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• Parallel programming in C#

  - by Alxandr

  I'm interested in learning about parallel programming in C#.NET (not like everything there is to know, but the basics and maybe some good-practices), therefore I've decided to reprogram an old program of mine which is called ImageSyncer. ImageSyncer is a really simple program, all it does is to scan trough a folder and find all files ending with .jpg, then it calculates the new position of the files based on the date they were taken (parsing of xif-data, or whatever it's called). After a location has been generated the program checks for any existing files at that location, and if one exist it looks at the last write-time of both the file to copy, and the file "in its way". If those are equal the file is skipped. If not a md5 checksum of both files is created and matched. If there is no match the file to be copied is given a new location to be copied to (for instance, if it was to be copied to "C:\test.jpg" it's copied to "C:\test(1).jpg" instead). The result of this operation is populated into a queue of a struct-type that contains two strings, the original file and the position to copy it to. Then that queue is iterated over untill it is empty and the files are copied. In other words there are 4 operations: 1. Scan directory for jpegs 2. Parse files for xif and generate copy-location 3. Check for file existence and if needed generate new path 4. Copy files And so I want to rewrite this program to make it paralell and be able to perform several of the operations at the same time, and I was wondering what the best way to achieve that would be. I've came up with two different models I can think of, but neither one of them might be any good at all. The first one is to parallelize the 4 steps of the old program, so that when step one is to be executed it's done on several threads, and when the entire of step 1 is finished step 2 is began. The other one (which I find more interesting because I have no idea of how to do that) is to create a sort of worker and consumer model, so when a thread is finished with step 1 another one takes over and performs step 2 at that object (or something like that). But as said, I don't know if any of these are any good solutions. Also, I don't know much about parallel programming at all. I know how to make a thread, and how to make it perform a function taking in an object as its only parameter, and I've also used the BackgroundWorker-class on one occasion, but I'm not that familiar with any of them. Any input would be appreciated.

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• Best way to test for a variable's existence in PHP; isset() is clearly broken

  - by chazomaticus

  From the isset() docs: isset() will return FALSE if testing a variable that has been set to NULL. Basically, isset() doesn't check for whether the variable is set at all, but whether it's set to anything but NULL. Given that, what's the best way to actually check for the existence of a variable? I tried something like: if(isset($v) || @is_null($v)) (the @ is necessary to avoid the warning when $v is not set) but is_null() has a similar problem to isset(): it returns TRUE on unset variables! It also appears that: @($v === NULL) works exactly like @is_null($v), so that's out, too. How are we supposed to reliably check for the existence of a variable in PHP? Edit: there is clearly a difference in PHP between variables that are not set, and variables that are set to NULL: <?php $a = array('b' => NULL); var_dump($a); PHP shows that $a['b'] exists, and has a NULL value. If you add: var_dump(isset($a['b'])); var_dump(isset($a['c'])); you can see the ambiguity I'm talking about with the isset() function. Here's the output of all three of these var_dump()s: array(1) { ["b"]=> NULL } bool(false) bool(false) Further edit: two things. One, a use case. An array being turned into the data of an SQL UPDATE statement, where the array's keys are the table's columns, and the array's values are the values to be applied to each column. Any of the table's columns can hold a NULL value, signified by passing a NULL value in the array. You need a way to differentiate between an array key not existing, and an array's value being set to NULL; that's the difference between not updating the column's value and updating the column's value to NULL. Second, Zoredache's answer, array_key_exists() works correctly, for my above use case and for any global variables: <?php $a = NULL; var_dump(array_key_exists('a', $GLOBALS)); var_dump(array_key_exists('b', $GLOBALS)); outputs: bool(true) bool(false) Since that properly handles just about everywhere I can see there being any ambiguity between variables that don't exist and variables that are set to NULL, I'm calling array_key_exists() the official easiest way in PHP to truly check for the existence of a variable. (Only other case I can think of is for class properties, for which there's property_exists(), which, according to its docs, works similarly to array_key_exists() in that it properly distinguishes between not being set and being set to NULL.)

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• Implementing coroutines in Java

  - by JUST MY correct OPINION

  This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines currently available in Java, what would be required to implement them? As I said in that question, I know about the following: You can implement "coroutines" as threads/thread pools behind the scenes. You can do tricksy things with JVM bytecode behind the scenes to make coroutines possible. The so-called "Da Vinci Machine" JVM implementation has primitives that make coroutines doable without bytecode manipulation. There are various JNI-based approaches to coroutines also possible. I'll address each one's deficiencies in turn. Thread-based coroutines This "solution" is pathological. The whole point of coroutines is to avoid the overhead of threading, locking, kernel scheduling, etc. Coroutines are supposed to be light and fast and to execute only in user space. Implementing them in terms of full-tilt threads with tight restrictions gets rid of all the advantages. JVM bytecode manipulation This solution is more practical, albeit a bit difficult to pull off. This is roughly the same as jumping down into assembly language for coroutine libraries in C (which is how many of them work) with the advantage that you have only one architecture to worry about and get right. It also ties you down to only running your code on fully-compliant JVM stacks (which means, for example, no Android) unless you can find a way to do the same thing on the non-compliant stack. If you do find a way to do this, however, you have now doubled your system complexity and testing needs. The Da Vinci Machine The Da Vinci Machine is cool for experimentation, but since it is not a standard JVM its features aren't going to be available everywhere. Indeed I suspect most production environments would specifically forbid the use of the Da Vinci Machine. Thus I could use this to make cool experiments but not for any code I expect to release to the real world. This also has the added problem similar to the JVM bytecode manipulation solution above: won't work on alternative stacks (like Android's). JNI implementation This solution renders the point of doing this in Java at all moot. Each combination of CPU and operating system requires independent testing and each is a point of potentially frustrating subtle failure. Alternatively, of course, I could tie myself down to one platform entirely but this, too, makes the point of doing things in Java entirely moot. So... Is there any way to implement coroutines in Java without using one of these four techniques? Or will I be forced to use the one of those four that smells the least (JVM manipulation) instead?

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• How to add new object to an IList mapped as a one-to-many with NHibernate?

