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  • Delphi: How to avoid EIntOverflow underflow when subtracting?

    - by Ian Boyd
    Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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  • How to avoid exceptions catches copy-paste in .NET

    - by Budda
    Working with .NET framework I have a service with a set of methods that can generates several types of exceptions: MyException2, MyExc1, Exception... To provide proper work for all methods, each of them contains following sections: void Method1(...) { try { ... required functionality } catch(MyException2 exc) { ... process exception of MyException2 type } catch(MyExc1 exc) { ... process exception of MyExc1 type } catch(Exception exc) { ... process exception of Exception type } ... process and return result if necessary } It is very boring to have exactly same stuff in EACH service method with exactly same exceptions processing functionality... Is there any possibility to "group" these catch-sections and use only one line (something similar to C++ macros)? Probably something new in .NET 4.0 is related to this topic? Thanks. P.S. Any thoughts are welcome.

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  • How to avoid Black Screen on starting an application

    - by ganesh
    hi, When i start my application initially ,i get a black screen which stays for a few seconds before my main activity starts.In case of iphone an image with name default is displayed for that split second.I am not sure how to do the same in android.Any help .I tried as below in vain <activity android:name=".Index" android:label="@string/app_name" android:screenOrientation="portrait" android:theme="@drawable/defaultimage"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity>

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  • Should I avoid using Java Label Statements?

    - by Kamikaze Mercenary
    Today I had a coworker suggest I refactor my code to use a label statement to control flow through 2 nested for loops I had created. I've never used them before because personally I think they decrease the readability of a program. I am willing to change my mind about using them if the argument is solid enough however. What are people's opinions on label statements?

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  • Queue access to the database to avoid multiple cache items

    - by MikeJ
    I have a music related ASP.NET web site which caches a lot of static information from the database on the first request. Sometimes, the application is reset and cache is cleared while the application is on heavy load and then all http requests go to the database to retrieve that static data and cache it for other requests. How can I ensure that only one request go to the database and cache the results, so that other request simply read that info from cache and not needlessly retrieve the same info over and over again. Can I use thread locking? For example, can I do something like lock(this) { db access here }?

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  • Elegant code question: How to avoid creating unneeded object

    - by SeaDrive
    The root of my question is that the C# compiler is too smart. It detects a path via which an object could be undefined, so demands that I fill it. In the code, I look at the tables in a DataSet to see if there is one that I want. If not, I create a new one. I know that dtOut will always be assigned a value, but the the compiler is not happy unless it's assigned a value when declared. This is inelegant. How do I rewrite this in a more elegant way? System.Data.DataTable dtOut = new System.Data.DataTable(); . . // find table with tablename = grp // if none, create new table bool bTableFound = false; foreach (System.Data.DataTable d1 in dsOut.Tables) { string d1_name = d1.TableName; if (d1_name.Equals(grp)) { dtOut = d1; bTableFound = true; break; } } if (!bTableFound) dtOut = RptTable(grp);

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  • Avoid postback on gridview event

    - by purushottam
    1 I've got popup (using javascript) working in a kind of gridview. When you click a button on one grid, it displays a popup window containing another grid of information, based on the row clicked in the first grid. This works well... I've enabled editing in the grid that is popped up. When you click edit though, the popup window disappears. If I click the display button in the first grid though to bring the popup window visible again it displays, and is now in edit mode. Is there a way to make postbacks in the popup not close the popup?

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  • How to avoid saving escape character (\) in db

    - by Huy
    I'm using zend frame work zend form and zend db for my project. The problem I have is, when the user enter some special characters in the text field (i.e "I'm"), it is saved in the database with the "\" character (i.e. "I\'"). I need to know how to fix this so it just saved as whatever the user entered.

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  • Rewrite URL to index.php but avoid index.php in the URL

    - by Tom
    I'm trying to internally redirect all requests to index.php and externally redirect all requests that contain index.php using a .htaccess file. So URLs like http://host/test should be processed by index.php and URLs like http://host/index.php/test should be redirected to http://host/test and then processed by index.php (without redirecting the browser to index.php) I tried the following but always get a message "Too many redirects...": RewriteRule ^index\.php/?(.*)$ /$1 [R,L] RewriteRule .* index.php/$0 [L]

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  • autocomplete: how do I avoid a duplicate search?

