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• Checking servlet session attribute value in jsp file

  - by Marta

  I have a no framework java application. It consists of jsp files for view and servlets for the business logic. I must set the user session is the servlet with a firstName parameter. In the jsp file, I need to check if my firstName parameter has a value or not. If the firstName parameter is set, I need to display some html in the jsp file. If it is not set, I need to display different html in the jsp file. Servlet.java: HttpSession session = request.getSession(); session.setAttribute("firstName", customer.getFristName()); String url = "/index.jsp"; RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url); dispatcher.forward(request, response); header.jsp: // Between the <p> tags bellow I need to put some HTML with the following rules // If firstName exist: Hello ${firstName} <a href="logout.jsp">Log out</a> // Else: <a href="login.jsp">Login</a> or <a href="register.jsp">Register</a> <p class="credentials" id="cr"></p> What would be the best way to do this? Any help is much appreciated! Thank you in advance. -Marta

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• Is there a set based solution for this problem?

  - by NYSystemsAnalyst

  We have a table set up as follows: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|2.0 | |2 |2 |2/12/2010|Vacation Earned|3.0 | |3 |1 |2/4/2010 |Vacation Used |1.0 | |4 |2 |5/18/2010|Vacation Earned|2.0 | |5 |2 |7/23/2010|Vacation Used |4.0 | The business rules are: Vacation balance is calculated by vacation earned minus vacation used. Vacation used is always applied against the oldest vacation earned amount first. We need to return the rows for Vacation Earned that have not been offset by vacation used. If vacation used has only offset part of a vacation earned record, we need to return that record showing the difference. For example, using the above table, the result set would look like: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|1.0 | |4 |2 |5/18/2010|Vacation Earned|1.0 | Note that record 2 was eliminated because it was completely offset by used time, but records 1 and 4 were only partially used, so they were calculated and returned as such. The only way we have thought of to do this is to get all of the vacation earned records in a temporary table. Then, get the total vacation used and loop through the temporary table, deleting the oldest record and subtracting that value from the total vacation used until the total vacation used is zero. We could clean it up for when the remaining vacation used is only part of the oldest vacation earned record. This would leave us with just the outstanding vacation earned records. This works, but it is very inefficient and performs poorly. Also, the performance will just degrade over time as more and more records are added. Are there any suggestions for a better solution, preferable set based? If not, we'll just have to go with this.

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• Use of Java [Interfaces / Abstract classes]

  - by Samuel

  Hello, Lately i decided to take a look at Java so i am still pretty new to it and also to the approach of OO programming, so i wanted to get some things straight before learning more, (i guess it's never to soon to start with good practices). I am programming a little 2D game for now but i think my question applies to any non trivial project. For the simplicity i'll provide examples from my game. I have different kinds of zombies, but they all have the same attributes (x, y, health, attack etc) so i wrote an interface Zombie which i implement by WalkingZombie, RunningZombie TeleportingZombie etc. Is this the best thing to do? Am i better of with an abstract class? Or with a super class? (I am not planning to partially implement functions - therefor my choice for an interface instead of an abstract class) I have one class describing the main character (Survivor) and since it is pretty big i wanted to write an interface with the different functions, so that i can easily see and share the structure of it. Is it good practice? Or is it simply a waste of space and time? I hope this question will not be rated as subjective because i thought that experienced programmers won't disagree about this kind of topic since the use of interfaces / super classes / abstract classes follows logical rules and is thereby not simply a personal choice. Thank you for your time -Samuel

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• Why use shorter VARCHAR(n) fields?

  - by chryss

  It is frequently advised to choose database field sizes to be as narrow as possible. I am wondering to what degree this applies to SQL Server 2005 VARCHAR columns: Storing 10-letter English words in a VARCHAR(255) field will not take up more storage than in a VARCHAR(10) field. Are there other reasons to restrict the size of VARCHAR fields to stick as closely as possible to the size of the data? I'm thinking of Performance: Is there an advantage to using a smaller n when selecting, filtering and sorting on the data? Memory, including on the application side (C++)? Style/validation: How important do you consider restricting colunm size to force non-sensical data imports to fail (such as 200-character surnames)? Anything else? Background: I help data integrators with the design of data flows into a database-backed system. They have to use an API that restricts their choice of data types. For character data, only VARCHAR(n) with n <= 255 is available; CHAR, NCHAR, NVARCHAR and TEXT are not. We're trying to lay down some "good practices" rules, and the question has come up if there is a real detriment to using VARCHAR(255) even for data where real maximum sizes will never exceed 30 bytes or so. Typical data volumes for one table are 1-10 Mio records with up to 150 attributes. Query performance (SELECT, with frequently extensive WHERE clauses) and application-side retrieval performance are paramount.

