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  • Why cant we create Object if constructor is in private section?

    - by Abhi
    Dear all I want to know why cant we create object if the constructor is in private section. I know that if i make a method static i can call that method using <classname> :: <methodname(...)>; But why cant we create object is my doubt... I also know if my method is not static then also i can call function by the following... class A { A(); public: void fun1(); void fun2(); void fun3(); }; int main() { A *obj =(A*)malloc(sizeof(A)); //Here we can't use new A() because constructor is in private //but we can use malloc with it, but it will not call the constructor //and hence it is harmful because object may not be in usable state. obj->fun1(); obj->fun2(); obj->fun3(); } So only doubt is why cant we create object when constructor is in private section? Thanks in advance

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  • Java Variable Initialization

    - by Samuel Brainard
    Here's a piece of code I wrote. public class cube { private int length; private int breadth; private int height; private int volume; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ volume=length*breadth*height; System.out.println("The Volume of the cube is "+this.volume); So if I implement the above cube class like this, public class cubeApp { public static void main(String[] args){ cube mycube = new cube(5,6,9,2); mycube.volumeShow(); I get an output that tells me Volume is 270. But I get an output that says Volume is 0 if I define the volume variable like this: public class cube { private int length; private int breadth; private int height; private int volume=length*breadth*height; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ System.out.println("The Volume of the cube is "+this.volume); Can somebody please explain why this is happening? Thanks, Samuel.

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  • Changing type of object in a conditional

    - by David Doria
    I'm having a bit of trouble with dynamic_casting. I need to determine at runtime the type of an object. Here is a demo: include include class PersonClass { public: std::string Name; virtual void test(){}; //it is annoying that this has to be here... }; class LawyerClass : public PersonClass { public: void GoToCourt(){}; }; class DoctorClass : public PersonClass { public: void GoToSurgery(){}; }; int main(int argc, char *argv[]) { PersonClass* person = new PersonClass; if(true) { person = dynamic_cast(person); } else { person = dynamic_cast(person); } person-GoToCourt(); return 0; } I would like to do the above. The only legal way I found to do it is to define all of the objects before hand: PersonClass* person = new PersonClass; LawyerClass* lawyer; DoctorClass* doctor; if(true) { lawyer = dynamic_cast(person); } else { doctor = dynamic_cast(person); } if(true) { lawyer-GoToCourt(); } The main problem with this (besides having to define a bunch of objects that won't be use) is that I have to change the name of the 'person' variable. Is there a better way? (I am not allowed to change any of the classes (Person, Lawyer, or Doctor) because they are part of a library that people who will use my code have and won't want to change). Thanks, Dave

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  • Checking if a function has C-linkage at compile-time

    - by scjohnno
    Is there any way to check if a given function is declared with C-linkage (that is, with extern "C") at compile-time? I am developing a plugin system. Each plugin can supply factory functions to the plugin-loading code. However, this has to be done via name (and subsequent use of GetProcAddress or dlsym). This requires that the functions be declared with C-linkage so as to prevent name-mangling. It would be nice to be able to throw a compiler error if the referred-to function is declared with C++-linkage (as opposed to finding out at runtime when a function with that name does not exist). Here's a simplified example of what I mean: extern "C" void my_func() { } void my_other_func() { } // Replace this struct with one that actually works template<typename T> struct is_c_linkage { static const bool value = true; }; template<typename T> void assertCLinkage(T *func) { static_assert(is_c_linkage<T>::value, "Supplied function does not have C-linkage"); } int main() { assertCLinkage(my_func); // Should compile assertCLinkage(my_other_func); // Should NOT compile } Thanks.

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  • C++ variable to const expression

    - by user1344784
    template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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  • XNA: What can cause SpriteBatch.End() to throw a NRE?