  - by Jørn Schou-Rode

  My model contains a class Section which has an ordered list of Statics that are part of this section. Leaving all the other properties out, the implementation of the model looks like this: public class Section { public virtual int Id { get; private set; } public virtual IList<Static> Statics { get; private set; } } public class Static { public virtual int Id { get; private set; } } In the database, the relationship is implemented as a one-to-many, where the table Static has a foreign key pointing to Section and an integer column Position to store its index position in the list it is part of. The mapping is done in Fluent NHibernate like this: public SectionMap() { Id(x => x.Id); HasMany(x => x.Statics).Cascade.All().LazyLoad() .AsList(x => x.WithColumn("Position")); } public StaticMap() { Id(x => x.Id); References(x => x.Section); } Now I am able to load existing Statics, and I am also able to update the details of those. However, I cannot seem to find a way to add new Statics to a Section, and have this change persisted to the database. I have tried several combinations of: mySection.Statics.Add(myStatic) session.Update(mySection) session.Save(myStatic) but the closest I have gotten (using the first two statements), is to an SQL exception reading: "Cannot insert the value NULL into column 'Position'". Clearly an INSERT is attempted here, but NHibernate does not seem to automatically append the index position to the SQL statement. What am I doing wrong? Am I missing something in my mappings? Do I need to expose the Position column as a property and assign a value to it myself? EDIT: Apparently everything works as expected, if I remove the NOT NULL constraint on the Static.Position column in the database. I guess NHibernate makes the insert and immediatly after updates the row with a Position value. While this is an anwers to the question, I am not sure if it is the best one. I would prefer the Position column to be not nullable, so I still hope there is some way to make NHibernate provide a value for that column directly in the INSERT statement. Thus, the question is still open. Any other solutions?

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• How to allow multiple filters to be selected - pagination?

  - by NewSOuser

  Hey, I am still trying to allow multiple filters to be selected for my pagination script but not sure how to do it being very new to php and programing in general. So in my pagination, when a user clicks the 'marketing' button(link) it queries the database just for the category that = marketing. The same goes for the other 2 filter buttons as seen in the script below. (automotive, sports). The problem is, I want to be able to select multiple filters like only marketing and auomotive or automotive and sports, for example if I click the marketing filter and then the automotive, it would display the categories that equal marketing, and automotive. I have no idea how to accomplish this, so I have come to the experts to help me out. This is the script I am working on: <h3>Filter results by:</h3> <a href='pagi_test.php?category=marketing'>marketing</a> <a href='pagi_test.php?category=automotive'>automotive</a> <a href='pagi_test.php?category=sports'>sports</a> <br /> <h3>Results:</h3> <?php //connecting to the database $error = "Could not connect to the database"; mysql_connect('localhost','root','root') or die($error); mysql_select_db('ajax_demo') or die($error); //max displayed per page $per_page = 3; //get start variable $start = $_GET['start']; $category = mysql_real_escape_string($_GET['category']); //count records $record_count = mysql_num_rows(mysql_query("SELECT * FROM explore WHERE category='$category'")); //count max pages $max_pages = $record_count / $per_page; //may come out as decimal if (!$start) $start = 0; //display data $get = mysql_query("SELECT * FROM explore WHERE category='$category' LIMIT $start, $per_page"); ?> <table width="800px"> <?php while ($row = mysql_fetch_assoc($get)) { // get data $id = $row['id']; $site_name = $row['site_name']; $site_description = $row['site_description']; ?> <tr> <td><?php echo $id; ?></td> <td><?php echo $site_name; ?></td> <td><?php echo $site_description; ?></td> </tr> <?php } //setup prev and next variables $prev = $start - $per_page; $next = $start + $per_page; //show prev button if (!($start<=0)) echo "<a href='pagi_test.php?category=$category&start=$prev'>Prev</a> "; //show page numbers //set variable for first page $i=1; for ($x=0;$x<$record_count;$x=$x+$per_page) { if ($start!=$x) echo " <a href='pagi_test.php?category=$category&start=$x'>$i</a> "; else echo " <a href='pagi_test.php?category=$category&start=$x'><b>$i</b></a> "; $i++; } //show next button if (!($start>=$record_count-$per_page)) echo " <a href='pagi_test.php?category=$category&start=$next'>Next</a>"; ?> Any help on this would be great. Thank you. -- EDIT -- If anyone has a better method of doing a pagination system with multiple filters than the one above, please let me know.

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• What to name 2 methods with same signatures

  - by coffeeaddict

  Initially I had a method in our DL that would take in the object it's updating like so: internal void UpdateCash(Cash Cash) { using (OurCustomDbConnection conn = CreateConnection("UpdateCash")) { conn.CommandText = @"update Cash set captureID = @captureID, ac_code = @acCode, captureDate = @captureDate, errmsg = @errorMessage, isDebit = @isDebit, SourceInfoID = @sourceInfoID, PayPalTransactionInfoID = @payPalTransactionInfoID, CreditCardTransactionInfoID = @CreditCardTransactionInfoID where id = @cashID"; conn.AddParam("@captureID", cash.CaptureID); conn.AddParam("@acCode", cash.ActionCode); conn.AddParam("@captureDate", cash.CaptureDate); conn.AddParam("@errorMessage", cash.ErrorMessage); conn.AddParam("@isDebit", cyberCash.IsDebit); conn.AddParam("@PayPalTransactionInfoID", cash.PayPalTransactionInfoID); conn.AddParam("@CreditCardTransactionInfoID", cash.CreditCardTransactionInfoID); conn.AddParam("@sourceInfoID", cash.SourceInfoID); conn.AddParam("@cashID", cash.Id); conn.ExecuteNonQuery(); } } My boss felt that creating an object every time just to update one or two fields is overkill. But I had a couple places in code using this. He recommended using just UpdateCash and sending in the ID for CAsh and field I want to update. Well the problem is I have 2 places in code using my original method. And those 2 places are updating 2 completely different fields in the Cash table. Before I was just able to get the existing Cash record and shove it into a Cash object, then update the properties I wanted to be updated in the DB, then send back the cash object to my method above. I need some advice on what to do here. I have 2 methods and they have the same signature. I'm not quite sure what to rename these because both are updating 2 completely different fields in the Cash table: internal void UpdateCash(int cashID, int paypalCaptureID) { using (OurCustomDbConnection conn = CreateConnection("UpdateCash")) { conn.CommandText = @"update Cash set CaptureID = @paypalCaptureID where id = @cashID"; conn.AddParam("@captureID", paypalCaptureID); conn.ExecuteNonQuery(); } } internal void UpdateCash(int cashID, int PayPalTransactionInfoID) { using (OurCustomDbConnection conn = CreateConnection("UpdateCash")) { conn.CommandText = @"update Cash set PaymentSourceID = @PayPalTransactionInfoID where id = @cashID"; conn.AddParam("@PayPalTransactionInfoID", PayPalTransactionInfoID); conn.ExecuteNonQuery(); } } So I thought hmm, maybe change the names to these so that they are now unique and somewhat explain what field its updating: UpdateCashOrderID UpdateCashTransactionInfoID ok but that's not really very good names. And I can't go too generic, for example: UpdateCashTransaction(int cashID, paypalTransactionID) What if we have different types of transactionIDs that the cash record holds besides just the paypalTransactionInfoID? such as the creditCardInfoID? Then what? Transaction doesn't tell me what kind. And furthermore what if you're updating 2 fields so you have 2 params next to the cashID param: UpdateCashTransaction(int cashID, paypalTransactionID, someOtherFieldIWantToUpdate) see my frustration? what's the best way to handle this is my boss doesn't like my first route?

