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• Have suggestions for these assembly mnemonics?

  - by Noctis Skytower

  Greetings! Last semester in college, my teacher in the Computer Languages class taught us the esoteric language named Whitespace. In the interest of learning the language better with a very busy schedule (midterms), I wrote an interpreter and assembler in Python. An assembly language was designed to facilitate writing programs easily, and a sample program was written with the given assembly mnemonics. Now that it is summer, a new project has begun with the objective being to rewrite the interpreter and assembler for Whitespace 0.3, with further developments coming afterwards. Since there is so much extra time than before to work on its design, you are presented here with an outline that provides a revised set of mnemonics for the assembly language. This post is marked as a wiki for their discussion. Have you ever had any experience with assembly languages in the past? Were there some instructions that you thought should have been renamed to something different? Did you find yourself thinking outside the box and with a different paradigm than in which the mnemonics were named? If you can answer yes to any of those questions, you are most welcome here. Subjective answers are appreciated! Stack Manipulation (IMP: [Space]) Stack manipulation is one of the more common operations, hence the shortness of the IMP [Space]. There are four stack instructions. hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item Arithmetic (IMP: [Tab][Space]) Arithmetic commands operate on the top two items on the stack, and replace them with the result of the operation. The first item pushed is considered to be left of the operator. add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo Heap Access (IMP: [Tab][Tab]) Heap access commands look at the stack to find the address of items to be stored or retrieved. To store an item, push the address then the value and run the store command. To retrieve an item, push the address and run the retrieve command, which will place the value stored in the location at the top of the stack. save Store load Retrieve Flow Control (IMP: [LF]) Flow control operations are also common. Subroutines are marked by labels, as well as the targets of conditional and unconditional jumps, by which loops can be implemented. Programs must be ended by means of [LF][LF][LF] so that the interpreter can exit cleanly. L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller halt End the program I/O (IMP: [Tab][LF]) Finally, we need to be able to interact with the user. There are IO instructions for reading and writing numbers and individual characters. With these, string manipulation routines can be written. The read instructions take the heap address in which to store the result from the top of the stack. print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack Question: How would you redesign, rewrite, or rename the previous mnemonics and for what reasons?

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• Are their any suggestions for this new assembly language?

  - by Noctis Skytower

  Greetings! Last semester in college, my teacher in the Computer Languages class taught us the esoteric language named Whitespace. In the interest of learning the language better with a very busy schedule (midterms), I wrote an interpreter and assembler in Python. An assembly language was designed to facilitate writing programs easily, and a sample program was written with the given assembly mnemonics. Now that it is summer, a new project has begun with the objective being to rewrite the interpreter and assembler for Whitespace 0.3, with further developments coming afterwards. Since there is so much extra time than before to work on its design, you are presented here with an outline that provides a revised set of mnemonics for the assembly language. This post is marked as a wiki for their discussion. Have you ever had any experience with assembly languages in the past? Were there some instructions that you thought should have been renamed to something different? Did you find yourself thinking outside the box and with a different paradigm than in which the mnemonics were named? If you can answer yes to any of those questions, you are most welcome here. Subjective answers are appreciated! Stack Manipulation (IMP: [Space]) Stack manipulation is one of the more common operations, hence the shortness of the IMP [Space]. There are four stack instructions. hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item Arithmetic (IMP: [Tab][Space]) Arithmetic commands operate on the top two items on the stack, and replace them with the result of the operation. The first item pushed is considered to be left of the operator. add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo Heap Access (IMP: [Tab][Tab]) Heap access commands look at the stack to find the address of items to be stored or retrieved. To store an item, push the address then the value and run the store command. To retrieve an item, push the address and run the retrieve command, which will place the value stored in the location at the top of the stack. save Store load Retrieve Flow Control (IMP: [LF]) Flow control operations are also common. Subroutines are marked by labels, as well as the targets of conditional and unconditional jumps, by which loops can be implemented. Programs must be ended by means of [LF][LF][LF] so that the interpreter can exit cleanly. L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller exit End the program I/O (IMP: [Tab][LF]) Finally, we need to be able to interact with the user. There are IO instructions for reading and writing numbers and individual characters. With these, string manipulation routines can be written. The read instructions take the heap address in which to store the result from the top of the stack. print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack Question: How would you redesign, rewrite, or rename the previous mnemonics and for what reasons?

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• Are there any suggestions for these new assembly mnemonics?

  - by Noctis Skytower

  Greetings! Last semester in college, my teacher in the Computer Languages class taught us the esoteric language named Whitespace. In the interest of learning the language better with a very busy schedule (midterms), I wrote an interpreter and assembler in Python. An assembly language was designed to facilitate writing programs easily, and a sample program was written with the given assembly mnemonics. Now that it is summer, a new project has begun with the objective being to rewrite the interpreter and assembler for Whitespace 0.3, with further developments coming afterwards. Since there is so much extra time than before to work on its design, you are presented here with an outline that provides a revised set of mnemonics for the assembly language. This post is marked as a wiki for their discussion. Have you ever had any experience with assembly languages in the past? Were there some instructions that you thought should have been renamed to something different? Did you find yourself thinking outside the box and with a different paradigm than in which the mnemonics were named? If you can answer yes to any of those questions, you are most welcome here. Subjective answers are appreciated! Stack Manipulation (IMP: [Space]) Stack manipulation is one of the more common operations, hence the shortness of the IMP [Space]. There are four stack instructions. hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item Arithmetic (IMP: [Tab][Space]) Arithmetic commands operate on the top two items on the stack, and replace them with the result of the operation. The first item pushed is considered to be left of the operator. add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo Heap Access (IMP: [Tab][Tab]) Heap access commands look at the stack to find the address of items to be stored or retrieved. To store an item, push the address then the value and run the store command. To retrieve an item, push the address and run the retrieve command, which will place the value stored in the location at the top of the stack. save Store load Retrieve Flow Control (IMP: [LF]) Flow control operations are also common. Subroutines are marked by labels, as well as the targets of conditional and unconditional jumps, by which loops can be implemented. Programs must be ended by means of [LF][LF][LF] so that the interpreter can exit cleanly. L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller halt End the program I/O (IMP: [Tab][LF]) Finally, we need to be able to interact with the user. There are IO instructions for reading and writing numbers and individual characters. With these, string manipulation routines can be written. The read instructions take the heap address in which to store the result from the top of the stack. print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack Question: How would you redesign, rewrite, or rename the previous mnemonics and for what reasons?

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• Redirecting to a dynamic page