    - 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.... UPDATE 2: This does cause an NRE: protected override void Draw(GameTime gameTime) { spriteBatch.Begin(); spriteBatch.End(); // boned here //screenManager.Draw(gameTime); base.Draw(gameTime); }

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  • C++ iterator and const_iterator problem for own container class

    - by BaCh
    Hi there, I'm writing an own container class and have run into a problem I can't get my head around. Here's the bare-bone sample that shows the problem. It consists of a container class and two test classes: one test class using a std:vector which compiles nicely and the second test class which tries to use my own container class in exact the same way but fails miserably to compile. #include <vector> #include <algorithm> #include <iterator> using namespace std; template <typename T> class MyContainer { public: class iterator { public: typedef iterator self_type; inline iterator() { } }; class const_iterator { public: typedef const_iterator self_type; inline const_iterator() { } }; iterator begin() { return iterator(); } const_iterator begin() const { return const_iterator(); } }; // This one compiles ok, using std::vector class TestClassVector { public: void test() { vector<int>::const_iterator I=myc.begin(); } private: vector<int> myc; }; // this one fails to compile. Why? class TestClassMyContainer { public: void test(){ MyContainer<int>::const_iterator I=myc.begin(); } private: MyContainer<int> myc; }; int main(int argc, char ** argv) { return 0; } gcc tells me: test2.C: In member function ‘void TestClassMyContainer::test()’: test2.C:51: error: conversion from ‘MyContainer::iterator’ to non-scalar type ‘MyContainer::const_iterator’ requested I'm not sure where and why the compiler wants to convert an iterator to a const_iterator for my own class but not for the STL vector class. What am I doing wrong?

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  • Does Interlocked guarantee visibility to other threads in C# or do I still have to use volatile?

    - by Lirik
    I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Interlocked. This is needed in scenarios where other libraries, interfaces or hardware can access your variable and update it anytime, or need the most recent version. Does Interlocked guarantee visibility of the atomic operation to all threads, or do I still have to use the volatile keyword on the value in order to guarantee visibility of the change? Here is my example: public class CountDownLatch { private volatile int m_remain; // <--- do I need the volatile keyword there since I'm using Interlocked? private EventWaitHandle m_event; public CountDownLatch (int count) { Reset(count); } public void Reset(int count) { if (count < 0) throw new ArgumentOutOfRangeException(); m_remain = count; m_event = new ManualResetEvent(false); if (m_remain == 0) { m_event.Set(); } } public void Signal() { // The last thread to signal also sets the event. if (Interlocked.Decrement(ref m_remain) == 0) m_event.Set(); } public void Wait() { m_event.WaitOne(); } }

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  • Is there a better way to throttle a high throughput job?

    - by ChaosPandion
    I created a simple class that shows what I am trying to do without any noise. Feel free to bash away at my code. That's why I posted it here. public class Throttled : IDisposable { private readonly Action work; private readonly Func<bool> stop; private readonly ManualResetEvent continueProcessing; private readonly Timer throttleTimer; private readonly int throttlePeriod; private readonly int throttleLimit; private int totalProcessed; public Throttled(Action work, Func<bool> stop, int throttlePeriod, int throttleLimit) { this.work = work; this.stop = stop; this.throttlePeriod = throttlePeriod; this.throttleLimit = throttleLimit; continueProcessing = new ManualResetEvent(true); throttleTimer = new Timer(ThrottleUpdate, null, throttlePeriod, throttlePeriod); } public void Dispose() { throttleTimer.Dispose(); ((IDisposable)continueProcessing).Dispose(); } public void Execute() { while (!stop()) { if (Interlocked.Increment(ref totalProcessed) > throttleLimit) { lock (continueProcessing) { continueProcessing.Reset(); } if (!continueProcessing.WaitOne(throttlePeriod)) { throw new TimeoutException(); } } work(); } } private void ThrottleUpdate(object state) { Interlocked.Exchange(ref totalProcessed, 0); lock (continueProcessing) { continueProcessing.Set(); } } }

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  • Double Linked List header node keeps returning first value as 0