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• Core Data Errors vs Exceptions Part 3

  - by John Gallagher

  My question is similar to this one. Background I'm creating a large number of objects in a core data store using NSOperations to speed things up. I've followed all the Core Data multithreading rules - I've got a single persistent store coordinator and a managed object context per thread that on save is merging back to the main managed object context. The Problem When the number of threads running at once is more than 1, I get the exception logged on save of my core data store: NSExceptionHandler has recorded the following exception: NSInternalInconsistencyException -- optimistic locking failure What I've Tried My code that creates new entities is quite complex - it makes entities that have relationships with other entities that could be being created in a separate thread. If I replace my object creation routine with some very simple code just making non-related entries, everything works perfectly. Initially, as well as the exceptions, I was getting a save error saying core data couldn't save due to the merge failing. I read the docs and realised I needed a merge policy on the Managed Object Context I was saving to. I set this up and as this question states, the save error goes away, but the exception remains. My Question Do I need to worry about these exceptions? If I do need to get rid of the exceptions, any ideas on how I do it?

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• Is it possible to modify the value of a record's primary key in Oracle when child records exist?

  - by Chris Farmer

  I have some Oracle tables that represent a parent-child relationship. They look something like this: create table Parent ( parent_id varchar2(20) not null primary key ); create table Child ( child_id number not null primary key, parent_id varchar2(20) not null, constraint fk_parent_id foreign key (parent_id) references Parent (parent_id) ); This is a live database and its schema was designed long ago under the assumption that the parent_id field would be static and unchanging for a given record. Now the rules have changed and we really would like to change the value of parent_id for some records. For example, I have these records: Parent: parent_id --------- ABC123 Child: child_id parent_id -------- --------- 1 ABC123 2 ABC123 And I want to modify ABC123 in these records in both tables to something else. It's my understanding that one cannot write an Oracle update statement that will update both parent and child tables simultaneously, and given the FK constraint, I'm not sure how best to update my database. I am currently disabling the fk_parent_id constraint, updating each table independently, and then enabling the constraint. Is there a better, single-step way to update this content?

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• Code casing question for private class fields

  - by user200295

  Take the following example public class Class1{ public string Prop1{ get {return m_Prop1;} set {m_Prop1 = value; } } private string m_Prop1; // this is standard private property variable name // how do we cap this variable name? While the compiler can figure out same casing // it makes it hard to read private Class2 Class2; // we camel case the parameter public Class1(Class2 class2){ this.Class2 = class2; } } Here are my stock rules The class name is capitalized (Class1) The public properties are capitalized (Prop1) The private field tied to a public property has m_ to indicate this. My coworker prefers _ There is some debate if using m_ or _ should be used at all, as it is like Hungarian notation. Private class fields are capitalized. The part I am trying to figure out is what do I do if when the Class name of a private field matches the private field name. For example, private Class2 Class2; This is confusing. If the private field name is not the same class, for example private string Name; , there isn't much issue. Or am I thinking about the issue wrong. Should my classes and private fields be named in such a way that they don't collide?

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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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• Is there a maximum number of input controls that can be used on an HTML form?

  - by Rich

  I have an ambitious requirement for an asp.net 2.0 web page that contains a table (gridview), and each row in the grid contains 6 select (dropdown) controls for data entry. The number of rows that will be displayed is dependent upon the user's search parameters, which are specified in another area of the page. Unfortunately, with the default (and even basic) search parameters specified, the grid could contain several hundred rows. I've noticed that the browser, in this case IE8, starts behaving rather erratically once I reach a large number of rows -- no documented evidence for the number of rows where this begins to be a problem. For example, trying to view the source of the page results in a message from IE stating that there was a problem with the page that forced the browser to reload it, and I never get the source. Obviously the page loads and renders rather slowly also. I know that my solution is probably going to involve paging the gridview such that it only displays 20 or so rows per page, and I'll have to write code to handle the saving of changes in the dropdown values when the user changes pages. I can probably turn off viewstate on the gridview also. However, the question I really want to pose is this -- has anyone seen a documented rule indicating the maximum number of input controls that an HTML browser form is supposed to be able to contain? I could not find anything on the Internet after doing a search, and I suspect the answer may be whatever the browser can handle based on the machine configuration it is running on. Any rules of thumb you use? Thanks for any suggestions. Rich

