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  • Is the recent trend toward widescreen (16:9) computer monitors a plus or minus for programmers?

    - by DanM
    It's almost gotten to the point where you can't buy a conventional (4:3) monitor anymore. Pretty much everything is widescreen. This is fine for watching movies or TV, but is it good or bad for programming? My initial thoughts on the issue are that widescreens are a net negative for programmers. Here are some of the disadvantages I see: Poor space utiliziation One disadvantage of widescreens you can't argue with is that they offer poor space utilization for the amount of total pixels you get. For example, my Thinkpad, which I bought just before the widescreen craze, has a 15" monitor with a native resolution of 1600 x 1200. The newer 15.4" Thinkpads run at most 1680 x 1050. So (if you do the math) you get fewer pixels in a wider (but not shorter) package. With desktop monitors, you pay a price in terms of desk space used. Two 1680 x 1050 monitors will simply take up more of your desk than two 1600 x 1200 monitors (assuming equal dot pitch). More scrolling If you compare a 1680 x 1050 monitor to a 1600 x 1200 monitor, you get 80 extra pixels of width but 150 fewer pixels of height. The height reduction means you lose approximately 11 lines of code. That's less you can see on the screen at one time and more scrolling you have to do. This harms productivity, maybe not dramatically, but insidiously. Less room for wide panels Widescreens also mean you lose space for wide but short panels common in programming environments. If you use Visual Studio, for example, your code window will be that much shorter when viewing the Find Results, Task List, or Error List (all of which I use frequently). This isn't to say the 80 pixels of extra width you get with widescreen would never be useful, but I tend to keep my lines of code short, so seeing more lines would be more valuable to me than seeing fewer, longer lines. What do you think? Do you agree/disagree? Are you now using one or more widescreen monitors for development? What resolution are you running on each? Do you ever miss the height of the traditional 4:3 monitor? Would you complain if your monitors were one inch narrower but two inches taller?

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  • Symfony : ajax call cause server to queue next queries

    - by Remiz
    Hello, I've a problem with my application when an ajax call on the server takes too much time : it queue all the others queries from the user until it's done server side (I realized that canceling the call client side has no effect and the user still have to wait). Here is my test case : <script type="text/javascript" src="jquery-1.4.1.min.js"></script> <a href="another-page.php">Go to another page on the same server</a> <script type="text/javascript"> url = 'http://localserver/some-very-long-complex-query'; $.get(url); </script> So when the get is fired and then after I click on the link, the server finish serving the first call before bringing me to the other page. My problem is that I want to avoid this behavior. I'm on a LAMP server and I'm looking in a way to inform the server that the user aborted the query with function like connection_aborted(), do you think that's the way to go ? Also, I know that the longest part of this PHP script is a MySQL query, so even if I know that connection_aborted() can detect that the user cancel the call, I still need to check this during the MySQL query... I'm not really sure that PHP can handle this kind of "event". So if you have any better idea, I can't wait to hear it. Thank you. Update : After further investigation, I found that the problem happen only with the Symfony framework (that I omitted to precise, my bad). It seems that an Ajax call lock any other future call. It maybe related to the controller or the routing system, I'm looking into it. Also for those interested by the problem here is my new test case : -new project with Symfony 1.4.3, default configuration, I just created an app and a default module. -jquery 1.4 for the ajax query. Here is my actions.class.php (in my unique module) : class defaultActions extends sfActions { public function executeIndex(sfWebRequest $request) { //Do nothing } public function executeNewpage() { //Do also nothing } public function executeWaitingaction(){ // Wait sleep(30); return false; } } Here is my indexSuccess.php template file : <script type="text/javascript" src="jquery-1.4.1.min.js"></script> <a href="<?php echo url_for('default/newpage');?>">Go to another symfony action</a> <script type="text/javascript"> url = '<?php echo url_for('default/waitingaction');?>'; $.get(url); </script> For the new page template, it's not very relevant... But with this, I'm able to reproduce the lock problem I've on my real application. Is somebody else having the same issue ? Thanks.

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  • What to name column in database table that holds versioning number

    - by rwmnau
    I'm trying to figure out what to call the column in my database table that holds an INT to specific "record version". I'm currently using "RecordOrder", but I don't like that, because people think higher=newer, but the way I'm using it, lower=newer (with "1" being the current record, "2" being the second most current, "3" older still, and so on). I've considered "RecordVersion", but I'm afraid that would have the same problem. Any other suggestions? "RecordAge"? I'm doing this because when I insert into the table, instead of having to find out what version is next, then run the risk of having that number stolen from me before I write, I just insert insert with a "RecordOrder" of 0. There's a trigger on the table AFTER INSERT that increments all the "RecordOrder" numbers for that key by 1, so the record I just inserted becomes "1", and all others are increased by 1. That way, you can get a person's current record by selection RecordOrder=1, instead of getting the MAX(RecordOrder) and then selecting that. PS - I'm also open to criticism about why this is a terrible idea and I should be incrementing this index instead. This just seemed to make lookups much easier, but if it's a bad idea, please enlighten me! Some details about the data, as an example: I have the following database table: CREATE TABLE AmountDue ( CustomerNumber INT, AmountDue DECIMAL(14,2), RecordOrder SMALLINT, RecordCreated DATETIME ) A subset of my data looks like this: CustomerNumber Amountdue RecordOrder RecordCreated 100 0 1 2009-12-19 05:10:10.123 100 10.05 2 2009-12-15 06:12:10.123 100 100.00 3 2009-12-14 14:19:10.123 101 5.00 1 2009-11-14 05:16:10.123 In this example, there are three rows for customer 100 - they owed $100, then $10.05, and now they owe nothing. Let me know if I need to clarify it some more. UPDATE: The "RecordOrder" and "RecordCreated" columns are not available to the user - they're only there for internal use, and to help figure out which is the current customer record. Also, I could use it to return an appropriately-ordered customer history, though I could just as easily do that with the date. I can accomplish the same thing as an incrementing "Record Version" with just the RecordCreated date, I suppose, but that removes the convenience of knowing that RecordOrder=1 is the current record, and I'm back to doing a sub-query with MAX or MIN on the DateTime to determine the most recent record.

