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• why unsigned int 0xFFFFFFFF is equal to int -1?

  - by conejoroy

  perhaps it's a very stupid question but I'm having a hard time figuring this out =) in C or C++ it is said that the maximum number a size_t (an unsigned int data type) can hold is the same as casting -1 to that data type. for example see http://stackoverflow.com/questions/1420982/invalid-value-for-sizet Why?? I'm confused.. I mean, (talking about 32 bit ints) AFAIK the most significant bit holds the sign in a signed data type (that is, bit 0x80000000 to form a negative number). then, 1 is 0x00000001.. 0x7FFFFFFFF is the greatest positive number a int data type can hold. then, AFAIK the binary representation of -1 int should be 0x80000001 (perhaps I'm wrong). why/how this binary value is converted to anything completely different (0xFFFFFFFF) when casting ints to unsigned?? or.. how is it possible to form a binary -1 out of 0xFFFFFFFF? I have no doubt that in C: ((unsigned int)-1) == 0xFFFFFFFF or ((int)0xFFFFFFFF) == -1 is equally true than 1 + 1 == 2, I'm just wondering why. thanks!

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• In C#, are event handler arguments covariant?

  - by Roger Lipscombe

  Maybe covariant's not the word, but if I have a class that raises an event, with (e.g.) FrobbingEventArgs, am I allowed to handle it with a method that takes EventArgs? Here's some code: class Program { static void Main(string[] args) { Frobber frobber = new Frobber(); frobber.Frobbing += FrobberOnFrobbing; frobber.Frob(); } private static void FrobberOnFrobbing(object sender, EventArgs e) { // Do something interesting. Note that the parameter is 'EventArgs'. } } internal class Frobber { public event EventHandler<FrobbingEventArgs> Frobbing; public event EventHandler<FrobbedEventArgs> Frobbed; public void Frob() { OnFrobbing(); // Frob. OnFrobbed(); } private void OnFrobbing() { var handler = Frobbing; if (handler != null) handler(this, new FrobbingEventArgs()); } private void OnFrobbed() { var handler = Frobbed; if (handler != null) handler(this, new FrobbedEventArgs()); } } internal class FrobbedEventArgs : EventArgs { } internal class FrobbingEventArgs : EventArgs { } The reason I ask is that ReSharper seems to have a problem with (what looks like) the equivalent in XAML, and I'm wondering if it's a bug in ReSharper, or a mistake in my understanding of C#.

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• How can I work around the fact that in C++, sin(M_PI) is not 0?

  - by Adam Doyle

  In C++, const double Pi = 3.14159265; cout << sin(Pi); // displays: 3.58979e-009 it SHOULD display the number zero I understand this is because Pi is being approximated, but is there any way I can have a value of Pi hardcoded into my program that will return 0 for sin(Pi)? (a different constant maybe?) In case you're wondering what I'm trying to do: I'm converting polar to rectangular, and while there are some printf() tricks I can do to print it as "0.00", it still doesn't consistently return decent values (in some cases I get "-0.00") The lines that require sin and cosine are: x = r*sin(theta); y = r*cos(theta); BTW: My Rectangular - Polar is working fine... it's just the Polar - Rectangular Thanks! edit: I'm looking for a workaround so that I can print sin(some multiple of Pi) as a nice round number to the console (ideally without a thousand if-statements) edit: In case anyone's curious, this was what I landed on: double sin2(double theta) // in degrees { double s = sin(toRadians(theta)); if (fabs(s - (int)s) < 0.000001) { return floor(s + 0.5); } return s; } where toRadians() is a macro that converts to radians

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• Javascript: Multiple mouseout events triggered