  - by binarydev

  I have a page displaying blog posts (latest_posts.php) and another page that display single blog posts (blog.php) . I intend to link the image title in latest_posts.php so that it redirects to blog.php where it would display the particular post that was clicked. latest_posts.php: <!-- Header --> <h2 class="underline"> <span>What&#039;s new</span> <span></span> </h2> <!-- /Header --> <!-- Posts list --> <ul class="post-list post-list-1"> <?php /* Fetches Date/Time, Post Content and title */ include 'dbconnect.php'; $sql = "SELECT * FROM wp_posts"; $res = mysql_query($sql); while ( $row = mysql_fetch_array($res) ) { ?> <!-- Post #1 --> <li class="clear-fix"> <!-- Date --> <div class="post-list-date"> <div class="post-date-box"> <?php //Timestamp broken down to show accordingly $timestamp = $row['post_date']; $datetime = new DateTime($timestamp); $date = $datetime->format("d"); $month = $datetime->format("M"); ?> <h3> <?php echo $date; ?> </h3> <span> <?php echo $month; ?> </span> </div> </div> <!-- /Date --> <!-- Image + comments count --> <div class="post-list-image"> <!-- Image --> <div class="image image-overlay-url image-fancybox-url"> <a href="post.php" class="preloader-image"> <?php echo '<img src="', $row['image'], '" alt="' , $row['post_title'] , '\'s Blog Image" />'; ?> </a> </div> <!-- /Image --> </div> <!-- /Image + comments count --> <!-- Content --> <div class="post-list-content"> <div> <!-- Header --> <h4> <a href="post.php? . $row['ID'] . "> <?php echo $row['post_title']; ?> </a> </h4> <!-- /Header --> <!-- Excerpt --> <p> <?php echo $row ['post_content']; }?> </p> <!-- /Excerpt --> </div> </div> <!-- /Content --> </li> <!-- /Post #1 --> </ul> <!-- /Posts list --> <a href="blog.php" class="button-browse">Browse All Posts</a> </div> <?php require_once('include/twitter_user_timeline.php'); ?> blog.php: <?php require_once('include/header.php'); ?> <body class="blog"> <?php require_once('include/navigation_bar_blog.php'); ?> <div class="blog"> <div class="main"> <!-- Header --> <h2 class="underline"> <span>What&#039;s new</span> <span></span> </h2> <!-- /Header --> <!-- Layout 66x33 --> <div class="layout-p-66x33 clear-fix"> <!-- Left column --> <!-- <div class="column-left"> --> <!-- Posts list --> <ul class="post-list post-list-2"> <?php /* Fetches Date/Time, Post Content and title with Pagination */ include 'dbconnect.php'; //sets to default page if(empty($_GET['pn'])){ $page=1; } else { $page = $_GET['pn']; } // Index of the page $index = ($page-1)*3; $sql = "SELECT * FROM `wp_posts` ORDER BY `post_date` DESC LIMIT " . $index . " ,3"; $res = mysql_query($sql); //Loops through the values while ( $row = mysql_fetch_array($res) ) { ?> <!-- Post #1 --> <li class="clear-fix"> <!-- Date --> <div class="post-list-date"> <div class="post-date-box"> <?php //Timestamp broken down to show accordingly $timestamp = $row['post_date']; $datetime = new DateTime($timestamp); $date = $datetime->format("d"); $month = $datetime->format("M"); ?> <h3> <?php echo $date; ?> </h3> <span> <?php echo $month; ?> </span> </div> </div> <!-- /Date --> <!-- Image + comments count --> <div class="post-list-image"> <!-- Image --> <div class="image image-overlay-url image-fancybox-url"> <a href="post.php" class="preloader-image"> <?php echo '<img src="', $row['image'], '" alt="' , $row['post_title'] , '\'s Blog Image" />'; ?> </a> </div> <!-- /Image --> </div> <!-- /Image + comments count --> <!-- Content --> <div class="post-list-content"> <div> <?php $id = $_GET['ID']; $post = lookup_post_somehow($id); if($post) { // render post } else { echo 'blog post not found..'; } ?> <!-- Header --> <h4> <a href="post.php"> <?php echo $row['post_title']; ?> </a> </h4> <!-- /Header --> <!-- Excerpt --> <p> <?php echo $row ['post_content']; ?> </p> <!-- /Excerpt --> </div> </div> <!-- /Content --> </li> <!-- /Post #1 --> <?php } // close while loop ?> </ul> <!-- /Posts list --> <div><!-- Pagination --> <ul class="blog-pagination clear-fix"> <?php //Count the number of rows $numberofrows = mysql_query("SELECT COUNT(ID) FROM `wp_posts`"); //Do ciel() to round the result according to number of posts $postsperpage = 4; $numOfPages = ceil($numberofrows / $postsperpage); for($i=1; $i < $numOfPages; $i++) { //echos links for each page $paginationDisplay = '<li><a href="blog.php?pn=' . $i . '">' . $i . '</a></li>'; echo $paginationDisplay; } ?> <!-- <li><a href="#" class="selected">1</a></li> <li><a href="#">2</a></li> <li><a href="#">3</a></li> <li><a href="#">4</a></li> --> </ul> </div><!-- /Pagination --> <!-- /div> --> <!-- Left column --> </div> <!-- /Layout 66x33 --> </div> </div> <?php require_once('include/twitter_user_timeline.php'); ?> <?php require_once('include/footer_blog.php'); ?> How do I render?

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• Where do I start ?

  - by Panthe

  Brief History: Just graduated high school, learned a bit of python and C++, have no friends with any helpful computer knowledge at all. Out of anyone i met in my school years I was probably the biggest nerd, but no one really knew. I consider my self to have a vast amount of knowledge on computers and tech then the average person. built/fixed tons of computers, and ability to troubleshoot pretty much any problem I came across. Now that high school is over, Ive really been thinking about my career. Loving, living computers for the past 15 years of my life I decided to take my ability's and try to learn computer programming, why I didn't start earlier I don't know, seems to be big mistake on my part... Doing some research I concluded that Python was the first programming language I should learn, since it was high level and easier to understand then C++ and Java. I also knew that to become good at what I did I needed to know more then just 2 or 3 languages, which didn't seem like a big problem considering once I learned the way Python worked, mainly syntax changed, and the rest would come naturally. I watched a couple of youtube videos, downloaded some book pdf's and snooped around from some tutorials here and there to get the hang of what to do. A two solid weeks had passed of trying to understand the syntax, create small programs that used the basic functions and understanding how it worked, I think i have got the hang of it. It breaks down into what ive been dealing with all this time (although i kinda knew) is that, input,output, loops, functions and other things derived from 0's and 1's storing data and recalling it, ect. (A VERY BASIC IDEA). Ive been able to create small programs, Hangman, file storing, temperature conversion, Caeser Cipher decode/encoding, Fibonacci Sequence and more, which i can create and understand how each work. Being 2 weeks into this, I have learned alot. Nothing at all compared to what i should be learning in the years to come if i get a grip on what I'm doing. While doing these programs I wont stop untill I've done doing a practice problem on a book, which embarresing enough will take me a couple hour depending on the complexity of it. I absolutly will not put aside the challenge until its complete, WHICH CAN BE EXTREMELY DRAINING, ive tried most problems without cheating and reached success, which makes me feel extremely proud of my self after completing something after much trial and error. After all this I have met the demon, alogrithm's which seem to be key to effiecent code. I cant seem to rap my head around some of the computer codes people put out there using numbers, and sometimes even basic functions, I have been able to understand them after a while but i know there are alot more complex things to come, considering my self smart, functions that require complex codes, actually hurt my brain. NOTHING EVER IN LIFE HURT MY BRAIN....... not even math classes in highschool, trying to understand some of the stuff people put out there makes me feel like i have a mental disadvantage lol... i still walk forward though, crossing my fingers that the understanding will come with time. Sorry if is this is long i just wish someone takes all these things into consideration when answering my question. even through all these downsides im still pushing through and continuing to try and get good at this, i know reading these tutorials wont make me any good unless i can become creative and make my own, understand other peoples programs, so this leads me to the simple question i could have asked in the beginning..... WHERE IN THE WORLD DO I START ? Ive been trying to find out how to understand some of the open source projects, how i can work with experianced coders to learn from them and help them, but i dont think thats even possible by the way how far people's knowledge is compared to me, i have no freinds who i can learn from, can someone help me and guide me into the right direction.. i have a huge motivation to get good at coding, anything information would be extremely helpful

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• How do I use constructor dependency injection to supply Models from a collection to their ViewModels

  - by GraemeF

  I'm using constructor dependency injection in my WPF application and I keep running into the following pattern, so would like to get other people's opinion on it and hear about alternative solutions. The goal is to wire up a hierarchy of ViewModels to a similar hierarchy of Models, so that the responsibility for presenting the information in each model lies with its own ViewModel implementation. (The pattern also crops up under other circumstances but MVVM should make for a good example.) Here's a simplified example. Given that I have a model that has a collection of further models: public interface IPerson { IEnumerable<IAddress> Addresses { get; } } public interface IAddress { } I would like to mirror this hierarchy in the ViewModels so that I can bind a ListBox (or whatever) to a collection in the Person ViewModel: public interface IPersonViewModel { ObservableCollection<IAddressViewModel> Addresses { get; } void Initialize(); } public interface IAddressViewModel { } The child ViewModel needs to present the information from the child Model, so it's injected via the constructor: public class AddressViewModel : IAddressViewModel { private readonly IAddress _address; public AddressViewModel(IAddress address) { _address = address; } } The question is, what is the best way to supply the child Model to the corresponding child ViewModel? The example is trivial, but in a typical real case the ViewModels have more dependencies - each of which has its own dependencies (and so on). I'm using Unity 1.2 (although I think the question is relevant across the other IoC containers), and I am using Caliburn's view strategies to automatically find and wire up the appropriate View to a ViewModel. Here is my current solution: The parent ViewModel needs to create a child ViewModel for each child Model, so it has a factory method added to its constructor which it uses during initialization: public class PersonViewModel : IPersonViewModel { private readonly Func<IAddress, IAddressViewModel> _addressViewModelFactory; private readonly IPerson _person; public PersonViewModel(IPerson person, Func<IAddress, IAddressViewModel> addressViewModelFactory) { _addressViewModelFactory = addressViewModelFactory; _person = person; Addresses = new ObservableCollection<IAddressViewModel>(); } public ObservableCollection<IAddressViewModel> Addresses { get; private set; } public void Initialize() { foreach (IAddress address in _person.Addresses) Addresses.Add(_addressViewModelFactory(address)); } } A factory method that satisfies the Func<IAddress, IAddressViewModel> interface is registered with the main UnityContainer. The factory method uses a child container to register the IAddress dependency that is required by the ViewModel and then resolves the child ViewModel: public class Factory { private readonly IUnityContainer _container; public Factory(IUnityContainer container) { _container = container; } public void RegisterStuff() { _container.RegisterInstance<Func<IAddress, IAddressViewModel>>(CreateAddressViewModel); } private IAddressViewModel CreateAddressViewModel(IAddress model) { IUnityContainer childContainer = _container.CreateChildContainer(); childContainer.RegisterInstance(model); return childContainer.Resolve<IAddressViewModel>(); } } Now, when the PersonViewModel is initialized, it loops through each Address in the Model and calls CreateAddressViewModel() (which was injected via the Func<IAddress, IAddressViewModel> argument). CreateAddressViewModel() creates a temporary child container and registers the IAddress model so that when it resolves the IAddressViewModel from the child container the AddressViewModel gets the correct instance injected via its constructor. This seems to be a good solution to me as the dependencies of the ViewModels are very clear and they are easily testable and unaware of the IoC container. On the other hand, performance is OK but not great as a lot of temporary child containers can be created. Also I end up with a lot of very similar factory methods. Is this the best way to inject the child Models into the child ViewModels with Unity? Is there a better (or faster) way to do it in other IoC containers, e.g. Autofac? How would this problem be tackled with MEF, given that it is not a traditional IoC container but is still used to compose objects?