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  • Android pluginable application

    - by Alxandr
    I've been trying to create an android-application the last couple of weeks, and mostly everything has worked out great, but there is one thing that I was wondering about, and that is pluginability trough the use of intents. What I'm trying to create is basically a comic-reader. As of the version I use now, I open the application and get a list of commics that are my favourites, then I enter one to get a detailed view, and finally I enter a page. This is managed trough 3 activities. List, Details and Page. However, as of now the application can only read comics of one source (a specialiced xml-feed comming from my server), and I was hoping to be able to expand this a litle (also, the page-activity and some other stuff needs to be cleaned up in, so I'm thinking about remaking from scratch, and just take the first go as a learning-round). And I came up with an idea which I think sounds great, but I don't know if it's possible, but this is what I'm thinking about: The user enters the application and get an (first time empty) list of comics. The user hits a button to find comics, this launces an intent that says something like "find comic" or something like that. This should cause the system to display all matching activities. This would make it possible to provide different comic-providers trough different applications. Another activity kicks in and might displays some options to the user (for instance a file-browser), or might not (in the example of an xml-feed, which should just load). The list is returned to the first activity and displayed to the user. The second (find) activity is closed. The user picks a comic from the list. This should open some details-activity. The details-activity should receive a key which corresponds to the comic selected. This should be unique amongst the comic-providers. The details-view should get it's data trough some cind of content-provider, or an activity (whichever is most suited, if one of them is). The user can select a page. This should be the same routine as step 5. My question is, is this possible in the android system, and if it is, is it a bad idea? And also, is there any better way to achieve more or less the same thing?

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  • iPhone Image Resources, ICO vs PNG, app bundle filesize

    - by Jasarien
    My application has a collection of around 1940 icons that are used throughout. They're currently in ICO and new images provided to me come in ICO format too. I have noticed that they contain a 16x16 and 32x32 representation of each icon in one file. Each file is roughly 4KB in filesize (as reported by finder, but ls reports that they vary from being ~1000 bytes to 5000 bytes) A very small number of these icons only contain the 32x32 representation, and as a result are only around 700 bytes in size. Currently I am bundling these icons with my application and they are inflating the size of the app a bit more than I would like. Altogether, the images total just about 25.5MB. Xcode must do some kind of compression because the resulting app bundle is about 12.4MB. Compressing this further into a ZIP (as it would be when submitted to the App Store), results in a final file of 5.8MB. I'm aware that the maximum limit for over the air App Store downloads has been raised to 20MB since the introduction of the iPad (I'm not sure if that extends to iPhone apps as well as iPad apps though, if not the limit would be 10MB). My worry is that new icons are going to be added (sometimes up to 10 icons per week), and will continue to inflate the app bundle over time. What is the best way to distribute these icons with my app? Things I've tried and not had much success with: Converting the icons from ICO to PNG: I tried this in the hopes that the pngcrush utility would help out with the filesize. But it appears that it doesn't make much of a difference between a normal PNG and a crushed png (I believe it just optimises the image for display on the iPhone's GPU rather than compress it's size). Also in going from ICO to PNG actually increased the size of the icon file... Zipping the images, and then uncompressing them on first run. While this did reduce the overall image sizes, I found that the effort needed to unzip them, copy them to the documents folder and ensure that duplication doesn't happen on upgrades was too much hassle to be worth the benefit. Also, on original and 3G iPhones unzipping and copying around 25MB of images takes too long and creates a bad experience... Things I've considered but not yet tried: Instead of distributing the icons within the app bundle, host them online, and download each icon on demand (it depends on the user's data as to which icons will actually be displayed and when). Issues with this is that bandwidth costs money, and image downloads will be bandwidth intensive. However, my app currently has a small userbase of around 5,500 users (of which I estimate around 1500 to be active based on Flurry stats), and I have a huge unused bandwidth allowance with my current hosting package. So I'm open to thoughts on how to solve this tricky issue.

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  • Calling a function within a class

    - by JM4
    I am having trouble calling a specific function within a class. The call is made: case "Mod10": if (!validateCreditCard($fields[$field_name])) $errors[] = $error_message; break; and the class code is: class CreditCardValidationSolution { var $CCVSNumber = ''; var $CCVSNumberLeft = ''; var $CCVSNumberRight = ''; var $CCVSType = ''; var $CCVSError = ''; function validateCreditCard($Number) { $this->CCVSNumber = ''; $this->CCVSNumberLeft = ''; $this->CCVSNumberRight = ''; $this->CCVSType = ''; $this->CCVSError = ''; // Catch malformed input. if (empty($Number) || !is_string($Number)) { $this->CCVSError = $CCVSErrNumberString; return FALSE; } // Ensure number doesn't overrun. $Number = substr($Number, 0, 20); // Remove non-numeric characters. $this->CCVSNumber = preg_replace('/[^0-9]/', '', $Number); // Set up variables. $this->CCVSNumberLeft = substr($this->CCVSNumber, 0, 4); $this->CCVSNumberRight = substr($this->CCVSNumber, -4); $NumberLength = strlen($this->CCVSNumber); $DoChecksum = 'Y'; // Mod10 checksum process... if ($DoChecksum == 'Y') { $Checksum = 0; // Add even digits in even length strings or odd digits in odd length strings. for ($Location = 1 - ($NumberLength % 2); $Location < $NumberLength; $Location += 2) { $Checksum += substr($this->CCVSNumber, $Location, 1); } // Analyze odd digits in even length strings or even digits in odd length strings. for ($Location = ($NumberLength % 2); $Location < $NumberLength; $Location += 2) { $Digit = substr($this->CCVSNumber, $Location, 1) * 2; if ($Digit < 10) { $Checksum += $Digit; } else { $Checksum += $Digit - 9; } } // Checksums not divisible by 10 are bad. if ($Checksum % 10 != 0) { $this->CCVSError = $CCVSErrChecksum; return FALSE; } } return TRUE; } } When I run the application - I get the following message: Fatal error: Call to undefined function validateCreditCard() in C:\xampp\htdocs\validation.php on line 339 any ideas?

