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  • how to implement a sparse_vector class

    - by Neil G
    I am implementing a templated sparse_vector class. It's like a vector, but it only stores elements that are different from their default constructed value. So, sparse_vector would store the index-value pairs for all indices whose value is not T(). I am basing my implementation on existing sparse vectors in numeric libraries-- though mine will handle non-numeric types T as well. I looked at boost::numeric::ublas::coordinate_vector and eigen::SparseVector. Both store: size_t* indices_; // a dynamic array T* values_; // a dynamic array int size_; int capacity_; Why don't they simply use vector<pair<size_t, T>> data_; My main question is what are the pros and cons of both systems, and which is ultimately better? The vector of pairs manages size_ and capacity_ for you, and simplifies the accompanying iterator classes; it also has one memory block instead of two, so it incurs half the reallocations, and might have better locality of reference. The other solution might search more quickly since the cache lines fill up with only index data during a search. There might also be some alignment advantages if T is an 8-byte type? It seems to me that vector of pairs is the better solution, yet both containers chose the other solution. Why?

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  • Is marshaling/ serialization in PHP as simple as serialize($var) ?

    - by Ygam
    here's a definition of marshaling from Wikipedia: In computer science, marshalling (similar to serialization) is the process of transforming the memory representation of an object to a data format suitable for storage or transmission. It is typically used when data must be moved between different parts of a computer program or from one program to another. I have always done data serialization in php via its serialize function, usually on objects or arrays. But how is wikipedia's definition of marshaling/serialization takes place in this serizalize() function?

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  • Object serialization practical uses?

    - by nash
    How many software projects have you worked on used object serialization? I personally never came across a scenario where object serialization was used. One use case i can think of is, a server software storing objects to disk to save memory. Are there other types of software where object serialization is essential or preferred over a database?

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  • .NET Regex Instance Caching

    - by jvenema
    I've read this article, which describes how instance vs static methods get called with a .NET regex. However, what about if the instance itself is static? Does anyone know if .NET does any sort of caching that could potentially cause a memory leak?

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  • Simaltaneous connections with PHP and SOAP?

    - by Dov
    I'm new to using SOAP and understanding the utmost basics of it. I create a client resource/connection, I then run some queries in a loop and I'm done. The issue I am having is when I increase the iterations of the loop, ie: from 100 to 1000, it seems to run out of memory and drops an internal server error. How could I possibly run either a) multiple simaltaneous connections or b) create a connection, 100 iterations, close connection, create connection.. etc. "a)" looks to be the better option but I have no clue as to how to get it up and running whilst keeping memory (I assume opening and closing connections) at a minimum. Thanks in advance! index.php <?php // set loops to 0 $loops = 0; // connection credentials and settings $location = 'https://theconsole.com/'; $wsdl = $location.'?wsdl'; $username = 'user'; $password = 'pass'; // include the console and client classes include "class_console.php"; include "class_client.php"; // create a client resource / connection $client = new Client($location, $wsdl, $username, $password); while ($loops <= 100) { $dostuff; } ?> class_console.php <?php class Console { // the connection resource private $connection = NULL; /** * When this object is instantiated a connection will be made to the console */ public function __construct($location, $wsdl, $username, $password, $proxyHost = NULL, $proxyPort = NULL) { if(is_null($proxyHost) || is_null($proxyPort)) $connection = new SoapClient($wsdl, array('login' => $username, 'password' => $password)); else $connection = new SoapClient($wsdl, array('login' => $username, 'password' => $password, 'proxy_host' => $proxyHost, 'proxy_port' => $proxyPort)); $connection->__setLocation($location); $this->connection = $connection; return $this->connection; } /** * Will print any type of data to screen, where supported by print_r * * @param $var - The data to print to screen * @return $this->connection - The connection resource **/ public function screen($var) { print '<pre>'; print_r($var); print '</pre>'; return $this->connection; } /** * Returns a server / connection resource * * @return $this->connection - The connection resource */ public function srv() { return $this->connection; } } ?>

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  • How to tile a 30000 x 6000 image for a 480 x 320 screen?

    - by Horace Ho
    (this is related to another question about implementation on iPhone) I have a large image, size around 30000 (w) x 6000 (h) pixels. You may consider it's like a big map. I assume I need to crop it up into smaller tiles. Questions: what is the tile strategy? Requirements: whole image (though cropped) can be scrolled up/down/left/right by swipes zoom in (up to pixel-to-pixel) out (down to screen-fit-by-height) by the 2-finger operation memory efficiency by lazy loading tiles Thanks!

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  • nokogiri vs hpricot?

