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  • C Map String to Function

    - by Scriptonaut
    So, I'm making a Unix minishell, and have come to a roadblock. I need to be able to execute built-in functions, so I made a function: int exec_if_built_in(char **args) It takes an array of strings(the first being the command, and the rest being arguments). For non built-in commands I simply use something like execvp, however I need to find a way to map the first string to a function. I was thinking of making two arrays, one of strings, and another with their corresponding function pointers. However, since many of these functions will be different(return and accept different things), this approach won't work. I also thought of making an array of structs with a name property and a function pointer property, however once again due to the varied nature of the functions I'll be using, this won't work. So, what's the best way to execute a function based on the input of a string? How do I map a string to a certain function? I'm not very familiar with function pointers so I may be missing something. Thank you guys for the help :)

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  • How do I implement IEnumerable?

    - by Stacey
    I have a class that contains a static number of objects. This class needs to be frequently 'compared' to other classes that will be simple List objects. public partial class Sheet { public Item X{ get; set; } public Item Y{ get; set; } public Item Z{ get; set; } } the items are obviously not going to be "X" "Y" "Z", those are just generic names for example. The problem is that due to the nature of what needs to be done, a List won't work; even though everything in here is going to be of type Item. It is like a checklist of very specific things that has to be tested against in both code and runtime. This works all fine and well; it isn't my issue. My issue is iterating it. For instance I want to do the following... List<Item> UncheckedItems = // Repository Logic Here. UncheckedItems contains all available items; and the CheckedItems is the Sheet class instance. CheckedItems will contain items that were moved from Unchecked to Checked; however due to the nature of the storage system, items moved to Checked CANNOT be REMOVED from Unchecked. I simply want to iterate through "Checked" and remove anything from the list in Unchecked that is already in "Checked". So naturally, that would go like this with a normal list. foreach(Item item in Unchecked) { if( Checked.Contains(item) ) Unchecked.Remove( item ); } But since "Sheet" is not a 'List', I cannot do that. So I wanted to implement IEnumerable so that I could. Any suggestions? I've never implemented IEnumerable directly before and I'm pretty confused as to where to begin.

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  • Why can't these generic type parameters be inferred?

    - by Jon M
    Given the following interfaces/classes: public interface IRequest<TResponse> { } public interface IHandler<TRequest, TResponse> where TRequest : IRequest<TResponse> { TResponse Handle(TRequest request); } public class HandlingService { public TResponse Handle<TRequest, TResponse>(TRequest request) where TRequest : IRequest<TResponse> { var handler = container.GetInstance<IHandler<TRequest, TResponse>>(); return handler.Handle(request); } } public class CustomerResponse { public Customer Customer { get; set; } } public class GetCustomerByIdRequest : IRequest<CustomerResponse> { public int CustomerId { get; set; } } Why can't the compiler infer the correct types, if I try and write something like the following: var service = new HandlingService(); var request = new GetCustomerByIdRequest { CustomerId = 1234 }; var response = service.Handle(request); // Shouldn't this know that response is going to be CustomerResponse? I just get the 'type arguments cannot be inferred' message. Is this a limitation with generic type inference in general, or is there a way to make this work?

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  • rails route question

    - by badnaam
    I am trying to build a search functionality which at a high level works like this. 1 - I have a Search model, controller with a search_set action and search views/partial to render the search. 2 - At the home page a serach form is loaded with an empty search object or a search object initialized with session[:search] (which contains user search preferences, zip code, proximity, sort order, per page etc). This form has a post(:put) action to search_set. 3 - When a registered user performs a set the params of the search form are collected and a search record is saved against that user. If a unregistered user performs a search then the search set action simply stores the params in the session[:search]. In either case, the search is executed with the given params and the results are displayed. At this point the url of in the location bar is something like.. http://localhost:3000/searches/search_set?stype=1 At this point if the user simply hits enter on the location bar, I get an error that says "No action responded to show" I am guessing because the URL contains search_set which uses a put method and even though I have a search_show (:get) action (which simply reruns the search in the session or saved in the database) does not get called. How can I handle this situation where I can route a user hitting enter into the location bar to a get method? If this does not explain the problem , please let me know I can share more details/code etc. Thanks!