    - by dnagirl
    I use JQuery plugin autocomplete as a kind of dataset chooser. If the user chooses a value from the autocomplete lookup, the database is queried for the matching dataset. If the user types in a new value, the user can enter a new dataset. An issue arises when the user types in an existing value rather than choosing it from the autocomplete lookup. When this is done, the autocomplete .result() method is not called and no dataset is retrieved. To fix this I added a .blur(function(){$(this).search();}); to the input element. This fixed the original problem. Now I have the problem that .result() fires on selection from lookup AND on blur. I would like .result() to fire on selection from lookup OR on blur. How do I make that happen? Here is my code: $('#groupset').autocomplete('ajax/php/leeruns.php'); $('#groupset').result( function(event, data, formatted) { if(data){ $('#groupsetdesc').val(formatted); groups.load(data[1]); //retrieve matching dataset } else { $('#groupsetdesc').val(''); } } ).blur(function(){$(this).search();});

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  • How to avoid becoming a programmer while still beign closely involved with computer science/Industry

    - by WeShallOvercome
    I am studying computer science (A masters at an Ivy league), however most of the jobs i find involve way too much of programming. And frankly programming is not an issue, however programming without a meaning (read financial institution (non trading), other non mainstream jobs) bore me to death! I dont want to end up becoming a .NET,C#, Java kind of programmer. Can someone tell where i should look for jobs if i wish to do some real computer science work such as Machine Learning etc. I don't mind programming but becoming a Financial Software dev at Bloomeberg or an SDET at Microsoft isn't actually one of my goals. [note: I have interviewed for intern both positions listed above, and thankfully i got an intern for a data mining position in a top 750 Alexa rank web company] Sorry if angered anyone with a subjective question

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  • C++: Avoid .cpp files with only an empty (de)constructor

    - by Martijn Courteaux
    Hi, When I have a header file like this: #ifndef GAMEVIEW_H_ #define GAMEVIEW_H_ #include <SDL/SDL.h> class GameView { public: GameView(); virtual ~GameView(); virtual void Update() = 0; virtual void Render(SDL_Surface* buffer) = 0; }; #endif /* GAMEVIEW_H_ */ I need to create a .cpp file like this: #include "GameView.h" GameView::~GameView() { } GameView::GameView() { } This is a bit stupid. Just a .cpp file for an empty constructor and deconstructor. I want to implement that method simply in the header file. That is much cleaner. How to do this?

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  • how to avoid clutch billiard balls?

    - by Nait87
    I'm working on the simple behaviour of billiard balls in a collision with each other. All works normal, but there was a problem when facing a few easy balls is the effect of coupling balls and they're cool with each other. Tell me how to prevent this. bool MGBilliard::CollisingBall(CCPoint curr_point, CCPoint next_point) { float dx = next_point.x - (curr_point.x + dvdt.x); float dy = next_point.y - (curr_point.y - dvdt.y); float d = dx*dx+dy*dy; return d <= BALL_RADIUS * BALL_RADIUS; } double MGBilliard::angleCollisionBalls(Ball* current, Ball* next) { double na; double dx = fabs(next->location.x - current->location.x); double dy = fabs(next->location.y - current->location.y); na = atan(fabs(dy/dx)); if(atan(fabs(current->location.y/current->location.x)) < atan(fabs(next->location.y/next->location.x))) na = current->angle - na; else if(atan(fabs(current->location.y/current->location.x)) > atan(fabs(next->location.y/next->location.x))) na = current->angle + na; return na; } for(unsigned int i = 0;i<BALL_COUNT;++i) { if(vBalls[i]->speed > 0){ vBalls[i]->speed += vBalls[i]->acceleration; float dsdt = vBalls[i]->speed*dt; dvdt.x = dsdt*cos(vBalls[i]->angle); dvdt.y = dsdt*sin(vBalls[i]->angle); vBalls[i]->location.x += dvdt.x; vBalls[i]->location.y += dvdt.y; for(unsigned int j = 1; j < BALL_COUNT; ++j) { if(i == j) continue; if(CollisingBall(vBalls[i]->spriteBall->getPosition(),vBalls[j]->spriteBall->getPosition())) { vBalls[j]->speed = 600; double angle; angle = angleCollisionBalls(vBalls[i],vBalls[j]); vBalls[i]->angle = (float)-angle; vBalls[j]->angle = (float)angle; } } } }

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  • How to Avoid Server Error 414 for Very Long QueryString Values

    - by Registered User
    I had a project that required posting a 2.5 million character QueryString to a web page. The server itself only parsed URI's that were 5,400 characters or less. After trying several different sets of code for WebRequest/WebResponse, WebClient, and Sockets, I finally found the following code that solved my problem: HttpWebRequest webReq; HttpWebResponse webResp = null; string Response = ""; Stream reqStream = null; webReq = (HttpWebRequest)WebRequest.Create(strURL); Byte[] bytes = Encoding.UTF8.GetBytes("xml_doc=" + HttpUtility.UrlEncode(strQueryString)); webReq.ContentType = "application/x-www-form-urlencoded"; webReq.Method = "POST"; webReq.ContentLength = bytes.Length; reqStream = webReq.GetRequestStream(); reqStream.Write(bytes, 0, bytes.Length); reqStream.Close(); webResp = (HttpWebResponse)webReq.GetResponse(); if (webResp.StatusCode == HttpStatusCode.OK) { StreamReader loResponseStream = new StreamReader(webResp.GetResponseStream(), Encoding.UTF8); Response = loResponseStream.ReadToEnd(); } webResp.Close(); reqStream = null; webResp = null; webReq = null;

