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  • Overriding vs Virtual

    - by anonymous
    What is the purpose of using the reserved word virtual in front of functions? If I want a child class to override a parent function, I just declare the same function such as "void draw(){}". class Parent{ public: void say(){ std::cout << "1"; }}; class Child : public Parent{public:void say(){ std::cout << "2"; } }; int main() { Child* a = new Child(); a->say(); return 0; } The output is 2. So again, why would the reserved word "virtual" be necessary in the header of say() ? Thanks a bunch.

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  • Beginner C++ Question

    - by Donal Rafferty
    I have followed the code example here toupper c++ example And implemented it in my own code as follows void CharString::MakeUpper() { char* str[strlen(m_pString)]; int i=0; str[strlen(m_pString)]=m_pString; char* c; while (str[i]) { c=str[i]; putchar (toupper(c)); i++; } } But this gives me the following compiler error CharString.cpp: In member function 'void CharString::MakeUpper()': CharString.cpp:276: error: invalid conversion from 'char*' to 'int' CharString.cpp:276: error: initializing argument 1of 'int toupper(int)' CharString.cpp: In member function 'void CharString::MakeLower()': This is line 276 putchar (toupper(c)); I understand that toupper is looking for int as a parameter and returns an int also, is that the problem? If so how does the example work?

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  • Event handling C# / Registering a callback

    - by Jeff Dahmer
    Events can only return void and recieve object sender/eventargs right? If so then craptastic.... how can I pass a function pointer to another obj, like: public bool ACallBackFunc(int n) { return n > 0; } public void RegisterCallback(Something s) { s.GiveCallBack(this.ACallBackFunc); } Something::GiveCallBack(Action? funcPtr) I tried using Action, but I need it to return some value and Actions can only return void. Also, we do not know what kind of a callback we will be recieving; it could return anything and have any params! Reflection will have to be used somehow I reckon.

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  • Why is the output like this?

    - by javatechi
    class another { public void method(Object o) { System.out.println("This is in method which takes object"); } public void method(String s) { System.out.println("This is method which takes string"); } } public class NewClass { public static void main(String args[]) { another an = new another(); an.method(null); } } When I try to execute this, I get This is method which takes string as the output. Why not "This is in method which takes object"? Object can also be null and string can also be null, why doesn't it invoke first method?

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  • does anyone see any issues with this thread pattern?

    - by prmatta
    Here is a simple thread pattern that I use when writing a class that needs just one thread, and needs to a specific task. The usual requirements for such a class are that it should be startable, stopable and restartable. Does anyone see any issues with this pattern that I use? public class MyThread implements Runnable { private boolean _exit = false; private Thread _thread = null; public void start () { if (_thread == null) { _thread = new Thread(this, "MyThread"); _thread.start(); } } public void run () { while (_exit) { //do something } } public void stop () { _exit = true; if (_thread != null) { _thread.interrupt(); _thread = null; } } } I am looking for comments around if I am missing something, or if there is a better way to write this.

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  • Why I have to redeclare a virtual function while overriding [C++]

    - by Neeraj
    #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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  • Accessing a function of an instance which is in an arraylist

    - by fadeir
    I'm tring to access a function of an instance which is in an arraylist. Is there any way to do that without using the class name of the instance? import java.util.ArrayList; import java.util.List; class apple{ int price; public void myFunction(int iPrice) { price=iPrice; } } class orange{ int price; public void myFunction(int iPrice) { price=iPrice; } } public class main { public static void main(String[] args) { List list= new ArrayList(); //create 3 apple object to list list.add( new apple() ); list.add( new apple() ); list.add( new orange() ); list.get(0).myFunction(1); /* Error: The method myFunction(int) is undefined for the type Object*/ } } I know that;((apple) list.get(0)).myFunction(1); is a way but I'dont want to use any class name while calling the function.

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  • Friendness and derived class

    - by ereOn
    Hi, Let's say I have the following class hierarchy: class Base { protected: virtual void foo() = 0; friend class Other; }; class Derived : public Base { protected: void foo() { /* Some implementation */ }; }; class Other { public: void bar() { Derived* a = new Derived(); a->foo(); // Compiler error: foo() is protected within this context }; }; I guess I could change it too a->Base::foo() but since foo() is pure virtual in the Base class, the call will result in calling Derived::foo() anyway. However, the compiler seems to refuse a->foo(). I guess it is logical, but I can't really understand why. Am I missing something ? Can't (shouldn't) it handle this special case ? Thank you.

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  • Access WindowedApplication from package class.

    - by Senling
    Hi, I'm developing an AIR application, where i need to access WindowedApplication's function from the package class. This is the Main application (Partial code) import mx.events.CloseEvent; import messages.MessageWindow public function undock():void { stage.nativeWindow.visible = true; stage.nativeWindow.orderToFront(); //Clearing the bitmaps array also clears the applcation icon from the systray NativeApplication.nativeApplication .icon.bitmaps = []; } ]] Package: (Partial code) package messages { public class MessageWindow extends NativeWindow { public function MessageWindow():void { stage.addEventListener(MouseEvent.MOUSE_DOWN,onClick); } private function onClick(event:MouseEvent):void { ****** Need to call the undock method from here. ***** } } } Is it possible to call this way or suggest any other solution Thanks in advance Senling.

