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• What kind of work benifits from OpenCL

  - by Daniel

  Hey All First of all: I am well aware that OpenCL does not magically make everything faster I am well aware that OpenCL has limitations So now to my question, i am used to do different scientific calculations using programming. Some of the things i work with is pretty intense in regards to the complexity and number of calculations. SO i was wondering, maybe i could speed things up bu using OpenCL. So, what i would love to hear from you all is answers to some of the following [bonus for links]: *What kind of calculations/algorithms/general problems is suitable for OpenCL *What is the general guidelines for determining if some particular code would benefit by migration to OpenCL? Regards

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• Expected symbol problems with this function declaration

  - by Derek

  I am just getting back into the C programming realm and I am having an issue that I think is linker related. I am using cmake for the first time as well, so that could be adding to my frustration. I have included a third party header file that contains a typedef that my code is trying to use, and it has this line: typedef struct a a_t so my code has a_t *var; //later..... var->member;// this line throws the error which throws the error: dereferencing pointer to incomplete type So am I just missing another include file, or is this a linker issue? I am building this code in QtCreator and using cmake. I can dive on a_t to see that typedef declaration in the included header, but I can't seem to dive on "struct a" itself to see where it's coming from. Thanks

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• Rails create_table query

  - by Steve

  Hi, I am a beginner in Rails. In the following code,there is an id which is set as false. What's the meaning of it? class CreateCoursesStudents < ActiveRecord::Migration def self.up create_table :courses_students, :id => false do |t| t.integer :course_id, :null => false t.integer :student_id, :null => false end # Add index to speed up looking up the connection, and ensure # we only enrol a student into each course once add_index :courses_students, [:course_id, :student_id], :unique => true end def self.down remove_index :courses_students, :column => [:course_id, :student_id] drop_table :courses_students end end Thanks

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• I serialized a C++ object, how to allocate memory for it without knowing what type it is?

  - by Neo_b

  Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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• C++ volatile required when spinning on boost::shared_ptr operator bool()?

  - by JaredC

  I have two threads referencing the same boost::shared_ptr: boost::shared_ptr<Widget> shared; On thread is spinning, waiting for the other thread to reset the boost::shared_ptr: while(shared) boost::thread::yield(); And at some point the other thread will call: shared.reset(); My question is whether or not I need to declare the shared pointer as volatile to prevent the compiler from optimizing the call to shared.operator bool() out of the loop and never detecting the change? I know that if I were simply looping on a variable, waiting for it to reach 0 I would need volatile, but I'm not sure if boost::shared_ptr is implemented in such a way that it is not necessary here.

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• Iterating over a database column in Django

  - by curious

  I would like to iterate a calculation over a column of values in a MySQL database. I wondered if Django had any built-in functionality for doing this. Previously, I have just used the following to store each column as a list of tuples with the name table_column: import MySQLdb import sys try: conn = MySQLdb.connect (host = "localhost", user = "user", passwd="passwd", db="db") except MySQLdb.Error, e: print "Error %d: %s" % (e.args[0], e.args[1]) sys.exit (1) cursor = conn.cursor() for table in ['foo', 'bar']: for column in ['foobar1', 'foobar2']: cursor.execute('select %s from %s' % (column, table)) exec "%s_%s = cursor.fetchall()" % (table, column) cursor.close() conn.commit() conn.close() Is there any functionality built into Django to more conveniently iterate through the values of a column in a database table? I'm dealing with millions of rows so speed of execution is important.

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• How to create a Mutex with security attribute to share resource from different application?

  - by Antony Tess

  How to create a Mutex with security attribute rigth to share resource from different application? In according with Microsoft SDK documentation the CreateMutex API accept as first parameter a SECURITY_ATTRIBUTES pointer. HANDLE WINAPI CreateMutex( __in LPSECURITY_ATTRIBUTES lpMutexAttributes, __in BOOL bInitialOwner, __in LPCTSTR lpName ); I want to create the rigth security attribute so only my application group can open the MUTEX and access to a specific resource (a file) where my application gruop read/write data operation. The target opertaing system are XP, Vista and Seven. The feature must working in both, administrator/standard user, login shenario.

