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• Visual Studio 2010 Bootstrap Folder?

  - by Matma

  We currently run a VS2005 app/environment and im investigating upgrading to 2010. But before i can say yes its all good, go buy bossman... I have to confirm that a bootstrap for a thridparty driver install which is included on our installation cd can be used/included (its a usb security dongle so drivers MUST be included/setup for our app to run). It is in the list of available pre-reqs but i didnt put it in the vs2010 bootstrap folder so is this coming from my vs2005 install? or the fact that i had previously selected it in the installer and its saved/loaded that in vs2010? Either way its got a little error icon and says its not found so i get errors on build. I want to resolve this and have it in the list of available pre-reqs as we did for 2005. i.e. copy it to the C:\Program Files (x86)\Microsoft Visual Studio 8\SDK\v2.0\BootStrapper folder... But i cant seem to find where the bootstraps are for vs2010? does it not use them? Naturally ive searched the entire vs folder structure for appropriate files/folders but nothing? Where/How is this now done?

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• can I put my sqlite connection and cursor in a function?

  - by steini

  I was thinking I'd try to make my sqlite db connection a function instead of copy/pasting the ~6 lines needed to connect and execute a query all over the place. I'd like to make it versatile so I can use the same function for create/select/insert/etc... Below is what I have tried. The 'INSERT' and 'CREATE TABLE' queries are working, but if I do a 'SELECT' query, how can I work with the values it fetches outside of the function? Usually I'd like to print the values it fetches and also do other things with them. When I do it like below I get an error Traceback (most recent call last): File "C:\Users\steini\Desktop\py\database\test3.py", line 15, in <module> for row in connection('testdb45.db', "select * from users"): ProgrammingError: Cannot operate on a closed database. So I guess the connection needs to be open so I can get the values from the cursor, but I need to close it so the file isn't always locked. Here's my testing code: import sqlite3 def connection (db, arg): conn = sqlite3.connect(db) conn.execute('pragma foreign_keys = on') cur = conn.cursor() cur.execute(arg) conn.commit() conn.close() return cur connection('testdb.db', "create table users ('user', 'email')") connection('testdb.db', "insert into users ('user', 'email') values ('joey', 'foo@bar')") for row in connection('testdb45.db', "select * from users"): print row How can I make this work?

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• Ruby on Rails: Uploading a modifed site.

  - by Califer

  I'm having a heck of a time getting a site I modified to work correctly. I didn't set the site up originally, and since the person that set it up no longer works with me I had to learn ruby just to make some changes. I made all the changes in the development server and everything worked fine. Then I did a diff on the production and development and moved only my changes over. Unfortunately when I loaded my changes onto the production server I got a lot of errors. I've changed all of the permissions to 755, which took care being able to access anything at all, but after that I started getting a lot of 500 errors. Nothing showed up in the production.log file. I really have no clue what's going wrong except that perhaps things are not noticing the new changes. I moved the old site to a backup folder, and the new site crashes whenever it goes to anything that I've changed. In particular, I added a link to a new setup with an extra controller/model/view group. It works fine on development but in production it gives me a 404. Yes, I did copy all the files up. I even put everything back how it was, but the website is still showing the broken version of it. I checked the tmp/cache folder but it was empty. Running dispatch.fcgi shows the old site (which I expected) but it still shows the flawed new site when I connect through a browser. I've been tearing my hair out trying to get this to work. Any ideas as to how I can get this to work?

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• Hosting an Access DB

  - by Mitciv

  Hey, So I'm inexperienced in hosting DB's and I've always had the luxury of someone else getting the db setup. I was going to help a friend out with getting a webpage setup, I've got experience in Asp.Net MVC so I'm going with that. They want to setup a search page to query a db and display the results. My question I have is in getting the DB setup and hosted. They currently just have the Access DB on a local computer. There is basically only one table that would need to be queried for the search. What is the best approach to getting this table/db accessible? They would like to keep the main copy of the db on the local machine, so copying the entire db over to the hosted site would be time consuming, could the lone table needed be solely copied to the host? Should I try to convince them to make changes on the hosted db and just make copies of that for their local machines? Any suggestions are welcome, Again I'm a total noob when it comes to hosting databases. Thanks

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• [Java] Safe way of exposing keySet().

