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• How to recalculate all-pairs shorthest paths on-line if nodes are getting removed?

  - by Pavel Shved

  Latest news about underground bombing made me curious about the following problem. Assume we have a weighted undirected graph, nodes of which are sometimes removed. The problem is to re-calculate shortest paths between all pairs of nodes fast after such removals. With a simple modification of Floyd-Warshall algorithm we can calculate shortest paths between all pairs. These paths may be stored in a table, where shortest[i][j] contains the index of the next node on the shortest path between i and j (or NULL value if there's no path). The algorithm requires O(n³) time to build the table, and eacho query shortest(i,j) takes O(1). Unfortunately, we should re-run this algorithm after each removal. The other alternative is to run graph search on each query. This way each removal takes zero time to update an auxiliary structure (because there's none), but each query takes O(E) time. What algorithm can be used to "balance" the query and update time for all-pairs shortest-paths problem when nodes of the graph are being removed?

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• Convert a Unit Vector to a Quaternion

  - by Hmm

  So I'm very new to quaternions, but I understand the basics of how to manipulate stuff with them. What I'm currently trying to do is compare a known quaternion to two absolute points in space. I'm hoping what I can do is simply convert the points into a second quaternion, giving me an easy way to compare the two. What I've done so far is to turn the two points into a unit vector. From there I was hoping I could directly plug in the i j k into the imaginary portion of the quaternion with a scalar of zero. From there I could multiply one quaternion by the other's conjugate, resulting in a third quaternion. This third quaternion could be converted into an axis angle, giving me the degree by which the original two quaternions differ by. Is this thought process correct? So it should just be [ 0 i j k ]. I may need to normalize the quaternion afterwards, but I'm not sure about that. I have a bad feeling that it's not a direct mapping from a vector to a quaternion. I tried looking at converting the unit vector to an axis angle, but I'm not sure this would work, since I don't know what angle to give as an input.

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• Is it just me? I find LINQ to XML to be sort of cumbersome, compared to XPath.

  - by Cheeso

  I am a C# programmer, so I don't get to take advantage of the cool XML syntax in VB. Dim itemList1 = From item In rss.<rss>.<channel>.<item> _ Where item.<description>.Value.Contains("LINQ") Or _ item.<title>.Value.Contains("LINQ") Using C#, I find XPath to be easier to think about, easier to code, easier to understand, than performing a multi-nested select using LINQ to XML. Look at this syntax, it looks like Greek swearing: var waypoints = from waypoint in gpxDoc.Descendants(gpx + "wpt") select new { Latitude = waypoint.Attribute("lat").Value, Longitude = waypoint.Attribute("lon").Value, Elevation = waypoint.Element(gpx + "ele") != null ? waypoint.Element(gpx + "ele").Value : null, Name = waypoint.Element(gpx + "name") != null ? waypoint.Element(gpx + "name").Value : null, Dt = waypoint.Element(gpx + "cmt") != null ? waypoint.Element(gpx + "cmt").Value : null }; All the casting, the heavy syntax, the possibility for NullPointerExceptions. None of this happens with XPath. I like LINQ in general, and I use it on object collections and databases, but my first go-round with querying XML led me right back to XPath. Is it just me? Am I missing something? EDIT: someone voted to close this as "not a real question". But it is a real question, stated clearly. The question is: Am I misunderstanding something with LINQ to XML?

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• I am using relational division with EAV, but I need to find results in EAV that have some of the cat

  - by NewToDB

  I have two tables: CREATE TABLE EAV ( subscriber_id INT(1) NOT NULL DEFAULT '0', attribute_id CHAR(62) NOT NULL DEFAULT '', attribute_value CHAR(62) NOT NULL DEFAULT '', PRIMARY KEY (subscriber_id,attribute_id) ) INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'color','red') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'size','xl') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'garment','shirt') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'color','red') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'size','xl') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'garment','pants') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (3,'garment','pants') CREATE TABLE CRITERIA ( attribute_id CHAR(62) NOT NULL DEFAULT '', attribute_value CHAR(62) NOT NULL DEFAULT '' ) INSERT INTO CRITERIA (attribute_id, attribute_value) VALUES ('color', 'red') INSERT INTO CRITERIA (attribute_id, attribute_value) VALUES ('size', 'xl') To find all subscribers in the EAV that match my criteria, I use relational division: SELECT DISTINCT(subscriber_id) FROM EAV WHERE subscriber_id IN (SELECT E.subscriber_id FROM EAV AS E JOIN CRITERIA AS CR ON E.attribute_id = CR.attribute_id AND E.attribute_value = CR.attribute_value GROUP BY E.subscriber_id HAVING COUNT() = (SELECT COUNT() FROM CRITERIA)) This gives me an unique list of subscribers who have all the criteria. So that means I get back subscriber 1 and 2 since they are looking for the color red and size xl, and that's exactly my criteria. But what if I want to extend this so that I also get subscriber 3 since this subscriber didn't specifically say what color or size they want (ie. there is no entry for attribute 'color' or 'size' in the EAV table for subscriber 3). Given my current design, is there a way I can extend my query to include subscribers that have zero or more of the attributes defined, and if they do have the attribute defined, then it must match the criteria? Or is there a better way to design the table to aid in querying?