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  • Reading and writing C++ vector to a file

    - by JB
    For some graphics work I need to read in a large amount of data as quickly as possible and would ideally like to directly read and write the data structures to disk. Basically I have a load of 3d models in various file formats which take too long to load so I want to write them out in their "prepared" format as a cache that will load much faster on subsequent runs of the program. Is it safe to do it like this? My worries are around directly reading into the data of the vector? I've removed error checking, hard coded 4 as the size of the int and so on so that i can give a short working example, I know it's bad code, my question really is if it is safe in c++ to read a whole array of structures directly into a vector like this? I believe it to be so, but c++ has so many traps and undefined behavour when you start going low level and dealing directly with raw memory like this. I realise that number formats and sizes may change across platforms and compilers but this will only even be read and written by the same compiler program to cache data that may be needed on a later run of the same program. #include <fstream> #include <vector> using namespace std; struct Vertex { float x, y, z; }; typedef vector<Vertex> VertexList; int main() { // Create a list for testing VertexList list; Vertex v1 = {1.0f, 2.0f, 3.0f}; list.push_back(v1); Vertex v2 = {2.0f, 100.0f, 3.0f}; list.push_back(v2); Vertex v3 = {3.0f, 200.0f, 3.0f}; list.push_back(v3); Vertex v4 = {4.0f, 300.0f, 3.0f}; list.push_back(v4); // Write out a list to a disk file ofstream os ("data.dat", ios::binary); int size1 = list.size(); os.write((const char*)&size1, 4); os.write((const char*)&list[0], size1 * sizeof(Vertex)); os.close(); // Read it back in VertexList list2; ifstream is("data.dat", ios::binary); int size2; is.read((char*)&size2, 4); list2.resize(size2); // Is it safe to read a whole array of structures directly into the vector? is.read((char*)&list2[0], size2 * sizeof(Vertex)); }

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  • Implementing a logging library in .NET with a database as the storage medium

    - by Dave
    I'm just starting to work on a logging library that everyone can use to keep track of any sort of system information while the user is running our application. The simplest example so far is to track Info, Warnings, and Errors. I want all plugins to be able to use this feature, but since each developer might have a different idea of what's important to report, I want to keep this as generic as possible. In the C++ world, I would normally use something like a stl::pair<string,string> to act as a key value pair structure, and have a stl::list of these to act as a "row" in the log. The log cache would then be a list<list<pair<string,string>>> (ugh!). This way, the developers can use a const string key like INFO, WARNING, ERROR to have a consistent naming for a column in the database (for SELECTing specific types of information). I'd like the database to be able to deal with any number of distinct column names. For example, John might have an INFO row with a column called USER, and Bill might have an INFO row with a column called FILENAME. I want the log viewer to be able to display all information, and if one report doesn't have a value for INFO / FILENAME, those fields should just appear blank. So one option is to use List<List<KeyValuePair<String,String>>, and the another is to have the log library consumer somehow "register" its schema, and then have the database do an ALTER TABLE to handle this situation. Yet another idea is to have a table that's just for key value pairs, with a foreign key that maps the key value pairs back to the original log entry. I obviously don't want logging to bog down the system, so I only lock the log cache to make a copy of the data (and remove the already-copied data), then a background thread will dump the information to the database. My specific questions regarding this are: Do you see any performance issues? In other words, have you ever tried something like this and found that certain things just don't work well in practice? Is there a more .NETish way to implement the key value pairs, other than List<List<KeyValuePair<String,String>>>? Even if there is a way to do #2 better, is the ALTER TABLE idea I proposed above a Bad Thing? Would you recommend multiple databases over a single one? I don't yet have an idea of how frequently the log would get written to, but we ideally would like to have lots of low level information. Perhaps there should be a DB with a fixed schema only for the low level stuff, and then another DB that's more flexible for reporting information back to users.

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  • Can this be imporved? Scrubing of dangerous html tags.

    - by chobo2
    Hi I been finding that for something that I consider pretty import there is very little information or libraries on how to deal with this problem. I found this while searching. I really don't know all the million ways that a hacker could try to insert the dangerous tags. I have a rich html editor so I need to keep non dangerous tags but strip out bad ones. So is this script missing anything? It uses html agility pack. public string ScrubHTML(string html) { HtmlDocument doc = new HtmlDocument(); doc.LoadHtml(html); //Remove potentially harmful elements HtmlNodeCollection nc = doc.DocumentNode.SelectNodes("//script|//link|//iframe|//frameset|//frame|//applet|//object|//embed"); if (nc != null) { foreach (HtmlNode node in nc) { node.ParentNode.RemoveChild(node, false); } } //remove hrefs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("href", "#"); } } //remove img with refs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("src", "#"); } } //remove on<Event> handlers from all tags nc = doc.DocumentNode.SelectNodes("//*[@onclick or @onmouseover or @onfocus or @onblur or @onmouseout or @ondoubleclick or @onload or @onunload]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("onFocus"); node.Attributes.Remove("onBlur"); node.Attributes.Remove("onClick"); node.Attributes.Remove("onMouseOver"); node.Attributes.Remove("onMouseOut"); node.Attributes.Remove("onDoubleClick"); node.Attributes.Remove("onLoad"); node.Attributes.Remove("onUnload"); } } // remove any style attributes that contain the word expression (IE evaluates this as script) nc = doc.DocumentNode.SelectNodes("//*[contains(translate(@style, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'expression')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("stYle"); } } return doc.DocumentNode.WriteTo(); }

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  • Audio/video streaming on Windows platform