  - by Jake

  This must be a fairly common occurrence where I have a map and wish to thread-safely expose its key set: public MyClass { Map<String,String> map = // ... public final Set<String> keys() { // returns key set } } Now, if my "map" is not thread-safe, this is not safe: public final Set<String> keys() { return map.keySet(); } And neither is: public final Set<String> keys() { return Collections.unmodifiableSet(map.keySet()); } So I need to create a copy, such as: public final Set<String> keys() { return new HashSet(map.keySet()); } However, this doesn't seem safe either because that constructor traverses the elements of the parameter and add()s them. So while this copying is going on, a ConcurrentModificationException can happen. So then: public final Set<String> keys() { synchronized(map) { return new HashSet(map.keySet()); } } seems like the solution. Does this look right?

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• How to "wrap" implementation in C#

  - by igor

  Hello, I have these classes in C# (.NET Framework 3.5) described below: public class Base { public int State {get; set;} public virtual int Method1(){} public virtual string Method2(){} ... public virtual void Method10(){} } public class B: Base { // some implementation } public class Proxy: Base { private B _b; public class Proxy(B b) { _b = b; } public override int Method1() { if (State == Running) return _b.Method1(); else return base.Method1(); } public override string Method2() { if (State == Running) return _b.Method2(); else return base.Method2(); } public override void Method10() { if (State == Running) _b.Method10(); else base.Method10(); } } I want to get something this: public Base GetStateDependentImplementation() { if (State == Running) // may be some other rule return _b; else return base; // compile error } and my Proxy's implementation will be: public class Proxy: Base { ... public override int Method1() { return GetStateDependentImplementation().Method1(); } public override string Method2() { return GetStateDependentImplementation().Method2(); } ... } Of course, I can do this (aggregation of base implementation): public RepeaterOfBase: Base // no any overrides, just inheritance { } public class Proxy: Base { private B _b; private RepeaterOfBase _Base; public class Proxy(B b, RepeaterOfBase aBase) { _b = b; _base = aBase; } } ... public Base GetStateDependentImplementation() { if (State == Running) return _b; else return _Base; } ... But instance of Base class is very huge and I have to avoid to have other additional copy in memory. So I have to simplify my code have to "wrap" implementation have to avoid a code duplication have to avoid aggregation of any additional instance of Base class (duplication) Is it possible to reach these goals?

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• A generic error has occurred in GDI+

  - by sysigy

  I know this has been asked a million times but I think I need to make it a million and one. I am getting "A generic error has occurred in GDI+" when trying to save a new bitmap. I have completely stripped down to the most basic lines of code and I still get the error with the following method: public class HomeController : Controller { public ActionResult Index() { return this.View(); } public void CreatePicture() { try { // THIS WORKS System.IO.File.Copy("C:\\copyTest.bmp", "C:\\test folder\\copyTest2.bmp"); // THIS WORKS System.IO.File.Delete("C:\\test folder\\deleteTest.bmp"); using (Bitmap newBitmap = new Bitmap(120, 120)) { // THIS FAILS newBitmap.Save("C:\\test folder\\test.bmp", ImageFormat.Bmp); } } catch (Exception ex) { throw ex; } } } The code is called from an html link on a blank page within an MVC 3.0 website using anonymous login. View: @Html.ActionLink("Create Picture", "CreatePicture", "Home", new { }) I have checked the folder permissions of "test folder" and have given full access to the following: ASPNET NETWORK SERVICE IUSR I still get the error... what have I missed / done wrong ?

