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  • What is the proper way to declare a specialization of a template for another template type?

    - by Head Geek
    The usual definition for a specialization of a template function is something like this: class Foo { [...] }; namespace std { template<> void swap(Foo& left, Foo& right) { [...] } } // namespace std But how do you properly define the specialization when the type it's specialized on is itself a template? Here's what I've got: template <size_t Bits> class fixed { [...] }; namespace std { template<size_t Bits> void swap(fixed<Bits>& left, fixed<Bits>& right) { [...] } } // namespace std Is this the right way to declare swap? It's supposed to be a specialization of the template function std::swap, but I can't tell whether the compiler is seeing it as such, or whether it thinks that it's an overload of it or something.

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  • Skip Lists -- ever used them?

    - by Head Geek
    I'm wondering whether anyone here has ever used a skip list. It looks to have roughly the same advantages as a balanced binary tree, but is simpler to implement. If you have, did you write your own, or use a pre-written library (and if so, what was its name)?

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  • Better Way To Use C++ Named Parameter Idiom?

    - by Head Geek
    I've been developing a GUI library for Windows (as a personal side project, no aspirations of usefulness). For my main window class, I've set up a hierarchy of option classes (using the Named Parameter Idiom), because some options are shared and others are specific to particular types of windows (like dialogs). The way the Named Parameter Idiom works, the functions of the parameter class have to return the object they're called on. The problem is that, in the hierarchy, each one has to be a different class -- the createWindowOpts class for standard windows, the createDialogOpts class for dialogs, and the like. I've dealt with that by making all the option classes templates. Here's an example: template <class T> class _sharedWindowOpts: public detail::_baseCreateWindowOpts { public: /////////////////////////////////////////////////////////////// // No required parameters in this case. _sharedWindowOpts() { }; typedef T optType; // Commonly used options optType& at(int x, int y) { mX=x; mY=y; return static_cast<optType&>(*this); }; // Where to put the upper-left corner of the window; if not specified, the system sets it to a default position optType& at(int x, int y, int width, int height) { mX=x; mY=y; mWidth=width; mHeight=height; return static_cast<optType&>(*this); }; // Sets the position and size of the window in a single call optType& background(HBRUSH b) { mBackground=b; return static_cast<optType&>(*this); }; // Sets the default background to this brush optType& background(INT_PTR b) { mBackground=HBRUSH(b+1); return static_cast<optType&>(*this); }; // Sets the default background to one of the COLOR_* colors; defaults to COLOR_WINDOW optType& cursor(HCURSOR c) { mCursor=c; return static_cast<optType&>(*this); }; // Sets the default mouse cursor for this window; defaults to the standard arrow optType& hidden() { mStyle&=~WS_VISIBLE; return static_cast<optType&>(*this); }; // Windows are visible by default optType& icon(HICON iconLarge, HICON iconSmall=0) { mIcon=iconLarge; mSmallIcon=iconSmall; return static_cast<optType&>(*this); }; // Specifies the icon, and optionally a small icon // ...Many others removed... }; template <class T> class _createWindowOpts: public _sharedWindowOpts<T> { public: /////////////////////////////////////////////////////////////// _createWindowOpts() { }; // These can't be used with child windows, or aren't needed optType& menu(HMENU m) { mMenuOrId=m; return static_cast<optType&>(*this); }; // Gives the window a menu optType& owner(HWND hwnd) { mParentOrOwner=hwnd; return static_cast<optType&>(*this); }; // Sets the optional parent/owner }; class createWindowOpts: public _createWindowOpts<createWindowOpts> { public: /////////////////////////////////////////////////////////////// createWindowOpts() { }; }; It works, but as you can see, it requires a noticeable amount of extra work: a type-cast on the return type for each function, extra template classes, etcetera. My question is, is there an easier way to implement the Named Parameter Idiom in this case, one that doesn't require all the extra stuff?

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  • Unnamed/anonymous namespaces vs. static functions

    - by Head Geek
    A little-used feature of C++ is the ability to create anonymous namespaces, like so: namespace { int cannotAccessOutsideThisFile() { ... } } // namespace You would think that such a feature would be useless -- since you can't specify the name of the namespace, it's impossible to access anything within it from outside. But these unnamed namespaces are accessible within the file they're created in, as if you had an implicit using-clause to them. My question is, why or when would this be preferable to using static functions? Or are they essentially two ways of doing the exact same thing?

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  • Why isn't functional language syntax more close to human language?

    - by JohnDoDo
    I'm interested in functional programming and decided to get head to head with Haskell. My head hurts... but I'll eventually get it... I have one curiosity though, why is the syntax so cryptic (in lack of another word)? Is there a reason why it isn't more expressive, more close to human language? I understand that FP is good at modelling mathematical concepts and it borrowed some of it's concise means of expression, but still it's not math... it's a language.

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  • Loading jQuery Consistently in a .NET Web App

