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Search found 7722 results on 309 pages for 'pitfalls to avoid'.

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• How to force calling of QWidget::paintEvent() when its hovered by other window?

  - by Pie_Jesu

  Hi there. I have occured a problem: I'm writing a widget, which displays current date's day number. It's like a button, but it's not derived from QPushButton class. Just from QWidget. So I reimplemented enterEvent(), leaveEvent(), mousePressEvent(), mouseReleaseEvent(). I call update() inside these methods and widget has realistic button behavior (paintEvent() is reimplemented too). But when I change system date and hover that widget with other window, my widget doesn't calls paintEvent() and displays old date. Only when I place mouse over it, widget repaints it's contents. I guess there is an option, which paints old contents on hover event to avoid unnecessary paint events. But I need to disable it. Tried to set many attributes (Qt::WidgetAttribute enum). But it doesn't helps. Please, help me (and sorry for my bad english).

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• Similar code detector

  - by Let_Me_Be

  I'm search for a tool that could compare source codes for similarity. We have a very trivial system right now that has huge amount of false positives and the real positives can easily get buried in them. My requirements are: reasonably small amount of false positives good detection rate (yeah these are going against each other) ideally with a more complex output than just a single value usable for C (C99) and C++ (C++03 and optimally C++11) still maintained usable for comparing two source files against each other usable in non-interactive mode EDIT: To avoid confusion, the following two code snippets are identical and should be detected as such: for (int i = 0; i < 10; i++) { bla; } int i; while (i < 10) { bla; i++; } The same here: int x = 10; y = x + 5; int a = 10; y = a + 5;

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• QFileDialog used as widget

  - by lvp

  Hi! My goal is: user can choose file (only *mp3) and after clicking twice on it it should play (so the QString to file should be send to play() funtion) Firstly I started to work with QTreeView, but it has signal when the file is selected. So I decided to create QFileDialog and used it as widget built-in into MainWindow. The only problem that I have, that after double-click it dissapers. It is possible to avoid it? Should I work with some QDialog::finished() signal or, QDialog::done()?

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• How can I combine multiple iPhone applications in to one application?

  - by Toret

  At the moment I have 2 completed iPhone applications. Both these applications must be contained in to one application. I can't have multiple apps on the app store and to avoid confusion among people using these apps I must have them contained to a single application that gives the user the capability to launch any application in the wrapper. How can I go about doing this. Some of the ideas that crossed my mind are: Building a Framework, or building a library. But Im not even sure if I'm heading in the right direction.

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• Facebook login within an iframe (but outside FB)

  - by Cystack

  At some point in my application, I use an iframe. In this iframe, some Facebook stuff could be useful and for that, I use the graph API a lot. Problem is : when someone isn't logged in to facebook or hasn't allowed my application yet, they are prompted to click the "connect with facebook" button. But as soon as they click it, the iframe gets destroyed and the top page is replaced with the Facebook login page. Eventually the top page is redireccted to the previous iframe URL, but the former parent page is lost forever. Is this the intended behaviour of FB connect ? Is there a way to avoid it or to hack around it ? (maybe using a popup instead of an iframe, but that sounds ugly (uglier than an iframe)). I am currently using the PHP SDK Thanks a lot

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• Preventing SQL injecting in a database class

  - by Josh

  I'm building a database class and thought it'd be a good idea to incorporate some form of SQL injection prevention (duh!). Here's the method that runs a database query: class DB { var $db_host = 'localhost'; var $db_user = 'root'; var $db_passwd = ''; var $db_name = 'whatever'; function query($sql) { $this->result = mysql_query($sql, $this->link); if(!$this->result) { $this->error(mysql_error()); } else { return $this->result; } } } There's more in the class than that but I'm cutting it down just for this. The problem I'm facing is if I just use mysql_real_escape_string($sql, $this->link); then it escapes the entire query and leads to a SQL syntax error. How can I dynamically find the variables that need to be escaped? I want to avoid using mysql_real_escape_string() in my main code blocks, i'd rather have it in a function. Thanks.

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• Should I pointer-cast from a private derived class to its base class?

