wvQComboBox::getNewVal(){ setNewValReady(false); return this->currentText(); } int wvQComboBox::getNewValIndex(){ setNewValReady(false); return this->currentIndex(); }

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• How to invoke a delegate with a null parameter?

  - by Rodney Burton

  I get a null exception if I try to pass a null parameter to a delegate during an invoke. Here's what the code looks like: public void RequestPhoto() { WCF.Service.BeginGetUserPhoto(Contact.UserID, new AsyncCallback(RequestPhotoCB), null); } public void RequestPhotoCB(IAsyncResult result) { var photo = WCF.Service.EndGetUserPhoto(result); UpdatePhoto(photo); } public delegate void UpdatePhotoDelegate(Binary photo); public void UpdatePhoto(Binary photo) { if (InvokeRequired) { var d = new UpdatePhotoDelegate(UpdatePhoto); Invoke(d, new object[] { photo }); } else { var ms = new MemoryStream(photo.ToArray()); var bmp = new Bitmap(ms); pbPhoto.BackgroundImage = bmp; } } The problem is with the line: Invoke(d, new object[] { photo }); If the variable "photo" is null. What is the correct way to pass a null parameter during an invoke? Thanks!

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• Abstract base class puzzle

  - by 0x80

  In my class design I ran into the following problem: class MyData { int foo; }; class AbstraktA { public: virtual void A() = 0; }; class AbstraktB : public AbstraktA { public: virtual void B() = 0; }; template<class T> class ImplA : public AbstraktA { public: void A(){ cout << "ImplA A()"; } }; class ImplB : public ImplA<MyData>, public AbstraktB { public: void B(){ cout << "ImplB B()"; } }; void TestAbstrakt() { AbstraktB *b = (AbstraktB *) new ImplB; b->A(); b->B(); }; The problem with the code above is that the compiler will complain that AbstraktA::A() is not defined. Interface A is shared by multiple objects. But the implementation of A is dependent on the template argument. Interface B is the seen by the outside world, and needs to be abstrakt. The reason I would like this is that it would allow me to define object C like this: Define the interface C inheriting from abstrakt A. Define the implementation of C using a different datatype for template A. I hope I'm clear. Is there any way to do this, or do I need to rethink my design?

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• Castle, sharing a transient component between a decorator and a decorated component

  - by Marius

  Consider the following example: public interface ITask { void Execute(); } public class LoggingTaskRunner : ITask { private readonly ITask _taskToDecorate; private readonly MessageBuffer _messageBuffer; public LoggingTaskRunner(ITask taskToDecorate, MessageBuffer messageBuffer) { _taskToDecorate = taskToDecorate; _messageBuffer = messageBuffer; } public void Execute() { _taskToDecorate.Execute(); Log(_messageBuffer); } private void Log(MessageBuffer messageBuffer) {} } public class TaskRunner : ITask { public TaskRunner(MessageBuffer messageBuffer) { } public void Execute() { } } public class MessageBuffer { } public class Configuration { public void Configure() { IWindsorContainer container = null; container.Register( Component.For<MessageBuffer>() .LifeStyle.Transient); container.Register( Component.For<ITask>() .ImplementedBy<LoggingTaskRunner>() .ServiceOverrides(ServiceOverride.ForKey("taskToDecorate").Eq("task.to.decorate"))); container.Register( Component.For<ITask>() .ImplementedBy<TaskRunner>() .Named("task.to.decorate")); } } How can I make Windsor instantiate the "shared" transient component so that both "Decorator" and "Decorated" gets the same instance? Edit: since the design is being critiqued I am posting something closer to what is being done in the app. Maybe someone can suggest a better solution (if sharing the transient resource between a logger and the true task is considered a bad design)

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• Should methods that are required to be executed in a specific order be private?

  - by TooFat

  I have a Class that retrieves some data and images does some stuff to them and them uploads them to a third party app using web services. The object needs to perform some specific steps in order. My question is should I be explicitly exposing each method publicly like so. myObject obj = new myObject(); obj.RetrieveImages(); obj.RetrieveAssociatedData(); obj.LogIntoThirdPartyWebService(); obj.UploadStuffToWebService(); or should all of these methods be private and encapsulated in a single public method like so. public class myObject() { private void RetrieveImages(){}; private void RetrieveAssociatedData(){}; private void LogIntoThirdPartyWebService(){}; private void UploadStuffToWebService(){}; public void DoStuff() { this.RetrieveImages(); this.RetrieveAssociatedData(); this.LogIntoThirdPartyWebService(); this.UploadStuffToWebService(); } } which is called like so. myObject obj = new myObject(); obj.DoStuff();

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• How do I define a template class and divide it into multiple files?

