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• Writing own Unix shell in C - Problems with PATH and execv

  - by user1287523

  I'm writing my own shell in C. It needs to be able to display the users current directory, execute commands based on the full path (must use execv), and allow the user to change the directory with cd. This IS homework. The teacher only gave us a basic primer on C and a very brief skeleton on how the program should work. Since I'm not one to give up easily I've been researching how to do this for three days, but now I'm stumped. This is what I have so far: Displays the user's username, computername, and current directory (defaults to home directory). Prompts the user for input, and gets the input Splits the user's input by " " into an array of arguments Splits the environment variable PATH by ":" into an array of tokens I'm not sure how to proceed from here. I know I've got to use the execv command but in my research on google I haven't really found an example I understand. For instance, if the command is bin/ls, how does execv know the display all files/folders from the home directory? How do I tell the system I changed the directory? I've been using this site a lot which has been helpful: http://linuxgazette.net/111/ramankutty.html but again, I'm stumped. Thanks for your help. Let me know if I should post some of my existing code, I'm wasn't sure if it was necessary though.

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• Method returns an IDisposable - Should I dispose of the result, even if it's not assigned to anythin

  - by mjd79

  This seems like a fairly straightforward question, but I couldn't find this particular use-case after some searching around. Suppose I have a simple method that, say, determines if a file is opened by some process. I can do this (not 100% correctly, but fairly well) with this: public bool IsOpen(string fileName) { try { File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None); } catch { // if an exception is thrown, the file must be opened by some other process return true; } } (obviously this isn't the best or even correct way to determine this - File.Open throws a number of different exceptions, all with different meanings, but it works for this example) Now the File.Open call returns a FileStream, and FileStream implements IDisposable. Normally we'd want to wrap the usage of any FileStream instantiations in a using block to make sure they're disposed of properly. But what happens in the case where we don't actually assign the return value to anything? Is it still necessary to dispose of the FileStream, like so: try { using (File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); { /* nop */ } } catch { return true; } Should I create a FileStream instance and dispose of that? try { using (FileStream fs = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); } ... Or are these totally unnecessary? Can we simply call File.Open and not assign it to anything (first code example), and let the GC dispose of it right away?

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• Should core application configuration be stored in the database, and if so what should be done to se

  - by Rl

  I'm writing an application around a lot of hierarchical data. Currently the hierarchy is fixed, but it's likely that new items will be added to the hierarchy in the future. (please let them be leaves) My current application and database design is fairly generic and nothing dealing with specific nodes in the hierarchy is hardcoded, with the exception of validation and lookup functions written to retrieve external data from each node's particular database. This pleases me from a design point of view, but I'm nervous at the realization that the entire application rests on a handful of records in the database. I'm also frustrated that I have to enforce certain aspects of data integrity with database triggers rather than by foreign key constraints (an example is where several different nodes in the hierarchy have their own proprietary IDs and I store them in a single column which, when coupled with the node ID can be used to locate the foreign data). I'm starting to wonder whether it may have been appropriate to simply hardcoded these known nodes into the system so that it would be more "type safe" and less generic. How does one know when something should be hardcoded, and when it should be a configuration item? Is it just a cost-benefit analysis of clarity/safety now vs less work later, or am I missing some metric I should be using to determine whether or not this is appropriate. The steps I'm taking to protect these valuable configurations are to add triggers that prevent updates/deletes. The database user that this application uses will only have the ability to manipulate data through stored procedures. What else can I do?

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• How to implement iterator as an attribute of a class in Java

  - by de3

  Hi, let's say I have this simple MyArray class, with two simple methods: add, delete and an iterator. In the main method we can see how it is supposed to be used: public class MyArray { int start; int end; int[] arr; myIterator it; public MyArray(){ this.start=0; this.end=0; this.arr=new int[500]; it=new myIterator(); } public void add(int el){ this.arr[this.end]=el; this.end++; } public void delete(){ this.arr[this.start]=0; this.start++; } public static void main(String[] args){ MyArray m=new MyArray(); m.add(3); m.add(299); m.add(19); m.add(27); while(m.it.hasNext()){ System.out.println(m.it.next()); } } And then MyIterator should be implemented somehow: import java.util.Iterator; public class myIterator implements Iterator{ @Override public boolean hasNext() { // TODO Auto-generated method stub return false; } @Override public Object next() { // TODO Auto-generated method stub return null; } @Override public void remove() { // TODO Auto-generated method stub } } MyIterator should iterate arr from MyArray class, from start to end values; both are also attributes of MyArray. So, as MyIterator should use MyArray attributes, how should MyIterator be implemented? Perhaps I can send the current object in the initialization: it=new myIterator(this); But I guess it's not the best soultion. Or maybe MyArray itself should implement Iterator interface? How is this solved?