    - by Rick Strahl
    One thing that frequently comes up in discussions when using jQuery is how to best load the jQuery library (as well as other commonly used and updated libraries) in a Web application. Specifically the issue is the one of versioning and making sure that you can easily update and switch versions of script files with application wide settings in one place and having your script usage reflect those settings in the entire application on all pages that use the script. Although I use jQuery as an example here, the same concepts can be applied to any script library - for example in my Web libraries I use the same approach for jQuery.ui and my own internal jQuery support library. The concepts used here can be applied both in WebForms and MVC. Loading jQuery Properly From CDN Before we look at a generic way to load jQuery via some server logic, let me first point out my preferred way to embed jQuery into the page. I use the Google CDN to load jQuery and then use a fallback URL to handle the offline or no Internet connection scenario. Why use a CDN? CDN links tend to be loaded more quickly since they are very likely to be cached in user's browsers already as jQuery CDN is used by many, many sites on the Web. Using a CDN also removes load from your Web server and puts the load bearing on the CDN provider - in this case Google - rather than on your Web site. On the downside, CDN links gives the provider (Google, Microsoft) yet another way to track users through their Web usage. Here's how I use jQuery CDN plus a fallback link on my WebLog for example: <!DOCTYPE HTML> <html> <head> <script src="//ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js"></script> <script> if (typeof (jQuery) == 'undefined') document.write(unescape("%3Cscript " + "src='/Weblog/wwSC.axd?r=Westwind.Web.Controls.Resources.jquery.js' %3E%3C/script%3E")); </script> <title>Rick Strahl's Web Log</title> ... </head>   You can see that the CDN is referenced first, followed by a small script block that checks to see whether jQuery was loaded (jQuery object exists). If it didn't load another script reference is added to the document dynamically pointing to a backup URL. In this case my backup URL points at a WebResource in my Westwind.Web  assembly, but the URL can also be local script like src="/scripts/jquery.min.js". Important: Use the proper Protocol/Scheme for  for CDN Urls [updated based on comments] If you're using a CDN to load an external script resource you should always make sure that the script is loaded with the same protocol as the parent page to avoid mixed content warnings by the browser. You don't want to load a script link to an http:// resource when you're on an https:// page. The easiest way to use this is by using a protocol relative URL: <script src="//ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js"></script> which is an easy way to load resources from other domains. This URL syntax will automatically use the parent page's protocol (or more correctly scheme). As long as the remote domains support both http:// and https:// access this should work. BTW this also works in CSS (with some limitations) and links. BTW, I didn't know about this until it was pointed out in the comments. This is a very useful feature for many things - ah the benefits of my blog to myself :-) Version Numbers When you use a CDN you notice that you have to reference a specific version of jQuery. When using local files you may not have to do this as you can rename your private copy of jQuery.js, but for CDN the references are always versioned. The version number is of course very important to ensure you getting the version you have tested with, but it's also important to the provider because it ensures that cached content is always correct. If an existing file was updated the updates might take a very long time to get past the locally cached content and won't refresh properly. The version number ensures you get the right version and not some cached content that has been changed but not updated in your cache. On the other hand version numbers also mean that once you decide to use a new version of the script you now have to change all your script references in your pages. Depending on whether you use some sort of master/layout page or not this may or may not be easy in your application. Even if you do use master/layout pages, chances are that you probably have a few of them and at the very least all of those have to be updated for the scripts. If you use individual pages for all content this issue then spreads to all of your pages. Search and Replace in Files will do the trick, but it's still something that's easy to forget and worry about. Personaly I think it makes sense to have a single place where you can specify common script libraries that you want to load and more importantly which versions thereof and where they are loaded from. Loading Scripts via Server Code Script loading has always been important to me and as long as I can remember I've always built some custom script loading routines into my Web frameworks. WebForms makes this fairly easy because it has a reasonably useful script manager (ClientScriptManager and the ScriptManager) which allow injecting script into the page easily from anywhere in the Page cycle. What's nice about these components is that they allow scripts to be injected by controls so components can wrap up complex script/resource dependencies more easily without having to require long lists of CSS/Scripts/Image includes. In MVC or pure script driven applications like Razor WebPages  the process is more raw, requiring you to embed script references in the right place. But its also more immediate - it lets you know exactly which versions of scripts to use because you have to manually embed them. In WebForms with different controls loading resources this often can get confusing because it's quite possible to load multiple versions of the same script library into a page, the results of which are less than optimal… In this post I look a simple routine that embeds jQuery into the page based on a few application wide configuration settings. It returns only a string of the script tags that can be manually embedded into a Page template. It's a small function that merely a string of the script tags shown at the begging of this post along with some options on how that string is comprised. You'll be able to specify in one place which version loads and then all places where the help function is used will automatically reflect this selection. Options allow specification of the jQuery CDN Url, the fallback Url and where jQuery should be loaded from (script folder, Resource or CDN in my case). While this is specific to jQuery you can apply this to other resources as well. For example I use a similar approach with jQuery.ui as well using practically the same semantics. Providing Resources in ControlResources In my Westwind.Web Web utility library I have a class called ControlResources which is responsible for holding resource Urls, resource IDs and string contants that reference those resource IDs. The library also provides a few helper methods for loading common scriptscripts into a Web page. There are specific versions for WebForms which use the ClientScriptManager/ScriptManager and script link methods that can be used in any .NET technology that can embed an expression into the output template (or code for that matter). The ControlResources class contains mostly static content - references to resources mostly. But it also contains a few static properties that configure script loading: A Script LoadMode (CDN, Resource, or script url) A default CDN Url A fallback url They are  static properties in the ControlResources class: public class ControlResources { /// <summary> /// Determines what location jQuery is loaded from /// </summary> public static JQueryLoadModes jQueryLoadMode = JQueryLoadModes.ContentDeliveryNetwork; /// <summary> /// jQuery CDN Url on Google /// </summary> public static string jQueryCdnUrl = "//ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js"; /// <summary> /// jQuery CDN Url on Google /// </summary> public static string jQueryUiCdnUrl = "//ajax.googleapis.com/ajax/libs/jqueryui/1.8.16/jquery-ui.min.js"; /// <summary> /// jQuery UI fallback Url if CDN is unavailable or WebResource is used /// Note: The file needs to exist and hold the minimized version of jQuery ui /// </summary> public static string jQueryUiLocalFallbackUrl = "~/scripts/jquery-ui.min.js"; } These static properties are fixed values that can be changed at application startup to reflect your preferences. Since they're static they are application wide settings and respected across the entire Web application running. It's best to set these default in Application_Init or similar startup code if you need to change them for your application: protected void Application_Start(object sender, EventArgs e) { // Force jQuery to be loaded off Google Content Network ControlResources.jQueryLoadMode = JQueryLoadModes.ContentDeliveryNetwork; // Allow overriding of the Cdn url ControlResources.jQueryCdnUrl = "http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"; // Route to our own internal handler App.OnApplicationStart(); } With these basic settings in place you can then embed expressions into a page easily. In WebForms use: <!DOCTYPE html> <html> <head runat="server"> <%= ControlResources.jQueryLink() %> <script src="scripts/ww.jquery.min.js"></script> </head> In Razor use: <!DOCTYPE html> <html> <head> @Html.Raw(ControlResources.jQueryLink()) <script src="scripts/ww.jquery.min.js"></script> </head> Note that in Razor you need to use @Html.Raw() to force the string NOT to escape. Razor by default escapes string results and this ensures that the HTML content is properly expanded as raw HTML text. Both the WebForms and Razor output produce: <!DOCTYPE html> <html> <head> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js" type="text/javascript"></script> <script type="text/javascript"> if (typeof (jQuery) == 'undefined') document.write(unescape("%3Cscript src='/WestWindWebToolkitWeb/WebResource.axd?d=-b6oWzgbpGb8uTaHDrCMv59VSmGhilZP5_T_B8anpGx7X-PmW_1eu1KoHDvox-XHqA1EEb-Tl2YAP3bBeebGN65tv-7-yAimtG4ZnoWH633pExpJor8Qp1aKbk-KQWSoNfRC7rQJHXVP4tC0reYzVw2&t=634535391996872492' type='text/javascript'%3E%3C/script%3E"));</script> <script src="scripts/ww.jquery.min.js"></script> </head> which produces the desired effect for both CDN load and fallback URL. The implementation of jQueryLink is pretty basic of course: /// <summary> /// Inserts a script link to load jQuery into the page based on the jQueryLoadModes settings /// of this class. Default load is by CDN plus WebResource fallback /// </summary> /// <param name="url"> /// An optional explicit URL to load jQuery from. Url is resolved. /// When specified no fallback is applied /// </param> /// <returns>full script tag and fallback script for jQuery to load</returns> public static string jQueryLink(JQueryLoadModes jQueryLoadMode = JQueryLoadModes.Default, string url = null) { string jQueryUrl = string.Empty; string fallbackScript = string.Empty; if (jQueryLoadMode == JQueryLoadModes.Default) jQueryLoadMode = ControlResources.jQueryLoadMode; if (!string.IsNullOrEmpty(url)) jQueryUrl = WebUtils.ResolveUrl(url); else if (jQueryLoadMode == JQueryLoadModes.WebResource) { Page page = new Page(); jQueryUrl = page.ClientScript.GetWebResourceUrl(typeof(ControlResources), ControlResources.JQUERY_SCRIPT_RESOURCE); } else if (jQueryLoadMode == JQueryLoadModes.ContentDeliveryNetwork) { jQueryUrl = ControlResources.jQueryCdnUrl; if (!string.IsNullOrEmpty(jQueryCdnUrl)) { // check if jquery loaded - if it didn't we're not online and use WebResource fallbackScript = @"<script type=""text/javascript"">if (typeof(jQuery) == 'undefined') document.write(unescape(""%3Cscript src='{0}' type='text/javascript'%3E%3C/script%3E""));</script>"; fallbackScript = string.Format(fallbackScript, WebUtils.ResolveUrl(ControlResources.jQueryCdnFallbackUrl)); } } string output = "<script src=\"" + jQueryUrl + "\" type=\"text/javascript\"></script>"; // add in the CDN fallback script code if (!string.IsNullOrEmpty(fallbackScript)) output += "\r\n" + fallbackScript + "\r\n"; return output; } There's one dependency here on WebUtils.ResolveUrl() which resolves Urls without access to a Page/Control (another one of those features that should be in the runtime, not in the WebForms or MVC engine). You can see there's only a little bit of logic in this code that deals with potentially different load modes. I can load scripts from a Url, WebResources or - my preferred way - from CDN. Based on the static settings the scripts to embed are composed to be returned as simple string <script> tag(s). I find this extremely useful especially when I'm not connected to the internet so that I can quickly swap in a local jQuery resource instead of loading from CDN. While CDN loading with the fallback works it can be a bit slow as the CDN is probed first before the fallback kicks in. Switching quickly in one place makes this trivial. It also makes it very easy once a new version of jQuery rolls around to move up to the new version and ensure that all pages are using the new version immediately. I'm not trying to make this out as 'the' definite way to load your resources, but rather provide it here as a pointer so you can maybe apply your own logic to determine where scripts come from and how they load. You could even automate this some more by using configuration settings or reading the locations/preferences out of some sort of data/metadata store that can be dynamically updated instead via recompilation. FWIW, I use a very similar approach for loading jQuery UI and my own ww.jquery library - the same concept can be applied to any kind of script you might be loading from different locations. Hopefully some of you find this a useful addition to your toolset. Resources Google CDN for jQuery Full ControlResources Source Code ControlResource Documentation Westwind.Web NuGet This method is part of the Westwind.Web library of the West Wind Web Toolkit or you can grab the Web library from NuGet and add to your Visual Studio project. This package includes a host of Web related utilities and script support features. © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  jQuery   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Dynamically creating meta tags in asp.net mvc

