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  • Implement abstract class as a local class? pros and cons

    - by sinec
    Hi, for some reason I'm thinking on implementing interface within a some function(method) as local class. Consider following: class A{ public: virtual void MethodToOverride() = 0; }; A * GetPtrToAImplementation(){ class B : public A { public: B(){} ~B(){} void MethodToOverride() { //do something } }; return static_cast<A *>(new B()); } int _tmain(int argc, _TCHAR* argv[]) { A * aInst = GetPtrToAImplementation(); aInst->MethodToOverride(); delete aInst; return 0; } the reason why I'm doing this are: I'm lazy to implement class (B) in separate files MethodToOverride just delegates call to other class Class B shouldn't be visible to other users no need to worry about deleting aInst since smart pointers are used in real implementation So my question is if I'm doing this right? Thanks in advance!

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  • How does the below program work in c++?

    - by Srinivasa Varadan
    I have just created 2 pointers which has undefined behavior and try to invoke a class member function which has no object created ? I don't understand this? #include<iostream> using namespace std; class Animal { public: void talk() { cout<<"I am an animal"<<endl; } }; class Dog : public Animal { public: void talk() { cout<<"bark"<<endl; } }; int main() { Animal * a; Dog * d; d->talk(); a->talk(); }

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  • Xcode method navigation

    - by Bill
    In Xcode 4, I can press Ctrl-6 to get a list of all the methods in the current file. The problem is, if I have private methods declared at the top of my implementation file, say: @interface Foo () -(void)tap:(id)sender; @end @implementation Foo ... -(void)tap:(id)sender { ... } then starting to type "tap" while the method list is visible will just take me to the declaration, since it comes first in the file, when what I really want is the implementation. Is there any way to exclude these declarations from the method list or do I need to resort to separate Foo.h and Foo+Private.h headers? Thanks!

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  • Why Timer does not work if we do not generate a window?

    - by Roman
    Here is the code: import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JFrame; import javax.swing.Timer; public class TimerSample { public static void main(String args[]) { new JFrame().setVisible(true); ActionListener actionListener = new ActionListener() { public void actionPerformed(ActionEvent actionEvent) { System.out.println("Hello World Timer"); } }; Timer timer = new Timer(500, actionListener); timer.start(); } } It generates a window and then periodically prints "Hello World Timer" in the terminal (Command Prompt). If I comment this line new JFrame().setVisible(true); the application do not print anything to the command line. Why?

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  • float addition 2.5 + 2.5 = 4.0? RPN

    - by AJ Clou
    The code below is my subprogram to do reverse polish notation calculations... basically +, -, *, and /. Everything works in the program except when I try to add 2.5 and 2.5 the program gives me 4.0... I think I have an idea why, but I'm not sure how to fix it... Right now I am reading all the numbers and operators in from command line as required by this assignment, then taking that string and using sscanf to get the numbers out of it... I am thinking that somehow the array that contains the three characters '2', '.', and '5', is not being totally converted to a float... instead i think just the '2' is. Could someone please take a look at my code and either confirm or deny this, and possibly tell me how to fix it so that i get the proper answer? Thank you in advance for any help! float fsm (char mystring[]) { int i = -1, j, k = 0, state = 0; float num1, num2, ans; char temp[10]; c_stack top; c_init_stack (&top); while (1) { switch (state) { case 0: i++; if ((mystring[i]) == ' ') { state = 0; } else if ((isdigit (mystring[i])) || (mystring[i] == '.')) { state = 1; } else if ((mystring[i]) == '\0') { state = 3; } else { state = 4; } break; case 1: temp[k] = mystring[i]; k++; i++; if ((isdigit (mystring[i])) || (mystring[i] == '.')) { state = 1; } else { state = 2; } break; case 2: temp[k] = '\0'; sscanf (temp, "%f", &num1); c_push (&top, num1); i--; k = 0; state = 0; break; case 3: ans = c_pop (&top); if (c_is_empty (top)) return ans; else { printf ("There are still items on the stack\n"); exit (0); case 4: num2 = c_pop (&top); num1 = c_pop (&top); if (mystring[i] == '+'){ ans = num1 + num2; return ans; } else if (mystring[i] == '-'){ ans = num1 - num2; return ans; } else if (mystring[i] == '*'){ ans = num1 * num2; return ans; } else if (mystring[i] == '/'){ if (num2){ ans = num1 / num2; return ans; } else{ printf ("Error: cannot divide by 0\n"); exit (0); } } c_push (&top, ans); state = 0; break; } } } } Here is my main program: #include <stdio.h> #include <stdlib.h> #include "boolean.h" #include "c_stack.h" #include <string.h> int main(int argc, char *argv[]) { char mystring[100]; int i; sscanf("", "%s", mystring); for (i=1; i<argc; i++){ strcat(mystring, argv[i]); strcat(mystring, " "); } printf("%.2f\n", fsm(mystring)); } and here is the header file with prototypes and the definition for c_stack: #include "boolean.h" #ifndef CSTACK_H #define CSTACK_H typedef struct c_stacknode{ char data; struct c_stacknode *next; } *c_stack; #endif void c_init_stack(c_stack *); boolean c_is_full(void); boolean c_is_empty(c_stack); void c_push(c_stack *,char); char c_pop(c_stack *); void print_c_stack(c_stack); boolean is_open(char); boolean is_brother(char, char); float fsm(char[]);