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• .net remoting - Better solution to wait for a service to initialize ?

  - by CitizenInsane

  Context I have a client application (which i cannot modify, i.e. i only have the binary) that needs to run from time to time external commands that depends on a resource which is very long to initialize (about 20s). I thus decided to initialize this resource once for all in a "CommandServer.exe" application (single instance in the system tray) and let my client application call an intermediate "ExecuteCommand.exe" program that uses .net remoting to perform the operation on the server. The "ExecuteCommand.exe" is in charge for starting the server on first call and then leave it alive to speed up further commands. The service: public interface IMyService { void ExecuteCommand(string[] args); } The "CommandServer.exe" (using WindowsFormsApplicationBase for single instance management + user friendly splash screen during resource initializations): private void onStartupFirstInstance(object sender, StartupEventArgs e) { // Register communication channel channel = new TcpServerChannel("CommandServerChannel", 8234); ChannelServices.RegisterChannel(channel, false); // Register service var resource = veryLongToInitialize(); service = new MyServiceImpl(resource); RemotingServices.Marshal(service, "CommandServer"); // Create icon in system tray notifyIcon = new NotifyIcon(); ... } The intermediate "ExecuteCommand.exe": static void Main(string[] args) { startCommandServerIfRequired(); var channel = new TcpClientChannel(); ChannelServices.RegisterChannel(channel, false); var service = (IMyService)Activator.GetObject(typeof(IMyService), "tcp://localhost:8234/CommandServer"); service.RunCommand(args); } Problem As the server is very long to start (about 20s to initialize the required resources), the "ExecuteCommand.exe" fails on service.RunCommand(args) line because the server is yet not available. Question Is there a elegant way I can tune the delay before to receive "service not available" when calling service.RunCommand ? NB1: Currently I'm working around the issue by adding a mutex in server to indicate for complete initiliazation and have "ExecuteCommand.exe" to wait for this mutex before to call service.RunCommand. NB2: I have no background with .net remoting, nor WCF which is recommended replacer. (I chose .net remoting because this looked easier to set-up for this single shot issue in running external commands).

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• find and replace values in csv using PHP

  - by peirix

  I'd think there was a question on this already, but I can't find one. Maybe the solution is too easy... Anyway, I have a csv and want to let the user change the values based on a name. I've already sorted out creating new name+value-pairs using the fopen('a') mode, using jQuery to send the AJAX call with newValue and newName. But say the content looks like this: host|http:www.stackoverflow.com folder|/questions/ folder2|/users/ And now I want to change the folder value. So I'll send in folder as oldName and /tags/ as newValue. What's the best way to overwrite the value? The order in the list doesn't matter, and the name will always be on the left, followed by a |(pipe), the value and then a new-line. My first thought was to read the list, store it in an array, search all the [0]'s for oldName, then change the [1] that belongs to it, and then write it back to a file. But I feel there is a better way around this? Any ideas? Maybe regex?

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• [MSBuild] Problem with setting properties 's values.

  - by Nam Gi VU

  Let's consider the below example. There, I have: target MAIN call target t then call target tt. target t call target ttt, target tt call target tttt. target t define property aa, target ttt modify aa. target tttt try to print property aa 's value. in short we have: MAIN - {t - {ttt-modify aa, define aa}, tt - tttt - print aa} But in target tttt, we can't "see" aa's updated value (by ttt)! Please help me to make that value visible to target tttt. Thank you! The whole script is as below: <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="MAIN" > <Target Name="MAIN" > <CallTarget Targets="t" /> <CallTarget Targets="tt" /> </Target> <Target Name="t"> <Message Text="t" /> <PropertyGroup> <aa>1</aa> </PropertyGroup> <CallTarget Targets="ttt" /> </Target> <Target Name="tt"> <Message Text="tt" /> <CallTarget Targets="tttt" /> </Target> <Target Name="ttt"> <PropertyGroup> <aa>122</aa> </PropertyGroup> <Message Text="ttt" /> </Target> <Target Name="tttt"> <Message Text="tttt" /> <Message Text="tttt:$(aa)" /> </Target> </Project>