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  • Global variable in a recursive function how to keep it at zero?

    - by Grammin
    So if I have a recursive function with a global variable var_: int var_; void foo() { if(var_ == 3) return; else var_++; foo(); } and then I have a function that calls foo() so: void bar() { foo(); return; } what is the best way to set var_ =0 everytime foo is called thats not from within itself. I know I could just do: void bar() { var_ =0; foo(); return; } but I'm using the recursive function a lot and I don't want to call foo and forget to set var_=0 at a later date. Does anyone have any suggestions on how to solve this? Thanks, Josh

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  • VideoView Not Playing, Error(1,-1)

    - by Jesse J
    I originally thought that the video format was wrong, but after trying .mov, .3gp, and .mp4 with H.264, I'm wondering if something is wrong with my code? public class IntroActivity extends Activity { VideoView videoHolder; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override protected void onStart() { getWindow().setFormat(PixelFormat.TRANSLUCENT); videoHolder = new VideoView(this); //videoHolder = (VideoView)findViewById(R.id.myvideoview); Uri video = Uri.parse("android.resource://" + getPackageName() + "/" + R.raw.menu); videoHolder.setVideoURI(video); videoHolder.start(); videoHolder.setOnCompletionListener(new MediaPlayer.OnCompletionListener() { public void onCompletion(MediaPlayer mp) { videoHolder.start(); } }); setContentView(videoHolder); super.onStart(); }

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  • android webView loading finished but it was a blank only I touch the screen can the content show Idont know why?and how it happened

    - by Sunday
    when my webView load this page , it was blank-page or white page only I touch the screen the content can only show private WebView webview; private ProgressDialog mProgressDialog; private Context mContext; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_web); mContext = this; webview = (WebView)findViewById(R.id.myWebView); String url = (String)getIntent().getExtras().get("url"); webview.getSettings().setJavaScriptEnabled(true); webview.setWebViewClient(new MyWebViewClient()); if(url!=null){ webview.loadUrl(url); } } class MyWebViewClient extends WebViewClient { @Override public void onPageStarted(WebView view, String url, Bitmap favicon) { super.onPageStarted(view, url, favicon); mProgressDialog = ProgressDialog.show(mContext, "tips", "wate···the view is loading", true, false); } @Override public void onPageFinished(WebView view, String url) { mProgressDialog.dismiss(); super.onPageFinished(view, url); } }

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  • What does this recursive function do?

    - by null
    What does this function do? And how do you evaluate it? How to trace it? How to understand recursive method? I just can't understand the recursion, and the exam date is coming soon, and I know in order to understand recursion, I must first understand recursion. But I just can't write a slightly complex recursive method, can anyone help me out using the simplest English words. public class BalancedStrings { public static void printBalanced(String prefix, int a, int b) { if (a > 0) printBalanced(prefix + "a", a - 1, b); if (b > 0) printBalanced(prefix + "b", a, b - 1); if (a == 0 && b == 0) System.out.println(prefix); } public static void printBalanced(int n) { if (n % 2 == 0) { printBalanced("", n / 2, n / 2); } } public static void main(String[] args) { printBalanced(4); } }

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  • Is it possible to use AutoMapper to map methods?

    - by Woj
    I have two classes: public class TestClass1 { public int TestInt { get; set; } public void TestMethod() { // Do something } } public class TestClass2 { public int TestInt { get; set; } public void TestMethod() { // Do something } } I want to create interface that I can use for both classes. The easiest solution is to implement the interface on TestClass1 and TestClass2 but I don;t have access to the implementation of these classes (external dll). I was wondering if I can create new interface and use AutoMapper to map TestClass1 and TestClass2 to ITestInterface: public interface ITestInterface { int TestInt { get; set; } void TestMethod(); }

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  • Why do you sometimes need to write <typename T> instead of just <T> ?

    - by StackedCrooked
    I was reading the Wikipedia article on SFINAE and encountered following code sample: struct Test { typedef int Type; }; template < typename T > void f( typename T::Type ) {} // definition #1 template < typename T > void f( T ) {} // definition #2 void foo() { f< Test > ( 10 ); //call #1 f< int > ( 10 ); //call #2 without error thanks to SFINAE } Now I've actually written code like this before, and somehow intuitively I knew that I needed to type "typename T" instead of just "T". However, it would be nice to know the actual logic behind it. Anyone care to explain?

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  • How to override virtual function in good style? [C++]

    - by Knowing me knowing you
    Hi, guys I know this question is very basic but I've met in few publications (websites, books) different style of override virtual function. What I mean is: if I have base class: class Base { public: virtual void f() = 0; }; in some publications I saw that to override this some authors would just say: void f(); and some would still repeat the virtual keyword before void. Which form of overwriting is in good style? Thank you for your answers.

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  • Calling inheriting class methods via interface.

