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• What does O(log n) mean exactly?

  - by Andreas Grech

  I am currently learning about Big O Notation running times and amortized times. I understand the notion of O(n) linear time, meaning that the size of the input affects the growth of the algorithm proportionally...and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by factorials. For example, the following function is O(n) because the algorithm grows in proportion to its input n: f(int n) { int i; for (i = 0; i < n; ++i) printf("%d", i); } Similarly, if there was a nested loop, the time would be O(n2). But what exactly is O(log n)? For example, what does it mean to say that the height of a complete binary tree is O(log n)? I do know (maybe not in great detail) what Logarithm is, in the sense that: log10 100 = 2, but I cannot understand how to identify a function with a logarithmic time.

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• ASP.NET error on Bitmap.Save "Exception (0x80004005): A generic error occurred in GDI+."

  - by Batu

  Hi, I have a function which first reads an image from disk, resizes it and then saves to another directory. when i use the Bitmap.Save(directory + theimagename) it returns the error as i stated in the question title. i checked the directory is right, and the given image name doesn't exist in that dir. what is weird, is that the same code works great on the local machine. but when i upload it to my shared server. it just doesn't work. the code is below. bmpOut = new Bitmap(Size, Size); Graphics g = Graphics.FromImage(bmpOut); g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; g.FillRectangle(Brushes.White, 0, 0, Size, Size); int topBottomPadding = 0; int leftRightPadding = 0; if (Size > lnNewWidth + 1) leftRightPadding = Convert.ToInt32((Size - lnNewWidth) / 2); else if (Size > lnNewHeight + 1) topBottomPadding = Convert.ToInt32((Size - lnNewHeight) / 2); g.DrawImage(loBMP, leftRightPadding, topBottomPadding, lnNewWidth, lnNewHeight); Bitmap bmp = new Bitmap(bmpOut); if (bmp != null) bmp.Save(ResizedOutput); bmp.Dispose(); bmpOut.Dispose(); g.Dispose(); loBMP.Dispose(); stack trace: [ExternalException (0x80004005): A generic error occurred in GDI+.] System.Drawing.Image.Save(String filename, ImageCodecInfo encoder, EncoderParameters encoderParams) +377630 System.Drawing.Image.Save(String filename, ImageFormat format) +69 System.Drawing.Image.Save(String filename) +25 Utilities.ResizeImage(String fileName, String mode) in c:\inetpub\vhosts\batuhanakcay.com\httpdocs\App_Code\Utilities.cs:181 Link.ToProductImage(String fileName) in c:\inetpub\vhosts\batuhanakcay.com\httpdocs\App_Code\Link.cs:79 Product.PopulateControls(ProductDetails pd) in c:\inetpub\vhosts\batuhanakcay.com\httpdocs\Product.aspx.cs:37 Product.Page_Load(Object sender, EventArgs e) in c:\inetpub\vhosts\batuhanakcay.com\httpdocs\Product.aspx.cs:20

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• ListView Final Column Autosize creates scrollbar

  - by Courtney de Lautour

  Hi There, I am implementing a custom control which derives from ListView. I would like for the final column to fill the remaining space (Quite a common task), I have gone about this via overriding the OnResize method: protected override void OnResize(EventArgs e) { base.OnResize(e); if (Columns.Count == 0) return; Columns[Columns.Count - 1].Width = -2; // -2 = Fill remaining space } or via another method: protected override void OnResize(EventArgs e) { base.OnResize(e); if (!_autoFillLastColumn) return; if (Columns.Count == 0) return; int TotalWidth = 0; int i = 0; for (; i < Columns.Count - 1; i++) { TotalWidth += Columns[i].Width; } Columns[i].Width = this.DisplayRectangle.Width - TotalWidth; } Edit: This works fine until I dock the ListView into a parent container and resize via that control. Every second time the control size shrinks (IE, drag the the border one pixel), I get a scroll bar on the bottom which can't move at all (not even one pixel). The result of which is when I drag the size of the parent I am left with a flickering scroll bar in the ListView, and a 50% chance it will be there when the dragging stops.

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• Wordpress creating plugin for most viewed posts problem?

