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  • Implement a simple class in your favorite language.

    - by Oscar Reyes
    I'm doing this to learn syntax of different programming languages. So, how would you defined the following class along with with it's operations in your favorite programming language? Image generated by http://yuml.me/ And a main method or equivalent to invoke it: For instance, for Java it would be: ... public static void main( String [] args ) { Fraction f = new Fraction(); f.numerator( 2 ); f.denominator( 5 ); f.print(); } ....

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  • C# SendMessage to C++ WinProc

    - by jws
    I need to send a string from C# to a C++ WindowProc. There are a number of related questions on SO related to this, but none of the answers have worked for me. Here's the situation: PInvoke: [DllImport("user32", CharSet = CharSet.Auto)] public extern static int SendMessage(IntPtr hWnd, uint wMsg, IntPtr wParam, string lParam); C#: string lparam = "abc"; NativeMethods.User32.SendMessage(handle, ConnectMsg, IntPtr.Zero, lparam); C++: API LRESULT CALLBACK HookProc (int code, WPARAM wParam, LPARAM lParam) { if (code >= 0) { CWPSTRUCT* cwp = (CWPSTRUCT*)lParam; ... (LPWSTR)cwp->lParam <-- BadPtr ... } return ::CallNextHookEx(0, code, wParam, lParam); } I've tried a number of different things, Marshalling the string as LPStr, LPWStr, also tried creating an IntPtr from unmanaged memory, and writing to it with Marshal.WriteByte. The pointer is the correct memory location on the C++ side, but the data isn't there. What am I missing?

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  • Understanding the concept of inheritance in Java

    - by Nirmal
    Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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  • Jquery UI Dialog Weird Behavior in Firefox - Whole screen becomes non-clickable on second overlay

    - by Dondon Vizcayno
    I have two links that show up two modal dialogs. These dialogs are static divs in the html of the page with their own ids. When I click the first link, the first dialog shows up and behaves correctly. But when I click the second link, the whole screen grays out and everything becomes unclickable, including the second dialog. It happens also the other way around, clicking the second link, and then the first link. This problems occurs only in Firefox but not in IE. Any ideas why this is happening in Firefox?

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  • Count How many lines in a Java String

    - by Simon Guo
    Need some compact code for counting how many lines in a string. It should be Java Code. And the string is separated by \r or \n will be considered as a separate line. For example, "Hello\nWorld\nThis\nIs\t" should return 4. The prototype is private static int countLines(String str) {...} Can someone provide a compact code? I have solution at here but it is too long, I think. Thank you.

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  • Best way to return a user-generated file, AJAX or Forms?

    - by Bill Zimmerman
    Hi, I'm new to web programming, so I need some help. I am writing a custom file-creation app for my site. A user visits the page, clicks on some various options and toggles some checkboxes, and the presses a 'download now' link. I have a PHP backend which will be processing the submission, and generating a PDF file. After the user presses the download link, I want the download to start like it would for any static link. My question is: What is the best way to do this? From my limited understanding, I have a choice between using AJAX or somehow using forms to submit the data. What are the advantages/disadvantages of each? Does anyone have any good links to examples? Thanks

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  • Best way to model map values in Grails?

    - by Mulone
    Hi guys, I have to implement map values in my Grails app. I have a class that can contain 0..N OsmTags, and the key is unique. In Java I would model this with a Map in each object, but I don't know how to map classes in Grails. So I defined this class: class OsmTag { /** OSM tag name, e.g. natural */ String key /** OSM tag value, e.g. park */ String value static constraints = { key blank:false, size:2..80,matches:/[\S]+/, unique:false value blank:false, size:1..250,matches:/[\S]+/, unique:false } } That works ok, but it's actually quite ugly because the tag key is not unique. Is there a better way to model this issue? Cheers

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  • Hash Digest / Array Comparison in C#

    - by Erik Karulf
    Hi All, I'm writing an application that needs to verify HMAC-SHA256 checksums. The code I currently have looks something like this: static bool VerifyIntegrity(string secret, string checksum, string data) { // Verify HMAC-SHA256 Checksum byte[] key = System.Text.Encoding.UTF8.GetBytes(secret); byte[] value = System.Text.Encoding.UTF8.GetBytes(data); byte[] checksum_bytes = System.Text.Encoding.UTF8.GetBytes(checksum); using (var hmac = new HMACSHA256(key)) { byte[] expected_bytes = hmac.ComputeHash(value); return checksum_bytes.SequenceEqual(expected_bytes); } } I know that this is susceptible to timing attacks. Is there a message digest comparison function in the standard library? I realize I could write my own time hardened comparison method, but I have to believe that this is already implemented elsewhere.

