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• Multithreaded SDL error in C++

  - by wyatt

  I'm building a program in C++, using SDL, and am occasionally receiving this error: * glibc detected * ./assistant: double free or corruption (!prev) It's difficult to replicate, so I can't find exactly what's causing it, but I just added a second thread to the program, and neither thread run on its own seems to cause the error. The threads don't share any variables, though they both run the functions SDL_BlitSurface and SDL_Flip. Could running these concurrently throw up such an error, or am I barking up the wrong tree? If this is the cause, should I simply throw a mutex around all SDL calls? Thanks

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• Throw blank even-numbered/left pages

  - by TimGJ

  I am trying to typeset a large document using ReportLab and Python 2.7. It has a number of sections (about 6 in a 1,000 page document) and I would like each to start on odd-numbered/right-hand page. I have no idea though whether the preceding page will be odd or even and so need the ability to optionally throw an additional blank page before a particular paragraph style (like you sometimes get in manuals where some pages are "intentionally left blank"). Can anyone suggest how this could be done, as the only conditional page break I can find works on the basis of the amount of text on the page not a page number. I also need to make sure that the blank page is included in the PDF so that double-sided printing works.

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• looping and arrays

  - by user1838418

  Hi I'm trying to construct a loop to execute 16 states of the 8 4 2 1 code in (C++) while( condition) { double Bubble[16], Bubble1[16]; Bubble[0] = ( a-2 - (b-2) ) + ( c-2 - (d-2)); // represents 0000 Bubble[1] = ( a-2 - (b-2) ) + ( c-2 - (d+2)); // represents 0001 Bubble[2] = ( a-2 - (b-2) ) + ( c+2 - (d-2)); // represents 0010 Bubble[3] = ( a-2 - (b-2) ) + ( c+2 - (d+2)); //represents 0011 ....... Bubble[15] =(a+2 - (b+2) ) + ( c+2 - (d+2)); //represents 1111 } Is there an easy way of coding using for loops? instead of writing bubble[] every time? 0 stands for -2 and 1 stands for +2. So I have 4 variables and each one need to be incremented and/or decremented. Can this be done using for loop? Appreciate your help

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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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• visual studio C++ toggle comment ? comment while not whole line is selected ?

  - by Mr_and_Mrs_D

  2 questions actually : 1) shortcut to toggle comment on selected lines ? Available on all iDEs I used starting with notepad++ 2)the ctrl-k, ctrl-c exhibits this behavior (quoted from someplace nicely worded): C#: Each line where some text is selected is commented at the line-start with double-slash. If nothing is selected, the line where the cursor is is commented. C++: If nothing is selected or complete lines are selected, it behaves as above. However, if parts of a line are selected, and no comment is selected as part of the selection (ex. select something in the middle of a code line), then the selection is surrounded by /* and */. since I code in C++ I find this behavior annoying - I want to be able to comment out lines partially selected - any workarounds ?

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• How to find the remainder of large number division in C++?

  - by Beelzeboul

  Hello, I have a question regarding modulus in C++. What I was trying to do was divide a very large number, lets say for example, M % 2, where M = 54,302,495,302,423. However, when I go to compile it says that the number is to 'long' for int. Then when I switch it to a double it repeats the same error message. Is there a way I can do this in which I will get the remainder of this very large number or possibly an even larger number? Thanks for your help, much appreciated.

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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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• 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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• TPageControl tab area OnMouseEnter OnMouseLeave events

  - by daemon_x

  Hello, I need to catch the "OnMouseEnter" and "0nMouseLeave" for a certain area of the TPageControl component. With that specific area I mean the whole "tab header" rectangle. The problem is, that the page control doesn't catch the messages (I'm catching internal control messages CM_MOUSEENTER and CM_MOUSELEAVE) in the "empty" space. The aim for me is to draw a small arrow in the right empty side when user hovers in the red framed area (and drawing is just piece of cake) and erase it when leaves this area. And I'm don't care about the overflow of the tabs (which causes to draw scrolling double button) - that will never happen.

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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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• Both sql LAST_INSERT_ID() and PHP insert_id return 0

  - by jakubplus

  I've been searching google a lot for this issue and really found nothing. People just keep copying MySQL documentation on last_insert_id and nothing else. I've got an issue regarding last_insert_id, because for both situations (php & sql) it returns 0. YES: I've set a PRIMARY & UNIQUE field with AUTO_INCREMENT value YES: i've done some inserting before NO: Making double query with INSERT AND SELECT LAST... doesn't work. I've created a class Db for maintaining connection & query: class Db { public function connect() { $db = new mysqli('','','','',''); ... return $db; } public function insert() { $this->connect()->query("INSERT INTO bla bla..."); return $this->connect()->insert_id; } } And it doesn't work.

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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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• 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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• 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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• Can I use a single pointer for my hash table in C?

  - by aks

  I want to implement a hash table in the following manner: struct list { char *string; struct list *next; }; struct hash_table { int size; /* the size of the table */ struct list **table; /* the table elements */ }; Instead of struct hash_table like above, can I use: struct hash_table { int size; /* the size of the table */ struct list *table; /* the table elements */ }; That is, can I just use a single pointer instead of a double pointer for the hash table elements? If yes, please explain the difference in the way the elements will be stored in the table?