  - by user303832

  Hello,I just want to create plugin that will when visitor(user,visitor,...) visit some post,remember what post,and to increment counter of that post,I wrote this code,but sometimes,counter is incremented,even post isn't viewed,or post with other Id is added to a table.Can someone help me with this,please.I know that there are plugins for this that I'm trying to do,but still want to write this plugin. function IncrementPostCount($the_content) { global $post; global $wpdb; if(($post->post_status == 'publish') && (int)$post->ID) { if(is_single()) { // just for single post - not for page $postID = (int)$post->ID; $postTitle = urlencode($post->post_title); $postLink = urlencode(get_permalink($post->ID)); $oneRow = $wpdb->get_row("SELECT * FROM wp_postovi WHERE postAjDi='$postID'"); if(empty ($oneRow)) { $postCounter = 1; $data_array = array( 'readnTimes' => $postCounter, 'linkPost'=>$postLink, 'TitlePost'=>$postTitle, 'postAjDi'=>$postID); $wpdb->insert('wp_najcitaniji_postovi', $data_array); } else { $postCounter = intval($oneRow->readnTimes) + 1; $data_array = array('readnTimes' => $postCounter); $where_array = array('postAjDi'=>intval($oneRow->postAjDi)); $wpdb->update('wp_postovi',$data_array,$where_array); } return $the_content; } return $the_content; } } add_filter('the_content','IncrementPostCount'); Sorry on my bad english,tnx in advance.

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• How do I apply a "template" or "skeleton" of code in C# here?

  - by Scott Stafford

  In my business layer, I need many, many methods that follow the pattern: public BusinessClass PropertyName { get { if (this.m_LocallyCachedValue == null) { if (this.Record == null) { this.m_LocallyCachedValue = new BusinessClass( this.Database, this.PropertyId); } else { this.m_LocallyCachedValue = new BusinessClass( this.Database, this.Record.ForeignKeyName); } } return this.m_LocallyCachedValue; } } I am still learning C#, and I'm trying to figure out the best way to write this pattern once and add methods to each business layer class that follow this pattern with the proper types and variable names substituted. BusinessClass is a typename that must be substituted, and PropertyName, PropertyId, ForeignKeyName, and m_LocallyCachedValue are all variables that should be substituted for. Are attributes usable here? Do I need reflection? How do I write the skeleton I provided in one place and then just write a line or two containing the substitution parameters and get the pattern to propagate itself? EDIT: Modified my misleading title -- I am hoping to find a solution that doesn't involve code generation or copy/paste techniques, and rather to be able to write the skeleton of the code once in a base class in some form and have it be "instantiated" into lots of subclasses as the accessor for various properties. EDIT: Here is my solution, as suggested but left unimplemented by the chosen answerer. // I'll write many of these... public BusinessClass PropertyName { get { return GetSingleRelation(ref this.m_LocallyCachedValue, this.PropertyId, "ForeignKeyName"); } } // That all call this. public TBusinessClass GetSingleRelation<TBusinessClass>( ref TBusinessClass cachedField, int fieldId, string contextFieldName) { if (cachedField == null) { if (this.Record == null) { ConstructorInfo ci = typeof(TBusinessClass).GetConstructor( new Type[] { this.Database.GetType(), typeof(int) }); cachedField = (TBusinessClass)ci.Invoke( new object[] { this.Database, fieldId }); } else { var obj = this.Record.GetType().GetProperty(objName).GetValue( this.Record, null); ConstructorInfo ci = typeof(TBusinessClass).GetConstructor( new Type[] { this.Database.GetType(), obj.GetType()}); cachedField = (TBusinessClass)ci.Invoke( new object[] { this.Database, obj }); } } return cachedField; }

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• Mysql error in stored procudure

  - by devuser

  This stored procedure is to search through all tables and columns in database. DELIMITER $$ DROP PROCEDURE IF EXISTS get_table $$ CREATE /*[DEFINER = { user | CURRENT_USER }]*/ PROCEDURE `auradoxdb`.`get_table`(in_search varchar(50)) READS SQL DATA BEGIN DECLARE trunc_cmd VARCHAR(50); DECLARE search_string VARCHAR(250); DECLARE db,tbl,clmn CHAR(50); DECLARE done INT DEFAULT 0; DECLARE COUNTER INT; DECLARE table_cur CURSOR FOR SELECT concat(SELECT COUNT(*) INTO @CNT_VALUE FROM `’,table_schema,’`.`’,table_name,’` WHERE `’, column_name,’` REGEXP ”’,in_search,”’) ,table_schema,table_name,column_name FROM information_schema.COLUMNS WHERE TABLE_SCHEMA NOT IN (‘information_schema’,'test’,'mysql’); DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1; # #Truncating table for refill the data for new search. PREPARE trunc_cmd FROM “TRUNCATE TABLE temp_details;” EXECUTE trunc_cmd ; OPEN table_cur; table_loop:LOOP FETCH table_cur INTO search_string,db,tbl,clmn; # #Executing the search SET @search_string = search_string; SELECT search_string; PREPARE search_string FROM @search_string; EXECUTE search_string; SET COUNTER = @CNT_VALUE; SELECT COUNTER; IF COUNTER>0 THEN # # Inserting required results from search to tablehhh INSERT INTO temp_details VALUES(db,tbl,clmn); END IF; IF done=1 THEN LEAVE table_loop; END IF; END LOOP; CLOSE table_cur; # #Finally Show Results SELECT * FROM temp_details; END $$ DELIMITER ; Following error occurs when execute this.. Error Code : 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT COUNT(*) INTO @CNT_VALUE FROM `’,table_schema,’`.`’,table_name,’`' at line 12 (0 ms taken) could any body please help me to solve this?