  - by hkBattousai

  I have written a simple template class for test purpose. It compiles without any errors, but when I try to use it in main(), it give some linker errors. main.cpp #include <iostream> #include "MyNumber.h" int wmain(int argc, wchar_t * argv[]) { MyNumber<float> num; num.SetValue(3.14); std::cout << "My number is " << num.GetValue() << "." << std::endl; system("pause"); return 0; } MyNumber.h #pragma once template <class T> class MyNumber { public: MyNumber(); ~MyNumber(); void SetValue(T val); T GetValue(); private: T m_Number; }; MyNumber.cpp #include "MyNumber.h" template <class T> MyNumber<T>::MyNumber() { m_Number = static_cast<T>(0); } template <class T> MyNumber<T>::~MyNumber() { } template <class T> void MyNumber<T>::SetValue(T val) { m_Number = val; } template <class T> T MyNumber<T>::GetValue() { return m_Number; } When I build this code, I get the following linker errors: Error 7 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\X64\Debug\Console Demo.exe 1 error LNK1120: 4 unresolved externals Error 3 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: __cdecl MyNumber::~MyNumber(void)" (??1?$MyNumber@M@@QEAA@XZ) referenced in function wmain Error 6 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: __cdecl MyNumber::MyNumber(void)" (??0?$MyNumber@M@@QEAA@XZ) referenced in function wmain Error 4 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: float __cdecl MyNumber::GetValue(void)" (?GetValue@?$MyNumber@M@@QEAAMXZ) referenced in function wmain Error 5 Console Demo C:\Development\IDE\Visual Studio 2010\SAVE\Grand Solution\Console Demo\main.obj error LNK2019: unresolved external symbol "public: void __cdecl MyNumber::SetValue(float)" (?SetValue@?$MyNumber@M@@QEAAXM@Z) referenced in function wmain But, if I leave main() empty, I don't get any linker errors. What is wrong with my template class? What am I doing wrong?

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• [C] Texture management / pointer question

  - by ndg

  I'm working on a texture management and animation solution for a small side project of mine. Although the project uses Allegro for rendering and input, my question mostly revolves around C and memory management. I wanted to post it here to get thoughts and insight into the approach, as I'm terrible when it comes to pointers. Essentially what I'm trying to do is load all of my texture resources into a central manager (textureManager) - which is essentially an array of structs containing ALLEGRO_BITMAP objects. The textures stored within the textureManager are mostly full sprite sheets. From there, I have an anim(ation) struct, which contains animation-specific information (along with a pointer to the corresponding texture within the textureManager). To give you an idea, here's how I setup and play the players 'walk' animation: createAnimation(&player.animations[0], "media/characters/player/walk.png", player.w, player.h); playAnimation(&player.animations[0], 10); Rendering the animations current frame is just a case of blitting a specific region of the sprite sheet stored in textureManager. For reference, here's the code for anim.h and anim.c. I'm sure what I'm doing here is probably a terrible approach for a number of reasons. I'd like to hear about them! Am I opening myself to any pitfalls? Will this work as I'm hoping? anim.h #ifndef ANIM_H #define ANIM_H #define ANIM_MAX_FRAMES 10 #define MAX_TEXTURES 50 struct texture { bool active; ALLEGRO_BITMAP *bmp; }; struct texture textureManager[MAX_TEXTURES]; typedef struct tAnim { ALLEGRO_BITMAP **sprite; int w, h; int curFrame, numFrames, frameCount; float delay; } anim; void setupTextureManager(void); int addTexture(char *filename); int createAnimation(anim *a, char *filename, int w, int h); void playAnimation(anim *a, float delay); void updateAnimation(anim *a); #endif anim.c void setupTextureManager() { int i = 0; for(i = 0; i < MAX_TEXTURES; i++) { textureManager[i].active = false; } } int addTextureToManager(char *filename) { int i = 0; for(i = 0; i < MAX_TEXTURES; i++) { if(!textureManager[i].active) { textureManager[i].bmp = al_load_bitmap(filename); textureManager[i].active = true; if(!textureManager[i].bmp) { printf("Error loading texture: %s", filename); return -1; } return i; } } return -1; } int createAnimation(anim *a, char *filename, int w, int h) { int textureId = addTextureToManager(filename); if(textureId > -1) { a->sprite = textureManager[textureId].bmp; a->w = w; a->h = h; a->numFrames = al_get_bitmap_width(a->sprite) / w; printf("Animation loaded with %i frames, given resource id: %i\n", a->numFrames, textureId); } else { printf("Texture manager full\n"); return 1; } return 0; } void playAnimation(anim *a, float delay) { a->curFrame = 0; a->frameCount = 0; a->delay = delay; } void updateAnimation(anim *a) { a->frameCount ++; if(a->frameCount >= a->delay) { a->frameCount = 0; a->curFrame ++; if(a->curFrame >= a->numFrames) { a->curFrame = 0; } } }

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