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• asmx web service returning xml instead of json in .net 4.0

  - by Baldy

  i have just upgraded a test copy of my site to asp.net 4.0 and have noticed a strange issue that only arises when i upload the site to my server. the site has an asmx web service that returns json, yet when i run the site on my server it returns xml. it as been working fine in asp.net 3.5 for over a year. the webMethod is decorated with the correct attributes... [WebMethod][ScriptMethod(ResponseFormat = ResponseFormat.Json)] public List<LocationRecentChange> RecentChanges() and on my local machine it returns json. yet on the server (Windows 2008 64bit) it returns xml. you can inspect the response on the test site here... my test site using firebug console you will see a 200 OK response and a bunch of XML, and on my local machine the data returned is the JSON i expect. Here is the javascript that calls the service.. function loadRecentData() { $.ajax({ type: "POST", url: "service/spots.asmx/RecentChanges", data: "{}", contentType: "application/json; charset=utf-8", dataType: "json", success: loadRecentUpdates, failure: function(msg) { //alert(msg); } }); } Any suggestions welcome, this has got me stumped!

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• Redeploying an ASP.NET site in IIS7 without files in use interfering

  - by fyjham

  Hey, We've got a process currently which causes ASP.NET websites to be redeployed. The code is itself an ASP.NET application. The current method, which has worked for quite a while, is simply to loop over all the files in one folder and copy them over the top of the files in the webroot. The problem that's arisen is that occasionally files end up being in use and hence can't be copied over. This has in the past been intermittent to the point it didn't matter but on some of our higher traffic sites it happens the majority of the time now. I'm wondering if anyone has a workaround or alternative approach to this that I haven't thought of. Currently my ideas are: Simply retry each file until it works. That's going to cause errors for a short time though which isn't really that good. Deploy to a new folder and update IIS's webroot to the new folder. I'm not sure how to do this short of running the application as an administrator and running batch files, which is very untidy. Does anyone know what the best way to do this is, or if it's possible to do #2 without running the publishing application as a user who has admin access (Willing to grant it special privileges, but I'd prefer to stop short of administrator)?

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• how to emulate thread local storage at user space in C++ ?

  - by vprajan

  I am working on a mobile platform over Nucleus RTOS. It uses Nucleus Threading system but it doesn't have support for explicit thread local storage i.e, TlsAlloc, TlsSetValue, TlsGetValue, TlsFree APIs. The platform doesn't have user space pthreads as well. I found that __thread storage modifier is present in most of the C++ compilers. But i don't know how to make it work for my kind of usage. How does __thread keyword can be mapped with explicit thread local storage? I read many articles but nothing is so clear for giving me the following basic information will __thread variable different for each thread ? How to write to that and read from it ? does each thread has exactly one copy of the variable ? following is the pthread based implementation: pthread_key_t m_key; struct Data : Noncopyable { Data(T* value, void* owner) : value(value), owner(owner) {} int* value; }; inline ThreadSpecific() { int error = pthread_key_create(&m_key, destroy); if (error) CRASH(); } inline ~ThreadSpecific() { pthread_key_delete(m_key); // Does not invoke destructor functions. } inline T* get() { Data* data = static_cast<Data*>(pthread_getspecific(m_key)); return data ? data->value : 0; } inline void set(T* ptr) { ASSERT(!get()); pthread_setspecific(m_key, new Data(ptr, this)); } How to make the above code use __thread way to set & get specific value ? where/when does the create & delete happen? If this is not possible, how to write custom pthread_setspecific, pthread_getspecific kind of APIs. I tried using a C++ global map and index it uniquely for each thread and retrieved data from it. But it didn't work well.

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• Sub Query making Query slow.

