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  • C++ Virtual Constructor, without clone()

    - by Julien L.
    I want to perform "deep copies" of an STL container of pointers to polymorphic classes. I know about the Prototype design pattern, implemented by means of the Virtual Ctor Idiom, as explained in the C++ FAQ Lite, Item 20.8. It is simple and straightforward: struct ABC // Abstract Base Class { virtual ~ABC() {} virtual ABC * clone() = 0; }; struct D1 : public ABC { virtual D1 * clone() { return new D1( *this ); } // Covariant Return Type }; A deep copy is then: for( i = 0; i < oldVector.size(); ++i ) newVector.push_back( oldVector[i]->clone() ); Drawbacks As Andrei Alexandrescu states it: The clone() implementation must follow the same pattern in all derived classes; in spite of its repetitive structure, there is no reasonable way to automate defining the clone() member function (beyond macros, that is). Moreover, clients of ABC can possibly do something bad. (I mean, nothing prevents clients to do something bad, so, it will happen.) Better design? My question is: is there another way to make an abstract base class clonable without requiring derived classes to write clone-related code? (Helper class? Templates?) Following is my context. Hopefully, it will help understanding my question. I am designing a class hierarchy to perform operations on a class Image: struct ImgOp { virtual ~ImgOp() {} bool run( Image & ) = 0; }; Image operations are user-defined: clients of the class hierarchy will implement their own classes derived from ImgOp: struct CheckImageSize : public ImgOp { std::size_t w, h; bool run( Image &i ) { return w==i.width() && h==i.height(); } }; struct CheckImageResolution; struct RotateImage; ... Multiple operations can be performed sequentially on an image: bool do_operations( std::vector< ImgOp* > v, Image &i ) { std::for_each( v.begin(), v.end(), /* bind2nd(mem_fun(&ImgOp::run), i ...) don't remember syntax */ ); } int main( ... ) { std::vector< ImgOp* > v; v.push_back( new CheckImageSize ); v.push_back( new CheckImageResolution ); v.push_back( new RotateImage ); Image i; do_operations( v, i ); } If there are multiple images, the set can be split and shared over several threads. To ensure "thread-safety", each thread must have its own copy of all operation objects contained in v -- v becomes a prototype to be deep copied in each thread.

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  • Writing white space to CSV fields in Python?

    - by matt
    When I try to write a field that includes whitespace in it, it gets split into multiple fields on the space. What's causing this? It's driving me insane. Thanks data = open("file.csv", "wb") w = csv.writer(data) w.writerow(['word1', 'word2']) w.writerow(['word 1', 'word2']) data.close() I'll get 2 fields(word1,word2) for first example and 3(word,1,word2) for the second.

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  • interactive login on cgi script