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• How do I create/use a Fluent NHibernate convention to automap UInt32 properties to an SQL Server 200

  - by dommer

  I'm trying to use a convention to map UInt32 properties to a SQL Server 2008 database. I don't seem to be able to create a solution based on existing web sources, due to updates in the way Fluent NHibernate works - i.e. examples are out of date. I'm trying to have NHibernate generate the schema (via ExposeConfiguration). I'm happy to have NHibernate map it to anything sensible (e.g. bigint). Here's my code as it currently stands (which, when I try to expose the schema, fails due to SQL Server not supporting UInt32). Apologies for the code being a little long, but I'm not 100% sure what is relevant to the problem, so I'm erring on the side of caution. Most of it is based on this post. The error reported is: System.ArgumentException : Dialect does not support DbType.UInt32 I think I'll need a relatively comprehensive example, as I don't seem to be able to pull the pieces together into a working solution, at present. FluentConfiguration configuration = Fluently.Configure() .Database(MsSqlConfiguration.MsSql2008 .ConnectionString(connectionString)) .Mappings(mapping => mapping.AutoMappings.Add( AutoMap.AssemblyOf<Product>() .Conventions.Add<UInt32UserTypeConvention>())); configuration.ExposeConfiguration(x => new SchemaExport(x).Create(false, true)); namespace NHibernateTest { public class UInt32UserTypeConvention : UserTypeConvention<UInt32UserType> { // Empty. } } namespace NHibernateTest { public class UInt32UserType : IUserType { // Public properties. public bool IsMutable { get { return false; } } public Type ReturnedType { get { return typeof(UInt32); } } public SqlType[] SqlTypes { get { return new SqlType[] { SqlTypeFactory.Int32 }; } } // Public methods. public object Assemble(object cached, object owner) { return cached; } public object DeepCopy(object value) { return value; } public object Disassemble(object value) { return value; } public new bool Equals(object x, object y) { return (x != null && x.Equals(y)); } public int GetHashCode(object x) { return x.GetHashCode(); } public object NullSafeGet(IDataReader rs, string[] names, object owner) { int? i = (int?)NHibernateUtil.Int32.NullSafeGet(rs, names[0]); return (UInt32?)i; } public void NullSafeSet(IDbCommand cmd, object value, int index) { UInt32? u = (UInt32?)value; int? i = (Int32?)u; NHibernateUtil.Int32.NullSafeSet(cmd, i, index); } public object Replace(object original, object target, object owner) { return original; } } }

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• PhpMyAdmin Hangs On MySQL Error

  - by user75228

  I'm currently running PhpMyAdmin 4.0.10 (the latest version supporting PHP 4.2.X) on my Amazon EC2 connecting to a MySQL database on RDS. Everything works perfectly fine except actions that return a mysql error message. Whether I perform "any" kind of action that will return a mysql error, Phpmyadmin will hang with the yellow "Loading" box forever without displaying anything. For example, if I perform the following command in MySQL CLI : select * from 123; It instantly returns the following error : ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '123' at line 1 which is completely normal because table 123 doesn't exist. However, if I execute the exact same command in the "SQL" box in Phpmyadmin, after I click "Go" it'll display "Loading" and stops there forever. Has anyone ever encountered this kind of issue with Phpmyadmin? Is this a bug or I have something wrong with my config.inc.php? Any help would be much appreciated. I also noticed these error messages in my apache error logs : /opt/apache/bin/httpd: symbol lookup error: /opt/php/lib/php/extensions/no-debug-non-zts-20060613/iconv.so: undefined symbol: libiconv_open /opt/apache/bin/httpd: symbol lookup error: /opt/php/lib/php/extensions/no-debug-non-zts-20060613/iconv.so: undefined symbol: libiconv_open /opt/apache/bin/httpd: symbol lookup error: /opt/php/lib/php/extensions/no-debug-non-zts-20060613/iconv.so: undefined symbol: libiconv_open Below are my config.inc.php settings : <?php /* vim: set expandtab sw=4 ts=4 sts=4: */ /** * phpMyAdmin sample configuration, you can use it as base for * manual configuration. For easier setup you can use setup/ * * All directives are explained in documentation in the doc/ folder * or at <http://docs.phpmyadmin.net/>. * * @package PhpMyAdmin */ /* * This is needed for cookie based authentication to encrypt password in * cookie */ $cfg['blowfish_secret'] = 'something_random'; /* YOU MUST FILL IN THIS FOR COOKIE AUTH! */ /* * Servers configuration */ $i = 0; /* * First server */ $i++; /* Authentication type */ $cfg['Servers'][$i]['auth_type'] = 'cookie'; /* Server parameters */ $cfg['Servers'][$i]['host'] = '*.rds.amazonaws.com'; $cfg['Servers'][$i]['connect_type'] = 'tcp'; $cfg['Servers'][$i]['compress'] = true; /* Select mysql if your server does not have mysqli */ $cfg['Servers'][$i]['extension'] = 'mysqli'; $cfg['Servers'][$i]['AllowNoPassword'] = false; $cfg['LoginCookieValidity'] = '3600'; /* * phpMyAdmin configuration storage settings. */ /* User used to manipulate with storage */ $cfg['Servers'][$i]['controlhost'] = '*.rds.amazonaws.com'; $cfg['Servers'][$i]['controluser'] = 'pma'; $cfg['Servers'][$i]['controlpass'] = 'password'; /* Storage database and tables */ $cfg['Servers'][$i]['pmadb'] = 'phpmyadmin'; $cfg['Servers'][$i]['bookmarktable'] = 'pma__bookmark'; $cfg['Servers'][$i]['relation'] = 'pma__relation'; $cfg['Servers'][$i]['table_info'] = 'pma__table_info'; $cfg['Servers'][$i]['table_coords'] = 'pma__table_coords'; $cfg['Servers'][$i]['pdf_pages'] = 'pma__pdf_pages'; $cfg['Servers'][$i]['column_info'] = 'pma__column_info'; $cfg['Servers'][$i]['history'] = 'pma__history'; $cfg['Servers'][$i]['table_uiprefs'] = 'pma__table_uiprefs'; $cfg['Servers'][$i]['tracking'] = 'pma__tracking'; $cfg['Servers'][$i]['designer_coords'] = 'pma__designer_coords'; $cfg['Servers'][$i]['userconfig'] = 'pma__userconfig'; $cfg['Servers'][$i]['recent'] = 'pma__recent'; /* Contrib / Swekey authentication */ // $cfg['Servers'][$i]['auth_swekey_config'] = '/etc/swekey-pma.conf'; /* * End of servers configuration */ /* * Directories for saving/loading files from server */ $cfg['UploadDir'] = ''; $cfg['SaveDir'] = ''; /** * Defines whether a user should be displayed a "show all (records)" * button in browse mode or not. * default = false */ //$cfg['ShowAll'] = true; /** * Number of rows displayed when browsing a result set. If the result * set contains more rows, "Previous" and "Next". * default = 30 */ $cfg['MaxRows'] = 50; /** * disallow editing of binary fields * valid values are: * false allow editing * 'blob' allow editing except for BLOB fields * 'noblob' disallow editing except for BLOB fields * 'all' disallow editing * default = blob */ //$cfg['ProtectBinary'] = 'false'; /** * Default language to use, if not browser-defined or user-defined * (you find all languages in the locale folder) * uncomment the desired line: * default = 'en' */ //$cfg['DefaultLang'] = 'en'; //$cfg['DefaultLang'] = 'de'; /** * default display direction (horizontal|vertical|horizontalflipped) */ //$cfg['DefaultDisplay'] = 'vertical'; /** * How many columns should be used for table display of a database? * (a value larger than 1 results in some information being hidden) * default = 1 */ //$cfg['PropertiesNumColumns'] = 2; /** * Set to true if you want DB-based query history.If false, this utilizes * JS-routines to display query history (lost by window close) * * This requires configuration storage enabled, see above. * default = false */ //$cfg['QueryHistoryDB'] = true; /** * When using DB-based query history, how many entries should be kept? * * default = 25 */ //$cfg['QueryHistoryMax'] = 100; /* * You can find more configuration options in the documentation * in the doc/ folder or at <http://docs.phpmyadmin.net/>. */ ?>