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• Combining XSLT transforms

  - by Flynn1179

  Is there a way to combine two XSLT documents into a single XSLT document that does the same as transforming using the original two in sequence? i.e. Combining XSLTA and XSLTB into XSLTC such that XSLTB( XSLTA( xml )) == XSLTC( xml )? There's three reasons I'd like to be able to do this: Simplifies development; some operations need sequential transforms, and although I can generate a combined one by hand, it's a lot more difficult to maintain that two much simpler, separate transforms. Speed; one transform is in most cases hopefully faster than two. I'm currently working on a program that literally just transforms a data file in XML into an XHTML page capable of editing it using one XSLT, and a second XSLT that transforms the XHTML page back into the data file when it's saved. One test I hope to be able to do is to combine the two, and easily confirm that the 'combined' XSLT should leave the data unchanged.

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• How to get "printer ready bytes" from a source in c#?

  - by luis_villase

  Hey everyone! I'm in a bit of trouble here, hoping you can help a fellow programmer out. I have an application that receives a pointer to raw bytes (plus length and stuff) and sends said raw data to a printer. This is important, I have no choice but to use this method to get any printing done. If I send a raw string, it will print with no problem. However, I need to be able to print formatted text, images, etc. So the thing is... I would like to be able to get printer ready bytes from a given source (maybe a pdf, or html, does not matter as long as it contains formatted text and/or images). It would be like "splitting" the print command like so: a) Open file and read data b) Load printer data into memory c) Send bytes to printer Obviously, I've got a) and c) covered, it's b) the one that's breaking my head. Any thoughts? Thanks in advance for your help.

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• Java training for .NET developers?

  - by C Keene

  We are working with a large retail bank on training 40-50 .Net developers to use Java. They are familiar with C# and .Net framework and have built dozens of "run the business" style apps in .Net. We need advice on how to provide basic Java familiarity, with a focus on back end logic, security and transaction management. Back end is Spring/Hibernate, front end is Ajax (Dojo). Are there any online, self-paced, Java courses that would be good for C#/.Net developers to get up to speed quickly?

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• How to get notified of modification in the memory in Linux

  - by Song Yuan

  In a userspace program in Linux, I get a piece of memory via allocation from the heap, then the pointer is distributed to a lot of other components running in other threads to use. I would like to get notified when the said piece of memory is modified. I can of course develop a custom userspace solution for other components to use when they try to modify the memory. The problem in my case is that these are legacy components and they can write to memory in many occasions. So I'm wondering whether there is a similar API like inotify (get notified when file is changed) or other approaches in order to get notified when a piece of memory is changed. I considered using mmap and inotify, which obviously won't work if the changes are not flushed. Any suggestions are appreciated :-)

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• Rails 3 namespacing requires model to be defined twice?

  - by RSG

  I'm pulling my hair out trying to understand namespacing in Rails 3. I've tried following a few different tutorials, and the only way I can get my models to work is if I define my model in both the base directory and my namespace directory. If I only define the model in the namespace directory it expects it to define both Model and Namespace::Model, as below: LoadError (Expected .../app/models/plugins/chat.rb to define Chat): or LoadError (Expected .../app/models/plugins/chat.rb to define Plugins::Chat): I'm sure I'm missing something obvious, but I could really use a pointer in the right direction. Here are the relevant excerpts. /models/plugins/chat.rb class Plugins::Chat include ActiveModel::Validations include ActiveModel::Conversion extend ActiveModel::Naming ... end /controllers/plugins/chats_controller.rb class Plugins::ChatsController < Plugins::ApplicationController load_and_authorize_resource ... end /config/routes.rb namespace :plugins do resources :chats end /config/application.rb config.autoload_paths += Dir["#{config.root}/app/models/**/"]

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• collect string in loop and printout all the string outside loop

  - by user1508163

  I'm newbie here and there is some question that I want have some lesson from you guys. For example: #include <stdio.h> #include<stdlib.h> #include<ctype.h> void main() { char name[51],selection; do { printf("Enter name: "); fflush(stdin); gets(name); printf("Enter another name?(Y/N)"); scanf("%c",&selection); selection=toupper(selection); }while (selection=='Y'); //I want to printout the entered name here but dunno the coding printf("END\n"); system("pause"); } As I know when the loops perform will overwrite the variable then how I perform a coding that will printout all the name user entered? I have already ask my tutor and he is ask me to use pointer, can anyone guide me in this case?