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• ADO/SQL Server: What is the error code for "timeout expired"?

  - by Ian Boyd

  i'm trying to trap a "timeout expired" error from ADO. When a timeout happens, ADO returns: Number: 0x80040E31 (DB_E_ABORTLIMITREACHED in oledberr.h) SQLState: HYT00 NativeError: 0 The NativeError of zero makes sense, since the timeout is not a function of the database engine (i.e. SQL Server), but of ADO's internal timeout mechanism. The Number (i.e. the COM hresult) looks useful, but the definition of DB_E_ABORTLIMITREACHED in oledberr.h says: Execution stopped because a resource limit was reached. No results were returned. This error could apply to things besides "timeout expired" (some potentially server-side), such as a governor that limits: CPU usage I/O reads/writes network bandwidth and stops a query. The final useful piece is SQLState, which is a database-independent error code system. Unfortunately the only reference for SQLState error codes i can find have no mention of HYT00. What to do? What do do? Note: i can't trust 0x80040E31 (DB_E_ABORTLIMITREACHED) to mean "timeout expired", anymore than i could trust 0x80004005 (E_UNSPECIFIED_ERROR) to mean "Transaction was deadlocked on lock resources with another process and has been chosen as the deadlock victim". My pseudo-question becomes: does anyone have documentation on what the SQLState "HYT000" means? And my real question still remains: How can i specifically trap an ADO timeout expired exception thrown by ADO? Gotta love the questions where the developer is trying to "do the right thing", but nobody knows how to do the right thing. Also gotta love how googling for DB_E_ABORTLIMITREACHED and this question is #9, with MSDN nowhere to be found. Update 3 From the OLEdb ICommand.Execute reference: DB_E_ABORTLIMITREACHED Execution has been aborted because a resource limit has been reached. For example, a query timed out. No results have been returned. "For example", meaning not an exhaustive list.

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• Static variable for communication among like-typed objects

  - by Dan Ray

  I have a method that asynchronously downloads images. If the images are related to an array of objects (a common use-case in the app I'm building), I want to cache them. The idea is, I pass in an index number (based on the indexPath.row of the table I'm making by way through), and I stash the image in a static NSMutableArray, keyed on the row of the table I'm dealing with. Thusly: @implementation ImageDownloader ... @synthesize cacheIndex; static NSMutableArray *imageCache; -(void)startDownloadWithImageView:(UIImageView *)imageView andImageURL:(NSURL *)url withCacheIndex:(NSInteger)index { self.theImageView = imageView; self.cacheIndex = index; NSLog(@"Called to download %@ for imageview %@", url, self.theImageView); if ([imageCache objectAtIndex:index]) { NSLog(@"We have this image cached--using that instead"); self.theImageView.image = [imageCache objectAtIndex:index]; return; } self.activeDownload = [NSMutableData data]; NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:url] delegate:self]; self.imageConnection = conn; [conn release]; } //build up the incoming data in self.activeDownload with calls to didReceiveData... - (void)connectionDidFinishLoading:(NSURLConnection *)connection { NSLog(@"Finished downloading."); UIImage *image = [[UIImage alloc] initWithData:self.activeDownload]; self.theImageView.image = image; NSLog(@"Caching %@ for %d", self.theImageView.image, self.cacheIndex); [imageCache insertObject:image atIndex:self.cacheIndex]; NSLog(@"Cache now has %d items", [imageCache count]); [image release]; } My index is getting through okay, I can see that by my NSLog output. But even after my insertObject: atIndex: call, [imageCache count] never leaves zero. This is my first foray into static variables, so I presume I'm doing something wrong. (The above code is heavily pruned to show only the main thing of what's going on, so bear that in mind as you look at it.)