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• ASP.NET MVC: How can I explain an invalid type violation to an end-user with Html.ValidationSummary?

  - by Terminal Frost

  Serious n00b warning here; please take mercy! So I finished the Nerd Dinner MVC Tutorial and I'm now in the process of converting a VB.NET application to ASP.NET MVC using the Nerd Dinner program as a sort of rough template. I am using the "IsValid / GetRuleViolations()" pattern to identify invalid user input or values that violate business rules. I am using LINQ to SQL and am taking advantage of the "OnValidate()" hook that allows me to run the validation and throw an application exception upon trying to save changes to the database via the CustomerRepository class. Anyway, everything works well, except that by the time the form values reach my validation method invalid types have already been converted to a default or existing value. (I have a "StreetNumber" property that is an integer, though I imagine this would be a problem for DateTime or any other non-strings as well.) Now, I am guessing that the UpdateModel() method throws an exception and then alters the value because the Html.ValidationMessage is displayed next to the StreetNumber field but my validation method never sees the original input. There are two problems with this: While the Html.ValidationMessage does signal that something is wrong, there is no corresponding entry in the Html.ValidationSummary. If I could even get the exception message to show up there indicating an invalid cast or something that would be better than nothing. My validation method which resides in my Customer partial class never sees the original user input so I do not know if the problem is a missing entry or an invalid type. I can't figure out how I can keep my validation logic nice and neat in one place and still get access to the form values. I could of course write some logic in the View that processes the user input, however that seems like the exact opposite of what I should be doing with MVC. Do I need a new validation pattern or is there some way to pass the original form values to my model class for processing? CustomerController Code // POST: /Customers/Edit/[id] [AcceptVerbs(HttpVerbs.Post)] public ActionResult Edit(int id, FormCollection formValues) { Customer customer = customerRepository.GetCustomer(id); try { UpdateModel(customer); customerRepository.Save(); return RedirectToAction("Details", new { id = customer.AccountID }); } catch { foreach (var issue in customer.GetRuleViolations()) ModelState.AddModelError(issue.PropertyName, issue.ErrorMessage); } return View(customer); }

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• How can a C/C++ program put itself into background?

  - by Larry Gritz

  What's the best way for a running C or C++ program that's been launched from the command line to put itself into the background, equivalent to if the user had launched from the unix shell with '&' at the end of the command? (But the user didn't.) It's a GUI app and doesn't need any shell I/O, so there's no reason to tie up the shell after launch. But I want a shell command launch to be auto-backgrounded without the '&' (or on Windows). Ideally, I want a solution that would work on any of Linux, OS X, and Windows. (Or separate solutions that I can select with #ifdef.) It's ok to assume that this should be done right at the beginning of execution, as opposed to somewhere in the middle. One solution is to have the main program be a script that launches the real binary, carefully putting it into the background. But it seems unsatisfying to need these coupled shell/binary pairs. Another solution is to immediately launch another executed version (with 'system' or CreateProcess), with the same command line arguments, but putting the child in the background and then having the parent exit. But this seems clunky compared to the process putting itself into background. Edited after a few answers: Yes, a fork() (or system(), or CreateProcess on Windows) is one way to sort of do this, that I hinted at in my original question. But all of these solutions make a SECOND process that is backgrounded, and then terminate the original process. I was wondering if there was a way to put the EXISTING process into the background. One difference is that if the app was launched from a script that recorded its process id (perhaps for later killing or other purpose), the newly forked or created process will have a different id and so will not be controllable by any launching script, if you see what I'm getting at. Edit #2: fork() isn't a good solution for OS X, where the man page for 'fork' says that it's unsafe if certain frameworks or libraries are being used. I tried it, and my app complains loudly at runtime: "The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec()." I was intrigued by daemon(), but when I tried it on OS X, it gave the same error message, so I assume that it's just a fancy wrapper for fork() and has the same restrictions. Excuse the OS X centrism, it just happens to be the system in front of me at the moment. But I am indeed looking for a solution to all three platforms.