    - by roshan
    Which one would you choose? My important attributes are (not in order) Support & Future enhancements Community & general knowledge base (on the Internet) Comprehensive (i.e proven to parse a wide range of *.*ml pages) Performance Memory Footprint (runtime, not the code-base)

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  • Is there a workaround for Linux mono's refusal to acknowledge that I have resized the columns of my

    - by fantius
    When I resize a column, it does not redraw the data with the updated alignment. I've tried Invalidating, Refreshing, and a few other things. Nothing has worked. Does anyone know a workaround? I have not tried this in mono for Windows. To see what I mean, drop this control on a form, and run it in mono for Linux: using System; using System.Collections.Generic; using System.Text; using System.Windows.Forms; using System.Drawing; class MyListView : ListView { private readonly List<ListViewItem> items_ = new List<ListViewItem>(); public MyListView() { VirtualMode = true; Columns.Add("Col 1"); Columns.Add("Col 2"); Columns.Add("Col 3"); Add(new ListViewItem(new[] { "a", "b", "c" })); Add(new ListViewItem(new[] { "a", "b", "c" })); Add(new ListViewItem(new[] { "a", "b", "c" })); Add(new ListViewItem(new[] { "a", "b", "c" })); Add(new ListViewItem(new[] { "a", "b", "c" })); } protected override void OnRetrieveVirtualItem(RetrieveVirtualItemEventArgs e) { e.Item = items_[e.ItemIndex]; base.OnRetrieveVirtualItem(e); } public void Add(ListViewItem item) { items_.Add(item); VirtualListSize = items_.Count; } protected override void OnDrawColumnHeader(DrawListViewColumnHeaderEventArgs e) { e.DrawText(); base.OnDrawColumnHeader(e); } protected override void OnDrawSubItem(DrawListViewSubItemEventArgs e) { var text = ((ListViewItem.ListViewSubItem)e.SubItem).Text; using (var brush = new SolidBrush(e.SubItem.ForeColor)) { e.Graphics.DrawString(text, Font, brush, e.Bounds); } base.OnDrawSubItem(e); } protected override void OnColumnWidthChanged(ColumnWidthChangedEventArgs e) { base.OnColumnWidthChanged(e); Invalidate(true); // Nope, that didn't work Refresh(); // Nope, that didn't work } }

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  • Win32: How to crash?

    - by Ian Boyd
    i'm trying to figure out where Windows Error Reports are saved; i hit Send on some earlier today, but i forgot that i want to "view the details" so i can examine the memory minidumps. But i cannot find where they are stored (and google doesn't know). So i want to write a dummy application that will crash, show the WER dialog, let me click "view the details" so i can get to the folder where the dumps are saved. How can i crash on Windows?

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  • xerces-c: Xml parsing multiple files

    - by user459811
    I'm atempting to learn xerces-c and was following this tutorial online. http://www.yolinux.com/TUTORIALS/XML-Xerces-C.html I was able to get the tutorial to compile and run through a memory checker (valgrind) with no problems however when I made alterations to the program slightly, the memory checker returned some potential leak bytes. I only added a few extra lines to main to allow the program to read two files instead of one. int main() { string configFile="sample.xml"; // stat file. Get ambigious segfault otherwise. GetConfig appConfig; appConfig.readConfigFile(configFile); cout << "Application option A=" << appConfig.getOptionA() << endl; cout << "Application option B=" << appConfig.getOptionB() << endl; // Added code configFile = "sample1.xml"; appConfig.readConfigFile(configFile); cout << "Application option A=" << appConfig.getOptionA() << endl; cout << "Application option B=" << appConfig.getOptionB() << endl; return 0; } I was wondering why is it when I added the extra lines of code to read in another xml file, it would result in the following output? ==776== Using Valgrind-3.6.0 and LibVEX; rerun with -h for copyright info ==776== Command: ./a.out ==776== Application option A=10 Application option B=24 Application option A=30 Application option B=40 ==776== ==776== HEAP SUMMARY: ==776== in use at exit: 6 bytes in 2 blocks ==776== total heap usage: 4,031 allocs, 4,029 frees, 1,092,045 bytes allocated ==776== ==776== 3 bytes in 1 blocks are definitely lost in loss record 1 of 2 ==776== at 0x4C28B8C: operator new(unsigned long) (vg_replace_malloc.c:261) ==776== by 0x5225E9B: xercesc_3_1::MemoryManagerImpl::allocate(unsigned long) (MemoryManagerImpl.cpp:40) ==776== by 0x53006C8: xercesc_3_1::IconvGNULCPTranscoder::transcode(unsigned short const*, xercesc_3_1::MemoryManager*) (IconvGNUTransService.cpp:751) ==776== by 0x4038E7: GetConfig::readConfigFile(std::string&) (in /home/bonniehan/workspace/test/a.out) ==776== by 0x403B13: main (in /home/bonniehan/workspace/test/a.out) ==776== ==776== 3 bytes in 1 blocks are definitely lost in loss record 2 of 2 ==776== at 0x4C28B8C: operator new(unsigned long) (vg_replace_malloc.c:261) ==776== by 0x5225E9B: xercesc_3_1::MemoryManagerImpl::allocate(unsigned long) (MemoryManagerImpl.cpp:40) ==776== by 0x53006C8: xercesc_3_1::IconvGNULCPTranscoder::transcode(unsigned short const*, xercesc_3_1::MemoryManager*) (IconvGNUTransService.cpp:751) ==776== by 0x40393F: GetConfig::readConfigFile(std::string&) (in /home/bonniehan/workspace/test/a.out) ==776== by 0x403B13: main (in /home/bonniehan/workspace/test/a.out) ==776== ==776== LEAK SUMMARY: ==776== definitely lost: 6 bytes in 2 blocks ==776== indirectly lost: 0 bytes in 0 blocks ==776== possibly lost: 0 bytes in 0 blocks ==776== still reachable: 0 bytes in 0 blocks ==776== suppressed: 0 bytes in 0 blocks ==776== ==776== For counts of detected and suppressed errors, rerun with: -v ==776== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)