  - by Channel72

  I'm aware of the different event models in Javascript (the WC3 model versus the Microsoft model), as well as the difference between bubbling and capturing. However, after a few hours reading various articles about this issue, I'm still unsure how to properly code the following seemingly simple behavior: If I have an outer div and an inner div element, I want a single mouse-out event to be triggered when the mouse leaves the outer-div. When the mouse crosses from the inner-div to the outer-div, nothing should happen, and when the mouse crosses from the outer-div to the inner-div nothing should happen. The event should only fire if the mouse moves from the outer-div to the surrounding page. <div id="outer" style = "width:20em; height:20em; border:1px solid #F00" align = "center" onmouseout="alert('mouseout event!')" > <div id="inner" style = "width:18em; height:18em; border:1px solid #000"></div> </div> Now, if I place the "mouseout" event on the outer-div, two mouse-out events are fired when the mouse moves from the inner-div to the surrounding page, because the event fires once when the mouse moves from inner to outer, and then again when it moves from outer to the surrounding page. I know I can cancel the event using ev.stopPropagation(), so I tried registering an event handler with the inner-div to cancel the event propagation. However, this won't prevent the event from firing when the mouse moves from the outer-div to the inner-div. So, unless I'm overlooking something, it seems to me this behavior can't be accomplished without complex mouse-tracking functions. In the future, I plan to reimplement a lot of this code using a more advanced framework, like JQuery, but for now, I'm wondering if there is a simple way to implement the above behavior in regular Javascript.

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• Console app showing message box on error

  - by holz

  I am trying to integrate with a vendors app by calling it with command args from c#. It is meant to automate a process that we need to do with out needing anyone to interact with the application. If there are no errors when running the process it works fine. However if there are any errors the vendors application will show a message box with the error code and error message and wait for someone to click the ok button. When the ok button is clicked it will exit the application returning the error code as the exit code. As my application is going to be a windows service on a server, needing someone to click an okay button will be an issue. Just wondering what the best solution would be to get around this. My code calling the vendor app is... ProcessStartInfo startInfo = new ProcessStartInfo(); startInfo.FileName = "someapp.exe" startInfo.Arguments = "somefile.txt"; Process jobProcess = Process.Start(startInfo); jobProcess.WaitForExit(); int exitCode = jobProcess.ExitCode;

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• Windows Batch file to echo a specific line number

  - by Lee

  So for the second part of my current dilemma, I have a list of folders in c:\file_list.txt. I need to be able to extract them (well, echo them with some mods) based on the line number because this batch script is being called by an iterative macro process. I'm passing the line number as a parameter. @echo off setlocal enabledelayedexpansion set /a counter=0 set /a %%a = "" for /f "usebackq delims=" %%a in (c:\file_list.txt) do ( if "!counter!"=="%1" goto :printme & set /a counter+=1 ) :printme echo %%a which gives me an output of %a. Doh! So, I've tried echoing !a! (result: ECHO is off.); I've tried echoing %a (result: a) I figured the easy thing to do would be to modify the head.bat code found here: http://stackoverflow.com/questions/130116/dos-batch-commands-to-read-first-line-from-text-file except rather than echoing every line - I'd just echo the last line found. Not as simple as one might think. I've noticed that my counter is staying at zero for some reason; I'm wondering if the set /a counter+=1 is doing what I think it's doing.

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• CSS: Horizontal scrolling with overflow-x

  - by ams

  Hello fellow programmers, I was wondering if there still isn't a good way to get a div to stretch and scroll horizontally, according to the images inside. -After all, it is 2011 now! The mega-width does the trick, but leaves an empty mega-space if not filled with images. If filled too much, images don't display. Same for the jQuery. The situation below is the best I can do after hours of Googling, but it isn't reliable enough. Thanks for your time. Ams * { margin:0; padding:0; } #one { width:200px; height:250px; overflow-x:auto; overflow-y:hidden; } #two { width:10000em; } #two img { float:left; } $(document).ready(function(){ var total=0; $(".calc").each(function(){ total += $(this).outerWidth(true); }); $("#two").css('width',total); alert(total); }); <div id="one"> <div id="two"> <img src="images/testimage3.jpg" width="480" height="192" class="calc"> <img src="images/testimage3.jpg" width="480" height="192" class="calc"> <img src="images/testimage3.jpg" width="480" height="192" class="calc"> <img src="images/testimage3.jpg" width="480" height="192" class="calc"> </div> </div>

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• Can't seem to load a webview from xml, why?

