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  • Efficient storage/retrieval method for replayable comet style applications (Google Wave, Etherpad)

    - by Gareth Simpson
    I am considering a web application that would have the same kind of multi user, automatic saving, infinite undo / replay capabilities that you see in Google Wave and Etherpad (albeit on a drastically smaller scale and userbase). Before I go away and reinvent the wheel, is this something that has already been addressed as either a piece of technology or library, or even just a design pattern. I know this isn't necessarily the best Stack Overflow question as there is probably not a "right" answer, but my Google-fu has failed me and I'd just like a reading list! Ordinarily I would be developing under python/django but this is not a firm requirement just a preference :)

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  • C: getopt with list of acceptable optarg. What is the best practise ?

    - by Xavier Maillard
    Hi, I am writing a C program which is a frontend to a myriad tools. This fronted will be launched like this: my-frontend --action <AN ACTION> As all the tools have the same prefix, let say for this example this prefix is "foo". I want to concatenate "AN ACTION" to this prefix and exec this (if the tool exists). I have written something but my implementation uses strcmp to test that "AN ACTION" is a valid action. Even if this works, I do not like it. So I am looking for a nicer solution that would do the same. The list of possibilities is pretty small (less than 10) and static (the list is "hardcoded") but I am sure there is a more "C-ish" way to do this (using a struct or something like that). As I am not a C expert, I am asking for your help. Regards

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  • What is the Action returned by the subscribe parameter of IObservable.Create actually for?

    - by James Hay
    The method definition of IObservable.Create is: public static IObservable<TSource> Create<TSource>( Func<IObserver<TSource>, Action> subscribe ) I get that the function is called once the observable is subscribed to, where by I can then call OnNext, OnError and OnComplete on the observer. But why do I need to return an Action from the subscibe parameter and when will it actually be called?

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  • Encapsulating user input of data for a class (C++)

    - by Dr. Monkey
    For an assignment I've made a simple C++ program that uses a superclass (Student) and two subclasses (CourseStudent and ResearchStudent) to store a list of students and print out their details, with different details shown for the two different types of students (using overriding of the display() method from Student). My question is about how the program collects input from the user of things like the student name, ID number, unit and fee information (for a course student) and research information (for research students): My implementation has the prompting for user input and the collecting of that input handled within the classes themselves. The reasoning behind this was that each class knows what kind of input it needs, so it makes sense to me to have it know how to ask for it (given an ostream through which to ask and an istream to collect the input from). My lecturer says that the prompting and input should all be handled in the main program, which seems to me somewhat messier, and would make it trickier to extend the program to handle different types of students. I am considering, as a compromise, to make a helper class that handles the prompting and collection of user input for each type of Student, which could then be called on by the main program. The advantage of this would be that the student classes don't have as much in them (so they're cleaner), but also they can be bundled with the helper classes if the input functionality is required. This also means more classes of Student could be added without having to make major changes to the main program, as long as helper classes are provided for these new classes. Also the helper class could be swapped for an alternative language version without having to make any changes to the class itself. What are the major advantages and disadvantages of the three different options for user input (fully encapsulated, helper class or in the main program)?

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  • creative way for implementing Data object with its corresponding business logic class in java

    - by ekeren
    I have a class that need to be serialized (for both persistentcy and client-server communication) for simplicity's sake let's call the classes Business a BusinessData and I prefix for their Interfaces. All the getter and setter are delegated from Business class to BusinessData class. I thought about implementing IBusinessData interface that will contain all the getter and setters and IBusiness interface that will extend it. I can either make Business extend BuisnessData so I will not need to implement all getter and setter delegates, or make some abstract class ForwardingBusinessData that will only delegate getter and setters. Any of the above option I lose my hierarchy freedom, do any of you have any creative solutions for this problem... I also reviewed DAO pattern: http://java.sun.com/blueprints/patterns/DAO.html

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  • Unable to get data from a WCF client