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  • Is it OK to pass SQLCommand as a parameter?

    - by TooFat
    I have a Business Layer that passes a Conn string and a SQLCommand to a Data Layer like so public void PopulateLocalData() { System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(); cmd.CommandType = System.Data.CommandType.StoredProcedure; cmd.CommandText = "usp_PopulateServiceSurveyLocal"; DataLayer.DataProvider.ExecSQL(ConnString, cmd); } The DataLayer then just executes the sql like so public static int ExecSQL(string sqlConnString, System.Data.SqlClient.SqlCommand cmd) { int rowsAffected; using (SqlConnection conn = new SqlConnection(sqlConnString)) { conn.Open(); cmd.Connection = conn; rowsAffected = cmd.ExecuteNonQuery(); cmd.Dispose(); } return rowsAffected; } Is it OK for me to pass the SQLCommand as a parameter like this or is there a better more accepted way of doing it. One of my concerns is if an error occurs when executing the query the cmd.dispose line will never execute. Does that mean it will continue to use up memory that will never be released?

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  • Implementig Java Iterable<E> interface

    - by Metz
    Hi, i wrote this code: public class C1 implements Iterable<NC1> { private LinkedList<NC1> list; public static class NC1 { ... } ... x public Iterator<NC1> iterator() { return list.iterator(); } } but eclipse whines (at the x-ed line): - The return type is incompatible with Iterable<NC1>.iterator() - implements java.lang.Iterable<NC1>.iterator i don't understand where the mistake is. thanks in advance.

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  • C++: warning: '...' declared with greater visibility than the type of its field '...::<anonymous>'

    - by Albert
    I'm getting these two warnings (with GCC 4.2 on MacOSX): /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154:0 /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154: warning: 'startMainLockDetector()::MainLockDetector' declared with greater visibility than the type of its field 'startMainLockDetector()::MainLockDetector::<anonymous' /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154:0 /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154: warning: 'startMainLockDetector()::MainLockDetector' declared with greater visibility than its base 'Action' In this code: struct Action { virtual ~Action() {} virtual int handle() = 0; }; static void startMainLockDetector() { /* ... */ struct MainLockDetector : Action { bool wait(Uint32 time) { /* ... */ } int handle() { /* ... */ } }; /* ... */ } I'm not exactly sure what these warnings mean (what visibility?) and how to fix them. (I really want the class MainLockDetector to be local for that function only.) I have already compiled the same code with a lot of other compilers (clang, GCC 3.*, GCC 4.0, GCC 4.4, etc) and never got any warning for this code.

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  • Finding the average of two number using classes and methods

    - by Have alook
    I want to use methods inside class. Q: find the average of two number using classes and methods. import java.util.*; class aaa { int a,b,sum,avrg; void average() { System.out.println("The average is ="+avrg); avrg=(sum/2); } } class ave { public static void main(String args[]){ aaa n=new aaa(); Scanner m=new Scanner(System.in); System.out.println("write two number"); n.a=m.nextInt(); n.b=m.nextInt(); n.average(); } }

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  • Panel is not displaying in JFrame

