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  • Operators vs Functions in C/C++

    - by user356106
    Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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  • Reference to an instance method of a particular object

    - by Andrey
    In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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  • F# function calling syntax confusion

    - by Daniel
    I have a piece of code: links |> Seq.map (fun x -> x.GetAttributeValue ("href", "no url")) Which I wanted to rewrite to: links |> Seq.map (fun x -> (x.GetAttributeValue "href" "no url")) But the F# compiler doesn't seem to like that. I was under the impression that these two function calls were interchangeable: f (a, b) (f a b) The error that I get is: The member or object constructor 'GetAttributeValue' taking 2 arguments are not accessible from this code location. All accessible versions of method 'GetAttributeValue' take 2 arguments. Which seems amusing, as it seems to indicate that it needs what I'm giving it. What am I missing here?

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  • What are your suggestions for best practises for regular data updates in a website database?

    - by bboyle1234
    My shared-hosting asp.net website must automatically run data update routines at regular times of day. Once it has finished running certain update routines, it can run update routines that are dependent on the previous updates. I have done this type of work before, using quite complicated setups. Some features of the framework I created are: A cron job from another server makes a request which starts a data update routine on the main server Each updater is loaded from web.config Each updater overrides a "canRunUpdate" method that determines whether its dependencies have finished updating Each updater overrides a "hasFinishedUpdate" method Each updater overrides a "runUpdate" method Updaters start and run in parallel threads The initial request from the cron job server started each updater in its own thread and then ended. As a result, the threads containing the updaters would be terminated before the updaters were finished. Therefore I had to give the updaters the ability to save partial results and continue the update job next time they are started up. As a result, the cron server had to call the updater many times to ensure the job is done. Sometimes the cron server would continue making update requests long after all the updates were completed. Sometimes the cron server would finish calling the update requests and leave some updates uncompleted. It's not the best system. I'm looking for inspiration. Any ideas please? Thank you :)

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  • Cast vector<T> to vector<const T>

    - by user345386
    I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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  • How to call C++ function from C?

    - by claws
    I know this. Calling C function from C++: If my application was in C++ and I had to call functions from a library written in C. Then I would have used //main.cpp extern "C" void C_library_function(int x, int y);//prototype C_library_function(2,4);// directly using it. This wouldn't mangle the name C_library_function and linker would find the same name in its input *.lib files and problem is solved. Calling C++ function from C??? But here I'm extending a large application which is written in C and I need to use a library which is written in C++. Name mangling of C++ is causing trouble here. Linker is complaining about the unresolved symbols. Well I cannot use C++ compiler over my C project because thats breaking lot of other stuff. What is the way out? By the way I'm using MSVC

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  • can't create partial objects with accepts_nested_attributes_for

    - by Isaac Cambron
    I'm trying to build a form that allows users to update some records. They can't update every field, though, so I'm going to do some explicit processing (in the controller for now) to update the model vis-a-vis the form. Here's how I'm trying to do it: Family model: class Family < ActiveRecord::Base has_many :people, dependent: :destroy accepts_nested_attributes_for :people, allow_destroy: true, reject_if: ->(p){p[:name].blank?} end In the controller def check edited_family = Family.new(params[:family]) #compare to the one we have in the db #update each person as needed/allowed #save it end Form: = form_for current_family, url: check_rsvp_path, method: :post do |f| = f.fields_for :people do |person_fields| - if person_fields.object.user_editable = person_fields.text_field :name, class: "person-label" - else %p.person-label= person_fields.object.name The problem is, I guess, that Family.new(params[:family]) tries to pull the people out of the database, and I get this: ActiveRecord::RecordNotFound in RsvpsController#check Couldn't find Person with ID=7 for Family with ID= That's, I guess, because I'm not adding a field for family id to the nested form, which I suppose I could do, but I don't actually need it to load anything from the database for this anyway, so I'd rather not. I could also hack around this by just digging through the params hash myself for the data I need, but that doesn't feel a slick. It seems nicest to just create an object out of the params hash and then work with it. Is there a better way? How can I just create the nested object?

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  • How to check if TypeIdenitifier(T) is an Object?

    - by John
    I'm creating a generic list class that has a member of type Array(Array of ). The problem is the class descruction,because the class is supposed to be used for types from byte to types inheriting TObject. Specifically: destructor Destroy; var elem:T; begin /*if(T is Tobject) then //Check if T inherits TObject {Compiler error!} for elem in FData do TObject(elem).Free;*/ // do not know how to do it SetLength(FItems,0); //FItems : Array of T inherited Destroy; end; How do I check if T is TObject so I can free every member if the typeidenitifier is a class,for example?