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• NSSortDescriptor for NSFetchRequestController causes crash when value of sorted attribute is changed

  - by AJ

  I have an Core Data Entity with a number of attributes, which include amount(float), categoryTotal(float) and category(string) The initial ViewController uses a FethchedResultsController to retrieve the entities, and sorts them based on the category and then the categoryTotal. No problems so far. NSManagedObjectContext *moc = [self managedObjectContext]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Transaction" inManagedObjectContext:moc]; NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; [request setEntity:entityDescription]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(dateStamp >= %@) AND (dateStamp =< %@)", startDate, endDate]; [request setPredicate:predicate]; NSSortDescriptor *sortByCategory = [[NSSortDescriptor alloc] initWithKey:@"category" ascending:sortOrder]; NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByTotals, sortByCategory, nil]; [request setSortDescriptors:sortDescriptors]; NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:@"category" cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; On selecting a row (tableView:didSelectRowAtIndexPath), another view controller is loaded that allows editing of the amount field for the selected entity. Before returning to the first view, categoryTotal is updated by the new ‘amount’. The problem comes when returning to the first view controller, the app bombs with *Serious application error. Exception was caught during Core Data change processing: Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted). with userInfo (null) Program received signal: “EXC_BAD_ACCESS”.* This seems to be courtesy of NSSortDescriptor *sortByTotals = [[NSSortDescriptor alloc] initWithKey:@"categoryTotal" ascending:sortOrder]; If I remove this everything works as expected, but obviously without the sorting I want. I'm guessing this is to do with the sorting order changing due to categoryTotal changing (deletion / insertion) but can't find away fix this. I've verified that values are being modified correctly in the second view, so it appears down to the fetchedResultsController being confused. If the categoryAmount is changed to one that does not change the sort order, then no error is generated I'm not physically changing (ie deleting) the number of items the fetchedResultsController is returning ... the only other issue I can find that seem to generate this error Any ideas would be most welcome Thanks, AJ

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• Is "Systems Designer" the job title that best describes what I do? [closed]

  - by ivo-rossi

  After having worked as Java developer for almost 3 years in the same company that I currently work at, I moved to a new position associated with the development of the same application. I’m in this new position for more than 1 year now. My official job title is Systems Designer, but I’m not sure this is a title that expresses well what I do. So my question here is what would be the most appropriate job title for me? I see this question as important for my career development. After all, I should be able to explain in one word what I do. And it’s no longer “Java Developer”. Well, in more than one word, this is what I do: The business analysts gather requirements / business problems to be solved with the clients and then discuss these requirements with me. Given the requirements, I design the high level solutions to be implemented in our system (e.g. a new screen on the client application, modifications to existing reports, extension to the XML export format of some objects, etc). I base my decision on the current capabilities of the system, the overall impact that the solutions would have on the system and the estimated effort to implement them (as I was a developer of this same application for almost 3 years before I moved to this position, I’m confident in my estimates). The solutions are discussed iteratively with the business analysts until we agree that they are good. The outcome of this analysis is what we call the “requirements design” document, which is written by me, shared with clients for approval and then also with the team that is going to implement the solutions and test them. Note that there are a few problems that I need to find a solution for that are non-functional. If the users are unhappy with the performance of a certain tool, I will investigate what can be done to speed it up. I will do some research – often based in the Java code itself - to identify possibilities of optimizations. But in this new position I no longer code, the main outcome of my work is really the “requirements design”. Is “Systems Designer” really the most appropriate job title?

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• SQL Server architecture guidance

  - by Liam

  Hi, We are designing a new version of our existing product on a new schema. Its an internal web application with possibly 100 concurrent users (max)This will run on a SQL Server 2008 database. On of the discussion items recently is whether we should have a single database of split the database for performance reasons across 2 separate databases. The database could grow anywhere from 50-100GB over 5 years. We are Developers and not DBAs so it would be nice to get some general guidance. [I know the answer is not simple as it depends on the schema, archiving policy, amount of data etc. ] Option 1 Single Main Database [This is my preferred option]. The plan would be to have all the tables in a single database and possibly to use file groups and partitioning to separate the data if required across multiple disks. [Use schema if appropriate]. This should deal with the performance concerns One of the comments wrt this was that the a single server instance would still be processing this data so there would still be a processing bottle neck. For reporting we could have a separate reporting DB but this is still being discussed. Option 2 Split the database into 2 separate databases DB1 - Customers, Accounts, Customer resources etc DB2 - This would contain the bulk of the data [i.e. Vehicle tracking data, financial transaction tables etc]. These tables would typically contain a lot of data. [It could reside on a separate server if required] This plan would involve keeping the main data in a smaller database [DB1] and retaining the [mainly] read only transaction type data in a separate DB [DB2]. The UI would mainly read from DB1 and thus be more responsive. [I'm aware that this option makes it harder for Referential Integrity to be enforced.] Points for consideration As we are at the design stage we can at least make proper use of indexes to deal performance issues so thats why option 1 to me is attractive and its more of a standard approach. For both options we are considering implementing an archiving database. Apologies for the long Question. In summary the question is 1 DB or 2? Thanks in advance, Liam

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• Trouble using South with Django and Heroku

  - by Dan

  I had an existing Django project that I've just added South to. I ran syncdb locally. I ran manage.py schemamigration app_name locally I ran manage.py migrate app_name --fake locally I commit and pushed to heroku master I ran syncdb on heroku I ran manage.py schemamigration app_name on heroku I ran manage.py migrate app_name on heroku I then receive this: $ heroku run python notecard/manage.py migrate notecards Running python notecard/manage.py migrate notecards attached to terminal... up, run.1 Running migrations for notecards: - Migrating forwards to 0005_initial. > notecards:0003_initial Traceback (most recent call last): File "notecard/manage.py", line 14, in <module> execute_manager(settings) File "/app/lib/python2.7/site-packages/django/core/management/__init__.py", line 438, in execute_manager utility.execute() File "/app/lib/python2.7/site-packages/django/core/management/__init__.py", line 379, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File "/app/lib/python2.7/site-packages/django/core/management/base.py", line 191, in run_from_argv self.execute(*args, **options.__dict__) File "/app/lib/python2.7/site-packages/django/core/management/base.py", line 220, in execute output = self.handle(*args, **options) File "/app/lib/python2.7/site-packages/south/management/commands/migrate.py", line 105, in handle ignore_ghosts = ignore_ghosts, File "/app/lib/python2.7/site-packages/south/migration/__init__.py", line 191, in migrate_app success = migrator.migrate_many(target, workplan, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 221, in migrate_many result = migrator.__class__.migrate_many(migrator, target, migrations, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 292, in migrate_many result = self.migrate(migration, database) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 125, in migrate result = self.run(migration) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 99, in run return self.run_migration(migration) File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 81, in run_migration migration_function() File "/app/lib/python2.7/site-packages/south/migration/migrators.py", line 57, in <lambda> return (lambda: direction(orm)) File "/app/notecard/notecards/migrations/0003_initial.py", line 15, in forwards ('user', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['auth.User'])), File "/app/lib/python2.7/site-packages/south/db/generic.py", line 226, in create_table ', '.join([col for col in columns if col]), File "/app/lib/python2.7/site-packages/south/db/generic.py", line 150, in execute cursor.execute(sql, params) File "/app/lib/python2.7/site-packages/django/db/backends/util.py", line 34, in execute return self.cursor.execute(sql, params) File "/app/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute return self.cursor.execute(query, args) django.db.utils.DatabaseError: relation "notecards_semester" already exists I have 3 models. Section, Semester, and Notecards. I've added one field to the Notecards model and I cannot get it added on Heroku. Thank you.