    - by raindrop18
    I am new for perl-cgi script. and my objective is to create user/pass interactive script to log and get information from multiple device at once. instead of add the user/pass credential on the script itself. since i am new if some one show me how to write the interactive part of the script. thanks much!!! here is the current code usr/local/bin/perl -wl use CGI ':standard'; use Net::Telnet::Cisco; ### set the error fields to nulls $selerror = ""; ### Input from the screen - make sure data was input if (param() and param('Switches') ne "" and (param('Mac') ne "" or param('Interface Description') ne "" or param('VLAN') ne "" )) { ### Put the input devices into an array. @devices = param('Switches'); ### format the header data print header(); print start_html(-title=>"ShowSwitches",-BGCOLOR=>'aqua'); print "\n",h1("<CENTER>Show Switches</CENTER>"); print "\n",hr(),"\n"; ### Go thru the device array. foreach(@devices) { $error_msg = ""; $TAC_login_error = ""; $open_error = ""; $retry_open_error = ""; $prompt_error = ""; $password_error = ""; ### Take input host and use to send to Telnet $host = $_; $session = Net::Telnet::Cisco->new(Errmode => 'return', Timeout => 30); ### Connect to the host $session->open(Host =>"$host", Timeout => 15); $open_error = $session->errmsg; ### Login with TACACS if host can be connected to if ($open_error eq "") { $session->login('USER', 'PASS'); $TAC_login_error = $session->errmsg; ### Login with TACACS failed - try standard login if ($TAC_login_error ne "") { ### Connect to host $session->open(Host =>"$host", Timeout => 15); $retry_open_error = $session->errmsg; ### Wait for password prompt - multiple matches - devices may have different device prompts. if ($retry_open_error eq "") { $session->waitfor(Match => '/Password:.*$/', Match => '/Enter password:.*$/', Timeout => 20); $prompt_error = $session->errmsg; if ($prompt_error eq "") { ### Input password $session->print('getmeout'); $password_error = $session->errmsg; $session->waitfor('/.*>$/'); $password_error = $session->errmsg; } } } } ### No errors, then issue "show commands". if ($open_error eq "" and ($TAC_login_error eq "" or $retry_open_error eq "") and $prompt_error eq "" and $password_error eq "") { ### Show Mac if (param('Mac')) { $cmd = 'sh mac'; @output = $session->cmd("$cmd"); $show_error = ""; $show_error = $session->errmsg; print "\n",h2($host . ' - ' . $cmd); if ($show_error ne "") { $error_msg = 'Error for show mac - ' . $show_error; print b($error_msg),(br); print hr(),"\n"; $error_msg = ''; } else { print pre(@output); print hr(),"\n"; } } ### Show Interface Description if (param('Interface Description')) { $cmd = 'sh interface description'; @output = $session->cmd("$cmd"); $show_error = ""; $show_error = $session->errmsg; print "\n",h2($host . ' - ' . $cmd); if ($show_error ne "") { $error_msg = 'Error for show mac - ' . $show_error; print b($error_msg),(br); print hr(),"\n"; $error_msg = ''; } else { print pre(@output); print hr(),"\n"; } } ### Show VLAN if (param('VLAN')) { $cmd = 'sh vlan'; @output = $session->cmd("$cmd"); $show_error = ""; $show_error = $session->errmsg; print "\n",h2($host . ' - ' . $cmd); if ($show_error ne "") { $error_msg = 'Error for show vlan - ' . $show_error; print b($error_msg),(br); print hr(),"\n"; $error_msg = ''; } else { print pre(@output); print hr(),"\n"; } } } elsif ($TAC_login_error ne "" and $password_error ne "") { $error_msg = "Error - $host " . $TAC_login_error . ' - possible incorrect TACACS or standard password parameters on device.'; } elsif ($open_error ne "") { $error_msg = "Error - $host " . $open_error . ' - cannot connect to host - is it down??'; } elsif ($prompt_error ne "") { $error_msg = "Error - $host " . $prompt_error . ' - password prompt not recognized - invalid TACACS (or user) password.'; } elsif ($password_error ne "") { $error_msg = "Error - $host " . $password_error . ' - possible incorrect user/password parameters on device.'; } if ($error_msg ne "" ) { print b($error_msg),(br); print hr(),"\n"; } print hr(),"\n"; print end_html(),"\n"; } } else { ### No Show command was selected. if (param('Submit') and param('Mac') eq "" and param('Interface Description') eq "" and param('VLAN') eq "" ) { $selerror = 'No Show Displays were selected. Try again please!!'; } elsif ### No switch was selected. (param('Submit') and param('Switches') eq "") { $selerror = 'No devices were selected. Try again please!!'; } ### This formats the initial Show Web page. print header(-Pragma='no-cache'), start_html(-title=>"Show Displays",-BGCOLOR=>'aqua'), h1("<CENTER>Show Switches</CENTER>"),hr(), start_form(), b("Select Show Commands:"), br(), br(), checkbox(-name=>'Mac'), checkbox(-name=>'Interface Description'), checkbox(-name=>'VLAN'), br(),br(),hr(),br(), b("Select One or More Devices:"), br(), br(), scrolling_list (-name => 'Switches', -default=> "NONE", -values => ['cs6a', 'cs7a', 'cs7b', 'cs8b', 'cs9a', 'c9b', 'csa' ], -multiple => 'true', -size => 7, ), p(submit('Submit'),reset('Reset')), b($selerror), end_form(),hr(), end_html(); } #

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  • How do I do high quality scaling of a image?