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• Can a conforming C# compiler optimize away a local (but unused) variable if it is the only strong re

  - by stakx

  The title says it all, but let me explain: void Case_1() { var weakRef = new WeakReference(new object()); GC.Collect(); // <-- doesn't have to be an explicit call; just assume that // garbage collection would occur at this point. if (weakRef.IsAlive) ... } In this code example, I obviously have to plan for the possibility that the new'ed object is reclaimed by the garbage collector; therefore the if statement. (Note that I'm using weakRef for the sole purpose of checking if the new'ed object is still around.) void Case_2() { var unusedLocalVar = new object(); var weakRef = new WeakReference(unusedLocalVar); GC.Collect(); // <-- doesn't have to be an explicit call; just assume that // garbage collection would occur at this point. Debug.Assert(weakReferenceToUseless.IsAlive); } The main change in this code example from the previous one is that the new'ed object is strongly referenced by a local variable (unusedLocalVar). However, this variable is never used again after the weak reference (weakRef) has been created. Question: Is a conforming C# compiler allowed to optimize the first two lines of Case_2 into those of Case_1 if it sees that unusedLocalVar is only used in one place, namely as an argument to the WeakReference constructor? i.e. is there any possibility that the assertion in Case_2 could ever fail?

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• How to have screen revert to BLACK between pages?

  - by user340667

  0 Hi - I tried out the Background Image Scaling script and with Cybr's update it works like magic. It SCALES the image perfectly. No distortion. BUT, my image isn't "computer friendly". I.e.: Not 1024 X 768 or even close to that. (Heck, my monitor has a wide screen, so it isn't 1024 X 768 either! Is anybody's anymore?) Anyhow, this creates a problem inasmuch as, unless I size the window from the bottom up it ends up with a white "stripe" beneath it. What I would REALLY like for it to do is have that white to be BLACK. My "usual" BG color/text etc. code is like: ""body bgcolor="#000000" text="#fcba1e" link="#0000ff" vlink="#800080" alink="#ff0000"" (Site won't let me add the arrows here.) I've tried inserting this in various places with no success. Any ideas for a workaround would surely be appreciated ! Thanks ! Bill

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• Page_Load or Page_Init

  - by balexandre

  Let's take a really simple example on using jQuery to ajaxify our page... $.load("getOrders.aspx", {limit: 25}, function(data) { // info as JSON is available in the data variable }); and in the ASP.NET (HTML part) page (only one line) <%@ Page Language="C#" AutoEventWireup="true" CodeFile="getOrders.aspx.cs" Inherits="getOrders" %> and in the ASP.NET (Code Behind) page public partial class getOrders : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { string lmt = Request["limit"]; List<Orders> ords = dll.GetOrders(limit); WriteOutput( Newtonsoft.Json.JsonConvert.SerializeObject(ords) ); } private void WriteOutput(string s) { Response.Clear(); Response.Write(s); Response.Flush(); Response.End(); } } my question is Should it be protected void Page_Load(object sender, EventArgs e) or protected void Page_Init(object sender, EventArgs e) So we can save some milliseconds as we don't actually need to process the events for the page, or will Page_Init lack of some sorting of a method by the time it is called? P.S. Currently works fine in both methods, but I just want to understand the ins and outs of choosing one method over the other

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• How to create a separate thread to do some operation periodically and update UI in WPF?I'm stack