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  • Shell Scripting: Generating output file name in script and then writing to it

    - by NewShellScripter
    Hello, I have a shell script where a user passes different sizes as command line arguments. For each of those sizes, I want to perform some task, then save the output of that task into a .txt file with the size in the name. How can I take the command line passed and make that part of a stringname for the output file? I save the output file in a directory specified by another command line argument. Perhaps an example will clear it up. In the foor lop, the i value represents the command line argument I need to use, but $$i doesnt work. ./runMe arg1 arg2 outputDir [size1 size2 size3...] for ((i=4; i<$#; i++ )) do ping -s $$i google.com >> $outputDir/$$iresults.txt done I need to know how to build the $outputDir/$$iresults.txt string. Also, the ping -s $$i doesnt work. Its like I need two levels of replacement. I need to replace the $[$i] inner $i with the value in the loop, like 4 for ex, making it $4. Then replace $4 with the 4th command line argument! Any help would be greatly appreciated. Thanks!

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  • I can not navigate to the next page in windows phone 7

    - by Vijay
    I am trying to navigate form one page to another page depends upon the login. If already user logged in, Welcome page should open. Else Log in Page should open. I am trying like this. The Splash Page is the start up page. This is a Splash Screen Xaml.cs: namespace NewExample.Views { public partial class SplashPage : PhoneApplicationPage { public SplashPage() { InitializeComponent(); this.DataContext = new SplashPageViewModel(); } } } This is Splash Screen View Model: Here I am check the user already logged in or not. namespace NewExample.ViewModel { public class SplashPageViewModel { public static bool isLogin = false; public SplashPageViewModel() { var rootFrame = (App.Current as App).RootFrame; if (isLogin) rootFrame.Navigate(new Uri("/Views/WelcomePage.xaml", UriKind.Relative)); else rootFrame.Navigate(new Uri("/Views/LoginPage.xaml", UriKind.Relative)); } } } But it is not working. The Splash Page only showing. This is not navigating to another page. Please help me to resolve this problem.

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  • Optional mix of filter parameters in a search the Rails way.

    - by GSP
    I've got a simple list page with a couple of search filters status which is a simple enumeration and a test query which I want to compare against both the title and description field of my model. In my controller, I want to do something like this: def index conditions = {} conditions[:status] = params[:status] if params[:status] and !params[:status].empty? conditions[???] = ["(descr = ? or title = ?)", params[:q], params[:q]] if params[:q] and !params[:q].empty? @items = Item.find(:all, :conditions => conditions) end Unfortunately, it doesn't look like I can mix the two types of conditions (the hash and the paramatized version). Is there a "Rails Way" of doing this or do I simply have to do something awful like this: has_status = params[:status] and !params[:status].empty? has_text = params[:q] and !params[:q].empty? if has_status and !has_text # build paramatized condition with just the status elsif has_text and !has_status # build paramatized condition with just the text query elsif has_text and has_status # build paramatized condition with both else # build paramatized condition with neither end I'm migrating from Hibernate and Criteria so forgive me if I'm not thinking of this correctly... Environment: Rails 2.3.4

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  • What's wrong (or right) with this JS Object Pattern?

    - by unsane1
    Here's an example of the pattern I'm using in my javascript objects these days (this example relies on jQuery). http://pastie.org/private/ryn0m1gnjsxdos9onsyxg It works for me reasonably well, but I'm guessing there's something wrong, or at least sub-optimal about it, I'm just curious to get people's opinions. Here's a smaller, inline example of it: sample = function(attach) { // set internal reference to self var self = this; // public variable(s) self.iAmPublic = true; // private variable(s) var debug = false; var host = attach; var pane = { element: false, display: false } // public function(s) self.show = function() { if (!pane.display) { position(); $(pane.element).show('fast'); pane.display = true; } } self.hide = function() { if (pane.display) { $(pane.element).hide('fast'); pane.display = false; } } // private function(s) function init () { // do whatever stuff is needed on instantiation of this object // like perhaps positioning a hidden div pane.element = document.createElement('div'); return self; } function position() { var h = { 'h': $(host).outerHeight(), 'w': $(host).outerWidth(), 'pos': $(host).offset() }; var p = { 'w': $(pane.element).outerWidth() }; $(pane.element).css({ top: h.pos.top + (h.h-1), left: h.pos.left + ((h.w - p.w) / 2) }); } function log () { if (debug) { console.log(arguments); } } // on-instantiation let's set ourselves up return init(); } I'm really curious to get people's thoughts on this.