  - by Bilthon

  Well, I'm trying to follow the tutorial from http://rapidandroid.org/wiki/Graphing. But I found a problem just in the first part of it. I'll describe the problem here, I just cannot understand how this could be wrong, it's pretty simple stuff. What am I doing wrong here? First I created a xml file called statistics.xml, in it among other things I put this code: <WebView android:id="@+id/webview" android:layout_height="fill_parent" android:layout_width="fill_parent"/> Now in the activity that is supposed to display this webview I'm doing this: public class DisplayStatistics extends Activity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); WebView wv = (WebView) findViewById(R.id.webview); The problem arises here, as I seem to be getting null for wv whenever I test for it. Which means of course that findViewById(R.id.webview) couldn't find the view. But again, what am I doing wrong?? Of course I know I could also instantiate the webview directly from code without the need to specify it from the xml, but I was just wondering what was wrong about this way of doing it. Just in case I also added the following line in my android manifest file: <uses-permission android:name="android.permission.INTERNET" /> I'm not really sure if it's necessary for displaying the webview (I think not) but I just put it there to see if that was the problem, and it turned out it isn't. Thanks Nelson

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• Binary Search Tree - Postorder logic

  - by daveb

  I am looking at implementing code to work out binary search tree. Before I do this I was wanting to verify my input data in postorder and preorder. I am having trouble working out what the following numbers would be in postorder and preorder I have the following numbers 4, 3, 14 ,8 ,1, 15, 9, 5, 13, 10, 2, 7, 6, 12, 11, that I am intending to put into an empty binary tree in that order. The order I arrived at for the numbers in POSTORDER is 2, 1, 6, 3, 7, 11, 12, 10, 9, 8, 13, 15, 14, 4. Have I got this right? I was wondering if anyone here would be able to kindly verify if the postorder sequence I came up with is indeed the correct sequence for my input i.e doing left subtree, right subtree and then root. The order I got for pre order (Visit root, do left subtree, do right subtree) is 4, 3, 1, 2, 5, 6, 14 , 8, 7, 9, 10, 12, 11, 15, 13. I can't be certain I got this right. Very grateful for any verification. Many Thanks

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• Java 2D Resize

  - by jon077

  I have some old Java 2D code I want to reuse, but was wondering, is this the best way to get the highest quality images? public static BufferedImage getScaled(BufferedImage imgSrc, Dimension dim) { // This code ensures that all the pixels in the image are loaded. Image scaled = imgSrc.getScaledInstance( dim.width, dim.height, Image.SCALE_SMOOTH); // This code ensures that all the pixels in the image are loaded. Image temp = new ImageIcon(scaled).getImage(); // Create the buffered image. BufferedImage bufferedImage = new BufferedImage(temp.getWidth(null), temp.getHeight(null), BufferedImage.TYPE_INT_RGB); // Copy image to buffered image. Graphics g = bufferedImage.createGraphics(); // Clear background and paint the image. g.setColor(Color.white); g.fillRect(0, 0, temp.getWidth(null),temp.getHeight(null)); g.drawImage(temp, 0, 0, null); g.dispose(); // j2d's image scaling quality is rather poor, especially when // scaling down an image to a much smaller size. We'll post filter // our images using a trick found at // http://blogs.cocoondev.org/mpo/archives/003584.html // to increase the perceived quality.... float origArea = imgSrc.getWidth() * imgSrc.getHeight(); float newArea = dim.width * dim.height; if (newArea <= (origArea / 2.)) { bufferedImage = blurImg(bufferedImage); } return bufferedImage; } public static BufferedImage blurImg(BufferedImage src) { // soften factor - increase to increase blur strength float softenFactor = 0.010f; // convolution kernel (blur) float[] softenArray = { 0, softenFactor, 0, softenFactor, 1-(softenFactor*4), softenFactor, 0, softenFactor, 0}; Kernel kernel = new Kernel(3, 3, softenArray); ConvolveOp cOp = new ConvolveOp(kernel, ConvolveOp.EDGE_NO_OP, null); return cOp.filter(src, null); }

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• Communication between EJB3 Instances (JEE inter-bean communication) possible?