  - by Muhammad Kashif Nadeem

  Please copy and paste following script. DECLARE @MainTable TABLE(MainTablePkId int) INSERT INTO @MainTable SELECT 1 INSERT INTO @MainTable SELECT 2 DECLARE @SomeTable TABLE(SomeIdPk int, MainTablePkId int, ViewedTime1 datetime) INSERT INTO @SomeTable SELECT 1, 1, DATEADD(dd, -10, getdate()) INSERT INTO @SomeTable SELECT 2, 1, DATEADD(dd, -9, getdate()) INSERT INTO @SomeTable SELECT 3, 2, DATEADD(dd, -6, getdate()) DECLARE @SomeTableDetail TABLE(DetailIdPk int, SomeIdPk int, Viewed INT, ViewedTimeDetail datetime) INSERT INTO @SomeTableDetail SELECT 1, 1, 1, DATEADD(dd, -7, getdate()) INSERT INTO @SomeTableDetail SELECT 2, 2, NULL, DATEADD(dd, -6, getdate()) INSERT INTO @SomeTableDetail SELECT 3, 2, 2, DATEADD(dd, -8, getdate()) INSERT INTO @SomeTableDetail SELECT 4, 3, 1, DATEADD(dd, -6, getdate()) SELECT m.MainTablePkId, (SELECT COUNT(Viewed) FROM @SomeTableDetail), (SELECT TOP 1 s2.ViewedTimeDetail FROM @SomeTableDetail s2 INNER JOIN @SomeTable s1 ON s2.SomeIdPk = s1.SomeIdPk WHERE s1.MainTablePkId = m.MainTablePkId) FROM @MainTable m Above given script is just sample. I have long list of columns in SELECT and around 12+ columns in Sub Query. In my From clause there are around 8 tables. To fetch 2000 records full query take 21 seconds and if I remove Subquiries it just take 4 seconds. I have tried to optimize query using 'Database Engine Tuning Advisor' and on adding new advised indexes and statistics but these changes make query time even bad. Note: As I have mentioned that this is test data to explain my question the real data has lot of tables joins columns but without Sub-Query the results us fine. Any help thanks.

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• Can I share code & resources between Android projects without using a library?

  - by Tom

  The standard advice for sharing code & resources between Android projects is to use a library. Personally I find this works poorly if (a) the shared code changes a lot, or (b) your computer isn't fast enough. I also don't want to get into deploying multiple APK's, which seems to be necessary when I use dependent projects (i.e. Java Build Path, Projects Tab). On the other hand, sharing a folder of source code by using the Eclipse linked source feature works great (Java Build Path, Source tab, Link Source button), but for these two issues: 1) I can't use the same technique to share resources. I can create the link to the resources parent folder but then things get wonky and the shared resources don't get compiled (I'm using ADT 21). 2) So then I settle for copying the shared resources into each project, but this doesn't work because either. The shared code can't import the copy of its resources because it doesn't know the package name of the project that uses it. The solution I've been using is to access the resources dynamically, but that has become cumbersome as the number of resources grows. So, I need a solution to either (1) or (2), or I'll have to go back to a library project. (Or maybe there is another option I haven't thought of?)

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• Advice: Python Framework Server/Worker Queue management (not Website)

  - by Muppet Geoff

  I am looking for some advice/opinions of which Python Framework to use in an implementation of multiple 'Worker' PCs co-ordinated from a central Queue Manager. For completeness, the 'Worker' PCs will be running Audio Conversion routines (which I do not need advice on, and have standalone code that works). The Audio conversion takes a long time, and I need to co-ordinate an arbitrary number of the 'Workers' from a central location, handing them conversion tasks (such as where to get the source files, or where to ask for the job configuration) with them reporting back some additional info, such as the runtime of the converted audio etc. At present, I have a script that makes a webservice call to get the 'configuration' for a conversion task, based on source files located on the worker already (we manually copy the source files to the worker, and that triggers a conversion routine). I want to change this, so that we can distribute conversion tasks ("Oy you, process this: xxx") based on availability, and in an ideal world, based on pending tasks too. There is a chance that Workers can go offline mid-conversion (but this is not likely). All the workers are Windows based, the co-ordinator can be WIndows or Linux. I have (in my initial searches) come across the following - and I know that some are cross-dependent: Celery (with RabbitMQ) Twisted Django Using a framework, rather than home-brewing, seems to make more sense to me right now. I have a limited timeframe in which to develop this functional extension. An additional consideration would be using a Framework that is compatible with PyQT/PySide so that I can write a simple UI to display Queue status etc. I appreciate that the specifics above are a little vague, and I hope that someone can offer me a pointer or two. Again: I am looking for general advice on which Python framework to investigate further, for developing a Server/Worker 'Queue management' solution, for non-web activities (this is why DJango didn't seem the right fit).