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• basic operations for modifying a source document with XSLT

  - by SpliFF

  All the tutorials and examples I've found of XSLT processing seem to assume your destination will be a significantly different format/structure to your source and that you know the structure of the source in advance. I'm struggling with finding out how to perform simple "in-place" modifications to a HTML document without knowing anything else about its existing structure. Could somebody show me a clear example that, given an arbitrary unknown HTML source will: 1.) delete the classname 'foo' from all divs 2.) delete a node if its empty (ie <p></p>) 3.) delete a <p> node if its first child is <br> 4.) add newattr="newvalue" to all H1 5.) replace 'heading' in text nodes with 'title' 6.) wrap all <u> tags in <b> tags (ie, <u>foo</u> -> <b><u>foo</u></b>) 7.) output the transformed document without changing anything else The above examples are the primary types of transform I wish to accomplish. Understanding how to do the above will go a long way towards helping me build more complex transforms. To help clarify/test the examples here is a sample source and output, however I must reiterate that I want to work with arbitrary samples without rewriting the XSLT for each source: <!doctype html> <html> <body> <h1>heading</h1> <p></p> <p><br>line</p> <div class="foo bar"><u>baz</u></div> <p>untouched</p> </body> </html> output: <!doctype html> <html> <body> <h1 newattr="newvalue">title</h1> <div class="bar"><b><u>baz</u></b></div> <p>untouched</p> </body> </html>

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• Unable to get index from jQuery UI slider range

  - by Phil.Wheeler

  I'm having a hell of a time trying to get (what I thought was) a simple index from a collection of multiple sliders. The HTML is as follows: <div id="left-values" class="line"> <span id="l1" style="padding: 0 1.8em;">0</span> <span id="l2" style="padding: 0 1.8em;">0</span> <span id="l3" style="padding: 0 1.8em;">0</span> <span id="l4" style="padding: 0 1.8em;">0</span> <span id="l5" style="padding: 0 1.8em;">0</span> <span id="l6" style="padding: 0 1.8em;">0</span> <span id="l7" style="padding: 0 1.8em;">0</span> <span id="l8" style="padding: 0 1.8em;">0</span> </div> And the jQuery code is: // setup audiometry sliders $("#eq > span").each(function (e) { // read initial values from markup and remove that var value = parseInt($(this).text()); // var index = $(this).index; <- this didn't work. $(this).empty(); $(this).slider({ value: value, slide: function (event, ui) { //console.log($(this).attr('id')); <- neither did this. //console.log(index); $('#left-values span:first').text(ui.value); } }) }); The problem is that jQuery UI - when creating a slider - replaces the existing HTML with its own markup. This includes any ID values and, for whatever reason, I can't get the index for a given slider to surface either. So I'm running out of ideas.

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• How do I create a thread-safe write-once read-many value in Java?

  - by Software Monkey

  This is a problem I encounter frequently in working with more complex systems and which I have never figured out a good way to solve. It usually involves variations on the theme of a shared object whose construction and initialization are necessarily two distinct steps. This is generally because of architectural requirements, similar to applets, so answers that suggest I consolidate construction and initialization are not useful. By way of example, let's say I have a class that is structured to fit into an application framework like so: public class MyClass { private /*ideally-final*/ SomeObject someObject; MyClass() { someObject=null; } public void startup() { someObject=new SomeObject(...arguments from environment which are not available until startup is called...); } public void shutdown() { someObject=null; // this is not necessary, I am just expressing the intended scope of someObject explicitly } } I can't make someObject final since it can't be set until startup() is invoked. But I would really like it to reflect it's write-once semantics and be able to directly access it from multiple threads, preferably avoiding synchronization. The idea being to express and enforce a degree of finalness, I conjecture that I could create a generic container, like so: public class WoRmObject<T> { private T object; WoRmObject() { object=null; } public WoRmObject set(T val) { object=val; return this; } public T get() { return object; } } and then in MyClass, above, do: private final WoRmObject<SomeObject> someObject; MyClass() { someObject=new WoRmObject<SomeObject>(); } public void startup() { someObject.set(SomeObject(...arguments from environment which are not available until startup is called...)); } Which raises some questions for me: Is there a better way, or existing Java object (would have to be available in Java 4)? Is this thread-safe provided that no other thread accesses someObject.get() until after it's set() has been called. The other threads will only invoke methods on MyClass between startup() and shutdown() - the framework guarantees this. Given the completely unsynchronized WoRmObject container, it is ever possible under either JMM to see a value of object which is neither null nor a reference to a SomeObject? In other words, does has the JMM always guaranteed that no thread can observe the memory of an object to be whatever values happened to be on the heap when the object was allocated.

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• Add class to elements which already have a class

  - by bwstud

  I have a group of divs which I'm dynamically generating when a button is clicked with the class, "brick". This gives them dimension and starting position of top: 0. I'm trying to get them to animate to the bottom of the view using a css transition with a second class assignment which gives them a bottom position: 0;. Can't figure out the syntax for adding a second class to elements with a pre-existing class. On inspection they only show the original class of, "brick". HTML <!DOCTYPE html> <html> <head> <script src="http://code.jquery.com/jquery-2.1.0.min.js"></script> <meta charset="utf-8"> <title>JS Bin</title> </head> <body> <div id="container"> <div id="button" >Click Me</div> </div> </body> </html> CSS #container { width: 100%; height: 100vh; padding: 10vmax; } #button { position: fixed; } .brick { position: relative; top: 0; height: 10vmax; width: 20vmax; background: white; margin: 0; padding: 0; transition: all 1s; } .drop { transition: all 1s; bottom 0; } The offending JS: var brickCount = function() { var count = prompt("How many boxes you lookin' for?"); for(var i=0; i < count; i++) { var newBrick = document.createElement("div"); newBrick.className="brick"; document.querySelector("#container") .appendChild(newBrick); } }; var getBricks = function(){ document.getElementByClass("brick"); }; var changeColor = function(){ getBricks.style.backgroundColor = '#'+Math.floor(Math.random()*16777215).toString(16); }; var addDrop = function() { getBricks.brick = "getBricks.brick" + " drop"; }; var multiple = function() { brickCount(); getBricks(); changeColor(); addDrop(); }; document.getElementById("button").onclick = function() {multiple();}; Thanks!

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• How to dynamically change the content of a facet in a custom component?