    - by Craig
    I will preface to say that this is my first question. I am currently getting my Masters degree in Information Security and I had to take C++ programming this semester. So this is homework related. I am not looking for you to answer my homework but I am running into a peculiar situation. I have created the program to work with a doubly linked list and everything works fine. However when I have the user create a list of values the first node keeps returning 0. I have tried finding some reading on this and I cannot locate any reference to it. My question is then is the header node(first node) always going to be zero? Or am I doing something wrong. case: 'C': cout<<"Please enter a list:"<<endl; while(n!=-999){ myList.insert(n); cin>> n;} break; I now enter: 12321, 1234,64564,346346. The results in 0, 12321, 1234, 64564,346346. Is this what should happen or am I doing something wrong? Also as this is my first post please feel free to criticize or teach me how to color code the keywords. Anyway this is a homework assignment so I am only looking for guidance and constructive criticism. Thank you all in advance So I cannot figure out the comment sections on this forum so I will edit the original post The first section is the constructor code: template <class Type> doublyLinkedList<Type>::doublyLinkedList() { first= NULL; last = NULL; count = 0; } Then there is my insert function : template <class Type> void doublyLinkedList<Type>::insert(const Type& insertItem) { nodeType<Type> *current; //pointer to traverse the list nodeType<Type> *trailCurrent; //pointer just before current nodeType<Type> *newNode; //pointer to create a node bool found; newNode = new nodeType<Type>; //create the node newNode->info = insertItem; //store the new item in the node newNode->next = NULL; newNode->back = NULL; if(first == NULL) //if the list is empty, newNode is //the only node { first = newNode; last = newNode; count++; } else { found = false; current = first; while (current != NULL && !found) //search the list if (current->info >= insertItem) found = true; else { trailCurrent = current; current = current->next; } if (current == first) //insert newNode before first { first->back = newNode; newNode->next = first; first = newNode; count++; } else { //insert newNode between trailCurrent and current if (current != NULL) { trailCurrent->next = newNode; newNode->back = trailCurrent; newNode->next = current; current->back = newNode; } else { trailCurrent->next = newNode; newNode->back = trailCurrent; last = newNode; } count++; }//end else }//end else }//end Then I have an initialization function too: template <class Type> void doublyLinkedList<Type>::initializeList() { destroy(); } Did I miss anything?

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  • Automatically converting an A* into a B*

    - by Xavier Nodet
    Hi, Suppose I'm given a class A. I would like to wrap pointers to it into a small class B, some kind of smart pointer, with the constraint that a B* is automatically converted to an A* so that I don't need to rewrite the code that already uses A*. I would therefore want to modify B so that the following compiles... struct A { void foo() {} }; template <class K> struct B { B(K* k) : _k(k) {} //operator K*() {return _k;} //K* operator->() {return _k;} private: K* _k; }; void doSomething(A*) {} void test() { A a; A* pointer_to_a (&a); B<A> b (pointer_to_a); //b->foo(); // I don't need those two... //doSomething(b); B<A>* pointer_to_b (&b); pointer_to_b->foo(); // 'foo' : is not a member of 'B<K>' doSomething(pointer_to_b); // 'doSomething' : cannot convert parameter 1 from 'B<K> *' to 'A *' } Note that B inheriting from A is not an option (instances of A are created in factories out of my control)... Is it possible? Thanks.

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  • threading and getting COM port of attached phone

    - by I__
    i have the following code: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Threading; namespace WindowsFormsApplication1 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } public class ThreadWork { public static void DoWork() { } } private void Form1_Load(object sender, EventArgs e) { ThreadStart myThreadDelegate = new ThreadStart(ThreadWork.DoWork); Thread myThread = new Thread(myThreadDelegate); myThread.Start(); // Begin communications serialPort1.Open(); serialPort1.Write("AT+CMGF=1\r\n"); //Thread.Sleep(500); serialPort1.Write("AT+CNMI=2,2\r\n"); //Thread.Sleep(500); serialPort1.Write("AT+CSCA=\"+4790002100\"\r\n"); //Thread.Sleep(500); } private void serialPort1_DataReceived_1(object sender, System.IO.Ports.SerialDataReceivedEventArgs e) { string response = serialPort1.ReadLine(); this.BeginInvoke(new MethodInvoker(() => textBox1.AppendText(response + "\r\n"))); } } } what i am trying to do is send AT COMMANDS to my phone which is attached to the computer through USB how do i know how to configure the properties of the serial port? (like which COM is the phone on [it's attached through USB], what about baudrate and databits?) when i run the program nothing really happens, i would like to send AT COMMANDS to my phone and the textbox is there to receive the response from my phone this is my first time using threads. am i using them correctly? what is the purpose of it in the current example? is it to just have a delay between send a response? what am i doing wrong?

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  • Java: over-typed structures?

