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• Deleting Part of An Array in Java to Free Memory on Heap

  - by kate

  I am implementing a dynamic programming algorithm for the knapsack problem in Java. I declare the array and then initialize its size to be [number of objects][capacity of knapsack]. When my number of objects or my capacity gets too large, I get a memory error because I run out of space on the heap. My questions is: If I delete rows from my double array as I go along, will Java free the memory as I delete? Or does Java reserve that memory space for the size of the array I originally created? If it's the latter, is there a way to manually free the memory in Java? Thanks for your Help!

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• im writing this code so the user would enter his/her name and followed by his/her marks to get the a

  - by WM

  What if the user wanted to enter his/her grades in the following way: Will 23, 34, 45, 45 how would i get rid of the commas public class StudentAverage { public static void main(String[] args) { int markSum = 0; double average = 0; Scanner input1 = new Scanner(System.in); System.out.print("Enter student record : "); String name = input1.next(); Scanner input2 = new Scanner(input1.nextLine()); int countTotal = 0; while (input2.hasNextInt()) { countTotal++; markSum += input2.nextInt(); } average = markSum / countTotal; // to calculate the total average System.out.print( name + " " + average ); } }

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• Why exactly is calling the destructor for the second time undefined behavior in C++?

  - by sharptooth

  As mentioned in this answer simply calling the destructor for the second time is already undefined behavior 12.4/14(3.8). For example: class Class { public: ~Class() {} }; // somewhere in code: { Class* object = new Class(); object->~Class(); delete object; // UB because at this point the destructor call is attempted again } In this example the class is designed in such a way that the destructor could be called multiple times - no things like double-deletion can happen. The memory is still allocated at the point where delete is called - the first destructor call doesn't call the ::operator delete() to release memory. For example, in Visual C++ 9 the above code looks working. Even C++ definition of UB doesn't directly prohibit things qualified as UB from working. So for the code above to break some implementation and/or platform specifics are required. Why exactly would the above code break and under what conditions?

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• Is there any way to retrieve a float from a varargs function's parameters?

  - by Jared P

  If the function was defined with a prototype which explicitly stated the types of the parameters, eg. void somefunc(int arg1, float arg2); but is implemented as void somefunc(int arg1, ...) { ... } is it possible to use va_arg to retrieve a float? It's normally prevented from doing this because varargs functions have implicit type promotions, like float to double, so trying to retrieve an unpromoted type is unsupported, even though the function is being called with the unpromoted type do to the more specific function prototype. The reason for this is to retrieve arguments of different types at runtime, as part of an obj-c interpreter, where one function will be reused for all different types of methods. This would be best as architecture independent (so that if nothing else the same code works on simulator and on device), although if there is no way to do this then device specific fixes will be accepted.

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• Explain the code: c# locking feature and threads

  - by Mendy

  I used this pattern in a few projects, (this snipped of code is from CodeCampServer), I understand what it does, but I'm really interesting in an explanation about this pattern. Specifically: Why is the double check of _dependenciesRegistered. Why to use lock (Lock){}. Thanks. public class DependencyRegistrarModule : IHttpModule { private static bool _dependenciesRegistered; private static readonly object Lock = new object(); public void Init(HttpApplication context) { context.BeginRequest += context_BeginRequest; } public void Dispose() { } private static void context_BeginRequest(object sender, EventArgs e) { EnsureDependenciesRegistered(); } private static void EnsureDependenciesRegistered() { if (!_dependenciesRegistered) { lock (Lock) { if (!_dependenciesRegistered) { new DependencyRegistrar().ConfigureOnStartup(); _dependenciesRegistered = true; } } } } }

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• Remove duplicates in entries, scala way

  - by andersbohn

  I have a list of entries stating a production value in a given interval. Entries stating the exact same value at a later time adds no information and can safely be left out. case class Entry(minute:Int, production:Double) val entries = List(Entry(0, 100.0), Entry(5, 100.0), Entry(10, 100.0), Entry(20, 120.0), Entry(30, 100.0), Entry(180, 0.0)) Experimenting with the scala 2.8 collection functions, so far I have this working implementation: entries.foldRight(List[Entry]()) { (entry, list) => list match { case head :: tail if (entry.production == head.production) => entry :: tail case head :: tail => entry :: list case List() => entry :: List() } } res0: List[Entry] = List(Entry(0,100.0), Entry(20,120.0), Entry(30,100.0), Entry(180,0.0)) Any comments? Am I missing out on some scala magic?