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  • SYN receives RST,ACK very frequently

    - by user1289508
    Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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  • Whats the difference between a C++ and a Cocoa Project in Xcode?

    - by david
    I need to work with TagLib for my project. I've created a framework (and I tried using it as a lib) but the compiler cannot find #include < strings on compiling (No such file or Directory). I've created a test C++ project and it #includes < strings just fine. I've looked at the project settings and I cannot find a difference between them. But the standard cocoa projects obviously so not have the search path set to include C++ libraries (Or am I completely getting it wrong?). I've searched for a solution but no one else seems to have run into this problem.

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  • iOS sdk question: how do I cast a UIView to a UIImage View (alternativly how do I get a UIImageView from a GestureRecognzer?)

    - by user439299
    Desired end result: user taps a UIImageView and the image changes to another image (a subsequent tap returns the image to the original state) Problem: I add a (unique) selector to a bunch of UIImageViews (in an array) and point the action at the same function - let's call this function imageTapped: for now. Here is my code so far: -(void)imageTapped:(UITapGestureRecognizer *)tapGesture { UIImageView *view = tapGesture.view; // rest of code... } This code actually works fine but gets a warning when I run it: "Incompatible objective c types initilizing 'struct UIView *', expected 'struct UIImageView *' Any way to get rid of this? Not sure how casting works in objective c... primitive types seem to work fine such as (int)someFloat works fine but (UIImageView)someUiView doesn't work. Like I said, code works alright when I run it but would like to get ride of the compiler warning. Any help would be awesome.... I am very new to objective c (or any non java language for that matter) so be gentle. Thanks in advance.

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  • creating tables in ruby-on-rails 3 through migrations?

    - by fayer
    im trying to understand the process of creating tables in ruby-on-rails 3. i have read about migrations. so i am supposed to create tables by editing in the files in: Database Migrations/migrate/20100611214419_create_posts Database Migrations/migrate/20100611214419_create_categories but they were generated by: rails generate model Post name:string description:text rails generate model Category name:string description:text does this mean i have to use "rails generate model" command everytime i want to create a table? what if i create a migration file but want to add columns. do i create another migration file for adding those or do i edit the existing migration file directly? the guide told me to add a new one, but here is the part i dont understand. why would i add a new one? cause then the new state will be dependent of 2 migration files. in symfony i just edit a schema.yml file directly, there are no migration files with versioning and so on. im new to RoR and want to get the picture of creating tables. thanks

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  • Running Java Program linking to thirdpary library (java -jar) issue ( Multiple methods tried )

    - by bamachrn
    This issue is related to running a Java program (jar) dependent on thirdparty jar library even after setting classpath and trying so many other methods by reading articles in Internet. I want to use a thirdparty Pack1.jar (it is not a part of jvm) as dependency of my programme. I do not know where the Pack1.jar file could be in the deployment machine and I want the deployer to specify the path for the thirdparty libraries I have tried the following alternatives in vain Setting the java.class.path programatically String class_path = args[0]; System.setProperty("java.class.path",class_path); Here I am assuming that deployer would supply the classpath as first argument while running the program Setting the CLASSPATH env_var to locate the thirdparty directory While running, using the classpath option java -classpath /path/to/Pack1.jar -jar Pack2.jar I think this would not work because documentation says that classpath is ignored when program is run with "java -jar" Setting the java.ext.dirs programatically. Setting the java.library.path programatically. I do not want to specify the Class-Path in manifest because that takes only relative path and I do not know where the thirdparty library would be kept in deployment machine But I am unable to get the jar running. How can I fix this problem any help please.

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  • Rails how to return a list of answers with a specific question_id

    - by mytwocentsisworthtwocents
    Let's say I have two Models, Answers and Questions (there are others, but irrelevant to the question). The models are as follows: Answer.rb class Answer < ActiveRecord::Base attr_accessible :description, :question_id has_one :question, :through => :user, :dependent => :destroy validates :description, :presence => true end Question.rb class Question < ActiveRecord::Base attr_accessible :budget, :description, :headline, :user_id, :updated_at, :created_at belongs_to :user has_many :answers validates :headline, :description, :user_id, :presence => true end I'd like to display on a page a list of all answers associated with a question, and only those questions. I got this far. I believe this variable finds all the questions in the database by the question_id (foreign key): @findanswers = Answer.all(params[:question_id]) And this one grabs the the id of the current question (this code will reside as an ERB on the page where the current question is located): @questionshow = Question.find(params[:id]) And now I'm stuck. How do I put the two together so that I list all the answers with the current question id?