    - by mallikarjun
    I created a chat panel and added to Jframe but the panel is not displaying. But my sop in the chat panel are displaying in the console. Any one please let me know what could be the problem My Frame public class MyFrame extends JFrame { MyPanel chatClient; String input; public MyFrame() { input = (String)JOptionPane.showInputDialog(null, "Name:", "Connect to chat server", JOptionPane.QUESTION_MESSAGE, null,null, "Test"); input=input.trim(); chatClient = new MyPanel("localhost",input); setVisible(true); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); add(chatClient); } public static void main(String...args){ new MyFrame(); } } MyPanel: public class MyPanel extends JPanel{ ChatClient chatClient; public MyPanel(String host, String uid) { chatClient= new ChatClient(host,uid); add(chatClient.getChatPanel()); this.setVisible(true); } } chat panel: public class ChatClient { Client client; String name; ChatPanel chatPanel; String hostid; public ChatClient(String host,String uid){ client = new Client(); client.start(); System.out.println("in constructor"); Network.register(client); client.addListener(new Listener(){ public void connected(Connection connection){ System.out.println("in client connected method"); Network.RegisterName registerName = new Network.RegisterName(); registerName.name=name; client.sendTCP(registerName); } public void received(Connection connection,Object object){ System.out.println("in client received method"); if (object instanceof Network.UpdateNames) { Network.UpdateNames updateNames = (Network.UpdateNames)object; //chatFrame.setNames(updateNames.names); System.out.println("got it message"); return; } if (object instanceof Network.ChatMessage) { Network.ChatMessage chatMessage = (Network.ChatMessage)object; //chatFrame.addMessage(chatMessage.text); System.out.println("send it message"); return; } } }); // end of listner name=uid.trim(); hostid=host.trim(); chatPanel = new ChatPanel(hostid,name); chatPanel.setSendListener(new Runnable(){ public void run(){ Network.ChatMessage chatMessage = new Network.ChatMessage(); chatMessage.chatMessage=chatPanel.getSendText(); client.sendTCP(chatMessage); } }); new Thread("connect"){ public void run(){ try{ client.connect(5000, hostid,Network.port); }catch(IOException e){ e.printStackTrace(); } } }.start(); }//end of constructor static public class ChatPanel extends JPanel{ CardLayout cardLayout; JList messageList,nameList; JTextField sendText; JButton sendButton; JPanel topPanel,bottomPanel,panel; public ChatPanel(String host,String user){ setSize(600, 200); this.setVisible(true); System.out.println("Chat panel "+host+"user: "+user); { panel = new JPanel(new BorderLayout()); { topPanel = new JPanel(new GridLayout(1,2)); panel.add(topPanel); { topPanel.add(new JScrollPane(messageList=new JList())); messageList.setModel(new DefaultListModel()); } { topPanel.add(new JScrollPane(nameList=new JList())); nameList.setModel(new DefaultListModel()); } DefaultListSelectionModel disableSelections = new DefaultListSelectionModel() { public void setSelectionInterval (int index0, int index1) { } }; messageList.setSelectionModel(disableSelections); nameList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); } { bottomPanel = new JPanel(new GridBagLayout()); panel.add(bottomPanel,BorderLayout.SOUTH); bottomPanel.add(sendText=new JTextField(),new GridBagConstraints(0,0,1,1,1,0,GridBagConstraints.CENTER,GridBagConstraints.BOTH,new Insets(0,0,0,0),0,0)); bottomPanel.add(sendButton=new JButton(),new GridBagConstraints(1,0,1,1,0,0,GridBagConstraints.CENTER,0,new Insets(0,0,0,0),0,0)); } } sendText.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ sendButton.doClick(); } }); } public void setSendListener (final Runnable listener) { sendButton.addActionListener(new ActionListener() { public void actionPerformed (ActionEvent evt) { if (getSendText().length() == 0) return; listener.run(); sendText.setText(""); sendText.requestFocus(); } }); } public String getSendText () { return sendText.getText().trim(); } public void setNames (final String[] names) { EventQueue.invokeLater(new Runnable(){ public void run(){ DefaultListModel model = (DefaultListModel)nameList.getModel(); model.removeAllElements(); for(String name:names) model.addElement(name); } }); } public void addMessage (final String message) { EventQueue.invokeLater(new Runnable() { public void run () { DefaultListModel model = (DefaultListModel)messageList.getModel(); model.addElement(message); messageList.ensureIndexIsVisible(model.size() - 1); } }); } } public JPanel getChatPanel(){ return chatPanel; } }

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  • Android EditText within a ListView

    - by metalideath
    I have created a custom Array Adapter to bind a custom row that contains some static text and an editable EditText. I am trying to register to be notified when the user changes the text within the edit text and when notified to determine which ArrayList row the modified EditText corresponds to. In the past with other types of views such as a Spinner I could simply put a reference to the parent view and the row number into the tag for the Spinner view. And then when I was notified that the value changed I read the tag to determine how to correlate it back to the master ArrayList. The problem with registering to be notifed with an EditText change is that you do not get back a view but instead get a TextWatcher and I have no way to correlate back to the parent view or ArrayList row. What is the technique that you need to use in this circumstance?

