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  • hand coding a parser

    - by John Leidegren
    For all you compiler gurus, I wanna write a recursive descent parser and I wanna do it with just code. No generating lexers and parsers from some other grammar and don't tell me to read the dragon book, i'll come around to that eventually. I wanna get into the gritty details about implementing a lexer and parser for a reasonable simple langauge, say CSS. And I wanna do this right. This will probably end up being a series of questions but right now I'm starting with a lexer. Tokenization rules for CSS can be found here. I find my self writing code like this (hopefully you can infer the rest from this snippet): public CssToken ReadNext() { int val; while ((val = _reader.Read()) != -1) { var c = (char)val; switch (_stack.Top) { case ParserState.Init: if (c == ' ') { continue; // ignore } else if (c == '.') { _stack.Transition(ParserState.SubIdent, ParserState.Init); } break; case ParserState.SubIdent: if (c == '-') { _token.Append(c); } _stack.Transition(ParserState.SubNMBegin); break; What is this called? and how far off am I from something reasonable well understood? I'm trying to balence something which is fair in terms of efficiency and easy to work with, using a stack to implement some kind of state machine is working quite well, but I'm unsure how to continue like this. What I have is an input stream, from which I can read 1 character at a time. I don't do any look a head right now, I just read the character then depending on the current state try to do something with that. I'd really like to get into the mind set of writing reusable snippets of code. This Transition method is currently means to do that, it will pop the current state of the stack and then push the arguments in reverse order. That way, when I write Transition(ParserState.SubIdent, ParserState.Init) it will "call" a sub routine SubIdent which will, when complete, return to the Init state. The parser will be implemented in much the same way, currently, having everyhing in a single big method like this allows me to easily return a token when I found one, but it also forces me to keep everything in one single big method. Is there a nice way to split these tokenization rules into seperate methods? Any input/advice on the matter would be greatly appriciated!

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  • Am I Leaking ADO.NET Connections?

    - by HardCode
    Here is an example of my code in a DAL. All calls to the database's Stored Procedures are structured this way, and there is no in-line SQL. Friend Shared Function Save(ByVal s As MyClass) As Boolean Dim cn As SqlClient.SqlConnection = Dal.Connections.MyAppConnection Dim cmd As New SqlClient.SqlCommand Try cmd.Connection = cn cmd.CommandType = CommandType.StoredProcedure cmd.CommandText = "proc_save_my_class" cmd.Parameters.AddWithValue("@param1", s.Foo) cmd.Parameters.AddWithValue("@param2", s.Bar) Return True Finally Dal.Utility.CleanupAdoObjects(cmd, cn) End Try End Function Here is the Connection factory (if I am using the correct term): Friend Shared Function MyAppConnection() As SqlClient.SqlConnection Dim cn As New SqlClient.SqlConnection(ConfigurationManager.ConnectionStrings("MyConnectionString").ToString) cn.Open() If cn.State <> ConnectionState.Open Then ' CriticalException is a custom object inheriting from Exception. Throw New CriticalException("Could not connect to the database.") Else Return cn End If End Function Here is the Dal.Utility.CleaupAdoObjects() function: Friend Shared Sub CleanupAdoObjects(ByVal cmd As SqlCommand, ByVal cn As SqlConnection) If cmd IsNot Nothing Then cmd.Dispose() If cn IsNot Nothing AndAlso cn.State <> ConnectionState.Closed Then cn.Close() End Sub I am getting a lot of "Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding." error messages reported by the users. The application's DAL opens a connection, reads or saves data, and closes it. No connections are ever left open - intentionally! There is nothing obvious on the Windows 2000 Server hosting the SQL Server 2000 that would indicate a problem. Nothing in the Event Logs and nothing in the SQL Server logs. The timeouts happen randomly - I cannot reproduce. It happens early in the day with only 1 to 5 users in the system. It also happens with around 50 users in the system. The most connections to SQL Server via Performance Monitor, for all databases, has been about 74. The timeouts happen in code that both saves to, and reads from, the database in different parts of the application. The stack trace does not point to one or two offending DAL functions. It's happened in many different places. Does my ADO.NET code appear to be able to leak connections? I've goolged around a bit, and I've read that if the connection pool fills up, this can happen. However, I'm not explicitly setting any connection pooling. I've even tried to increase the Connection Timeout in the connection string, but timeouts happen long before the 300 second (5 minute) value: <add name="MyConnectionString" connectionString="Data Source=MyServer;Initial Catalog=MyDatabase;Integrated Security=SSPI;Connection Timeout=300;"/> I'm at a total loss already as to what is causing these Timeout issues. Any ideas are appreciated.