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  • to avoid page refresh during button click event in asp.net

    - by ush
    public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) // If page loads for first time { Session["update"] = Server.UrlEncode(System.DateTime.Now.ToString()); // Assign the Session["update"] with unique value //=============== Page load code ========================= //============== End of Page load code =================== } } protected void Button1_Click(object sender, EventArgs e) { if (Session["update"].ToString() == ViewState["update"].ToString()) // If page not Refreshed { //=============== On click event code ========================= Label1.Text = TextBox1.Text; //lblDisplayAddedName.Text = txtName.Text; //=============== End of On click event code ================== // After the event/ method, again update the session Session["update"] = Server.UrlEncode(System.DateTime.Now.ToString()); } else // If Page Refreshed { // Do nothing } } protected override void OnPreRender(EventArgs e) { ViewState["update"] = Session["update"]; } } this is not working for high resolution gradient background

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  • Avoid stuck calling callback

    - by andlomba
    Hello all, This is a question about generic c++ event driven applications design. Lets assume that we have two threads, a "Dispatcher" (or "Engine"...) and a "Listener" (or "Client"...). Let's assume that I write the Dispatcher code, and release it as a library. I also write the Listener interface, of course. When the Dispatcher executes (after Listener registration) listenerInstance.onSomeEvent(); the event handling code will actually be executed by the Dispatcher thread, so if the person that implements the Listener writes something like void Listener::onSomeEvent() { while(true) ; } The Dispatcher will stuck forever. Is there a "plain old c++" (I mean no boost or libsigc++) way to "decouple" the two classes, so I can be sure that my Dispatcher will work fine whatever the Listeners does in the callbacks? bye and thanks in advance, Andrea

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  • Firefox extension dev: observing preferencies, avoid multiple notifications

    - by Michael
    Let's say my Firefox extension has multiple preferences, but some of them are grouped, like check interval, fail retry interval, destination url. Those are used in just single function. When I subscribe to preference service and add observer, the observe callback will be called for each changed preference, so if by chance user changed all of the settings in group, then I will have to do the same routine for the same subsystem as many times as I have items in that preferences group. What I want is observe to be called just once for group of preferences. Say extensions.myextension.interval1 extensions.myextension.site extensions.myextension.retry so if one or all of those preferences are changed, I receive only 1 notification about it.

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  • Filtering two arrays to avoid Inf/NaN values

    - by Gacek
    I have two arrays of doubles of the same size, containg X and Y values for some plots. I need to create some kind of protection against Inf/NaN values. I need to find all that pairs of values (X, Y) for which both, X and Y are not Inf nor NaN If I have one array, I can do it using lambdas: var filteredValues = someValues.Where(d=> !(double.IsNaN(d) || double.IsInfinity(d))).ToList(); Now, for two arrays I use following loop: List<double> filteredX=new List<double>(); List<double> filteredX=new List<double>(); for(int i=0;i<XValues.Count;i++) { if(!double.IsNan(XValues[i]) && !double.IsInfinity(XValues[i]) && !double.IsNan(YValues[i]) && !double.IsInfinity(YValues[i]) ) { filteredX.Add(XValues[i]); filteredY.Add(YValues[i]); } } Is there any way of filtering two arrays at the same time using LINQ/Lambdas, as it was done for single array?

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  • Avoid using InetAddress - Getting a raw IP address in network byte order

    - by Mylo
    Hey, I am trying to use the MaxMind GeoLite Country database on the Google App Engine. However, I am having difficulty getting the Java API to work as it relies on the InetAddress class which is not available to use on the App Engine. However, I am not sure if there is a simple workaround as it appears it only uses the InetAddress class to determine the IP of a given hostname. In my case, the hostname is always an IP anyway. What I need is a way to convert an IP address represented as a String into a byte array of network byte order (which the addr.getAddress() method of the InetAddress class provides). This is the code the current API uses, I need to find a way of removing all references to InetAddress whilst ensuring it still works! Thanks for your time. /** * Returns the country the IP address is in. * * @param ipAddress String version of an IP address, i.e. "127.0.0.1" * @return the country the IP address is from. */ public Country getCountry(String ipAddress) { InetAddress addr; try { addr = InetAddress.getByName(ipAddress); } catch (UnknownHostException e) { return UNKNOWN_COUNTRY; } return getCountry(bytesToLong(addr.getAddress())); }

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  • Avoid slowdowns while using off-site database

