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• Using multiple sockets, is non-blocking or blocking with select better?

  - by JPhi1618

  Lets say I have a server program that can accept connections from 10 (or more) different clients. The clients send data at random which is received by the server, but it is certain that at least one client will be sending data every update. The server cannot wait for information to arrive because it has other processing to do. Aside from using asynchronous sockets, I see two options: Make all sockets non-blocking. In a loop, call recv on each socket and allow it to fail with WSAEWOULDBLOCK if there is no data available and if I happen to get some data, then keep it. Leave the sockets as blocking. Add all sockets to a fd_set and call select(). If the return value is non-zero (which it will be most of the time), loop through all the sockets to find the appropriate number of readable sockets with FD_ISSET() and only call recv on the readable sockets. The first option will create a lot more calls to the recv function. The second method is a bigger pain from a programming perspective because of all the FD_SET and FD_ISSET looping. Which method (or another method) is preferred? Is avoiding the overhead on letting recv fail on a non-blocking socket worth the hassle of calling select()? I think I understand both methods and I have tried both with success, but I don't know if one way is considered better or optimal. Only knowledgeable replies please!

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• Uncompress OpenOffice files for better storage in version control

  - by Craig McQueen

  I've heard discussion about how OpenOffice (ODF) files are compressed zip files of XML and other data. So making a tiny change to the file can potentially totally change the data, so delta compression doesn't work well in version control systems. I've done basic testing on an OpenOffice file, unzipping it and then rezipping it with zero compression. I used the Linux zip utility for my testing. OpenOffice will still happily open it. So I'm wondering if it's worth developing a small utility to run on ODF files each time just before I commit to version control. Any thoughts on this idea? Possible better alternatives? Secondly, what would be a good and robust way to implement this little utility? Bash shell that calls zip (probably Linux only)? Python? Any gotchas you can think of? Obviously I don't want to accidentally mangle a file, and there are several ways that could happen. Possible gotchas I can think of: Insufficient disk space Some other permissions issue that prevents writing the file or temporary files ODF document is encrypted (probably should just leave these alone; the encryption probably also causes large file changes and thus prevents efficient delta compression)

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• Silverlight - how to render image from non-visible data bound user control?

  - by MagicMax

  Hello! I have such situation - I'd like to build timeline control. So I have UserControl and ItemsControl on it (every row represents some person). The ItemsControl contains another ItemsControl as ItemsControl.ItemTemplate - it shows e.g. events for the person arranged by event's date. So it looks as some kind of grid with dates as a column headers and e.g. peoples as row headers. ........................|.2010.01.01.....2010.01.02.....2010.01.03 Adam Smith....|......[some event#1].....[some event#2]...... John Dow.......|...[some event#3].....[some event#4]......... I can have a lot of persons (ItemsControl #1 - 100-200 items) and a lot of events occured by some day (1-10-30 events per person in one day) the problem is that when user scrolls ItemsControl #1/#2 it happened toooo sloooooowwww due to a lot of elements should be rendered in one time (as I have e.g. a bit of text boxes and other elements in description of particular event) Question #1 - how can I improve it? May be somebody knows better way to build such user control? I have to mention that I'm using custom Virtual panel, based on some custom Virtual panel implementation found somewhere in internet... Question #2 - I'd like to make image with help of WriteableBitmap and render data bound control to image and to show image instead of a lot of elements. Problem is that I'm trying to render invisible data bound control (created in code behind) and it has actualWidth/Height equals to zero (so nothing rendered). How can I solve it? Thank you very much for you help!