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• Writing fortran robust and "modern" code

  - by Blklight

  In some scientific environments, you often cannot go without FORTRAN as most of the developers only know that idiom, and there is lot of legacy code and related experience. And frankly, there are not many other cross-platform options for high performance programming ( C++ would do the task, but the syntax, zero-starting arrays, and pointers are too much for most engineers ;-) ). I'm a C++ guy but I'm stuck with some F90 projects. So, let's assume a new project must use FORTRAN (F90), but I want to build the most modern software architecture out of it. while being compatible with most "recent" compilers (intel ifort, but also including sun/HP/IBM own compilers) So I'm thinking of imposing: global variable forbidden, no gotos, no jump labels, "implicit none", etc. "object-oriented programming" (modules with datatypes + related subroutines) modular/reusable functions, well documented, reusable libraries assertions/preconditions/invariants (implemented using preprocessor statements) unit tests for all (most) subroutines and "objects" an intense "debug mode" (#ifdef DEBUG) with more checks and all possible Intel compiler checks possible (array bounds, subroutine interfaces, etc.) uniform and enforced legible coding style, using code processing tools C stubs/wrappers for libpthread, libDL (and eventually GPU kernels, etc.) C/C++ implementation of utility functions (strings, file operations, sockets, memory alloc/dealloc reference counting for debug mode, etc.) ( This may all seem "evident" modern programming assumptions, but in a legacy fortran world, most of these are big changes in the typical programmer workflow ) The goal with all that is to have trustworthy, maintainable and modular code. Whereas, in typical fortran, modularity is often not a primary goal, and code is trustworthy only if the original developer was very clever, and the code was not changed since then ! (i'm a bit joking here, but not much) I searched around for references about object-oriented fortran, programming-by-contract (assertions/preconditions/etc.), and found only ugly and outdated documents, syntaxes and papers done by people with no large-scale project involvement, and dead projects. Any good URL, advice, reference paper/books on the subject?

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• How can I work around the fact that in C++, sin(M_PI) is not 0?

  - by Adam Doyle

  In C++, const double Pi = 3.14159265; cout << sin(Pi); // displays: 3.58979e-009 it SHOULD display the number zero I understand this is because Pi is being approximated, but is there any way I can have a value of Pi hardcoded into my program that will return 0 for sin(Pi)? (a different constant maybe?) In case you're wondering what I'm trying to do: I'm converting polar to rectangular, and while there are some printf() tricks I can do to print it as "0.00", it still doesn't consistently return decent values (in some cases I get "-0.00") The lines that require sin and cosine are: x = r*sin(theta); y = r*cos(theta); BTW: My Rectangular - Polar is working fine... it's just the Polar - Rectangular Thanks! edit: I'm looking for a workaround so that I can print sin(some multiple of Pi) as a nice round number to the console (ideally without a thousand if-statements) edit: In case anyone's curious, this was what I landed on: double sin2(double theta) // in degrees { double s = sin(toRadians(theta)); if (fabs(s - (int)s) < 0.000001) { return floor(s + 0.5); } return s; } where toRadians() is a macro that converts to radians

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• nhibernate - mapping with contraints

  - by Tobias Müller

  Hello everybody, I am having a Problem with my nhibernate-mapping and I can't find a solution by searching on stackoverflow/google/documentation. The database I am using has (amongst others) two tables. One is unit with the following fields: id enduring_id starts ends damage_enduring_id [...] The other one is damage, which has the following fields: id enduring_id starts ends [...] The units are assigned to a damage and one damage can have zero, one or more units working on it. Every time a unit moves to annother damage, the dataset is copied. The field "ends" of the old record and "starts" of the new record are set to the current time stamp, enduring_id stays the same. So if I want to know which units were working on a damage at a certain time, I do the following select: select * from unit join damage on damage.enduring_id = unit.damage_enduring_id where unit.starts <= 'time' and unit.ends = 'time' (This is not an actualy query from the database, I made it up to make clear what I mean. The the real database is a little more complex) Now I want to map it that way, so I can load all the damages which are valid at one time (starts <= wanted time <= ends) and that each of them has a Bag with all the attached units at that time (again starts <= wanted time <= ends). Is this possible within the mapping? Sorry if this is a stupid question, but I am pretty new to nhibernate and I have no clue how to do it. Thanks a lot for reading my post! Bye, Tobias

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• Which is the best jQuery-powered site?