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  • Signature of Collections.min/max method

    - by Marco
    In Java, the Collections class contains the following method: public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> c) Its signature is well-known for its advanced use of generics, so much that it is mentioned in the Java in a Nutshell book and in the official Sun Generics Tutorial. However, I could not find a convincing answer to the following question: Why is the formal parameter of type Collection<? extends T>, rather than Collection<T>? What's the added benefit?

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  • Session Logout in every two minutes.

    - by Pankaj Mishra
    I have Web Application in asp.net. Where I am maintaining Session for every User. And every Time I got logout in Approx 2 min. I tried to increase this time through web Config File upto 60 min but it is not working For me and I m getting same problem. I have created A class file For maintaining session.I am Using This Code. public static void createSession(System.Web.SessionState.HttpSessionState session) { Session = session; } This is my class file code. And I am calling this function in login Page load like this. BusinessClasses.SessionHandler.createSession(Page.Session); Then After I am Checking In everyPage. But this code is not working for me. Please Give Suggest me correct solution for this problem.

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  • Big data: An evening in the life of an actual buyer

    - by Jean-Pierre Dijcks
    Here I am, and this is an actual story of one of my evenings, trying to spend money with a company and ultimately failing. I just gave up and bought a service from another vendor, not the incumbent. Here is that story and how I think big data could actually fix this (and potentially prevent some of this from happening). In the end this story should illustrate how big data can benefit me (get me what I want without causing grief) and the company I am trying to buy something from. Note: Lots of details left out, I have no intention of being the annoyed blogger moaning about a specific company. What did I want to get? We watch TV, we have internet and we do have a land line. The land line is from a different vendor then the TV and the internet. I have decided that this makes no sense and I was going to get a bundle (no need to infer who this is, I just picked the generic bundle word as this is what I want to get) of all three services as this seems to save me money. I also want to not talk to people, I just want to click on a website when I feel like it and get it all sorted. I do think that is reality. I want to just do my shopping at 9.30pm while watching silly reruns on TV. Problem 1 - Bad links So, I'm an existing customer of the company I want to buy my bundle from. I go to the website, I click on offers. Turns out they are offers for new customers. After grumbling about how good they are, I click on offers for existing customers. Bummer, it goes to offers for new customers, so I click again on the link for offers for existing customers. No cigar... it just does not work. Big data solutions: 1) Do not show an existing customer the offers for new customers unless they are the same => This is only partially doable without login, but if a customer logs in the application should always know that this is an existing customer. But in general, imagine I do this from my home going through the internet service of this vendor to their domain... an instant filter should move me into the "existing customer route". 2) Flag dead or incorrect links => I've clicked the link for "existing customer offers" at least 3 times in under 5 seconds... Identifying patterns like this is easy in Hadoop and can very quickly make a list of potentially incorrect links. No need for realtime fixing, just the fact that this link can be pro-actively fixed across my entire web domain is a good thing. Preventative maintenance! Problem 2 - Purchase cannot be completed Apart from the fact that the browsing pattern to actually get to what I want is poorly designed, my purchase never gets past a specific point. In other words, I put something into my shopping cart and when I want to move on the application either crashes (with me going to an error page) or hangs or goes into something like chat. So I try again, and again and again. I think I tried this entire path (while being logged in!!) at least 10 times over the course of 20 minutes. I also clicked on the feedback button and, frustrated as I was, tried to explain this did not work... Big Data Solutions: 1) This web site does shopping cart analysis. I got an email next day stating I have things in my shopping cart, just click here to complete my purchase. After the above experience, this just added insult to my pain... 2) What should have happened, is a Hadoop job going over all logged in customers that are on the buy flow. It should flag anyone who is trying (multiple attempts from the same user to do the same thing), analyze the shopping card, the clicks to identify what the customers wants, his feedback provided (note: always own your own website feedback, never just farm this out!!) and in a short turn around time (30 minutes to 2 hours or so) email me with a link to complete my purchase. Not with a link to my shopping cart 12 hours later, but a link to actually achieve what I wanted... Why should this company go through the big data effort? I do believe this is relatively easy to do using our Oracle Event Processing and Big Data Appliance solutions combined. It is almost so simple (to my mind) that it makes no sense that this is not in place? But, now I am ranting... Why is this interesting? It is because of $$$$. After trying really hard, I mean I did this all in the evening, and again in the morning before going to work. I kept on failing, But I really wanted this to work... so an email that said, sorry, we noticed you tried to get a bundle (the log knows what I wanted, where I failed, so easy to generate), here is the link to click and complete your purchase. And here is 2 movies on us as an apology would have kept me as a customer, and got the additional $$$$ per month for the next couple of years. It would also lead to upsell on my phone package etc. Instead, I went to a completely different company, bought service from them. Lost money for company A, negative sentiment for company A and me telling this story at the water cooler so I'm influencing more people to think negatively about company A. All in all, a loss of easy money, a ding in sentiment and image where a relatively simple solution exists and can be in place on the software I describe routinely in this blog... For those who are coming to Openworld and maybe see value in solving the above, or are thinking of how to solve this, come visit us in Moscone North - Oracle Red Lounge or in the Engineered Systems Showcase.