    - by Jalpesh P. Vadgama
    As we all know that Meta tag has very important roles in Search engine optimization and if we want to have out site listed with good ranking on search engines then we have to put meta tags. Before some time I have blogged about dynamically creating meta tags in asp.net 2.0/3.5 sites, in this blog post I am going to explain how we can create a meta tag dynamically very easily. To have meta tag dynamically we have to create a meta tag on server-side. So I have created a method like following. public string HomeMetaTags() { System.Text.StringBuilder strMetaTag = new System.Text.StringBuilder(); strMetaTag.AppendFormat(@"<meta content='{0}' name='Keywords'/>","Home Action Keyword"); strMetaTag.AppendFormat(@"<meta content='{0}' name='Descption'/>", "Home Description Keyword"); return strMetaTag.ToString(); } Here you can see that I have written a method which will return a string with meta tags. Here you can write any logic you can fetch it from the database or you can even fetch it from xml based on key passed. For the demo purpose I have written that hardcoded. So it will create a meta tag string and will return it. Now I am going to store that meta tag in ViewBag just like we have a title tag. In this post I am going to use standard template so we have our title tag there in viewbag message. Same way I am going save meta tag like following in ViewBag. public ActionResult Index() { ViewBag.Message = "Welcome to ASP.NET MVC!"; ViewBag.MetaTag = HomeMetaTags(); return View(); } Here in the above code you can see that I have stored MetaTag ViewBag. Now as I am using standard ASP.NET MVC3 template so we have our we have out head element in Shared folder _layout.cshtml file. So to render meta tag I have modified the Head tag part of _layout.cshtml like following. <head> <title>@ViewBag.Title</title> <link href="@Url.Content("~/Content/Site.css")" rel="stylesheet" type="text/css" /> <script src="@Url.Content("~/Scripts/jquery-1.5.1.min.js")" type="text/javascript"></script> @Html.Raw(ViewBag.MetaTag) </head> Here in the above code you can see I have use @Html.Raw method to embed meta tag in _layout.cshtml page. This HTML.Raw method will embed output to head tag section without encoding html. As we have already taken care of html tag in string function we don’t need the html encoding. Now it’s time to run application in browser. Now once you run your application in browser and click on view source you will find meta tag for home page as following. That’s its It’s very easy to create dynamically meta tag. Hope you liked it.. Stay tuned for more.. Till then happy programming.

