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• IPhone CoreData: How should I relate many child entities to thier parents

  - by Robert

  I am trying to import data from a database that uses primary key / forign key relations to a core data database in Xcode. I have code that creates hundreds of child entities in a managed object context: Each child has an ID that corresponds to a parent. child1 parentID = 3 child2 parentID = 17 child3 parentID = 17 ... childn parentID = 5 I now need to relate each child to its parent. The parents are all stored in persistent memory. My first thought was to preform a fetch for each child to get its parent. However, I think this would be slow. Am I correct? How should I do this instead?

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• Getting list of all existing vtables.

  - by Patrick

  In my application I have quite some void-pointers (this is because of historical reasons, application was originally written in pure C). In one of my modules I know that the void-pointers points to instances of classes that could inherit from a known base class, but I cannot be 100% sure of it. Therefore, doing a dynamic_cast on the void-pointer might give problems. Possibly, the void-pointer even points to a plain-struct (so no vptr in the struct). I would like to investigate the first 4 bytes of the memory the void-pointer is pointing to, to see if this is the address of the valid vtable. I know this is platform, maybe even compiler-version-specific, but it could help me in moving the application forward, and getting rid of all the void-pointers over a limited time period (let's say 3 years). Is there a way to get a list of all vtables in the application, or a way to check whether a pointer points to a valid vtable, and whether that instance pointing to the vtable inherits from a known base class?

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• How do I write a Java text file viewer for big log files

  - by Hannes de Jager

  I am working on a software product with an integrated log file viewer. Problem is, its slow and unstable for really large files because it reads the whole file into memory when you view a log file. I'm wanting to write a new log file viewer that addresses this problem. What are the best practices for writing viewers for large text files? How does editors like notepad++ and VIM acomplish this? I was thinking of using a buffered Bi-directional text stream reader together with Java's TableModel. Am I thinking along the right lines and are such stream implementations available for Java?

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• what mysql table structure is better

  - by Sergey

  I have very complicated search algorithm on my site, so i decided to make a table with cache or maybe all possible results. I wanna ask what structure would be better, or maybe not the one of them? (mySQL) 1) word VARCHAR, results TEXT or BLOB where i'll store ids of found objects (for example 6 chars for each id) 2) word VARCHAR, result INT, but words are not unique now i think i'll have about 200 000 rows in 1) with 1000-10000 ids each row or 200 000 000+ rows in 2) First way takes more storage memory but i think it would be much faster to find 1 unique row among 200 000, than 1000 rows among 200 mln non unique rows i think about index on word column and no sphinx. So that do YOU think? p.s. as always, sorry for my english if it's not very good.

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• Undefined behaviour with non-virtual destructors - is it a real-world issue?

  - by Roddy

  Consider the following code: class A { public: A() {} ~A() {} }; class B: public A { B() {} ~B() {} }; A* b = new B; delete b; // undefined behaviour My understanding is that the C++ standard says that deleting b is undefined behaviour - ie, anything could happen. But, in the real world, my experience is that ~A() is always invoked, and the memory is correctly freed. if B introduces any class members with their own destructors, they won't get invoked, but I'm only interested in the simple kind of case above, where inheritance is used maybe to fix a bug in one class method for which source code is unavailable. Obviously this isn't going to be what you want in non-trivial cases, but it is at least consistent. Are you aware of any C++ implementation where the above does NOT happen, for the code shown?

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• Do you bother to write a pretty error page?

  - by Chacha102

  So, everyone is really used to the errors that PHP gives you. They look kind of like this: Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to allocate 2 bytes) in /path/to/file(437) on line 21 My question is, do you put in the time to make your error pages more useful? I find that I am able to debug a lot faster using my own error page: I find this to be a lot better than the PHP errors because it gives me a stack trace, the usual error message, along with the actual location of the error, and more. Also, are there any downsides from creating your own development error pages. Obviously you wouldn't want to have a user see this page, but what about during development?

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• Less Mathematical Approaches to Machine Learning?

  - by Ed

  Out of curiosity, I've been reading up a bit on the field of Machine Learning, and I'm surprised at the amount of computation and mathematics involved. One book I'm reading through uses advanced concepts such as Ring Theory and PDEs (note: the only thing I know about PDEs is that they use that funny looking character). This strikes me as odd considering that mathematics itself is a hard thing to "learn." Are there any branches of Machine Learning that use different approaches? I would think that a approaches relying more on logic, memory, construction of unfounded assumptions, and over-generalizations would be a better way to go, since that seems more like the way animals think. Animals don't (explicitly) calculate probabilities and statistics; at least as far as I know.

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• Linq To Sql Entity Updated from Trigger

  - by James Helms

  I have a Table called Address. I have a Trigger for insert on that table that does some spacial calculations on the address that determines what neighborhood boundaries it is in. address = new Address { Street = this.Street, City = this.City, State = this.State, ZipCode = this.ZipCode, latitude = this.Latitude, longitude = this.Longitude, YearBuilt = this.YearBuilt, LotSize = this.LotSize, FinishedSize = this.FinishedSize, Bedrooms = this.Bedrooms, Bathrooms = this.Bathrooms, UseCode = this.UseCode, HOA = this.HOA, UpdateDate = DateTime.Now }; db.AddToAddresses(address); db.SaveChanges(); In the database i can clearly see that the Trigger ran and updated the neighborhoodID in the address table for the row. I tried to just reload that record to get the assigned id like this: address = (from a in db.Addresses where a.AddressID == address.AddressID select a).First(); In the debugger i can clearly see that the address.AddressID is correct, entity doesn't update in memory. Is there any work around for this?