    - by pbhogan
    I'm writing some code to scale a 32 bit RGBA image in C/C++. I have written a few attempts that have been somewhat successful, but they're slow and most importantly the quality of the sized image is not acceptable. I compared the same image scaled by OpenGL (i.e. my video card) and my routine and it's miles apart in quality. I've Google Code Searched, scoured source trees of anything I thought would shed some light (SDL, Allegro, wxWidgets, CxImage, GD, ImageMagick, etc.) but usually their code is either convoluted and scattered all over the place or riddled with assembler and little or no comments. I've also read multiple articles on Wikipedia and elsewhere, and I'm just not finding a clear explanation of what I need. I understand the basic concepts of interpolation and sampling, but I'm struggling to get the algorithm right. I do NOT want to rely on an external library for one routine and have to convert to their image format and back. Besides, I'd like to know how to do it myself anyway. :) I have seen a similar question asked on stack overflow before, but it wasn't really answered in this way, but I'm hoping there's someone out there who can help nudge me in the right direction. Maybe point me to some articles or pseudo code... anything to help me learn and do. Here's what I'm looking for: 1. No assembler (I'm writing very portable code for multiple processor types). 2. No dependencies on external libraries. 3. I am primarily concerned with scaling DOWN, but will also need to write a scale up routine later. 4. Quality of the result and clarity of the algorithm is most important (I can optimize it later). My routine essentially takes the following form: DrawScaled( uint32 *src, uint32 *dst, src_x, src_y, src_w, src_h, dst_x, dst_y, dst_w, dst_h ); Thanks! UPDATE: To clarify, I need something more advanced than a box resample for downscaling which blurs the image too much. I suspect what I want is some kind of bicubic (or other) filter that is somewhat the reverse to a bicubic upscaling algorithm (i.e. each destination pixel is computed from all contributing source pixels combined with a weighting algorithm that keeps things sharp. EXAMPLE: Here's an example of what I'm getting from the wxWidgets BoxResample algorithm vs. what I want on a 256x256 bitmap scaled to 55x55. And finally: the original 256x256 image

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  • Django admin breaking with non-default primary_key for model with a m2m relationship ?

    - by Gj
    I have a simple Post model with a m2m field to a Tag model. The Tag had for some reason to use a non default primary key. Inside the admin page for a Post, the labels for the multiple selection field for Tags appear, but not the input field itself. I also tried using the filter_horizontal for the tags, but still only the labels appear without the actual field. Any ideas why it breaks and/or workarounds? Thanks!

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  • Active record NEW causing a warning

    - by Jon
    I got this snippet of controller code from Railscast 193, functionally its all working, but i am getting a warning message. http://railscasts.com/episodes/193-tableless-model @search = Search.new(:text => params[:search]) getting warning: /Users/Server/.gem/ruby/1.8/gems/activerecord-2.3.4/lib/active_record/named_scope.rb:13: warning: multiple values for a block parameter (0 for 1) from /Users/Server/.gem/ruby/1.8/gems/activerecord-2.3.4/lib/active_record/named_scope.rb:92 Any ideas why i am getting the warning? thanks

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  • UitableView Problem in deleating items from database

    - by Arun Sharma
    Hi All, I am using in UitableView database.My table view works successfully (add single item,add multiple item,delete all) only problem is there when i want to delete single item for this i using Uitableview edit option. so how i add database method for deleting single item from database and also from table view. Please help me.

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  • Is this ruby code thread safe?