    - by Scott
    I am developing a DLL that will provide sychronized time stamps to multiple applications running on the same machine. The timestamps are altered in a thread that uses a high performance timer and a scalar to provide the appearance of moving faster than real-time. For obvious reasons I want only 1 instance of this time library, and I thought I could use WCF for the other processes to connect to this and poll for timestamps whenever they want. When I connect however I never get a valid time stamp, just an empty DateTime. I should point out that the library does work. The original implementation was a single DLL that each application incorporated and each one was synced using windows messages. I'm fairly sure it has something to do with how I'm setting up the WCF stuff, to which I am still pretty new. Here are the contract definitions: public interface ITimerCallbacks { [OperationContract(IsOneWay = true)] void TimerElapsed(String id); } [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ITimerCallbacks))] public interface ISimTime { [OperationContract] DateTime GetTime(); } Here is my class definition: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] public class SimTimeServer: ISimTime The host setup: // set up WCF interprocess comms host = new ServiceHost(typeof(SimTimeServer), new Uri[] { new Uri("net.pipe://localhost") }); host.AddServiceEndpoint(typeof(ISimTime), new NetNamedPipeBinding(), "SimTime"); host.Open(); and the implementation of the interface function server-side: public DateTime GetTime() { if (ThreadMutex.WaitOne(20)) { RetTime = CurrentTime; ThreadMutex.ReleaseMutex(); } return RetTime; } Lastly the client-side implementation: Callbacks myCallbacks = new Callbacks(); DuplexChannelFactory pipeFactory = new DuplexChannelFactory(myCallbacks, new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/SimTime")); ISimTime pipeProxy = pipeFactory.CreateChannel(); while (true) { string str = Console.ReadLine(); if (str.ToLower().Contains("get")) Console.WriteLine(pipeProxy.GetTime().ToString()); else if (str.ToLower().Contains("exit")) break; }

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  • array of structures, or structure of arrays?

    - by Jason S
    Hmmm. I have a table which is an array of structures I need to store in Java. The naive don't-worry-about-memory approach says do this: public class Record { final private int field1; final private int field2; final private long field3; /* constructor & accessors here */ } List<Record> records = new ArrayList<Record>(); If I end up using a large number ( 106 ) of records, where individual records are accessed occasionally, one at a time, how would I figure out how the preceding approach (an ArrayList) would compare with an optimized approach for storage costs: public class OptimizedRecordStore { final private int[] field1; final private int[] field2; final private long[] field3; Record getRecord(int i) { return new Record(field1[i],field2[i],field3[i]); } /* constructor and other accessors & methods */ } edit: assume the # of records is something that is changed infrequently or never I'm probably not going to use the OptimizedRecordStore approach, but I want to understand the storage cost issue so I can make that decision with confidence. obviously if I add/change the # of records in the OptimizedRecordStore approach above, I either have to replace the whole object with a new one, or remove the "final" keyword. kd304 brings up a good point that was in the back of my mind. In other situations similar to this, I need column access on the records, e.g. if field1 and field2 are "time" and "position", and it's important for me to get those values as an array for use with MATLAB, so I can graph/analyze them efficiently.

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  • Cakephp, Retreive Data for HABTM Models using find

    - by user298079
    I am new to cakephp and I'm trying to accomplish something that should be relatively easy. I have 2 models projects & categories bind by HABTM relationship. I am trying to perform the following query - find all projects that belong to a category $projects = $this->Project->find('all', array('conditions' => array('Category.slug' => $category))); However when I'm doing so it generates an SQL error: SQL Error: 1054: Unknown column 'Category.slug' in 'where clause' What am I doing wrong??

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  • get data from asp page

    - by sam
    I am wondering if there is anyway to grab the html that is generated from an ASP page. I am trying to pull a table from the page, and I foolishly used a static html page so I would not have to be constantly querying the server where this page resides while I tested out my code. The javascript code I wrote to grab to unlabeled table from the page works. Then when I put it into practice with the real page and found that the ASP page does not generate a viewable page with a jquery .get request on the URL. Is there any way to query the page for the table I need so that the ASP page returns a valid page on request? (I am also limited to using javascript and perl for this, the server where this will reside will not run php and I have no desire to learn ASP.NET to solve this by adding to the issue of proprietary software)

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  • How to create a clip region from a path that includes the 'outline'?