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  • Scripts Casing Flash Intro Animation To Stop [migrated]

    - by ubique
    When my Flash website loads, it freezes halfway through the initial animation for 2-3 seconds and then continues. This obviously doesn't look great and I can't figure out what is causing it. Am thinking it is one of the scripts in index.html causing the issue and have tried all sorts of ways to correct it - what have I done wrong? <!DOCTYPE html> <html lang="en"> <head> <title>company name</title> . . . <link href="style.css" rel="stylesheet" type="text/css" /> <script type="text/javascript" src="js/flashobject.js"></script> <!--[if lt IE 7]> <link href="ie6.css" rel="stylesheet" type="text/css" /> <![endif]--> </head> <body> <header> <hgroup> <h1>company</h1> <h2>company</h2> </hgroup> </header> <div id="container"> <div id="head"> <div class="aligncenter"><a href="http://www.adobe.com/go/EN_US-H-GET-FLASH"> <img src="http://www.adobe.com/images/shared/download_buttons/get_adobe_flash_player.png" alt="" /></a> </div> </div> </div> <div class="g-plus" data-href="https://plus.google.com/100925740920754223119?rel=publisher" data-width="170" data-height="69" data-theme="light"> </body> <!-- Flash --> <script type="text/javascript"> var fo = new FlashObject("main_v10.swf", "head", "100%", "100%", "8", ""); fo.addParam("quality", "high"); fo.addParam("allowFullScreen", "true"); fo.write("head"); </script> <!-- Hello Bar --> <script type="text/javascript" src="//www.hellobar.com/hellobar.js"></script> <script type="text/javascript"> new HelloBar(39040,52484); </script> <!-- GPlus --> <script type="text/javascript"> window.___gcfg = {lang: 'en'}; (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js"; var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s); })();</script> <!-- Google --> <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-xxxxxxxx-1']); _gaq.push(['_setSiteSpeedSampleRate', 10]); _gaq.push(['_trackPageview']); (function init() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga,s); })(); window.onload = init; </script> </html>

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  • Organization &amp; Architecture UNISA Studies &ndash; Chap 6

    - by MarkPearl
    Learning Outcomes Discuss the physical characteristics of magnetic disks Describe how data is organized and accessed on a magnetic disk Discuss the parameters that play a role in the performance of magnetic disks Describe different optical memory devices Magnetic Disk The way data is stored on and retried from magnetic disks Data is recorded on and later retrieved form the disk via a conducting coil named the head (in many systems there are two heads) The writ mechanism exploits the fact that electricity flowing through a coil produces a magnetic field. Electric pulses are sent to the write head, and the resulting magnetic patterns are recorded on the surface below with different patterns for positive and negative currents The physical characteristics of a magnetic disk   Summarize from book   The factors that play a role in the performance of a disk Seek time – the time it takes to position the head at the track Rotational delay / latency – the time it takes for the beginning of the sector to reach the head Access time – the sum of the seek time and rotational delay Transfer time – the time it takes to transfer data RAID The rate of improvement in secondary storage performance has been considerably less than the rate for processors and main memory. Thus secondary storage has become a bit of a bottleneck. RAID works on the concept that if one disk can be pushed so far, additional gains in performance are to be had by using multiple parallel components. Points to note about RAID… RAID is a set of physical disk drives viewed by the operating system as a single logical drive Data is distributed across the physical drives of an array in a scheme known as striping Redundant disk capacity is used to store parity information, which guarantees data recoverability in case of a disk failure (not supported by RAID 0 or RAID 1) Interesting to note that the increase in the number of drives, increases the probability of failure. To compensate for this decreased reliability RAID makes use of stored parity information that enables the recovery of data lost due to a disk failure.   The RAID scheme consists of 7 levels…   Category Level Description Disks Required Data Availability Large I/O Data Transfer Capacity Small I/O Request Rate Striping 0 Non Redundant N Lower than single disk Very high Very high for both read and write Mirroring 1 Mirrored 2N Higher than RAID 2 – 5 but lower than RAID 6 Higher than single disk Up to twice that of a signle disk for read Parallel Access 2 Redundant via Hamming Code N + m Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Parallel Access 3 Bit interleaved parity N + 1 Much higher than single disk Highest of all listed alternatives Approximately twice that of a single disk Independent Access 4 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, significantly lower than single disk for write Similar to RAID 0 for read, significantly lower than single disk for write Independent Access 5 Block interleaved parity N + 1 Much higher than single disk Similar to RAID 0 for read, lower than single disk for write Similar to RAID 0 for read, generally  lower than single disk for write Independent Access 6 Block interleaved parity N + 2 Highest of all listed alternatives Similar to RAID 0 for read; lower than RAID 5 for write Similar to RAID 0 for read, significantly lower than RAID 5  for write   Read page 215 – 221 for detailed explanation on RAID levels Optical Memory There are a variety of optical-disk systems available. Read through the table on page 222 – 223 Some of the devices include… CD CD-ROM CD-R CD-RW DVD DVD-R DVD-RW Blue-Ray DVD Magnetic Tape Most modern systems use serial recording – data is lade out as a sequence of bits along each track. The typical recording used in serial is referred to as serpentine recording. In this technique when data is being recorded, the first set of bits is recorded along the whole length of the tape. When the end of the tape is reached the heads are repostioned to record a new track, and the tape is again recorded on its whole length, this time in the opposite direction. That process continued back and forth until the tape is full. To increase speed, the read-write head is capable of reading and writing a number of adjacent tracks simultaneously. Data is still recorded serially along individual tracks, but blocks in sequence are stored on adjacent tracks as suggested. A tape drive is a sequential access device. Magnetic tape was the first kind of secondary memory. It is still widely used as the lowest-cost, slowest speed member of the memory hierarchy.