    - by HH
    Term over-type structure = a data structure that accepts different types, can be primitive or user-defined. I think ruby supports many types in structures such as tables. I tried a table with types 'String', 'char' and 'File' in Java but errs. How can I have over-typed structure in Java? How to show types in declaration? What about in initilization? Suppose a structure: INDEX VAR FILETYPE //0 -> file FILE //1 -> lineMap SizeSequence //2 -> type char //3 -> binary boolean //4 -> name String //5 -> path String Code import java.io.*; import java.util.*; public class Object { public static void print(char a) { System.out.println(a); } public static void print(String s) { System.out.println(s); } public static void main(String[] args) { Object[] d = new Object[6]; d[0] = new File("."); d[2] = 'T'; d[4] = "."; print(d[2]); print(d[4]); } } Errors Object.java:18: incompatible types found : java.io.File required: Object d[0] = new File("."); ^ Object.java:19: incompatible types found : char required: Object d[2] = 'T'; ^

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  • C++ ambiguous template instantiation

    - by aaa
    the following gives me ambiguous template instantiation with nvcc (combination of EDG front-end and g++). Is it really ambiguous, or is compiler wrong? I also post workaround à la boost::enable_if template<typename T> struct disable_if_serial { typedef void type; }; template<> struct disable_if_serial<serial_tag> { }; template<int M, int N, typename T> __device__ //static typename disable_if_serial<T>::type void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const T &thread) { // ... } template<size_t M, size_t N> __device__ static void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const serial_tag&) { for (size_t i = 0; i < M; ++i) add_evaluate_polynomial1(R, C, x, i); } // ambiguous template instantiation here. add_evaluate_polynomial1(R, C, x, serial_tag());

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  • why i change the alpha value of UIImageView but no effect?

    - by chancy
    I am working on a reader app. when you read one magazine, it will display first five pages and download the rest pages one by one. there is a scrollview to view the thumbnail image of pages. At the beginning, if the page needs downloading, the corresponding thumbnail view's alpha value is set to 0.5. when the page is downloaded, i will update the thumbnail view's value to 1.0. I use one operation to download the page, and when one is downloaded i use delegate to set thumbnail view's alpha. But when i update thumbnail view's alpha value, it still the same as the beginning. it seems the alpha has no effect. I wonder is there anything wrong with my code? some snippets are as follows: In the PageViewController.m - (void)downloadPages { DownloadOperation *op = [[DownloadOperation alloc] initWithMagazine:magazine]; op.delegate = self; [[(AppDelegate *)[[UIApplication sharedApplication] delegate] sharedOperationQueue] addOperation:op]; } - (void)downloadOperation:(DownloadOperation *)operation finishedAtIndex:(NSUInteger)index { if (thumbScrollView){ [thumbScrollView viewWithTag:THUMBVIEW_OFFSET+index].alpha = 1.0; } } In DownloadOperation.m - (void)main { // ... NSUInteger index = 0; for (Page *page in mMagazine.pages) { if (/*page doesn't exist*/){ // download the page; if ([delegate respondsToSelector:@selector(downloadOperation:finishedAtIndex:)]) { [delegate downloadOperation:self finishedAtIndex:index]; } } index++; } }

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  • Specializing function templates outside class temp. definition - what is the correct way of doing t

    - by LoudNPossiblyRight
    I am attempting to specialize a function template that is a member of a template class. The two of them have different template parameters. The template function specialization inside the temp. class definition is never called and the one func. spec. outside the class definition does not even compile. Should i expect this to work in the first place, and if so, what do i have to change in this code to both compile and make it work correctly: using VS2010 #include<iostream> using namespace std; template <typename T> class klass{ public: template <typename U> void func(const U &u){ cout << "I AM A TEMPLATE FUNC" << endl; } //THIS NEVER GETS CALLED !!! template <> void klass<T>::func(const string &s){ cout << "I AM A STRING SPECIALIST" << endl; } }; //THIS SPECIALIZATION WILL NOT COMPILE !!! template <typename T> template <> void klass<T>::func(const double &s){ cout << "I AM A DOUBLE SPECIALIST" << endl; } int main(){ double d = 3.14159265; klass<int> k; k.func(1234567890); k.func("string"); k.func(3.14159265); return 0; }

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  • Can foreground threads be aborted on application shutdown in C#.Net?