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  • MVC2 AJAX - determining UpdateTargetId based on the returned data

    - by DanielJW
    The scenario: I'm creating a login form for an MVC2 application. How i'm doing it: The form submits to an MVC2 action which validates the username/password. If it fails validation the action returns the form (a partial view) for the user to try again. If it passes validation the action returns the page the user was visiting before they logged in (a view). What i want to happen: 1 - when the form is submitted and the user validates successfully, The returned result should replace the current page (like what happens if you don't set an UpdateTargetId). 2 - When the form is submitted and the user fails validation, the returned result should replace the form (like what happens if you set the UpdateTargetID to the form's containing element). The problem: I can make both of those things work, but not at the same time. I can either have it always replace the current page, or always just replace the contents of the UpdateTargetId element. But I need it to be able to do either depending on whether the user successfully validated or not. What I need The ideal solution would be to be able to examine the result of the ajax request and determine whether to use the UpdateTargetId (replacing just the form) or not (replacing the whole page). I expect it would involve some work with jquery (assuming it's possible) but i'm not really that great with jquery yet to figure out how to do it myself. If it can't be done this way I'm also open to other methods/solutions for making it work in a similar fashion. Thanks in advance ..

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  • Why would gnu ld link order causes Signal 11 (SEGV) on startup?

    - by Benoit
    We are building a large application in C++ that includes the use of many (static) libraries. We have a problem where the application crashes on startup with a Signal 11, before we even reach main. After much debugging, we have observed that if we explicitly reference an object file so its link order is early, the program crashes on startup. If the file is referenced later (or not referenced at all), the program does not crash. To be clear, there is NO code invoked directly from this object file. However, as it is C++, there might be static objects that do get constructed (it's a CORBA IDL generated file). We use the -Wl,--start-group ... --end-group arguments to multi-pass link the symbols since the libraries are interdependent. Here is a representation of what I mean. This is what the linker's object file order is: Order 1 Order 2 Order 3 foo.o foo.o foo.o ... ... ... main.o main.o main.o crasher.o libA.o libA.o libA.o LibB.o LibB.o LibB.o LibC.o LibC.o LibC.o crasher.o Results: NO CRASH NO CRASH CRASH Does any one have an idea why the linkage order has an effect on the crash? It would be nice if we could force the crasher.o to link later, but we're really after an explanation. Also, is there a way to force the linker to place crasher.o towards the end? Just to add to the fun, in actuality, crasher.o is part of a Library in the --start/--end-group.

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  • Error while setting UserAcces permission for WebForms?

    - by ksg
    I've created a class named BaseClass.cs and I've written a function in its constructor. Here's how it looks public class BasePage:Page { public BasePage() { setUserPermission(); } private void setUserPermission() { String strPathAndQuery = HttpContext.Current.Request.Url.PathAndQuery; string strulr = strPathAndQuery.Replace("/SGERP/", "../"); Session["Url"] = strulr; GEN_FORMS clsForm = new GEN_FORMS(); clsForm.Form_Logical_Name = Session["Url"].ToString(); clsForm.User_ID = Convert.ToInt32(Session["User_ID"]); DataSet dsPermission = clsForm.RETREIVE_BUTTON_PERMISSIONS(); if (dsPermission.Tables.Count > 0) { if (dsPermission.Tables[1].Rows.Count > 0) { Can_Add = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Add"].ToString()); Can_Delete = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Delete"].ToString()); Can_Edit = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Edit"].ToString()); Can_Print = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Print"].ToString()); Can_View = Convert.ToBoolean(dsPermission.Tables[1].Rows[0]["Can_Print"].ToString()); } } } } I've inherited this class on my webform so that when the page loads, the setUserPermission function is executed. My webpage looks like this public partial class Setting_CompanyDetails : BasePage My problem is that I cannot access Session["Url"] in my BasePage. I'm getting the following error Session state can only be used when enableSessionState is set to true, either in a configuration file or in the Page directive. Please also make sure that System.Web.SessionStateModule or a custom session state module is included in the <configuration>\<system.web>\<httpModules> section in the application configuration. How can I solve this issue? Is this the right way to set UserPermission access?