    - by bushtucker
    I'm building an interactive language learning application to be used in a classroom environment. The idea is that a teacher should be able to talk to the students (=audio stream to all students), let students talk to each other (= audio P2P) in groups of two or more, let students watch a video coming from a the DVD player or coming from a media server. It should be possible to save the audio/video streams. The teacher should also be able to monitor, take-over or block the desktop of the students. The platform is Windows and it's a desktop application, no web application. The audio delay should be as minimal as poosible. Optionally a student sitting at home should be supported, but it's not a high priority. I am now finished with the classroom control part of the application (login, monitor, block, ...) and want to start the audio and video part. I've been evaluating several options like DirectX, GStreamer and SIP but now I have to make a decision. DirectX seems an obvious choice for the Windows platform, but it only lets me capture and playback audio and video. The encoding/decoding/network part I should do myself. GStreamer contains all kinds of options to capture/encode/stream/save audio and video streams. I've experimented a bit with it (ossbuild) and it does seem to involve a lot of trial and error to make something work: - microphone capture (via directsoundsrc) produces cracking noises on some computers - rtpL16 payloader didn't work well - streaming raw audio over the network only working at a sampling rate of 8000, no higher - there are a lot of errors when receiving mpeg4 video (bad I-frame), on some computers worse than others It is my impression that gstreamer is primary targetted at linux platforms. Development and support for the Windows platform seems to be a little behind. Nevertheless it's a powerful framework that could save me months and years of work. SIP seems to be able to do everything I want, but it is targeted towards telephony and IM. I don't know how flexible SIP is. It seems to me that the SIP layer would just be overhead as I already have a central (teacher) application that can control and setup all the streams. The interesting parts of frameworks like opalvoip and freeswitch are the actual audio/video capture, the encoding and transmission. Does anyone know how these interesting parts relate a framework like gstreamer? Are they easy to integrate into a custom application? Are they flexible enough? Does anyone have experience with all or one of these technologies? Maybe there are even other options I can look at? Many thanks for your advice

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  • Serialization of non-required fields in protobuf-net

    - by David Hedlund
    I have a working java client that is communicating with Google, through ProtoBuf serialized messages. I am currently trying to translate that client into C#. I have a .proto file where the parameter appId is an optional string. Its default value in the C# representation as generated by the protobuf-net library is an empty string, just as it is in the java representation of the same file. message AppsRequest { optional AppType appType = 1; optional string query = 2; optional string categoryId = 3; optional string appId = 4; optional bool withExtendedInfo = 6; } I find that when I explicitly set appId to "" in the java client, the client stops working (403 Bad Request from Google). When I explicitly set appId to null in the java client, everything works, but only because hasAppId is being set to false (I'm uncertain as to how that affects the serialization). In the C# client, I always get 403 responses. I don't see any logic behind the distinction between not setting a value, and setting the default value, that seems to make all the difference in the java client. Since the output is always a binary stream, I am not sure if the successful java messages are being serialized with an empty string, or not serialized at all. In the C# client, I've tried setting IsRequired to true on the ProtoMember attribute, to force them to serialize, and I've tried setting the default value to null, and explicitly set "", so I'm quite sure I've tried some configuration where the value is being serialized. I've also played around with ProtoBuf.ProtoIgnore and at some point, removing the appId parameter altogether, but I haven't been able to avoid the 403 errors in C#. I've tried manually copying the serialized string from java, and that resolved my issues, so I'm certain that the rest of the HTTP Request is working, and the error can be traced to the serialized object. My serialization is simply this: var clone = ProtoBuf.Serializer.DeepClone(request); MemoryStream ms = new MemoryStream(2000); ProtoBuf.Serializer.Serialize(ms, clone); var bytearr = ms.ToArray(); string encodedData = Convert.ToBase64String(bytearr); I'll admit to not being quite sure about what DeepClone does. I've tried both with and without it...

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  • PHP GD Allowed memory size exhausted

    - by gurun8
    I'm trying to process a directory of JPEG images (roughly 600+, ranging from 50k to 500k) using PHP: GD to resize and save the images but I've hit a bit of a snag quite early in the process. After correctly processing just 3 images (30K, 18K and 231K) I get a Allowed memory size of 16777216 bytes exhausted PHP Fatal error. I'm cycling through the images and calling the code below: list($w, $h) = getimagesize($src); if ($w > $it->width) { $newwidth = $it->width; $newheight = round(($newwidth * $h) / $w); } elseif ($w > $it->height) { $newheight = $it->height; $newwidth = round(($newheight * $w) / $h); } else { $newwidth = $w; $newheight = $h; } // create resize image $img = imagecreatetruecolor($newwidth, $newheight); $org = imagecreatefromjpeg($src); // Resize imagecopyresized($img, $org, 0, 0, 0, 0, $newwidth, $newheight, $w, $h); imagedestroy($org); imagejpeg($img, $dest); // Free up memory imagedestroy($img); I've tried to free up memory with the imagedestroy function but it doesn't seem to have any affect. The script just keeps consistently choking at the imagecreatefromjpeg line of code. I checked the php.ini and the memory_limit = 16M setting seems like it's holding correctly. But I can't figure out why the memory is filling up. Shouldn't it be releasing the memory back to the garbage collector? I don't really want to increase the memory_limit setting. This seems like a bad workaround that could potentially lead to more issues in the future. FYI: I'm running my script from a command prompt. It shouldn't affect the functionality but might influence your response so I thought I should mention it. Can anyone see if I'm just missing something simple or if there's a design flaw here? You'd think that this would be a pretty straightforward task. Surely this has to be possible, right?