    - by Cartman
    I inherited a c# winforms app (.NET 2.0) which creates a thread upon startup in a singleton class. This thread handles messages from a messaging topic (Tibco EMS). When the app is shutdown, the thread doesn't remain the the background? How is this possible? Is there something else happening that can abort this thread? Code snippet: public class Startup { public static void main(string [] args) { MySingletonClass.Instance.Init(); // do other things below Application.Run(new MainForm()); } public class MySingletonClass { // singleton code //.. //.. private Thread t; public void Init() { t = new Thread(new ThreadStart(poll)); } private void poll() { while(true} { // listen for messages and process but there is no break clause // exceptions are also handled within to ensure control doesnt go out } } Pls. don't write to tell me this is bad code. I know it and i was going to refactor it when i realised that the app actually shutdowns correctly inspite of this aberration. So i want to understand how this is possible. Thanks for your help

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  • How to draw mutiple rectangles using c#

    - by Nivas
    I have drawn and saved the Rectangle on the image i loaded in the picture box. How i like to draw multiple rectangles for that i tried array in the rectangle but it gives error ("Object reference not set to an instance of an object." (Null reference Exception was unhandled). enter code here private void pictureBox1_MouseDown(object sender, MouseEventArgs e) { if (mybitmap == null) { mybitmap = new Bitmap(sz.Width, sz.Height); } rect = new Rectangle(e.X, e.Y, 0, 0); this.Invalidate(); } private void pictureBox1_MouseMove(object sender, MouseEventArgs e) { if (stayToolStripMenuItem.Checked == true) { switch (e.Button) { case MouseButtons.Left: { rect = new Rectangle(rect.Left, rect.Top, e.X - rect.Left, e.Y - rect.Top); pictureBox1.Invalidate(); break; } } } } private void pictureBox1_Paint(object sender, PaintEventArgs e) { if (stayToolStripMenuItem.Checked == true) { button1.Visible = true; button2.Visible = true; if (mybitmap == null) { return; } using (g = Graphics.FromImage(mybitmap)) { using (Pen pen = new Pen(Color.Red, 2)) { //g.Clear(Color.Transparent); e.Graphics.DrawRectangle(pen, rect); label1.Top = rect.Top; label1.Left = rect.Left; label1.Width = rect.Width; label1.Height = rect.Height; if (label1.TextAlign == ContentAlignment.TopLeft) { e.Graphics.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawRectangle(pen, rect); } } } } } How can i do this.....

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  • c# threading and getting COM port of attached phone

    - by I__
    i have the following code: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Threading; namespace WindowsFormsApplication1 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } public class ThreadWork { public static void DoWork() { } } private void Form1_Load(object sender, EventArgs e) { ThreadStart myThreadDelegate = new ThreadStart(ThreadWork.DoWork); Thread myThread = new Thread(myThreadDelegate); myThread.Start(); // Begin communications serialPort1.Open(); serialPort1.Write("AT+CMGF=1\r\n"); //Thread.Sleep(500); serialPort1.Write("AT+CNMI=2,2\r\n"); //Thread.Sleep(500); serialPort1.Write("AT+CSCA=\"+4790002100\"\r\n"); //Thread.Sleep(500); } private void serialPort1_DataReceived_1(object sender, System.IO.Ports.SerialDataReceivedEventArgs e) { string response = serialPort1.ReadLine(); this.BeginInvoke(new MethodInvoker(() => textBox1.AppendText(response + "\r\n"))); } } } what i am trying to do is send AT COMMANDS to my phone which is attached to the computer through USB how do i know how to configure the properties of the serial port? (like which COM is the phone on [it's attached through USB], what about baudrate and databits?) when i run the program nothing really happens, i would like to send AT COMMANDS to my phone and the textbox is there to receive the response from my phone this is my first time using threads. am i using them correctly? what is the purpose of it in the current example? is it to just have a delay between send a response? what am i doing wrong?