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  • swap! alter and alike

    - by mekka
    Hello, I am having a problem understanding how these functions update the underlying ref, atom etc. The docs say: (apply f current-value-of-identity args) (def one (atom 0)) (swap! one inc) ;; => 1 So I am wondering how it got "expanded" to the apply form. It's not mentioned what exactly 'args' in the apply form is. Is it a sequence of arguments or are these separate values? Was it "expanded" to: (apply inc 0) ; obviously this wouldnt work, so that leaves only one possibility (apply inc 0 '()) (swap! one + 1 2 3) ;; #=> 7 Was it: (apply + 1 1 2 3 '()) ;or (apply + 1 [1 2 3]) (def two (atom [])) (swap! two conj 10 20) ;; #=> [10 20] Was it: (apply conj [] [10 20]) ;or (apply conj [] 10 20 '()) If I swap with a custom function like this: (def three (atom 0)) (swap! three (fn [current elem] (println (class elem))) 10) ;;#=> java.Lang.Integer Which means that the value '10' doesnt magically get changed into a seq '(10) and leads me to the conclusion, that it gets "expanded" to: (apply f current-value-of-identity arg1 arg2 arg3... '()) Is that a correct assumption and the docs are simply lacking a better description?

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  • selected area to cut an image

    - by Oskar Marciniak
    Hi I would do the selected area to cut an image on picturebox control. I have the following code: using System; using System.Drawing; using System.Windows.Forms; namespace WindowsFormsApplication1 { public partial class Form1 : Form { private Rectangle rect; private Pen p; public Form1() { InitializeComponent(); } private void pictureBox1_Paint(object sender, PaintEventArgs e) { if (this.p == null) this.p = new Pen(Color.FromArgb(100, 200, 200, 200), 5); if (this.rect.Width > 0) e.Graphics.DrawRectangle(this.p, this.rect); } private void pictureBox1_MouseUp(object sender, MouseEventArgs e) { if (e.X < this.rect.X) { this.rect.Width = this.rect.X - e.X; this.rect.X = e.X; } else { this.rect.Width = e.X - this.rect.X; } if (e.Y < this.rect.Y) { this.rect.Height = this.rect.Y - e.Y; this.rect.Y = e.Y; } else { this.rect.Height = e.Y - this.rect.Y; } this.Invalidate(this.rect); } private void pictureBox1_MouseDown(object sender, MouseEventArgs e) { this.rect.X = e.X; this.rect.Y = e.Y; } } } It returns an error here: Application.Run(new Form1()); Why? thanks for all replies ;p

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  • Dynamic WebService implementation

    - by chardex
    I have a set of different interfaces and I need to give them access via web services. I have implemented this task in .NET as follows: dynamically generated interface implementation on the IL, marked methods with WebMethod annotation, and in *.asmx handler called generated stub. More needs to be able to change the method signatures (eg change the type of certain argument or add new arguments), ie not always explicitly implement an interface, and use it as a decorator pattern. Example: interface ISomeService { void simpleMetod (String arg1); void customMetod (CusomType arg1, Integer arg2); } // Need to dynamically generate such class @WebService class SomeWebService { private ISomeService someService = new SomeServiceImpl (); @WebMethod public void simpleMethod (String arg1) { someService.simpleMethod (arg1); } @WebMethod public void customMethod (String arg1, Integer arg2) { someService.customMethod (CusomType.fromString (arg1), arg2); } } Interfaces such as ISomeService quite a lot. And manually write code like this I don't want. I work with Java recently, what technology/libraries should be used to solve such task. Thanks.