  - by Reigel

  This "Top 10 JavaScript (jQuery) Powered Sites", posted about 2 years ago, was the one that invites me(after seeing the list) to use jQuery. All the sites in that list made me realize how cool it is to build sites powered by jQuery. And now more and more sites are being powered by jQuery. More and more developers are learning jQuery. Two years have past now but I still do a search to google for best sites and still got me to that link and which the link is not updated from the first time I have looked at it. Here at stackoverflow, there are lots of jQuery user. I was thinking if we can here show some of the sites that you know that is powered by jQuery which you think is best. If you can, please make it one site one answer, so that we can make a vote if it's really best jQuery powered site. We will take a look if it is really well implemented ( the way the codes are written, fast speed site, etc...) and deserves to be the best. Lot's of viewers will benefit from it. Like, we can view and have an idea of how we will make our next project cooler, faster, and powerful.

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• Saving NSBitmapImageRep as NSBMPFileType file. Wrong BMP headers and bitmap content

  - by niko34

  I save a NSBitmapImageRep to a BMP file (Snow Leopard). It seems ok when i open it on macos. But it makes an error on my multimedia device (which can show any BMP file from internet). I cannot figure out what is wrong, but when i look inside the file (with the cool hexfiend app on macos), 2 things wrong: the header have a wrong value for the biHeight parameter : 4294966216 (hex=C8FBFFFF) the header have a correct biWidth parameter : 1920 the first pixel in the bitmap content (after 54 bytes headers in BMP format) correspond to the upper left corner of the original image. In the original BMP file and as specified in the BMP format, it should be the down left corner pixel first. To explain the full workflow in my app, i have an NSImageView where i can drag a BMP image. This View is bind to an NSImage. After a drag & drop i have an action to save this image (with some text drawing over it) to a BMP file. Here's the code for saving the new BMP file : CGColorSpaceRefcolorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB); CGContextRefcontext = CGBitmapContextCreate(NULL, (int)1920, (int)1080, 8, 4*(int)1920, colorSpace, kCGImageAlphaNoneSkipLast); [duneScreenViewdrawBackgroundWithDuneFolder:self inContext:context inRect:NSMakeRect(0,0,1920,1080) needScale:NO]; if(folderType==DXFolderTypeMovie) { [duneScreenViewdrawSynopsisContentWithDuneFolder:self inContext:context inRect:NSMakeRect(0,0,1920,1080) withScale:1.0]; } CGImageRef backgroundImageRef = CGBitmapContextCreateImage(context); NSBitmapImageRep*bitmapBackgroundImageRef = [[NSBitmapImageRepalloc] initWithCGImage:backgroundImageRef]; NSData*data = [destinationBitmap representationUsingType:NSBMPFileType properties:nil]; [data writeToFile:[NSStringstringWithFormat:@"%@/%@", folderPath,backgroundPath] atomically: YES]; The duneScreenViewdrawSynopsisContentWithDuneFolder method uses CGContextDrawImage to draw the image. The duneScreenViewdrawSynopsis method uses CoreText to draw some text in the same context. Do you know what's wrong?

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• SqlCe odd results why? -- Same SQL, different results in different apps. Issue with

  - by NitroxDM

  When I run this SQl in my mobile app I get zero rows. select * from inventory WHERE [ITEMNUM] LIKE 'PUMP%' AND [LOCATION] = 'GARAGE' When I run the same SQL in Query Analyzer 3.5 using the same database I get my expected one row. Why the difference? Here is the code I'm using in the mobile app: SqlCeCommand cmd = new SqlCeCommand(Query); cmd.Connection = new SqlCeConnection("Data Source="+filePath+";Persist Security Info=False;"); DataTable tmpTable = new DataTable(); cmd.Connection.Open(); SqlCeDataReader tmpRdr = cmd.ExecuteReader(); if (tmpRdr.Read()) tmpTable.Load(tmpRdr); tmpRdr.Close(); cmd.Connection.Close(); return tmpTable; UPDATE: For the sake of trying I used the code found in one of the answers found here and it works as expected. So my code looks like this: SqlCeConnection conn = new SqlCeConnection("Data Source=" + filePath + ";Persist Security Info=False;"); DataTable tmpTable = new DataTable(); SqlCeDataAdapter AD = new SqlCeDataAdapter(Query, conn); AD.Fill(tmpTable); The issue appears to be with the SqlCeDataReader. Hope this helps someone else out!