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  • Why does Color.IsNamedColor not work when I create a color using Color.FromArgb()?

    - by Jon B
    In my app I allow the user to build a color, and then show him the name or value of the color later on. If the user picks red (full red, not red-ish), I want to show him "red". If he picks some strange color, then the hex value would be just fine. Here's sample code that demonstrates the problem: static string GetName(int r, int g, int b) { Color c = Color.FromArgb(r, g, b); // Note that specifying a = 255 doesn't make a difference if (c.IsNamedColor) { return c.Name; } else { // return hex value } } Even with very obvious colors like red IsNamedColor never returns true. Looking at the ARGB values for my color and Color.Red, I see no difference. However, calling Color.Red.GetHashCode() returns a different hash code than Color.FromArgb(255, 0, 0).GetHashCode(). How can I create a color using user specified RGB values and have the Name property come out right?

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  • Condition Variable in Shared Memory - is this code POSIX-conformant?

    - by GrahamS
    We've been trying to use a mutex and condition variable to synchronise access to named shared memory on a LynuxWorks LynxOS-SE system (POSIX-conformant). One shared memory block is called "/sync" and contains the mutex and condition variable, the other is "/data" and contains the actual data we are syncing access to. We're seeing failures from pthread_cond_signal() if both processes don't perform the mmap() calls in exactly the same order, or if one process mmaps in some other piece of shared memory before it mmaps the sync memory. This example code is about as short as I can make it: #include <sys/types.h> #include <sys/stat.h> #include <sys/mman.h> #include <sys/file.h> #include <stdlib.h> #include <pthread.h> #include <errno.h> #include <iostream> #include <string> using namespace std; static const string shm_name_sync("/sync"); static const string shm_name_data("/data"); struct shared_memory_sync { pthread_mutex_t mutex; pthread_cond_t condition; }; struct shared_memory_data { int a; int b; }; //Create 2 shared memory objects // - sync contains 2 shared synchronisation objects (mutex and condition) // - data not important void create() { // Create and map 'sync' shared memory int fd_sync = shm_open(shm_name_sync.c_str(), O_CREAT|O_RDWR, S_IRUSR|S_IWUSR); ftruncate(fd_sync, sizeof(shared_memory_sync)); void* addr_sync = mmap(0, sizeof(shared_memory_sync), PROT_READ|PROT_WRITE, MAP_SHARED, fd_sync, 0); shared_memory_sync* p_sync = static_cast<shared_memory_sync*> (addr_sync); // init the cond and mutex pthread_condattr_t cond_attr; pthread_condattr_init(&cond_attr); pthread_condattr_setpshared(&cond_attr, PTHREAD_PROCESS_SHARED); pthread_cond_init(&(p_sync->condition), &cond_attr); pthread_condattr_destroy(&cond_attr); pthread_mutexattr_t m_attr; pthread_mutexattr_init(&m_attr); pthread_mutexattr_setpshared(&m_attr, PTHREAD_PROCESS_SHARED); pthread_mutex_init(&(p_sync->mutex), &m_attr); pthread_mutexattr_destroy(&m_attr); // Create the 'data' shared memory int fd_data = shm_open(shm_name_data.c_str(), O_CREAT|O_RDWR, S_IRUSR|S_IWUSR); ftruncate(fd_data, sizeof(shared_memory_data)); void* addr_data = mmap(0, sizeof(shared_memory_data), PROT_READ|PROT_WRITE, MAP_SHARED, fd_data, 0); shared_memory_data* p_data = static_cast<shared_memory_data*> (addr_data); // Run the second process while it sleeps here. sleep(10); int res = pthread_cond_signal(&(p_sync->condition)); assert(res==0); // <--- !!!THIS ASSERT WILL FAIL ON LYNXOS!!! munmap(addr_sync, sizeof(shared_memory_sync)); shm_unlink(shm_name_sync.c_str()); munmap(addr_data, sizeof(shared_memory_data)); shm_unlink(shm_name_data.c_str()); } //Open the same 2 shared memory objects but in reverse order // - data // - sync void open() { sleep(2); int fd_data = shm_open(shm_name_data.c_str(), O_RDWR, S_IRUSR|S_IWUSR); void* addr_data = mmap(0, sizeof(shared_memory_data), PROT_READ|PROT_WRITE, MAP_SHARED, fd_data, 0); shared_memory_data* p_data = static_cast<shared_memory_data*> (addr_data); int fd_sync = shm_open(shm_name_sync.c_str(), O_RDWR, S_IRUSR|S_IWUSR); void* addr_sync = mmap(0, sizeof(shared_memory_sync), PROT_READ|PROT_WRITE, MAP_SHARED, fd_sync, 0); shared_memory_sync* p_sync = static_cast<shared_memory_sync*> (addr_sync); // Wait on the condvar pthread_mutex_lock(&(p_sync->mutex)); pthread_cond_wait(&(p_sync->condition), &(p_sync->mutex)); pthread_mutex_unlock(&(p_sync->mutex)); munmap(addr_sync, sizeof(shared_memory_sync)); munmap(addr_data, sizeof(shared_memory_data)); } int main(int argc, char** argv) { if(argc>1) { open(); } else { create(); } return (0); } Run this program with no args, then another copy with args, and the first one will fail at the assert checking the pthread_cond_signal(). But change the open() function to mmap() the "/sync" memory first and it will all work fine. This seems like a major bug in LynxOS but LynuxWorks claim that using mutex and condition variable in this way is not covered by the POSIX standard, so they are not interested. Can anyone determine if this code does violate POSIX? Or does anyone have any convincing documentation that it is POSIX compliant?