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  • git | error: Unable to append to .git/logs/refs/remotes/origin/master: Permission denied [SOLVED]

    - by Corbin Tarrant
    I am having a strange issue that I can't seem to resolve. Here is what happend: I had some log files in a github repository that I didn't want there. I found this script that removes files completely from git history like so: #!/bin/bash set -o errexit # Author: David Underhill # Script to permanently delete files/folders from your git repository. To use # it, cd to your repository's root and then run the script with a list of paths # you want to delete, e.g., git-delete-history path1 path2 if [ $# -eq 0 ]; then exit 0are still fi # make sure we're at the root of git repo if [ ! -d .git ]; then echo "Error: must run this script from the root of a git repository" exit 1 fi # remove all paths passed as arguments from the history of the repo files=$@ git filter-branch --index-filter "git rm -rf --cached --ignore-unmatch $files" HEAD # remove the temporary history git-filter-branch otherwise leaves behind for a long time rm -rf .git/refs/original/ && git reflog expire --all && git gc --aggressive --prune I, of course, made a backup first and then tried it. It seemed to work fine. I then did a git push -f and was greeted with the following messages: error: Unable to append to .git/logs/refs/remotes/origin/master: Permission denied error: Cannot update the ref 'refs/remotes/origin/master'. Everything seems to have pushed fine though, because the files seem to be gone from the GitHub repository, if I try and push again I get the same thing: error: Unable to append to .git/logs/refs/remotes/origin/master: Permission denied error: Cannot update the ref 'refs/remotes/origin/master'. Everything up-to-date EDIT $ sudo chgrp {user} .git/logs/refs/remotes/origin/master $ sudo chown {user} .git/logs/refs/remotes/origin/master $ git push Everything up-to-date Thanks! EDIT Uh Oh. Problem. I've been working on this project all night and just went to commit my changes: error: Unable to append to .git/logs/refs/heads/master: Permission denied fatal: cannot update HEAD ref So I: sudo chown {user} .git/logs/refs/heads/master sudo chgrp {user} .git/logs/refs/heads/master I try the commit again and I get: error: Unable to append to .git/logs/HEAD: Permission denied fatal: cannot update HEAD ref So I: sudo chown {user} .git/logs/HEAD sudo chgrp {user} .git/logs/HEAD And then I try the commit again: 16 files changed, 499 insertions(+), 284 deletions(-) create mode 100644 logs/DBerrors.xsl delete mode 100644 logs/emptyPHPerrors.php create mode 100644 logs/trimXMLerrors.php rewrite public/codeCore/Classes/php/DatabaseConnection.php (77%) create mode 100644 public/codeSite/php/init.php $ git push Counting objects: 49, done. Delta compression using up to 2 threads. Compressing objects: 100% (27/27), done. Writing objects: 100% (27/27), 7.72 KiB, done. Total 27 (delta 15), reused 0 (delta 0) To [email protected]:IAmCorbin/MooKit.git 59da24e..68b6397 master -> master Hooray. I jump on http://GitHub.com and check out the repository, and my latest commit is no where to be found. ::scratch head:: So I push again: Everything up-to-date Umm...it doesn't look like it. I've never had this issue before, could this be a problem with github? or did I mess something up with my git project? EDIT Nevermind, I did a simple: git push origin master and it pushed fine.

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  • Mutation Problem - Clojure

    - by Silanglaya Valerio
    having trouble changing an element of my function represented as a list. code for random function: (defn makerandomtree-10 [pc maxdepth maxwidth fpx ppx] (if-let [output (if (and (< (rand) fpx) (> maxdepth 0)) (let [head (nth operations (rand-int (count operations))) children (doall (loop[function (list) width maxwidth] (if (pos? width) (recur (concat function (list (makerandomtree-10 pc (dec maxdepth) (+ 2 (rand-int (- maxwidth 1))) fpx ppx))) (dec width)) function)))] (concat (list head) children)) (if (and (< (rand) ppx) (>= pc 0)) (nth parameters (rand-int (count parameters))) (rand-int 100)))] output )) I will provide also a mutation function, which is still not good enough. I need to be able to eval my statement, so the following is still insufficient. (defn mutate-5 "chooses a node changes that" [function pc maxwidth pchange] (if (< (rand) pchange) (let [output (makerandomtree-10 pc 3 maxwidth 0.5 0.6)] (if (seq? output) output (list output))) ;mutate the children of root ;declare an empty accumulator list, with root as its head (let [head (list (first function)) children (loop [acc(list) walker (next function)] (println "----------") (println walker) (println "-----ACC-----") (println acc) (if (not walker) acc (if (or (seq? (first function)) (contains? (set operations) (first function))) (recur (concat acc (mutate-5 walker pc maxwidth pchange)) (next walker)) (if (< (rand) pchange) (if (some (set parameters) walker) (recur (concat acc (list (nth parameters (rand-int (count parameters))))) (if (seq? walker) (next walker) nil)) (recur (concat acc (list (rand-int 100))) (if (seq? walker) (next walker) nil))) (recur acc (if (seq? walker) (next walker) nil)))) ))] (concat head (list children))))) (side note: do you have any links/books for learning clojure?)