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• Php: Overriding abstract method goes wrong

  - by Lu4

  Hi! I think there is a problem in php's OOP implementation. EDIT: Consider more illustrative example: abstract class Animal { public $name; // public function Communicate(Animal $partner) {} // Works public abstract function Communicate(Animal $partner); // Gives error } class Panda extends Animal { public function Communicate(Panda $partner) { echo "Hi {$partner->name} I'm a Panda"; } } class Human extends Animal { public function Communicate(Human $partner) { echo "Hi {$partner->name} I'm a Human"; } } $john = new Human(); $john->name = 'John'; $mary = new Human(); $mary->name = 'Mary'; $john->Communicate($mary); // should be ok $zuzi = new Panda(); $zuzi->name = 'Zuzi'; $zuzi->Communicate($john); // should give error The problem is that when Animal::Communicate is an abstract method, php tells that the following methods are illegal: "public function Communicate(Panda $partner)" "public function Communicate(Human $partner)" but when Animal::Communicate is non-abstract but has zero-implementation Php thinks that these methods are legal. So in my opinion it's not right because we are doing override in both cases, and these both cases are equal, so it seems like it's a bug... Older part of the post: Please consider the following code: Framework.php namespace A { class Component { ... } abstract class Decorator { public abstract function Decorate(\A\Component $component); } } Implementation.php namespace B { class MyComponent extends \A\Component { ... } } MyDecorator.php namespace A { class MyDecorator extends Decorator { public function Decorate(\B\MyComponent $component) { ... } } } The following code gives error in MyDecorator.php telling Fatal error: Declaration of MyDecorator::Decorate() must be compatible with that of A\Decorator::Decorate() in MyDecorator.php on line ... But when I change the Framework.php::Decorator class to the following implementation: abstract class Decorator { public function Decorate(\A\Component $component) {} } the problem disappears.

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• Straw Poll - K&R vs BSD

  - by Gordon Mackie JoanMiro

  No holy wars please - (ultimately a standardised and consistently-observed house-style on a project always wins out whatever is chosen), but I am genuinely interested in the preferences of people for K&R style formatting: public bool CompareObjects(object first, object second) { if (first == second) { return true; } else { return false; } } over BSD style: public bool CompareObjects(object first, object second) { if (first == second) { return true; } else { return false; } } K&R seems to be making a bit of a comeback recently (I'm an old programmer, so I've seen these things fluctuate); do people think K&R looks more professional, more cool, more readable, is compactness when viewing more important than extending the structure down the screen? Please use the 2 community wiki answers below to vote for K&R vs. BSD. Polls shouldn't earn rep for the first person that manages to type "BSD FTW!" My God! This question is nearly 2 years old and people are still down-voting it; ENOUGH!

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• How to html encode the output of an NHaml view (or any MVC view)?

  - by jessegavin

  I have several views written in NHaml that I would like to render as encoded html. Here's one. %table.data %thead %tr %th Country Name %th ISO 2 %th ISO 3 %th ISO # %tbody - foreach(var c in ViewData.Model.Countries) %tr %td =c.Name %td =c.Alpha2 %td =c.Alpha3 %td =c.Number I know that NHaml provides syntax to Html encode the output for given lines using &=. However, in order to encode the entire view, I would essentially lose the benefit of writing my view in NHaml since it would have to look like this.... &= "<table class='data'> &= " <thead> So I was wondering if there was any cool way to be able to capture the rendered view as a string, then to html encode that string. Maybe something like the following??? public ContentResult HtmlTable(string format) { var m = new CountryViewModel(); m.Countries = _countryService.GetAll(); // Somehow render the view and store it as a string? // Not sure how to achieve this. var viewHtml = View("HtmlTable", m); // ??? return Content(viewHtml); } This question may actually have no particular relevance to the View engine that I am using I guess. Any help or thoughts would be appreciated.

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• Convert rank-per-candidate format to OpenSTV BLT format

  - by kibibu

  I recently gathered, using a questionnaire, a set of opinions on the importance of various software components. Figuring that some form of Condorcet voting method would be the best way to obtain an overall rank, I opted to use OpenSTV to analyze it. My data is in tabular format, space delimited, and looks more or less like: A B C D E F G # Candidates 5 2 4 3 7 6 1 # First ballot. G is ranked first, and E is ranked 7th 4 2 6 5 1 7 3 # Second ballot etc In this format, the number indicates the rank and the sequence order indicates the candidate. Each "candidate" has a rank (required) from 1 to 7, where a 1 means most important and a 7 means least important. No duplicates are allowed. This format struck me as the most natural way to represent the output, being a direct representation of the ballot format. The OpenSTV/BLT format uses a different method of representing the same info, conceptually as follows: G B D C A F E # Again, G is ranked first and E is ranked 7th E B G A D C F # etc The actual numeric file format uses the (1-based) index of the candidate, rather than the label, and so is more like: 7 2 4 3 1 6 5 # Same ballots as before. 5 2 7 1 4 3 6 # A -> 1, G -> 7 In this format, the number indicates the candidate, and the sequence order indicates the rank. The actual, real, BLT format also includes a leading weight and a following zero to indicate the end of each ballot, which I don't care too much about for this. My question is, what is the most elegant way to convert from the first format to the (numeric) second?

