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  • What are the pros and cons of using manual list iteration vs recursion through fail

    - by magus
    I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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  • Confused about "override" vs. "new" in C#

    - by iTayb
    I'm having the following classes: class Base { public virtual void Print() { Console.WriteLine("Base"); } } class Der1 : Base { public new virtual void Print() { Console.WriteLine("Der1"); } } class Der2 : Der1 { public override void Print() { Console.WriteLine("Der2"); } } This is my main method: Base b = new Der2(); Der1 d1 = new Der2(); Der2 d2 = new Der2(); b.Print(); d1.Print(); d2.Print(); The output is Base, Der2, Der2. As far as I know, Override won't let previous method to run, even if the pointer is pointing to them. So the first line should output Der2 as well. However Base came out. How is it possible? How the override didn't work there?

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  • Sql Server Replication: Snapshot vs Merge

    - by Zyphrax
    Background information Let's say I have two database servers, both SQL Server 2008. One is in my LAN (ServerLocal), the other one is on a remote hosting environment (ServerRemote). I have created a database on ServerLocal and have an exact copy of that database on ServerRemote. The database on ServerRemote is part of a web application and I would like to keep it's data up-to-date with the data in the database ServerLocal. ServerLocal is able to communicate with ServerRemote, this is one-way traffic. Communication from ServerRemote to ServerLocal isn't available. Current solution I thought it would be a nice solution to use replication. So I've made ServerLocal a publisher and subscriptions are pushed to the ServerRemote. This works fine, when a snapshot is transfered to ServerRemote the existing data will be purged and the ServerRemote database is once again an exact replica of the database on ServerLocal. The problem Records that exist on ServerRemote that don't exist on ServerLocal are removed. This doesn't matter for most of my tables but in some of my tables I'd like to keep the existing data (aspnet_users for instance), and update the records if necessary. What kind of replication fits my problem?

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  • view-port resize vs document resize in IE

    - by mkoryak
    window.resize event in IE doesnt do what i thought it does. I thought it only triggered when the physical window/view-port changed size (ie user hits maximize on the browser window for example), but it is also triggered if i change the document size, introducing scroll bars. is there any way to tell those two things apart: view port resize, and document resize without writing an elaborate hack?

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  • C++ arrays as parameters, subscript vs. pointer

    - by awshepard
    Alright, I'm guessing this is an easy question, so I'll take the knocks, but I'm not finding what I need on google or SO. I'd like to create an array in one place, and populate it inside a different function. I define a function: void someFunction(double results[]) { for (int i = 0; i<100; ++i) { for (int n = 0; n<16; ++n) //note this iteration limit { results[n] += i * n; } } } That's an approximation to what my code is doing, but regardless, shouldn't be running into any overflow or out of bounds issues or anything. I generate an array: double result[16]; for(int i = 0; i<16; i++) { result[i] = -1; } then I want to pass it to someFunction someFunction(result); When I set breakpoints and step through the code, upon entering someFunction, results is set to the same address as result, and the value there is -1.000000 as expected. However, when I start iterating through the loop, results[n] doesn't seem to resolve to *(results+n) or *(results+n*sizeof(double)), it just seems to resolve to *(results). What I end up with is that instead of populating my result array, I just get one value. What am I doing wrong?

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  • Behaviour difference Dim oDialog1 as Dialog1 = New Dialog1 VS Dim oDialog1 as Dialog1 = Dialog1

    - by user472722
    VB.Net 2005 I have a now closed Dialog1. To get information from the Dialog1 from within a module I need to use Dim oDialog1 as Dialog1 = New Dialog1. VB.Net 2008 I have a still open Dialog1. To get information from the Dialog1 from within a module I need to use Dim oDialog1 as Dialog1 = Dialog1. VB.Net 2005 does not compile using Dim oDialog1 as Dialog1 = Dialog1 and insists on NEW What is going on and why do I need the different initialisation syntax?

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  • #include - brackets vs quotes in XCode?

    - by Chris Becke
    In MSVC++ #include files are searched for differently depending on whether the file is enclosed in "" or <. The quoted form searches first in the local folder, then in /I specified locations, The angle bracket form avoids the local folder. This means, in MSVC++, its possible to have header files with the same name as runtime and SDK headers. So, for example, I need to wrap up the windows sdk windows.h file to undefine some macro's that cause trouble. With MSVS I can just add a (optional) windows.h file to my project as long as I include it using the quoted form :- // some .cpp file #include "windows.h" // will include my local windows.h file And in my windows.h, I can pull in the real one using the angle bracket form: // my windows.h #include <windows.h> // will load the real one #undef ConflictingSymbol Trying this trick with GCC in XCode didn't work. angle bracket #includes in system header files in fact are finding my header files with similar names in my local folder structure. The MSVC system means its quite safe to have a "String.h" header file in my own folder structre. On XCode this seems to be a major no no. Is there some way to control this search path behaviour in XCode to be more like MSVC's? Or do I just have to avoid naming any of my headers anything that might possibly conflict with a system header. Writing cross platform code and using lots of frameworks means the possibility of incidental conflicts seems large.