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• LNK2001 error when compiling windows forms application with VC++ 2008

  - by Blin

  I've been trying to write a small application which will work with mysql in C++. I am using MySQL server 5.1.41 and MySQL C++ connector 1.0.5. Everything compiles fine when i write console applications, but when i try to compile windows forms application exactly the same way (same libraries, same paths, same project properties) i get this errors: Error 1 error LNK2001: unresolved external symbol "public: virtual int __clrcall sql::mysql::MySQL_Savepoint::getSavepointId(void)" (?getSavepointId@MySQL_Savepoint@mysql@sql@@$$FUAMHXZ) test1.obj test1 Error 2 error LNK2001: unresolved external symbol "public: virtual class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __clrcall sql::mysql::MySQL_Savepoint::getSavepointName(void)" (?getSavepointName@MySQL_Savepoint@mysql@sql@@$$FUAM?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ) test1.obj test1 following instructions from here, i've got this: Undecoration of :- "?getSavepointId@MySQL_Savepoint@mysql@sql@@UEAAHXZ" is :- "public: virtual int __cdecl sql::mysql::MySQL_Savepoint::getSavepointId(void) __ptr64" Undecoration of :- "?getSavepointName@MySQL_Savepoint@mysql@sql@@UEAA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@XZ" is :- "public: virtual class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl sql::mysql::MySQL_Savepoint::getSavepointName(void) __ptr64" but what should i do now?

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• Is there something wrong with this code? AMFReader vs AMFWriter

  - by Triynko

  Something doesn't seem right about the source code for Flash Remoting's Date(AS3) <- DateTime(.NET) stream reader/writer methods, when it comes to handling UTC <- Local times. It seems to write the DateTime data fine, including a 64-bit representation as milliseconds elapsed since Jan 1, 1970, as well as a UTC offset. public void WriteDateTime(DateTime d) { this.BaseStream.WriteByte(11); DateTime time = new DateTime(0x7b2, 1, 1); long totalMilliseconds = (long)d.Subtract(time).TotalMilliseconds; long l = BitConverter.DoubleToInt64Bits((double)totalMilliseconds); this.WriteLong(l); int hours = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Today).Hours; this.WriteShort(hours); } But when the data is read... it seems to be ignoring the short UTC offset value that was written, and appears to just discard it! private DateTime ReadDateValue() { long num2 = (long)this.ReadDouble(); DateTime time2 = new DateTime(0x7b2, 1, 1).AddMilliseconds((double)num2); int num3 = this.ReadInt16() / 60; //num3 is not used for anything! return time2; } Can anyone make sense of this? I also found some similar source code for AMFReader here, which has a ReadDateTime method, that seems to do something very similar... but goes on to use the UTC offset for something.

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• Drawing only part of a

  - by Ben Reeves

  ..Continued on from my previous question I have a 320*480 RGB565 framebuffer which I wish to draw using OpenGL ES 1.0 on the iPhone. - (void)setupView { glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, (int[4]){0, 0, 480, 320}); glEnable(GL_TEXTURE_2D); } // Updates the OpenGL view when the timer fires - (void)drawView { // Make sure that you are drawing to the current context [EAGLContext setCurrentContext:context]; //Get the 320*480 buffer const int8_t * frameBuf = [source getNextBuffer]; //Create enough storage for a 512x512 power of 2 texture int8_t lBuf[2*512*512]; memcpy (lBuf, frameBuf, 320*480*2); //Upload the texture glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 512, 512, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, lBuf); //Draw it glDrawTexiOES(0, 0, 1, 480, 320); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; } If I produce the original texture in 512*512 the output is cropped incorrectly but other than that looks fine. However using the require output size of 320*480 everything is distorted and messed up. I'm pretty sure it's the way I'm copying the framebuffer into the new 512*512 buffer. I have tried this routine int8_t lBuf[512][512][2]; const char * frameDataP = frameData; for (int ii = 0; ii < 480; ++ii) { memcpy(lBuf[ii], frameDataP, 320); frameDataP += 320; } Which is better, but the width appears to be stretched and the height is messed up. Any help appreciated.