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  • Java generic function for performing calculations on integer, on double?

    - by Daniel
    Is this possible? Surely if you passed in a double, any sort of function implementation code which casts an object to an Integer would not be able to work unless the cast 'Integer' was specifically used? I have a function like: public static void increment(Object o){ Integer one = (Integer)o; system.out.println(one++); } I cant see how this could be made generic for a double? I tried public static <E> void increment(E obj){ E one = (E)o; system.out.println(one++); } but it didn't like it?

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  • Call a non member funcion on an instance before is constructed.

    - by Tom
    Hi everyone. I'm writing a class, and this doubt came up. Is this undef. behaviour? On the other hand, I'm not sure its recommended, or if its a good practice. Is it one if I ensure no exceptions to be thrown in the init function? //c.h class C{ float vx,vy; friend void init(C& c); public: C(); ~C(); }; //c.cpp C::C() { init(*this); } void init(C& c) //throws() to ensure no exceptions ? { c.vx = 0; c.vy = 0; } Thanks in advance

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  • Silverlight Windows Phone 7: Load Images From URL

    - by Lennie De Villiers
    Hi, I got the code below that is trying to load an image from the web into an Image control, when I run it I get an error on the given line that no network access is allowed: private void button1_Click(object sender, RoutedEventArgs e) { WebClient webClientImgDownloader = new WebClient(); webClientImgDownloader.OpenReadCompleted += new OpenReadCompletedEventHandler(webClientImgDownloader_OpenReadCompleted); webClientImgDownloader.OpenReadAsync(new Uri("http://dilbert.com/dyn/str_strip/000000000/00000000/0000000/000000/80000/5000/100/85108/85108.strip.print.gif", UriKind.Absolute)); } void webClientImgDownloader_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) { BitmapImage bitmap = new BitmapImage(); bitmap.SetSource(e.Result); // ERROR HERE! image1.Source = bitmap; } Silverlight for Windows Phone 7

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  • Beginner Android Dev question navigating through intents, getting errors not sure how to fix it. I've tried rearranging and everything even tabbing.

    - by user554786
    /*I created this Sign-In page. I start by declaring variables for username/password & buttons. If user enters "test" as username & "test" as password and hits the login button, its supposed to go to the DrinksTwitter.class activity, else throw error message I created. To me the code and login makes perfect sense. I'm not sure why it wont go to the next activity I want it to go to */ package com.android.drinksonme; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; public class Screen2 extends Activity { // Declare our Views, so we can access them later private EditText etUsername; private EditText etPassword; private Button btnLogin; private Button btnSignUp; private TextView lblResult; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Get the EditText and Button References etUsername = (EditText)findViewById(R.id.username); etPassword = (EditText)findViewById(R.id.password); btnLogin = (Button)findViewById(R.id.login_button); btnSignUp = (Button)findViewById(R.id.signup_button); lblResult = (TextView)findViewById(R.id.result); // Check Login String username = etUsername.getText().toString(); String password = etPassword.getText().toString(); if(username.equals("test") && password.equals("test")){ final Intent i = new Intent(Screen2.this, DrinksTwitter.class); btnLogin.setOnClickListener(new OnClickListener() { public void onClick(View v) { startActivity(i); } // lblResult.setText("Login successful."); else { /* ERROR- Syntax error on token "else", { expected */ lblResult.setText("Invalid username or password."); } } }); final Intent k = new Intent(Screen2.this, SignUp.class); btnSignUp.setOnClickListener(new OnClickListener() { public void onClick(View v) { startActivity(k); } }); /* ERROR- Syntax error, insert "}" to complete Statement*/ } }

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  • Call a non member function on an instance before is constructed.

    - by Tom
    Hi everyone. I'm writing a class, and this doubt came up. Is this undef. behaviour? On the other hand, I'm not sure its recommended, or if its a good practice. Is it one if I ensure no exceptions to be thrown in the init function? //c.h class C{ float vx,vy; friend void init(C& c); public: C(); }; //c.cpp C::C() { init(*this); } void init(C& c) //throws() to ensure no exceptions ? { c.vx = 0; c.vy = 0; } Thanks in advance

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  • C# new class with only single property : derive from base or encapsulate into new ?