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• Using Excel as front end to Access database (with VBA)

  - by Alex

  I am building a small application for a friend and they'd like to be able to use Excel as the front end. (the UI will basically be userforms in Excel). They have a bunch of data in Excel that they would like to be able to query but I do not want to use excel as a database as I don't think it is fit for that purpose and am considering using Access. [BTW, I know Access has its shortcomings but there is zero budget available and Access already on friend's PC] To summarise, I am considering dumping a bunch of data into Access and then using Excel as a front end to query the database and display results in a userform style environment. Questions: How easy is it to link to Access from Excel using ADO / DAO? Is it quite limited in terms of functionality or can I get creative? Do I pay a performance penalty (vs.using forms in Access as the UI)? Assuming that the database will always be updated using ADO / DAO commands from within Excel VBA, does that mean I can have multiple Excel users using that one single Access database and not run into any concurrency issues etc.? Any other things I should be aware of? I have strong Excel VBA skills and think I can overcome Access VBA quite quickly but never really done Excel / Access link before. I could shoehorn the data into Excel and use as a quasi-database but that just seems more pain than it is worth (and not a robust long term solution) Any advice appreciated. Alex

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• PHPUnit - multiple stubs of same class

  - by keithjgrant

  I'm building unit tests for class Foo, and I'm fairly new to unit testing. A key component of my class is an instance of BarCollection which contains a number of Bar objects. One method in Foo iterates through the collection and calls a couple methods on each Bar object in the collection. I want to use stub objects to generate a series of responses for my test class. How do I make the Bar stub class return different values as I iterate? I'm trying to do something along these lines: $stubs = array(); foreach ($array as $value) { $barStub->expects($this->any()) ->method('GetValue')) ->will($this->returnValue($value)); $stubs[] = $barStub; } // populate stubs into `Foo` // assert results from `Foo->someMethod()` So Foo->someMethod() will produce data based on the results it receives from the Bar objects. But this gives me the following error whenever the array is longer than one: There was 1 failure: 1) testMyTest(FooTest) with data set #2 (array(0.5, 0.5)) Expectation failed for method name is equal to <string:GetValue> when invoked zero or more times. Mocked method does not exist. /usr/share/php/PHPUnit/Framework/MockObject/Mock.php(193) : eval()'d code:25 One thought I had was to use ->will($this->returnCallback()) to invoke a callback method, but I don't know how to indicate to the callback which Bar object is making the call (and consequently what response to give). Another idea is to use the onConsecutiveCalls() method, or something like it, to tell my stub to return 1 the first time, 2 the second time, etc, but I'm not sure exactly how to do this. I'm also concerned that if my class ever does anything other than ordered iteration on the collection, I won't have a way to test it.

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• Time complexity of a certain program

  - by HokageSama

  In a discussion with my friend i am not able to predict correct and tight time complexity of a program. Program is as below. /* This Function reads input array "input" and update array "output" in such a way that B[i] = index value of nearest greater value from A[i], A[i+1] ... A[n], for all i belongs to [1, n] Time Complexity: ?? **/ void createNearestRightSidedLargestArr(int* input, int size, int* output){ if(!input || size < 1) return; //last element of output will always be zero, since no element is present on its right. output[size-1] = -1; int curr = size - 2; int trav; while(curr >= 0){ if(input[curr] < input[curr + 1]){ output[curr] = curr + 1; curr--; continue; } trav = curr + 1; while( input[ output [trav] ] < input[curr] && output [trav] != -1) trav = output[trav]; output[curr--] = output[trav]; } } I said time complexity is O(n^2) but my friend insists that this is not correct. What is the actual time complexity?

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• Efficient algorithm to find first available name

  - by Avrahamshuk

  I have an array containing names of items. I want to give the user the option to create items without specifying their name, so my program will have to supply a unique default name, like "Item 1". The challenge is that the name has to be unique so i have to check all the array for that default name, and if there is an item with the same name i have to change the name to be "Item 2" and so on until i find an available name. The obvious solution will be something like that: String name; for (int i = 0 , name = "Item " + i ; !isAvailable(name) ; i++); My problem with that algorithm is that it runs at O(N^2). I wonder if there is a known (or new) more efficient algorithm to solve this case. In other words my question is this: Is there any algorithm that finds the first greater-than-zero number that dose NOT exist in a given array, and runs at less that N^2? Thanks!