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  • Print newline in PHP in single quotes

    - by Matt
    Hey all, I try to use single quotes as much as possible and I've noticed that I can't use \n in single quotes. I know I can just enter a newline literally by pressing return, but that screws up the indentation of my code.. Is there some ASCII character or something that I can type that will produce newline when I'm using single quotes? Thanks! Matt Mueller

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  • How to convert String to Java.sql.date and Java.sql.time

    - by Mr Morgan
    Hello If I have a method like this: public static String convertDateTimeToString(DateTime dt) { return dt.getDate() + " " + dt.getTime(); } Which takes a Datetime object of my own which contains a Java.sql.date and a Java.sql.time, what is the best way of reversing the process so that I can substring a Java.sql.date and a Java.sql.time from a string? Or if DateTime dt is a JodaTime DateTime object? If this can be done without reference to Java.util.date. Thanks Mr Morgan.

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  • reverse this function

    - by ooo
    i have code that takes a csharp datetime and converts it into a long to plot in the "flot" graph. here is the code public static long GetJavascriptTimestamp(DateTime input) { TimeSpan span = new TimeSpan(DateTime.Parse("1/1/1970").Ticks); DateTime time = input.Subtract(span); return (long)(time.Ticks / 10000); } I now need an opposite function where i take this long value and get the csharp datetime object back. any idea if the above method can be reversed ?

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  • Jquery Automatic Image Slider w/ CSS & jQuery

    - by Jacinto
    This is Automatic Image Slider w/ CSS & jQuery by Soh Tanaka I am trying to customize it to show .desc when the mouse hover overs the slider but it does not seem to work any help? //Set Default State of each portfolio piece $(".paging").show(); $(".paging a:first").addClass("active"); //Get size of images, how many there are, then determin the size of the image reel. var imageWidth = $(".window").width(); var imageSum = $(".image_reel ul.examples").size(); var imageReelWidth = imageWidth * imageSum; //Adjust the image reel to its new size $(".image_reel").css({'width' : imageReelWidth}); //Paging + Slider Function rotate = function(){ var triggerID = $active.attr("rel") - 1; //Get number of times to slide var image_reelPosition = triggerID * imageWidth; //Determines the distance the image reel needs to slide $(".paging a").removeClass('active'); //Remove all active class $active.addClass('active'); //Add active class (the $active is declared in the rotateSwitch function) //Slider Animation $(".image_reel").animate({ left: -image_reelPosition }, 500 ); }; //Rotation + Timing Event rotateSwitch = function(){ play = setInterval(function(){ //Set timer - this will repeat itself every 3 seconds $active = $('.paging a.active').next(); if ( $active.length === 0) { //If paging reaches the end... $active = $('.paging a:first'); //go back to first } rotate(); //Trigger the paging and slider function }, 7000); //Timer speed in milliseconds (3 seconds) }; rotateSwitch(); //Run function on launch //On Hover $(".image_reel").hover(function() { clearInterval(play); //Stop the rotation }, function() { rotateSwitch(); //Resume rotation }); //Hide the tooglebox when page load $(".desc").hide(); //slide up and down when hover over heading 2 $(".image_reel").hover(function(){ // slide toggle effect set to slow you can set it to fast too. $(this).next(".desc").slideToggle("slow"); return true; }); //On Click $(".paging a").click(function() { $active = $(this); //Activate the clicked paging //Reset Timer clearInterval(play); //Stop the rotation rotate(); //Trigger rotation immediately rotateSwitch(); // Resume rotation return false; //Prevent browser jump to link anchor });

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  • How to fine tune a Membership Provider?