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  • Does jQuery strip some html elements from a string when using .html()?

    - by Nic Hubbard
    I have a var that contains a full html page, including the head, html, body, etc. When I pass that string into the .html() function, jQuery strips out all those elements, such as body, html, head, etc, which I don't want. My data var contains: <html> <head> <title>Untitled Document</title> </head> <body> </body> </html> // data is a full html document string data = $('<div/>').html(data); // jQuery stips my document string! alert(data.find('head').html()); I am needing to manipulate a full html page string, so that I can return what is in the element. I would like to do this with jQuery, but it seems all of the methods, append(), prepend() and html() all try to convert the string to dom elements, which remove all the other parts of a full html page. Is there another way that I could do this? I would be fine using another method. My final goal is to find certain elements inside my string, so I figured jQuery would be best, since I am so used to it. But, if it is going to trim and remove parts of my string, I am going to have to look for another method. Ideas?

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  • jquery selector problem with script tags

    - by Tauren
    I'm attempting to select all <script type="text/html"> tags in a page. I use <script> tags to store HTML templates, similar to how John Resig does it. For some reason, the following jquery selector doesn't seem to be selecting anything: $("script[type*=html]").each(function() { alert("Found script "+this.id); }); This markup is in the BODY of the HTML document: <body> <script id="filter-search" type="text/html"> <dt>Search</dt> <dd><input type="text"/></dd> </script> </body> I've also tried putting it into the HEAD of the HTML document, and it is still not found. No alert is ever shown. If I instead change my code to this: $("script[type*=javascript]").each(function() { alert("Found script "+this.id); }); Then it finds only the scripts in the HEAD that have a src to an external file. Scripts in the actual page are not found. For instance, with the following in HEAD: <head> <script type="text/javascript" src="jquery.js" id="jquery"></script> <script type="text/javascript" src="jquery-ui.js" id="ui"></script> <script type="text/javascript" id="custom"> $(document).ready( function() { $("script[type*=javascript]").each(function() { alert("Found script "+this.id); }); $("script[type*=html]").each(function() { alert("Found TEMPLATE script "+this.id); }); }); </script> <script id="filter-test" type="text/html"> <dt>Test</dt> </script> </head> <body> <script id="filter-search" type="text/html"> <dt>Search</dt> <dd><input type="text"/></dd> </script> </body> I get the following alerts: Found script jquery Found script ui The custom and filter-test scripts in the HEAD are not selected, nor is the filter-search script in the body tag. Is this the expected behavior? Why does this not work? I can work around it, but it is annoying that it doesn't work.

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  • Git: can't undo local changes (error: path ... is unmerged)

    - by mklhmnn
    I have following working tree state $ git status foo/bar.txt # On branch master # Unmerged paths: # (use "git reset HEAD <file>..." to unstage) # (use "git add/rm <file>..." as appropriate to mark resolution) # # deleted by us: foo/bar.txt # no changes added to commit (use "git add" and/or "git commit -a") File foo/bar.txt is there and I want to get it to the "unchanged state" again (similar to 'svn revert'): $ git checkout HEAD foo/bar.txt error: path 'foo/bar.txt' is unmerged $ git reset HEAD foo/bar.txt Unstaged changes after reset: M foo/bar.txt Now it is getting confusing: $ git status foo/bar.txt # On branch master # Changes to be committed: # (use "git reset HEAD <file>..." to unstage) # # new file: foo/bar.txt # # Changed but not updated: # (use "git add <file>..." to update what will be committed) # (use "git checkout -- <file>..." to discard changes in working directory) # # modified: foo/bar.txt # The same file in both sections, new and modified? What should I do? Thanks in advance.

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  • .NET XML Serialization without <?xml> root node

    - by Graphain
    Hi, I'm trying to generate XML like this: <?xml version="1.0"?> <!DOCTYPE APIRequest SYSTEM "https://url"> <APIRequest> <Head> <Key>123</Key> </Head> <ObjectClass> <Field>Value</Field </ObjectClass> </APIRequest> I have a class (ObjectClass) decorated with XMLSerialization attributes like this: [XmlRoot("ObjectClass")] public class ObjectClass { [XmlElement("Field")] public string Field { get; set; } } And my really hacky intuitive thought to just get this working is to do this when I serialize: ObjectClass inst = new ObjectClass(); XmlSerializer serializer = new XmlSerializer(inst.GetType(), ""); StringWriter w = new StringWriter(); w.WriteLine(@"<?xml version=""1.0""?>"); w.WriteLine("<!DOCTYPE APIRequest SYSTEM"); w.WriteLine(@"""https://url"">"); w.WriteLine("<APIRequest>"); w.WriteLine("<Head>"); w.WriteLine(@"<Field>Value</Field>"); w.WriteLine(@"</Head>"); XmlSerializerNamespaces ns = new XmlSerializerNamespaces(); ns.Add("", ""); serializer.Serialize(w, inst, ns); w.WriteLine("</APIRequest>"); However, this generates XML like this: <?xml version="1.0"?> <!DOCTYPE APIRequest SYSTEM "https://url"> <APIRequest> <Head> <Key>123</Key> </Head> <?xml version="1.0" encoding="utf-16"?> <ObjectClass> <Field>Value</Field> </ObjectClass> </APIRequest> i.e. the serialize statement is automatically adding a <?xml root element. I know I'm attacking this wrong so can someone point me in the right direction? As a note, I don't think it will make practical sense to just make an APIRequest class with an ObjectClass in it (because there are say 20 different types of ObjectClass that each needs this boilerplate around them) but correct me if I'm wrong.

