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• question abouut string sort

  - by davit-datuashvili

  i have question from programming pearls problem is following show how to use lomuto's partitioning scheme to sort varying length bit strings in time proportional to the sum oof their length and algorithm is following each record in x[0..n-1] has an integer length and pointer to the array bit[0..length-1] code void bsort(l,u,depth){ if (l>=u) return; for (int i=l;i<u;i++) if (x[i].length<depth) swap(i,l++); m=l; if (x[i].bit[depth] ==0) swap(i,m++); bsort(l,m-1,depth+1); bsort(m,u,depth+1); please help me i need following things 1. how this algorith works 2.how implement in java?

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• Doubling a number - shift left vs. multiplication

  - by ToxicAvenger

  What are the differences between int size = (int)((length * 200L) / 100L); // (1) and int size = length << 1; // (2) (length is int in both cases) I assume both code snippets want to double the length parameter. I'd be tempted to use (2) ... so are there any advantages for using (1)? I looked at the edge cases when overflow occurs, and both versions seem to have the same behavior. Please tell me what am I missing.

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• between syntax, are there any equal function

  - by gcc

  /* char **mainp=malloc(sizeof(char *)*2); mainp[0]=malloc(sizeof(char)*300); mainp[1]=malloc(sizeof(char )*300); */ *I have some input about propositional calculus *After calculating some math funtion-removing paranthesis-changing"&" with ","-replacing "|" with"," I have >> (1) P,-Q,Q,-R is stored in mainp[0] R,A,P,B,F is stored in mainp[1] *My question is: Between comma , I have want to compare two pointer array. If there is any equal two or more functions(Q,-R is function representation) ,function which you will show me how to write must return int. According to example (1),function will return 1 (I expect like that) /*I have som thought://which function should I have use:*/ in for loop if( strspn(mainp[0][i])==1 ) increment d; continue; or in for loop srtcmp(mainp[0][i],mainp[1]);

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• error message fix

  - by user1722654

  for (int i = 0; i < dataGridView1.Rows.Count; i++) { //bool sleected = false; if (dataGridView1.Rows[i].Cells[3].Value != null) { selected.Add(i); } } //string donew = ""; // line off error textBox1.Text = ((String)dataGridView1.Rows[1].Cells[2].Value); /* for (int i = 0; i < selected.Count; i++) { textAdded.Add((String)dataGridView1.Rows[0].Cells[2].Value); // donew += (String)dataGridView1.Rows[selected[i]].Cells[2].Value; }*/ I keep getting the error Unable to cast object of type 'System.Double' to type 'System.String' What can I do to overcome this?

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• String.Format with NumberGroupSeparator outputting 0xa0 not comma

  - by andrevdm

  I'm seeing strange results when doing a string.Format( "C" ); E.g. double val = 123456.78; Console.WriteLine( val.ToString( "C" ) ); This prints the thousand separator as 0xa0 rather than a comma (0x2c). I get the same result if I use string.Format( "{0:0,0.00}", 1234567.12D ); Here is the full output R 123ÿ456,78 52333A333233 201230456C78 My regional settings are English (South African) and I'm getting the same result on multiple machines. Any ideas? Thanks.

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• Method to register method to be called when event is raised

  - by zaidwaqi

  I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share.

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• Help with implementing a function to change size of dynamic array

  - by iRobot

  I'm trying to write a function that will change the size of a dynamic array to a new size. In my header file, I have: Image **images; //pointer to a dynamic array of image pointers int maximum; //size I want to do this by allocating a new array and copying the values over without changing their indices. If there are non-null pointers outside the range newmax, then we cant do this. So heres what I have: There are no compilation or runtime errors. However, I find that the new array isnt getting sized right. When I run the following test case: I should get an index out of bounds error, but instead the system lets it slide. Can anyone see the mistake? I've looked for hours but cant find anything.

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• Android SurfaceView/Canvas flickering after trying to clear it

  - by Mark D

  So I am trying to clear the Canvas using canvas.drawColor(Color.BLACK) but if I just call this once, the display flickers and displays the old drawing which should have been covered up by the drawColor. Here is the important bits of my code - public void update() { //This method is called by a Thread Canvas canvas = holder.lockCanvas(null); if (canvas != null) { onDraw(canvas); } holder.unlockCanvasAndPost(canvas); } @Override protected void onDraw(Canvas canvas) { if (toClear) { canvas.drawColor(Color.BLACK); //if this is not set to change back to false, it does not flicker toClear = false; } //Draw some objects that are moving around } public void clearScreen() { //This method is called when the user pressed a button toClear = true; } After Googling around a litte, I heard about double buffering but came to the understanding that lockCanvas() and unlockCanvasAndPost() should handle this for me. What is going wrong here?

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• When is (true == x) === !!x false?

  - by Paul S.