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• WPF BackgroundWorker Execution

  - by Sanju

  Hi All, I've been programming C# for a while now (I'm a Computer Science major), and have never had to implement threading. I am currently building an application for a client that requires threading for a series of operations. Due to the nature of the client/provider agreement, I cannot release the source I am working with. The code that I have posted is in a general form. Pretty much the basic idea of what I am implementing, excluding the content specific source. The first Snippet demonstrates my basic structure, The Progress class is a custom progress window that is displayed as a dialog to prevent user UI interaction. I am currently using the code to complete database calls based on a collection of objects in another area of the application code. For example, I have a collection of "Objects" of one of my custom classes, that I perform these database calls on or on behalf of. My current set up works just fine when I call the "GeneralizedFunction" one and only one time. What I need to do is call this function once for every object in the collection. I was attempting to use a foreach loop to iterate through the collection, then I tried a for loop. For both loops, the result was the same. The Async operation performs exactly as desired for the first item in the collection. This, however, is the only one it works for. For each subsequent item, the progress box (my custom window) displays and immediately closes. In terms of the database calls, the calls for the first item in the collection are the only ones that successfully complete. All others aren't attempted. I've tried everything that I know and don't know to do, but I just cannot seem to get it to work. How can I get this to work for my entire collection? Any and all help is very greatly appreciated. Progress progress; BackgroundWorker worker; // Cancel the current process private void CancelProcess(object sender, EventArgs e) { worker.CancelAsync(); } // The main process ... "Generalized" private void GeneralizedFunction() { progress = new Progress(); progress.Cancel += CancelProcess; progress.Owner = this; Dispatcher pDispatcher = progress.Dispatcher; worker = new BackgroundWorker(); worker.WorkerSupportsCancellation = true; object[] workArgs = { arg1, arg2, arg3}; worker.DoWork += delegate(object s, DoWorkEventArgs args) { /* All main logic here */ foreach(Class ClassObject in ClassObjectCollection) { //Some more logic here UpdateProgressDelegate update = new UpdateProgressDelegate(updateProgress); pDispatcher.BeginInvoke(update, arg1,arg2,arg3); Thread.Sleep(1000); } }; worker.RunWorkerCompleted += delegate(object s, RunWorkerCompletedEventArgs args) { progress.Close(); }; worker.RunWorkerAsync(workArgs); progress.ShowDialog(); } public delegate void UpdateProgressDelegate(arg1,arg2,arg3); private void updateProgress(arg1,arg2,arg3) { //Update progress }

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• Recursing data into a 2 dimensional array in PHP 5

  - by user315699

  I'm getting bamboozled by "for each" loops and two dimensional arrays, and I'm a php newb so please bear with me (and ignore any variables with the word "image" - it's all about the mp3s, I just didn't change it from the xml tutorial) I found a php function on the net that list files in a directory, the output of which is: Array ( [0] = audio/1.mp3 [1] = audio/2.mp3 [2] = audio/3.mp3 [3] = audio/4.mp3 [4] = audio/5.mp3 ) As expected. And another that lists some info about mp3 files. $mp3datafile = 'audio/1.mp3'; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); print_r($mp3dataArray); unset($mp3dataArray); The output of which is Array ( [Filesize] = 31972 [Encoding] = CBR [etc] ) In order to automatically build RSS for a podcast, I need to generate XML for each item. So far so good. This is how I'm making the xml foreach ($imagearray as $key = $val) { $tnsoundfile = $xml_generator-addChild('item'); $tnsoundfile-addChild('title', $podcasttitle); $enclosure = $tnsoundfile-addChild('enclosure'); $enclosure-addAttribute('url', $val); // that's the filename $enclosure-addAttribute('length', $mp3dataArray[Filesize]); // << Length is file length, not time. But later I also need $mp3dataArray[Length mm:ss] for duration tag. $enclosure-addAttribute('type', 'audio/mpeg'); $tnsoundfile-addChild('guid', $path_to_image_dir.'/'.$val); } (The above has been truncated, I realise it's not proper xml right now, but it was just to show what was going on). Perfect. But I need to do it for as many files as there are in the directory. So, I have an array of the names of the files in the directory in $mp3data And, I have an array of mp3 data in $mp3dataArray from one iteration of the get_metadata() function. If I do the following, then I get a nice list of the mp3 data of the 5 files in the directory: foreach ($mp3data as $key = $val) { $mp3datafile = $val; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); print_r($mp3dataArray); unset($mp3dataArray); } As expected. Where I'm struggling, and have been for most of the day in spite of reading many forums and tutorials, is how to populate the "second dimension" of the array, so that it goes through 1,2,3,4 and 5.mp3 (or however many there are), extracts the metadata, then allows me to use it in the xml section above. Here's what I have foreach ($mp3data as $key = $val) { $mp3datafile = $val; $m = new mp3file($mp3datafile); $mp3dataArray = $m-get_metadata(); $mp3testarray = array($mp3dataArray); } print_r($mp3dataArray); Shouldn't that line print_r($mp3dataArray); give me a nice list of 5 lots of mp3 data, in the way it did when I recursed through the loop as before? Cos this is driving me nuts! It must be something so simple, and any help would be greatly appreciated. Thank you in advance.

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• C socket: problem with connect() and/or accept() between clients. 111: Connection refused