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  • Some questions about focus on WPF

    - by ThitoO
    Hello, I've a little problem about focus on WPF. I whant to create a window, always on top, and that never get the focus (even if we click on it). Here's my solution : public partial class SkinWindow : Window { public SkinWindow() { InitializeComponent(); Loaded += ( object sender, RoutedEventArgs e ) => SetNoActiveWindow(); } private void SetNoActiveWindow() { WindowInteropHelper helper = new WindowInteropHelper( this ); SetWindowLong( helper.Handle, GWL_EXSTYLE, WS_EX_NOACTIVATE ); LockSetForegroundWindow( LSFW_LOCK ); } const int GWL_EXSTYLE = -20; const int WS_EX_NOACTIVATE = 134217728; const int LSFW_LOCK = 1; [DllImport( "user32" )] public static extern bool LockSetForegroundWindow( uint UINT ); [DllImport( "user32" )] public static extern IntPtr SetWindowLong( IntPtr hWnd, int nIndex, int dwNewLong ); } First problem : It's works, but I've to select an other window to "remove" the focus of my application (after the focus is not gave again, even if I click on my window). Second problem : When I move or resize the window, the modifications happens when I drop the window. Do you have any ideas / links / docs ? Thank you :)

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  • form_form and custom parameter in path_prefix

    - by fguillen
    Hi people, I have this route: # config/routes.rb map.namespace :backshop, :path_prefix => '/:shop_id/admin' do |backshop| backshop.resources :items end And I want to use the form_for magic to reuse the same form on both: new and edit views: <% form_for [:backshop, @item] do |f| %> This used to works, and used to build a create url for the item or update url for the item depending on the status of the @item object. But this is not working on this case because the routes don't exists without the shop_id parameter, and I don't know how to say to the form_for something like this: <% form_for [:backshop, @item], :shop_id => @shop do |f| %> Because it tries to use the @item like the :shop_id parameter. Or like this <% form_for [:backshop, @shop, @item] do |f| %> Because it tries to build this url: backshop_shop_order_path I Know I can just to extract the form_for declaration from the partial and do different calls on depending if new or edit: <% form_for( @item, :url => backshop_items_path( @shop ) ) do |f| %> and <% form_for( @item, :url => backshop_item_path( @shop, @item ) ) do |f| %> But I just wanted don't do this because I have a bunch of models and is a few boring :) Thanks for any suggestion f.

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  • How do i use Form.ShowDialog?

    - by Daniel Lip
    private void button2_Click(object sender, EventArgs e) { ChangeLink cl = new ChangeLink(); // Show testDialog as a modal dialog and determine if DialogResult = OK. if (cl.ShowDialog() == DialogResult.OK) { // Read the contents of testDialog's TextBox. // cl.AcceptButton.DialogResult = DialogResult.OK; this.label4.Text = cl.textBox1Text; } else { this.label4.Text = "Cancelled"; } cl.Dispose(); } When i click the button i see the new Form and the textBox1 in the new Form and i can type in the textBox1 something but i dont see anywhere an OK or CANCEL buttons. Should i add them manualy in the new Form designer ? And how to use them then ? This is the code in my new Form what i wanted to do is to type something in the new Form textBox1 and pass the text in the textBox1 to Form1 label4. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace GatherLinks { public partial class ChangeLink : Form { public ChangeLink() { InitializeComponent(); } public string textBox1Text { get { return textBox1Text = textBox1.Text; } set { } } } } So where are the OK and CANCEL buttons of the Form.ShowDialog ?

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  • Cryptography for P2P card game

    - by zephyr
    I'm considering writing a computer adaptation of a semi-popular card game. I'd like to make it function without a central server, and I'm trying to come up with a scheme that will make cheating impossible without having to trust the client. The basic problem as I see it is that each player has a several piles of cards (draw deck, current hand and discard deck). It must be impossible for either player to alter the composition of these piles except when allowed by the game rules (ie drawing or discarding cards), nor should players be able to know what is in their or their oppponent's piles. I feel like there should be some way to use something like public-key cryptography to accomplish this, but I keep finding holes in my schemes. Can anyone suggest a protocol or point me to some resources on this topic? [Edit] Ok, so I've been thinking about this a bit more, and here's an idea I've come up with. If you can poke any holes in it please let me know. At shuffle time, a player has a stack of cards whose value is known to them. They take these values, concatenate a random salt to each, then hash them. They record the salts, and pass the hashes to their opponent. The opponent concatenates a salt of their own, hashes again, then shuffles the hashes and passes the deck back to the original player. I believe at this point, the deck has been randomized and neither player can have any knowledge of the values. However, when a card is drawn, the opponent can reveal their salt, allowing the first player to determine what the original value is, and when the card is played the player reveals their own salt, allowing the opponent to verify the card value.