  - by black sensei

  Hello Experts! I'm trying to do a periodic separated thread operation let's say check for internet connection or check for user's info via web service and update the user interface. i've tried with quartz.net to implement that.So i created an inner class for the window i need to update.That inner class does what is meant for but the problem is that i don't know how to access parent's(window class) members form the child(inner class). for example public partial class Window2 : Window { private int i; public Window2() { InitializeComponent(); } public string doMyOperation() { //code here return result; } public class Myclass :IJob { public void Execute(JobExecutionContext context) { string result = doMyOperation(); //Now here i could be able to call a label of name lblNotif //lblNotif.Content = result; } } } Well the whole idea works but i'm stacked at here i need to access a controls of Window2 Since i'm stacked i tried Spring.Net way of implementing Quartz hoping that i could use MethodInvokingJobDetailFactoryObject and rather have the Operation done on Window2 itself.But for some reason i'm having an exception Cannot resolve type [System.Windows.Window2,System.Windows];, could not load type from string value System.Windows.Window2,System.Windows and the wiring is done so <object name="UpdateLabelJob" type="System.Windows.Window2,System.Windows"/> What i'm i doing wrong here?Is that a way round? thanks for reading and for helping out

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• javascript/html/php: Is it possible to insert a value into a form with Ajax?

  - by user1260310

  I have a form where users enter some text manually. Then I'd like to let the users choose a tag from a database through AJAX, not unlike how tag suggestions appear in the SO question form. While the div where the ajax call places the tag is inside the form, it does not seem to register and the tag is not picked up by the form. Am I missing something in my code, is this impossible or, if impossible there a better way to do this? Thanks for any suggestions. Here is code: html <form method="post" action="enterdata.php"> <input type="text" name="text">Enter text here. <div id="inserttags"></div><a href="javascript:void(0);" onclick="getTags()";>Get tags</a> <form type="button" name="submit" value="Enter Text and Tag"> </form> javascript getTags() { various Ajax goes here, then //following line inserts value into div of html document.getElementById("inserttags").innerHTML=xmlhttp.responseText; // a bit more ajax, then following pulls tag from db xmlhttp.open("GET","findtags.php",true); xmlhttp.send(); } //end function php //gettags.php //first pull tag from db. Then: echo 'input type="text" name="tag" value= "html">Enter tag'; //above output gets inserted in div and is visible on page. Though the above output is visible on page, the form does not seem to pick it up when you click "Enter Text and Tag" to submit the form.

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• Should I put actors in the Domain-Model/Class-Diagram?

  - by devoured elysium

  When designing both the domain-model and class-diagrams I am having some trouble understanding what to put in them. I'll give an example of what I mean: I am doing a vacations scheduler program, that has an Administrator and End-Users. The Administrator does a couple of things like registering End-Users in the program, changing their previleges, etc. The End-User can choose his vacations days, etc. I initially defined an Administrator and End-User as concepts in the domain-model, and later as classes in the class-diagram. In the class-diagram, both classes ended up having a couple of methods like Administrator.RegisterNewUser(); Administrator.UnregisterUser(int id); etc. Only after some time I realised that actually both Administrator and End-User are actors, and maybe I got this design totally wrong. Instead of filling Administrator and End-User classes with methods to do what my Use-Cases request, I could define other classes from the domain to do them, and have controllers handle the Use-Cases(actually, I decided to do one for each Use-Case). I could have a UserDatabase.RegisterNewUser() and UserDatabase.UnregisterUser(int id);, for example, instead of having those methods on the Administrator class. The idea would be to try to think of the whole vacation-scheduler as a "closed-program" that has a set of features and doesn't bother with things such as authentication, that should be internal/protected, being that the only public things I'd let the outside world see would be its controllers. Is this the right approach? Or am I getting this totally wrong? Is it generally bad idea to put Actors in the domain-model/class-diagrams? What are good rules of thumb for this? My lecturer is following Applying UML and Patterns, which I find awful, so I'd like to know where I could look up more info on this described actor-models situation. I'm still a bit confused about all of this, as this new approach is radically different from anything I've done before.

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• Interview Q: sorting an almost sorted array (elements misplaced by no more than k)

  - by polygenelubricants

  I was asked this interview question recently: You're given an array that is almost sorted, in that each of the N elements may be misplaced by no more than k positions from the correct sorted order. Find a space-and-time efficient algorithm to sort the array. I have an O(N log k) solution as follows. Let's denote arr[0..n) to mean the elements of the array from index 0 (inclusive) to N (exclusive). Sort arr[0..2k) Now we know that arr[0..k) are in their final sorted positions... ...but arr[k..2k) may still be misplaced by k! Sort arr[k..3k) Now we know that arr[k..2k) are in their final sorted positions... ...but arr[2k..3k) may still be misplaced by k Sort arr[2k..4k) .... Until you sort arr[ik..N), then you're done! This final step may be cheaper than the other steps when you have less than 2k elements left In each step, you sort at most 2k elements in O(k log k), putting at least k elements in their final sorted positions at the end of each step. There are O(N/k) steps, so the overall complexity is O(N log k). My questions are: Is O(N log k) optimal? Can this be improved upon? Can you do this without (partially) re-sorting the same elements?