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  • HTML input text box vs CakePHP Automagic Form Elements

    - by kwokwai
    Hi all, I was manually creating a simple form with one input text box field like this: <form action="/user/add" method="post"> <input type="text" name="data[user_id]" value="1"> But when I call $this->model->save($this->data) in the Controller, nothing was saved to the Table. Only when I used this and the data in the field was written to the database successfully: $form->create(null, array('url' => '/user/add')); echo $form->input('user_id', array('label' => 'User ID', 'value' => '1'));

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  • VS 2008 linking error

    - by AvatarBlue
    I'm using Visual Studio 2008 C++ and working on a dll project. Debug compiled and linked perfectly but when I compile the release version, it shows this: VImgPtr.obj : error LNK2001: unresolved external symbol @__security_check_cookie@4 VLibraryPtr.obj : error LNK2001: unresolved external symbol "void __cdecl operator delete[](void *)" (??_V@YAXPAX@Z) D:\Source Code\VImgLib\Release-vc9u\VImgLib-vc9u.dll : fatal error LNK1120: 2 unresolved externals If I selected Multi-threaded (/MT) in "C/C++-Code Generation tab), it linked ok. The problem is only when I choose Multi-threaded DLL (/MD). I'm releasing a dll, so should be /MD right?

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  • Android vs iPhone

    - by Moshe
    I know iPhone development fairly well. From personal experience, how hard would it be for me to get into Android. I am concerned less about code than I am about distribution of my software, given the fragmentation of the Android OS on compatible devices.

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  • help with installing clamav for remote apache server vs WAMP localserver

    - by Scarface
    Hey guys, I have never installed an extension before so I am not really sure where to start. I want to do 2 things: install clamav virus scanner http://sourceforge.net/projects/php-clamav/ on my remote server which is a linux apache setup using cpanel as a gui. install clamav on my localserver on my home computer which operates on windows and has WAMP server installed for server-side activity What is the difference between the two installation methods? What is required for each installation? If anyone can point me in the right direction in any way, I would really appreciate it. Even if it is just an article or tutorial on how to get started.

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  • Android -- Object Creation/Memory Allocation vs. Performance

    - by borg17of20
    Hello all, This is probably an easy one. I have about 20 TextViews/ImageViews in my current project that I access like this: ((TextView)multiLayout.findViewById(R.id.GameBoard_Multi_Answer1_Text)).setText(""); //or ((ImageView)multiLayout.findViewById(R.id.GameBoard_Multi_Answer1_Right)).setVisibility(View.INVISIBLE); My question is this, am I better off, from a performance standpoint, just assigning these object variables? Further, am I losing some performance to the constant "search" process that goes on as a part of the findViewById(...) method? (i.e. Does findsViewById(...) use some sort of hashtable/hashmap for look-ups or does it implement an iterative search over the view hierarchy?) At present, my program never uses more than 2.5MB of RAM, so will assigning 20 or so more object variables drastically affect this? I don't think so, but I figured I'd ask. Thanks.

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  • LINQ extention SelectMany in 3.5 vs 4.0?

    - by Moberg
    Hi When I saw Darins suggestion here .. IEnumerable<Process> processes = new[] { "process1", "process2" } .SelectMany(Process.GetProcessesByName); ( http://stackoverflow.com/questions/3059667/process-getprocessesbyname/3059733#3059733 ) .. I was a bit intrigued and I tried it in VS2008 with .NET 3.5 - and it did not compiling unless I changed it to .. IEnumerable<Process> res = new string[] { "notepad", "firefox", "outlook" } .SelectMany(s => Process.GetProcessesByName(s)); Having read some Darins answers before I suspected that it was me that were the problem, and when I later got my hands on a VS2010 with.NET 4.0 - as expected - the original suggestion worked beautifully. My question is : What have happend from 3.5 to 4.0 that makes this (new syntax) possible? Is it the extentionmethods that have been extended(hmm) or new rules for lambda syntax or? I've tried to search but my google-fu was not strong enough. Please forgive if the question is a bit naive and note that I've taged it as beginner :)

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  • jQuery UI Element vs Dojo (Dijit) Form Element

    - by Muers
    Dojo seems to have a useful feature in that it can setup event handlers and default options, etc for Dijit.form elements as it is inserting it into the DOM. For example, Dojo: var slider = new dijit.form.HorizontalSlider({ name: sliderContainerId+'_slider', value: sliderValue, minimum: sliderMax, maximum: sliderMin, onChange: function(value){ // some event handling logic } }, sliderContainerId); However, the jQuery UI Slider traditionally is applied to DOM elements that already exist: $( sliderContainerId ).slider({ value:100, min: 0, max: 500, step: 50, slide: function( event, ui ) { $( "#amount" ).val( "$" + ui.value ); } }); I need to be able to 'programmatically' create new Sliders (and other form elements), but I'm not sure how that could be achieved with the way jQuery is structured? Maybe I'm missing something obvious here.... MTIA