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• Problem understanding Inheritance

  - by dhruvbird

  I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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• What type of objects can be sent back to an action Method using HTML.HIDDEN()

  - by Richard77

  Hello, 1)Let's say I've this form: <%Using(Html.BeginForm()){%> <% = Html.Hidden("myObject", (cast to the appropriate type)ViewData["KeyForMyObject"]%> <input type = "submit" "Submit Object"> <%}%> 2) Here's the Action which's supposed to intercept the value of the object public ActionResult MyAction(Type myObject) { //Do Something with the object } Here's my question: What type of objects the Hidden field can support? In fact, when ViewData["KeyForMyObject"] contains a string, int, or bool, myAction is able to retrieve the value. But, when it comes to objects, such as List, and dictionary, nothing happens. When I debug to check the local values, I see null for Type myObject in the MyMethod. So what are the rules in MVC when it comes to a List or Dictionary? ================================= EDIT To make things simpler, can I write something like this <% = Html.Hidden("contactDic", (Dictionary<string, string>) ViewData["contacts"])%> and expect to retrieve the dictionary in the action Method like this public ActionResult myMethod(Dictionary<string, string> contactDic) { //Do something with the dictionary } Thanks for Helping

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• What makes my code DDD (domain-driven design) qualified?

  - by oykuo

  Hi All, I'm new to DDD and am thinking about using this design technique in my project. However, what strikes me about DDD is that how basic the idea is. Unlike other design techniques such as MVC and TDD, it doesn't seems to contain any ground breaking ideas. For example, I'm sure some of you will have the same feeling that the idea of root aggregates and repositories are nothing new because when you are was writing MVC web applications you have to have one single master object (i.e. the root aggregate) that contain other minor objects (i.e. value objects and entities) in the model layer in order to send data to a strongly typed view. To me, the only new idea in DDD is probably the "Smart" entities (i.e. you are supposed to have business rules on root aggregates) Separation between value object, root aggregate and entities. Can anyone tell me if I have missed out anything here? If that's all there is to DDD, if I update one of my existing MVC application with the above 2 new ideas, can I claim it's an TDD, MVC and DDD applcation?

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• My iPhone app runs fine in simulator but quit in device (iPod touch 3.1.2) test, I got the following

  - by Mickey Shine

  I was running myapp on an iPod touch and I noticed it missed some libraries. Is that the reason? [Session started at 2010-03-19 15:57:04 +0800.] GNU gdb 6.3.50-20050815 (Apple version gdb-1128) (Fri Dec 18 10:08:53 UTC 2009) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "--host=i386-apple-darwin --target=arm-apple-darwin".tty /dev/ttys007 Loading program into debugger… Program loaded. target remote-mobile /tmp/.XcodeGDBRemote-237-78 Switching to remote-macosx protocol mem 0x1000 0x3fffffff cache mem 0x40000000 0xffffffff none mem 0x00000000 0x0fff none run Running… [Switching to thread 11779] [Switching to thread 11779] sharedlibrary apply-load-rules all (gdb) continue warning: Unable to read symbols for "/Library/MobileSubstrate/MobileSubstrate.dylib" (file not found). 2010-03-19 15:57:18.892 myapp[2338:207] MS:Notice: Installing: com.yourcompany.myapp [myapp] (478.52) 2010-03-19 15:57:19.145 myapp[2338:207] MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib warning: Unable to read symbols for "/Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib" (file not found). warning: Unable to read symbols for "/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/lib/libsubstrate.dylib" (file not found). MS:Warning: message not found [myappAppDelegate applicationWillResignActive:] MS:Warning: message not found [myappAppDelegate applicationDidBecomeActive:] 2010-03-19 15:57:19.550 myapp[2338:207] in FirstViewController 2010-03-19 15:57:20.344 myapp[2338:207] in load table view 2010-03-19 15:57:20.478 myapp[2338:207] in loading splash view 2010-03-19 15:57:22.793 myapp[2338:207] in set interface Program received signal: “0”. warning: check_safe_call: could not restore current frame

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• How to achieve to following C++ output formatting?