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  • C++ classes & linked list: adding & counting items

    - by user342289
    I need to make a linked list with classes. Each list will store two values: a URI and IP. After doing all the adding, I need to be able count the total number of items in the linked list. I have tried the following code but it doesn't compile. Any suggestions please? #include <iostream> #include <cstdlib> #include <string> using namespace std; class ip_uri_store { protected: string ip; string uri; ip_uri_store *next; public: ip_uri_store(string huri, string hip); void additem(string auri, string aip); void deleteitem(string duri); void findbyuri(string furi); void findbyip(string fip); int totalitems(); }; ip_uri_store *head = NULL; ip_uri_store *curr = NULL; void ip_uri_store::additem(string auri, string aip) { curr = head; while (curr->next != NULL) { curr = curr->next; } curr->uri = auri; curr->next = new ip_uri_store; curr->ip = aip; curr->next = new ip_uri_store; curr = curr->next; curr = head; } int ip_uri_store::totalitems() { int i = 0; curr = head; while (curr->next != NULL) { i += 1; curr = curr->next; } return i; } int main(int argc, char *argv[]) { if (argc == 1) { cout << "123456, [email protected], Gordon Brown" << endl; return (0); } head = new ip_uri_store; curr = head; int i; for (i = 1; i < argc; i++) { if (argv[i][0] == 'A') //add item { ip_uri_store.additem(argv[i + 1], argv[i + 2]); i += 2; } else if (argv[i][0] == 'N') //print total tiems { cout << ip_uri_store.totalitems() << endl; } else { cout << "command error\n"; return 0; } } return (0); }

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  • n elements in singly linked list

    - by Codenotguru
    The following function is trying to find the nth to last element of a singly linked list. for ex: if the elements are 8-10-5-7-2-1-5-4-10-10 then the result is 7th to last node is 7. Can anybody help me on how this code is working or is there a better and simpler approach? LinkedListNode nthToLast(LinkedListNode head, int n) { if (head == null || n < 1) { return null; } LinkedListNode p1 = head; LinkedListNode p2 = head; for (int j = 0; j < n - 1; ++j) { // skip n-1 steps ahead if (p2 == null) { return null; // not found since list size < n } p2 = p2.next; } while (p2.next != null) { p1 = p1.next; p2 = p2.next; } return p1; }

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  • What should I learn after HTML and CSS?

    - by Ryan B
    I am 5 days into learning how to make my website, flying through my HTML & CSS book and having fun. I’m starting to consider what to order next. I’m not sure what to study next, so please give me some advice if you can. My end goal is to create a site that has a lot of the functionality that www.edufire.com and similar sites have, just for example. I think I’m learning well with the Head First Series, and the style will probably serve me well as an intro to programming. However, I don't think the books dive too deeply into any 1 subject. I could order: A: Head First Programming: A Learner’s Guide to Programming Using the Python Language B: Head First Javascript C: Head First PHP & MySQL D: a different programming book or E: another CSS or design book to solidify my basic HTML & CSS skills Any guidance would be appreciated. Thanks!

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  • Can you explain to me git reset in plain english?

    - by e-satis
    I have seen interesting posts explaining subtleties about git reset. Unfortunately, the more I read about it, the more it appear that I don't understand it fully. I come from a SVN background and git is a whole new paradigm. I got mercurial easily, but git is much more technical. I think git reset is close to hg revert, but it seems there are differences. So what exactly does git reset do? Please include detailed explanations about: the options --hard, --soft and --merge; the strange notation you use with HEAD such as HEAD^ and HEAD~1; concrete use cases and workflows; consequences on the working copy, the HEAD and your global stress level. I will put a bounty on this ASAP cause it's really important and I find the git doc cryptic. Holly blessing and tons of chocolate/beer/name_your_stuff to the guy who makes a no-brainer answer :-)

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  • .NET: What's the difference between HttpMethod and RequestType of HttpRequest?

    - by Ian Boyd
    The HttpRequest class defines two properties: HttpMethod: Gets the HTTP data transfer method (such as GET, POST, or HEAD) used by the client. public string HttpMethod { get; } The HTTP data transfer method used by the client. and RequestType: Gets or sets the HTTP data transfer method (GET or POST) used by the client. public string RequestType { get; set; } A string representing the HTTP invocation type sent by the client. What is the difference between these two properties? When would i want to use one over the other? Which is the proper one to inspect to see what data transfer method was used by the client? The documentation indicates that HttpMethod will return whatever verb was used: such as GET, POST, or HEAD while the documentation on RequestType seems to indicate only one of two possible values: GET or POST i test with a random sampling of verbs, and both properties seem to support all verbs, and both return the same values: Testing: Client Used HttpMethod RequestType GET GET GET POST POST POST HEAD HEAD HEAD CONNECT CONNECT CONNECT MKCOL MKCOL MKCOL PUT PUT PUT FOOTEST FOOTEST FOOTEST What is the difference between: HttpRequest.HttpMethod HttpRequest.RequestType and when should i use one over the other? Keywords: iis asp.net http httprequest httphandler

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  • Implementing Java Priority Queue

    - by Kay
    public class PriorityQueue<T> { private PriorityNode<T> head, tail; private int numItems; public PriorityQueue(){ numItems = 0; head=null; tail=null; } public void add(int priority, T value){ PriorityNode<T> newNode = new PriorityNode<T>(priority,value); if(numItems == 0){ head = newNode; tail = newNode; } else{ head.setNext(newNode); head = newNode; } } } Where PriorityNode is defined as: public class PriorityNode<T> implements Comparable<T> { private T value; private PriorityNode<T> next; private int priority; public PriorityNode(int priority,T newValue){ value = newValue; next = null; priority = 0; } public PriorityNode(T newValue){ value = newValue; next = null; priority = 0; } public void setPriority(int priority){ this.priority = priority; } public int getPriority(){ return this.priority; } public T getValue(){ return value; } public PriorityNode<T> getNext(){ return next; } public void setNext(PriorityNode<T> nextNode){ this.next = nextNode; } public void setValue(T newValue){ value = newValue; } public int compareTo(int pri) { // TODO Auto-generated method stub if(this.priority<pri){ return -1; } else if(this.priority == pri){ return 0; } else{ return 1; } } } I'm having a lot of difficulty using the Comparator here and implementing a priority queue - please point me in the right direction.