    - by Gobol
    I've tried to be descriptive :) It's rather programming-style problem than coding problem in itself. Let's suppose we have : A: public class MyDict { public Dictionary<int,string> dict; // do custom-serialization of "dict" public void SaveToFile(...); // customized deserialization of "dict" public void LoadFromFile(...); } B: public class MyDict : Dictionary<int,string> { } Which option would be better in the matter of programming style ? class B: is to be de/serialized externally. Main problem is : is it better to create new class (which would have only one property - like opt A:) or to create a new class derived - like opt B: ? I don't want any other data processing than adding/removing and de/serializing to stream. Thanks in advance!

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  • Media Player Problem

    - by kostas_menu
    button.setOnClickListener(new View.OnClickListener() { public void onClick(View v){ if(mp2.isPlaying()==true) {mp2.stop(); mp.start(); } else mp.start(); } }); button2.setOnClickListener(new View.OnClickListener() { public void onClick(View v){ if(mp.isPlaying()==true) {mp.stop();mp2.start();} else mp2.start(); } }); I press the first btn and the 1st song is playing.i press the second,the first stops and the second begins.But then, as i press the first btn, the second song stops but the first song is not playing...please help!!:)

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  • Wait for inline thread to complete before moving to next method...

    - by Tyler
    Hello, I have an android app where I am doing the following: private void onCreate() { final ProgressDialog dialog = ProgressDialog.show(this, "Please wait..", "Doing stuff..", true); new Thread() { public void run() { //do some serious stuff... dialog.dismiss(); } }.start(); stepTwo(); } And I would like to ensure that my thread is complete before stepTwo(); is called. How can I do this? Thanks!

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  • Object reference not set to an instance of an object

    - by Ste
    I have this function that create runtime textbox: int i = 0; private TextBox[] addressBox = new TextBox[100]; private void appendNewTab() { addressBox[i] = new TextBox(); addressBox[i].KeyPress += new KeyPressEventHandler(this.addressBox_KeyPress); i++; } void addressBox_KeyPress(object sender, KeyPressEventArgs e) { if (e.KeyChar == (char)13) { MessageBox.Show(addressBox[i].Text); } } but i have Object reference not set to an instance of an object here MessageBox.Show(addressBox[i].Text); any suggestion?

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  • Does a CPU assigns a value atomically to memory?

    - by Poni
    Hi! A quick question I've been wondering about for some time; Does the CPU assign values atomically, or, is it bit by bit (say for example a 32bit integer). If it's bit by bit, could another thread accessing this exact location get a "part" of the to-be-assigned value? Think of this: I have two threads and one shared "unsigned int" variable (call it "g_uiVal"). Both threads loop. On is printing "g_uiVal" with printf("%u\n", g_uiVal). The second just increase this number. Will the printing thread ever print something that is totally not or part of "g_uiVal"'s value? In code: unsigned int g_uiVal; void thread_writer() { g_uiVal++; } void thread_reader() { while(1) printf("%u\n", g_uiVal); }

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  • [C++] Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • How do i resolve method Overlapping in java/Processing [duplicate]

    - by user3718913
    This question already has an answer here: How do I compare strings in Java? 24 answers I have two methods/function in a class, called, Qestion1 and Question2, i want it in such a way that after the user has answered Question one correctly, the Question 2 method is called. Whenever i call the method 2, it displays both of them together instead exiting the first method first. Here's a dummy code to illustrate what i'm saying: void Question1() { String question="What is the capital of England?"; String Answer="London"; if(Answer=='London') { Question2(); } } void Question2() { String question="What is the capital of California?"; String Answer="Sacramento"; if(Answer=='Sacramento') { Question3(); } } Pls, this question is in no way related to that other question. Pls peruse the thread again.

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  • Java generics: actual class as a generic parameter.

    - by user554916
    What do I write instead of "TheClass" to make this work? Or is there an alternative way to do it (possibly without making WithName and WithAge generic)? class Item { NeigborList<TheClass> neighbors; } class WithName extends Item { // here I want neighbors to be a NeighborList<WithName> String name; void someMethod() { System.out.println(neighbors.nearestTo(this).name); } } class WithAge extends Item { // here I want neighbors to be a NeighborList<WithAge> int age; void someOtherMethod() { System.out.println(neighbors.nearestTo(this).age); } }

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  • java: useful example of a shutdown hook?