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  • How to check for palindrome using Python logic

    - by DrOnline
    My background is only a 6 month college class in basic C/C++, and I'm trying to convert to Python. I may be talking nonsense, but it seems to me C, at least at my level, is very for-loop intensive. I solve most problems with these loops. And it seems to me the biggest mistake people do when going from C to Python is trying to implement C logic using Python, which makes things run slowly, and it's just not making the most of the language. I see on this website: http://hyperpolyglot.org/scripting (serach for "c-style for", that Python doesn't have C-style for loops. Might be outdated, but I interpret it to mean Python has its own methods for this. I've tried looking around, I can't find much up to date (Python 3) advice for this. How can I solve a palindrome challenge in Python, without using the for loop? I've done this in C in class, but I want to do it in Python, on a personal basis. The problem is from the Euler Project, great site btw. def isPalindrome(n): lst = [int(n) for n in str(n)] l=len(lst) if l==0 || l==1: return True elif len(lst)%2==0: for k in range (l) ##### else: while (k<=((l-1)/2)): if (list[]): ##### for i in range (999, 100, -1): for j in range (999,100, -1): if isPalindrome(i*j): print(i*j) break I'm missing a lot of code here. The five hashes are just reminders for myself. Concrete questions: 1) In C, I would make a for loop comparing index 0 to index max, and then index 0+1 with max-1, until something something. How to best do this in Python? 2) My for loop (in in range (999, 100, -1), is this a bad way to do it in Python? 3) Does anybody have any good advice, or good websites or resources for people in my position? I'm not a programmer, I don't aspire to be one, I just want to learn enough so that when I write my bachelor's degree thesis (electrical engineering), I don't have to simultaneously LEARN an applicable programming language while trying to obtain good results in the project. "How to go from basic C to great application of Python", that sort of thing. 4) Any specific bits of code to make a great solution to this problem would also be appreciated, I need to learn good algorithms.. I am envisioning 3 situations. If the value is zero or single digit, if it is of odd length, and if it is of even length. I was planning to write for loops... PS: The problem is: Find the highest value product of two 3 digit integers that is also a palindrome.

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  • Some clarification on rvalue references

    - by Dennis Zickefoose
    First: where are std::move and std::forward defined? I know what they do, but I can't find proof that any standard header is required to include them. In gcc44 sometimes std::move is available, and sometimes its not, so a definitive include directive would be useful. When implementing move semantics, the source is presumably left in an undefined state. Should this state necessarily be a valid state for the object? Obviously, you need to be able to call the object's destructor, and be able to assign to it by whatever means the class exposes. But should other operations be valid? I suppose what I'm asking is, if your class guarantees certain invariants, should you strive to enforce those invariants when the user has said they don't care about them anymore? Next: when you don't care about move semantics, are there any limitations that would cause a non-const reference to be preferred over an rvalue reference when dealing with function parameters? void function(T&); over void function(T&&); From a caller's perspective, being able to pass functions temporary values is occasionally useful, so it seems as though one should grant that option whenever it is feasible to do so. And rvalue references are themselves lvalues, so you can't inadvertently call a move-constructor instead of a copy-constructor, or something like that. I don't see a downside, but I'm sure there is one. Which brings me to my final question. You still can not bind temporaries to non-const references. But you can bind them to non-const rvalue references. And you can then pass along that reference as a non-const reference in another function. void function1(int& r) { r++; } void function2(int&& r) { function1(r); } int main() { function1(5); //bad function2(5); //good } Besides the fact that it doesn't do anything, is there anything wrong with that code? My gut says of course not, since changing rvalue references is kind of the whole point to their existence. And if the passed value is legitimately const, the compiler will catch it and yell at you. But by all appearances, this is a runaround of a mechanism that was presumably put in place for a reason, so I'd just like confirmation that I'm not doing anything foolish.

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  • Can this be improved? Scrubing of dangerous html tags.

    - by chobo2
    I been finding that for something that I consider pretty import there is very little information or libraries on how to deal with this problem. I found this while searching. I really don't know all the million ways that a hacker could try to insert the dangerous tags. I have a rich html editor so I need to keep non dangerous tags but strip out bad ones. So is this script missing anything? It uses html agility pack. public string ScrubHTML(string html) { HtmlDocument doc = new HtmlDocument(); doc.LoadHtml(html); //Remove potentially harmful elements HtmlNodeCollection nc = doc.DocumentNode.SelectNodes("//script|//link|//iframe|//frameset|//frame|//applet|//object|//embed"); if (nc != null) { foreach (HtmlNode node in nc) { node.ParentNode.RemoveChild(node, false); } } //remove hrefs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//a[starts-with(translate(@href, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("href", "#"); } } //remove img with refs to java/j/vbscript URLs nc = doc.DocumentNode.SelectNodes("//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'javascript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'jscript')]|//img[starts-with(translate(@src, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'vbscript')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.SetAttributeValue("src", "#"); } } //remove on<Event> handlers from all tags nc = doc.DocumentNode.SelectNodes("//*[@onclick or @onmouseover or @onfocus or @onblur or @onmouseout or @ondoubleclick or @onload or @onunload]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("onFocus"); node.Attributes.Remove("onBlur"); node.Attributes.Remove("onClick"); node.Attributes.Remove("onMouseOver"); node.Attributes.Remove("onMouseOut"); node.Attributes.Remove("onDoubleClick"); node.Attributes.Remove("onLoad"); node.Attributes.Remove("onUnload"); } } // remove any style attributes that contain the word expression (IE evaluates this as script) nc = doc.DocumentNode.SelectNodes("//*[contains(translate(@style, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), 'expression')]"); if (nc != null) { foreach (HtmlNode node in nc) { node.Attributes.Remove("stYle"); } } return doc.DocumentNode.WriteTo(); }

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  • .NET: Is there a way to finagle a default namespace in an XPath 1.0 query?