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• highlight page selected in pagination?

  - by Mahmoud

  Hey There i have a php page, that shows all products that are stored on the database, so everything in fine, but my problem is that i am trying to highlight or give a color when a selected number is clicked, example, let say i all my product are showing and there are 2 pages, so when the user clicks on next the next fade and number 2 is colored yellow this well help the user to on which page he is below is my php code <?php echo"<a style:'color:#FFF;font-style:normal;'> "; include "im/config.php"; include('im/ps_pagination.php'); $result = ("Select * from product "); $pager = new PS_Pagination($conn, $result, 5, 6, "product=product"); $rs = $pager->paginate(); echo"<div id='image_container'>"; echo $pager->renderFullNav(); echo "<br /><br />\n"; while($row = mysql_fetch_array($rs)){ echo" <div class='virtualpage hidepiece'><a href='gal/".$row['pro_image']."' rel='lightbox[roadtrip]' title='".$row['pro_name']." : ".$row['pro_mini_des']."' style='color:#000'><img src='thumb/".$row['pro_thumb']."' /> </a></div>"; } echo"</div>"; echo "<br /><br />\n"; echo $pager->renderFullNav(); echo"</a>"; ?> Thank everyone

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• Calling function and running it

  - by devs

  I am quite new to objects and OOP. I really don't know how to explain it well but I'll try. So I am trying to read though JSON with JS, the JSON is passed from PHP. This would be easy if all of the information was on the same html page, but I' am trying something that I am new too. So let me show my code... First is the JS which is in app.js var Donors = function(){ var api = this.list; $(document).ready(function(){ $.getJSON(api, function(){ var donorObj = api.payload; $.each(donorObj, function(i, donor){ //console.log(donor.ign); }); }); }); } What I want this part to do is read from the JSON I'm giving it and console.log each name (or donor.ign) when the document is ready. On the html page, or header.php <script> $(function(){ var list = <?php cbProxy(); ?>; var Dons = new Donors(); Dons.list = list; }); </script> the data that's in list is the below JSON. You already know what the rest does, it just passes the JSON to the Donors() function. JSON example: { "code": 0, "payload": [ { "time": 1349661897, "packages": [ "49381" ], "ign": "Notch", "price": "15.99", "currency": "USD" } I'm use to just making functions and calling it on the same page or file and this is my first doing this kind of function. How can I get the function to run with the data I sent it so it console.log() each name.

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• Sorting by some field and fetching whole tree from DB

  - by Niaxon

  Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and only files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) After that for each result which is folder i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such thing?

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• How can I use io.StringIO() with the csv module?

  - by Tim Pietzcker

  I tried to backport a Python 3 program to 2.7, and I'm stuck with a strange problem: >>> import io >>> import csv >>> output = io.StringIO() >>> output.write("Hello!") # Fail: io.StringIO expects Unicode Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unicode argument expected, got 'str' >>> output.write(u"Hello!") # This works as expected. 6L >>> writer = csv.writer(output) # Now let's try this with the csv module: >>> csvdata = [u"Hello", u"Goodbye"] # Look ma, all Unicode! (?) >>> writer.writerow(csvdata) # Sadly, no. Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unicode argument expected, got 'str' According to the docs, io.StringIO() returns an in-memory stream for Unicode text. It works correctly when I try and feed it a Unicode string manually. Why does it fail in conjunction with the csv module, even if all the strings being written are Unicode strings? Where does the str come from that causes the Exception? (I do know that I can use StringIO.StringIO() instead, but I'm wondering what's wrong with io.StringIO() in this scenario)

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• The shell dotfile cookbook