  - by Fantastic Fourier

  Hello ladies and gents, I'm having a bit of problem with accept(). I have a multiple clients and one server. The clients can connect and communicate just fine with server. But at one point, I need some clients to be directly connected to each other and I'm having a bit of difficulty there. The clients have bunch of threads going on, where one of them is handle_connection() and it has a while(1), looping forever to listen() and accept() whatever incoming connections. Whenever a client tries to connect() to other client, connect() returns an error, 111: Connection Refused. I know I have the right IP address and right port (I have specified a port just for between-client connections). The client that is waiting for connection doesn't notice anything, no new connection, nada. I copied some parts of the code, in hopes that someone can point out what I'm doing wrong. Thanks for any inputs! This is all client side code. void * handle_connections(void * arg) is a thread that loops forever to accept() any incoming connections. My server has a very similar thang going on and it works very well. (not sure why it doesn't work here..) This is the part of client that is waiting for a new incoming connection. int handle_request(void * arg, struct message * msg) is called at one point during program and tries to connect to a client that is specified in struct message * msg which includes struct sockaddr_in with IP address and port number and whatever. #define SERVER_PORT 10000 #define CLIENT_PORT 3456 #define MAX_CONNECTION 20 #define MAX_MSG 50 void * handle_connections(void * arg) { struct fd_info * info; struct sockaddr_in client_address; struct timeval timeout; fd_set readset, copyset; bzero((char * ) &client_address, sizeof(client_address)); // copy zeroes into string client_address.sin_family = AF_INET; client_address.sin_addr.s_addr = htonl(INADDR_ANY); client_address.sin_port = htons(CLIENT_PORT); sockfd = socket(AF_INET, SOCK_STREAM, 0); rv = listen(sockfd,MAX_CONNECTION); while(1) { new_sockfd = accept(sockfd, (struct sockaddr *) &client_address, &client_addr_len); //blocks if (new_sockfd < 0) { printf("C: ERROR accept() %i: %s \n", errno, strerror(errno)); sleep(2); } else { printf("C: accepted\n"); FD_SET(new_sockfd, &readset); // sets bit for new_sockfd to list of sockets to watch out for if (maxfd < new_sockfd) maxfd = new_sockfd; if (minfd > new_sockfd) minfd = new_sockfd; } //end if else (new_sockfd) } // end of the forever while loop } int handle_request(void * arg, struct message * msg) { char * cname, gname, payload; char * command[3]; int i, rv, sockfd, client_addr_len; struct sockaddr_in client_address; struct fd_info * info; info = (struct fd_info *) arg; sockfd = info->sock_fd; sockfd = socket(AF_INET, SOCK_STREAM, 0); if (sockfd == -1) { printf("HR: ERROR socket() %i: %s \n", errno, strerror(errno)); break; } else if (sockfd > 0) { printf("HR: new socks is %i \n", sockfd); printf("HR: sin_family is %i: %i\n", msg->peer.client_address.sin_family, msg->peer.client_address.sin_port); //************************************************************* //this is the part that returns error 111: Connection refused!!! //************************************************************* rv = connect(sockfd, (struct sockaddr *) &msg->peer.client_address, sizeof(struct sockaddr)); if (rv == -1) { printf("HR: ERROR: connect() %i: %s \n", errno, strerror(errno)); printf("HR: at %li \n", msg->peer.client_address.sin_addr.s_addr); break; } else if (rv > 0) { info->max_fd = sockfd; printf("HR: connected successfully!! \n"); } } }

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• Do you have suggestions for these assembly mnemonics?

  - by Noctis Skytower

  Greetings! Last semester in college, my teacher in the Computer Languages class taught us the esoteric language named Whitespace. In the interest of learning the language better with a very busy schedule (midterms), I wrote an interpreter and assembler in Python. An assembly language was designed to facilitate writing programs easily, and a sample program was written with the given assembly mnemonics. Now that it is summer, a new project has begun with the objective being to rewrite the interpreter and assembler for Whitespace 0.3, with further developments coming afterwards. Since there is so much extra time than before to work on its design, you are presented here with an outline that provides a revised set of mnemonics for the assembly language. This post is marked as a wiki for their discussion. Have you ever had any experience with assembly languages in the past? Were there some instructions that you thought should have been renamed to something different? Did you find yourself thinking outside the box and with a different paradigm than in which the mnemonics were named? If you can answer yes to any of those questions, you are most welcome here. Subjective answers are appreciated! Stack Manipulation (IMP: [Space]) Stack manipulation is one of the more common operations, hence the shortness of the IMP [Space]. There are four stack instructions. hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item Arithmetic (IMP: [Tab][Space]) Arithmetic commands operate on the top two items on the stack, and replace them with the result of the operation. The first item pushed is considered to be left of the operator. add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo Heap Access (IMP: [Tab][Tab]) Heap access commands look at the stack to find the address of items to be stored or retrieved. To store an item, push the address then the value and run the store command. To retrieve an item, push the address and run the retrieve command, which will place the value stored in the location at the top of the stack. save Store load Retrieve Flow Control (IMP: [LF]) Flow control operations are also common. Subroutines are marked by labels, as well as the targets of conditional and unconditional jumps, by which loops can be implemented. Programs must be ended by means of [LF][LF][LF] so that the interpreter can exit cleanly. L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller halt End the program I/O (IMP: [Tab][LF]) Finally, we need to be able to interact with the user. There are IO instructions for reading and writing numbers and individual characters. With these, string manipulation routines can be written. The read instructions take the heap address in which to store the result from the top of the stack. print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack Question: How would you redesign, rewrite, or rename the previous mnemonics and for what reasons?

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• Help with refactoring PHP code

  - by Richard Knop

  I had some troubles implementing Lawler's algorithm but thanks to SO and a bounty of 200 reputation I finally managed to write a working implementation: http://stackoverflow.com/questions/2466928/lawlers-algorithm-implementation-assistance I feel like I'm using too many variables and loops there though so I am trying to refactor the code. It should be simpler and shorter yet remain readable. Does it make sense to make a class for this? Any advice or even help with refactoring this piece of code is welcomed: <?php /* * @name Lawler's algorithm PHP implementation * @desc This algorithm calculates an optimal schedule of jobs to be * processed on a single machine (in reversed order) while taking * into consideration any precedence constraints. * @author Richard Knop * */ $jobs = array(1 => array('processingTime' => 2, 'dueDate' => 3), 2 => array('processingTime' => 3, 'dueDate' => 15), 3 => array('processingTime' => 4, 'dueDate' => 9), 4 => array('processingTime' => 3, 'dueDate' => 16), 5 => array('processingTime' => 5, 'dueDate' => 12), 6 => array('processingTime' => 7, 'dueDate' => 20), 7 => array('processingTime' => 5, 'dueDate' => 27), 8 => array('processingTime' => 6, 'dueDate' => 40), 9 => array('processingTime' => 3, 'dueDate' => 10)); // precedence constrainst, i.e job 2 must be completed before job 5 etc $successors = array(2=>5, 7=>9); $n = count($jobs); $optimalSchedule = array(); for ($i = $n; $i >= 1; $i--) { // jobs not required to precede any other job $arr = array(); foreach ($jobs as $k => $v) { if (false === array_key_exists($k, $successors)) { $arr[] = $k; } } // calculate total processing time $totalProcessingTime = 0; foreach ($jobs as $k => $v) { if (true === array_key_exists($k, $arr)) { $totalProcessingTime += $v['processingTime']; } } // find the job that will go to the end of the optimal schedule array $min = null; $x = 0; $lastKey = null; foreach($arr as $k) { $x = $totalProcessingTime - $jobs[$k]['dueDate']; if (null === $min || $x < $min) { $min = $x; $lastKey = $k; } } // add the job to the optimal schedule array $optimalSchedule[$lastKey] = $jobs[$lastKey]; // remove job from the jobs array unset($jobs[$lastKey]); // remove precedence constraint from the successors array if needed if (true === in_array($lastKey, $successors)) { foreach ($successors as $k => $v) { if ($lastKey === $v) { unset($successors[$k]); } } } } // reverse the optimal schedule array and preserve keys $optimalSchedule = array_reverse($optimalSchedule, true); // add tardiness to the array $i = 0; foreach ($optimalSchedule as $k => $v) { $optimalSchedule[$k]['tardiness'] = 0; $j = 0; foreach ($optimalSchedule as $k2 => $v2) { if ($j <= $i) { $optimalSchedule[$k]['tardiness'] += $v2['processingTime']; } $j++; } $i++; } echo '<pre>'; print_r($optimalSchedule); echo '</pre>';

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• C++ - Unwanted characters printed in output file.

  - by Gabe

  This is the last part of the program I am working on. I want to output a tabular list of songs to cout. And then I want to output a specially formatted list of song information into fout (which will be used as an input file later on). Printing to cout works great. The problem is that tons of extra character are added when printing to fout. Any ideas? Here's the code: void Playlist::printFile(ofstream &fout, LinkedList<Playlist> &allPlaylists, LinkedList<Songs*> &library) { fout.open("music.txt"); if(fout.fail()) { cout << "Output file failed. Information was not saved." << endl << endl; } else { if(library.size() > 0) fout << "LIBRARY" << endl; for(int i = 0; i < library.size(); i++) // For Loop - "Incremrenting i"-Loop to go through library and print song information. { fout << library.at(i)->getSongName() << endl; // Prints song name. fout << library.at(i)->getArtistName() << endl; // Prints artist name. fout << library.at(i)->getAlbumName() << endl; // Prints album name. fout << library.at(i)->getPlayTime() << " " << library.at(i)->getYear() << " "; fout << library.at(i)->getStarRating() << " " << library.at(i)->getSongGenre() << endl; } if(allPlaylists.size() <= 0) fout << endl; else if(allPlaylists.size() > 0) { int j; for(j = 0; j < allPlaylists.size(); j++) // Loops through all playlists. { fout << "xxxxx" << endl; fout << allPlaylists.at(j).getPlaylistName() << endl; for(int i = 0; i < allPlaylists.at(j).listSongs.size(); i++) { fout << allPlaylists.at(j).listSongs.at(i)->getSongName(); fout << endl; fout << allPlaylists.at(j).listSongs.at(i)->getArtistName(); fout << endl; } } fout << endl; } } } Here's a sample of the output to music.txt (fout): LIBRARY sadljkhfds dfgkjh dfkgh 3 3333 3 Rap sdlkhs kjshdfkh sdkjfhsdf 3 33333 3 Rap xxxxx PayröÈöè÷÷(÷H÷h÷÷¨÷È÷èøø(øHøhøø¨øÈøèùù(ùHùhùù¨ùÈùèúú(úHúhúú¨úÈúèûû(ûHûhûû¨ûÈûèüü(üHühüü¨üÈüèýý(ýHýhý ! sdkjfhsdf!õüöýÄõ¼5! sadljkhfds!þõÜö|ö\ þx þ  þÈ þð ÿ ÿ@ ÿh ÿ ÿ¸ ÿà 0 X ¨ Ð ø enter code here enter code here