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  • C# WPF Unable to control Textboxes

    - by Bo0m3r
    I'm a beginner in coding into C#. While I'm launching a process I can't controls my textboxes. I found some answers on this forum but the explaination is a bit to difficult for me to implement it for my problem. I created a small program that will run a batch file to make a backup. While the backup is running I can't modify my textboxes, disabling buttons etc... I already saw that this is normal but I don't know how to implement the solutions. My last attempt was with Dispatcher.invoke as you can see below. public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); tb_Status.Text = "Ready"; } public void status() { Dispatcher.Invoke(DispatcherPriority.Send, new Action( () => { tb_Status.Text = "The backup is running!"; } ) ); } public void process() { try { Process p = new Process(); p.StartInfo.WindowStyle = ProcessWindowStyle.Minimized; p.StartInfo.CreateNoWindow = true; p.StartInfo.UseShellExecute = false; p.StartInfo.RedirectStandardOutput = true; p.StartInfo.FileName = "Robocopy.bat"; p.Start(); string output = p.StandardOutput.ReadToEnd(); p.WaitForExit(); tb_Output.Text = File.ReadAllText("Backup\\log.txt"); } catch (Exception ex) { tb_Status.Text = ex.Message.ToString(); } } private void Bt_Start_Click(object sender, EventArgs e) { status(); Directory.CreateDirectory("Backup"); process(); tb_Status.Text = "The backup finished"; File.Delete("Backup\\log.txt"); } } } Any help is appreciated!

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  • Header redirect and Session start() generating errors

    - by RPK
    I am using following code. I get errors: Warning: Cannot modify header information - headers already sent by (output started at /home/public_html/mc/cpanel/Source/verifylogin.php:11) Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/public_html/mv/cpanel/Source/verifylogin.php:11) Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/public_html/mv/cpanel/Source/verifylogin.php:11) <?php error_reporting(E_ALL^ E_NOTICE); ob_start(); require("../Lib/dbaccess.php"); $inQuery = "SELECT mhuserid, mhusername FROM cpanelusers WHERE mhusername = '". $_POST['UserName'] ."' AND mhpassword = '". hash('sha512', $_POST['Password']) ."'"; try { $Result = dbaccess::GetRows($inQuery); echo $Result; $NumRows = mysql_num_rows($Result); if ($NumRows > 0) { header("Location: http://www.example.com/cpanel/mainwindow.php"); session_start(); } else { header("Location: http://www.example.com/cpanel/"); echo "Last login attempt failed."; exit; } } catch(exception $e) { } ob_clean(); ?>

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  • Use a table as container or not?

    - by Camran
    I have created my entire website by using a main table, and having the content inside the table. Some ppl suggest this is wrong, and I would like to know what to do specifically in my situation. On my index.html I have a <table align="center"> and then all content in it. Now the content is in form of DIVS and they all have relative positioning, so they are relative to the table. For example: <table align="center"> <tr> <td> <div style="position:relative; left:14px; top:50px;"> CONTENT HERE... (Form, divs, images) </div> </td> </tr> </table> I have just gotten to the stage of browser compatibility. Without making any changes whatsoever, my website works perfect in FF, SAFARI, Chrome and Opera. Only trouble with IE. So for my Q, if you where me, would you change my layout and remove the tables, and instead use alot more css and alot more DIVS, or would you go with what I have? And please if you answer me, don't just provide me with the answer, but also a "why" that is... in other words, give me arguments and facts... Thanks

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  • What guarantees are there on the run-time complexity (Big-O) of LINQ methods?