  - by Jason Baker

  I constantly hear from other people about how much of the stuff they've used to customize their *nix setup they've shamelessly stolen from other people. So in that spirit, I'd like to start a place to share that stuff here on SO. Here are the rules: DON'T POST YOUR ENTIRE DOTFILE. Instead, just show us the cool stuff. One recipe per answer You may, however, post multiple versions of your recipe in the same answer. For example, you may post a version that works for bash, a version that works for zsh, and a version that works for csh in the same answer. State what shells you know your recipe will work with in the answer. Let's build this cookbook as a team. If you find out that an answer works with other shells other than the one the author posted, edit it in. If you like an idea and rewrite it to work with another shell, edit the modified version in to the original post. Give credit where credit is due. If you got your idea from someone else, give them credit if possible. And for those of you (justifiably) asking "Why do we need another one of these threads?": Most of what I've seen is along the lines of "post your entire dotfile." Personally, I don't want to try to parse through a person's entire dotfile to figure out what I want. I just want to know about all the cool parts of it. It's helpful to have a single dotfile thread. I think most of the stuff that works in bash will work in zsh and it may be adapted to work with csh fairly easily.

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• Do double forward slashes direct IE to use specific css?

  - by kjh

  I have just found something very weird while developing a website. While trying to get a div element to display across the top of the screen, I noticed that I wasn't achieving a desired result in any browser except for old versions of IE. In order to test some different code, instead of deleting the faulty line, I used '//' to comment it out (I'm not really even sure if that works in css) but what happened was, the compatible browsers used the uncommented code, while IE used the code marked by '//'. here is the code: #ban-menu-div{ position:fixed;top:0; //position:relative; //<-- IE keeps the banner with rel pos while the other display:block; // browsers used fixed margin:auto; padding:0px; width:100%; text-align:center; background:black; } so basically, it seems as though // can be used to instruct newer browsers to ignore specific lines of code, and instruct older versions of IE to use it? If this is common practice someone please let me know. it sure makes developing for older browsers a hell of a lot easier

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• jCarousel jQuery ajax loading 1000 records

  - by user1714862

  I'm using jCarousel to present a vertical scolling list of +-1000 names. I am using ajax to load the data 100 records at a time then when all the data has loaded I just let the jCarousel loop in the DOM. I have the ajax and loop all working but would like to make the code work no matter how large the total record count becomes. 1) I'd like to eliminate the 1201 fixed number and use a variable. 2) I currently loop on every record I see (carousel.first) to see if it matches my reload position(s) (albeit the loop is ony 12x it still seems a little "loopy") Any suggestions on improving this? function mycarousel_itemLoadCallback(carousel, state) { //if (carousel.has(carousel.first, carousel.last)) { //return; //} var getCount = 100; // Number of records to grab at a time var maxCount = 1201; // total possible number of records var visible = 9; // the number of records you can see in the window so this creates a pre-load by this number of records for (var i = 1; i < maxCount; i+=getCount ) { if (carousel.first === 1 || carousel.first === (i-visible)){ var getFrom = i; var getTo = getFrom+(getCount-1); //alert('TOP Record ='+carousel.first+'\n Now GET '+getFrom+'-'+getTo); jQuery.get('#ajaxscript#', { first: getFrom, last: getTo }, function(xml) { mycarousel_itemAddCallback(carousel, getFrom, getTo, xml); }, 'xml' ); break; } } };

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• Template neglects const (why?)

  - by Gabriel

  Does somebody know, why this compiles?? template< typename TBufferTypeFront, typename TBufferTypeBack = TBufferTypeFront> class FrontBackBuffer{ public: FrontBackBuffer( const TBufferTypeFront front, const TBufferTypeBack back): ////const reference assigned to reference??? m_Front(front), m_Back(back) { }; ~FrontBackBuffer() {}; TBufferTypeFront m_Front; ///< The front buffer TBufferTypeBack m_Back; ///< The back buffer }; int main(){ int b; int a; FrontBackBuffer<int&,int&> buffer(a,b); // buffer.m_Back = 33; buffer.m_Front = 55; } I compile with GCC 4.4. Why does it even let me compile this? Shouldn't there be an error that I cannot assign a const reference to a non-const reference?

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• short-cutting equality checking in F#?