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  • Ruby on rails 2 level model

    - by jony17
    I need some help creating a very simple forum in a existing model. What I want in a Game page, have a mini forum, where is possible create some topics and some comments to this topics. In the beginning I'm only implement topics. This is the error I have: Mysql2::Error: Column 'user_id' cannot be null: INSERT INTO `topics` (`game_id`, `question`, `user_id`) VALUES (1, 'asd', NULL) This is my main model: game.rb class Game < ActiveRecord::Base attr_accessible :name validates :user_id, presence: true validates :name, presence: true, length: { maximum: 50 } belongs_to :user has_many :topics, dependent: :destroy end topic.rb class Topic < ActiveRecord::Base validates_presence_of :question validates_presence_of :game_id attr_accessible :question, :user_id validates :question, length: {maximum: 50}, allow_blank: false belongs_to :game belongs_to :user end topic_controller.rb def create @game = Game.find(params[:game_id]) @topic = @game.topics.create(params[:topic]) @topic.user_id = current_user.id respond_to do |format| if @topic.save format.html { redirect_to @game, notice: 'Topic was successfully created.' } else format.html { render action: "new" } end end end game/show.html.erb <h2>Topics</h2> <% @game.topics.each do |topic| %> <p> <b>Question:</b> <%= topic.question %> </p> <% end %> <h2>Add a topic:</h2> <%= form_for([@game, @game.topics.build]) do |f| %> <div class="field"> <%= f.label :question %><br /> <%= f.text_field :question %> </div> <div class="actions"> <%= f.submit %> </div> <% end %> Thanks ;)

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  • how to use replace_regex_copy() from boost::algorithm library?

    - by Vincenzo
    This is my code: #include <string> #include <boost/algorithm/string/regex.hpp> string f(const string& s) { using namespace boost::algorithm; return replace_regex_copy(s, "\\w", "?"); } This is what compiler says: no matching function for call to ‘replace_regex_copy(const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::string, std::string) The link to the library: http://www.boost.org/doc/libs/1_43_0/doc/html/boost/algorithm/replace_regex_copy.html Could anyone please help? Thanks! ps. Boost library is in place, since other functions from it work fine.

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  • Create object of unknown class (two inherited classes)

    - by Paul
    I've got the following classes: class A { void commonFunction() = 0; } class Aa: public A { //Some stuff... } class Ab: public A { //Some stuff... } Depending on user input I want to create an object of either Aa or Ab. My imidiate thought was this: A object; if (/*Test*/) { Aa object; } else { Ab object; } But the compiler gives me: error: cannot declare variable ‘object’ to be of abstract type ‘A’ because the following virtual functions are pure within ‘A’: //The functions... Is there a good way to solve this?

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  • Operations on 64bit words in 32bit system

    - by Vilo
    I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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  • Determine an object's class returned by a factory method (Error: function does not take 1 arguments

    - by tzippy
    I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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  • How do I replace "this" in Java with something that works.

    - by Luke Alderton
    I'm looking to get the showGUI() method work, the compiler says "this" is not a static variable and cannot be referenced from a static context, what would I use to replace "this"? I've tried test.main (test being the package it's in). The reason I'm using the static method showGUI() is because I need the method to be called from another static method, as well as the startup() method. Below are my two main classes. public class Main extends SingleFrameApplication { @Override protected void startup() { showGUI(); } @Override protected void configureWindow(java.awt.Window root) { } public static Main getApplication() { return Application.getInstance(Main.class); } public static void main(String[] args) { launch(Main.class, args); } public static void showGUI() { show(new GUI(this)); } } public class GUI extends FrameView { public GUI(SingleFrameApplication app) { super(app); initComponents(); } private void initComponents() { //all the GUI stuff is somehow defined here } }

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  • How can I integrate advanced computations into a database field?

    - by ciclistadan
    My biological research involves the measurement of a cellular structure as it changes length throughout the course of observation (capturing images every minute for several hours). As my data sets have become larger I am trying to store them in an Access database, from which I would like to perform various queries about their changes in size. I know that the SELECT statement can incorporate some mathematical permutations, but I have been unable to incorporate many of my necessary calculations (probably due to my lack of knowledge). For example, one calculation involves determining the rate of change during specifically defined periods of growth. This calculation is entirely dependent on the raw data saved in the table, therefore I didn't this it would be appropriate to just calculate it in excel prior to entry into the field. So my question is, what would be the most appropriate method of performing this calculation. Should I attempt to string together a huge SELECT calculation in my QUERY, or is there a way to use another language (I know perl?) which can be called to populate the new query field? I'm not looking for someone to write the code, just where is it appropriate to incorporate each step. Also, I am currently using Office Access but would be interested in any mySQL answers as I may be moving to this platform at a later date. Thanks all!