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• TCL How to read , extract and count the occurent in .txt file (Current Directory)

  - by Passion

  Hi Folks, I am beginner to scripting and vigorously learning TCL for the development of embedded system. I have to Search for the files with only .txt format in the current directory, count the number of cases of each different "Interface # nnnn" string in .txt file, where nnnn is a four or 32 digits max hexadecimal no and o/p of a table of Interface number against occurrence. I am facing implementation issues while writing a script i.e, Unable to implement the data structure like Linked List, Two Dimensional array. I am rewriting a script using multi dimension array (Pass values into the arrays in and out of procedure) in TCL to scan through the every .txt file and search for the the string/regular expression ‘Interface # ’ to count and display the number of occurrences. If someone could help me to complete this part will be much appreciated. Search for only .txt extension files and obtain the size of the file Here is my piece of code for searching a .txt file in present directory set files [glob *.txt] if { [llength $files] > 0 } { puts "Files:" foreach f [lsort $files] { puts " [file size $f] - $f" } } else { puts "(no files)" } I reckon these are all the possible logical steps behind to complete it i) Once searched and find the .txt file then open all .txt files in read only mode ii) Create a array or list using the procedure (proc) Interface number to NULL and Interface count to zero 0 iii) Scan thro the .txt file and search for the string or regular expression "interface # iv) When a match found in .txt file, check the Interface Number and increment the count for the corresponding entry. Else add new element to the Interface Number list v) If there are no files return to the first directory My o/p is like follows Interface Frequency 123f 3 1232 4

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• How to render a DateTime in a specific format in ASP.NET MVC 3?

  - by Slauma

  If I have in my model class a property of type DateTime how can I render it in a specific format - for example in the format which ToLongDateString() returns? I have tried this... @Html.DisplayFor(modelItem => item.MyDateTime.ToLongDateString()) ...which throws an exception because the expression must point to a property or field. And this... @{var val = item.MyDateTime.ToLongDateString(); Html.DisplayFor(modelItem => val); } ...which doesn't throw an exception, but the rendered output is empty (although val contains the expected value, as I could see in the debugger). Thanks for tips in advance! Edit ToLongDateString is only an example. What I actually want to use instead of ToLongDateString is a custom extension method of DateTime and DateTime?: public static string FormatDateTimeHideMidNight(this DateTime dateTime) { if (dateTime.TimeOfDay == TimeSpan.Zero) return dateTime.ToString("d"); else return dateTime.ToString("g"); } public static string FormatDateTimeHideMidNight(this DateTime? dateTime) { if (dateTime.HasValue) return dateTime.Value.FormatDateTimeHideMidNight(); else return ""; } So, I think I cannot use the DisplayFormat attribute and DataFormatString parameter on the ViewModel properties.

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• Sendkeys problem from .NET program

  - by user203123

  THe code below I copied from MSDN with a bit of modification: [DllImport("user32.dll", CharSet = CharSet.Unicode)] public static extern IntPtr FindWindow(string lpClassName,string lpWindowName); DllImport("User32")] public static extern bool SetForegroundWindow(IntPtr hWnd); int cnt = 0; private void button1_Click(object sender, EventArgs e) { IntPtr calculatorHandle = FindWindow("Notepad", "Untitled - Notepad"); if (calculatorHandle == IntPtr.Zero) { MessageBox.Show("Calculator is not running."); return; } SetForegroundWindow(calculatorHandle); SendKeys.SendWait(cnt.ToString()); SendKeys.SendWait("{ENTER}"); cnt++; SendKeys.Flush(); System.Threading.Thread.Sleep(1000); } The problem is the number sequence in Notepad is not continuously. The first click always results 0 (as expected). but from the second click, the result is unpredictable (but the sequence is still in order, e.g. 3, 4, 5, 10, 14, 15, ....) If I click the button fast enough, I was able to get the result in continuous order (0,1,2,3,4,....) but sometimes it produces more than 2 same numbers (e.g. 0,1,2,3,3,3,4,5,6,6,6,7,8,9,...)