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• Intel IA-32 Assembly

  - by Kay

  I'm having a bit of difficulty converting the following java code into Intel IA-32 Assembly: class Person() { char name [8]; int age; void printName() {...} static void printAdults(Person [] list) { for(int k = 0; k < 100; k++){ if (list[k].age >= 18) { list[k].printName(); } } } } My attempt is: Person: push ebp; save callers ebp mov ebp, esp; setup new ebp push esi; esi will hold name push ebx; ebx will hold list push ecx; ecx will hold k init: mov esi, [ebp + 8]; mov ebx, [ebp + 12]; mov ecx, 0; k=0 forloop: cmp ecx, 100; jge end; if k>= 100 then break forloop cmp [ebx + 4 * ecx], 18 ; jl auxloop; if list[k].age < 18 then go to auxloop jmp printName; printName: auxloop: inc ecx; jmp forloop; end: pop ecx; pop ebx; pop esi; pop ebp; Is my code correct? NOTE: I'm not allowed to use global variables.

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• Copy constructor using private attributes

  - by Pedro Magueija

  Hello all, My first question here so be gentle. I would like arguments for the following code: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.name = e.name; // accessing a private attribute of an instance this.age = e.age; } ... } I believe this breaks the modularity of the instance passed to the copy construct. This is what I believe to be correct: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.setName(e.getName()); this.setAge(e.getAge()); } ... } A friend has exposed a valid point of view, saying that in the copy construct we should create the object as fast as possible. And adding getter/setter methods would result in unnecessary overhead. I stand on a crossroad. Can you shed some light?

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• "Unable to open file", when the program tries to open file in /proc

  - by tristartom

  Hi, I try to read file /proc/'pid'/status, using c program. The code is as follows, and even I use sudo to run it, the prompt still keeps throwing "Unable to open file". Please let me know if you have any ideas on how to fix this. thanks Richard ... int main (int argc, char* argv[]) { string line; char* fileLoc; if(argc != 2) { cout << "a.out file_path" << endl; fileLoc = "/proc/net/dev"; } else { sprintf(fileLoc, "/proc/%d/status", atoi(argv[1])); } cout<< fileLoc << endl; ifstream myfile (fileLoc); if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; } myfile.close(); } else cout << "Unable to open file"; return 0; }

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• Proper Usage of SqlConnection in .NET

  - by Jojo

  Hi guys, I just want an opinion on the proper usage or a proper design with regards to using SqlConnection object. Which of the 2 below is the best use: A data provider class whose methods (each of them) contain SqlConnection object (and disposed when done). Like: IList<Employee> GetAllEmployees() { using (SqlConnection connection = new SqlConnection(this.connectionString)) { // Code goes here... } } Employee GetEmployee(int id) { using (SqlConnection connection = new SqlConnection(this.connectionString)) { // Code goes here... } } or SqlConnection connection; // initialized in constructor IList<Employee> GetAllEmployees() { this.TryOpenConnection(); // tries to open member SqlConnection instance // Code goes here... this.CloseConnection(); // return } Employee GetEmployee(int id) { this.TryOpenConnection(); // tries to open member SqlConnection instance // Code goes here... this.CloseConnection(); // return } Or is there a better approach than this? I have a focused web crawler type of application and this application will crawl 50 or more websites simultaneously (multithreaded) with each website contained in a crawler object and each crawler object has an instance of a data provider class (above). Please advise. Thanks.

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• How do I update blackberry UI items from a thread?

  - by Andrei T. Ursan

  public class PlayText extends Thread { private int duration; private String text; private PlayerScreen playerscrn; public PlayText(String text, int duration) { this.duration = duration; this.text = text; this.playerscrn = (PlayerScreen)UiApplication.getUiApplication().getActiveScreen(); } public void run() { synchronized(UiApplication.getEventLock()) { try{ RichTextField text1player = new RichTextField(this.text, Field.NON_FOCUSABLE); playerscrn.add(text1player); playerscrn.invalidate(); Thread.sleep(this.duration); RichTextField text2player = new RichTextField("hahhaha", Field.NON_FOCUSABLE); playerscrn.add(text2player); playerscrn.invalidate(); Thread.sleep(1000); RichTextField text3player = new RichTextField("Done", Field.NON_FOCUSABLE); playerscrn.add(text3player); playerscrn.invalidate(); }catch(Exception e){ System.out.println("I HAVE AN ERROR"); } } } } With the above code I'm trying to create a small text player. Instead to get all the text labels one by one, something like display text1player wait this.duration milliseconds display text2player wait 1000 milliseconds display text3player thread done. The screens waits this.duration + 1000 milliseconds and displays all the labels at once. I tried with a runnable and calling .invokeLater or .invokeAndWait but I still get the same behavior, and even if I get dirty like above using synchronized it still doesn't work. Does anyone know how I can display each label at a time? Thank you!