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  • What's the best practice to "look up" Java Enums?

    - by Marcus
    We have a REST API where clients can supply parameters representing values defined on the server in Java Enums. So we can provide a descriptive error, we add this lookup method to each Enum. Seems like we're just copying code (bad). Is there a better practice? public enum MyEnum { A, B, C, D; public static MyEnum lookup(String id) { try { return MyEnum.valueOf(id); } catch (IllegalArgumentException e) { throw new RuntimeException("Invalid value for my enum blah blah: " + id); } } } Update: The default error message provided by valueOf(..) would be No enum const class a.b.c.MyEnum.BadValue. I would like to provide a more descriptive error from the API.

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  • Trying to reduce the speed overhead of an almost-but-not-quite-int number class

    - by Fumiyo Eda
    I have implemented a C++ class which behaves very similarly to the standard int type. The difference is that it has an additional concept of "epsilon" which represents some tiny value that is much less than 1, but greater than 0. One way to think of it is as a very wide fixed point number with 32 MSBs (the integer parts), 32 LSBs (the epsilon parts) and a huge sea of zeros in between. The following class works, but introduces a ~2x speed penalty in the overall program. (The program includes code that has nothing to do with this class, so the actual speed penalty of this class is probably much greater than 2x.) I can't paste the code that is using this class, but I can say the following: +, -, +=, <, > and >= are the only heavily used operators. Use of setEpsilon() and getInt() is extremely rare. * is also rare, and does not even need to consider the epsilon values at all. Here is the class: #include <limits> struct int32Uepsilon { typedef int32Uepsilon Self; int32Uepsilon () { _value = 0; _eps = 0; } int32Uepsilon (const int &i) { _value = i; _eps = 0; } void setEpsilon() { _eps = 1; } Self operator+(const Self &rhs) const { Self result = *this; result._value += rhs._value; result._eps += rhs._eps; return result; } Self operator-(const Self &rhs) const { Self result = *this; result._value -= rhs._value; result._eps -= rhs._eps; return result; } Self operator-( ) const { Self result = *this; result._value = -result._value; result._eps = -result._eps; return result; } Self operator*(const Self &rhs) const { return this->getInt() * rhs.getInt(); } // XXX: discards epsilon bool operator<(const Self &rhs) const { return (_value < rhs._value) || (_value == rhs._value && _eps < rhs._eps); } bool operator>(const Self &rhs) const { return (_value > rhs._value) || (_value == rhs._value && _eps > rhs._eps); } bool operator>=(const Self &rhs) const { return (_value >= rhs._value) || (_value == rhs._value && _eps >= rhs._eps); } Self &operator+=(const Self &rhs) { this->_value += rhs._value; this->_eps += rhs._eps; return *this; } Self &operator-=(const Self &rhs) { this->_value -= rhs._value; this->_eps -= rhs._eps; return *this; } int getInt() const { return(_value); } private: int _value; int _eps; }; namespace std { template<> struct numeric_limits<int32Uepsilon> { static const bool is_signed = true; static int max() { return 2147483647; } } }; The code above works, but it is quite slow. Does anyone have any ideas on how to improve performance? There are a few hints/details I can give that might be helpful: 32 bits are definitely insufficient to hold both _value and _eps. In practice, up to 24 ~ 28 bits of _value are used and up to 20 bits of _eps are used. I could not measure a significant performance difference between using int32_t and int64_t, so memory overhead itself is probably not the problem here. Saturating addition/subtraction on _eps would be cool, but isn't really necessary. Note that the signs of _value and _eps are not necessarily the same! This broke my first attempt at speeding this class up. Inline assembly is no problem, so long as it works with GCC on a Core i7 system running Linux!