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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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• Python to C# Conversion of RGBA values not working

  - by clangers

  I'm currently converting some python code to C#, and I'm having an issue with the RGBA C# libraries # Original Python Code: d = math.sqrt( (x - size/2.0)**2 + (y - size/2.0)**2 ) rgbVal = int(200*d/md + 50) rgba = (0,0,0, 255 - rgbVal) img.putpixel((x,y), rgba) // My C# Code double d = Math.Sqrt(Math.Pow((x - DotSize / 2.0), 2) + Math.Pow((y - DotSize / 2.0), 2)); int rgbVal = (int) (200 * d / md + 50); Color color = Color.FromArgb(255 - rgbVal, 0, 0, 0); // ** ERROR ** img.SetPixel(x,y, color); At both instances of the code d is equal to 106 and md is equal to 53. However the resulting rgbVal value is 450. This would obviously mean that 255 - 450 is -195, which causes an error to be thrown as each individual value must be between 0 and 255. Anyone have any idea how I can fix this. Please note that the data is the same when running both the python and C# versions.

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• Why am I not getting correct result when I calculate exponent with ^ in C++?

  - by xbonez

  I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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• inheritance from the django user model results in error when changing password

  - by Jerome

  I inherited form the django user model like so: from django.db import models from django.contrib.auth.models import User, UserManager from django.utils.translation import ugettext_lazy as _ class NewUserModel(User): custom_field_1 = models.CharField(_('custom field 1'), max_length=250, null=True, blank=True) custom_field_2 = models.CharField(_('custom field 2'), max_length=250, null=True, blank=True) objects = UserManager() When i go to the admin and add an entry into this model, it saves fine, but below the "Password" field where it has this text "Use '[algo]$[salt]$[hexdigest]' or use the change password form.", if i click on the "change password form' link, it produces this error Truncated incorrect DOUBLE value: '7/password' What can i do to fix this?

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• Calculating the angle between two points

  - by kingrichard2005

  I'm currently developing a simple 2D game for Android. I have a stationary object that's situated in the center of the screen and I'm trying to get that object to rotate and point to the area on the screen that the user touches. I have the constant coordinates that represent the center of the screen and I can get the coordinates of the point that the user taps on. I'm using the formula outlined in this forum: How to get angle between two points? -It says as follows "If you want the the angle between the line defined by these two points and the horizontal axis: double angle = atan2(y2 - y1, x2 - x1) * 180 / PI;". -I implemented this, but I think the fact the I'm working in screen coordinates is causing a miscalculation, since the Y-coordinate is reversed. I'm not sure if this is the right way to go about it, any other thoughts or suggestions are appreciated.

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• Behaviour of System.Timer when Interval property changed

  - by lowlyintern

  I have a System.Timer setup to trigger an event every day at 2AM. If the process the timer starts fails then I want the timer to be reset to run every 15 minutes until the process completes succesfully. // this is how the timer is set up. // this is working correctly. double startTime = milliseconds_of_hour_to_start. Timer = new System.Timers.Timer( startTime); Here is the code to reset the timer on success or failure of the event handler. NOTE the timer is not being stopped, just the Interval property is being reset. if (ProcessSuccess) { Timer.Interval = TimeSpan.FromHours(24).TotalMilliseconds; } else { Timer.Interval = TimeSpan.FromMinutes(15).TotalMilliseconds; } My question is this, if the process fails say 4 times, then succeeds will the Timer now be running at around 3AM? i.e. after failing will the original start time of 2AM be advanced by 15 minutes?

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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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• read text file line by line and insert/update values in table

  - by I__

  i am exploring the option of whether DoCmd.TransferText will do what i need, and it seems like it wont. i need to insert data if it does not exist and update it if it does exist i am planning to read a text file line by line like this: Dim intFile As Integer Dim strLine As String intFile = FreeFile() Open myFile For Input As #intFile Line Input #intFile, strLine Close #intFile i guess each individual line will be a record. it will probably be comma separated and some fields will have a " text qualifier because within the field itself i will have commas my question is how would i read a comma delimited text file that has double quotes sometimes as text qualifiers into a table in access?

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• Floating point innacuracies

  - by Greg

  While writing a function which will perform some operation with each number in a range I ran into some problems with floating point inaccuracies. The problem can be seen in the code below: #include <iostream> using namespace std; int main() { double start = .99999, end = 1.00001, inc = .000001; int steps = (end - start) / inc; for(int i = 0; i <= steps; ++i) { cout << (start + (inc * i)) << endl; } } The problem is that the numbers the above program outputs look like this: 0.99999 0.999991 0.999992 0.999993 0.999994 0.999995 0.999996 0.999997 0.999998 0.999999 1 1 1 1 1 1.00001 1.00001 1.00001 1.00001 1.00001 1.00001 They only appear to be correct up to the first 1. What is the proper way to solve this problem?

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• How to build a LINQ query from text at runtime?