    - by mackenir
    I am creating a rounded rectangle GraphicsPath (see red outline image below), and then using this as a clip region both when drawing graphics, and as the Region of a Form. Unfortunately, although the path looks good, it doesn't work well as a region (see solid black image below) Is there a way that I can generate a clipping region from the path that includes all the 'outline' pixels of the path? Do I need to generate a bitmap and then process this to create a region? The rounded rectangle path: When used as a clip region: The discrepancy (red pixels are in the path outline, but outside the region. blue pixels are in both):

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  • Checking status after wait()

    - by Helper Method
    After creating a child process and exiting it immediately (_exit()), I want to perform a wait and check the status. Now I wonder if in the 'else' branch of the if/else construct I also need to check for WIFSIGNALED. As far as I understand, if I perform a wait, a) an error could have occured (-1), the child could have terminated normally by an (exit() or _exit()), or it could have been terminated by a signal, so the check could be omitted, right? //remainder omitted int status; pid_t t_pid = wait(&status); if (t_pid == -1) { perror("wait"); exit(EXIT_FAILURE); } if (WIFEXITED(status)) { printf("child terminated normally, status = %d\n", WEXITSTATUS(status) ); } else { // <-- do it have to check for WIFSIGNALED() here? printf("child was terminated by a signal, signum = %d\n", WTERMSIG(status) ); }

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  • Multiple Actions (Forms) on one Page - How not to lose master data, after editing detail data?

    - by nWorx
    Hello all, I've got a form where users can edit members of a group. So they have the possibilty to add members or remove existing members. So the Url goes like ".../Group/Edit/4" Where 4 is the id of the group. the view looks like this <% using (Html.BeginForm("AddUser", "Group")) %> <%{%> <label for="newUser">User</label> <%=Html.TextBox("username")%> <input type="submit" value="Add"/> </div> <%}%> <% using (Html.BeginForm("RemoveUser", "Group")) %> <%{%> <div class="inputItem"> <label for="groupMember">Bestehende Mitglieder</label> <%= Html.ListBox("groupMember", from g in Model.GetMembers() select new SelectListItem(){Text = g}) %> <input type="submit" value="Remove" /> </div> <%}%> The problem is that after adding or removing one user i lose the id of the group. What is the best solution for solving this kind of problem? Should I use hidden fields to save the group id? Thanks in advance.

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  • String or binary data would be truncated -- Heisenberg problem

    - by harpo
    When you get this error, the first thing you ask is, which column? Unfortunately, SQL Server is no help here. So you start doing trial and error. Well, right now I have a statement like: INSERT tbl (A, B, C, D, E, F, G) SELECT A, B * 2, C, D, E, q.F, G FROM tbl ,othertable q WHERE etc etc Note that Some values are modified or linked in from another table, but most values are coming from the original table, so they can't really cause truncation going back to the same field (that I know of). Eliminating fields one at a time eventually makes the error go away, if I do it cumulatively, but — and here's the kicker — it doesn't matter which fields I eliminate. It's as if SQL Server is objecting to the total length of the row, which I doubt, since there are only about 40 fields in all, and nothing large. Anyone ever seen this before? Thanks. UPDATE: I have also done "horizontal" testing, by filtering out the SELECT, with much the same result. In other words, if I say WHERE id BETWEEN 1 AND 100: Error WHERE id BETWEEN 1 AND 50: No error WHERE id BETWEEN 50 AND 100: No error I tried many combinations, and it cannot be limited to a single row.

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  • hibernate not throwing stale state exception nor it is overwriting data

    - by Reddy
    Our application do the following. 1. Start the transaction. 2. Execute a query using prepared statement 3. Check a condition to see the number of rows updated are equal to the required number. 4. It commits on success of above condition otherwise it will roll back However the problem is that when two threads are simultaneously enter this code. Thread-1 is updating a row in step 2. It checked the condition and committed successfully since the condition is successful. Thread-2 started execution somewhere between steps 1 & 4, and it is failing on at condition checking at step 3 (as it is getting number of updated rows as 0). I expected second thread to throw an exception but it is not. What could be the problem?