  - by Yan Cheng CHEOK

  I wish to print out double as the following rules : 1) No scietific notation 2) Maximum decimal point is 3 3) No trailing 0. For example : 0.01 formated to "0.01" 2.123411 formatted to "2.123" 2.11 formatted to "2.11" 2.1 formatted to "2.1" 0 formatted to "0" By using .precision(3) and std::fixed, I can only achieve rule 1) and rule 2), but not rule 3) 0.01 formated to "0.010" 2.123411 formatted to "2.123" 2.11 formatted to "2.110" 2.1 formatted to "2.100" 0 formatted to "0" Code example is as bellow : #include <iostream> int main() { std::cout.precision(3); std::cout << std::fixed << 0.01 << std::endl; std::cout << std::fixed << 2.123411 << std::endl; std::cout << std::fixed << 2.11 << std::endl; std::cout << std::fixed << 2.1 << std::endl; std::cout << std::fixed << 0 << std::endl; getchar(); } any idea?

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• How to document an existing small web site (web application), inside and out?

  - by Ricket

  We have a "web application" which has been developed over the past 7 months. The problem is, it was not really documented. The requirements consisted of a small bulleted list from the initial meeting 7 months ago (it's more of a "goals" statement than software requirements). It has collected a number of features which stemmed from small verbal or chat discussions. The developer is leaving very soon. He wrote the entire thing himself and he knows all of the quirks and underlying rules to each page, but nobody else really knows much more than the user interface side of it; which of course is the easy part, as it's made to be intuitive to the user. But if someone needs to repair or add a feature to it, the entire thing is a black box. The code has some minimal comments, and of course the good thing about web applications is that the address bar points you in the right direction towards fixing a problem or upgrading a page. But how should the developer go about documenting this web application? He is a bit lost as far as where to begin. As developers, how do you completely document your web applications for other developers, maintainers, and administrative-level users? What approach do you use, where do you start, do you have a template? An idea of magnitude: it uses PHP, MySQL and jQuery. It has about 20-30 main (frontend) files, along with about 15 included files and a couple folders of some assets. So overall it's a pretty small application. It interfaces with 7 MySQL tables, each one well-named, so I think the database end is pretty self-explanatory. There is a config.inc.php file with definitions of consts like the MySQL user details, some from/to emails, and URLs which PHP uses to insert into emails and pages (relative and absolute paths, basiecally). There is some AJAX via jQuery. Please comment if there is any other information that would help you help me and I will be glad to edit it in.

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• Identifying memory leaks in C++

  - by Dororo

  I've got the following bit of code, which I've narrowed down to be causing a memory leak (that is, in Task Manager, the Private Working Set of memory increases with the same repeated input string). I understand the concepts of heaps and stacks for memory, as well as the general rules for avoiding memory leaks, but something somewhere is still going wrong: while(!quit){ char* thebuffer = new char[210]; //checked the function, it isn't creating the leak int size = FuncToObtainInputTextFromApp(thebuffer); //stored in thebuffer string bufferstring = thebuffer; int startlog = bufferstring.find("$"); int endlog = bufferstring.find("&"); string str_text=""; str_text = bufferstring.substr(startlog,endlog-startlog+1); String^ str_text_m = gcnew String(str_text_m.c_str()); //some work done delete str_text_m; delete [] thebuffer; } The only thing I can think of is it might be the creation of 'string str_text' since it never goes out of scope since it just reloops in the while? If so, how would I resolve that? Defining it outside the while loop wouldn't solve it since it'd also remain in scope then too. Any help would be greatly appreciated.

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• Why aren't Java's generics implicitly polymorphic?

  - by froadie

  I'm a bit confused about how Java generics handle inheritance / polymorphism. Assume the following hierarchy - Animal (Parent) Dog - Cat (Children) So suppose I have a method doSomething(List<Animal> animals). By all the rules of inheritance and polymorphism, I would assume that a List<Dog> is a List<Animal> and a List<Cat> is a List<Animal> - and so either one could be passed to this method. Not so. If I want to achieve this behavior, I have to explicitly tell the method to accept a list of any subset of Animal by saying doSomething(List<? extends Animal> animals). I understand that this is Java's behavior. My question is why? Why is polymorphism generally implicit, but when it comes to generics it must be specified?