    - by Venemo
    After all the answers to my last question about fine-tuning turned out to be more useful than I expected, I thought that I would ask another similar Question about the MembershipProviders as well. Okay, so firstly, to clarify: I know what a Membership, Role, and Profile provider is, how to implement my own, and how to configure them, and most of the things about them. Implementing a role and profile provider is pretty straightforward, because they only require simple CRUD most of the time. (A single line of LINQ is enough for about half of the RoleProvider's methods.) However, the Membership provider is a differend beast. Many of you may realize that it violates the SR (Single Responsibility) principle, because it has to do EVERYTHING related to user management. While this leaves a lot of room for customizations, it has its downsides as well. There is no information on the Internet about what their EXACT expected behaviour is, such as when should they throw exceptions or simply return null, and stuff like that. I use this sample implementation for reference, but it also contains several contradictions. For example, it uses its own ValidateUser method for checking for credentials in the ChangePassword method. But the ValidateUser also updates the user's LastLoginDate to the current date. So, does the framework expect that I set it in my own provider as well, or is it simply a mistake in the sample? The other is: the ChangePassword method throws an exception every time when validating the new password, but CreateUser doesn't ever throw an exception, it simply returns false. And last, but not least: it counts the invalid password attempts of the user and locks them if it passes a threshold. While this is good, but it requires manual action to unlock the users. Is it a problem if my provider automatically unlocks the user after a certain amount of time? (EDIT) I almost forgot: the CreateUser method in the sample inserts the ID from the method parameter. I actually think this is bad practice, because I use inters with auto incement as IDs, so inserting them from some method parameter is not an option. Should I just ignore the parameter, or require that its value is null and throw an exception if it isn't? All in all, does ASP.NET have any assumptions about the behaviour of a MembershipProvider? Is there any documentation which describes when should I throw an exception or just return null? I also tried to find a set of generic unit tests which would provide some guidance about the expected behaviour, but no luck, I found plenty of articles about "Unit testing is good", and "How to unit test a MembershipProvider", but not one where there would be any actual tests. Thanks in advance for everyone!

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  • Uses of a C++ Arithmetic Promotion Header

    - by OlduvaiHand
    I've been playing around with a set of templates for determining the correct promotion type given two primitive types in C++. The idea is that if you define a custom numeric template, you could use these to determine the return type of, say, the operator+ function based on the class passed to the templates. For example: // Custom numeric class template <class T> struct Complex { Complex(T real, T imag) : r(real), i(imag) {} T r, i; // Other implementation stuff }; // Generic arithmetic promotion template template <class T, class U> struct ArithmeticPromotion { typedef typename X type; // I realize this is incorrect, but the point is it would // figure out what X would be via trait testing, etc }; // Specialization of arithmetic promotion template template <> class ArithmeticPromotion<long long, unsigned long> { typedef typename unsigned long long type; } // Arithmetic promotion template actually being used template <class T, class U> Complex<typename ArithmeticPromotion<T, U>::type> operator+ (Complex<T>& lhs, Complex<U>& rhs) { return Complex<typename ArithmeticPromotion<T, U>::type>(lhs.r + rhs.r, lhs.i + rhs.i); } If you use these promotion templates, you can more or less treat your user defined types as if they're primitives with the same promotion rules being applied to them. So, I guess the question I have is would this be something that could be useful? And if so, what sorts of common tasks would you want templated out for ease of use? I'm working on the assumption that just having the promotion templates alone would be insufficient for practical adoption. Incidentally, Boost has something similar in its math/tools/promotion header, but it's really more for getting values ready to be passed to the standard C math functions (that expect either 2 ints or 2 doubles) and bypasses all of the integral types. Is something that simple preferable to having complete control over how your objects are being converted? TL;DR: What sorts of helper templates would you expect to find in an arithmetic promotion header beyond the machinery that does the promotion itself?

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  • Java multithreaded server - each connection returns data. Processing on main thread?

    - by oliwr
    I am writing a client with an integrated server that should wait indefinitely for new connections - and handle each on a Thread. I want to process the received byte array in a system wide available message handler on the main thread. However, currently the processing is obviously done on the client thread. I've looked at Futures, submit() of ExecutorService, but as I create my Client-Connections within the Server, the data would be returned to the Server thread. How can I return it from there onto the main thread (in a synchronized packet store maybe?) to process it without blocking the server? My current implementation looks like this: public class Server extends Thread { private int port; private ExecutorService threadPool; public Server(int port) { this.port = port; // 50 simultaneous connections threadPool = Executors.newFixedThreadPool(50); } public void run() { try{ ServerSocket listener = new ServerSocket(this.port); System.out.println("Listening on Port " + this.port); Socket connection; while(true){ try { connection = listener.accept(); System.out.println("Accepted client " + connection.getInetAddress()); connection.setSoTimeout(4000); ClientHandler conn_c= new ClientHandler(connection); threadPool.execute(conn_c); } catch (IOException e) { System.out.println("IOException on connection: " + e); } } } catch (IOException e) { System.out.println("IOException on socket listen: " + e); e.printStackTrace(); threadPool.shutdown(); } } } class ClientHandler implements Runnable { private Socket connection; ClientHandler(Socket connection) { this.connection=connection; } @Override public void run() { try { // Read data from the InputStream, buffered int count; byte[] buffer = new byte[8192]; InputStream is = connection.getInputStream(); ByteArrayOutputStream out = new ByteArrayOutputStream(); // While there is data in the stream, read it while ((count = is.read(buffer)) > 0) { out.write(buffer, 0, count); } is.close(); out.close(); System.out.println("Disconnect client " + connection.getInetAddress()); connection.close(); // handle the received data MessageHandler.handle(out.toByteArray()); } catch (IOException e) { System.out.println("IOException on socket read: " + e); e.printStackTrace(); } return; } }

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  • Making a COM dll to be invoked from c#, HRESULT error handling?