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  • Client-side or server-side processing?

    - by Nick
    So, I'm new to dynamic web design (my sites have been mostly static with some PHP), and I'm trying to learn the latest technologies in web development (which seems to be AJAX), and I was wondering, if you're transferring a lot of data, is it better to construct the page on the server and "push" it to the user, or is it better to "pull" the data needed and create the HTML around it on the clientside using JavaScript? More specifically, I'm using CodeIgniter as my PHP framework, and jQuery for JavaScript, and if I wanted to display a table of data to the user (dynamically), would it be better to format the HTML using CodeIgniter (create the tables, add CSS classes to elements, etc..), or would it be better to just serve the raw data using JSON and then build it into a table with jQuery? My intuition says to do it clientside, as it would save bandwidth and the page would probably load quicker with the new JavaScript optimizations all these browsers have now, however, then the site would break for someone not using JavaScript... Thanks for the help

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  • Why is my code not printing anything to stdout?

    - by WM
    I'm trying to calculate the average of a student's marks: import java.util.Scanner; public class Average { public static void main(String[] args) { int mark; int countTotal = 0; // to count the number of entered marks int avg = 0; // to calculate the total average Scanner Scan = new Scanner(System.in); System.out.print("Enter your average: "); String Name = Scan.next(); while (Scan.hasNextInt()) { mark = Scan.nextInt(); countTotal++; avg = avg + ((mark - avg) / countTotal); } System.out.print( Name + " " + avg ); } }

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  • Managing important runtime business logic with regard to a codebase

    - by Daniel Beardsley
    I'm working on a project which will end up have a lot of application information stored in the form of records in a database. In this case, it's the configuration of data views: which grid columns to show/hide default filters to apply to each grid view column titles sorting subtotaling ... This information is a big part of the value of the application and is essential to it's function. The data will be altered by admins a fair amount, so it's not static and it wouldn't be appropriate to have to deploy a new version of the app every time the data changes. The question is, Where should this data be stored? It will definitely live in the database because that's how it's accessed, but I feel like it needs to also be kept with the version controlled codebase because it's an integral part of functioning of the application. Has anyone dealt with an issue like this before? What did you end up doing?

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  • Replicating Java's DecimalFormat in C#

    - by Frank Krueger
    I am trying to replicate a subset of Java's DecimalFormat class. Below is what I've come up with. Does this look right to everyone? public class DecimalFormat : NumberFormat { int _maximumFractionDigits; int _minimumFractionDigits; string _format; void RebuildFormat () { _format = "{0:0."; _format += new string ('0', _minimumFractionDigits); if (_maximumFractionDigits > _minimumFractionDigits) { _format += new string ('#', _maximumFractionDigits - _minimumFractionDigits); } _format += "}"; } public override string format (object value) { return string.Format (_format, value); } public override void setMaximumFractionDigits (int n) { _maximumFractionDigits = n; RebuildFormat (); } public override void setMinimumFractionDigits (int n) { _minimumFractionDigits = n; RebuildFormat (); } public override void setGroupingUsed (bool g) { } public static NumberFormat getInstance () { return new DecimalFormat (); } }

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