  - by Danvil

  I have a class A { public int X; public double Y; public string Z; // and more fields/properties ... }; and a List<A> data and can build a linq query like e.g. var q = from a in data where a.X > 20 select new {a.Y, a.Z}; Then dataGridView1.DataSource = q.ToList(); displays the selection in my DataGridView. Now the question, is it possible to build the query from a text the user has entered at runtime? Like var q = QueryFromText("from a in data where a.X > 20 select new {a.Y, a.Z}"); The point being, that the user (having programming skills) can dynamically and freely select the displayed data.

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• To Switch To The Design View Of A Windows Form

  - by June

  Hi Friends I create new project in Windows Form Application using Visual Studio in VB.Net. I place some controls on my form. I don't write any code at this time. I close this project. When i open this project again , i found Form1.vb. I double-click that file , but the design view doesn't appear. I also find Form1.Designer.vb. What in this file is code. How can i switch to Design View of Form1 ? I need to write some codes for that form's objects like Button Click Event. June

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• Data-binding taking to 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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• Looking at the C++ new[] cookie. How portable is this code?

  - by carleeto

  I came up with this as a quick solution to a debugging problem - I have the pointer variable and its type, I know it points to an array of objects allocated on the heap, but I don't know how many. So I wrote this function to look at the cookie that stores the number of bytes when memory is allocated on the heap. template< typename T > int num_allocated_items( T *p ) { return *((int*)p-4)/sizeof(T); } //test #include <iostream> int main( int argc, char *argv[] ) { using std::cout; using std::endl; typedef long double testtype; testtype *p = new testtype[ 45 ]; //prints 45 std::cout<<"num allocated = "<<num_allocated_items<testtype>(p)<<std::endl; delete[] p; return 0; } I'd like to know just how portable this code is.

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• How can I make external script output link to code in Visual Studio?

  - by JoelFan

  I sometimes need to search code for patterns in a way that goes beyond the regex capabilities of Visual Studio (e.g. patterns that depend on what was seen previously in the file or on the contents of other files). So I use Perl to analyze the source and output matching lines, along with the file name and line number. Since this is the exact same format as is produced by the search feature of Visual Studio, I wonder if there is a way to duplicate the functionality where I can double-click on a line and it will display that line in context in Visual Studio. Any ideas?

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• Storing objects in STL vector - minimal set of methods

  - by osgx

  Hello What is "minimal framework" (necessary methods) of object, which I will store in STL <vector>? For my assumptions: #include <vector> #include <cstring> using namespace std; class Doit { private: char *a; public: Doit(){a=(char*)malloc(10);} ~Doit(){free(a);} }; int main(){ vector<Doit> v(10); } gives *** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0804b008 *** Aborted and in valgrind: malloc/free: 2 allocs, 12 frees, 50 bytes allocated.

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• ODBC - multiple connections from one app to the same data source

  - by Marcin K

  I vaguely remember reading somewhere (in MSDN ODBC documentation?) that one application cannot make more than one connection to a single data source. It seemed to me that I need one connection that all the threads of the application will have to share. I was trying to look this information up, but I can't seem to find it anymore. Does anyone know/remember how this works? It all might become a problem in our app, since some of its threads will dynamically connect to data sources of their choice. I don't want to see random connection errors if two of them will connect at the same time to one source, so I wanted to double check this info.

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• How to model localized items

  - by tweir

  I'm currently designing a e-commerce solution. One of the primary requirements is for the store to support localized item details. The same store must be able to support multiple languages via the user's language selection and/or browser preference. I have two tables: Item (id, sku, price, ...) ItemDetails (item_id, language, title, ...) For each Item, there will be multiple rows corresponding to the item, where the (item_id,language) pair will be unique. I would like to model this as: class Item { public string sku; public double price; public ItemDetails Details; } Based on the user's session, I would like the items returned to have the Details object corresponds to the user's selected language (from their session). What are some approaches for representing this?

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• what do you expect from flash in the near future?

  - by algro

  The recent article of steve jobs link made me think about the future of flash. I'm learning actionscript 3.0 in my studies but is it the right decision still to go for it? I was pretty sure that I will be able to build application in as3 for iphones/ipads in the near future. It seems to me, while I would stay with flash, the market will be polarized by apple and adobe and you will always work double for both clientele, or just lose half of them. Which decision would you take as a designer, if you were still at university and you intend to become a freelancer?

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• The type initializer for {Data.DataModule} threw an exception.

  - by squirms

  In visual basic, when in the "frmMain Events: Load", I get the following error The type initializer for 'projData.projDataModule' threw an exception. when running the code: var = 180 "var" is defined in projDataModule as Module projDataModule Public var As Double End Module When I rebuild the solution, It says "0 errors, 0 warnings" and will actually compile, however the Error list shows the following error: Error 1 Custom tool error: Failed to generate file: There is an error in XML document (1, 1). I:\Documents and Settings\Bill\Desktop\Projects\Data\My Project\Application.myapp 1 1 Data Any ideas or help at all would be greatly appreciated. Thanks in advance.

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