    - by Daniel
    I'm making a COM interface that c# will be using, however i am wondering how i am to check for errors and exception handling on the c# end as at the moment i am just returning a HRESTULT or bool for most methods. But several things can go wrong in some of these methods and returning a E_FAIL just doesn't cut it. What can i do in order to return more information? Can i make a HRESULT of my own?

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  • Distinct with Count and SQl Server

    - by chopps
    Hey everyone, Trying to work on a query that will return the top 3 selling products with the three having a distinct artist. Im getting stuck on getting the unique artist. Simplified Table schema Product ProductID Product Name Artist Name OrderItem ProductID Qty So results would look like this... PID artist qty 34432, 'Jimi Hendrix', 6543 54833, 'stevie ray vaughan' 2344 12344, 'carrie underwood', 1

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  • Log4Net in App object?

    - by David Veeneman
    I am getting started with Logging in a WPF desktop app, using Log4Net as the logging component. Here is my question: In a simple desktop app, is there any reason not to instantiate my logger as a property ov the App class (App.xaml.cs), like this? public partial class App : Application { private static readonly ILog p_Logger = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType); public ILog Logger { get { return p_Logger; } } #endregion } } That would allow me to invoke the logger

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  • amfPHP Function Input Trouble

    - by she hates me
    Hello, I'm writing an amfPHP function which should take string input. It takes alphanumeric characters without a problem, but unfortunately it returns data as "2" if I send "2.UgnFl4kAWovazp_tVo6fHg__.86400.1260025200-571701419" as parameter. here is the function (real simple as you can see) function checkOpenSession($guid, $session_key) { return $session_key; }

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  • NHibernate query CreateCriteria

    - by Jacob
    Is it possible to chose what columns I want in return from Session.CreateCriteria() ? egz.: var x = session.CreateCriteria(); x.CreateAlias("EmployeePosition", "employeePosition"); x.Add(Restrictions.Eq("employeePosition.Name", "Developer")); and is there a way to add something like "select LastName" to avoid downloading the whole row.

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  • Explanation of this SQL sanitization code

    - by Derek
    I got this from for a login form tutorial: function clean($str) { $str = @trim($str); if(get_magic_quotes_gpc()) { $str = stripslashes($str); } return mysql_real_escape_string($str); } Could some one explain exactly what this does? I know that the 'clean' var is called up afterwards to sanitize the fields; I.e. $email = clean($_POST['email']);

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  • Get values of textareas generated dynamically

    - by Hulk
    In the below code,the textaraes are generated dynamically ,now how to get these values for validations in valid() function.. <script> function valid() { //get all textarea vales for validation } function add(col_det) { var row = '<tr>'; row += '<td>'; row += '<textarea rows = "8" cols = "8" class = "input" WRAP id="row_details'+r_count+'" name ="row_details'+r_count+'"></textarea>'; row += '</td>'; for (var i=0;i<col_det.length;i++) { row += '<td> <div id = "div_content_bold"> <textarea rows = "2" cols = "8" class = "input" id="c_details'+c_count+'" name="col_details'+l_count+'" WRAP ></textarea> </div> </td>'; } row += '<td></td>'; row += '</tr>'; return row; } $(document).ready(function() { var cnt = '<input type="text" name="title" id="title" ><br><br>'; cnt += '<table cellspacing="0" cellpadding="0" border="1" width="100%" id="l_table">'; cnt += '<tr>'; cnt += '<th width="30%">Category</th>'; cnt += headers(col_data); cnt += '<th width="10%">Grade obtained</th>'; cnt += '</tr>'; for(var i=0;i<criteria;i++) { cnt += add(col_data,i); } cnt += '</table>'; $('#content').append(cnt); }); </script> <form action="create/" method="post" name="aa"> <div id="content"></div> <table> <tr><td> <input type="submit" value="Save" id="Save" onclick="javascript:var ret=validate(row_c,c_count);return ret;"/></td></tr> Thanks....

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  • Am I using EJBs properly?