  - by skydoor

  I found this from C++FAQ Generally, No. From a member function or friend of a privately derived class, the relationship to the base class is known, and the upward conversion from PrivatelyDer* to Base* (or PrivatelyDer& to Base&) is safe; no cast is needed or recommended. However users of PrivatelyDer should avoid this unsafe conversion, since it is based on a private decision of PrivatelyDer, and is subject to change without notice. How to understand the above words? I don't think the explanation is correct or accurate. I have a code like this class A{ }; class B: private A{ }; int main(){ B *b = new B(); A *a = new A(); a = b; //wrong a = (A*)b; //right }

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• Getting deadlocks in MySQL

  - by at

  We're very frustratingly getting deadlocks in MySQL. It isn't because of exceeding a lock timeout as the deadlocks happen instantly when they do happen. Here's the SQL code that is executing on 2 separate threads (with 2 separate connections from the connection pool) that produces a deadlock: UPDATE Sequences SET Counter = LAST_INSERT_ID(Counter + 1) WHERE Sequence IS NULL Sequences table has 2 columns: Sequence and Counter The LAST_INSERT_ID allows us to retrieve this updated counter value as per MySQL's recommendation. That works perfect for us, but we get these deadlocks! Why are we getting them and how can we avoid them?? Thanks so much for any help with this.

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• What does a mercurial revision with no parent mean?

  - by Wilka

  I have a Mercurial repository that is in a strange state now. This is what it looks like in TortoiseHG: I didn't think this would be possible. Revision 54 has a parent of "-1 (000000000000)" (i.e. nothing). There's clearly something I don't understand yet about Mercurial, can anyone let me know what this means - and what must have happened for it to get into this state. As far as I know, it's only had stuff pushed and pulled from it - and nobody has been using any wacky extensions. Revisions 54 and 55 were just adding tags, but if I 'update -C' to revision 54 I end up with ONLY the .hgtags file. I've made a clone from revision 53 to fix this. But I'd rather understand what happened here, so I can avoid it happening again.

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• Creating audit triggers in SQL Server

  - by Mike C.

  I need to implement change tracking on two tables in my SQL Server 2005 database. I need to audit additions, deletions, updates (with detail on what was updated). I was planning on using a trigger to do this, but after poking around on Google I found that it was incredibly easy to do this incorrectly, and I wanted to avoid that on the get-go. Can anybody post an example of an update trigger that accomplishes this successfully and in an elegant manner? I am hoping to end up with an audit table with the following structure: ID LogDate TableName TransactionType (update/insert/delete) RecordID FieldName OldValue NewValue ... but I am open for suggestions. Thanks!

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• Building a jar to be used in an eclipse PDE?

  - by tul

  I have written an application that use a third party library. I have then packaged this as an executable jar using the maven-assembly-plugin (producing a jar with all dependencies including some of the third-party jars). Next I need to add this jar to a PDE project so it can be launched from eclipse. But to make this work I need to add some of the thirs-party dependencies to my PDE project which is already located in the packaged jar. So I get duplicated dependencies. Any ideas on how to avoid this? Or suggestion to documentation that describes how this is done properly?

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• CSS: reposition element on hover state but maintain clickable area position

  - by abirduphigh

  I'm trying to create the effect of a button that 'lifts' from the page when rolled over. Using CSS, I have a block style <a> element that, when hovered, re-positions itself up and to the left 5px, and a shadow is left behind: a { display: inline-block; position: relative; } a:hover { top: -5px; left: -5px; box-shadow: rgba(0,0,0,.2) 5px 5px 2px; } The problem: When the <a> block jumps 5px away from the cursor during the hover, the cursor is no longer actually hovering over the block and the block then jumps back when the cursor is moved only slightly thereafter. How can I maintain the original hover area so that the element doesn't keep jumping back and forth when the cursor is only slightly moved? I'd like to avoid adding superfluous container elements to my code if at all possible.