  - by Hank

  I'm designing a part of a JEE6 application, consisting of EJB3 beans. Part of the requirements are multiple parallel (say a few hundred) long running (over days) database hunts. Individual hunts have different search parameters (start time, end time, query filter). Parameters may get changed over time. Currently I'm thinking of the following: SearchController (Stateless Session Bean) formulates a set of search parameters, sends it off to a SearchListener via JMS SearchListener (Message Driven Bean) receives search parameters, instantiates a SearchWorker with the parameters SearchWorker (SLSB) hunts repeatedly through the database; when it finds something, the result is sent off via JMS, and the search continues; when the given 'end-time' has reached, it ends What I'm wondering now: Is there a problem, with EJB3 instances running for days? (Other than that I need to be able to deal with container restarts...) How do I know how many and which EJB instances of SearchWorker are currently running? Is it possible to communicate with them individually (similar to sending a System V signal to a unix process), e.g. to send new parameters, to end an instance, etc..

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• Rate limiting a ruby file stream

  - by Matthew Savage

  I am working on a project which involves uploading flash video files to a S3 bucket from a number of geographically distributed nodes. The video files are about 2-3mb each, and we are only sending one file (per node) every ten minutes, however the bandwidth we consume needs to be rate limited to ~20k/s, as these nodes are delivering streaming media to a CDN, and due to the locations we are only able to get 512k max upload. I have been looking into the ASW-S3 gem and while it doesn't offer any kind of rate limiting I am aware that you can pass in a IO Stream. Given this I am wondering if it might be possible to create a rate-limited stream which overrides the read method, adds in the rate limiting logic (e.g. in its simplest form a call to sleep between reads) and then call out to the super of the overridden method. Another option I considered is hacking the code for Net::HTTP and putting the rate limiting into the send_request_with_body_stream method which is using a while loop, but I'm not entirely sure which would be the best option. I have attempted at extending the IO class, however that didn't work at all, simply inheriting from the class with class ThrottledIO < IO didn't do anything. Any suggestions will be greatly appreciated.

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• Best way to replace mass emails sent from Entourage with a proper mailing list solution?

  - by aaandre

  I am helping a Los Angeles choreographer to transition away from sending her announcements via Entourage. Here's the situation: She has multiple conact groups, and sends classes and performance announcements several times a month, to different groups. She manages the contact groups manually. The group size is between 1500 and 2500 people. Recently verizon blocked her outgoing port 25, presumably for spam activity. Again, her contacts are interested in the content. She is aware of mailchimp, constantcontact etc. but would like to be able to send the email via her email software and not have to create a newsletter for every single mailing. Also, she's very short on $$. So, what would be the best way to set up a system allowing her to send announcements from Entourage, with attached images, to her lists, without having Entourage send every single email? I am thinking of setting up a set of mailing lists, each corresponding to one of her groups. I have never set up a mailing list before and am wondering if it's possible to have a list accept emails from only one person (Admin) and distribute them to the group? Recipients should be able to unsubscribe easily, and by default reply to her but not the list. She should be the only one able to use the list for distribution, and should be able to send messages (with attachments) directly from her email client without modification. Is this possible? Where can I find step-by-step instructions? What are best practices to avoid her domain being blacklisted? What's the easiest way to convert her contact groups to mailing list subscribers? I am helping her for free, so the simpler the better :) Thank you! UPDATE: She has a standard linux hosting account allowing her to run php etc. And, ideally, the emails would come from her personally or at least from her domain name.

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• How to find unique values in jagged array

  - by David Liddle

  I would like to know how I can count the number of unique values in a jagged array. My domain object contains a string property that has space delimitered values. class MyObject { string MyProperty; //e.g = "v1 v2 v3" } Given a list of MyObject's how can I determine the number of unique values? The following linq code returns an array of jagged array values. A solution would be to store a temporary single array of items, looped through each jagged array and if values do not exist, to add them. Then a simple count would return the unique number of values. However, was wondering if there was a nicer solution. db.MyObjects.Where(t => !String.IsNullOrEmpty(t.MyProperty)) .Select(t => t.Categories.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)) .ToArray() Below is a more readable example: array[0] = { "v1", "v2", "v3" } array[1] = { "v1" } array[2] = { "v4", "v2" } array[3] = { "v1", "v5" } From all values the unique items are v1, v2, v3, v4, v5. The total number of unique items is 5. Is there a solution, possibly using linq, that returns either only the unique values or returns the number of unique values?