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  • Linked List pop() function

    - by JKid314159
    Consider the following list: [LinkNode * head -- LinkNode * node1 -- LinkNode * node2] I'm creating a stack of FIFO. I Call pop() which I want to pop node1. LinkNode::LinkNode(int numIn) { this->numIn = numIn; next = null; } . . . int LinkNode::pop() { Link * temp = head->next; head = temp->next; int popped = head->nodeNum; delete temp; Return numOut; Question: 1) head should be a pointer or a LinkNode *? 2) Link * temp is created on the call stack and when pop finishes doesn't temp delete automatically? 3) My major confusion is on what is the value of temp-next? Does this point to node1.next which equals node2? Appreciate your help? My reference is C++ for Java Programmers by Weiss.

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  • Dynamically loading css stylesheet doesn't work on IE

    - by pistacchio
    Hi, I dynamically load a css stylesheet (with a little help from jQuery) like this: var head = document.getElementsByTagName('head')[0]; $(document.createElement('link')) .attr({ type: 'text/css', href: '../../mz/mz.css', rel: 'stylesheet' }) .appendTo(head); This works fine in Firefox and Google Chrome, but not in IE. Any help? Thanks

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  • C -Segmentation fault !

    - by FILIaS
    It seems at least weird to me... The program runs normally.But after I call the enter() function for the 4th time,there is a segmentation fault!I would appreciate any help. With the following function enter() I wanna add user commands' datas to a list. [Some part of the code is already posted on another question of me, but I think I should post it again...as it's a different problem I'm facing now.] /* struct for all the datas that user enters on file*/ typedef struct catalog { char short_name[50]; char surname[50]; signed int amount; char description[1000]; struct catalog *next; }catalog,*catalogPointer; catalogPointer current; catalogPointer head = NULL; void enter(void) //user command: i <name> <surname> <amount> <description> { int n,j=2,k=0; char temp[1500]; char *short_name,*surname,*description; signed int amount; char* params = strchr(command,' ') + 1; //strchr returns a pointer to the 1st space on the command.U want a pointer to the char right after that space. strcpy(temp, params); //params is saved as temp. char *curToken = strtok(temp," "); //strtok cuts 'temp' into strings between the spaces and saves them to 'curToken' printf("temp is:%s \n",temp); printf("\nWhat you entered for saving:\n"); for (n = 0; curToken; ++n) //until curToken ends: { if (curToken) { short_name = malloc(strlen(curToken) + 1); strncpy(short_name, curToken, sizeof (short_name)); } printf("Short Name: %s \n",short_name); curToken = strtok(NULL," "); if (curToken) { surname = malloc(strlen(curToken) + 1); strncpy(surname, curToken,sizeof (surname)); } printf("SurName: %s \n",surname); curToken = strtok(NULL," "); if (curToken) { //int * amount= malloc(sizeof (signed int *)); char *chk; amount = (int) strtol(curToken, &chk, 10); if (!isspace(*chk) && *chk != 0) fprintf(stderr,"Warning: expected integer value for amount, received %s instead\n",curToken); } printf("Amount: %d \n",amount); curToken = strtok(NULL,"\0"); if (curToken) { description = malloc(strlen(curToken) + 1); strncpy(description, curToken, sizeof (description)); } printf("Description: %s \n",description); break; } if (findEntryExists(head, surname,short_name) != NULL) //call function in order to see if entry exists already on the catalog printf("\nAn entry for <%s %s> is already in the catalog!\nNew entry not entered.\n",short_name,surname); else { printf("\nTry to entry <%s %s %d %s> in the catalog list!\n",short_name,surname,amount,description); newEntry(&head,short_name,surname,amount,description); printf("\n**Entry done!**\n"); } // Maintain the list in alphabetical order by surname. } catalogPointer findEntryExists (catalogPointer head, char num[],char first[]) { catalogPointer p = head; while (p != NULL && strcmp(p->surname, num) != 0 && strcmp(p->short_name,first) != 0) { p = p->next; } return p; } catalogPointer newEntry (catalog** headRef,char short_name[], char surname[], signed int amount, char description[]) { catalogPointer newNode = (catalogPointer)malloc(sizeof(catalog)); catalogPointer first; catalogPointer second; catalogPointer tmp; first=head; second=NULL; strcpy(newNode->short_name, short_name); strcpy(newNode->surname, surname); newNode->amount=amount; strcpy(newNode->description, description); while (first!=NULL) { if (strcmp(surname,first->surname)>0) second=first; else if (strcmp(surname,first->surname)==0) { if (strcmp(short_name,first->short_name)>0) second=first; } first=first->next; } if (second==NULL) { newNode->next=head; head=newNode; } else //SEGMENTATION APPEARS WHEN IT GETS HERE! { tmp=second->next; newNode->next=tmp; first->next=newNode; } } UPDATE: SegFault appears only when it gets on the 'else' loop of InsertSort() function. I observed that segmentation fault appears when i try to put on the list names that are after it. For example, if in the list exists: [Name:b Surname:b Amount:6 Description:b] [Name:c Surname:c Amount:5 Description:c] [Name:d Surname:d Amount:4 Description:d] [Name:e Surname:e Amount:3 Description:e] [Name:g Surname:g Amount:2 Description:g] [Name:x Surname:x Amount:1 Description:x] and i put: " x z 77 gege" there is a segmentation but if i put "x a 77 gege" it continues normally....

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