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• iPhone slide view passing variables

  - by sebastyuiop

  Right, I'm trying to make an app that has a calculation that involves a stopwatch. When a button on the calculation view is clicked a stopwatch slides in from the bottom. This all works fine, the problem I can't get my head around is how to send the recorded time back to the previous controller to update a textfield. I've simplified the code and stripped out most irrelevant stuff. Many thanks. CalculationViewController.h #import <UIKit/UIKit.h> @interface CalculationViewController : UIViewController <UITableViewDelegate, UITableViewDataSource> { IBOutlet UITextField *inputTxt; } @property (nonatomic, retain) UITextField *inputTxt; - (IBAction)showTimer:(id)sender; @end CalculationViewController.m #import "CalculationViewController.h" #import "TimerViewController.h" @implementation CalculationViewController - (IBAction)showTimer:(id)sender { TimerViewController *timerView = [[TimerViewController alloc] init]; [self.navigationController presentModalViewController:timerView animated:YES]; } TimerViewController.h #import <UIKit/UIKit.h> @interface TimerViewController : UIViewController { IBOutlet UILabel *time; NSTimer *myTicker; } - (IBAction)start; - (IBAction)stop; - (IBAction)reset; - (void)showActivity; @end TimerViewController.m #import "TimerViewController.h" #import "CalculationViewController.h" @implementation TimerViewController - (IBAction)start { myTicker = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(showActivity) userInfo:nil repeats:YES]; } - (IBAction)stop { [myTicker invalidate]; #Update inputTxt on calculation view here [self dismissModalViewControllerAnimated:YES]; } - (IBAction)reset { time.text = @"0"; } - (void)showActivity { int currentTime = [time.text intValue]; int newTime = currentTime + 1; time.text = [NSString stringWithFormat:@"%d", newTime]; } @end

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• Performance of map overlay in conjunction with ItemizedOverlay is very poor

  - by oviroa

  I am trying to display one png (drawable) on a map in about 300 points. I am retrieving the coordinates from a Sqlite table, dumping them in a cursor. When I try to display them by parsing through the cursor, it takes for ever for the images to be drawn, about .5 second per image. I find that to be suspiciously slow, so some insight on how I can increase performance would help. Here is the snippet of my code that does the rendering: while (!mFlavorsCursor.isAfterLast()) { Log.d("cursor",""+(i++)); point = new GeoPoint( (int)(mFlavorsCursor.getFloat(mFlavorsCursor.getColumnIndex(DataBaseHelper.KEY_LATITUDE))*1000000), (int)(mFlavorsCursor.getFloat(mFlavorsCursor.getColumnIndex(DataBaseHelper.KEY_LONGITUDE))*1000000)); overlayitem = new OverlayItem(point, "", ""); itemizedoverlay.addOverlay(overlayitem); itemizedoverlay.doPopulate(); mFlavorsCursor.moveToNext(); } mapOverlays.add(itemizedoverlay); I tried to isolate all the steps and it looks like the slow one is this: itemizedoverlay.doPopulate(); This is a public method in my class that extends ItemizedOverlay that runs the private populate() method.

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• LINQ XML query at c# wp7

  - by Karloss

  I am working at Windows Phone 7 C#, Xaml, XML and LINQ programming. I need to organize search by part of the name at following XML: <Row> <Myday>23</Myday> <Mymonth>12</Mymonth> <Mynames>Alex, Joanna, Jim</Mynames> </Row> <Row> <Myday>24</Myday> <Mymonth>12</Mymonth> <Mynames>John, David</Mynames> </Row> I have following query: var myData = from query in loadedData.Descendants("Row") where query.Element("Mynames").Value.Contains("Jo") select new Kalendars { Myday = (int)query.Element("Myday"), Mymonth = (int)query.Element("Mymonth"), Mynames = (string)query.Element("Mynames") }; listBoxSearch.ItemsSource = myData; Query problem is, that it will return full part of the names like "Alex, Joanna, Jim" and "John, David". How can i get only Joanna and John? Second question is how it is possible to do that user enters ...Value.Contains("jo") and query still returns Joanna and John? Possible solution (needs some corrections) public string Search_names { get { return search_names; } set { string line = this.Mynames; string[] names = line.Split(new[] { ", " }, StringSplitOptions.None); var jos = from name in names where name.Contains("is") select name; // ["Joanna"] // HOW TO BIND search_names? } }

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• Can parser combinators be made efficient?