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• Sphinx without using an auto_increment id

  - by squeeks

  I am current in planning on creating a big database (2+ million rows) with a variety of data from separate sources. I would like to avoid structuring the database around auto_increment ids to help prevent against sync issues with replication, and also because each item inserted will have a alphanumeric product code that is guaranteed to be unique - it seems to me more sense to use that instead. I am looking at a search engine to index this database with Sphinx looking rather appealing due to its design around indexing relational databases. However, looking at various tutorials and documentation seems to show database designs being dependent on an auto_increment field in one form or another and a rather bold statement in the documentation saying that document ids must be 32/64bit integers only or things break. Is there a way to have a database indexed by Sphinx without auto_increment fields as the id?

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• Append an onClick event to an anchor tag using jquery?

  - by M.Woodard

  I am trying to add an onClick event to an anchor tag ... Previously i had ... <a href="somlink.html" onClick="pageTracker._link(this.href); return false;"> But i am trying to avoid the inline onClick event because it interferes with another script.. So using jQuery i am trying the following code ... <script> $(document).ready(function() { $('a#tracked').attr('onClick').click(function() {window.onbeforeunload = null; pageTracker._link(this.href); return false; }); }); </script> with the html like so <a id="tracked" href="something.html"> So my question is should this be working, and if not what would be the best solution?

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• Using Option all over the place feels a bit awkward. Am I doing something wrong?

  - by Geo

  As a result of articles I read about the Option class which helps you avoid NullPointerException's, I started to use it all over the place. Imagine something like this: var file:Option[File] = None and later when I use it: val actualFile = file.getOrElse(new File("nonexisting")) if(actualFile.getName.equals("nonexisting")) { // instead of null checking } else { // value of file was good } Doing stuff like this doesn't feel all that "right" to me. I also noticed that .get has become deprecated. . Is this sort of stuff what you guys are doing with Option's too, or am I going the wrong way?

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• nested has_many

  - by Nick Vanderbilt

  I am using Rails 2.3.5. Class User < ActiveRecord::Base has_many :phones end class Phone < ActiveRecord::Base has_many :frequency_bands end I want to get all the frequency_bands for a user. I know I can write a method def freq_bands for User but I would like to know if it is possible to have has_many freq_bands for a User. In this way I can chain the call. What I would like to have is class User < ActiveRecor::Base has_many :frequence_bands, :through => phones end I think it is possible to have nested has_many using this plugin http://github.com/ianwhite/nested_has_many_through However if possible I would like to avoid using another plugin and rely solely on rails.

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• try finally block around every Object.Create?

  - by max

  Hi, I have a general question about best practice in OO Delphi. Currently, I but a try finally block around everywhere, where I create an object, to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; To you think, it is good practice, or too much overhead? And what about the performance?

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• access a property via string with array in php?

  - by sprugman

  (This is in drupal, but I don't really think that matters.) I have a big list of properties that I need to map between two objects, and in one, the value that I need to map is buried inside an array. I'm hoping to avoid hard-coding the property names in the code. If I have a class like this: class Product { public $colors, $sizes; } I can access the properties like this: $props = array('colors', 'sizes'); foreach ($props as $p) { $this->$p = $other_object->$p; } As far as I can tell, if each of the properties on the left are an array, I can't do this: foreach ($props as $p) { $this->$p[0]['value'] = $other_object->$p; } Is that correct, or am I missing some clever way around this?

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• .NET DB Query Without Allocations?

  - by Michael Covelli

  I have been given the task of re-writing some libraries written in C# so that there are no allocations once startup is completed. I just got to one project that does some DB queries over an OdbcConnection every 30 seconds. I've always just used .ExecuteReader() which creates an OdbcDataReader. Is there any pattern (like the SocketAsyncEventArgs socket pattern) that lets you re-use your own OdbcDataReader? Or some other clever way to avoid allocations? I haven't bothered to learn LINQ since all the dbs at work are Oracle based and the last I checked, there was no official Linq To Oracle provider. But if there's a way to do this in Linq, I could use one of the third-party ones.

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• Why Do try ... catch Blocks Require Braces?

  - by Bidou

  Hello. While in other statements like if ... else you can avoid braces if there is only one instruction in a block, you cannot do that with try ... catch blocks: the compiler doesn't buy it. For instance: try do_something_risky(); catch (...) std::cerr << "Blast!" << std::endl; With the code above, g++ simply says it expects a '{' before do_something_risky(). Why this difference of behavior between try ... catch and, say, if ... else ? Thanks!