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• alternative in .Net to building Tables/TR/TD manually?

  - by egrunin

  I've got a pile of code here that looks like this: if (stateTax > 0) { tr = new TableRow(); tbl.Rows.Add(tr); td = new TableCell(); td.CssClass = "stdLabel"; td.Text = "NY State Tax"; tr.Cells.Add(td); td = new TableCell(); td.Text = string.Format("{0:C}", stateTax); td.CssClass = "justRight"; tr.Cells.Add(td); } This is a horrible hash of data and layout, but creating a special class or control every time something like this comes up seems almost as bad. What I usually do is write a helper function, which is concise but ugly: if (stateTax > 0) MakeRow(tbl, "NY State Tax", "stdLabel", string.Format("{0:C}", stateTax), "justRight"); And now I'm thinking: haven't I done this 100 times before? Isn't there a more modern way? Just to be explicit: it's a whole list of miscellaneous labels and values. They don't come from any particular data source, and the rules for when rows should be suppressed vary. This example has only two columns, but I have other places with more.

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• Override one css class with another?

  - by user246114

  Hi, I have a list, with an li style defined. I want to replace the style of an individual element, but it doesn't seem to have any visual effect. Example: .myList li { background-color: yellow; } .foo { background-color: green; } <ul class='myList'> <li>Hello</li> </ul> When I add an item to the list, it has the .myList li style applied properly. I try now to remove all styles and apply the foo style to a single item (using jquery): $(item).removeClass(); $(item).addClass("foo"); the item does not change color to green though, but this reports the class is set to 'foo': alert($(item).attr('class')); so I guess I'm not understanding css rules here, looks like the li class definition is just overriding whatever else I do, however I want the reverse to be true, I want to override the li style definition with foo. How do we do this? Thanks

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• Starting a personal reuasable code repository.

  - by Rob Stevenson-Leggett

  Hi, I've been meaning to start a library of reusable code snippets for a while and never seem to get round to it. At the moment I just tend to have some transient classes/files that I drag out of old projects. I think my main problems are: Where to start. What structure should my repository take? Should it be a compiled library (where appropriate) or just classes/files I can drop into any project? Or a library project that can be included? What are the licencing implications of that? In my experience, a built/minified library will quickly become out of date and the source will get lost. So I'm leaning towards source that I can export from SVN and include in any project. Intellectual property. I am employeed, so a lot of the code I write is not my IP. How can I ensure that I don't give my own IP away using it on projects in work and at home? I'm thinking the best way would be to licence my library with an open source licence and make sure I only add to it in my own time using my own equipment and therefore making sure that if I use it in a work project the same rules apply as if I was using a third party library. I write in many different languages and often would require two or more parts of this library. Should I look at implementing a few template projects and a core project for each of my chosen reusable components and languages? Has anyone else got this sort of library and how do you organise and update it?

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• Heap Algorithmic Issue

  - by OberynMarDELL

  I am having this algorithmic problem that I want to discuss about. Its not about find a solution but about optimization in terms of runtime. So here it is: Suppose we have a race court of Length L and a total of N cars that participate on the race. The race rules are simple. Once a car overtakes an other car the second car is eliminated from the race. The race ends when no more overtakes are possible to happen. The tricky part is that the k'th car has a starting point x[k] and a velocity v[k]. The points are given in an ascending order, but the velocities may differ. What I've done so far: Given that a car can get overtaken only by its previous, I calculated the time that it takes for each car to reach its next one t = (x[i] - x[i+1])/(v[i] - v[i+1]) and I insert these times onto a min heap in O(n log n). So in theory I have to pop the first element in O(logn), find its previous, pop it as well , update its time and insert it in the heap once more, much like a priority queue. My main problem is how I can access specific points of a heap in O(log n) or faster in order to keep the complexity in O(n log n) levels. This program should be written on Haskell so I would like to keep things simple as far as possible EDIT: I Forgot to write the actual point of the race. The goal is to find the order in which cars exit the game

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• Most effecient way to create a "slider" timeline in HTML, CSS, and JavaScript?