    - by Cheeso
    I'm building a tool that performs xpath 1.0 queries on XHTML documents. The requirement to use a namespace prefix in the query is killing me. The query looks like this: html/body/div[@class='contents']/div[@class='body']/ div[@class='pgdbbyauthor']/h2[a[@name][starts-with(.,'Quick')]]/ following-sibling::ul[1]/li/a (all on one line) ...which is bad enough, except because it's xpath 1.0, I need to use an explicit namespace prefix on each QName, so it looks like this: ns1:html/ns1:body/ns1:div[@class='contents']/ns1:div[@class='body']/ ns1:div[@class='pgdbbyauthor']/ns1:h2[ns1:a[@name][starts-with(.,'Quick')]]/ following-sibling::ns1:ul[1]/ns1:li/ns1:a To set up the query, I do something like this: var xpathDoc = new XPathDocument(new StringReader(theText)); var nav = xpathDoc.CreateNavigator(); var xmlns = new XmlNamespaceManager(nav.NameTable); foreach (string prefix in xmlNamespaces.Keys) xmlns.AddNamespace(prefix, xmlNamespaces[prefix]); XPathNodeIterator selection = nav.Select(xpathExpression, xmlns); But what I want is for the xpathExpression to use the implicit default namespace. Is there a way for me to transform the unadorned xpath expression, after it's been written, to inject a namespace prefix for each element name in the query? I'm thinking, anything between two slashes, I could inject a prefix there. Excepting of course axis names like "parent::" and "preceding-sibling::" . And wildcards. That's what I mean by "finagle a default namespace". Is this hack gonna work? Addendum Here's what I mean. suppose I have an xpath expression, and before passing it to nav.Select(), I transform it. Something like this: string FixupWithDefaultNamespace(string expr) { string s = expr; s = Regex.Replace(s, "^(?!::)([^/:]+)(?=/)", "ns1:$1"); // beginning s = Regex.Replace(s, "/([^/:]+)(?=/)", "/ns1:$1"); // stanza s = Regex.Replace(s, "::([A-Za-z][^/:*]*)(?=/)", "::ns1:$1"); // axis specifier s = Regex.Replace(s, "\\[([A-Za-z][^/:*\\(]*)(?=[\\[\\]])", "[ns1:$1"); // predicate s = Regex.Replace(s, "/([A-Za-z][^/:]*)(?!<::)$", "/ns1:$1"); // end s = Regex.Replace(s, "^([A-Za-z][^/:]*)$", "ns1:$1"); // edge case s = Regex.Replace(s, "([-A-Za-z]+)\\(([^/:\\.,\\)]+)(?=[,\\)])", "$1(ns1:$2"); // xpath functions return s; } This actually works for simple cases I tried. To use the example from above - if the input is the first xpath expression, the output I get is the 2nd one, with all the ns1 prefixes. The real question is, is it hopeless to expect this Regex.Replace approach to work, as the xpath expressions get more complicated?

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  • Neo4j 1.9.4 (REST Server,CYPHER) performance issue

    - by user2968943
    I have Neo4j 1.9.4 installed on 24 core 24Gb ram (centos) machine and for most queries CPU usage spikes goes to 200% with only few concurrent requests. Domain: some sort of social application where few types of nodes(profiles) with 3-30 text/array properties and 36 relationship types with at least 3 properties. Most of nodes currently has ~300-500 relationships. Current data set footprint(from console): LogicalLogSize=4294907 (32MB) ArrayStoreSize=1675520 (12MB) NodeStoreSize=1342170 (10MB) PropertyStoreSize=1739548 (13MB) RelationshipStoreSize=6395202 (48MB) StringStoreSize=1478400 (11MB) which is IMHO really small. most queries looks like this one(with more or less WITH .. MATCH .. statements and few queries with variable length relations but the often fast): START targetUser=node({id}), currentUser=node({current}) MATCH targetUser-[contact:InContactsRelation]->n, n-[:InLocationRelation]->l, n-[:InCategoryRelation]->c WITH currentUser, targetUser,n, l,c, contact.fav is not null as inFavorites MATCH n<-[followers?:InContactsRelation]-() WITH currentUser, targetUser,n, l,c,inFavorites, COUNT(followers) as numFollowers RETURN id(n) as id, n.name? as name, n.title? as title, n._class as _class, n.avatar? as avatar, n.avatar_type? as avatar_type, l.name as location__name, c.name as category__name, true as isInContacts, inFavorites as isInFavorites, numFollowers it runs in ~1s-3s(for first run) and ~1s-70ms (for consecutive and it depends on query) and there is about 5-10 queries runs for each impression. Another interesting behavior is when i try run query from console(neo4j) on my local machine many consecutive times(just press ctrl+enter for few seconds) it has almost constant execution time but when i do it on server it goes slower exponentially and i guess it somehow related with my problem. Problem: So my problem is that neo4j is very CPU greedy(for 24 core machine its may be not an issue but its obviously overkill for small project). First time i used AWS EC2 m1.large instance but over all performance was bad, during testing, CPU always was over 100%. Some relevant parts of configuration: neostore.nodestore.db.mapped_memory=1280M wrapper.java.maxmemory=8192 note: I already tried configuration where all memory related parameters where HIGH and it didn't worked(no change at all). Question: Where to digg? configuration? scheme? queries? what i'm doing wrong? if need more info(logs, configs) just ask ;)

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  • CSS Collapsing/Hiding divs with no data in <span>

    - by Chance
    I am trying to display an address which includes the following information: Title, division, address1, address2, town/state/zip, and country (5 seperate lines worth of data). The problem is sometimes the company may only have the title, address1, and town/state/zip yet other times it may be all but address2. This is determined upon a db record request server side. Therefore how can I make my output look proper when some of my labels will be blank? I would like div's that contain an empty span to be essentially collapsed/removed. My only idea of how was to use jquery and a selector to find all divs with blank spans (since thats all an asp.net label really is) and then remove those divs however this seems like such bad form. Is there any way to do this with css? Possible Code would be something like: $('span:empty:only-child').parent('div').remove(); Picture Examples (Ignore spacing/indentation issues which I will fix) Missing Division, Address2, and Country All Possible Fields The Html <asp:Label runat="server" ID="lblBillingAddressHeader" CssClass="lblBillingAddressHeader" Text="Billing Address:" /> <div style="position:relative; top:150px; left: 113px;"> <div class="test"> <asp:Label runat="server" ID="lblBillingDivision" CssClass="lblBillingShippingDivisionFont" /> </div> <div class="test"> <asp:Label runat="server" ID="lblBillingAddress" CssClass="lblBillingShippingFont" /> </div> <div class="test"> <asp:Label runat="server" ID="lblBillingAddress2" CssClass="lblBillingShippingFont" /> </div> <div class="test"> <asp:Label runat="server" ID="lblBillingAddress3" CssClass="lblBillingShippingFont" /> </div> <div class="test"> <asp:Label runat="server" ID="lblBillingAddress4" CssClass="lblBillingShippingFont" /> </div> </div> The CSS .test { position: relative; top: 0px; left: 0px; height: 12px; width: 300px; } .lblBillingShippingDivisionFont { font-size: small; font-weight: bold; } .lblBillingShippingFont { font-size: 10.6px; }