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• Processing large recordsets in Rails

  - by japancheese

  Hello, I'm trying to perform a daily operation on a larger than normal dataset (2m+ records). However, Rails seems to take a very long time performing operations on such a dataset. Operations like Dataset.all.each do |data| ... end take a very long time to complete (I assume this is because it can't fit all the items into memory at once, right?). Does anyone have any strategies on how I could handle this situation? I know SQL would probably speed up the process, but I'm looking to use the Rails environment as I can do many more complicated things to the data than I can with just SQL statements.

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• Way around ASP.NET session being shared across multiple tab windows

  - by ace

  I'm storing some value in an asp.net session on the first page. On the next page, this session value is being read. However if multiple tabs are opened and there are multiple page 1-page 2 navigation going on, the value stored in session gets mixed up since the session is shared between the browser tabs. I'm wondering what are the options around this : Query String: Passing value between the pages using query string, I don't want to take this approach since there can be multiple anchor tags on page 1 linking to page 2 and I can not rewrite the URLs of each tag since they are dynamic. Cookies??? In-memory cookies are shared across browser tabs too, same as the session cookie, rite ? Any other option?

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• C string program

  - by mrblippy

  Hi, i have been given a task to do ar school that must read three strings in, store the third string in dynamically allocated memory and print out the last 4 letters of the first word alphabetically. Here is the program i have so far but the strings are all stored in different variables, making them hard to sort. if anyone could give me a hand and help me finish this program i would be very grateful. thanks #include <stdio.h> #include <stdlib.h> #include <string.h> int main() { char word1[101]; char word2[101]; char* word3; char buffer[101]; scanf("%s", word1); scanf("%s", word2); scanf("%s", buffer); word3 = (char *) malloc(strlen(buffer)+1); strcpy(word3, buffer); return 0; }

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• How can one use multi threading in php applications

  - by Steve Obbayi

  Is there a realistic way of implementing a multi-threaded model in php whether truly or just simulating it. Some time back it was suggested that you can force the operating system to load another instance of the php executable and handle other simultaneous processes. The problem with this is that when the php code finished executing the php instance remains in memory because there is no way to kill it from within php. so if you are simulating several threads you can imagine whats going to happen. So am still looking for a way multi-threading can be done or simulated effectively from within php. Any ideas?

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• Table Variables in SSIS

  - by aceinthehole

  In one SQL Task can I create a table variable DELCARE @TableVar TABLE (...) Then in another SQL Task or DataSource destination and select or insert into the table variable? The other option I have considered is using a Temp Table. CREATE TABLE #TempTable (...) I would prefer to use Table Variable so that it remains in memory. But can use temp table if it is not possible to use table variable. Also I cannot use the record set destination as I need to preform straight SQL tasks on it later on.

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• Linq to SQL and Realtime Data

  - by Jeremy

  I have an application that needs to constantly (every 50ms), call to an MVC action, and pickup/drop off data. I am using Linq to SQL and MVC because of how simple they are to implement, and I know that they aren't perfect when it comes to performance, but it works relatively well, but the best speed I can get with my current approach is 200ms (without requests overlapping). Each call to the site will create a new instance of the datacontext, query/insert it and return that data. Is there a way to have the datacontext static, but submitchanges say every 5 seconds, so that i am pretty much hitting an in-memory version of the data?

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• What's a good place to unregister an observer from the notification center?

  - by mystify

  When I add an observer to the default notification center, where would I unregister that? Example: I have a UIView subclass which lives inside a view controller. That subclass is an observer for the FooBarNotification. If this notification is posted, that view will get it. But now, the view controller decides to throw away the view. Is the best place the -dealloc method of the view itself? Are there any rules like memory management rules? For example: Must I unregister an observer where I registered it? i.e. the view registers itself in it's init method, so it should unregister itself in it's -dealloc method? (not talking about push notifications, but NSNotificationCenter)

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• How to deal with callback to your UIController after your UIController unloads?

  - by erotsppa

  Suppose your controller is a table view and one of the cells you are going off to do a length task (say download a thumbnail) to be viewed in the cell. Typically you would have the network call do a callback to your controller when it is done downloading. The callback can then reload the table or do some other form of UI update (hides a spinner etc). However, what if the controller is unloaded? Say the user navigated away from this controller and it got released? What happens? Will the callback still work despite the controller now not in memory? Also, if the callback operates on some objects (say the UITableView) what happens when the controller is deallocated? I suppose the controller can release all the objects and the callback would just be calling methods on nil to prevent crash. But is this the convention?

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• Netbeans or Eclipse for C++?

