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  • Can I use the [] operator in C++ to create virtual arrays

    - by Shane MacLaughlin
    I have a large code base, originally C ported to C++ many years ago, that is operating on a number of large arrays of spatial data. These arrays contain structs representing point and triangle entities that represent surface models. I need to refactor the code such that the specific way these entities are stored internally varies for specific scenarios. For example if the points lie on a regular flat grid, I don't need to store the X and Y coordinates, as they can be calculated on the fly, as can the triangles. Similarly, I want to take advantage of out of core tools such as STXXL for storage. The simplest way of doing this is replacing array access with put and get type functions, e.g. point[i].x = XV; becomes Point p = GetPoint(i); p.x = XV; PutPoint(i,p); As you can imagine, this is a very tedious refactor on a large code base, prone to all sorts of errors en route. What I'd like to do is write a class that mimics the array by overloading the [] operator. As the arrays already live on the heap, and move around with reallocs, the code already assumes that references into the array such as point *p = point + i; may not be used. Is this class feasible to write? For example writing the methods below in terms of the [] operator; void MyClass::PutPoint(int Index, Point p) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); StoreGridPoint(xoffs,yoffs,p.z); } else m_PointArray[Index] = p; } } Point MyClass::GetPoint(int Index) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); return GetGridPoint(xoffs,yoffs); // GetGridPoint returns Point } else return m_PointArray[Index]; } } My concern is that all the array classes I've seen tend to pass by reference, whereas I think I'll have to pass structs by value. I think it should work put other than performance, can anyone see any major pitfalls with this approach. n.b. the reason I have to pass by value is to get point[a].z = point[b].z + point[c].z to work correctly where the underlying storage type varies.

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  • How do I make a GUI that behaves like this?

    - by Karl Knechtel
    This is difficult to explain without illustration, so - behold, an illustration, cobbled together from screenshots of a few hello-world examples and a lot of Paint work: I have started out using Windows Forms on .NET (via IronPython, but that shouldn't be important), and haven't been able to figure out very much. GUI libraries in general are very intimidating, simply because every class has so many possible attributes. Documentation is good at explaining what everything does, but not so good at helping you figure out what you need. I will be assembling the GUI dynamically, but I'm not expecting that to be the hard part. The sticking points for me right now are: How do I get text labels to size themselves automatically to the width of the contained text (so that the text doesn't clip, and I also don't reserve unnecessary space for them when resizing the window)? How do I make the vertical scrollbar always appear? Setting the VScroll property (why is this protected when AutoScroll is public, BTW?) doesn't seem to do anything. How come the horizontal scrollbar is not added by AutoScroll when contents are laid out vertically (via Dock = DockStyle.Top)? I can use a minimum size for panels to prevent the label and corresponding control from overlapping when the window is shrunk horizontally, but then the scrollbar doesn't appear and the control is inaccessible. How can I put limits on window resizing (e.g. set a minimum width) without disabling it completely? (Just set minimum/maximum sizes for the Form?) Related to that, is there any way to set minimum/maximum widths or heights without setting a minimum/maximum size (i.e. can I constrain the size in only one dimension)? Is there a built-in control suitable for hex editing or am I going to have to build something myself? ... And should I be using something else (perhaps something more capable?) I've heard WPF mentioned, but I understand that this involves XML and I really want to build a GUI from XML - I already have data in an object graph, and doing some kind of weird XML pseudo-serialization (in Python, no less!) in order to create a GUI seems incredibly roundabout.

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  • javascript - how to call a function newly added from ajax

    - by strike_noir
    I have a coding difficulty which have been asked in this forum before: Calling a JavaScript function returned from a Ajax response But I didn't find the answers quite satisfying. To be more precise of the problem I'm dealing, here is the details: I dynamically load a document (HTML and javascript) using jquery var url = 'document.php'; $('#container').load(url); And then I want to call the functions from that document.php. Due to my requirement, I don't want to call the function after the documents' loaded, but rather to call it later when I need it. Because it was dynamically loaded, the DOM doesn't recognize the functions. How to properly call this function? Thank you

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  • Have to put files in static_dir but need to read them afterwards

    - by SanjamX
    I just started using google app engine. In order to use templates, I'm using jinja2. I want to add images dynamically after I set the width and height of the img tag. I used PIL in order to read the image size and put the one I want. However when I open the image with PIL, I need it not to be in a static_dir and to put the image in the img tag, I need it to be in the static_dir. As a testing solution I've copied the folder to see if I get results and I did. But as you can see having each image saved twice is kind of bad.

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  • How can I merge two Linq IEnumerable<T> queries without running them?