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• uploading database file in assets not returning a record

  - by Alexander

  I have a problem with a database file not being read I have added the database file in assets called mydb but when i run my code it says its not being located. It is calling this toast Toast.makeText(this, "No contact found", Toast.LENGTH_LONG).show(); This is being called because no records are being returned. This is an example form Android Application Development book. public class DatabaseActivity extends Activity { /** Called when the activity is first created. */ TextView quest, response1, response2; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView quest = (TextView) findViewById(R.id.quest); try { String destPath = "/data/data/" + getPackageName() + "/databases/MyDB"; File f = new File(destPath); if (!f.exists()) { CopyDB( getBaseContext().getAssets().open("mydb"), new FileOutputStream(destPath)); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } DBAdapter db = new DBAdapter(this); //---get a contact--- db.open(); Cursor c = db.getContact(2); if (c.moveToFirst()) DisplayContact(c); else Toast.makeText(this, "No contact found", Toast.LENGTH_LONG).show(); db.close(); } public void CopyDB(InputStream inputStream, OutputStream outputStream) throws IOException { //---copy 1K bytes at a time--- byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) > 0) { outputStream.write(buffer, 0, length); } inputStream.close(); outputStream.close(); } public void DisplayContact(Cursor c) { quest.setText(String.valueOf(c.getString(1))); //quest.setText(String.valueOf("this is a text string")); } }

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• Looking for resources to explain a security risk.

  - by Dave

  I've a developer which has given users the ability to download a zip archive which contains an html document which references a relative javascript file and flash document. The flash document accepts as one of it's parameters a url which is embedded in the html document. I believe that this archive is meant to be used as a means to transfer an advertisement to someone who would use the source to display the ad on their site, however the end user appears to want to view it locally. When one opens the html document the flash document is presented and when the user clicks on the flash document it redirects to this embedded url. However, if one extracts the archive on the desktop and opens the html document in a browser and clicks the flash object, nothing observable happens, they will not be redirected to the external url. I believe this is a security risk because one is transferring from the local computer zone to an external zone. I'm trying to determine the best way to explain this security risk in the simplest of terms to a very end user. They simply believe it's "broken" when it's not broken, they're being protected from a known vulnerability. The developer attempted to explain how to copy the files to a local iis instance, which I highly doubt is running on the users machine, and I do not consider this to be a viable explanation.

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• Subversion Partial Export

  - by Jared

  I have somewhat interesting development situation. The client and deployment server are inside a firewall without access to the Subversion server. But the developers are outside the firewall and are able to use the Subversion server. Right now the solution I have worked out is to update my local copy of the code and then pull out the most recently updated files using UnleashIT. The question is how to get just the updated files out of Subversion so that they can be physically transported through the firewall and put on the deployment server. I'm not worried about trying to change the firewall setup or trying to figure out an easier way to get to the Subversion server from inside the firewall. I'm just interested in a way to get a partial export from the repository of the most recently changed files. Are there any other suggestions? Answer found: In addition to the answer I marked as Answer, I've also found the following here to be able to do this from TortoiseSVN: from http://svn.haxx.se/tsvn/archive-2006-08/0051.shtml * select the two revisions * right-click, "compare revisions" * select all files in the list * right-click, choose "export to..."

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• Can I have two names for the same variable?