  JavaScript has different equality comparison operators Equal == Strict equal === It also has a logical NOT ! and I've tended to think of using a double logical NOT, !!x, as basically the same as true == x. However I know this is not always the case, e.g. x = [] because [] is truthy for ! but falsy for ==. So, for which xs would (true == x) === !!x give false? Alternatively, what is falsy by == but not !! (or vice versa)?

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• Some pro regular expressions help needed here

  - by Camran

  I need a special regular expression, have no experience in them whatsoever so I am turning to you guys on this one: I need to validate a classifieds title field so it doesn't have any special characters in it, almost. Only letters and numbers should be allowed, and also the swedish three letters å, ä, ö, and also not case sensitive. Besides the above, these should also be allowed: The "&" sign. Parenthesis sign "()" Mathematical signs "-", "+", "%", "/", "*" Dollar and Euro signs Accent sign or whatever it's called, for example in "coupé" the apostrophe above the "e". Double quote and singel quote signs. The comma "," and point "." signs Thanks

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• seg violation using pycapsule_new

  - by user1733051

  I am trying some simple c API, where I am using PyCapsule_New to encapsulate a pointer. I am running into segment violation, can some body help me. mystruct *func1(int streamno, char mode,unsigned int options) { char * s; s=malloc(100); return s; } PyObject *Wrapper_func1(PyObject *self, PyObject *args) { int streamno; char mode; unsigned int options; mystruct* result; if (!PyArg_ParseTuple(args,"icI",&streamno,&mode,&options)) return NULL; result = func1(streamno,mode,options); return PyCapsule_New( result,NULL,NULL); }

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• Are unspecified and undefined behavior required to be consistent between compiles?

  - by sharptooth

  Let's pretend my program contains a specific construct the C++ Standard states to be unspecified behavior. This basically means the implementation has to do something reasonable but is allowed not to document it. But is the implementation required to produce the same behavior every time it compiles a specific construct with unspecified behavior or is it allowed to produce different behavior in different compiles? What about undefined behavior? Let's pretend my program contains a construct that is UB according to the Standard. The implementation is allowed to exhibit any behavior. But can this behavior differ between compiles of the same program on the same compiler with same settings in the same environment? In other words, if I dereference a null pointer on line 78 in file X.cpp and the implementation formats the drive in such case does it mean that it will do the same after the program is recompiled?

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• How can Java assignment be made to point to an object instead of making a copy?

  - by Matthew Piziak

  In a class, I have: private Foo bar; public Constructor(Foo bar) { this.bar = bar; } Instead of creating a copy of bar from the object provided in the parameter, is it possible to include a pointer to bar in the constructor such that changing the original bar changes the field in this object? Another way of putting it: int x = 7; int y = x; x = 9; System.out.print(y); //Prints 7. It is possible to set it up so that printing y prints 9 instead of 7?

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• Button border radius and cursor

  - by noober

  CSS border radius does affect button rendering (I see it's round form), but does not affect how it interacts with the user (I still can click button outside its border). How should I fix it? I see the behavior in Chrome. button { cursor: pointer; outline: none; background-size: 100% 100%; background-color: red; /*transparent;*/ /* It's actually red and ROUND. */ background-position: center center; background-repeat: no-repeat; border: 0px; -webkit-border-top-left-radius: 73px; -webkit-border-top-right-radius: 73px; -webkit-border-bottom-left-radius: 73px; -webkit-border-bottom-right-radius: 73px; width: 146px; height: 146px; background-image: url('leftarrow.png'); } Regards,

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• Break the limit of threading, segmentation fault

  - by user353573

  use pthread_create to create limited number of threads running concurrently Successfully compile and run However, after adding function pointer array to run the function, Segmentation fault Where is wrong? workserver number: 0 Segmentation fault void* workserver(void arg) { int status; while(true) { printf("workserver number: %d\n", (int)arg); ( job_queue[(int)arg])(); sleep(3); status = pthread_mutex_lock(&data.mutex); if(status != 0) printf("%d lock mutex", status); data.value = 1; status = pthread_cond_signal(&data.cond); if(status != 0) printf("%d signal condition", status); status = pthread_mutex_unlock(&data.mutex); if(status != 0) printf("%d unlock mutex", status); } }

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• Can a thread call wait() on two locks at once in Java (6)

  - by Dr. Monkey

  I've just been messing around with threads in Java to get my head around them (it seems like the best way to do so) and now understand what's going on with synchronize, wait() and notify(). I'm curious about whether there's a way to wait() on two resources at once. I think the following won't quite do what I'm thinking of: synchronized(token1) { synchronized(token2) { token1.wait(); token2.wait(); //won't run until token1 is returned System.out.println("I got both tokens back"); } } In this (very contrived) case token2 will be held until token1 is returned, then token1 will be held until token2 is returned. The goal is to release both token1 and token2, then resume when both are available (note that moving the token1.wait() outside the inner synchronized loop is not what I'm getting at). A loop checking whether both are available might be more appropriate to achieve this behaviour (would this be getting near the idea of double-check locking?), but would use up extra resources - I'm not after a definitive solution since this is just to satisfy my curiosity.