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  • Reason why UIImageView gives me a 'distorted' image sometimes

    - by Cedric Vandendriessche
    I have a custom UIView with a UILabel and a UIImageView subview. (tried using UIImageView subclass aswell). I assign an image to it and add the view to the screen. I wrote a function which adds the amount of LetterBoxes to the screen as there are letters in the word: - (void)drawBoxesForWord:(NSString *)word { if(boxesContainer == nil) { /* Create a container for the LetterBoxes (animation purposes) */ boxesContainer = [[UIView alloc] initWithFrame:CGRectMake(0, 205, 320, 50)]; [self.view addSubview:boxesContainer]; } /* Calculate width of letterboxes */ NSInteger numberOfCharacters = [word length]; CGFloat totalWidth = numberOfCharacters * 28 + (numberOfCharacters - 1) * 3; CGFloat leftCap = (320 - totalWidth) / 2; [letters removeAllObjects]; /* Draw the boxes to the screen */ for (int i = 0; i < numberOfCharacters; i++) { LetterBox *letter = [[LetterBox alloc] initWithFrame:CGRectMake(leftCap + i * 31 , 0, 28, 40)]; [letters addObject:letter]; [boxesContainer addSubview:letter]; [letter release]; }} This gives me the image below: http://www.imgdumper.nl/uploads2/4ba3b2c72bb99/4ba3b2c72abfd-Goed.png But sometimes it gives me this: imgdumper.nl/uploads2/4ba3b2d888226/4ba3b2d88728a-Fout.png I add them to the same boxesContainer but they first remove themselves from the superview, so it's not like you see them double or something. What I find weird is that they are all good or all bad.. This is the init function for my LetterBox: if (self == [super initWithFrame:aRect]) { /* Create the box image with same frame */ boxImage = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height)]; boxImage.contentMode = UIViewContentModeScaleAspectFit; boxImage.image = [UIImage imageNamed:@"SpaceOpen.png"]; [self addSubview:boxImage]; /* Create the label with same frame */ letterLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height)]; letterLabel.backgroundColor = [UIColor clearColor]; letterLabel.font = [UIFont fontWithName:@"ArialRoundedMTBold" size:26]; letterLabel.textColor = [UIColor blackColor]; letterLabel.textAlignment = UITextAlignmentCenter; [self addSubview:letterLabel]; } return self;} Does anyone have an idea why this could be? I'd rather have them display correctly every time :)

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  • How to Load Dependent Files on Demand + Check if They're Loaded or Not?

    - by br4inwash3r
    I'm trying to implement an assets/dependency loader that i've found from an old article at 24Ways.org. most of you might be familiar with it. it's from this article by Christian Heilmann: http://24ways.org/2007/keeping-javascript-dependencies-at-bay i've modified the script to load CSS files as well. and it's now quite close to what i want. but i still need to do some checking to see wether an asset have been completely loaded or not. just wondering if you guys have any ideas :) here's what my script currently looked like: var assetLoader = { assets: { products: { js: 'products.js', css: 'products.css', loaded: false }, articles: { js: 'articles.js', css: 'articles.css', loaded: false }, [...] cycle: { js: 'jquery.cycle.min.js', loaded: false }, swfobject: { js: 'jquery.swfobject.min.js', loaded: false } }, add: function(asset) { var comp = assetLoader.assets[asset]; var path = '/path/to/assets/'; if (comp && comp.loaded == false) { if (comp.js) { // load js var js = document.createElement('script'); js.src = path + 'js/' + comp.js; js.type = 'text/javascript'; js.charset = 'utf-8'; // append to document document.getElementsByTagName('body')[0].appendChild(js); } if (comp.css) { // load css var css = document.createElement('link'); css.rel = 'stylesheet'; css.href = path + 'css/' + comp.css; css.type = 'text/css'; css.media = 'screen, projection'; css.charset = 'utf-8'; // append to document document.getElementsByTagName('head')[0].appendChild(css); } } }, check: function(asset) { assetLoader.assets[asset].loaded = true; } } Christian explains this method in his article in great detail. I don't want to confuse you guys anymore with my bad english :P and here's an example of how i run the script: ... // load jquery cycle plugin if (page=='tvc' || page=='products') { if (!assetLoader.assets.cycle.loaded) { assetLoader.add('cycle'); } } // load products page assets if (!assetLoader.assets.products.loaded) { assetLoader.add('products'); } ... this kind of approach is very problematic though. coz assets loads asynchronously, which means some of the code inside products.js that depends on jquery.cycle.js might continue running before jquery.cycle.js is even loaded resulting in errors. while i'm quite aware that scripts can be attached with an onload event, i'm just not really sure how to implement it to my script. anyone care to help me? please... :P

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  • Check my anagram code from a job interview in the past.

    - by Michael Dorgan
    Had the following as an interview question a while ago and choked so bad on basic syntax that I failed to advance (once the adrenalin kicks in, coding goes out the window.) Given a list of string, return a list of sets of strings that are anagrams of the input set. i.e. "dog","god", "foo" should return {"dog","god"}. Afterward, I created the code on my own as a sanity check and it's been around now for a bit. I'd welcome input on it to see if I missed anything or if I could have done it much more efficiently. Take it as a chance to improve myself and learn other techniques: void Anagram::doWork(list input, list &output) { typedef list SortType; SortType sortedInput; // sort each string and pair it with the original for(list<string>::iterator i = input.begin(); i != input.end(); ++i) { string tempString(*i); std::sort(tempString.begin(), tempString.end()); sortedInput.push_back(make_pair(*i, tempString)); } // Now step through the new sorted list for(SortType::iterator i = sortedInput.begin(); i != sortedInput.end();) { set<string> newSet; // Assume (hope) we have a match and pre-add the first. newSet.insert(i->first); // Set the secondary iterator one past the outside to prevent // matching the original SortType::iterator j = i; ++j; while(j != sortedInput.end()) { if(i->second == j->second) { // If the string matches, add it to the set and remove it // so that future searches need not worry about it newSet.insert(j->first); j = sortedInput.erase(j); } else { // else, next element ++j; } } // If size is bigger than our original push, we have a match - save it to the output if(newSet.size() > 1) { output.push_back(newSet); } // erase this element and update the iterator i = sortedInput.erase(i); } }