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• trie reg exp parse step over char and continue

  - by forest.peterson

  Setup: 1) a string trie database formed from linked nodes and a vector array linking to the next node terminating in a leaf, 2) a recursive regular expression function that if A) char '*' continues down all paths until string length limit is reached, then continues down remaining string paths if valid, and B) char '?' continues down all paths for 1 char and then continues down remaining string paths if valid. 3) after reg expression the candidate strings are measured for edit distance against the 'try' string. Problem: the reg expression works fine for adding chars or swapping ? for a char but if the remaining string has an error then there is not a valid path to a terminating leaf; making the matching function redundant. I tried adding a 'step-over' ? char if the end of the node vector was reached and then followed every path of that node - allowing this step-over only once; resulted in a memory exception; I cannot find logically why it is accessing the vector out of range - bactracking? Questions: 1) how can the regular expression step over an invalid char and continue with the path? 2) why is swapping the 'sticking' char for '?' resulting in an overflow? Function: void Ontology::matchRegExpHelper(nodeT *w, string inWild, Set<string> &matchSet, string out, int level, int pos, int stepover) { if (inWild=="") { matchSet.add(out); } else { if (w->alpha.size() == pos) { int testLength = out.length() + inWild.length(); if (stepover == 0 && matchSet.size() == 0 && out.length() > 8 && testLength == tokenLength) {//candidate generator inWild[0] = '?'; matchRegExpHelper(w, inWild, matchSet, out, level, 0, stepover+1); } else return; //giveup on this path } if (inWild[0] == '?' || (inWild[0] == '*' && (out.length() + inWild.length() ) == level ) ) { //wild matchRegExpHelper(w->alpha[pos].next, inWild.substr(1), matchSet, out+w->alpha[pos].letter, level, 0, stepover);//follow path -> if ontology is full, treat '*' like a '?' } else if (inWild[0] == '*') matchRegExpHelper(w->alpha[pos].next, '*'+inWild.substr(1), matchSet, out+w->alpha[pos].letter, level, 0, stepover); //keep adding chars if (inWild[0] == w->alpha[pos].letter) //follow self matchRegExpHelper(w->alpha[pos].next, inWild.substr(1), matchSet, out+w->alpha[pos].letter, level, 0, stepover); //follow char matchRegExpHelper(w, inWild, matchSet, out, level, pos+1, stepover);//check next path } } Error Message: +str "Attempt to access index 1 in a vector of size 1." std::basic_string<char,std::char_traits<char>,std::allocator<char> > +err {msg="Attempt to access index 1 in a vector of size 1." } ErrorException Note: this function works fine for hundreds of test strings with '*' wilds if the extra stepover gate is not used Semi-Solved: I place a pos < w->alpha.size() condition on each path that calls w->alpha[pos]... - this prevented the backtrack calls from attempting to access the vector with an out of bounds index value. Still have other issues to work out - it loops infinitely adding the ? and backtracking to remove it, then repeat. But, moving forward now. Revised question: why during backtracking is the position index accumulating and/or not deincrementing - so at somepoint it calls w->alpha[pos]... with an invalid position that is either remaining from the next node or somehow incremented pos+1 when passing upward?

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• How do I learn algorithms?

  - by Panthe

  Brief History: Just graduated high school, learned a bit of python and C++, have no friends with any helpful computer knowledge at all. Out of anyone i met in my school years I was probably the biggest nerd, but no one really knew. I consider my self to have a vast amount of knowledge on computers and tech then the average person. built/fixed tons of computers, and ability to troubleshoot pretty much any problem I came across. Now that high school is over, Ive really been thinking about my career. Loving, living computers for the past 15 years of my life I decided to take my ability's and try to learn computer programming, why I didn't start earlier I don't know, seems to be big mistake on my part... Doing some research I concluded that Python was the first programming language I should learn, since it was high level and easier to understand then C++ and Java. I also knew that to become good at what I did I needed to know more then just 2 or 3 languages, which didn't seem like a big problem considering once I learned the way Python worked, mainly syntax changed, and the rest would come naturally. I watched a couple of youtube videos, downloaded some book pdf's and snooped around from some tutorials here and there to get the hang of what to do. A two solid weeks had passed of trying to understand the syntax, create small programs that used the basic functions and understanding how it worked, I think i have got the hang of it. It breaks down into what ive been dealing with all this time (although i kinda knew) is that, input,output, loops, functions and other things derived from 0's and 1's storing data and recalling it, ect. (A VERY BASIC IDEA). Ive been able to create small programs, Hangman, file storing, temperature conversion, Caeser Cipher decode/encoding, Fibonacci Sequence and more, which i can create and understand how each work. Being 2 weeks into this, I have learned alot. Nothing at all compared to what i should be lear ning in the years to come if i get a grip on what I'm doing. While doing these programs I wont stop untill I've done doing a practice problem on a book, which embarresing enough will take me a couple hour depending on the complexity of it. I absolutly will not put aside the challenge until its complete, WHICH CAN BE EXTREMELY DRAINING, ive tried most problems without cheating and reached success, which makes me feel extremely proud of my self after completing something after much trial and error. After all this I have met the demon, alogrithm's which seem to be key to effiecent code. I cant seem to rap my head around some of the computer codes people put out there using numbers, and sometimes even basic functions, I have been able to understand them after a while but i know there are alot more complex things to come, considering my self smart, functions that require complex codes, actually hurt my brain. NOTHING EVER IN LIFE HURT MY BRAIN....... not even math classes in highschool, trying to understand some of the stuff people put out there makes me feel like i have a mental disadvantage lol... i still walk forward though, crossing my fingers that the understanding will come with time. Sorry if is this is long i just wish someone takes all these things into consideration when answering my question. even through all these downsides im still pushing through and continuing to try and get good at this, i know reading these tutorials wont make me any good unless i can become creative and make my own, understand other peoples programs, so this leads me to the simple question i could have asked in the beginning..... WHERE IN THE WORLD DO I START ? Ive been trying to find out how to understand some of the open source projects, how i can work with experianced coders to learn from them and help them, but i dont think thats even possible by the way how far people's knowledge is compared to me, i have no freinds who i can learn from, can someone help me and guide me into the right direction.. i have a huge motivation to get good at coding, anything information would be extremely helpful

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• Java code optimization leads to numerical inaccuracies and errors

  - by rano

  I'm trying to implement a version of the Fuzzy C-Means algorithm in Java and I'm trying to do some optimization by computing just once everything that can be computed just once. This is an iterative algorithm and regarding the updating of a matrix, the clusters x pixels membership matrix U, this is the update rule I want to optimize: where the x are the element of a matrix X (pixels x features) and v belongs to the matrix V (clusters x features). And m is a parameter that ranges from 1.1 to infinity. The distance used is the euclidean norm. If I had to implement this formula in a banal way I'd do: for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < V.length; j++) { double num = D[i][j]; double sumTerms = 0; for(int k = 0; k < V.length; k++) { double thisDistance = D[i][k]; sumTerms += Math.pow(num / thisDistance, (1.0 / (m - 1.0))); } U[i][j] = (float) (1f / sumTerms); } } In this way some optimization is already done, I precomputed all the possible squared distances between X and V and stored them in a matrix D but that is not enough, since I'm cycling througn the elements of V two times resulting in two nested loops. Looking at the formula the numerator of the fraction is independent of the sum so I can compute numerator and denominator independently and the denominator can be computed just once for each pixel. So I came to a solution like this: int nClusters = V.length; double exp = (1.0 / (m - 1.0)); for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < nClusters; j++) { double distance = D[i][j]; double denominator = D[i][nClusters]; double numerator = Math.pow(distance, exp); U[i][j] = (float) (1f / (numerator * denominator)); } } Where I precomputed the denominator into an additional column of the matrix D while I was computing the distances: for (int i = 0; i < X.length; i++) { for (int j = 0; j < V.length; j++) { double sum = 0; for (int k = 0; k < nDims; k++) { final double d = X[i][k] - V[j][k]; sum += d * d; } D[i][j] = sum; D[i][B.length] += Math.pow(1 / D[i][j], exp); } } By doing so I encounter numerical differences between the 'banal' computation and the second one that leads to different numerical value in U (not in the first iterates but soon enough). I guess that the problem is that exponentiate very small numbers to high values (the elements of U can range from 0.0 to 1.0 and exp , for m = 1.1, is 10) leads to ver y small values, whereas by dividing the numerator and the denominator and THEN exponentiating the result seems to be better numerically. The problem is it involves much more operations. Am I doing something wrong? Is there a possible solution to get both the code optimized and numerically stable? Any suggestion or criticism will be appreciated.