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• asp.net mvc ajax form helper/post additional data

  - by Jopache

  I would like to use the ajax helper to create ajax requests that send additional, dynamic data with the post (for example, get the last element with class = blogCommentDateTime and send the value of that last one to the controller which will return only blog comments after it). I have successfully done so with the help of jQuery Form plugin like so: $(document).ready(function () { $("#addCommentForm").submit(function () { var lastCommentDate = $(".CommentDateHidden:last").val(); var lastCommentData = { lastCommentDateTicks: lastCommentDate }; var formSubmitParams = { data: lastCommentData, success: AddCommentResponseHandler } $("#addCommentForm").ajaxSubmit(formSubmitParams); return false; }); This form was created with html.beginform() method. I am wondering if there is an easy way to do this using the ajax.beginform() helper? When I try to use the same code but replace html.beginform() with ajax.beginform(), when i try to submit the form, I am issuing 2 posts (which is understandable, one being taken care of by the helper, the other one by me with the JS above. I can't create 2 requests, so this option is out) I tried getting rid of the return false and changing ajaxSubmit() to ajaxForm() so that it would only "prepare" the form, and this leads in only one post, but it does not include the extra parameter that I defined, so this is worthless as well. I then tried keeping the ajaxForm() but calling that whenever the submit button on the form gets clicked rather than when the form gets submitted (I guess this is almost the same thing) and that results in 2 posts also. The biggest reason I am asking this question is that I have run in to some issues with the javascript above and using mvc validation provided by the mvc framework (which i will set up another question for) and would like to know this so I can dive further in to my validation issue.

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• Google App Engine - Uploading blobs and authentication

  - by Keyur

  (I tried asking this on the GAE forums but didn't get an answer so am trying it here.) Currently to upload blobs, the app engine's blob store service creates a unique one- time URL that a user can post blobs to. My requirement is that I only want authenticated / authorized users to post blobs in my application. I can achieve this currently if the page that includes the multipart form to upload blobs is in my application. However, I am looking to providing a "REST API" for my users to upload their blobs. While it is true that the one-time nature of the upload URL mitigates the chances of rogue use but it's still possible. I was wondering if there is anyone on the app engine team here that can consider a feature where developers can register an upload listener. (Or if there is already a way, I'll be all ears). A standard servlet filter could also potentially do the job. This will give us an opportunity to authenticate / validate / decorate requests before the request gets forwarded to the blob store service. Thanks, Keyur

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• log4js ConsoleAppender initialization

  - by perrierism

  I'm wondering if anyone happens to have some experience using Log4js? It seems its normal ConsoleAppender isn't always ready to use immediately after it's added to a logger object... If I have two sequential script tags in a document like: //Initialize logger <script type="text/javascript"> var logger = new Log4js.getLogger("JSLOG"); logger.addAppender(new Log4js.ConsoleAppender(logger, false)); logger.setLevel(Log4js.Level.INFO); </script> //Use logger <script type="text/javascript"> logger.info('Test test'); </script> ... It causes the console pop-up (pop-up window) to appear with an error message on page load: 12:58:23 PM WARN Log4js - Could not run the listener function () { return fn.apply(object, arguments); }. TypeError: this.outputElement is null The console is still initialised, it's there afterward, but for just that first logger call it doesn't seem to be there fully. If I make the first logger call setTimeout("logger.info('test test')", 1000), it doesn't have the error. So it's like it's not ready immediately. Anyone see this before or know what a workaround might be? Cheers

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• Rails named_scope across multiple tables

  - by wakiki

  I'm trying to tidy up my code by using named_scopes in Rails 2.3.x but where I'm struggling with the has_many :through associations. I'm wondering if I'm putting the scopes in the wrong place... Here's some pseudo code below. The problem is that the :accepted named scope is replicated twice... I could of course call :accepted something different but these are the statuses on the table and it seems wrong to call them something different. Can anyone shed light on whether I'm doing the following correctly or not? I know Rails 3 is out but it's still in beta and it's a big project I'm doing so I can't use it in production yet. class Person < ActiveRecord::Base has_many :connections has_many :contacts, :through => :connections named_scope :accepted, :conditions => ["connections.status = ?", Connection::ACCEPTED] # the :accepted named_scope is duplicated named_scope :accepted, :conditions => ["memberships.status = ?", Membership::ACCEPTED] end class Group < ActiveRecord::Base has_many :memberships has_many :members, :through => :memberships end class Connection < ActiveRecord::Base belongs_to :person belongs_to :contact, :class_name => "Person", :foreign_key => "contact_id" end class Membership < ActiveRecord::Base belongs_to :person belongs_to :group end I'm trying to run something like person.contacts.accepted and group.members.accepted which are two different things. Shouldn't the named_scopes be in the Membership and Connection classes? One solution is to just call the two different named scope something different in the Person class or even to create separate associations (ie. has_many :accepted_members and has_many :accepted_contacts) but it seems hackish and in reality I have many more than just accepted (ie. banned members, ignored connections, pending, requested etc etc)