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  • gnuplot - multiple lines with different x ranges

    - by Aly
    Hi, I am using gnuplot to try and plot several lines but each have different x ranges. I am running the following script: # gnuplot script for 'omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat' plot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:2 with lines title '1' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:3 with lines title '2' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:4 with lines title '3' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:5 with lines title '4' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:6 with lines title '5' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:7 with lines title '6' replot "omarConf2EvONLY-vs-everyone-gta-lag-lpas-omarConf1-random-tag-tpas.dat" using 1:8 with lines title '7' set terminal png size 800,600 set output "omar_vs_everyone-EVONLY.png" replot and the .dat file is just a file with columns such as: 1 0.5 0.5 0.1 2 0.6 1.3 0.8 3 0.7 0.32 4 0.7 0.35 5 1.3 4.32 6 1.67 notice that the columns have different lengths as each line has different x ranges. The problem I have is that it plots funny as shown below:

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  • Trial vs free with limited functionality

    - by Morten K
    Hi everyone, Not a programming question as such, but a bit more business oriented question about software product development. We have just released a small app, and is offering a free, fully functional trial which lasts for 15 days. I have the gut feeling however, that to reach any kind of penetration on the web, we'd need to offer a version which is free forever, but then has a few limitations in terms of functionality (still quite usable, but not full-throttle). For example, the Roboform browser plugin is somewhat similar in purpose to ours. Not functionality wise, but it's basically a little util that saves time and removes some repetitive-action pain. They offer a free version with limitations and then a pro version for around 30 USD. Roboform has gotten very much attention over the years, and I can't help to think that this is because they have a product which is obviously good, but also free, thus adoption becomes much higher than if they had only offered a 15 day trial. I am wondering if any of you have experience in a similar scenario? Or any thoughts on the two models? Again, I know it's not directly programming related, but it's still a question I feel best answered by a community of developers.

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  • Real pagination vs Next and Previous buttons

    - by Pablo
    By real pagination i mean something like this when in page 3: <<Previous 1 | 2 | {3} | 4 | 5 |...| 15 | Next>> By Next and Previous buttons i mean something like this when in page 3: <<previous Next>> Performance wise im sure the Previous and Next Buttons are better since unlike the real pagination it doesn't require over-querying the database. By over-querying the database i mean getting more information from the database than what you will need to display on the page. My theory is that the Previous and Next Buttons can drastically increase a site performance as it only requires the exact information you will need to display on a page, please correct me if im wrong on this. so, do users really have preference when it comes to this two options? is it just a Developer preference and its convenience? Which one do you prefer? why? *Note: Previous and Next Buttons are usually labeled Newer and older.

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  • Stored proc in .net dataset class vs studio management

    - by Robert
    Morning all. Got myself a simple query which returns ten rows in SQL Server Management Studio. I call the stored proc by right clicking it and feeding in the parameters. The results are returned immediately. In .NET we have set up a dataset class, added a table adapter whose select is this same procedure. I pass in the very same parameters and the execution times out after the standard 30 seconds. It continues to run immediately when called in sql server management studio. Any ideas why the execution time is seemingly infinite in the .net dataset class. The query is very simple.

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  • casting vs using the 'as' keyword in the CLR

    - by Frank V
    I'm learning about design patterns and because of that I've ended using a lot of interfaces. One of my "goals" is to program to an interface, not an implementation. What I've found is that I'm doing a lot of casting or object type conversion. What I'd like to know is if there is a difference between these two methods of conversion: public interface IMyInterface { void AMethod(); } public class MyClass : IMyInterface { public void AMethod() { //Do work } // other helper methods.... } public class Implementation { IMyInterface _MyObj; MyClass _myCls1; MyClass _myCls2; public Implementation() { _MyObj = new MyClass(); // What is the difference here: _myCls1 = (MyClass)_MyObj; _myCls2 = (_MyObj as MyClass); } } If there is a difference, is there a cost difference or how does this affect my program? Hopefully this makes sense. Sorry for the bad example; it is all I could think of... Update: What is "in general" the preferred method? (I had a question similar to this posted in the 'answers'. I moved it up here at the suggestion of Michael Haren. Also, I want to thank everyone who's provided insight and perspective on my question.

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  • MySQL Prepared Statements vs Stored Procedures Performance

    - by amardilo
    Hi there, I have an old MySQL 4.1 database with a table that has a few millions rows and an old Java application that connects to this database and returns several thousand rows from this this table on a frequent basis via a simple SQL query (i.e. SELECT * FROM people WHERE first_name = 'Bob'. I think the Java application uses client side prepared statements but was looking at switching this to the server, and in the example mentioned the value for first_name will vary depending on what the user enters). I would like to speed up performance on the select query and was wondering if I should switch to Prepared Statements or Stored Procedures. Is there a general rule of thumb of what is quicker/less resource intensive (or if a combination of both is better)

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