  - by romaintaz

  Hello, Let's consider that I want to extend an existing JSF component, such as the <rich:datatable/>. My main requirement is to dynamically modify the content of a <f:facet>, to change its content. What is the best way to achieve that? Or where is the best place in the code to achieve that? In my faces-config.xml, I have the following declaration: <faces-config> ... <component> <component-type>my.component.dataTable</component-type> <component-class>my.project.component.table.MyHtmlDataTable</component-class> </component> ... <render-kit> <render-kit-id>HTML_BASIC</render-kit-id> <renderer> <component-family>org.richfaces.DataTable</component-family> <renderer-type>my.renderkit.dataTable</renderer-type> <renderer-class>my.project.component.table.MyDataTableRenderer</renderer-class> </renderer> ... Also, my my-project.taglib.xml file (as I use Facelets) looks like: <facelet-taglib> <namespace>http://my.project/jsf</namespace> <tag> <tag-name>dataTable</tag-name> <component> <component-type>my.component.dataTable</component-type> <renderer-type>my.renderkit.dataTable</renderer-type> </component> </tag> So as you can see, I have two classes in my project for my custom datatable: MyHtmlDataTable and MyDataTableRenderer. One of my idea is to modify the content of the <f:facet> directly in the doEncodeBegin() method of my renderer. This is working (in fact almost working), but I don't really think that's the better place to achieve my modification. What do you think? Technical information: JSF 1.2, Facelets, Richfaces 3.3.2, Java 1.6

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• How to resolve strange conflict between form post and ajax post?

  - by Oliver Hyde

  On the one page, I am trying to use ajax to edit existing values. I am doing this by using jQuery Inline Edit and posting away the new data, updating the record and returning with success. This is working fine. Next I have implemented the ability to add new records, to do this I have a form at the end of the table, which submits post data then redirects back to the original page. Each of them work individually, but after I have used the form to add a new record, the inline editing stops to work. If I close the webpage and reopen it, it works fine again until I have used the form and it goes of the rails again. I have tried a number of solutions, clearing session data, giving the form a separate name, redirecting to an alternative page (which does work, but is not ideal as I want the form to redirect back to the original location ). Here is a sample of the view form data: <?php foreach($week->incomes as $income):?> <tr> <td><?php echo $income->name;?></td> <td width="70" style="text-align:right;" class="editableSingle income id<?php echo $income->id;?>">$<?php echo $income->cost;?></td> </tr> <?php endforeach;?> <?php echo form_open('budget/add/'.$week->id.'/income/index', 'class="form-vertical" id="add_income"'); ?> <tr> <td> <input type="text" name="name" class="input-small" placeholder="Name"> <input type="text" name="cost" class="input-small" placeholder="Cost"> </td> <td> <button type="submit" class="btn btn-small pull-right"><i class="icon-plus "></i></button> </td> </tr> <?php echo form_close(); ?> This is the javascript initialisation code: $(function(){ $.inlineEdit({ income: 'budget/update_income/', expense: 'budget/update_expense/' }, { animate: false, filterElementValue: function($o){ if ($o.hasClass('income')) { return $o.html().match(/\$(.+)/)[1]; } else if ($o.hasClass('expense')) { return $o.html().match(/\$(.+)/)[1]; } else { return $o.html(); } }, afterSave: function(o){ if (o.type == 'income') { $('.income.id' + o.id).prepend('$'); } if (o.type == 'expense') { $('.expense.id' + o.id).prepend('$'); } }, colors: { error:'green' } }); }); If I can provide any more information to clarify what I have attempted etc, let me know. Temporary Fix It seems I have come up with a work around, not ideal as I still am not sure what is causing the issue. I have created a method called redirect. public function redirect(){ redirect(''); } am now calling that after the form submit which has temporarily allows my multiple post submits to work.

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• FILE_NOT_FOUND when trying to open COM port C++

  - by Moutabreath

  I am trying to open a com port for reading and writing using C++ but I can't seem to pass the first stage of actually opening it. I get an INVALID_HANDLE_VALUE on the handle with GetLastError FILE_NOT_FOUND. I have searched around the web for a couple of days I'm fresh out of ideas. I have searched through all the questions regarding COM on this website too. I have scanned through the existing ports (or so I believe) to get the name of the port right. I also tried combinations of _T("COM1") with the slashes, without the slashes, with colon, without colon and without the _T I'm using windows 7 on 64 bit machine. this is the code i got I'll be glad for any input on this void SendToCom(char* data, int len) { DWORD cbNeeded = 0; DWORD dwPorts = 0; EnumPorts(NULL, 1, NULL, 0, &cbNeeded, &dwPorts); //What will be the return value BOOL bSuccess = FALSE; LPCSTR COM1 ; BYTE* pPorts = static_cast<BYTE*>(malloc(cbNeeded)); bSuccess = EnumPorts(NULL, 1, pPorts, cbNeeded, &cbNeeded, &dwPorts); if (bSuccess){ PORT_INFO_1* pPortInfo = reinterpret_cast<PORT_INFO_1*>(pPorts); for (DWORD i=0; i<dwPorts; i++) { //If it looks like "COMX" then size_t nLen = _tcslen(pPortInfo->pName); if (nLen > 3) { if ((_tcsnicmp(pPortInfo->pName, _T("COM"), 3) == 0) ){ COM1 =pPortInfo->pName; //COM1 ="\\\\.\\COM1"; HANDLE m_hCommPort = CreateFile( COM1 , GENERIC_READ|GENERIC_WRITE, // access ( read and write) 0, // (share) 0:cannot share the COM port NULL, // security (None) OPEN_EXISTING, // creation : open_existing FILE_FLAG_OVERLAPPED, // we want overlapped operation NULL // no templates file for COM port... ); if (m_hCommPort==INVALID_HANDLE_VALUE) { DWORD err = GetLastError(); if (err == ERROR_FILE_NOT_FOUND) { MessageBox(hWnd,"ERROR_FILE_NOT_FOUND",NULL,MB_ABORTRETRYIGNORE); } else if(err == ERROR_INVALID_NAME) { MessageBox(hWnd,"ERROR_INVALID_NAME",NULL,MB_ABORTRETRYIGNORE); } else { MessageBox(hWnd,"unkown error",NULL,MB_ABORTRETRYIGNORE); } } else{ WriteAndReadPort(m_hCommPort,data); } } pPortInfo++; } } } }

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• WinForm-style Invoke() in unmanaged C++