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  • segmented reduction with scattered segments

    - by Christian Rau
    I got to solve a pretty standard problem on the GPU, but I'm quite new to practical GPGPU, so I'm looking for ideas to approach this problem. I have many points in 3-space which are assigned to a very small number of groups (each point belongs to one group), specifically 15 in this case (doesn't ever change). Now I want to compute the mean and covariance matrix of all the groups. So on the CPU it's roughly the same as: for each point p { mean[p.group] += p.pos; covariance[p.group] += p.pos * p.pos; ++count[p.group]; } for each group g { mean[g] /= count[g]; covariance[g] = covariance[g]/count[g] - mean[g]*mean[g]; } Since the number of groups is extremely small, the last step can be done on the CPU (I need those values on the CPU, anyway). The first step is actually just a segmented reduction, but with the segments scattered around. So the first idea I came up with, was to first sort the points by their groups. I thought about a simple bucket sort using atomic_inc to compute bucket sizes and per-point relocation indices (got a better idea for sorting?, atomics may not be the best idea). After that they're sorted by groups and I could possibly come up with an adaption of the segmented scan algorithms presented here. But in this special case, I got a very large amount of data per point (9-10 floats, maybe even doubles if the need arises), so the standard algorithms using a shared memory element per thread and a thread per point might make problems regarding per-multiprocessor resources as shared memory or registers (Ok, much more on compute capability 1.x than 2.x, but still). Due to the very small and constant number of groups I thought there might be better approaches. Maybe there are already existing ideas suited for these specific properties of such a standard problem. Or maybe my general approach isn't that bad and you got ideas for improving the individual steps, like a good sorting algorithm suited for a very small number of keys or some segmented reduction algorithm minimizing shared memory/register usage. I'm looking for general approaches and don't want to use external libraries. FWIW I'm using OpenCL, but it shouldn't really matter as the general concepts of GPU computing don't really differ over the major frameworks.

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  • Ruby: Parse, replace, and evaluate a string formula

    - by Swartz
    I'm creating a simple Ruby on Rails survey application for a friend's psychological survey project. So we have surveys, each survey has a bunch of questions, and each question has one of the options participants can choose from. Nothing exciting. One of the interesting aspects is that each answer option has a score value associated with it. And so for each survey a total score needs to be calculated based on these values. Now my idea is instead of hard-coding calculations is to allow user add a formula by which the total survey score will be calculated. Example formulas: "Q1 + Q2 + Q3" "(Q1 + Q2 + Q3) / 3" "(10 - Q1) + Q2 + (Q3 * 2)" So just basic math (with some extra parenthesis for clarity). The idea is to keep the formulas very simple such that anyone with basic math can enter them without resolving to some fancy syntax. My idea is to take any given formula and replace placeholders such as Q1, Q2, etc with the score values based on what the participant chooses. And then eval() the newly formed string. Something like this: f = "(Q1 + Q2 + Q3) / 2" # some crazy formula for this survey values = {:Q1 => 1, :Q2 => 2, :Q3 => 2} # values for substitution result = f.gsub(/(Q\d+)/) {|m| values[$1.to_sym] } # string to be eval()-ed eval(result) So my questions are: Is there a better way to do this? I'm open to any suggestions. How to handle formulas where not all placeholders were successfully replaced (e.g. one question wasn't answered)? Ex: {:Q3 = 2} wasn't in values hash? My idea is to rescue eval()... any thoughts? How to get proper result? Should be 2.5, but due to integer arithmetic, it will truncate to 2. I can't expect people who provide the correct formula (e.g. / 2.0 ) to understand this nuance. I do not expect this, but how to best protect eval() from abuse (e.g. bad formula, manipulated values coming in)? Thank you!

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • Basic Custom String Class for C++

    - by wdow88
    Hey all, I'm working on building my own string class with very basic functionality. I am having difficulty understand what is going on with the basic class that I have define, and believe there is some sort of error dealing with the scope occurring. When I try to view the objects I created, all the fields are described as (obviously bad pointer). Also, if I make the data fields public or build an accessor method, the program crashes. For some reason the pointer for the object is 0xccccccccc which points to no where. How can a I fix this? Any help/comments are much appreciated. //This is a custom string class, so far the only functions are //constructing and appending #include<iostream> using namespace std; class MyString1 { public: MyString1() { //no arg constructor char *string; string = new char[0]; string[0] ='\0'; std::cout << string; size = 1; } //constructor receives pointer to character array MyString1(char* chars) { int index = 0; //Determine the length of the array while (chars[index] != NULL) index++; //Allocate dynamic memory on the heap char *string; string = new char[index+1]; //Copy the contents of the array pointed by chars into string, the char array of the object for (int ii = 0; ii < index; ii++) string[ii] = chars[ii]; string[index+1] = '\0'; size = index+1; } MyString1 append(MyString1 s) { //determine new size of the appended array and allocate memory int newsize = s.size + size; MyString1 MyString2; char *newstring; newstring = new char[newsize+1]; int index = 0; //load the first string into the array while (string[index] != NULL) { newstring[index] = string[index]; index++; } //load the second string while (s.string[index] != NULL) { newstring[index] = s.string[index]; index++; } //null terminate newstring[newsize+1] = '\0'; delete string; //generate the object for return MyString2.string=newstring; MyString2.size=newsize; return MyString2; } private: char *string; int size; }; int main() { MyString1 string1; MyString1 string2("Hello There"); MyString1 string3("Buddy"); string2.append(string3); return 0; }

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