  - by Jon Harrop

  Around 6 years ago, I benchmarked my own parser combinators in OCaml and found that they were ~5× slower than the parser generators on offer at the time. I recently revisited this subject and benchmarked Haskell's Parsec vs a simple hand-rolled precedence climbing parser written in F# and was surprised to find the F# to be 25× faster than the Haskell. Here's the Haskell code I used to read a large mathematical expression from file, parse and evaluate it: import Control.Applicative import Text.Parsec hiding ((<|>)) expr = chainl1 term ((+) <$ char '+' <|> (-) <$ char '-') term = chainl1 fact ((*) <$ char '*' <|> div <$ char '/') fact = read <$> many1 digit <|> char '(' *> expr <* char ')' eval :: String -> Int eval = either (error . show) id . parse expr "" . filter (/= ' ') main :: IO () main = do file <- readFile "expr" putStr $ show $ eval file putStr "\n" and here's my self-contained precedence climbing parser in F#: let rec (|Expr|) (P(f, xs)) = Expr(loop (' ', f, xs)) and loop = function | ' ' as oop, f, ('+' | '-' as op)::P(g, xs) | (' ' | '+' | '-' as oop), f, ('*' | '/' as op)::P(g, xs) -> let h, xs = loop (op, g, xs) let op = match op with | '+' -> (+) | '-' -> (-) | '*' -> (*) | '/' -> (/) loop (oop, op f h, xs) | _, f, xs -> f, xs and (|P|) = function | '('::Expr(f, ')'::xs) -> P(f, xs) | c::xs when '0' <= c && c <= '9' -> P(int(string c), xs) My impression is that even state-of-the-art parser combinators waste a lot of time back tracking. Is that correct? If so, is it possible to write parser combinators that generate state machines to obtain competitive performance or is it necessary to use code generation?

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• check if a tree is a binary search tree

  - by TimeToCodeTheRoad

  I have written the following code to check if a tree is a Binary search tree. Please help me check the code: Pair p{ boolean isTrue; int min; int max; } public boo lean isBst(BNode v){ return isBST1(v).isTrue; } public Pair isBST1(BNode v){ if(v==null) return new Pair(true, INTEGER.MIN,INTEGER.MAX); if(v.left==null && v.right==null) return new Pair(true, v.data, v.data); Pair pLeft=isBST1(v.left); Pair pRight=isBST1(v.right); boolean check=pLeft.max<v.data && v.data<= pRight.min; Pair p=new Pair(); p.isTrue=check&&pLeft.isTrue&&pRight.isTrue; p.min=pLeft.min; p.max=pRight.max; return p; } Note: This function checks if a tree is a binary search tree

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• Optimizing C# code in MVC controller

  - by cc0

  I am making a number of distinct controllers, one relating to each stored procedure in a database. These are only used to read data and making them available in JSON format for javascripts. My code so far looks like this, and I'm wondering if I have missed any opportunities to re-use code, maybe make some help classes. I have way too little experience doing OOP, so any help and suggestions here would be really appreciated. Here is my generalized code so far (tested and works); using System; using System.Configuration; using System.Web.Mvc; using System.Data; using System.Text; using System.Data.SqlClient; using Prototype.Models; namespace Prototype.Controllers { public class NameOfStoredProcedureController : Controller { char[] lastComma = { ',' }; String oldChar = "\""; String newChar = "&quot;"; StringBuilder json = new StringBuilder(); private String strCon = ConfigurationManager.ConnectionStrings["SomeConnectionString"].ConnectionString; private SqlConnection con; public StoredProcedureController() { con = new SqlConnection(strCon); } public string do_NameOfStoredProcedure(int parameter) { con.Open(); using (SqlCommand cmd = new SqlCommand("NameOfStoredProcedure", con)) { cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.AddWithValue("@parameter", parameter); using (SqlDataReader reader = cmd.ExecuteReader()) { while (reader.Read()) { json.AppendFormat("[{0},\"{1}\"],", reader["column1"], reader["column2"]); } } con.Close(); } if (json.Length.ToString().Equals("0")) { return "[]"; } else { return "[" + json.ToString().TrimEnd(lastComma) + "]"; } } //http://host.com/NameOfStoredProcedure?parameter=value public ActionResult Index(int parameter) { return new ContentResult { ContentType = "application/json", Content = do_NameOfStoredProcedure(parameter) }; } } }

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• Methods and properties in scheme - is object oriented programming possible in scheme?