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• Linked Lists in Java - Help with assignment

  - by doron2010

  I have been trying to solve this assignment all day, please help me. I'm completely lost. Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) public char charAt (int i) - returns the char in the place i in the string. Assume that the value of i is in the right range. public StringList concat (String str) - returns a string that consists of the string that it is operated on and in its end the string "str" is concatenated. public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. public int indexOf (int ch, int fromIndex) - returns the index in the string it is operated on of the first appeareance of the char "ch", as the search begins in the index "fromIndex". If the char "ch" doesn't appear in the string, returns -1. public boolean equals (String str) - returns true if the string that it is operated on is equal to the string str. Otherwise returns false. This method must be written in recursion, without using loops at all. public int compareTo (String str) - compares between the string that the method is operated on to the string "str" that is in the parameter. The method returns 0 if the strings are equal. If the string in the object is smaller lexicographic from the string "str" in the paramater, a negative number will be returned. And if the string in the object is bigger lexicographic from the string "str", a positive number will be returned. public StringList substring (int i) - returns the list of the substring that starts in the place i in the string on which it operates. Meaning, the sub-string from the place i until the end of the string. Assume the value of i is in the right range. public StringList substring (int i, int j) - returns the list of the substring that begins in the place i and ends in the place j (not included) in the string it operates on. Assume the values of i, j are in the right range. public int length() - will return the length of the string on which it operates. Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations.

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• First time using select(), maybe a basic question?

  - by darkletter

  Hello people, i've been working for a few days with this server using select(). What it does, is that, i have two arrays of clients (one is "suppliers", and the other is "consumers"), and the mission of the server is to check whether the suppliers have something to send to the consumers, and in case affirmative, send it. The second part of the server is that, when the consumers have received the suppliers' info, they send a confirmation message to the same suppliers that sent the info. When a client connects, it gets recognized as "undefined", until it sends a message with the word "supplier" or "consumer" (in Spanish, as i'm from there), when the server puts it in the correct clients array. Well, what the server does is not very important here. What's important is that, i'm doing both parts with two different "for" loops, and that's where i'm getting the problems. When the first user connects to the server (be it a supplier or a consumer), the server gets stuck in the first or second loop, instead of just continuing its execution. As it's the first time i'm using select(), i may be missing something. Could you guys give me any sort of help? Thanks a lot in advance. for(;;) { rset=allset; nready=select(maxfd+1,&rset,NULL,NULL,NULL); if (FD_ISSET(sockfd, &rset)){ clilen=sizeof(cliente); if((connfd=accept(sockfd,(struct sockaddr *)&cliente,&clilen))<0) printf("Error"); IP=inet_ntoa(cliente.sin_addr); for(i=0;i<COLA;i++){if(indef[i]<0){indef[i]=connfd;IPind[i]=IP;break;}} FD_SET(connfd,&allset); if(connfd > maxfd) maxfd=connfd; if(i>maxii) maxii=i; if(--nready<=0) continue; }// Fin ISSET(sockfd) for(i=0;i<=maxii;i++){ if((sockfd1=indef[i])<0){ continue;} //! if(FD_ISSET(sockfd1,&rset)){ if((n=read(sockfd1,comp,MAXLINE))==0){close(sockfd1);FD_CLR(sockfd1,&allset);indef[i]=-1;printf("Cliente indefinido desconectado \n");} else{ comp[n]='\0'; if(strcmp(comp,"suministrador")==0){ for(j=0;j<=limite;j++){if(sumi[j]<0){IPsum[j]=IPind[i];sumi[j]=indef[i]; indef[i]=-1;if(j>maxis) {maxis=j;}break; } } } else if(strcmp(comp,"consumidor")==0){ for(o=0;j<=limite;j++){if(consum[o]<0){IPcons[o]=IPind[i];consum[o]=indef[i]; indef[o]=-1;if(o>maxic) {maxic=o;}break; } } } if(--nready <=0)break; } } }//fin bucle for maxii for(i=0;i<=maxis;i++){ if((sockfd2=sumi[i])<0){continue;} if(FD_ISSET(sockfd2,&rset)){ if((n=read(sockfd2,buffer2,MAXLINE))==0){close(sockfd2);FD_CLR(sockfd2,&allset);sumi[i]=-1;printf("Suministrador desconectado \n");} else{ buffer2[n]='\0'; for(j=0;j<=maxic;j++){ if((sockfd3=consum[j])<0){ continue;} else {strcpy(final,IPsum[i]);strcat(final,":");strcat(final,buffer2);write(sockfd3,final,sizeof(final));respuesta[i]=1;} } break; // ? } } }//fin for maxis for(i=miniic;i<=maxic;i++){ if((sockfd4=consum[i])<0){continue;} if(FD_ISSET(sockfd4,&rset)){ if((n=read(sockfd4,buffer3,MAXLINE))==0){close(sockfd4);FD_CLR(sockfd4,&allset);consum[i]=-1;printf("Consumidor desconectado \n");} else{ buffer3[n]='\0'; IP2=strtok(buffer3,":"); obj=strtok(NULL,":"); for(j=0;j<100;j++){ if((strcmp(IPsum[j],IP2)==0) && (respuesta[j]==1)) {write(sumi[j],obj,sizeof(obj)); miniic=i+1; respuesta[j]=0; break; } } } } }

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• Why doesn't PHP's oci_connect return false?

  - by absolethe

  I have a situation in which we have two production databases that synchronize with one other. Server One is considered the primary. Sometimes due to maintenance or a disaster Server Two will become primary. In some of our code that means we have to manually go in and edit the server name for database connections. I find this annoying, so the last thing I wrote I put the server information for both and set up a loop. If oci_connect failed on the Server One 3 times it would move on to Server Two. If Server Two failed 3 times it would notify the user a connection couldn't be made. This has worked fine most times we've had the situation of switching the servers. Yesterday, for example, it worked fine. Today it didn't. It just sat and spun endlessly. No error in the PHP error log. No failure to move on from. No error output to the screen. Nothing for 5 minutes. So then I had to manually edit the stupid config file. I asked what could possibly be different and I was told "yesterday the database was down, but not the server. today the server is down." Okay...? But I don't see a distinction. I would expect oci_connect to return false if it can't establish any sort of communication with the server. I'd expect it to timeout and error. Not just pass it on when it receives an error code from the server. What if there's a network problem, for example? Is this a bug in oci_connect or is there a possibility that something in our PHP configuration gives oci_connect a crazily long timeout? If it is a sort of "bug" is there some way I can check to see if the server is up first? Like a ping? (Of course when I did a ping through the command prompt I got a response from Server One and then was told, "it's back now" although I am skeptical about the timing on that.) Anyway, if anyone could shed some light on why oci_connect might run endlessly without failing and how to keep it from doing so I'd be grateful. -- Edit: My code looks like the examples on PHP.net only in some loops. $count = count($servers); for($i = 0; $i < $count; $i++){ if((!isset($connection)) || ($connection == false)){ // Attempt to connect to the oracle database $connection = @oci_connect($servers[$i]["user"], $servers[$i]["pass"], $servers[$i]["conid"]) or ($conn_error = oracle_error()); // Try again if there was a failure if(($connection == false) || (isset($con_error))){ // Three (two more) tries per alternative for($j = $st; $j < $fn; $j++){ // Try again to connect $connection = @oci_connect($servers[$i]["user"], $servers[$i]["pass"], $servers[$i]["conid"]) or ($conn_error = oracle_error()); } // for($j = 2; $j < 4; $j++) } // if($connection == false) } // if(!isset($connection) || ($connection == false)) } // for($i = 0; $i < $count; $i++)