    - by Ben K.
    Is this code threadsafe? It seems like it should be, because @myvar will never be assigned from multiple threads (assuming block completes in < 1s). But do I need to be worried about a situation where the second block is trying to read @myvar as it's being written? require 'rubygems' require 'eventmachine' @myvar = Time.now.to_i EventMachine.run do EventMachine.add_periodic_timer(1) do EventMachine.defer do @myvar = Time.now.to_i # some calculation and reassign end end EventMachine.add_periodic_timer(0.5) do puts @myvar end end

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  • What sql server isolation level should I choose to prevent concurrent reads?

    - by Brian Bolton
    I have the following transaction: SQL inserts a 1 new record into a table called tbl_document SQL deletes all records matching a criteria in another table called tbl_attachment SQL inserts multiple records into the tbl_attachment Until this transaction finishes, I don't want others users to be aware of the (1) new records in tbl_document, (2) deleted records in tbl_attachment, and (3) modified records in tbl_attachment. Would Read Committed Isolation be the correct isolation level?

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  • WPF MVVM View with varying number of objects. How to?

    - by 0xDEAD BEEF
    HI! I want to design view which will contain multiple objects in different locations. For example - it would be great if viewmodel could have field like list of objects (rectangles) and when i change/add members to list, new rectangles appear on view in specified positions. How do i create such view/viewmodel?

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  • C# Multi-Comparisons possible?

    - by Iggy Ma
    is it possible in some way to compare multiple variables to one constant in a if statement? It would be very helpful if instead of if ( col.Name != "Organization" && col.Name != "Contacts" && col.Name != "Orders" ) { } I could just say if ( col.Name != "Organization" || "Contacts" || "Orders" ) { } And I know I could use a list but in some instances I dont want to... Thanks!

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  • Which design pattern should be used to create an emulator?

    - by Facon
    I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English. EDITED - Asking for multiple patterns.

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  • Visual SVN diff and compare tools for Linux

    - by Lakshman Prasad
    Which is the best Visual SVN Diff displayer for Linux. BeyondCompare and VisualSVN1.5 work well on Windows. What are the equivallent tools for Linux. Specifically Ubuntu. I know command line diff works; But I'd like multiple column syntax highlighted and differences. Better if the tool has a support for Git and Hg as well.

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  • Did Java invent interfaces?

    - by Jordão
    I know about C++ pure virtual classes, but Java went one step further and created a first-class (no pun intended) concept for multiple-interface (not implementation) inheritance, the interface. It's now a staple of major statically-typed languages. Did Java invent the interface concept? Or did it appear in older languages also as a first-class concept?

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  • More then one emacs terminal

    - by Mad Wombat
    I am getting more and more used to doing everything from inside emacs, but it seems that eshell, shell and term will only run one instance each. Is there a way to run multiple terminals (preferably term) inside emacs?

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  • How to keep alive an HttpModule (a.k.a register it as a singleton)

    - by Micah
    I pretty sure I've seen this somewhere but I can't seem to find it anywhere. I have an HttpModule that can be used across multiple requests. In other words instead of creating a new instance of the Module on every request it only ever needs to create it once. Does this ring a bell to anyone? If so, what's the method for configuring to work this way?

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  • Sealed alternative

    - by Jeriho
    According to "Programming in scala" a sealed class cannot have any new subclasses added except the ones in the same ?le. In the same book was described a way to enumerate classes that can extend class or trait in multiple files. I have forgotten it and can't find again. Remind it to me, please.

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  • How to surpress screen savers on Linux?

    - by Die in Sente
    I need to prevent the screen saver from running while my application is running. I know how to do this on the Windows versions, with SendInput calls, but I need to do something similar for Linux ports. It looks complicated, because ideally, I'd like something that would work on multiple Linux distros (SuSe, Red Hat, Ubunutu...) and it looks like there are at least 3 different screen-saver frameworks: xscreensaver, gnome-screensaver, and something else in KDE.

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  • killing all instances of chrome on the command line?

    - by Fedor
    In some cases killing a single tab/process doesn't do it and I need to close Chrome entirely. Since Chrome has multiple processes, how can I close all of them at once? I know that... pgrep chrome returns all the pids, can someone tell me a trick that would allow me to close all of them by feeding them to another command or merging them to a csv or something?

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