  - by incrediman

  I will use a simple example to illustrate my question. In Java, C, or any other OOP language, I could create a pie class in a way similar to this: class Apple{ public String flavor; public int pieces; private int tastiness; public goodness(){ return tastiness*pieces; } } What's the best way to do that with Scheme? I suppose I could do with something like this: (define make-pie (lambda (flavor pieces tastiness) (list flavor pieces tastiness))) (define pie-goodness (lambda (pie) (* (list-ref pie 1) (list-ref pie 2)))) (pie-goodness (make-pie 'cherry 2 5)) ;output: 10 ...where cherry is the flavor, 2 is the pieces, and 5 is the tastiness. However then there's no type-safety or visibility, and everything's just shoved in an unlabeled list. How can I improve that? Sidenote: The make-pie procedure expects 3 arguments. If I want to make some of them optional (like I'd be able to in curly-brace languages like Java or C), is it good practice to just take the arguments in as a list (that is treat the arguments as a list - not require one argument which is a list) and deal with them that way?

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• System.Math.Round bug?

  - by Jeevan

  Hi All, I was writing a function for rounding a number to two places. And I found a bug when I was trying to round specific values. So, I ran the code: class Program { static void Main(string[] args) { int limit = 100; for (int number = 0; number <= limit; number++) { Console.WriteLine((System.Math.Round((double)(number+0.995),2,MidpointRounding.AwayFromZero))); } } } And I found that: 8.99 9.99 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 32.99 33.99 34.99 35.99 36.99 37.99 38.99 39.99 numbers are not rounded to their next value. When I run the same code till 1500: I get the numbers: 8.99 9.99 32.99 33.99 34.99 35.99 36.99 37.99 38.99 39.99 1024.99 1025.99 1026.99 1027.99 1028.99 1029.99 1030.99 1031.99 1032.99 1033.99 1034.99 1035.99 1036.99 1037.99 1038.99 1039.99 1040.99 1041.99 1042.99 1043.99 1044.99 1045.99 1046.99 1047.99 1048.99 1049.99 1050.99 1051.99 1052.99 1053.99 1054.99 1055.99 1056.99 1057.99 1058.99 1059.99 1060.99 1061.99 1062.99 1063.99 1064.99 1065.99 1066.99 1067.99 1068.99 1069.99 1070.99 1071.99 1072.99 1073.99 1074.99 1075.99 1076.99 1077.99 1078.99 1079.99 1080.99 1081.99 1082.99 1083.99 1084.99 1085.99 1086.99 1087.99 1088.99 1089.99 1090.99 1091.99 1092.99 1093.99 1094.99 1095.99 1096.99 1097.99 1098.99 1099.99 1100.99 1101.99 1102.99 1103.99 1104.99 1105.99 1106.99 1107.99 1108.99 1109.99 1110.99 1111.99 1112.99 1113.99 1114.99 1115.99 1116.99 1117.99 1118.99 1119.99 1120.99 1121.99 1122.99 1123.99 1124.99 1125.99 1126.99 1127.99 1128.99 1129.99 1130.99 1131.99 1132.99 1133.99 1134.99 1135.99 1136.99 1137.99 1138.99 1139.99 1140.99 1141.99 1142.99 1143.99 1144.99 1145.99 1146.99 1147.99 1148.99 1149.99 1150.99 1151.99 1152.99 1153.99 1154.99 1155.99 1156.99 1157.99 1158.99 1159.99 1160.99 1161.99 1162.99 1163.99 1164.99 1165.99 1166.99 1167.99 1168.99 1169.99 1170.99 1171.99 1172.99 1173.99 1174.99 1175.99 1176.99 1177.99 1178.99 1179.99 1180.99 1181.99 1182.99 1183.99 1184.99 1185.99 1186.99 1187.99 1188.99 1189.99 1190.99 1191.99 1192.99 1193.99 1194.99 1195.99 1196.99 1197.99 1198.99 1199.99 1200.99 1201.99 1202.99 1203.99 1204.99 1205.99 1206.99 1207.99 1208.99 1209.99 1210.99 1211.99 1212.99 1213.99 1214.99 1215.99 1216.99 1217.99 1218.99 1219.99 1220.99 1221.99 1222.99 1223.99 1224.99 1225.99 1226.99 1227.99 1228.99 1229.99 1230.99 1231.99 1232.99 1233.99 1234.99 1235.99 1236.99 1237.99 1238.99 1239.99 1240.99 1241.99 1242.99 1243.99 1244.99 1245.99 1246.99 1247.99 1248.99 1249.99 1250.99 1251.99 1252.99 1253.99 1254.99 1255.99 1256.99 1257.99 1258.99 1259.99 1260.99 1261.99 1262.99 1263.99 1264.99 1265.99 1266.99 1267.99 1268.99 1269.99 1270.99 1271.99 1272.99 1273.99 1274.99 1275.99 1276.99 1277.99 1278.99 1279.99 1280.99 1281.99 1282.99 1283.99 1284.99 1285.99 1286.99 1287.99 1288.99 1289.99 1290.99 1291.99 1292.99 1293.99 1294.99 1295.99 1296.99 1297.99 1298.99 1299.99 1300.99 1301.99 1302.99 1303.99 1304.99 1305.99 1306.99 1307.99 1308.99 1309.99 which are not rounded to next number! Has anyone any idea about why its happening for these specific numbers!