  - by John Clements

  In F#, the equality operator (=) is generally extensional, rather than intensional. That's great! Unfortunately, it appears to me that F# does not use pointer equality to short-cut these extensional comparisons. For instance, this code: type Z = MT | NMT of Z ref // create a Z: let a = ref MT // make it point to itself: a := NMT a // check to see whether it's equal to itself: printf "a = a: %A\n" (a = a) ... gives me a big fat segmentation fault[*], despite the fact that 'a' and 'a' both evaluate to the same reference. That's not so great. Other functional languages (e.g. PLT Scheme) get this right, using pointer comparisons conservatively, to return 'true' when it can be determined using a pointer comparison. So: I'll accept the fact that F#'s equality operator doesn't use short-cutting; is there some way to perform an intensional (pointer-based) equality check? The (==) operator is not defined on my types, and I'd love it if someone could tell me that it's available somehow. Or tell me that I'm wrong in my analysis of the situation: I'd love that, too... [*] That would probably be a stack overflow on Windows; there are things about Mono that I'm not that fond of...

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• How do I make a lock that allows only ONE thread to read from the resource ?

  - by mare

  I have a file that holds an integer ID value. Currently reading the file is protected with ReaderWriterLockSlim as such: public int GetId() { _fileLock.EnterUpgradeableReadLock(); int id = 0; try { if(!File.Exists(_filePath)) CreateIdentityFile(); FileStream readStream = new FileStream(_filePath, FileMode.Open, FileAccess.Read); StreamReader sr = new StreamReader(readStream); string line = sr.ReadLine(); sr.Close(); readStream.Close(); id = int.Parse(line); return int.Parse(line); } finally { SaveNextId(id); // increment the id _fileLock.ExitUpgradeableReadLock(); } } The problem is that subsequent actions after GetId() might fail. As you can see the GetId() method increments the ID every single time, disregarding what happens after it has issued an ID. The issued ID might be left hanging (as said, exceptions might occur). As the ID is incremented, some IDs might be left unused. So I was thinking of moving the SaveNextId(id) out, remove it (the SaveNextId() actually uses the lock too, except that it's EnterWriteLock). And call it manually from outside after all the required methods have executed. That brings out another problem - multiple threads might enter the GetId() method before the SaveNextId() gets executed and they might all receive the same ID. I don't want any solutions where I have to alter the IDs after the operation, correcting them in any way because that's not nice and might lead to more problems. I need a solution where I can somehow callback into the FileIdentityManager (that's the class that handles these IDs) and let the manager know that it can perform the saving of the next ID and then release the read lock on the file containing the ID. Essentialy I want to replicate the relational databases autoincrement behaviour - if anything goes wrong during row insertion, the ID is not used, it is still available for use but it also never happens that the same ID is issued. Hopefully the question is understandable enough for you to provide some solutions..

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• Set the amount of rows JList show (Java)

  - by Alex Cheng

  Hi all. Problem: I have a method that creates a list from the parsed ArrayList. I manage to show the list in the GUI, without scrollbar. However, I am having problem setting it to show only the size of ArrayList. Meaning, say if the size is 6, there should only be 6 rows in the shown List. Below is the code that I am using. I tried setting the visibleRowCount as below but it does not work. I tried printing out the result and it shows that the change is made. private void createSuggestionList(ArrayList<String> str) { int visibleRowCount = str.size(); System.out.println("visibleRowCount " + visibleRowCount); listForSuggestion = new JList(str.toArray()); listForSuggestion.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); listForSuggestion.setSelectedIndex(0); listForSuggestion.setVisibleRowCount(visibleRowCount); System.out.println(listForSuggestion.getVisibleRowCount()); listScrollPane = new JScrollPane(listForSuggestion); MouseListener mouseListener = new MouseAdapter() { @Override public void mouseClicked(MouseEvent mouseEvent) { JList theList = (JList) mouseEvent.getSource(); if (mouseEvent.getClickCount() == 2) { int index = theList.locationToIndex(mouseEvent.getPoint()); if (index >= 0) { Object o = theList.getModel().getElementAt(index); System.out.println("Double-clicked on: " + o.toString()); } } } }; listForSuggestion.addMouseListener(mouseListener); textPane.add(listScrollPane); repaint(); } To summarize: I want the JList to show as many rows as the size of the parsed ArrayList, without a scrollbar. Any ideas? Please help. Thanks. Please let me know if a picture of the problem is needed in case I did not phrase my question correctly.

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