    - by Anders Holmström
    The basic layout of my problem is this: Website (ASP.NET/C#) hosted at a dedicated hosting company (location 1) Company database (SQL Server) with records of relevant data (location 2). Location 1 & 2 connected through VPN. Customer visiting the website and wanting to pull data from the company database. No possibility of changing the server locations or layout (i.e. moving the website to an in-office server isn't possible). What I want to do is figure out the best way to handle the data acces in this case, minimizing the need for time-expensive database calls over the VPN. The first idea I'm getting is this: When a user enters the section of the website needing the DB data, you pull all the needed tables from the database into a in-memory dataset. All subsequent views/updates to the data is done on this dataset. When the user leaves (logout, session timeout, browser closed etc) the dataset gets sent to the SQL server. I'm not sure if this is a realistic solution, and it obviously has some problems. If two web visitors are performing updates on the same data, the one finishing up last will have their changes overwriting the first ones. There's also no way of knowing you have the latest data (i.e. if a customer pulls som info on their projects and we update this info while they are viewing them, they won't see these changes PLUS the above overwriting issue will arise). The other solution would be to somehow aggregate database calls and make sure they only happen when you need them, e.g. during data updates but not during data views. But then again the longer a pause between these refreshing DB calls, the bigger a chance that the data view is out of date as per the problem described above. Any input on the above or some fresh ideas would be most welcome.

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  • How to avoid truncation of text with UITableViewCellStyleValue2

    - by Regan
    I use this code to make my UITableViewCells cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue2 reuseIdentifier:CellIdentifier] autorelease]; If you're unfamiliar with UITableViewCellStyleValue2, the main text is shown, and then the detail text is shown after it, generally in a different color. However, when I do this, my main text is truncated, if it is longer than a short word. I want to force it to not truncate the main text and show the entire main text, and then the detail text after it. How can I do that?

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  • How to generalize a method call in Java (to avoid code duplication)

    - by dln385
    I have a process that needs to call a method and return its value. However, there are several different methods that this process may need to call, depending on the situation. If I could pass the method and its arguments to the process (like in Python), then this would be no problem. However, I don't know of any way to do this in Java. Here's a concrete example. (This example uses Apache ZooKeeper, but you don't need to know anything about ZooKeeper to understand the example.) The ZooKeeper object has several methods that will fail if the network goes down. In this case, I always want to retry the method. To make this easy, I made a "BetterZooKeeper" class that inherits the ZooKeeper class, and all of its methods automatically retry on failure. This is what the code looked like: public class BetterZooKeeper extends ZooKeeper { private void waitForReconnect() { // logic } @Override public Stat exists(String path, Watcher watcher) { while (true) { try { return super.exists(path, watcher); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } @Override public byte[] getData(String path, boolean watch, Stat stat) { while (true) { try { return super.getData(path, watch, stat); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } @Override public void delete(String path, int version) { while (true) { try { super.delete(path, version); return; } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } } (In the actual program there is much more logic and many more methods that I took out of the example for simplicity.) We can see that I'm using the same retry logic, but the arguments, method call, and return type are all different for each of the methods. Here's what I did to eliminate the duplication of code: public class BetterZooKeeper extends ZooKeeper { private void waitForReconnect() { // logic } @Override public Stat exists(final String path, final Watcher watcher) { return new RetryableZooKeeperAction<Stat>() { @Override public Stat action() { return BetterZooKeeper.super.exists(path, watcher); } }.run(); } @Override public byte[] getData(final String path, final boolean watch, final Stat stat) { return new RetryableZooKeeperAction<byte[]>() { @Override public byte[] action() { return BetterZooKeeper.super.getData(path, watch, stat); } }.run(); } @Override public void delete(final String path, final int version) { new RetryableZooKeeperAction<Object>() { @Override public Object action() { BetterZooKeeper.super.delete(path, version); return null; } }.run(); return; } private abstract class RetryableZooKeeperAction<T> { public abstract T action(); public final T run() { while (true) { try { return action(); } catch (KeeperException e) { // We will retry. } waitForReconnect(); } } } } The RetryableZooKeeperAction is parameterized with the return type of the function. The run() method holds the retry logic, and the action() method is a placeholder for whichever ZooKeeper method needs to be run. Each of the public methods of BetterZooKeeper instantiates an anonymous inner class that is a subclass of the RetryableZooKeeperAction inner class, and it overrides the action() method. The local variables are (strangely enough) implicitly passed to the action() method, which is possible because they are final. In the end, this approach does work and it does eliminate the duplication of the retry logic. However, it has two major drawbacks: (1) it creates a new object every time a method is called, and (2) it's ugly and hardly readable. Also I had to workaround the 'delete' method which has a void return value. So, here is my question: is there a better way to do this in Java? This can't be a totally uncommon task, and other languages (like Python) make it easier by allowing methods to be passed. I suspect there might be a way to do this through reflection, but I haven't been able to wrap my head around it.

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