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• C++ Urban Myths

  - by Neil Butterworth

  I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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• Google App Engine - Dealing with concurrency issues of storing an object

  - by Spines

  My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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• How do I use compiler intrinsic __fmul_?

  - by Eric Thoma

  I am writing a massively parallel GPU application. I have been optimizing it by hand. I received a 20% performance increase with _fdividef(x, y), and according to The Cuda C Programming Guide (section C.2.1), using similar functions for multiplication and adding is also beneficial. The function is stated as this: "_fmulrn,rz,ru,rd". __fdividef(x,y) was not stated with the arguments in brackets. I was wondering, what are those brackets? If I run the simple code: int t = __fmul_(5,4); I a compiler error about how _fmul is undefined. I have the CUDA runtime included, so I don't think it is a setup thing; rather it is something to do with those square brackets. How do I correctly use this function? Thank you.

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• RewriteRule in htaccess in subdirectory

  - by Jay

  Windows server, running Apache. In my Apache conf, I have AllowOverride None for the root of a site and then I have a subdirectory set to AllowOverride All: <Directory /> AllowOverride None </Directory> <Directory "/safe/"> AllowOverride All </Directory> However, when I try to set up a rewrite rule in the subdirectory's htaccess file, nothing happens, I just get a 404 page not found error. Example: RewriteEngine On RewriteRule (.*) /blah?test=$1 [R=302,NC,NE,L] Rwewriting URLs are working fine from the root via the Apache conf. I don't understand why the rule is ignored. I don't want to do the URL re-writing within the conf because for this case I may need to be changing the redirects constantly and don't want to reload the server every time a change is made. I also don't want to affect server performance by enabling htaccess files site-wide, just in the subdirectory I need it.

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• Why and when should one call _fpreset( )?

  - by STingRaySC

  The only documentation I can find (on MSDN or otherwise) is that a call to _fpreset() "resets the floating-point package." What is the "floating point package?" Does this also clear the FPU status word? I see documentation that says to call _fpreset() when recovering from a SIGFPE, but doesn't _clearfp() do this as well? Do I need to call both? I am working on an application that unmasks some FP exceptions (using _controlfp()). When I want to reset the FPU to the default state (say, when calling to .NET code), should I just call _clearfp(), _fpreset(), or both. This is performance critical code, so I don't want to call both if I don't have to...

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• Should I use a global var or call the function every time? C++

  - by extintor

  Im using: bool GetOS(LPTSTR pszOS) { OSVERSIONINFOEX osve; BOOL bOsVersionInfoEx; ZeroMemory(&osve, sizeof(OSVERSIONINFOEX)); osve.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX); if( !(bOsVersionInfoEx = GetVersionEx ((OSVERSIONINFO *) &osve)) ) return false; TCHAR buf[80]; StringCchPrintf( buf, 80, TEXT("%u.%u.%u.%u"), osve.dwPlatformId, osve.dwMajorVersion, osve.dwMinorVersion, osve.dwBuildNumber); StringCchCat(pszOS, BUFSIZE, buf); return true; } to get the windows version, and I am planning to use pszOS every a few minutes, Should I use pszOS as a global var or call GetOS() every time? What's the best option from a performance point of view.

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• What are block expressions actually good for?

  - by Helper Method

  I just solved the first problem from Project Euler in JavaFX for the fun of it and wondered what block expressions are actually good for? Why are they superior to functions? Is it the because of the narrowed scope? Less to write? Performance? Here's the Euler example. I used a block here but I don't know if it actually makes sense // sums up all number from low to high exclusive which are divisible by a or b function sumDivisibleBy(a: Integer, b: Integer, high: Integer) { def low = if (a <= b) a else b; def sum = { var result = 0; for (i in [low .. <high] where i mod 3 == 0 or i mod 5 == 0) { result += i } result } } Does a block makes sense here?

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• MySQL: Get unique values across multiple columns in alphabetical order

  - by RuCh

  Hey everyone, If my table looks like this: id | colA | colB | colC =========================== 1 | red | blue | yellow 2 | orange | red | red 3 | orange | blue | cyan What SELECT query do I run such that the results returned are: blue, cyan, orange, red, yellow Basically, I want to extract a collective list of distinct values across multiple columns and return them in alphabetical order. I am not concerned with performance optimization, because the results are being parsed to an XML file that will serve as a cache (database is hardly updated). So even a dirty solution would be fine. Thanks for any help!