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• Getting Factors of a Number

  - by Dave

  Hi Problem: I'm trying to refactor this algorithm to make it faster. What would be the first refactoring here for speed? public int GetHowManyFactors(int numberToCheck) { // we know 1 is a factor and the numberToCheck int factorCount = 2; // start from 2 as we know 1 is a factor, and less than as numberToCheck is a factor for (int i = 2; i < numberToCheck; i++) { if (numberToCheck % i == 0) factorCount++; } return factorCount; }

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• How to to dump JS array... (boommarklet?)

  - by Soulhuntre

  A page on a site I use is holding some of my data hostage. Once I have logged into the site and navigated to the right page, the data I need is in the array eeData[] - it is 720 elements long (once every 2 minutes of a given day). Rather than simulate the requests to the underlying stuff json supplier and since its only once a day, I am happy to simply develop a bookmarklet to grab the data - preferably as a XML or CSV file. Any pointers to sample code or hints would help. I found a bookmarklet here that is based on this script that does part of this - but I am not up to speed on any potential JS file IO to see if it is possible to induce a file "download" of the data, or pop it opn in a new window I can copy / paste.

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• Swap byte 2 and 4 from integer

  - by czar x

  I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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• MySQL: host name universal change.

  - by ctrlShiftBryan

  I am making some updates to a php site which I did not design. I have a local copy of the site. At the top of each page there are settings for the host name for the db connection. Is there someway I can setup a pointer to the remote address. The address is 'mysqlhost' for example and I want that to point to 'mysql.myhost.com'. I tried creating a HOST record for mysqlhost pointing to the IP address it resolves to but that doesn't work. If I put 'mysql.myhost.com' in the connection it works. If I put that IP address it doesn't so that is probably why the HOST record idea doesn't work. Other than creating a local copy of the DB is there a quick way so that I don't have to modify each file in my dev environment and then again when I redeploy?

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• Event handling C# / Registering a callback

  - by Jeff Dahmer

  Events can only return void and recieve object sender/eventargs right? If so then craptastic.... how can I pass a function pointer to another obj, like: public bool ACallBackFunc(int n) { return n > 0; } public void RegisterCallback(Something s) { s.GiveCallBack(this.ACallBackFunc); } Something::GiveCallBack(Action? funcPtr) I tried using Action, but I need it to return some value and Actions can only return void. Also, we do not know what kind of a callback we will be recieving; it could return anything and have any params! Reflection will have to be used somehow I reckon.

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• GWT : NULL Session

  - by jidma

  I'm using spring4gwt in my project. I have the following login service implementation: @Service("loginService") public class LoginServiceImpl extends RemoteServiceServlet implements LoginService { @Override @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class) public UserBean checkUser(String userName, String password) throws Exception { HttpSession httpSession = getThreadLocalRequest().getSession(); } } When i call the loginService.checkUser("test","test") (In hosted mode), I get a null pointer exception, as getThreadLocalRequest() returns NULL instead of the actual session. I didn't try in web mode yet. Why would I get a null session ? Does it have something to do with spring4gwt ? Thank you

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• HRESULT exception not caught in VS 2008

  - by arionik

  Hello all, I've got a stange situation in visual studio 2008 C++. I work on code that was originally written for visual studio 2003, where everything works well. Now, ported to VS 2008, the exception handling, which unfortuantely exists widely in the code, does not work anymore. standard code example: try { HRESULT hr = S_OK; // do stuff... if( FAILED( hr ) ) throw hr; } catch( HRESULT hr ) { // error handling, but we never get here } catch( ... ) { // ... not even here } Under VS 2008, no exception is encountered, but I get a crash somewhere else, indicating that the stack pointer must be screwed up. Did anybody come across this behaviour? Any help is appreciated.

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• HTML5 placing image where i want it on screen

  - by corrigan_sam

  I have a little start screen running and i want the image, which is acting as a button, to placed at a certain point, but when i try to it stays in the same place, and i don't know how i can get it to stay in the place i want it. Here is my code, its is HTML with some css: <style> #SplashScreen{ position:relative; overflow:hidden; } #StartButton { cursor:pointer; position:absoloute; left:100px; top:100px; } </style> <div id="SplashScreen" width="400" height="400"> <h1>Game Title</h1> <img id="StartButton" src="play.png"/> </div> The image just draws underneath the title and not where i want it. Any help?