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• Customize jQuery.aptags plugin - mouseclick submit from .ac_results list

  - by atmorell

  Hello, I am using jquery.autocomplete.js and jquery.apitags to select a few elements from a div (.ac_results) This works great, and I can select multiple elements etc. However the jquery-aptags plugin does only fire when enter is pressed. This might confuse some users if they use the mouse to click instead of the arrows/enter on the keyboard. I think this is the code inside jquery.aptags that submits the tag. // // Hook to the keypress event. // $(this).bind('keypress', { __c: __c }, function (e) { var c = ''; var i = 0; var v = $(this).val(); if (e.keyCode == 13) { e.stopPropagation(); e.preventDefault(); __createSpans(this, v, e.data.__c, true); } }); I am wondering if it is possible to call the method directly from a new event. $('.ac_results > ul > li').livequery(function() { $(this).bind('click', function() { $('#address_city'). //how do I fire the "enter" event from here? }); }); Any thoughts?

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• singleton factory connection pdo

  - by Scarface

  Hey guys I am having a lot of trouble trying to understand this and I was just wondering if someone could help me with some questions. I found some code that is supposed to create a connection with pdo. The problem I was having was having my connection defined within functions. Someone suggested globals but then pointed to a 'better' solution http://stackoverflow.com/questions/130878/global-or-singleton-for-database-connection. My questions with this code are. PS I cannot format this code on this page so see the link if you cannot read What is the point of the connection factory? What goes inside new ConnectionFactory(...) When the connection is defined $db = new PDO(...); why is there no try or catch (I use those for error handling)? Does this then mean I have to use try and catch for every subsequent query? class ConnectionFactory { private static $factory; public static function getFactory() { if (!self::$factory) self::$factory = new ConnectionFactory(...); return self::$factory; } private $db; public function getConnection() { if (!$db) $db = new PDO(...); return $db; } } function getSomething() { $conn = ConnectionFactory::getFactory()-getConnection(); . . . }

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• Read HTML file into email

  - by cast01

  Ive written a script to send html emails and all works well. I have the email stored in a separate HTML file which is then read in usin a while loop and fgets(). However, i want to be able to pass variables into the html. For example, in a html file i may have something like.. <body> Dear Name <br/> Thank you for your recent purhcase </body> and i read this into a string like so $file = fopen($filename, "r"); while(!feof($file)) { $html.= fgets($file, 4096); } fclose ($file); I want to be able to replace "Name" in the html file by a variable and im not entirely sure on the best way to do this. I could always make my own tag and then use regex to replace that with the name once ive read the file into the string, but im wondering if there is a better/easier method to do this. (On a side note, if anyone knows whether its better to use file_get_contents instead of multiple calls to fgets, id be interested to know)

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• Creating a scm browser for an RCP application.

  - by mdamman

  I have an RCP app that saves its project as an xml file and currently the user just selections a directory to save that file and then uses the open file dialog to open the project. We are thinking about enhancing it to allow users to check in/out from a source code manager. This will make it easier for users to share their projects with each others with all the benefits of a scm. I need something similar to Subclipses, but i was thinking of using the maven svn plugin so that it is more flexible which on which scm is used. It would probably better to keep it simple because most users won't have a clue what a scm is. An ideal would be just having a Checkout menu option which opens a dialog similar to the Open File dialog. I was wondering if anyone had an example of how to use the maven scm. What calls to make to set the scm location and to get the file? Or if there is a better way of going about this. Thanks!