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• Fastest tr:hover method

  - by Alex

  What is the single fastest method for table row hover css change? I've tried jQuery (onmouseover/out) and CSS with tr:hover, but once I make my page fullscreen (1920x1200) the performance on my grid is getting just sluggish enough to give the entire page a feel of being sub-par. That's on a grid with 25 rows, and some spans and divs per row. I've tried IE and Google Chrome. Is there another, faster method? What is generally considered the fastest method across browsers for doing hover CSS changes?

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• POS Desktop Application using DB or Localfiles ? using WPF

  - by Panindra

  I am planning to build a POS Application for my shop. I have enough knowledge to build the application using DB and also using local files( system.IO - binary files ) to store and access the data for my application. But , i have no deployment experience and confused in choosing data storing option. Database using MDF may be good option ( may ease plenty of coding ) but i don't want to have SQL server on my desktop. as i am using WPF for building , my concern is that my application may get slow due to server response and design rendering of WPF. Then i tried to use only local data (binary files) to store the data and retrive using class and objects. but this coding is taking lot of time , so in the middle of the process i struck in the dilemma of going back to Database . Please help , for performance wise whic one is better . and in Practical World ,in professional applications which one is widely using .. please give suggestions ..

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• Why do I get CA1811 when I call a private method from a public method in C++/CLI?

  - by brickner

  I've recently upgraded my project from Visual Studio 2008 to Visual Studio 2010. By enabling Code Analysis and building on Release, I'm getting warning CA1811: Avoid uncalled private code. I've managed to reduce the code to this: .h file: public ref class Foo { public: virtual System::String^ ToString() override; private: static System::String^ Bar(); }; .cpp file: String^ Foo::ToString() { return Bar(); } String^ Foo::Bar() { return "abc"; } The warning I get: CA1811 : Microsoft.Performance : 'Foo::Bar(void)' appears to have no upstream public or protected callers. It doesn't matter if Bar() is static or not. I've tried to reproduce it in C# but I can't. I can only reproduce it in C++/CLI. Why do I get this warning? Is this a Visual Studio 2010 bug?

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• Implications of Fulltext Search over many columns

  - by Alex

  Hello, I have a really wide table which includes separate columns for billing address, shipping address, primary address, names, aliases etc. (I can't normalize this table further, and that's not the question here anyways). I'm implementing SQL Server fulltext search, and I'm wondering whether I should limit the search ability to just the primary fields (primary address and names for example), or if I can extend the search ability across all columns without occurring too much of a performance or memory penalty. I've done some basic testing with 10,000 sample rows and it's quite fast but I don't have much experience with fulltext indexing, especially its dictionary internals, so I don't know if the index is going to grow over time, or if there is anything else to consider. Thoughts?

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• .Net programming on a Apple computer

  - by VoodooChild

  Hello, I really would like to write an app or apps for iPhone / iPad. I've never done this so far because most of my work has been in windows environment. I recently got an i7 with windows 7 and love it, and this is what I am using to do development on currently. I would love to try out writing a simple App on a mac for either an iPhone or iPad. The question I had was are there any developers using a macbook to do windows based programming as well as writing apps? And what is their setups like? (example: using bootcamp) Most importantly, is it recommended based on the experience they had doing so? any problems / performance issue? These are the concerns I have to address before justifying spending time and money on this. Thanks, Voodoo

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• NSMutableSet addObject question

  - by Jacob Relkin

  I've got a class that wraps around an NSMutableSet object, and I have an instance method that adds objects (using the addObject: method) to the NSMutableSet. This works well, but I'm smelling a performance hitch because inside the method i'm explicitly calling containsObject: before adding the object to the set. Three part question: Do I need to be calling containsObject: before I add an object to the set? If so, then what actual method should I be using, containsObject or containsObjectIdenticalTo:? If that is not so, what contains method gets invoked under the hood of addObject:? This is important to me because if I pass an object to containsObject: it would return true, but if I pass it to containsObjectIdenticalTo: it would return false.