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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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• 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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• Force type of C++ template

  - by gregseth

  Hi, I've a basic template class, but I'd like to restrain the type of the specialisation to a set of classes or types. e.g.: template <typename T> class MyClass { .../... private: T* _p; }; MyClass<std::string> a; // OK MYCLass<short> b; // OK MyClass<double> c; // not OK Those are just examples, the allowed types may vary. Is that even possible? If it is, how to do so? Thanks.

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• Data-binding taking too long to update

  - by Justin

  In my application I have this code in my view model: hiddenTextContainer.PreHideVerticalOffset = VerticalOffset; hiddenTextContainer.HiddenText = Text.Remove(SelectionStart, SelectionLength); hiddenTextContainer.HasHiddenText = true; hiddenTextContainer.NonHiddenTextStart = SelectionStart; Text = Text.Substring(SelectionStart, SelectionLength); SelectionStart = Text.Length; hiddenTextContainer.ImmediatePostHideVerticalOffset = VerticalOffset; This code is used to hide selected text in a textbox. Text is a string property data bound to the text property of a textbox and VerticalOffset is a double property data bound to the VerticalOffset property of that same textbox. I need to save the VerticalOffset before and after the hiding of selected text takes place, but with my code below both hiddenTextContainer.PreHideVerticalOffset and hiddenTextContainer.ImmediatePostHideVerticalOffset are always set to the same value no matter what. I have figured out that this is because the text of the textbox has not been updated by the time the code reaches: hiddenTextContainer.ImmediatePostHideVerticalOffset = VerticalOffset; Is there any way I can fix this?

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• MySQL query with JOINS and GROUP BY

  - by user1854049

  I'm building a MySQL query but I can't seem to get it right. I have four tables: - customers - orders - sales_rates - purchase_rates There is a 1:n relation 'customernr' between customers and orders. There is a 1:n relation 'ordernr' between orders and sales_rates. There is a 1:n relation 'ordernr' between orders and purchase_rates. What I would like to do is produce an output of all customers with their total purchase and sales amounts. So far I have the following query. SELECT c.customernr, c.customer_name, SUM(sr.sales_price) AS sales_price, SUM(pr.purchase_price) AS purchase_price FROM orders o, customers c, sales_rates sr, purchase_rates pr WHERE o.customernr = c.customernr AND o.ordernr = sr.ordernr AND o.ordernr = pr.ordernr GROUP BY k.bedrijfsnaam The result of the sales_price and purchase_price is far too high. I seem to be getting double counts. What am I doing wrong? Is it possible to perform this in a single query? Thank for your response!

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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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• What is the purpose of AnyVal?

  - by DaoWen

  I can't think of any situation where the type AnyVal would be useful, especially with the addition of the Numeric type for abstracting over Int, Long, etc. Are there any actual use cases for AnyVal, or is it just an artifact that makes the type hierarchy a bit prettier? Just to clarify, I know what AnyVal is, I just can't think of any time that I would actually need it in Scala. When would I ever need a type that encompassed Int, Character and Double? It seems like it's just there to make the type hierarchy prettier (i.e. it looks nicer to have AnyVal and AnyRef as siblings rather than having Int, Character, etc. inherit directly from Any).

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• In .NET, how can I convert from "0.000" to a 'long'?

  - by willem

  I have a string, "0.000" (or any similar string), that I would like to convert to a long. I am happy to "chop-off" anything after the decimal. What is the best way to go about this? I can convert to double and then to long, but I'm just wondering if there is an easier way. All the following statements throw exceptions: long l3 = Convert.ToInt64(nrToConvert); long l1; long.TryParse(nrToConvert, out l1); long l2 = long.Parse(nrToConvert);

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• bash screen title usage (screen -t "something")

  - by atrioom

  I was working with screen lately and wanted to use the -t option for it. What's the point of the-t option if the title of the screen does not show anywhere like when using -list or within the screen when it's attached? There is a command CTRL-A double-quote(") to see all active screens, and then it shows the title, but that does not really do the job, because I have to have the screen attached already. I want to read out the title BEFORE attaching any screens, to attach the right one in the first place. Is there a method to use -t in a convenient way? Edit: There is one method: "ctrl-a "" and then "ctrl-a {numberofscreen}". I guess that's the best way to use the screen titles?

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• RSpec "undefined local variable or method `user'"

  - by Justin

  I have the following test written in RSpec: describe '#create' do ... it 'redirects users to profile page' do response.should redirect_to user_path(user) end ... ... And the following in my UsersController: def create @user = User.new(params[:user]) if @user.save redirect_to user_path(@user) end end Does anyone know why this is returning the following error: NameError: undefined local variable or method 'user' I also tried changing this to be root_url in both cases instead of user_path(user) and it gave a different error saying: Expected response to be a <:redirect>, but was <200> Does anyone know what the issue might be? I have double-checked my code and have seen similar questions posted online, but haven't been able to find a solution. Thanks in advance for any help!

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