  - by Matt Green

  I've been playing with a DataBus-type design for a hobby project, and I ran into an issue. Back-end components need to notify the UI that something has happened. My implementation of the bus delivers the messages synchronously with respect to the sender. In other words, when you call Send(), the method blocks until all the handlers have called. (This allows callers to use stack memory management for event objects.) However, consider the case where an event handler updates the GUI in response to an event. If the handler is called, and the message sender lives on another thread, then the handler cannot update the GUI due to Win32's GUI elements having thread affinity. More dynamic platforms such as .NET allow you to handle this by calling a special Invoke() method to move the method call (and the arguments) to the UI thread. I'm guessing they use the .NET parking window or the like for these sorts of things. A morbid curiosity was born: can we do this in C++, even if we limit the scope of the problem? Can we make it nicer than existing solutions? I know Qt does something similar with the moveToThread() function. By nicer, I'll mention that I'm specifically trying to avoid code of the following form: if(! this->IsUIThread()) { Invoke(MainWindowPresenter::OnTracksAdded, e); return; } being at the top of every UI method. This dance was common in WinForms when dealing with this issue. I think this sort of concern should be isolated from the domain-specific code and a wrapper object made to deal with it. My implementation consists of: DeferredFunction - functor that stores the target method in a FastDelegate, and deep copies the single event argument. This is the object that is sent across thread boundaries. UIEventHandler - responsible for dispatching a single event from the bus. When the Execute() method is called, it checks the thread ID. If it does not match the UI thread ID (set at construction time), a DeferredFunction is allocated on the heap with the instance, method, and event argument. A pointer to it is sent to the UI thread via PostThreadMessage(). Finally, a hook function for the thread's message pump is used to call the DeferredFunction and de-allocate it. Alternatively, I can use a message loop filter, since my UI framework (WTL) supports them. Ultimately, is this a good idea? The whole message hooking thing makes me leery. The intent is certainly noble, but are there are any pitfalls I should know about? Or is there an easier way to do this?

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• Simplifying const Overloading?

  - by templatetypedef

  Hello all- I've been teaching a C++ programming class for many years now and one of the trickiest things to explain to students is const overloading. I commonly use the example of a vector-like class and its operator[] function: template <typename T> class Vector { public: T& operator[] (size_t index); const T& operator[] (size_t index) const; }; I have little to no trouble explaining why it is that two versions of the operator[] function are needed, but in trying to explain how to unify the two implementations together I often find myself wasting a lot of time with language arcana. The problem is that the only good, reliable way that I know how to implement one of these functions in terms of the other is with the const_cast/static_cast trick: template <typename T> const T& Vector<T>::operator[] (size_t index) const { /* ... your implementation here ... */ } template <typename T> T& Vector<T>::operator[] (size_t index) { return const_cast<T&>(static_cast<const Vector&>(*this)[index]); } The problem with this setup is that it's extremely tricky to explain and not at all intuitively obvious. When you explain it as "cast to const, then call the const version, then strip off constness" it's a little easier to understand, but the actual syntax is frightening,. Explaining what const_cast is, why it's appropriate here, and why it's almost universally inappropriate elsewhere usually takes me five to ten minutes of lecture time, and making sense of this whole expression often requires more effort than the difference between const T* and T* const. I feel that students need to know about const-overloading and how to do it without needlessly duplicating the code in the two functions, but this trick seems a bit excessive in an introductory C++ programming course. My question is this - is there a simpler way to implement const-overloaded functions in terms of one another? Or is there a simpler way of explaining this existing trick to students? Thanks so much!

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• ajaxSubmit and Other Code. Can someone help me determine what this code is doing?

  - by Matt Dawdy

  I've inherited some code that I need to debug. It isn't working at present. My task is to get it to work. No other requirements have been given to me. No, this isn't homework, this is a maintenance nightmare job. ASP.Net (framework 3.5), C#, jQury 1.4.2. This project makes heavy use of jQuery and AJAX. There is a drop down on a page that, when an item is chosen, is supposed to add that item (it's a user) to an object in the database. To accomplish this, the previous programmer first, on page load, dynamically loads the entire page through AJAX. To do this, he's got 5 div's, and each one is loaded from a jquery call to a different full page in the website. Somehow, the HTML and BODY and all the other stuff is stripped out and the contents of the div are loaded with the content of the aspx page. Which seems incredibly wrong to me since it relies on the browser to magically strip out html, head, body, form tags and merge with the existing html head body form tags. Also, as the "content" page is returned as a string, the previous programmer has this code running on it before it is appended to the div: function CleanupResponseText(responseText, uniqueName) { responseText = responseText.replace("theForm.submit();", "SubmitSubForm(theForm, $(theForm).parent());"); responseText = responseText.replace(new RegExp("theForm", "g"), uniqueName); responseText = responseText.replace(new RegExp("doPostBack", "g"), "doPostBack" + uniqueName); return responseText; } When the dropdown itself fires it's onchange event, here is the code that gets fired: function SubmitSubForm(form, container) { //ShowLoading(container); $(form).ajaxSubmit( { url: $(form).attr("action"), success: function(responseText) { $(container).html(CleanupResponseText(responseText, form.id)); $("form", container).css("margin-top", "0").css("padding-top", "0"); //HideLoading(container); } } ); } This blows up in IE, with the message that "Microsoft JScript runtime error: Object doesn't support this property or method" -- which, I think, has to be that $(form).ajaxSubmit method doesn't exist. What is this code really trying to do? I am so turned around right now that I think my only option is to scrap everything and start over. But I'd rather not do that unless necessary. Is this code good? Is it working against .Net, and is that why we are having issues?

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• Infinite Refresh Loop in Firefox 3.0

  - by Martin Gordon

  I'm having a strange issue with my Javascript in Firefox 3.0.x. In Firefox 3.0.12, the page constantly reloads as soon as the list body is loaded. Neither Firefox 3.5, Safari 4 nor Chrome 5 (all on Mac) experience this issue. EDIT: I've created an isolated example rather than pulling this from my existing code. test.js function welcomeIndexOnLoad() { $("#options a").live('click', function () { optionClicked($(this), "get_list_body.html"); return false; }); $(document).ready(function() { optionClicked(null, "get_list_body.html"); }); } function optionClicked(sender, URL) { queryString = ""; if (sender != null) { queryString = $(sender).attr("rel"); } $("#list_body").load(URL + "?" + queryString, function(resp, status, AJAXReq) { console.log(resp); console.log("" + status); location.hash = queryString; }); }? test.html <html> <head> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js"></script> <script type="text/javascript" src="test.js"></script> <script> welcomeIndexOnLoad(); </script> </head> <body> <div id="container"> Outside of list body. <div id="list_body"> </div> </div> </body> </html> get_list_body.html <h3> <div id="options"> <a href="#" rel="change_list">Change List</a> </div> <ul> <li>li</li> </ul> jQuery line 5252 (an xhr.send() call) shows up in the console as soon as the page reloads: xhr.send( type === "POST" || type === "PUT" || type === "DELETE" ? s.data : null );

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