  - by ZapChance

  Alright, so here's my dilemma. I've got these two "slides" lined up, one ready to be passed into view. I have it working and all, but I can scroll over to the right to see the second slide! How could I have it you can only view the one slide? JavaScript used: function validate(form) { var user = form.username.value; var pass = form.password.value; if(user === "test") { if(pass === "pass") { var hideoptions = {"direction" : "left", "mode" : "hide"}; var showoptions = {"direction" : "left", "mode" : "show"}; /*$("#loginView").toggle("slide", hideoptions, 1000, function() { $("#loginView").css("margin-left", "100%"); }); $("#mainView").toggle("slide", showoptions, 1000, function() { $("#mainView").css("margin-left", 0); });*/ $("#loginView").animate({ marginLeft: "-100%" }, 1000); $("#mainView").animate({ marginLeft: "0" }, 1000); } else { alert("nope"); } } else { alert("nope 2"); } } As you can see here @ http://jsfiddle.net/D7Va3/1/ (JSFiddle), once you enter "test" and "pass", then click enter, the tiles slide. But. If you reload, you can see that you can scroll to the right of the screen and view the second slide prematurely, which is just not going to work for me. I still need to achieve the same seamless transition, but you must only be able to view one slide at a time. Also, I plan to expand with more slides, so if you're feeling lucky today, I'd really love to see an example of how I could support multiple frames. I'm very new to JavaScript (yet I know syntax rules, and general coding knowledge from other languages), so the better you explain, the more knowledgeable I can be, and I'd be very grateful for that. Thanks in advance!

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• C++ const-reference semantics?

  - by Kristoffer

  Consider the sample application below. It demonstrates what I would call a flawed class design. #include <iostream> using namespace std; struct B { B() : m_value(1) {} long m_value; }; struct A { const B& GetB() const { return m_B; } void Foo(const B &b) { // assert(this != &b); m_B.m_value += b.m_value; m_B.m_value += b.m_value; } protected: B m_B; }; int main(int argc, char* argv[]) { A a; cout << "Original value: " << a.GetB().m_value << endl; cout << "Expected value: 3" << endl; a.Foo(a.GetB()); cout << "Actual value: " << a.GetB().m_value << endl; return 0; } Output: Original value: 1 Expected value: 3 Actual value: 4 Obviously, the programmer is fooled by the constness of b. By mistake b points to this, which yields the undesired behavior. My question: What const-rules should you follow when designing getters/setters? My suggestion: Never return a reference to a member variable if it can be set by reference through a member function. Hence, either return by value or pass parameters by value. (Modern compilers will optimize away the extra copy anyway.)

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• Separating code logic from the actual data structures. Best practices?

  - by Patrick

  I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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• GetLocalValueEnumerator() Not Returning All Properties

  - by a_hardin

  I am trying to perform validation in my WPF application using the solution in Detecting WPF Validation Errors. public static bool IsValid(DependencyObject parent) { // Validate all the bindings on the parent bool valid = true; LocalValueEnumerator localValues = parent.GetLocalValueEnumerator(); while (localValues.MoveNext()) { LocalValueEntry entry = localValues.Current; if (BindingOperations.IsDataBound(parent, entry.Property)) { Binding binding = BindingOperations.GetBinding(parent, entry.Property); foreach (ValidationRule rule in binding.ValidationRules) { ValidationResult result = rule.Validate(parent.GetValue(entry.Property), null); if (!result.IsValid) { BindingExpression expression = BindingOperations.GetBindingExpression(parent, entry.Property); System.Windows.Controls.Validation.MarkInvalid(expression, new ValidationError(rule, expression, result.ErrorContent, null)); valid = false; } } } } // Validate all the bindings on the children for (int i = 0; i != VisualTreeHelper.GetChildrenCount(parent); ++i) { DependencyObject child = VisualTreeHelper.GetChild(parent, i); if (!IsValid(child)) { valid = false; } } return valid; } The problem I am running into is that when I step through the code for a TextBox, I'm not getting the Text property. The only properties I get are "PageHeight", "Instance", and "UndoManagerInstance". Therefore, I can not Validate the rules for the binding on the TextBox. Does anyone have any idea why I wouldn't be getting the correct properties? Is there another way to force validaton on controls in WPF? I haven't been able to find anyone else who has had this problem. Update: The TextBoxes I am trying to validate are within a DataTemplate. I found that if I copy one of the TextBoxes and place it directly in the Window, I am able to get the data. Using Woodstock, I saw that the data source for the TextBoxes in the template is "ParentTemplate", but it's "Local" for the TextBox outside of the template. So, the question now is, how can I get the DependencyProperties for controls inside a DataTemplate?

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