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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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• 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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• How to use NSWindowDidExposeNotification

  - by Jeena

  Hi, I am trying to update another windows when the one becomes visible. So I found the NSWindowDidExposeNotification and tried to work with it, so I wrote in my awakeFromNib: // MyClass.m - (void)awakeFromNib { NSNotificationCenter *nc = [NSNotificationCenter defaultCenter]; [nc addObserver:self selector:@selector(mentionsWindowDidExpose:) name:NSWindowDidExposeNotification object:nil]; } and implemented the method // MyClass.h - (void)mentionsWindowDidExpose:(id)sender; // MyClass.m - (void)mentionsWindowDidExpose:(id)sender { NSLog(@"test"); } But it never gets called which is odd. What do I do wrong here?

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• Java : Using parent class method to access child class variable

  - by Jayant

  I have the following scenario : public class A { private int x = 5; public void print() { System.out.println(x); } } public class B extends A { private int x = 10; /*public void print() { System.out.println(x); }*/ public static void main(String[] args) { B b = new B(); b.print(); } } On executing the code, the output is : 5. How to access the child class(B's) variable(x) via the parent class method? Could this be done without overriding the print() method (i.e. uncommenting it in B)? [This is important because on overriding we will have to rewrite the whole code for the print() method again]

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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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• What is the trick in pAddress & ~(PAGE_SIZE - 1) to get the page's base address

  - by Dbger

  Following function is used to get the page's base address of an address which is inside this page: void* GetPageAddress(void* pAddress) { return (void*)((ULONG_PTR)pAddress & ~(PAGE_SIZE - 1)); } But I couldn't quite get it, what is the trick it plays here? Conclusion: Personally, I think Amardeep's explanation plus Alex B's example are best answers. As Alex B's answer has already been voted up, I would like to accept Amardeep's answer as the official one to highlight it! Thanks you all.

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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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• 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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• 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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• 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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• Android SurfaceView/Canvas flickering after trying to clear it

  - by Mark D

  So I am trying to clear the Canvas using canvas.drawColor(Color.BLACK) but if I just call this once, the display flickers and displays the old drawing which should have been covered up by the drawColor. Here is the important bits of my code - public void update() { //This method is called by a Thread Canvas canvas = holder.lockCanvas(null); if (canvas != null) { onDraw(canvas); } holder.unlockCanvasAndPost(canvas); } @Override protected void onDraw(Canvas canvas) { if (toClear) { canvas.drawColor(Color.BLACK); //if this is not set to change back to false, it does not flicker toClear = false; } //Draw some objects that are moving around } public void clearScreen() { //This method is called when the user pressed a button toClear = true; } After Googling around a litte, I heard about double buffering but came to the understanding that lockCanvas() and unlockCanvasAndPost() should handle this for me. What is going wrong here?

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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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• question about Batcher odd-even sort

  - by davit-datuashvili

  hi i ave question about Batcher's odd-even sort i have following code public class Batcher{ public static void batchsort(int a[],int l,int r){ int n=r-l+1; for (int p=1;p<n;p+=p) for (int k=p;k>0;k/=2) for (int j=k%p;j+k<n;j+=(k+k)) for (int i=0;i<n-j-k;i++) if ((j+i)/(p+p)==(j+i+k)/(p+p)) exch(a,l+j+i,l+j+i+k); } public static void main(String[]args){ int a[]=new int[]{2,4,3,4,6,5,3}; batchsort(a,0,a.length-1); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static void exch(int a[],int i,int j){ int t=a[i]; a[i]=a[j]; a[j]=t; } } //result is 3 3 4 4 5 2 6 what i missed ? hat is wrong?

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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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• 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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• 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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• 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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• 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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• Reference and Value confusion

  - by rgamber

  Hi I read this question on Stack overflow, and tried to do an example. I had the below code: public static void main(String[] args){ int i = 5; Integer I = new Integer(5); increasePrimitive(i); increaseObject(I); System.out.println(i); //Prints 5 - correct System.out.println(I); //Still prints 5 System.out.println(increaseObject2(I)); //Still prints 5 } public static void increasePrimitive(int n){ n++; } public static void increaseObject(Integer n){ n++; } public static int increaseObject2(Integer n){ return n++; } Does the increaseObject print 5 because the value of reference is changing inside that function? Am I right? I am confused why the increasedObject2 prints 5 and not 6. Can anyone please explain?

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• Default http/admin port in dropwizard project

  - by mithrandir

  I have a dropwizard project and I have maintained a config.yml file at the ROOT of the project (basically at the same level as pom.xml). Here I have specified the HTTP port to be used as follows: http: port:9090 adminPort:9091 I have the following code in my TestService.java file public class TestService extends Service<TestConfiguration> { @Override public void initialize(Bootstrap<TestConfiguration> bootstrap) { bootstrap.setName("test"); } @Override public void run(TestConfiguration config, Environment env) throws Exception { // initialize some resources here.. } public static void main(String[] args) throws Exception { new TestService().run(new String[] { "server" }); } } I expect the config.yml file to be used to determine the HTTP port. However the app always seems to start with the default ports 8080 and 8081. Also note that I am running this from eclipse. Any insights as to what am I doing wrong here ?

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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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• c# event and delegate question

  - by user359562

  I want to detach the custom event but could not detach. Please find below I am using -= to detach the event. I assume after this, TextChanged2 method should not be invoked as I have unregistered the event. Let me know if my understanding is wrong. public delegate void TextChangedEventHandler1(object sender, TextBoxargs ta); public event TextChangedEventHandler1 TextChanged1; private void textBox1_TextChanged(object sender, EventArgs e) { this.TextChanged1 -= new TextChangedEventHandler1(TextChanged2); TextChanged2(sender, e); } public void TextChanged2(object sender, EventArgs e) { textBox1.Text = textBox1.Text.ToUpper(); }

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• how to use string in va_start?

  - by Newbie

  for some reason, i cant get this working: void examplefunctionname(string str, ...){ ... va_start(ap, str.c_str()); nor do i get this work: void examplefunctionname(string str, ...){ ... int len = str.length(); char *strlol = new char[len+1]; for(int i = 0; i < len; i++){ strlol[i] = str[i]; } strlol[len] = 0; va_start(ap, strlol); but this does: void examplefunctionname(const char *str, ...){ ... va_start(ap, str); could someone show me how i can use string instead of const char * there? its outputting random numbers when i call examplefunctionname("%d %d %d", 1337, 1337, 1337)

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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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• Macros giving problems with dladdr()

  - by Veger

  I have implemented tracing behavior using the -finstrument-functions option of gcc and this (simplified) code: void __cyg_profile_func_enter(void *this_fn, void *call_site) { Dl_info di; if(dladdr(this_fn, &di)) printf("entered %s\n", (di.dli_sname?di_dli_sname:"<unknown>")); } This works great, except for one thing: macros are processed as well, but the function prints the information of the function which contains the macro. So functions containing macros have their information printed multiple times (which is of course undesired). Is there anything to detect that a macro is being processed? Or is is possible to turn off instrumenting macros at all? PS Same problems occur with sizeof()

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