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Invalid argument in sendfile() with two regular files

  - by Daniel Hershcovich

  I'm trying to test the sendfile() system call under Linux 2.6.32 to zero-copy data between two regular files. As far as I understand, it should work: ever since 2.6.22, sendfile() has been implemented using splice(), and both the input file and the output file can be either regular files or sockets. The following is the content of sendfile_test.c: #include <sys/sendfile.h> #include <fcntl.h> #include <stdio.h> int main(int argc, char **argv) { int result; int in_file; int out_file; in_file = open(argv[1], O_RDONLY); out_file = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644); result = sendfile(out_file, in_file, NULL, 1); if (result == -1) perror("sendfile"); close(in_file); close(out_file); return 0; } And when I'm running the following commands: $ gcc sendfile_test.c $ ./a.out infile The output is sendfile: Bad file descriptor Which means that the system call resulted in errno = -EINVAL, I think. What am I doing wrong?

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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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• 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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• Retrieving dll version info via Win32 - VerQueryValue(...) crashes under Win7 x64

  - by user256890

  The respected open source .NET wrapper implementation (SharpBITS) of Windows BITS services fails identifying the underlying BITS version under Win7 x64. Here is the source code that fails. NativeMethods are native Win32 calls wrapped by .NET methods and decorated via DllImport attribute. private static BitsVersion GetBitsVersion() { try { string fileName = Path.Combine( System.Environment.SystemDirectory, "qmgr.dll"); int handle = 0; int size = NativeMethods.GetFileVersionInfoSize(fileName, out handle); if (size == 0) return BitsVersion.Bits0_0; byte[] buffer = new byte[size]; if (!NativeMethods.GetFileVersionInfo(fileName, handle, size, buffer)) { return BitsVersion.Bits0_0; } IntPtr subBlock = IntPtr.Zero; uint len = 0; if (!NativeMethods.VerQueryValue(buffer, @"\VarFileInfo\Translation", out subBlock, out len)) { return BitsVersion.Bits0_0; } int block1 = Marshal.ReadInt16(subBlock); int block2 = Marshal.ReadInt16((IntPtr)((int)subBlock + 2 )); string spv = string.Format( @"\StringFileInfo\{0:X4}{1:X4}\ProductVersion", block1, block2); string versionInfo; if (!NativeMethods.VerQueryValue(buffer, spv, out versionInfo, out len)) { return BitsVersion.Bits0_0; } ... The implementation follows the MSDN instructions by the letter. Still during the second VerQueryValue(...) call, the application crashes and kills the debug session without hesitation. Just a little more debug info right before the crash: spv = "\StringFileInfo\040904B0\ProductVersion" buffer = byte[1900] - full with binary data block1 = 1033 block2 = 1200 I looked at the targeted "C:\Windows\System32\qmgr.dll" file (The implementation of BITS) via Windows. It says that the Product Version is 7.5.7600.16385. Instead of crashing, this value should return in the verionInfo string. Any advice?

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• Efficient splitting of elements in a field

  - by Gary

  I have a field in a text file exported from a database. The field contains addresses but sometimes they are quite long and the database allows them to contain multiple lines. When exported, the newline character gets replaced with a dollar sign like this: first part of very long address$second part of very long address$third part of very long address Not every address has multiple lines and no address contains more than three lines. The length of each line is variable. I'm massaging the data for import into MS Access which is used for a mailmerge. I want to split the field on the $ sign if it's there but if the field only contains 1 line, I want to set my two extra output fields to a zero length string so that I don't wind up with blank lines in the address when it gets printed. I have an awk file that's working correctly on all the other data in the textfile but I need to get this last bit working. I tried the below code. Aside from the fact that I get a syntax error at the else, I'm not sure this is a good way to do what I want. This is being done with gawk on Windows. BEGIN { FS = "|" } $1 != "HEADER" { if ($6 ~ /\$/) split($6, arr, "$") address = arr[1] addresstwo = arr[2] addressthree = arr[3] addressLength = length(address) addressTwoLength = length(addresstwo) addressThreeLength = length(addressthree) else { address = $6 addressLength = length($6) addresstwo = "" addressTwoLength = length(addresstwo) addressthree = "" addressThreeLength = length(addressthree) } printf("%*s\t%*s\t\%*s\n", addressLength, address, addressTwoLength, addresstwo, addressThreeLength, addressthree) }

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