    - by makerofthings7
    How do I merge a List<T> of TPL-based tasks for later execution? public async IEnumerable<Task<string>> CreateTasks(){ /* stuff*/ } My assumption is .Concat() but that doesn't seem to work: void MainTestApp() // Full sample available upon request. { List<string> nothingList = new List<string>(); nothingList.Add("whatever"); cts = new CancellationTokenSource(); delayedExecution = from str in nothingList select AccessTheWebAsync("", cts.Token); delayedExecution2 = from str in nothingList select AccessTheWebAsync("1", cts.Token); delayedExecution = delayedExecution.Concat(delayedExecution2); } /// SNIP async Task AccessTheWebAsync(string nothing, CancellationToken ct) { // return a Task } I want to make sure that this won't spawn any task or evaluate anything. In fact, I suppose I'm asking "what logically executes an IQueryable to something that returns data"? Background Since I'm doing recursion and I don't want to execute this until the correct time, what is the correct way to merge the results if called multiple times? If it matters I'm thinking of running this command to launch all the tasks var AllRunningDataTasks = results.ToList(); followed by this code: while (AllRunningDataTasks.Count > 0) { // Identify the first task that completes. Task<TableResult> firstFinishedTask = await Task.WhenAny(AllRunningDataTasks); // ***Remove the selected task from the list so that you don't // process it more than once. AllRunningDataTasks.Remove(firstFinishedTask); // TODO: Await the completed task. var taskOfTableResult = await firstFinishedTask; // Todo: (doen't work) TrustState thisState = (TrustState)firstFinishedTask.AsyncState; // TODO: Update the concurrent dictionary with data // thisState.QueryStartPoint + thisState.ThingToSearchFor Interlocked.Decrement(ref thisState.RunningDirectQueries); Interlocked.Increment(ref thisState.CompletedDirectQueries); if (thisState.RunningDirectQueries == 0) { thisState.TimeCompleted = DateTime.UtcNow; } }

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  • What can you do in C without "std" includes? Are they part of "C," or just libraries?

    - by Chris Cooper
    I apologize if this is a subjective or repeated question. It's sort of awkward to search for, so I wasn't sure what terms to include. What I'd like to know is what the basic foundation tools/functions are in C when you don't include standard libraries like stdio and stdlib. What could I do if there's no printf(), fopen(), etc? Also, are those libraries technically part of the "C" language, or are they just very useful and effectively essential libraries?

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  • Download button that send application to blackberry and asks everyone else to register???

    - by Stefan
    Hello all I would like to know your opinions on how to handle this. I need to create a link or advertisement that offers a phone app to be downloaded. I need that users who are viewing the page with their blackberry receive the download when they click the button but everyone else who would be viewing the page would get a form which asks that they insert a phone number to send the application to. Has anyone else already tackled this or something similar?

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  • Does std::multiset guarantee insertion order?

    - by Naveen
    I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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  • algorithm to find longest non-overlapping sequences

    - by msalvadores
    I am trying to find the best way to solve the following problem. By best way I mean less complex. As an input a list of tuples (start,length) such: [(0,5),(0,1),(1,9),(5,5),(5,7),(10,1)] Each element represets a sequence by its start and length, for example (5,7) is equivalent to the sequence (5,6,7,8,9,10,11) - a list of 7 elements starting with 5. One can assume that the tuples are sorted by the start element. The output should return a non-overlapping combination of tuples that represent the longest continuos sequences(s). This means that, a solution is a subset of ranges with no overlaps and no gaps and is the longest possible - there could be more than one though. For example for the given input the solution is: [(0,5),(5,7)] equivalent to (0,1,2,3,4,5,6,7,8,9,10,11) is it backtracking the best approach to solve this problem ? I'm interested in any different approaches that people could suggest. Also if anyone knows a formal reference of this problem or another one that is similar I'd like to get references. BTW - this is not homework. Edit Just to avoid some mistakes this is another example of expected behaviour for an input like [(0,1),(1,7),(3,20),(8,5)] the right answer is [(3,20)] equivalent to (3,4,5,..,22) with length 20. Some of the answers received would give [(0,1),(1,7),(8,5)] equivalent to (0,1,2,...,11,12) as right answer. But this last answer is not correct because is shorter than [(3,20)].

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  • In Java how instance of and type cast(i.e (ClassName)) works on proxy object ?

    - by learner
    Java generates a proxy class for a given interface and provides the instance of the proxy class. But when we type cast the proxy object to our specific Object, how java handles this internally? Is this treated as special scenario? For example I have class 'OriginalClass' and it implements 'OriginalInterface', when I create proxy object by passing 'OriginalInterface' interface java created proxy class 'ProxyClass' using methods in the provided interface and provides object of this class(i.e ProxyClass). If my understanding is correct then can you please answer following queries 1) When I type cast object of ProxyClass to my class OriginalClass this works, but how java is allowing this? Same in case of instace of? 2) As my knowledge java creates a proxy class only with the methods, but what happen when I try to access attributes on this object? 3) Only interface methods are getting implemented in Proxy, but what happens when I try to access a method which not in interface and only mentioned in the class? Thanks, Student

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  • Stored Connection Strings per user

    - by pehaada
    In the past I've used a Singleton Pattern to load the connection string when the application starts via the global.asa file. I have a project now where each user has a unique connection string to the database. I would like to load this connection string once. The issue is that the singleton pattern will not work for me since each user has there own connection string. Basically the connection string is created dynamically. I do not want to store it is session. If anyway has a clever way of doing this in .NET let me know ?