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• Strange behaviour when simply adding strings in Lazarus - FreePascal

  - by linkcharger

  The program has several "encryption" algorithms. This one should blockwise reverse the input. "He|ll|o " becomes "o |ll|He" (block length of 2). I add two strings, in this case appending the result string to the current "block" string and making that the result. When I add the result first and then the block it works fine and gives me back the original string. But when i try to reverse the order it just gives me the the last "block". Several other functions that are used for "rotation" are above. //amount of blocks function amBl(i1:integer;i2:integer):integer; begin if (i1 mod i2) <> 0 then result := (i1 div i2) else result := (i1 div i2) - 1; end; //calculation of block length function calcBl(keyStr:string):integer; var i:integer; begin result := 0; for i := 1 to Length(keyStr) do begin result := (result + ord(keyStr[i])) mod 5; result := result + 2; end; end; //desperate try to add strings function append(s1,s2:string):string; begin insert(s2,s1,Length(s1)+1); result := s1; end; function rotation(inStr,keyStr:string):string; var //array of chars -> string block,temp:string; //position in block variable posB:integer; //block length and block count variable bl, bc:integer; //null character as placeholder n : ansiChar; begin //calculating block length 2..6 bl := calcBl(keyStr); setLength(block,bl); result := ''; temp := ''; {n := #00;} for bc := 0 to amBl(Length(inStr),bl) do begin //filling block with chars starting from back of virtual block (in inStr) for posB := 1 to bl do begin block[posB] := inStr[bc * bl + posB]; {if inStr[bc * bl + posB] = ' ' then block[posB] := n;} end; //adding the block in front of the existing result string temp := result; result := block + temp; //result := append(block,temp); //result := concat(block,temp); end; end; (full code http://pastebin.com/6Uarerhk) After all the loops "result" has the right value, but in the last step (between "result := block + temp" and the "end;" of the function) "block" replaces the content of "result" with itself completely, it doesn't add result at the end anymore. And as you can see I even used a temp variable to try to work around that.. doesnt change anything though.

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• Effective optimization strategies on modern C++ compilers

  - by user168715

  I'm working on scientific code that is very performance-critical. An initial version of the code has been written and tested, and now, with profiler in hand, it's time to start shaving cycles from the hot spots. It's well-known that some optimizations, e.g. loop unrolling, are handled these days much more effectively by the compiler than by a programmer meddling by hand. Which techniques are still worthwhile? Obviously, I'll run everything I try through a profiler, but if there's conventional wisdom as to what tends to work and what doesn't, it would save me significant time. I know that optimization is very compiler- and architecture- dependent. I'm using Intel's C++ compiler targeting the Core 2 Duo, but I'm also interested in what works well for gcc, or for "any modern compiler." Here are some concrete ideas I'm considering: Is there any benefit to replacing STL containers/algorithms with hand-rolled ones? In particular, my program includes a very large priority queue (currently a std::priority_queue) whose manipulation is taking a lot of total time. Is this something worth looking into, or is the STL implementation already likely the fastest possible? Along similar lines, for std::vectors whose needed sizes are unknown but have a reasonably small upper bound, is it profitable to replace them with statically-allocated arrays? I've found that dynamic memory allocation is often a severe bottleneck, and that eliminating it can lead to significant speedups. As a consequence I'm interesting in the performance tradeoffs of returning large temporary data structures by value vs. returning by pointer vs. passing the result in by reference. Is there a way to reliably determine whether or not the compiler will use RVO for a given method (assuming the caller doesn't need to modify the result, of course)? How cache-aware do compilers tend to be? For example, is it worth looking into reordering nested loops? Given the scientific nature of the program, floating-point numbers are used everywhere. A significant bottleneck in my code used to be conversions from floating point to integers: the compiler would emit code to save the current rounding mode, change it, perform the conversion, then restore the old rounding mode --- even though nothing in the program ever changed the rounding mode! Disabling this behavior significantly sped up my code. Are there any similar floating-point-related gotchas I should be aware of? One consequence of C++ being compiled and linked separately is that the compiler is unable to do what would seem to be very simple optimizations, such as move method calls like strlen() out of the termination conditions of loop. Are there any optimization like this one that I should look out for because they can't be done by the compiler and must be done by hand? On the flip side, are there any techniques I should avoid because they are likely to interfere with the compiler's ability to automatically optimize code? Lastly, to nip certain kinds of answers in the bud: I understand that optimization has a cost in terms of complexity, reliability, and maintainability. For this particular application, increased performance is worth these costs. I understand that the best optimizations are often to improve the high-level algorithms, and this has already been done.

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• Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

  - by Ricket

  Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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• Normalizing a table

  - by Alex

  I have a legacy table, which I can't change. The values in it can be modified from legacy application (application also can't be changed). Due to a lot of access to the table from new application (new requirement), I'd like to create a temporary table, which would hopefully speed up the queries. The actual requirement, is to calculate number of business days from X to Y. For example, give me all business days from Jan 1'st 2001 until Dec 24'th 2004. The table is used to mark which days are off, as different companies may have different days off - it isn't just Saturday + Sunday) The temporary table would be created from a .NET program, each time user enters the screen for this query (user may run query multiple times, with different values, table is created once), so I'd like it to be as fast as possible. Approach below runs in under a second, but I only tested it with a small dataset, and still it takes probably close to half a second, which isn't great for UI - even though it's just the overhead for first query. The legacy table looks like this: CREATE TABLE [business_days]( [country_code] [char](3) , [state_code] [varchar](4) , [calendar_year] [int] , [calendar_month] [varchar](31) , [calendar_month2] [varchar](31) , [calendar_month3] [varchar](31) , [calendar_month4] [varchar](31) , [calendar_month5] [varchar](31) , [calendar_month6] [varchar](31) , [calendar_month7] [varchar](31) , [calendar_month8] [varchar](31) , [calendar_month9] [varchar](31) , [calendar_month10] [varchar](31) , [calendar_month11] [varchar](31) , [calendar_month12] [varchar](31) , misc. ) Each month has 31 characters, and any day off (Saturday + Sunday + holiday) is marked with X. Each half day is marked with an 'H'. For example, if a month starts on a Thursday, than it will look like (Thursday+Friday workdays, Saturday+Sunday marked with X): ' XX XX ..' I'd like the new table to look like so: create table #Temp (country varchar(3), state varchar(4), date datetime, hours int) And I'd like to only have rows for days which are off (marked with X or H from previous query) What I ended up doing, so far is this: Create a temporary-intermediate table, that looks like this: create table #Temp_2 (country_code varchar(3), state_code varchar(4), calendar_year int, calendar_month varchar(31), month_code int) To populate it, I have a union which basically unions calendar_month, calendar_month2, calendar_month3, etc. Than I have a loop which loops through all the rows in #Temp_2, after each row is processed, it is removed from #Temp_2. To process the row there is a loop from 1 to 31, and substring(calendar_month, counter, 1) is checked for either X or H, in which case there is an insert into #Temp table. [edit added code] Declare @country_code char(3) Declare @state_code varchar(4) Declare @calendar_year int Declare @calendar_month varchar(31) Declare @month_code int Declare @calendar_date datetime Declare @day_code int WHILE EXISTS(SELECT * From #Temp_2) -- where processed = 0) BEGIN Select Top 1 @country_code = t2.country_code, @state_code = t2.state_code, @calendar_year = t2.calendar_year, @calendar_month = t2.calendar_month, @month_code = t2.month_code From #Temp_2 t2 -- where processed = 0 set @day_code = 1 while @day_code <= 31 begin if substring(@calendar_month, @day_code, 1) = 'X' begin set @calendar_date = convert(datetime, (cast(@month_code as varchar) + '/' + cast(@day_code as varchar) + '/' + cast(@calendar_year as varchar))) insert into #Temp (country, state, date, hours) values (@country_code, @state_code, @calendar_date, 8) end if substring(@calendar_month, @day_code, 1) = 'H' begin set @calendar_date = convert(datetime, (cast(@month_code as varchar) + '/' + cast(@day_code as varchar) + '/' + cast(@calendar_year as varchar))) insert into #Temp (country, state, date, hours) values (@country_code, @state_code, @calendar_date, 4) end set @day_code = @day_code + 1 end delete from #Temp_2 where @country_code = country_code AND @state_code = state_code AND @calendar_year = calendar_year AND @calendar_month = calendar_month AND @month_code = month_code --update #Temp_2 set processed = 1 where @country_code = country_code AND @state_code = state_code AND @calendar_year = calendar_year AND @calendar_month = calendar_month AND @month_code = month_code END I am not an expert in SQL, so I'd like to get some input on my approach, and maybe even a much better approach suggestion. After having the temp table, I'm planning to do (dates would be coming from a table): select cast(convert(datetime, ('01/31/2012'), 101) -convert(datetime, ('01/17/2012'), 101) as int) - ((select sum(hours) from #Temp where date between convert(datetime, ('01/17/2012'), 101) and convert(datetime, ('01/31/2012'), 101)) / 8) Besides the solution of normalizing the table, the other solution I implemented for now, is a function which does all this logic of getting the business days by scanning the current table. It runs pretty fast, but I'm hesitant to call a function, if I can instead add a simpler query to get result. (I'm currently trying this on MSSQL, but I would need to do same for Sybase ASE and Oracle)

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• How to define template directives (from an API perspective)?