  - by Robert Gould

  I'm currently working on a pet project and need to do C++ development on Windows, Mac, Linux, and Solaris, and I've narrowed it down to Netbeans and Eclipse, so I was wonderig which is more solid as a C++ editor. I just need solid editing, good autocompletion for templated code ad external libraries, and project file management, the build tools are external, so thats irrelevant here, for my comparison. Thus which is a better choice? Note: I know I should be using emacs or vim, but the issue is, my theory at least, that I'm left handed, so I use my right side (design,creativity) of the brain more than the left side (logic, memory), so I just simply cannot use emacs or vim, my brain simply isn't compatible, I tried them many times too, even used emacs for a few months but it drove me crazy... Thanks

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• iPhone xcode array losing state after load

  - by Frames84

  Right i've had a search around and can't find anything. @synthesize list; // this is an NSArry -(void) viewDidLoad { NSArray *arr = [self getJSONFeed]; self.List = [arr retain]; // if i copy the access code into here it works fine. } -(void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { NSUInteger row = [indexPath row]; NSArray *vals = [list objectAtIndex:row] retain]; NSString *id = [vals valueForKey:@"id"]; // ERROR } right i've taken some of the code to try and provide it as simple as possible, ignore typo's and memory leaks this is sorted. Basically when I select a row I can't get data out of my 'list' array object. Please can anyone help me out?

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• Recognize active objects with a capacitive touch screen display

  - by lucgian84

  I'm trying to develop an app that can recognize an active object (for example: a memory) that touch the smartphone display. Before I start to develop I've to know if there's any objects that my touch screen display can recognize? Which device can be recognizable by a smartphone display? I'm interested to know that for iPhone or for Android phone. I found this app and you can see that with a card I can interact with a mobile device, now I'm asking you if anyone know how to do this kind of app with an iPhone or with an Android phone. Does anyone knows how to do that? There's a library (iOS or Android) to recognize object that I put over the display?

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• C++ boost thread id and Singleton

  - by aaa

  hi. Sorry to flood so many questions this week. I assume thread index returned by thread.get_id is implementation specific. In case of the pthreads, is index reused? IE, if thread 0 runs and joins, is thread launched afterwords going to have a different ID? the reason I ask this is a need to implement Singleton pattern with a twist: each thread gets its own instance. I know it sounds very crazy, but threads control hardware (cuda) which does not permit device memory sharing. What is a good way to implement such pattern?

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• whats wrong with this piece of code for saving contacts

  - by Shadow

  Hi, i am using the latest Nokia Qt SDK. i have tried to add the contacts, its not getting added.. what is missing here.. // Construct contact manager for default contact backend QContactManager* cm = new QContactManager("simulator"); // QContactManager* cm = new QContactManager("memory"); // i tried this, its also not working // Create example contact QContact example; // Add contact name QContactName name; name.setFirstName("John"); name.setLastName("Doe"); example.saveDetail(&name); // Add contact email address //QContactEmailAddress email; // email.setContexts(QContactDetail::ContextHome); //email.setEmailAddress(“[email protected]”); // example.saveDetail(&email); // Finally, save the contact details cm->saveContact(&example); delete cm; Thanks

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• Is it safe to take the address of std::wstring's internal pointer?

  - by LCC

  I have an interface which is used like the following: if (SUCCEEDED(pInterface->GetSize(&size)) { wchar_t tmp = new wchar_t[size]; if (SUCCEEDED(pInterface->GetValue(tmp, size))) { std::wstring str = tmp; // do some work which doesn't throw } delete[] tmp; } Is it safe and portable to do this instead? if (SUCCEEDED(pInterface->GetSize(&size)) { std::wstring str; str.resize(size); if (SUCCEEDED(pInterface->GetValue(&str[0], size))) { // do some work } } Now, obviously this works (doesn't crash/corrupt memory) or I wouldn't have asked, but I'm mostly wanting to know if there's a compelling reason not to do this.

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• How do stream rows from a MSSQL table into a .NET app, in 10000 row chunks?

  - by Gravitas

  I have a table with 300 million rows in Microsoft SQL Server 2008 R2. There is a clustered index on the date column [DataDate] which means that the entire table is ordered by the date column. How do I stream out the data from this table, into my .NET application, in 10000 row chunks? Environment: Using C#. Have to be able to pause the data stream at any point, to allow the client to process the rows. Unfortunately, cannot use a select * from as this will select the entire table (its 50GB - it won't fit into memory).

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• Streaming large result sets with MySQL

  - by configurator

  I'm developing a spring application that uses large MySQL tables. When loading large tables, I get an OutOfMemoryException, since the driver tries to load the entire table into application memory. I tried using statement.setFetchSize(Integer.MIN_VALUE); but then every ResultSet I open hangs on close(); looking online I found that that happens because it tries loading any unread rows before closing the ResultSet, but that is not the case since I do this: ResultSet existingRecords = getTableData(tablename); try { while (existingRecords.next()) { // ... } } finally { existingRecords.close(); // this line is hanging, and there was no exception in the try clause } The hangs happen for small tables (3 rows) as well, and if I don't close the RecordSet (which happened in one method) then connection.close() hangs.

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