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• how can exec change the behavior of exec'ed program

  - by R Samuel Klatchko

  I am trying to track down a very odd crash. What is so odd about it is a workaround that someone discovered and which I cannot explain. The workaround is this small program which I'll refer to as 'runner': #include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> int main(int argc, char *argv[]) { if (argc == 1) { fprintf(stderr, "Usage: %s prog [args ...]\n", argv[0]); return 1; } execvp(argv[1], argv + 1); fprintf(stderr, "execv failed: %s\n", strerror(errno)); // If exec returns because the program is not found or we // don't have the appropriate permission return 255; } As you can see, all this program does is use execvp to replace itself with a different program. The program crashes when it is directly invoked from the command line: /path/to/prog args # this crashes but works fine when it is indirectly invoked via my runner shim: /path/to/runner /path/to/prog args # works successfully For the life of me, I can figure out how having an extra exec can change the behavior of the program being run (as you can see the program does not change the environment). Some background on the crash. The crash itself is happening in the C++ runtime. Specifically, when the program does a throw, the crashing version incorrectly thinks there is no matching catch (although there is) and calls terminate. When I invoke the program via runner, the exception is properly caught. My question is any idea why the extra exec changes the behavior of the exec'ed program?

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• Why aren't my coordinates matching my JFrame size?

  - by AsLanFromNarnia

  I want to do some drawing in a JPanel but the enclosing JFrame size doesn't seem to match where I've asked the coordinates to be drawn. In my example code, the JFrame size is set to (700, 700) and the last point is drawn at (600, 600). I would expect this point to be drawn 100 pixels away from the right and bottom edges but it isn't (please see screenshot). Here's the code I'm using: import java.awt.Graphics; import javax.swing.JFrame; import javax.swing.JPanel; public class Scratch extends JPanel { static int frameWidth = 700; static int frameHeight = 700; public static void main(String[] args) { JFrame frame = new JFrame(); frame.setSize(frameWidth, frameHeight); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Scratch scratch = new Scratch(); frame.getContentPane().add(scratch); frame.setVisible(true); } @Override public void paintComponent(Graphics g) { g.drawRect(100, 100, 1, 1); g.drawString("100", 100, 100); g.drawRect(200, 200, 1, 1); g.drawString("200", 200, 200); g.drawRect(300, 300, 1, 1); g.drawString("300", 300, 300); g.drawRect(400, 400, 1, 1); g.drawString("400", 400, 400); g.drawRect(500, 500, 1, 1); g.drawString("500", 500, 500); g.drawRect(600, 600, 1, 1); g.drawString("600", 600, 600); } }

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• Java: Combine 2 List <String[]>

  - by battousai622

  I have two List of array string. I want to be able to create a New List (newList) by combining the 2 lists. But it must meet these 3 conditions: 1) Copy the contents of store_inventory into newList. 2) Then if the item names in store_inventory & new_acquisitions match, just add the two quantities together and change it in newList. 3) If new_acquisitions has a new item that does not exist in store_inventory, then add it to the newList. The titles for the CSV list are: Item Name, Quantity, Cost, Price. The List contains an string[] of item name, quantity, cost and price for each row. CSVReader from = new CSVReader(new FileReader("/test/new_acquisitions.csv")); List <String[]> acquisitions = from.readAll(); CSVReader to = new CSVReader(new FileReader("/test/store_inventory.csv")); List <String[]> inventory = to.readAll(); List <String[]> newList; Any code to get me started would be great! =] this is what i have so far... for (int i = 0; i < acquisitions.size(); i++) { temp1 = acquisitions.get(i); for (int j = 1; j < inventory.size(); j++) { temp2 = inventory.get(j); if (temp1[0].equals(temp2[0])) { //if match found... do something? //break out of loop } } //if new item found... do something? }

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