    - by tzaman
    I've recently started using LINQ quite a bit, and I haven't really seen any mention of run-time complexity for any of the LINQ methods. Obviously, there are many factors at play here, so let's restrict the discussion to the plain IEnumerable LINQ-to-Objects provider. Further, let's assume that any Func passed in as a selector / mutator / etc. is a cheap O(1) operation. It seems obvious that all the single-pass operations (Select, Where, Count, Take/Skip, Any/All, etc.) will be O(n), since they only need to walk the sequence once; although even this is subject to laziness. Things are murkier for the more complex operations; the set-like operators (Union, Distinct, Except, etc.) work using GetHashCode by default (afaik), so it seems reasonable to assume they're using a hash-table internally, making these operations O(n) as well, in general. What about the versions that use an IEqualityComparer? OrderBy would need a sort, so most likely we're looking at O(n log n). What if it's already sorted? How about if I say OrderBy().ThenBy() and provide the same key to both? I could see GroupBy (and Join) using either sorting, or hashing. Which is it? Contains would be O(n) on a List, but O(1) on a HashSet - does LINQ check the underlying container to see if it can speed things up? And the real question - so far, I've been taking it on faith that the operations are performant. However, can I bank on that? STL containers, for example, clearly specify the complexity of every operation. Are there any similar guarantees on LINQ performance in the .NET library specification?

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  • How to implement a Linked List in Java?

    - by nbarraille
    Hello! I am trying to implement a simple HashTable in Java that uses a Linked List for collision resolution, which is pretty easy to do in C, but I don't know how to do it in Java, as you can't use pointers... First, I know that those structures are already implemented in Java, I'm not planning on using it, just training here... So I created an element, which is a string and a pointer to the next Element: public class Element{ private String s; private Element next; public Element(String s){ this.s = s; this.next = null; } public void setNext(Element e){ this.next = e; } public String getString(){ return this.s; } public Element getNext(){ return this.next; } @Override public String toString() { return "[" + s + "] => "; } } Of course, my HashTable has an array of Element to stock the data: public class CustomHashTable { private Element[] data; Here is my problem: For example I want to implement a method that adds an element AT THE END of the linked List (I know it would have been simpler and more efficient to insert the element at the beginning of the list, but again, this is only for training purposes). How do I do that without pointer? Here is my code (which could work if e was a pointer...): public void add(String s){ int index = hash(s) % data.length; System.out.println("Adding at index: " + index); Element e = this.data[index]; while(e != null){ e = e.getNext(); } e = new Element(s); } Thanks!

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  • Cannot understand the behaviour of C# compiler while instantiating a class thru interface

    - by Newbie
    I have a class that implements an interface. The interface is public interface IRiskFactory { void StartService(); void StopService(); } The class that implements the interface is public class RiskFactoryService : IRiskFactory { } Now I have a console application and one window service. From the console application if I write the following code static void Main(string[] args) { IRiskFactory objIRiskFactory = new RiskFactoryService(); objIRiskFactory.StartService(); Console.ReadLine(); objIRiskFactory.StopService(); } It is working fine. However, when I mwrite the same piece of code in Window service public partial class RiskFactoryService : ServiceBase { IRiskFactory objIRiskFactory = null; public RiskFactoryService() { InitializeComponent(); objIRiskFactory = new RiskFactoryService(); <- ERROR } /// <summary> /// Starts the service /// </summary> /// <param name="args"></param> protected override void OnStart(string[] args) { objIRiskFactory.StartService(); } /// <summary> /// Stops the service /// </summary> protected override void OnStop() { objIRiskFactory.StopService(); } } It throws error: Cannot implicitly convert type 'RiskFactoryService' to 'IRiskFactory'. An explicit conversion exists (are you missing a cast?) When I type cast to the interface type, it started working objIRiskFactory = (IRiskFactory)new RiskFactoryService(); My question is why so?

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  • std::bind overload resolution

    - by bpw1621
    The following code works fine #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); This does not #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } int operator()( int i ) { return -i; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); I have tried playing around with the syntax to try and explicitly resolve which function I want in the code that does not work without luck so far. How do I write the bind line in order to choose the call that takes the two integer arguments?

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