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• Array as struct database?

  - by user2985179

  I have a struct that reads data from the user: typedef struct { int seconds; } Time; typedef struct { Time time; double distance; } Training; Training input; scanf("%d %lf", input.time.seconds, input.distance); This scanf will be looped and the user can input different data every time, I want to store this data in an array for later use. I THINK I want something like arr[0].seconds and arr[0].distance. I tried to store the entered data in an array but it didn't really work at all... Training data[10]; data[10].seconds = input.time.seconds; data[10].distance = input.distance; The data will wipe when the program closes and that's how I like it to be. So I want it to be stored in an array, no files or databases!

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• Array-size macro that rejects pointers

  - by nneonneo

  The standard array-size macro that is often taught is #define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0])) or some equivalent formation. However, this kind of thing silently succeeds when a pointer is passed in, and gives results that can seem plausible at runtime until things mysteriously fall apart. It's all-too-easy to make this mistake: a function that has a local array variable is refactored, moving a bit of array manipulation into a new function called with the array as a parameter. So, the question is: is there a "sanitary" macro to detect misuse of the ARRAYSIZE macro in C, preferably at compile-time? In C++ we'd just use a template specialized for array arguments only; in C, it seems we'll need some way to distinguish arrays and pointers. (If I wanted to reject arrays, for instance, I'd just do e.g. (arr=arr, ...) because array assignment is illegal).

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• mysql_real_escape_string & slashes (again, oh yes)

  - by Fizzadar

  Righto, firstly magic quotes & runtime are disabled correctly in php.ini, and confirmed by phpinfo(). PHP version: 5.3.4 MySQL version: 5.1.52 I'm only use mysql_real_escape_string on the data, after htmlspecialchars and a trim, that's all the data cleaning on the variable. Yet, when I submit a single quote, the slash remains in the database. When running mysql_query I'm using "' . $var . '", although in the past this hasn't changed anything (could be due to the double quotes?). Any ideas? and please don't tell me about PDO/prepared statements, I'm aware of them and I have my reasons for doing it this way. Thanks!

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• Abstract class and operator!= in c++

  - by Alessandro Teruzzi

  Hi All, I have problem implementing the operator!= in a set class deriving from an abstact one. The code looks like this: class Abstract { public: //to make the syntax easier let's use a raw pointer virtual bool operator!=(const Abstract* other) = 0; }; class Implementation { SomeObject impl_; //that already implement the operator!= public: bool operator!=(const Abstract* other) { return dynamic_cast<Implementation*>(other)->impl_ != this->impl_; } }; This code works but it has the drawback to use dynamic_cast and I need to handle error in casting operation. This is a generic problem that occur when a function of a concrete class it is trying to using some internal information (not available at the abstract class level) to perform a task. Is there any better way to solve this kind of problem? Cheers

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• C++ Inheritance Question

  - by shaz

  I have a base class MessageHandler and 2 derived classes, MessageHandler_CB and MessageHandler_DQ. The derived classes redefine the handleMessage(...) method. MH_DQ processes a message and puts the result in a deque while MH_CB processes the message and then executes a callback function. The base class has a static callback function that I pass along with a this pointer to a library which calls the static callback when a new message is available for processing. My problem comes when I am in the static callback with a void * pointing to either a MH_DQ or a MH_CB. If I cast it to the base class the empty MessageHandler::handleMessage(...) method is called, rather than the version in the appropriate derived class. What is the best way to address this situation from a design perspective and/or what language features might help me to implement a solution to my problem? Thanks in advance!

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• QFileDialog used as widget

  - by lvp

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

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• How to do hex8 encoding in c?

  - by Tech163

  I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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• EF Linq Product Sum when no records returned

  - by user1622713

  I’ve seen variations of this question all over the place but none of the answers work for me. Most of them are just trying to sum a single column too – nothing more complex such as the sum of a product as below: public double Total { get { return _Context.Sales.Where(t => t.Quantity > 0) .DefaultIfEmpty() .Sum(t => t.Quantity * t.Price); } } If no rows are returned I want to return zero. However if no rows are returned the .Sum() fails. There are various options of trying to insert Convert.ToDouble and using null coalesce operators, but they all still gave me errors. I’m sure I am missing a simple way to do this – any help greatly appreciated after too long banging head against google brick wall!

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• log (1-var) operation in C

  - by heike

  I am trying to code this algorithm. I am stuck in the part of log((1.0-u)/u))/beta; As I understand, I can not get the result of this in C, as it will always return me with negative value log (returning imaginary value). Tried to print the result of log(1-5) for instance, it gives me with Nan. How can I get the result of double x = (alpha - log((1.0-u)/u))/beta then? Would appreciate for any pointers to solve this problem. Thank you

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