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• c++ Sorting a vector based on values of other vector, or what's faster?

  - by pollux

  Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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• SQL Server, fetching data from multiple joined tables. Why is slow?

  - by user562192

  I have problem with performance when retrieving data from SQL Server. My sql query looks something like this: SELECT table_1.id, table_1.value, table_2.id, table_2.value,..., table_20.id, table_20.value From table_1 INNER JOIN table_2 ON table_1.id = table_2.table_1_id INNER JOIN table_3 ON table_2.id = table_3.table_2_id... WHERE table_1.row_number BETWEEN 1 AND 20 So, I am fetching 20 results. This query takes about 5 seconds to execute. When I select only table_1.id, it returns results instantly. Because of that, I guess that problem is not in JOINs, it is in retrieving data from multiple tables. Any suggestions how I would speed up this query?

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• Python as your main language. Possible?

  - by Deinumite

  I am currently attending college and the languages that I will 'know' by graduation are C++ and Java. That being said, i am also in the process of teaching myself Python. I know that every programming language has its own pros and cons, but would it be possible to become a python developer out of school? I always have more 'fun' programming in Python than i do in C++ or Java, and I am also in love with Pythons documentation. I know C++ will always be on top in terms of speed, but what would be the benefit of memorizing every javadoc against focusing on Python instead? are there good jobs to be had with Python? edit: also, would it be beneficial for me to look at C# as well? Microsoft is really throwing their support at it so that could be a decent career path as well.

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• CSS Position Help (horizontal sidebar showing up when animate content over)

  - by jstacks

  Let me try my best to explain what I'd like to have happen, show you the code I have an hopefully I can get some help. So, I'm trying to do a sliding navigation UI from the left side of the screen (like a lot of mobile apps). The main content slides over, displaying the navigation menu beneath. Right now the browser thinks the screen is getting wider and introduces a horizontal scroll bar. However, I don't want that to happen... How do I get the div to animate off screen but not enlarge the width of the screen (i.e. keep it partially off screen)? Anyway here is my fiddle: http://jsfiddle.net/2vP67/6/ And here is the code within the post: HTML <div id='wrapper'> <div id='navWide'> </div> <div id='containerWide'> </div> <div id='containerTall'> <div id='container'> <div id='nav'> <div id='navNavigate'> Open Menu </div> <div id='navNavigateHide'> Close Menu </div> </div> </div> </div> <div id='sideContainerTall'> <div id='sideContainer'> <div id='sideNav'>Side Navigation </div> </div> </div> </div> CSS #wrapper { width:100%; min-width:1000px; height:100%; min-height:100%; position:relative; top:0; left:0; z-index:0; } #navWide { color: #ffffff; background:#222222; width:100%; min-width:1000px; height:45px; position:fixed; top:0; left:0; z-index:100; } #containerWide { width:100%; min-width:1000px; min-height:100%; position:absolute; top:45px; z-index:100; } #containerTall { color: #000000; background:#dadada; width:960px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:1000; } /***** main container *****/ #container { width:960px; min-height:585px; } #nav { color: #ffffff; background:#222222; width:960px; height:45px; position:fixed; top:0; z-index:10000; } #navNavigate { background:yellow; font-size:10px; color:#888888; width:32px; height:32px; padding:7px 6px 6px 6px; float:left; cursor:pointer; } #navNavigateHide { background:yellow; font-size:10px; color:#888888; width:32px; height:32px; padding:7px 6px 6px 6px; float:left; cursor:pointer; display:none; } #sideContainerTall { background:#888888; width:264px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:500; } #sideContainer { width:264px; min-height:585px; display:none; } #sideContainerTall { background:#888888; width:264px; min-height:100%; margin-left:-480px; position:absolute; top:0; left:50%; z-index:500; } #sideContainer { width:264px; min-height:585px; display:none; } #sideNav { width:264px; height:648px; float:left; } Javascript $(document).ready(function() { $('div#navNavigate').click(function() { $('div#navNavigate').hide(); $('div#navNavigateHide').show(); $('div#sideContainer').show(); $('div#containerTall').animate({ 'left': '+=264px' }); }); $('div#navNavigateHide').click(function() { $('div#navNavigate').show(); $('div#navNavigateHide').hide(); $('div#containerTall').animate({ 'left': '-=264px' }, function() { $('div#sideContainer').hide(); }); }); });

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