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• Python template engine

  - by jturo

  Hello there, Could it be possible if somebody could help me get started in writing a python template engine? I'm new to python and as I learn the language I've managed to write a little MVC framework running in its own light-weight-WSGI-like server. I've managed to write a script that finds and replaces keys for values: (Obviously this is not how my script is structured or implemented. this is just an example) from string import Template html = '<html>\n' html += ' <head>\n' html += ' <title>This is so Cool : In Controller HTML</title>\n' html += ' </head>\n' html += ' <body>\n' html += ' Home | <a href="/hi">Hi ${name}</a>\n' html += ' </body>\n' html += '<html>' Template(html).safe_substitute(dict(name = 'Arturo')) My next goal is to implement custom statements, modifiers, functions, etc (like 'for' loop) but i don't really know if i should use another module that i don't know about. I thought of regular expressions but i kind feel like that wouldn't be an efficient way of doing it Any help is appreciated, and i'm sure this will be of use to other people too. Thank you

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• Null reference exception While Navigating to PlayListItem.

  - by Subhen

  Hi, I am trying to play the selected media from PlayList,if the selected index is not zero as below: if (playList.Items.Count == 0) { setPlayList(); if (selectedIndex!= 0) { if(custMediaElement.Playlist!=null) custMediaElement.GoToPlaylistItem(selectedIndex); } } The setPlayLIst method is as below: private void setPlayList() { IEnumerable eLevelData = pMainPage.GetDataFromDictonary(pMainPage.strChildFolderID); foreach (RMSMedia folderItems in eLevelData) { string strmediaURL = folderItems.strMediaFileName; string strmediaExtension = GetExtension(strmediaURL); if (strmediaExtension == "wmv" || strmediaExtension == "mp4" || strmediaExtension == "mp3" || strmediaExtension == "mpg") { PlaylistItem playListItem = new PlaylistItem(); string thumbSource = folderItems.strAlbumcoverImage; playListItem.MediaSource = new Uri(strmediaURL, UriKind.RelativeOrAbsolute); playListItem.Title = folderItems.strAlbumName; if (!string.IsNullOrEmpty(thumbSource)) playListItem.ThumbSource = new Uri(thumbSource, UriKind.RelativeOrAbsolute); playList.Items.Add(playListItem); } } custMediaElement.Playlist = playList; } But I am getting a Null reference Exception while trying to go to PlayList Item with the help of selected index , as explained in top. This works fine if I don't use custMediaElement.GoToPlaylistItem(selectedIndex); but in that case the Media Player Always plays the 1st Item , No matter , Which ever Song I select from the List Box. Below is few details from Stack Trace: ExpressionMediaPlayer.MediaPlayer.DoOpenPlaylistItem(PlaylistItem playlistItem) at ExpressionMediaPlayer.MediaPlayer.GoToPlaylistItem(Int32 playlistItemIndex) Thanks, Subhen

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• Can a class inherit from LambdaExpression in .NET? Or is this not recommended?

  - by d.

  Consider the following code (C# 4.0): public class Foo : LambdaExpression { } This throws the following design-time error: Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) There's absolutely no problem with public class Foo : Expression { } but, out of curiosity and for the sake of learning, I've searched in Google System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) and guess what: zero results returned (when was the last time you saw that?). Needless to say, I haven't found any documentation on this method anywhere else. As I said, one can easily inherit from Expression; on the other hand LambdaExpression, while not marked as sealed (Expression<TDelegate> inherits from it), seems to be designed to prevent inheriting from it. Is this actually the case? Does anyone out there know what this method is about? EDIT (1): More info based on the first answers - If you try to implement Accept, the editor (C# 2010 Express) automatically gives you the following stub: protected override Expression Accept(System.Linq.Expressions.ExpressionVisitor visitor) { return base.Accept(visitor); } But you still get the same error. If you try to use a parameter of type StackSpiller directly, the compiler throws a different error: System.Linq.Expressions.Compiler.StackSpiller is inaccessible due to its protection level. EDIT (2): Based on other answers, inheriting from LambdaExpression is not possible so the question as to whether or not it is recommended becomes irrelevant. I wonder if, in cases like this, the error message should be Foo cannot implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) because [reasons go here]; the current error message (as some answers prove) seems to tell me that all I need to do is implement Accept (which I can't do).