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  • Accessing Instance Variables from NSTimer selector

    - by Timbo
    Firstly newbie question: What's the difference between a selector and a method? Secondly newbie question (who would have thought): I need to loop some code based on instance variables and pause between loops until some condition (of course based on instance variables) is met. I've looked at sleep, I've looked at NSThread. In both discussions working through those options many asked why don't I use NSTimer, so here I am. Ok so it's simple enough to get a method (selector? ) to fire on a schedule. Problem I have is that I don't know how to see instance variables I've set up outside the timer from within the code NSTimer fires. I need to see those variables from the NSTimer selector code as I 1) will be updating their values and 2) will set labels based on those values. Here's some code that shows the concept… eventually I'd invalidate the timers based on myVariable too, however I've excluded that for code clarity. MyClass *aMyClassInstance = [MyClass new]; [aMyClassInstance setMyVariable:0]; [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(doStuff) userInfo:nil repeats:YES]; [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(doSomeOtherStuff) userInfo:nil repeats:YES]; - (void) doStuff { [aMyClassInstance setMyVariable:11]; // don't actually have access to set aMyClassInstance.myVariable [self updateSomeUILabel:[NSNumber numberWithInt:aMyClassInstance.myVariable]]; // don't actually have access to aMyClassInstance.myVariable } - (void) doSomeOtherStuff { [aMyClassInstance setMyVariable:22]; // don't actually have access to set aMyClassInstance.myVariable [self updateSomeUILabel:[NSNumber numberWithInt:aMyClassInstance.myVariable]]; // don't actually have access to aMyClassInstance.myVariable } - (void) updateSomeUILabel:(NSNumber *)arg{ int value = [arg intValue]; someUILabel.text = [NSString stringWithFormat:@"myVariable = %d", value]; // Updates the UI with new instance variable values }

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  • How to correctly pass a float from C# to C++ (dll)

    - by RavelT
    I'm getting huge differences when I pass a float from C# to C++. I'm passing a dynamic float wich changes over time. With a debuger I get this: c++ lonVel -0.036019072 float c# lonVel -0.029392920 float I did set my MSVC++2010 floating point model to /fp:fast wich should be the standard in .NET if I'm not mistaken, but this didnt help. Now I cant give out the code but I can show a fraction of it. From C# side it looks like this: namespace Example { public class Wheel { public bool loging = true; #region Members public IntPtr nativeWheelObject; #endregion Members public Wheel() { this.nativeWheelObject = Sim.Dll_Wheel_Add(); return; } #region Wrapper methods public void SetVelocity(float lonRoadVelocity,float latRoadVelocity){Sim.Dll_Wheel_SetVelocity(this.nativeWheelObject,lonRoadVelocity,latRoadVelocity);} #endregion Wrapper methods } internal class Sim { #region PInvokes [DllImport(pluginName, CallingConvention=CallingConvention.Cdecl)] public static extern void Dll_Wheel_SetVelocity(IntPtr wheel,float lonRoadVelocity,float latRoadVelocity); #endregion PInvokes } } And in C++ side @ exportFunctions.cpp: EXPORT_API void Dll_Wheel_SetVelocity(CarWheel* wheel,float lonRoadVelocity,float latRoadVelocity){ wheel->SetVelocity(lonRoadVelocity,latRoadVelocity);} So any sugestions on what I should do in order to get 1:1 results or atleast 99% correct results.

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  • Wait between tasks with SingleThreadExecutor

    - by Lord.Quackstar
    I am trying to (simply) make a blocking thread queue, where when a task is submitted the method waits until its finished executing. The hard part though is the wait. Here's my 12:30 AM code that I think is overkill: public void sendMsg(final BotMessage msg) { try { Future task; synchronized(msgQueue) { task = msgQueue.submit(new Runnable() { public void run() { sendRawLine("PRIVMSG " + msg.channel + " :" + msg.message); } }); //Add a seperate wait so next runnable doesn't get executed yet but //above one unblocks msgQueue.submit(new Runnable() { public void run() { try { Thread.sleep(Controller.msgWait); } catch (InterruptedException e) { log.error("Wait to send message interupted", e); } } }); } //Block until done task.get(); } catch (ExecutionException e) { log.error("Couldn't schedule send message to be executed", e); } catch (InterruptedException e) { log.error("Wait to send message interupted", e); } } As you can see, there's alot of extra code there just to make it wait 1.7 seconds between tasks. Is there an easier and cleaner solution out there or is this it?