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  • Default Sorting in DynamicData

    - by Jens A.
    I am using DynamicData in the version that shipped with VS2008. In the default List view, the data is sorted by order of entry into the database. I'd like to get it sorted by a field of a specific name (descending). As a last resort I tried to use the OrderByParameter of the LinqDataSource with a QueryStringParameter, but I could not get it to sort anything. =) Is there an easy way to accomplish this?

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  • Why doesn't C++ allow you to request a pointer to the most derived class?

    - by Matthew Lowe
    (This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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  • Why would someone use WHERE 1=1 AND <conditions> in a SQL clause?

    - by Bogdan Maxim
    Why would someone use WHERE 1=1 AND <conditions> in a SQL clause (Either SQL obtained through concatenated strings, either view definition) I've seen somewhere that this would be used to protect against SQL Injection, but it seems very weird. If there is injection WHERE 1 = 1 AND injected OR 1=1 would have the same result as injected OR 1=1. Later edit: What about the usage in a view definition?

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  • Secure to store an ID in an ASP.NET control ID?

    - by Curtis White
    I'm auto-generating a form in my ASP.NET page. This is already tested and working. I want to know if: If there are any security problems with storing the database ID as part of my controls ID? I can see think of 2 issues: the id will be visible in page source (not really important in this case), and the possibility someone could change the name of the control somehow? This second possibility is more serious. Is this a potential problem and how to void it? If there would be a better preferred way to associate a unique data with any type of control? Is it possible to store a custom item in the viewstate for the control?

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  • Problem FlashVars parameter asp.net

    - by sofie-vo
    Code for asp.net page <%@ Page Language="VB" AutoEventWireup="false" CodeFile="trainingupload.aspx.vb" Inherits="trainingupload" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> </head> <body> <form id="form1" runat="server"> <div height> <object width="1000" height="800"> <param name="movie" value="player.swf" /> <param name="FlashVars" value='userid=<%=String.Format(getuser())%>" '/> <embed src="bin-release/trainingscentrum.swf" FlashVars='userid=<%=String.Format(getuser())%>" ' width="1500" height="800" /> </embed> </object> </div> </form> </body> </html> Code behind Public Function getuser() As Guid Dim user As MembershipUser = Membership.GetUser() Dim userid As Guid = (CType(user.ProviderUserKey, Guid)) Return userid End Function In the code above I use an function to return the userid. When I replace <%=String.Format(getuser())% with an actual userid, I get the value in my flex application. But this code returns nothing. What am I doing wrong?

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  • Does video tag (HTML 5) injection via JavaScript work in any browsers?

    - by JoshNaro
    I'm trying to dynamically spawn a video element on a page using JavaScript. JavaScript <script type="text/javascript"> $(document).ready(function() { var video = $(document.createElement('video')) .attr('id', 'VideoElement') .attr('controls', 'controls') .attr('src', 'videopath.mp4') // Changed 'href' attribute to 'src' .css({ width: 640, height: 360 }); $('#VideoContainer').append(video); }); HTML <body> <div id="VideoContainer"></div> </body> In Firefox I get the video harness, but the actual video doesn't load. In IE8 the video harness doesn't even appear. Is HTML 5 just not supported enough to accomplish this yet? Edit: Got this to work with Artiom's fix. Looks like this works fine with Chrome and Safari. I'm using a codec Firefox doesn't support, so it doesn't work there; although I suspect it will work with a supported codec. IE8 sure enough doesn't work (high five IE).

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  • Persisting user control values afer postback in asp.net

    - by user557135
    Hi, I have a few user controls which I add to the aspx form depending on the user's choice from a combo box. I have a user control which has a textbox in it and a getValue() method that returns the value of the textbox. After user selects the related item I load the control and add to a panel using loadControl method. User enters some text. After a postback I want to keep the user control and the user input in the same state before . Hope i could be clear. Thanks in advanced

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  • Attribute & Reflection libraries for C++?

    - by Fabian
    Most mature C++ projects seem to have an own reflection and attribute system, i.e for defining attributes which can be accessed by string and are automatically serializable. At least many C++ projects I participated in seemed to reinvent the wheel. Do you know any good open source libraries for C++ which support reflection and attribute containers, specifically: Defining RTTI and attributes via macros Accessing RTTI and attributes via code Automatic serialisation of attributes Listening to attribute modifications (e.g. OnValueChanged)

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