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• Get a property value with only the object and the name of the property (but not the type)

  - by Vaccano

  Suppose I have a method that passes in the name of a property (as a string) and the object that the property is on (as object). How could I get the value of the property? Here is some code to make it a bit more concrete: protected override void Paint(Graphics g, Rectangle bounds, CurrencyManager source, int rowNum, Brush backBrush, Brush foreBrush, bool alignToRight) { // The next line is made up code var currentValue = source.Current.CoolMethodToTakePropertyNameAndReturnValue(MappingName); // Paint out the retrieved value g.DrawString(currentValue.ToString() , _gridFont, new SolidBrush(Color.Black), bounds.Left + 1, bounds.Top); } MappingName is the name of the property I want to get the value for. What I need is CoolMethodToTakePropertyNameAndReturnValue. Any ideas? I am running on the Compact Framework. I would also prefer to avoid reflection (but if that is my only recourse then so be it). Thanks for any help.

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• How to manage memory for ios with large csv files?

  - by Pell000

  I'm new to ios development, and I'm running into issues relating to memory management and my approaches to dealing with large datasets. Right now, I am loading the csv files and storing the relevant data as objects in memory at app initialization. Some of the csv files are larger than 1MB, and in total, my app uses about 180MB of memory. This is obviously way too high of a number (unless the info I found is wrong and this is an acceptable number, then please let me know). I feel as though there is a fundamental flaw in my approach: is there a way I can avoid storing the csv files in the project itself? Or, is there a kind of "lazy" loading I can do so that I can simply look up info in the csv file, as opposed to loading all of the data from it at once? Any help would do. I think that I need a new perspective in how to manage this more efficiently.

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• Make SQL query more efficient

  - by Webnet

  I currently have this query which runs 2 of the exact same sub queries but pull different data. When I make the values comma separated it throws an SQL error saying the sub query can return only one value. Is there anything else I can do to avoid running multiple sub queries? SELECT product_id, ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id) as listing_count, sku, type_id, ( SELECT AVG(ebay_archive_listing.current_price), AVG(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing WHERE id IN ( SELECT listing_id FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id ) AND ebay_archive_listing.start_time >= '.$startTimestamp.' AND ebay_archive_listing.start_time <= '.$endTimestamp.' AND ebay_archive_listing.current_price > 0 ) as average_bid_price, ( SELECT FROM ebay_archive_listing WHERE id IN ( SELECT listing_id FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id ) AND ebay_archive_listing.start_time >= '.$startTimestamp.' AND ebay_archive_listing.start_time <= '.$endTimestamp.' AND ebay_archive_listing.buy_it_now_price > 0 ) as average_buyout_price FROM product_master I'm aware of the syntax error... I'm selecting 2 seperate averages and am wondering if I can do it any simpler way.

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• Does C# 4's covariance support nesting of generics?

  - by Scott Bilas

  I don't understand why 'x' below converts, but 'y' and 'z' do not. var list = new List<List<int>>(); IEnumerable<List<int>> x = list; List<IEnumerable<int>> y = list; IEnumerable<IEnumerable<int>> z = list; Does the new covariance feature simply not work on generics of generics or am I doing something wrong? (I'd like to avoid using .Cast< to make y and z work.)

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• Select distinct ... inner join vs. select ... where id in (...)

  - by Tonio

  I'm trying to create a subset of a table (as a materialized view), defined as those records which have a matching record in another materialized view. For example, let's say I have a Users table with user_id and name columns, and a Log table, with entry_id, user_id, activity, and timestamp columns. First I create a materialized view of the Log table, selecting only those rows with timestamp some_date. Now I want a materliazed view of the Users referenced in my snapshot of the Log table. I can either create it as select * from Users where user_id in (select user_id from Log_mview), or I can do select distinct u.* from Users u inner join Log_mview l on u.user_id = l.user_id (need the distinct to avoid multiple hits from users with multiple log entries). The former seems cleaner and more elegant, but takes much longer. Am I missing something? Is there a better way to do this?

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