    - by Stacey
    Given the scenario... interface IBase{ void Process(int value); } abstract class Base : IBase { public virtual void Process(int value){ throw new NotImplementedException(); } } class Implemented: Base, IBase { public void Process(int value) { // .. some code here.. } } I'm trying to write a loop similar to the following. foreach( Base b in CollectionOfImplemented ) { b.Process( // something will go here // ); } Trying this, it keeps calling Base.Process, instead of Implemented.Process; but the type in the collection is Implemented, not Base. Boxing it seems to work, but I was hoping to see if I could find a more intelligent approach to it, since the Collection will contain other types of objects that also inherit from Base.

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  • Communication between c++ objects.

    - by Pradyot
    This is an issue, that I have come acrosss earlier. Basically a c++ object has a member object that does some work, once the work is done , a notification needs to made to the parent. What is the most elegant solution to allow this communication. Does being in this position indicate a flaw with the design to begin with? To elaborate. class A { B member; void do_something(); } class B{ void talk_to_network(); }; void do_something() { //Conditional wait on a variable that will change when talk to network completes. //So need a way for B to inform A, that it is done. }

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  • How to insert any string in sqlite3 in c

    - by ashishtripathi.hcu
    Hi I have to insert a string into a sqlite data base my command .. Err=sqlite_exec(DB, "create table tbl5(TEXT varchar(100));", xCallback, (void*)"First Test", &ErrMsg); Err=sqlite_exec(DB, "insert into tbl5 values ('some string');", xCallback, (void*)"First Test", &ErrMsg); works fine but when I want to put s="some string" ie Err=sqlite_exec(DB, "insert into tbl5 values (s);", xCallback, (void*)"First Test", &ErrMsg); then this is not working so how to add variable then It is not working so how to insert variable in sqlite database thank u

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  • Referencing an array to a pointer

    - by james
    I want to refer a pointer to an array by another pointer. Example: void exp() { double var[2]; exp1(&var[0]); printf("\n varvalue is %lf\n",var[0]); } void exp1(double *var) { //updating the value *var[0]=4.0; exp2(&var[0]); } void exp2(double *var) { *var[0]=7.0; } This should update the value as 7.0(the last update).I am getting an array like invalid argument type of unary(*) . How can i correct this?where i am going wrong here?

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  • C++ Declaring an uninitialized variable without a null constructor

    - by xbonez
    Consider the DUPoint class, whose declaration appears below. Assume this code appears in a file named DUPoint.h: #include <string> class DUPoint { public: DUPoint (int x, int y); int getX () const; int getY () const; void setX (int x); void setY (int y); void print(); private: int x_; int y_; }; Is it true that you cannot declare an uninitialized DUPoint variable with a statement such as DUPoint P; using this class as currently configured because it has no null constructor?

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  • Writing a C++ wrapper for a C library

    - by stripes
    I have a legacy C library, written in an OO type form. Typical functions are like: LIB *lib_new(); void lib_free(LIB *lib); int lib_add_option(LIB *lib, int flags); void lib_change_name(LIB *lib, char *name); I'd like to use this library in my C++ program, so I'm thinking a C++ wrapper is required. The above would all seem to map to something like: class LIB { public: LIB(); ~LIB(); int add_option(int flags); void change_name(char *name); ... }; I've never written a C++ wrapper round C before, and can't find much advice about it. Is this a good/typical/sensible approach to creating a C++/C wrapper?

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  • A pointer member variable having different values

    - by Rohan Prabhu
    Ok, to begin with, this is my code: HyperSprite::HyperSprite() { _view = 0; } void HyperSprite::publish(QGraphicsView* view) { _view = view; } void HyperSprite::getKFrame() { if(_view != 0) { qDebug()<<(void*)_view; } } Now, if I call HyperSprite::getKFrame() from within main(), I get the output: 0xbf8ffb84 I have a TCP server, which requires this QGraphicsView* variable. So whenever a new connection is made, HyperSprite::getKFrame() is called. However, whenever I make a connection to my server, this is the output: 0x1e425ff I honestly don't understand this. Shouldn't the value of a member remain same throughout? Why is the pointer value changing? As is obvious, whenever I try to use the _view pointer to access any of its members, a Segmentation Fault occurs. I tried using QSharedPointer, but it also results in the same problem. The data of the QSharedPointer automatically changes. Why is this happening?

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  • Form Closing help

    - by Michael Quiles
    How can I call the button1_Click event in the form closing event so I don't have to copy and paste the code from button1_Click? public void button1_Click(object sender, EventArgs e) { //Yes or no message box to exit the application DialogResult Response; Response = MessageBox.Show("Are you sure you want to Exit?", "Exit", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2); if (Response == DialogResult.Yes) // Exits the application Application.Exit(); } public void xGameThemeComboBox_SelectedIndexChanged(object sender, EventArgs e) { string folder = Application.StartupPath; string theme = (string)xGameThemeComboBox.Items[xGameThemeComboBox.SelectedIndex]; string path = System.IO.Path.Combine(folder, theme + ".jpg"); Image newImage = new Bitmap(path); if (this.BackgroundImage != null) this.BackgroundImage.Dispose(); { this.BackgroundImage = newImage; } } private void xGameForm_FormClosing(object sender, FormClosingEventArgs e) { // call button1_Click here }

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