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• What are some "mental steps" a developer must take to begin moving from SQL to NO-SQL (CouchDB, Fath

  - by Byron Sommardahl

  I have my mind firmly wrapped around relational databases and how to code efficiently against them. Most of my experience is with MySQL and SQL. I like many of the things I'm hearing about document-based databases, especially when someone in a recent podcast mentioned huge performance benefits. So, if I'm going to go down that road, what are some of the mental steps I must take to shift from SQL to NO-SQL? If it makes any difference in your answer, I'm a C# developer primarily (today, anyhow). I'm used to ORM's like EF and Linq to SQL. Before ORMs, I rolled my own objects with generics and datareaders. Maybe that matters, maybe it doesn't. Here are some more specific: How do I need to think about joins? How will I query without a SELECT statement? What happens to my existing stored objects when I add a property in my code? (feel free to add questions of your own here)

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• How can a Delphi TPersistent object calculate its own deserialization time?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": start of the deserialization process after the deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event So the log for TMyForm.Create(nil) could look like: - 00.000 instance created - 00.010 before deserialization - 01.823 after deserialization - 02.340 before OnFormCreate Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• How can I measure TForm deserialization time in Delphi?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": before the beginning of the deserialization process after the completion of deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• Multiple Producers Single Consumer Queue

  - by Talguy

  I am new to multithreading and have designed a program that receives data from two microcontroller measuring various temperatures (Ambient and Water) and draws the data to the screen. Right now the program is singly threaded and its performance SUCKS A BIG ONE. I get basic design approaches with multithreading but not well enough to create a thread to do a task but what I don't get is how to get threads to perform seperate task and place the data into a shared data pool. I figured that I need to make a queue that has one consumer and multiple producers (would like to use std::queue). I have seen some code on the gtkmm threading docs that show a single Con/Pro queue and they would lock the queue object produce data and signal the sleeping thread that it is finished then the producer would sleep. For what I need would I need to sleep a thread, would there be data conflicts if i didn't sleep any of the threads, and would sleeping a thread cause a data signifcant data delay (I need realtime data to be drawn 30 frames a sec) How would I go about coding such a queue using the gtkmm/glibmm library.

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• How to implement a mailing system with Rails that sends emails in the background

  - by Tam

  I want to implement a reliable mailing system with Ruby on Rails that sends emails in the background as sending email sometimes takes like 10 seconds or more so I don't want the user to wait. Some ideas I thought of: 1- Write to a table in DB a have a background process that go over and send email (concern: potential many reads/writes to DB slows down my application) 2- Messaging Queue background process / Rake task (concern: if server crashes queued mails will be lost also might eat up a lot of memory if many emails) I was wondering if you a know of a good solution that provides a balance between reliability and performance.

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• Data Warehouse: One Database or many?

  - by drrollins

  At my new company, they keep all data associated with the data warehouse, including import, staging, audit, dimension and fact tables, together in the same physical database. I've been a database developer for a number of years now and this consolidation of function and form seems counter to everything I know. It seems to make security, backup/restore and performance management issues more manually intensive. Is this something that is done in the industry? Are there substantial reasons for doing or not doing it? The platform is Netezza. The size is in terabytes, hundreds of millions of rows. What I'm looking to get from answers to this question is a solid understanding of how right or wrong this path is. From your experience, what are the issues I should be focused on arguing if this is a path that will cause trouble for us down the road. If it is no big deal, then I'd like to know that as well.

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• Is it possible to find out what FlashBuilder is doing during compilation?

  - by justkevin

  I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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• Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

  - by Kaleb Brasee

  I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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• Determine if a decimal can be stored as int32

  - by anchandra

  I am doing some custom serializing, and in order to save some space, i want to serialize the decimals as int, if possible value wise. Performance is a concern, since i am dealing with a high volume of data. The current method i use is: if ((value > Int32.MinValue) && (value < Int32.MaxValue) && ((valueAsInt = Decimal.ToInt32(value)) == value)) { return true; } Can this be improved?

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• Tracing or Logging Resource Governor classification function behavior in Sql Server 2008

  - by nganju

  I'm trying to use the Resource Governor in SQL Server 2008 but I find it hard to debug the classification function and figure out what the input variables will have, i.e. does SUSER_NAME() contain the domain name? What does the APP_NAME() string look like? It's also hard to verify that it's working correctly. What group did the function return? The only way I can see this is to fire up the performance monitor and watch unblinkingly for little blips in the right CPU counter. Is there some way I can either run it in Debug mode, where I can set a breakpoint and step through and look at variable values, or can I at least do the old-school method of writing trace statements to a file so I can see what's going on? Thanks...

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• When does it make sense to use a map?

  - by kiwicptn

  I am trying to round up cases when it makes sense to use a map (set of key-value entries). So far I have two categories (see below). Assuming more exist, what are they? Please limit each answer to one unique category and put up an example. Property values (like a bean) age -> 30 sex -> male loc -> calgary Presence, with O(1) performance peter -> 1 john -> 1 paul -> 1

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