    - by kgrad
    I am using a JEE6 stack including JPA 2.0, JSF 2.0, EJB 3.1 etc. The way my architecture is setup is the following: I have JPA annotated DAOs using hibernate as my JPA provider. I have JSF Managed beans which correspond to my facelet/xhtml pages. I have EJBs that handle all of my database requests. My XHTML pages have JSF EL which make calls to my Managed beans. My managed beans contain references to my DAO entities which are managed by EJBs. For example, I have a user entity which is mapped to a db table. I have a user EJB which handles all CRUD operations that return Users. I have a page that edits a user. The highlevel workflow would be: navigate to user edit page - EL calls a method located in the managed bean that loads a user. The method calls userEJB.loadUser(user) from the EJB to get the user from the database. The user is edited and submit - a function is called in the managed bean which calls a function in the EJB to save the user. etc. I am running into issues accessing my data within my JSF pages using EJBs. I am having a lot of problems with lazy initialization errors, which I believe is due to how I have set things up. For example, I have a Client entity that has a List of users which are lazily loaded. In order to get a client I call a method in my EJB which goes to the database, finds a client and returns it. Later on i wish to access this clients list of users, in order to do so i have to go back to the EJB by calling some sort of method in order to load those users (since they are lazily loaded). This means that I have to create a method such as public List<User> getUserListByClient(Client c) { c = em.merge(c); return c.getUserList(); } The only purpose of this method is to load the users (and I'm not even positive this approach is good or works). If i was doing session management myself, I would like just leave the session open for the entire request and access the property directly, this would be fine as the session would be open anyway, there seems to be this one extra layer of indirection in EJBs which is making things difficult for me. I do like EJBs as I like the fact that they are controlled by the container, pooled, offer transaction management for free etc. However, I get the feeling that I am using them incorrectly, or I have set up my JSF app incorrectly. Any feedback would be greatly appreciated. thanks,

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  • Godaddy security exception

    - by stighy
    Hi at all. I can't resolve this issue. My web hoster, GoDaddy , return this error: Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.SecurityPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed. And i really don't know how to solve it. Are there Anyone with similar experience ? Thanks

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  • How to delegate SwingWorker's publish to other methods

    - by Savvas Dalkitsis
    My "problem" can be described by the following. Assume we have an intensive process that we want to have running in the background and have it update a Swing JProgress bar. The solution is easy: import java.util.List; import javax.swing.JOptionPane; import javax.swing.JProgressBar; import javax.swing.SwingWorker; /** * @author Savvas Dalkitsis */ public class Test { public static void main(String[] args) { final JProgressBar progressBar = new JProgressBar(0,99); SwingWorker<Void, Integer> w = new SwingWorker<Void, Integer>(){ @Override protected void process(List<Integer> chunks) { progressBar.setValue(chunks.get(chunks.size()-1)); } @Override protected Void doInBackground() throws Exception { for (int i=0;i<100;i++) { publish(i); Thread.sleep(300); } return null; } }; w.execute(); JOptionPane.showOptionDialog(null, new Object[] { "Process", progressBar }, "Process", JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, null, null); } } Now assume that i have various methods that take a long time. For instance we have a method that downloads a file from a server. Or another that uploads to a server. Or anything really. What is the proper way of delegating the publish method to those methods so that they can update the GUI appropriately? What i have found so far is this (assume that the method "aMethod" resides in some other package for instance): import java.awt.event.ActionEvent; import java.util.List; import javax.swing.AbstractAction; import javax.swing.Action; import javax.swing.JOptionPane; import javax.swing.JProgressBar; import javax.swing.SwingWorker; /** * @author Savvas Dalkitsis */ public class Test { public static void main(String[] args) { final JProgressBar progressBar = new JProgressBar(0,99); SwingWorker<Void, Integer> w = new SwingWorker<Void, Integer>(){ @Override protected void process(List<Integer> chunks) { progressBar.setValue(chunks.get(chunks.size()-1)); } @SuppressWarnings("serial") @Override protected Void doInBackground() throws Exception { aMethod(new AbstractAction() { @Override public void actionPerformed(ActionEvent e) { publish((Integer)getValue("progress")); } }); return null; } }; w.execute(); JOptionPane.showOptionDialog(null, new Object[] { "Process", progressBar }, "Process", JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, null, null); } public static void aMethod (Action action) { for (int i=0;i<100;i++) { action.putValue("progress", i); action.actionPerformed(null); try { Thread.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); } } } } It works but i know it lacks something. Any thoughts?

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