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• Fastest way to generate delimited string from 1d numpy array

  - by Abiel

  I have a program which needs to turn many large one-dimensional numpy arrays of floats into delimited strings. I am finding this operation quite slow relative to the mathematical operations in my program and am wondering if there is a way to speed it up. For example, consider the following loop, which takes 100,000 random numbers in a numpy array and joins each array into a comma-delimited string. import numpy as np x = np.random.randn(100000) for i in range(100): ",".join(map(str, x)) This loop takes about 20 seconds to complete (total, not each cycle). In contrast, consider that 100 cycles of something like elementwise multiplication (x*x) would take than one 1/10 of a second to complete. Clearly the string join operation creates a large performance bottleneck; in my actual application it will dominate total runtime. This makes me wonder, is there a faster way than ",".join(map(str, x))? Since map() is where almost all the processing time occurs, this comes down to the question of whether there a faster to way convert a very large number of numbers to strings.

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• Caching sitemaps in django

  - by michuk

  I implemented a simple sitemap class using django's default sitemap app. As it was taking a long time to execute, I added manual caching: class ShortReviewsSitemap(Sitemap): changefreq = "hourly" priority = 0.7 def items(self): # try to retrieve from cache result = get_cache(CACHE_SITEMAP_SHORT_REVIEWS, "sitemap_short_reviews") if result!=None: return result result = ShortReview.objects.all().order_by("-created_at") # store in cache set_cache(CACHE_SITEMAP_SHORT_REVIEWS, "sitemap_short_reviews", result) return result def lastmod(self, obj): return obj.updated_at The problem is that memcache allows only max 1MB object. This one was bigger that 1MB, so storing into cache failed: >7 SERVER_ERROR object too large for cache The problem is that django has an automated way of deciding when it should divide the sitemap file into smalled ones. According to the docs (http://docs.djangoproject.com/en/dev/ref/contrib/sitemaps/): You should create an index file if one of your sitemaps has more than 50,000 URLs. In this case, Django will automatically paginate the sitemap, and the index will reflect that. What do you think would be the best way to enable caching sitemaps? - Hacking into django sitemaps framework to restrict a single sitemap size to, let's say, 10,000 records seems like the best idea. Why was 50,000 chosen in the first place? Google advice? random number? - Or maybe there is a way to allow memcached store bigger files? - Or perhaps onces saved, the sitemaps should be made available as static files? This would mean that instead of caching with memcached I'd have to manually store the results in the filesystem and retrieve them from there next time when the sitemap is requested (perhaps cleaning the directory daily in a cron job). All those seem very low level and I'm wondering if an obvious solution exists...

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• To what degree should I use Marshal.ReleaseComObject with Excel Interop objects?

  - by DanM

  I've seen several examples where Marshal.ReleaseComObject() is used with Excel Interop objects (i.e., objects from namespace Microsoft.Office.Interop.Excel), but I've seen it used to various degrees. I'm wondering if I can get away with something like this: var application = new ApplicationClass(); try { // do work with application, workbooks, worksheets, cells, etc. } finally { Marashal.ReleaseComObject(application) } Or if I need to release every single object created, as in this method: public void CreateExcelWorkbookWithSingleSheet() { var application = new ApplicationClass(); var workbook = application.Workbooks.Add(_missing); var worksheets = workbook.Worksheets; for (var worksheetIndex = 1; worksheetIndex < worksheets.Count; worksheetIndex++) { var worksheet = (WorksheetClass)worksheets[worksheetIndex]; worksheet.Delete(); Marshal.ReleaseComObject(worksheet); } workbook.SaveAs( WorkbookPath, _missing, _missing, _missing, _missing, _missing, XlSaveAsAccessMode.xlExclusive, _missing, _missing, _missing, _missing, _missing); workbook.Close(true, _missing, _missing); application.Quit(); Marshal.ReleaseComObject(worksheets); Marshal.ReleaseComObject(workbook); Marshal.ReleaseComObject(application); } What prompted me to ask this question is that, being the LINQ devotee I am, I really want to do something like this: var worksheetNames = worksheets.Cast<Worksheet>().Select(ws => ws.Name); ...but I'm concerned I'll end up with memory leaks or ghost processes if I don't release each worksheet (ws) object. Any insight on this would be appreciated.

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