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  • Android :WindowManager$BadTockenException on Spinner Click

    - by Miya
    Hi, I have a spinner in my home.class. When I click on the spinner, the process is stopped showing exception that WindowManager$BadTockenException is caught. I am calling this home.class from main.class which extends ActivityGroup. If I am simply run only the home.class, the spinner is showing all items. But the problem is only with calling home.class from main.class. The following are my code. Please tell me why this is happened. main.class public class main extends ActivityGroup { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Intent intent=new Intent(this,home.class); View view=getLocalActivityManager().startActivity("1", intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)).getDecorView(); setContentView(view); } } home.class String[] country={"Please selects","US","INDIA","UK"}; Spinner s2 = (Spinner) findViewById(R.id.spinnerCountry); ArrayAdapter<CharSequence> adapterCountry=new ArrayAdapter(this,android.R.layout.simple_spinner_item,country); adapterCountry.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); s2.setAdapter(adapterCountry); s2.setOnItemSelectedListener(new OnItemSelectedListener() { public void onItemSelected( AdapterView<?> parent, View view, int position, long id) { countryName=country[position]; } public void onNothingSelected(AdapterView<?> parent) { countryName=country[0]; } }); Stack Thread [<1 main] (Suspended (exception WindowManager$BadTokenException)) AlertDialog(Dialog).show() line: 245 AlertDialog$Builder.show() line: 802 Spinner.performClick() line: 260 View$PerformClick.run() line: 9080 ViewRoot(Handler).handleCallback(Message) line: 587 ViewRoot(Handler).dispatchMessage(Message) line: 92 Looper.loop() line: 123 ActivityThread.main(String[]) line: 3647 Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method] Method.invoke(Object, Object...) line: 507 ZygoteInit$MethodAndArgsCaller.run() line: 839 ZygoteInit.main(String[]) line: 597 NativeStart.main(String[]) line: not available [native method] Thank You....

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  • Why do you need "extern C" for C++ callbacks to C functions?

    - by Artyom
    Hello, I find such examples in Boost code. namespace boost { namespace { extern "C" void *thread_proxy(void *f) { .... } } // anonymous void thread::thread_start(...) { ... pthread_create(something,0,&thread_proxy,something_else); ... } } // boost Why do you actually need this extern "C"? It is clear that thread_proxy function is private internal and I do not expect that it would be mangled as "thread_proxy" because I actually do not need it mangled at all. In fact in all my code that I had written and that runs on may platforms I never used extern "C" and this had worked as-as with normal functions. Why extern "C" is added? My problem is that extern "C" function pollute global name-space and they do not actually hidden as author expects. This is not duplicate! I'm not talking about mangling and external linkage. It is obvious in this code that external linkage is unwanted! Answer: Calling convention of C and C++ functions are not necessary the same, so you need to create one with C calling convention. See 7.5 (p4) of C++ standard.

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  • tracking the position of dragview

    - by user262325
    Hello everyone I put a dragview on an UIView, I hope when I drag the dragview, its superview (UIView) tracks the position of the dragview and moves itself to the position where to keep dragview at the original position on the UIView. The codes show below: #import <UIKit/UIKit.h> @interface DragView : UIImageView { CGPoint startLocation; } @end #import "DragView.h" @implementation DragView - (id)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { // Initialization code } return self; } - (void)drawRect:(CGRect)rect { // Drawing code } -(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent*)event { CGPoint pt=[[touches anyObject] locationInView:self]; startLocation=pt; [[self superview] bringSubviewToFront:self]; } -(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { CGPoint pt=[[touches anyObject] locationInView:self]; CGRect frame=[self frame]; frame.origin.x+=pt.x-startLocation.x; frame.origin.y+=pt.y-startLocation.y; CGRect frame1=[[self superview] frame];//superview of the dragview frame1.origin.x+=frame.origin.x; //tracks the postion of dragview frame1.origin.y+=frame.origin.y; [[self superview] setFrame: frame1 ]; //move to new position [self setFrame:frame]; } my problem is that the UIView moved but lagged to the movement of the drageview(RED BLOCK). Welcome any comment Thanks interdev

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