  - by Ralph

  Preface I'm writing a template language (don't bother trying to talk me out of it), and in it, there are two kinds of user-extensible nodes. TemplateTags and TemplateDirectives. A TemplateTag closely relates to an HTML tag -- it might look something like div(class="green") { "content" } And it'll be rendered as <div class="green">content</div> i.e., it takes a bunch of attributes, plus some content, and spits out some HTML. TemplateDirectives are a little more complicated. They can be things like for loops, ifs, includes, and other such things. They look a lot like a TemplateTag, but they need to be processed differently. For example, @for($i in $items) { div(class="green") { $i } } Would loop over $items and output the content with the variable $i substituted in each time. So.... I'm trying to decide on a way to define these directives now. Template Tags The TemplateTags are pretty easy to write. They look something like this: [TemplateTag] static string div(string content = null, object attrs = null) { return HtmlTag("div", content, attrs); } Where content gets the stuff between the curly braces (pre-rendered if there are variables in it and such), and attrs is either a Dictionary<string,object> of attributes, or an anonymous type used like a dictionary. It just returns the HTML which gets plunked into its place. Simple! You can write tags in basically 1 line. Template Directives The way I've defined them now looks like this: [TemplateDirective] static string @for(string @params, string content) { var tokens = Regex.Split(@params, @"\sin\s").Select(s => s.Trim()).ToArray(); string itemName = tokens[0].Substring(1); string enumName = tokens[1].Substring(1); var enumerable = data[enumName] as IEnumerable; var sb = new StringBuilder(); var template = new Template(content); foreach (var item in enumerable) { var templateVars = new Dictionary<string, object>(data) { { itemName, item } }; sb.Append(template.Render(templateVars)); } return sb.ToString(); } (Working example). Basically, the stuff between the ( and ) is not split into arguments automatically (like the template tags do), and the content isn't pre-rendered either. The reason it isn't pre-rendered is because you might want to add or remove some template variables or something first. In this case, we add the $i variable to the template variables, var templateVars = new Dictionary<string, object>(data) { { itemName, item } }; And then render the content manually, sb.Append(template.Render(templateVars)); Question I'm wondering if this is the best approach to defining custom Template Directives. I want to make it as easy as possible. What if the user doesn't know how to render templates, or doesn't know that he's supposed to? Maybe I should pass in a Template instance pre-filled with the content instead? Or maybe only let him tamper w/ the template variables, and then automatically render the content at the end? OTOH, for things like "if" if the condition fails, then the template wouldn't need to be rendered at all. So there's a lot of flexibility I need to allow in here. Thoughts?

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• C++ Compound Interest Exercise

  - by Lameste

  I'm a beginner trying to learn C++ using "C++ Primer Plus Sixth Edition". I'm on Chapter 5, going over loops. Anyways I was doing this programming exercise from the book, the problem is: Daphne invests $100 at 10% simple interest.That is, every year, the investment earns 10% of the original investment, or $10 each and every year: interest = 0.10 × original balance At the same time, Cleo invests $100 at 5% compound interest.That is, interest is 5% of the current balance, including previous additions of interest: interest = 0.05 × current balance Cleo earns 5% of $100 the first year, giving her $105.The next year she earns 5% of $105, or $5.25, and so on.Write a program that finds how many years it takes for the value of Cleo’s investment to exceed the value of Daphne’s investment and then displays the value of both investments at that time. Here is the code I have written for this exercise, I'm not getting good results though. #include <iostream> #include <array> double Daphne(int, double, double); double Chleo(double, double); int main() { using namespace std; int p = 100; //Principle double i1 = 0.1; // 10% interest rate double i2 = 0.05; // 5% interest rate double dInv = 0; //Daphnes investment double cInv = 0; // Chleos investment int t=1; //Starting at year 1 double s1 = 0; //Sum 1 for Daphne double s2 = 0; // Sum 2 for Chleo s1 = p + 10; //Initial interest (base case after year 1) for Daphne s2 = p + (i2*p); //Initial interest (base case after year 1) for Chleo /*cout << s1 << endl; cout << s2 << endl;*/ while (cInv < dInv) { dInv = Daphne(p, i1, s1); cInv = Chleo(i2, s2); t++; } cout << "The time taken for Chleos investment to exceed Daphnes was: " << t << endl; cout << "Daphnes investment at " << t << " years is: " << dInv << endl; cout << "Chleos invesment at " << t << " years is: " << cInv << endl; system("pause"); return 0; } double Daphne(int p, double i, double s1) { s1 = s1 + (p*i); return s1; } double Chleo(double i, double s2){ s2 = s2 + (s2*i); return s2; } Output from console: The time taken for Chleos investment to exceed Daphnes was: 1 Daphnes investment at 1 years is: 0 Chleos invesment at 1 years is: 0 Press any key to continue . . . Can anyone explain why I'm getting this current result? The while loop is supposed to continue executing statements until Chleo's investment exceeds Daphnes.

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• C++ - getline() keeps reading the same line over and over again for some reason

  - by Jammanuser

  I am wondering WTF my while loop which calls istream& getline ( istream& is, string& str ); keeps reading the same line again. I have the following while loop (nested down several levels of other while loops and if statements) which calls getline, but my output statement which is the first code line in the while loop's block of code tells me it is reading the same line over and over again, which explains why my output file doesn't contain the right data when my program is finished. while (getline(file_handle, buffer_str)) { cout<< buffer_str <<endl; cin.get(); if ((buffer_str.find(';', 0) != string::npos) && (buffer_str.find('\"', 0) != string::npos)) { //we're now at the end of the 'exc' initialiation statement buffer_str.erase(buffer_str.size() - 2, 1); buffer_str += '\n'; for (size_t i = 0; i < pos; i++) { buffer_str += ' '; } buffer_str += "throw(exc);\n"; for (size_t i = 0; i < (pos - 3); i++) { buffer_str += ' '; } buffer_str += '}'; } else if (buffer_str.find(search_str6, 0) != string::npos) { //we're now at the second problem line of the first case buffer_str += " {\n"; output_str += buffer_str; output_str += '\n'; getline(file_handle, buffer_str); //We're now at the beginning of the 'exc' initialiation statement output_str += buffer_str; output_str += '\n'; while (getline(file_handle, buffer_str)) { if ((buffer_str.find(';', 0) != string::npos) && (buffer_str.find('\"', 0) != string::npos)) { //we're now at the end of the 'exc' initialiation statement buffer_str.erase(buffer_str.size() - 2, 1); buffer_str += '\n'; for (size_t i = 0; i < pos; i++) { buffer_str += ' '; } buffer_str += "throw(exc);\n"; for (size_t i = 0; i < (pos - 3); i++) { buffer_str += ' '; } buffer_str += '}'; } output_str += buffer_str; output_str += '\n'; if (buffer_str.find("return", 0) != string::npos) { getline(file_handle, buffer_str); output_str += buffer_str; output_str += '\n'; about_to_break = true; break; //out of this while loop } } } if (about_to_break) { break; //out of the level 3 while loop (execution then goes back up to beginning of level 2 while loop) } output_str += buffer_str; output_str += '\n'; } Because of this problem, my if statement and then my else statement in my loop are not functioning as they should, and it doesn't break out of that loop when it should (though it eventually does break out of it, but I don't know exactly how yet). Anyone have any idea what could be causing this problem?? Thanks in advance.

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