  - by Roman

  The short version of the question: I do: x = y. Then I change x, and y is unchanged. What I want is to "bind" x and y in such a way that I change y whenever I change x. The extended version (with some details): I wrote a class ("first" class) which generates objects of another class ("second" class). In more details, every object of the second class has a name as a unique identifier. I call a static method of the first class with a name of the object from the second class. The first class checks if such an object was already generated (if it is present in the static HashMap of the first class). If it is already there, it is returned. If it is not yet there, it is created, added to the HashMap and returned. And then I have the following problem. At some stage of my program, I take an object with a specific name from the HashMap of the first class. I do something with this object (for example change values of some fields). But the object in the HashMap does not see these changes! So, in fact, I do not "take" an object from the HashMap, I "create a copy" of this object and this is what I would like to avoid.

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• using ftpWebRequest with an error: the remote server returned error 530 not loged in

  - by user1361207

  I am trying to use the ftpWebRequest in c# my code is // Get the object used to communicate with the server. FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://192.168.20.10/file.txt"); request.Method = WebRequestMethods.Ftp.UploadFile; // This example assumes the FTP site uses anonymous logon. request.Credentials = new NetworkCredential("dev\ftp", "devftp"); // Copy the contents of the file to the request stream. StreamReader sourceStream = new StreamReader(@"\file.txt"); byte[] fileContents = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd()); sourceStream.Close(); request.ContentLength = fileContents.Length; request.UsePassive = true; Stream requestStream = request.GetRequestStream(); requestStream.Write(fileContents, 0, fileContents.Length); requestStream.Close(); FtpWebResponse response = (FtpWebResponse)request.GetResponse(); Console.WriteLine("Upload File Complete, status {0}", response.StatusDescription); response.Close(); and I get an Error in request.GetRequestStream(); the error is: the remote server returned error 530 not loged in if I try to go in to a browser page and in the url I write ftp://192.168.20.10/ the brows page is asking me for a name and password, I put the same name and password and I see all the files and folders in the ftp folder. can any one help me with this problem?

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• What is a recommended Android utility class collection?

  - by Sebastian Roth

  I often find myself writing very similar code across projects. And more often than not, I copy stuff over from old projects. Things like: Create images with round corners read density into a static variable & re-use. 4 lines.. disable / hide multiple views / remote views at once. Example: } public static void disableViews(RemoteViews views, int... ids) { for (int id : ids) { views.setInt(id, SET_VISIBILITY, View.GONE); } } public static void showViews(RemoteViews views, int... ids) { for (int id : ids) { views.setInt(id, SET_VISIBILITY, View.VISIBLE); } } I'd love to package these kind of functions into 1 letter / 2 letter class names, i.e. V.showViews(RemoteViews views, int... ids) would be easy to write & remember I hope. I'm searching for Github recommendations, links and if nothing is found, I perhaps will start a small project on github to collect.

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• Is it okay for multiple objects to retain the same object in Objective-C/Cocoa?

  - by Andrew Arrow

  Say I have a tableview class that lists 100 Foo objects. It has: @property (nonatomic, retain) NSMutableArray* fooList; and I fill it up with Foos like: self.fooList = [NSMutableArray array]; while (something) { Foo* foo = [[Foo alloc] init]; [fooList addObject:foo]; [foo release]; } First question: because the NSMutableArray is marked as retain, that means all the objects inside it are retained too? Am I correctly adding the foo and releasing the local copy after it's been added to the array? Or am I missing a retain call? Then if the user selects one specific row in the table and I want to display a detail Foo view I call: FooView* localView = [[FooView alloc] initWithFoo:[self.fooList objectAtIndex:indexPath.row]]; [self.navigationController pushViewController:localView animated:YES]; [localView release]; Now the FooView class has: @property (nonatomic, retain) Foo* theFoo; so now BOTH the array is holding on to that Foo as well as the FooView. But that seems okay right? When the user hits the back button dealloc will be called on FooView and [theFoo release] will be called. Then another back button is hit and dealloc is called on the tableview class and [fooList release] is called. You might argue that the FooView class should have: @property (nonatomic, assign) Foo* theFoo; vs. retain. But sometimes the FooView class is called with a Foo that's not also in an array. So I wanted to make sure it was okay to have two objects holding on to the same other object.