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• Troubleshooting failover cluster problem in W2K8 / SQL05

  - by paulland

  I have an active/passive W2K8 (64) cluster pair, running SQL05 Standard. Shared storage is on a HP EVA SAN (FC). I recently expanded the filesystem on the active node for a database, adding a drive designation. The shared storage drives are designated as F:, I:, J:, L: and X:, with SQL filesystems on the first 4 and X: used for a backup destination. Last night, as part of a validation process (the passive node had been offline for maintenance), I moved the SQL instance to the other cluster node. The database in question immediately moved to Suspect status. Review of the system logs showed that the database would not load because the file "K:\SQLDATA\whatever.ndf" could not be found. (Note that we do not have a K: drive designation.) A review of the J: storage drive showed zero contents -- nothing -- this is where "whatever.ndf" should have been. Hmm, I thought. Problem with the server. I'll just move SQL back to the other server and figure out what's wrong.. Still no database. Suspect. Uh-oh. "Whatever.ndf" had gone into the bit bucket. I finally decided to just restore from the backup (which had been taken immediately before the validation test), so nothing was lost but a few hours of sleep. The question: (1) Why did the passive node think the whatever.ndf files were supposed to go to drive "K:", when this drive didn't exist as a resource on the active node? (2) How can I get the cluster nodes "re-syncd" so that failover can be accomplished? I don't know that there wasn't a "K:" drive as a cluster resource at some time in the past, but I do know that this drive did not exist on the original cluster at the time of resource move.

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• Windows Batch file to echo a specific line number

  - by Lee

  So for the second part of my current dilemma, I have a list of folders in c:\file_list.txt. I need to be able to extract them (well, echo them with some mods) based on the line number because this batch script is being called by an iterative macro process. I'm passing the line number as a parameter. @echo off setlocal enabledelayedexpansion set /a counter=0 set /a %%a = "" for /f "usebackq delims=" %%a in (c:\file_list.txt) do ( if "!counter!"=="%1" goto :printme & set /a counter+=1 ) :printme echo %%a which gives me an output of %a. Doh! So, I've tried echoing !a! (result: ECHO is off.); I've tried echoing %a (result: a) I figured the easy thing to do would be to modify the head.bat code found here: http://stackoverflow.com/questions/130116/dos-batch-commands-to-read-first-line-from-text-file except rather than echoing every line - I'd just echo the last line found. Not as simple as one might think. I've noticed that my counter is staying at zero for some reason; I'm wondering if the set /a counter+=1 is doing what I think it's doing.

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• Delphi - Capture stdout and stderr output from statically linked MSVC++ compiled DLL

  - by Alan G.

  I have been trying to capture stdout and stderr output from a DLL compiled in MSVC++ that my Delphi app statically links to, but so far have been unsuccessful. procedure Test; var fs: TFileStream; begin fs := TFileStream.Create('C:\temp\output.log', fmCreate or fmShareDenyWrite); SetStdHandle(STD_OUTPUT_HANDLE, fs.Handle); SetStdHandle(STD_ERROR_HANDLE, fs.Handle); dllFunc(0); // Writes to stdout in MSVC++ console app, but not here // fs.Length is always zero fs.Free; end; Thought I was on the right track, but it does not work. Is SetStdHandle() enough? Is TFileStream the right thing to use here? Am I using TFileStream properly for SetStdHandle()? Is it possible that the DLL sets its stdout/stderr handles when the app loads? If so, where is the best place to use SetStdHandle() or equivalent? Any help would be appreciated.

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• How can I create a WebBrowser control (ActiveX / IWebBrowser2) without a UI?