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  • Changing the direction of a Combo box dropdown in SWT

    - by Kris
    Hi, I'm building an Eclipse plugin in SWT, and I have the following problem: one of my fields is a combo box, and in some cases it may have fairly long items as selection options. My plugin runs on the right side of the screen, so when you go to use the combo-box, the right side of the combo box is cut off. So, my question is: is there any way to change the dropdown's alignment relative to the combo control? It seems to be permanently left-aligned... and I'm pretty sure you can change the direction in Swing (though the only place I've seen it done is in the Substance UI demo. The Combo Box tab has boxes with North, South East, and West flyout directions... for my application, I need something like the West flyout) Note: Setting actual text limits is a last-case-scenario option; it would be quite a bit of guesswork to set the text limit dynamically (since the widget's view can be resized). Here's a picture (sorry, I can only have one link and no images :( ... I need some more rep :p) Left side of the line: Proper width - the view is the wide enough for the combo dropdown to display all the text; you can see the scrollbars on the right side. Right side of the line: Too small - Here, the view has been resized, and the combo dropdown scrollbar (as well as some of the text) is cut off by the right side of the screen. I always have more screen space available to the left (since this is always on the right hand side of the screen), but the combo dropdown always appears to the lower right. Hopefully this is clear enough.

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  • What features would you like to see removed from C++?

    - by Justin Ethier
    This question was inspired by what-features-would-you-like-to-see-added-to-c. anBasically, C++ is a great general-purpose language. But perhaps too general and feature-rich... multiple inheritance, operator overloading, manual memory management, templates, smart pointers, virtual destructors, legacy frameworks (think MFC), and I could just go on. Is there any one feature / aspect of C++ that you would like taken away, to make our lives easier as C++ developers? One feature per answer, please.

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  • how to load part of the HTML page which is currently on display ?

    - by ganapati hegde
    Hi, i have an ebook(relatively large size say 800 pages),in HTML format. I am opening that book as webpage using webkit-gtk+. If i load the whole book at a time,it takes too much memory(RAM ).So i dont want to load the whole book at a time, but load the part of the book which is currently on display. and when the user scrolls down, next part should be displayed.How can i implement that ?

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  • SQLAlchemy - SQLite for testing and Postgresql for devlopment - How to port?

    - by StackUnderflow
    I want to use sqlite memory database for all my testing and Postgresql for my development/production server. But the SQL syntax is not same in both dbs. for ex: SQLite has autoincrement, and Postgresql has serial Is it easy to port the SQL script from sqlite to postgresql... what are your solutions? If you want me to use standard SQL, how should I go about generating primary key in both the databases?

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  • Retrieving all objects in code upfront for performance reasons

    - by ming yeow
    How do you folks retrieve all objects in code upfront? I figure you can increase performance if you bundle all the model calls together? This makes for a bigger deal, especially if your DB cannot keep everything in memory def hitDBSeperately { get X users ...code get Y users... code get Z users... code } Versus: def hitDBInSingleCall { get X+Y+Z users code for X code for Y... }

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