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• "end()" iterator for back inserters?

  - by Thanatos

  For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• Are there any less costlier alternatives to Amazon's Relational Database Services (RDS)?

  - by swapnonil

  Hi All, I have the following requirement. I have with me a database containing the contact and address details of at least 2000 members of my school alumni organization. We want to store all that information in a relation model so that This data can be created and edited on demand. This data is always backed up and should be simple to restore in case the master copy becomes unusable. All sensitive personal information residing in this database is guaranteed to be available only to authorized users. This database won't be online in the first 6 months. It will become online only after a website is built on top of it. I am not a DBA and I don't want to spend time doing things like backups. I thought Amazon's RDS with it's automatic backup facility was the perfect solution for our needs. The only problem is that being a voluntary organization we cannot spare the monthly $100 to $150 fees this service demands. So my question is, are there any less costlier alternatives to Amazon's RDS?

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• How can I avoid encoding mixups of strings in a C/C++ API?

  - by Frerich Raabe

  I'm working on implementing different APIs in C and C++ and wondered what techniques are available for avoiding that clients get the encoding wrong when receiving strings from the framework or passing them back. For instance, imagine a simple plugin API in C++ which customers can implement to influence translations. It might feature a function like this: const char *getTranslatedWord( const char *englishWord ); Now, let's say that I'd like to enforce that all strings are passed as UTF-8. Of course I'd document this requirement, but I'd like the compiler to enforce the right encoding, maybe by using dedicated types. For instance, something like this: class Word { public: static Word fromUtf8( const char *data ) { return Word( data ); } const char *toUtf8() { return m_data; } private: Word( const char *data ) : m_data( data ) { } const char *m_data; }; I could now use this specialized type in the API: Word getTranslatedWord( const Word &englishWord ); Unfortunately, it's easy to make this very inefficient. The Word class lacks proper copy constructors, assignment operators etc.. and I'd like to avoid unnecessary copying of data as much as possible. Also, I see the danger that Word gets extended with more and more utility functions (like length or fromLatin1 or substr etc.) and I'd rather not write Yet Another String Class. I just want a little container which avoids accidental encoding mixups. I wonder whether anybody else has some experience with this and can share some useful techniques. EDIT: In my particular case, the API is used on Windows and Linux using MSVC 6 - MSVC 10 on Windows and gcc 3 & 4 on Linux.

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• How to support comparisons for QVariant objects containing a custom type?

  - by Tyler McHenry

  According to the Qt documentation, QVariant::operator== does not work as one might expect if the variant contains a custom type: bool QVariant::operator== ( const QVariant & v ) const Compares this QVariant with v and returns true if they are equal; otherwise returns false. In the case of custom types, their equalness operators are not called. Instead the values' addresses are compared. How are you supposed to get this to behave meaningfully for your custom types? In my case, I'm storing an enumerated value in a QVariant, e.g. In a header: enum MyEnum { Foo, Bar }; Q_DECLARE_METATYPE(MyEnum); Somewhere in a function: QVariant var1 = QVariant::fromValue<MyEnum>(Foo); QVariant var2 = QVariant::fromValue<MyEnum>(Foo); assert(var1 == var2); // Fails! What do I need to do differently in order for this assertion to be true? I understand why it's not working -- each variant is storing a separate copy of the enumerated value, so they have different addresses. I want to know how I can change my approach to storing these values in variants so that either this is not an issue, or so that they do both reference the same underlying variable. It don't think it's possible for me to get around needing equality comparisons to work. The context is that I am using this enumeration as the UserData in items in a QComboBox and I want to be able to use QComboBox::findData to locate the item index corresponding to a particular enumerated value.

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