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  • Android application displays black screen after running

    - by frgnvola
    When I click "Run as an Android Application" on Eclipse, the following is displayed in the console [2014-06-05 20:07:18 - StudentConnect] Android Launch! [2014-06-05 20:07:18 - StudentConnect] adb is running normally. [2014-06-05 20:07:18 - StudentConnect] Performing sandhu.student.connect.SplashActivity activity launch [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Refreshing resource folders. [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Starting incremental Pre Compiler: Checking resource changes. [2014-06-05 20:07:18 - StudentConnect] Nothing to pre compile! [2014-06-05 20:07:18 - StudentConnect] Starting incremental Package build: Checking resource changes. [2014-06-05 20:07:18 - StudentConnect] Using default Build Tools revision 19.0.0 [2014-06-05 20:07:18 - StudentConnect] Skipping over Post Compiler. [2014-06-05 20:07:20 - StudentConnect] Application already deployed. No need to reinstall. [2014-06-05 20:07:20 - StudentConnect] Starting activity sandhu.student.connect.SplashActivity on device 0f0898b2 [2014-06-05 20:07:21 - StudentConnect] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=sandhu.student.connect/.SplashActivity } [2014-06-05 20:07:21 - StudentConnect] ActivityManager: Warning: Activity not started, its current task has been brought to the front After deployed to my phone, it only displays a black screen. I recently implemented a splash screen, but it was working fine before; however I think it might have something to do with the problem. Here are my java and xml files: MainActivity.java package sandhu.student.connect; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import android.view.View; import android.webkit.WebSettings; import android.webkit.WebView; import android.webkit.WebViewClient; public class MainActivity extends Activity { public WebView student_zangle; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); WebView student_zangle = (WebView) findViewById(R.id.student_zangle); student_zangle.loadUrl("https://zangleweb01.clovisusd.k12.ca.us/studentconnect/"); student_zangle.setWebViewClient(new WebViewClient()); student_zangle.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY); WebSettings settings = student_zangle.getSettings(); settings.setJavaScriptEnabled(true); settings.setBuiltInZoomControls(true); settings.setLoadWithOverviewMode(true); settings.setUseWideViewPort(true); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { WebView student_zangle = (WebView) findViewById(R.id.student_zangle); if ((keyCode == KeyEvent.KEYCODE_BACK) && student_zangle.canGoBack()) { student_zangle.goBack(); return true; } else { finish(); } return super.onKeyDown(keyCode, event); } } activity_main.xml <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/blue" tools:context=".MainActivity" > <WebView android:id="@+id/student_zangle" android:layout_width="match_parent" android:layout_height="match_parent" /> </RelativeLayout> SplashActivity.java package sandhu.student.connect; import android.os.Bundle; import android.preference.PreferenceActivity; public class SplashActivity extends PreferenceActivity { @SuppressWarnings("deprecation") @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.prefs); } } splash_activity.xml <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/blue" android:orientation="vertical" > <ImageView android:id="@+id/imageView1" android:layout_width="250dp" android:layout_height="100dp" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" android:layout_marginTop="145dp" android:contentDescription="@string/zangle_logo" android:src="@drawable/logo" /> </RelativeLayout> Also, here is a full copy of the logcat error output: 06-05 20:19:46.698: E/Watchdog(817): !@Sync 1952 06-05 20:20:09.971: E/memtrack(16438): Couldn't load memtrack module (No such file or directory) 06-05 20:20:09.971: E/android.os.Debug(16438): failed to load memtrack module: -2 06-05 20:20:11.012: E/memtrack(16451): Couldn't load memtrack module (No such file or directory) 06-05 20:20:11.012: E/android.os.Debug(16451): failed to load memtrack module: -2 06-05 20:20:11.202: E/EnterpriseContainerManager(817): ContainerPolicy Service is not yet ready!!! Please help me figure out what is wrong, or at least point me in the right direction. Thanks in advance.

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  • Constructors in Inner classes (implementing Interfaces)

    - by thepandaatemyface
    Hi, How would I go about writing a constructor for an inner class which is implementing an interface? I know I could make a whole new class, but I figure there's got to be a way to do something along the line of this: JButton b = new JButton(new AbstractAction() { public AbstractAction() { super("This is a button"); } public void actionPerformed(ActionEvent e) { System.out.println("button clicked"); } }); When I enter this it doesn't recognize the AbstractAction method as a constructor (compiler asks for return type). Anyone have an idea? Thanks

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  • Normal C++ code in Qt doesnt build and run

    - by Nick
    Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

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