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  • Group MySQL Data into Arbitrarily Sized Time Buckets

    - by Eric J.
    How do I count the number of records in a MySQL table based on a timestamp column per unit of time where the unit of time is arbitrary? Specifically, I want to count how many record's timestamps fell into 15 minute buckets during a given interval. I understand how to do this in buckets of 1 second, 1 minute, 1 hour, 1 day etc. using MySQL date functions, e.g. SELECT YEAR(datefield) Y, MONTH(datefield) M, DAY(datefield) D, COUNT(*) Cnt FROM mytable GROUP BY YEAR(datefield), MONTH(datefield), DAY(datefield) but how can I group by 15 minute buckets?

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  • How to bind a complex dictionary to a Gridview in asp.net?

    - by Mehdi
    I've used an early binding of a dictionary<string, string> to a gridview to show Urls Text and its HRef as key-value and it works like a charm. But since I want to replace the dictionary with this one : dictionary<string, LinkInfo> the binding goes wrong! Should I handle some events like as onItemDataBound or something? and the LinkInfo structure is: public struct LinkInfo{ public string href; public bool Enabled; }

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  • Fastest way to represent a collection of bits in PHP?

    - by Piskvor
    What is a good way to represent a collection of bits? I have a set of various on/off toggles (thousands of them) and need to store and retrieve their state. The naïve implementation would be an array of booleans, but I'm wondering if there's a better way (better in terms of access speed and/or memory requirements). I've found this BitArray implementation, but it's limited to 32 bits, which is not enough for this case.

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  • advanced python autovivification

    - by Zhang18
    This question is about implementing the full PERL autovivification in python. I know similary questions were asked before and so far the best answre is http://stackoverflow.com/questions/635483/what-is-the-best-way-to-implement-nested-dictionaries-in-python/652284#652284. However, I'm looking to do this: a['x']['y'].append('z') without declaring a['x']['y'] = [] first, or rather, not declaring a['x'] = {} either. I know dict and list classes sorta don't mix so this is hard, but I'm interested in seeing if someone has an ingenius solution probably involving creating an inherited class from dict but defined a new append method on it? I also know this might throw off some python purists who will ask me to stick with Perl. But even just for a challenge, I'd like to see something. thx!

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  • reRendering is not happening in jsf using data table

    - by palakolanusrinu
    HI, Rerendering is not working in my code please help in this <rich:dataTable id="bookIncome" value="#{myBean.ftBoookIncomelst}" var="item" rowKeyVar="row" first="0" width="100%"> <rich:subTable id="subBookIncome"value="#{item.txIncome}" var="income" rowKeyVar="row"> <rich:column id="descrtiptionColumn" width="30%"> <h:outputText value="#{income.descriptionCell.value}" rendered="#{!item.editableRow}" style="#{income.descriptionCell.boldClass}"> </h:outputText> <rich:inplaceInput layout="block" value="#{income.descriptionCell.value}" required="true" rendered="#{item.editableRow}" requiredMessage="Description at row #{row+1} wasn't filled." changedHoverClass="hover" viewHoverClass="hover" viewClass="inplace" changedClass="inplace" selectOnEdit="true" editEvent="onclick"> </rich:inplaceInput> In the above code i have proper id for datatable and i'm calling my ajax call using But its not showing any response but its hitting the server and its calling proper method and updating the required list also..Please help in this why its not rendering its not showing any exception on console also...

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  • list or container O(1)-ish insertion/deletion performance, with array semantics

    - by Chris Kaminski
    I'm looking for a collection that offers list semantics, but also allows array semantics. Say I have a list with the following items: apple orange carrot pear then my container array would: container[0] == apple container[1] == orangle container[2] == carrot Then say I delete the orange element: container[0] == apple container[1] == carrot I don't particularly care if sort order is maintained, I'd just like the array values to function as accelerators to the list items, and I want to collapse gaps in the array without having to do an explicit resizing.

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  • Getting RAW Soap Data from a Web Reference Client running in ASP.net

    - by Harry
    I'm trying to trouble shoot a web service client in my current project. I'm not sure of the platform of the Service Server (Most likely LAMP). I believe there is a fault on their side of the fence as i have eliminated the potential issues with my client. The client is a standard ASMX type web reference proxy auto generated from the service WSDL. What I need to get to is the RAW SOAP Messages (Request and Responses) What is the best way to go about this?

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