    - by Jason S
    I'm trying to make sure my Java application takes reasonable steps to be robust, and part of that involves shutting down gracefully. I am reading about shutdown hooks and I don't actually get how to make use of them in practice. Is there a practical example out there? Let's say I had a really simple application like this one below, which writes numbers to a file, 10 to a line, in batches of 100, and I want to make sure a given batch finishes if the program is interrupted. I get how to register a shutdown hook but I have no idea how to integrate that into my application. Any suggestions? package com.example.test.concurrency; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.PrintWriter; public class GracefulShutdownTest1 { final private int N; final private File f; public GracefulShutdownTest1(File f, int N) { this.f=f; this.N = N; } public void run() { PrintWriter pw = null; try { FileOutputStream fos = new FileOutputStream(this.f); pw = new PrintWriter(fos); for (int i = 0; i < N; ++i) writeBatch(pw, i); } catch (FileNotFoundException e) { e.printStackTrace(); } finally { pw.close(); } } private void writeBatch(PrintWriter pw, int i) { for (int j = 0; j < 100; ++j) { int k = i*100+j; pw.write(Integer.toString(k)); if ((j+1)%10 == 0) pw.write('\n'); else pw.write(' '); } } static public void main(String[] args) { if (args.length < 2) { System.out.println("args = [file] [N] " +"where file = output filename, N=batch count"); } else { new GracefulShutdownTest1( new File(args[0]), Integer.parseInt(args[1]) ).run(); } } }

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  • Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • A question about making a C# class persistant during a file load

    - by Adam
    Apologies for the indescriptive title, however it's the best I could think of for the moment. Basically, I've written a singleton class that loads files into a database. These files are typically large, and take hours to process. What I am looking for is to make a method where I can have this class running, and be able to call methods from within it, even if it's calling class is shut down. The singleton class is simple. It starts a thread that loads the file into the database, while having methods to report on the current status. In a nutshell it's al little like this: public sealed class BulkFileLoader { static BulkFileLoader instance = null; int currentCount = 0; BulkFileLoader() public static BulkFileLoader Instance { // Instanciate the instance class if necessary, and return it } public void Go() { // kick of 'ProcessFile' thread } public void GetCurrentCount() { return currentCount; } private void ProcessFile() { while (more rows in the import file) { // insert the row into the database currentCount++; } } } The idea is that you can get an instance of BulkFileLoader to execute, which will process a file to load, while at any time you can get realtime updates on the number of rows its done so far using the GetCurrentCount() method. This works fine, except the calling class needs to stay open the whole time for the processing to continue. As soon as I stop the calling class, the BulkFileLoader instance is removed, and it stops processing the file. What I am after is a solution where it will continue to run independently, regardless of what happens to the calling class. I then tried another approach. I created a simple console application that kicks off the BulkFileLoader, and then wrapped it around as a process. This fixes one problem, since now when I kick off the process, the file will continue to load even if I close the class that called the process. However, now the problem I have is that cannot get updates on the current count, since if I try and get the instance of BulkFileLoader (which, as mentioned before is a singleton), it creates a new instance, rather than returning the instance that is currently in the executing process. It would appear that singletons don't extend into the scope of other processes running on the machine. In the end, I want to be able to kick off the BulkFileLoader, and at any time be able to find out how many rows it's processed. However, that is even if I close the application I used to start it. Can anyone see a solution to my problem?

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  • How to set a value from another class

    - by Ram
    Its said that property should not be "Set" only and it should be "Get" as well. What should i do if I need to set value to a variable from some other class? The will keep changing so I cannot pass it through constructor. Shall I create a function for this as shown below? class A { public void SetValue() { b = new B(); b.SetTest(10); } } class B { int test; public void SetTest(int value) { test = value; } } What are the other alternatives?

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  • How to make a rectangle on screen invisible to screen capture ?

    - by Kesarion
    How can I create a rectangle on the screen that is invisible to any sort of screen capture(printscreen or aplications) ? By create a rectangle on screen I mean something like this: #include <Windows.h> #include <iostream> void drawRect(){ HDC screenDC = ::GetDC(0); ::Rectangle(screenDC, 200, 200, 300, 300); ::ReleaseDC(0, screenDC); } int main(void){ char c; std::cin >> c; if (c == 'd') drawRect(); std::cin >> c; return 0; } I'm using Visual Studio 2010 on Windows XP

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  • Keeping object in memory (iPhone SDK)

    - by Chris
    I am trying to create a UIImageView called theImageView in the touchesBegan method that I can then then move to a new location in touchesMoved. Currently I am receiving an "undeclared" error in touchesMoved where I set the new location for theImageView. What can I do to keep theImageView in memory between these two methods? - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { ... UIImageView *theImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image.png"]]; theImageView.frame = CGRectMake(263, 228, 193, 300); [theImageView retain]; ... } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { ... theImageView.frame = CGRectMake(300, 300, 193, 300); ... }

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