  - by wangminhere

  I cannot figure out how to use the WebBrowser control without having it create a window in the taskbar. I am using the IWebBrowser2 ActiveX control directly because I need to use some of the advanced features like blocking downloading JAVA/ActiveX/images etc. That apparently is not available in the WPF or winforms WebBrowser wrappers (but these wrappers do have the ability to create the control with no UI) Here is my code for creating the control: Type webbrowsertype = Type.GetTypeFromCLSID(Iid_Clsids.CLSID_WebBrowser, true); m_WBWebBrowser2 = (IWebBrowser2)System.Activator.CreateInstance(webbrowsertype); m_WBWebBrowser2.Visible = false; m_WBOleObject = (IOleObject)m_WBWebBrowser2; int iret = m_WBOleObject.SetClientSite(this); iret = m_WBOleObject.SetHostNames("me", string.Empty); tagRECT rect = new tagRECT(0, 0, 0, 0); tagMSG nullMsg = new tagMSG(); m_WBOleInPlaceObject = (IOleInPlaceObject)m_WBWebBrowser2; //INPLACEACTIVATE the WB iret = m_WBOleObject.DoVerb((int)OLEDOVERB.OLEIVERB_INPLACEACTIVATE, ref nullMsg, this, 0, IntPtr.Zero, ref rect); IConnectionPointContainer cpCont = (IConnectionPointContainer)m_WBWebBrowser2; Guid guid = typeof(DWebBrowserEvents2).GUID; IConnectionPoint m_WBConnectionPoint = null; cpCont.FindConnectionPoint(ref guid, out m_WBConnectionPoint); m_WBConnectionPoint.Advise(this, out m_dwCookie); This code works perfectly but it shows a window in the taskbar. If i omit the DoVerb(OLEDOVERB.OLEIVERB_INPLACEACTIVATE) call, then Navigating to a webpage is not working properly. Navigate() will not download everything on the page and it never fires the DocumentComplete event. If I add a DoVerb(OLEIVERB_HIDE) then I get the same behavior as if I omitted the DoVerb(OLEDOVERB.OLEIVERB_INPLACEACTIVATE) call. This seems like a pretty basic question but I couldn't find any examples anywhere.

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• How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: class Array def shuffle ret = dup j = length i = 0 while j > 1 r = i + rand(j) ret[i], ret[r] = ret[r], ret[i] i += 1 j -= 1 end ret end end (0..9).to_a.shuffle.each{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle is used to efficiently provide random ordering. My problem is that shuffle needs to operate on an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. Imagine replacing (0..9) with (0..99**99). This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do? [Edit1]: Why do I want to do this? I'm trying to exhaust the search space of a hash algorithm for a N-length input string looking for partial collisions. Each number I generate is equivalent to a unique input string, entropy and all. Basically, I'm "counting" using a custom alphabet. [Edit2]: This means that f(x) in the above examples is a method that generates a hash and compares it to a constant, target hash for partial collisions. I do not need to store the value of x after I call f(x) so memory should remain constant over time. [Edit3/4/5/6]: Further clarification/fixes.

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• NHibernate: how to handle entity-based validation using session-per-request pattern, without control

  - by Seth Petry-Johnson

  What is the best way to do entity-based validation (each entity class has an IsValid() method that validates its internal members) in ASP.NET MVC, with a "session-per-request" model, where the controller has zero (or limited) knowledge of the ISession? Here's the pattern I'm using: Get an entity by ID, using an IFooRepository that wraps the current NH session. This returns a connected entity instance. Load the entity with potentially invalid data, coming from the form post. Validate the entity by callings its IsValid() method. If valid, call IFooRepository.Save(entity). Otherwise, display error message. The session is currently opened when the request begins and flushed when the request ends. Since my entity is connected to a session, flushing the session attempts to save the changes even if the object is invalid. What's the best way to keep validation logic in the entity class, limit controller knowledge of NH, and avoid saving invalid changes at the end of a request? Option 1: Explicitly evict on validation failure, implicitly flush: if the validation fails, I could manually evict the invalid object in the action method. If successful, I do nothing and the session is automatically flushed. Con: error prone and counter-intuitive ("I didn't call .Save(), why are my invalid changes being saved anyways?") Option 2: Explicitly flush, do nothing by default: By default I can dispose of the session on request end, only flushing if the controller indicates success. I'd probably create a SaveChanges() method in my base controller that sets a flag indicating success, and then query this flag when closing the session at request end. Pro: More intuitive to troubleshoot if dev forgets this step [relative to option 1] Con: I have to call IRepository.Save(entity)' and SaveChanges(). Option 3: Always work with disconnected objects: I could modify my repositories to return disconnected/transient objects, and modify the Repo.Save() method to re-attach them. Pro: Most intuitive, given that controllers don't know about NH. Con: Does this defeat many of the benefits I'd get from NH?

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