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  • Elo rating system: start value

    - by Marco W.
    I've implemented an Elo rating system in a game. There is no limit for the number players. Players can join the game constantly so the number of players probably rises gradually. How the Elo values are exactly calculated isn't important because of this fact: If team A beats team B then A's Elo win equals B's Elo loss. Hence I've got a problem concerning the starting values for my rating system: Should I use the starting value "0" for every player? The sum of all Elo values would be constant. But since the number of players is increasing there would be some kind of Elo deflation, wouldn't it? Should I use any starting value greater than 0? In this case, the sum of all Elo values would constantly increase. So there could be an Elo inflation. The problem: Elo points lose value but the starting value keeps always the same. What should I do? Can you help me? Thanks in advance!

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  • Which cms or script for social network wiki?

    - by Jason
    Hi, I am building a social network. I need a cms that will allow users to contribute content. Each content item will need to have a google map, list of features, ratings, comments, etc. And the content must be editable by other users with revision control. Also, each user should have a profile with their bookmarked content items, contributed items, comments, etc. It's very important that I can create a template for the wiki/content entries so that each item looks uniform. (and as a kick in the teeth, I would like to be able to search for wiki items using a radial search or map) Joomla was my first choice, as I've used it for many projects, but the wiki functionality is not there. I was also setting up a grou.ps site, but the wiki is so-so - not feature rich and it really doesn't have the option I need. Additionally, I know someone out there will mention Drupal. I may consider it if I can see it put to use without and overabundance of custom programming (I don't mind initial coding, but drupal requires constant coding & recoding - with this site, I dont' have that time commitment) I thought about using mediawiki with buddypress, but i'm not sure if that's the way to go. Thoughts?

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  • Efficient database access when dealing with multiple abstracted repositories

    - by Nathan Ridley
    I want to know how most people are dealing with the repository pattern when it involves hitting the same database multiple times (sometimes transactionally) and trying to do so efficiently while maintaining database agnosticism and using multiple repositories together. Let's say we have repositories for three different entities; Widget, Thing and Whatsit. Each repository is abstracted via a base interface as per normal decoupling design processes. The base interfaces would then be IWidgetRepository, IThingRepository and IWhatsitRepository. Now we have our business layer or equivalent (whatever you want to call it). In this layer we have classes that access the various repositories. Often the methods in these classes need to do batch/combined operations where multiple repositories are involved. Sometimes one method may make use of another method internally, while that method can still be called independently. What about, in this scenario, when the operation needs to be transactional? Example: class Bob { private IWidgetRepository _widgetRepo; private IThingRepository _thingRepo; private IWhatsitRepository _whatsitRepo; public Bob(IWidgetRepository widgetRepo, IThingRepository thingRepo, IWhatsitRepository whatsitRepo) { _widgetRepo = widgetRepo; _thingRepo= thingRepo; _whatsitRepo= whatsitRepo; } public void DoStuff() { _widgetRepo.StoreSomeStuff(); _thingRepo.ReadSomeStuff(); _whatsitRepo.SaveSomething(); } public void DoOtherThing() { _widgetRepo.UpdateSomething(); DoStuff(); } } How do I keep my access to that database efficient and not have a constant stream of open-close-open-close on connections and inadvertent invocation of MSDTS and whatnot? If my database is something like SQLite, standard mechanisms like creating nested transactions are going to inherently fail, yet the business layer should not have to be concerning itself with such things. How do you handle such issues? Does ADO.Net provide simple mechanisms to handle this or do most people end up wrapping their own custom bits of code around ADO.Net to solve these types of problems?

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  • Java string to double conversion.

    - by wretrOvian
    Hi, I've been reading up on the net about the issues with handling float and double types in java. Unfortunately, the image is still not clear. Hence, i'm asking here direct. :( My MySQL table has various DECIMAL(m,d) columns. The m may range from 5 to 30. d stays a constant at 2. Question 1. What equivalent data-type should i be using in Java to work (i.e store, retrieve, and process) with the size of the values in my table? (I've settled with double - hence this post). Question 2. While trying to parse a double from a string, i'm getting errors Double dpu = new Double(dpuField.getText()); for example - "1" -> java.lang.NumberFormatException: empty String "10" -> 1.0 "101" -> 10.0 "101." -> 101.0 "101.1" -> 101.0 "101.19" -> 101.1 What am i doing wrong? What is the correct way to convert a string to a double value? And what measures should i take to perform operations on such values?

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  • Argument type deduction, references and rvalues

    - by uj2
    Consider the situation where a function template needs to forward an argument while keeping it's lvalue-ness in case it's a non-const lvalue, but is itself agnostic to what the argument actually is, as in: template <typename T> void target(T&) { cout << "non-const lvalue"; } template <typename T> void target(const T&) { cout << "const lvalue or rvalue"; } template <typename T> void forward(T& x) { target(x); } When x is an rvalue, instead of T being deduced to a constant type, it gives an error: int x = 0; const int y = 0; forward(x); // T = int forward(y); // T = const int forward(0); // Hopefully, T = const int, but actually an error forward<const int>(0); // Works, T = const int It seems that for forward to handle rvalues (without calling for explicit template arguments) there needs to be an forward(const T&) overload, even though it's body would be an exact duplicate. Is there any way to avoid this duplication?

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  • Why it's important to specify the complete class name in your association when using namespaces

    - by Carmine Paolino
    In my Rails application there is a model that has some has_one associations (this is a fabricated example): class Person::Admin < ActiveRecord::Base has_one :person_monthly_revenue has_one :dude_monthly_niceness accepts_nested_attributes_for :person_monthly_revenue, :dude_monthly_niceness end class Person::MonthlyRevenue < ActiveRecord::Base belongs_to :person_admin end class Dude::MonthlyNiceness < ActiveRecord::Base belongs_to :person_admin end The application talks to a backend that computes some data and returns a piece of JSON like this: { "dude_monthly_niceness": { "february": 1.1153232569518972, "october": 1.1250217200558268, "march": 1.3965786869658541, "august": 1.6293418014601631, "september": 1.4062771500697835, "may": 1.7166279693955291, "january": 1.0086401628086725, "june": 1.5711510228365859, "april": 1.5614525597326563, "december": 0.99894169970474289, "july": 1.7263264324994585, "november": 0.95044938418509506 }, "person_monthly_revenue": { "february": 10.585596551505297, "october": 10.574823016656749, "march": 9.9125274764852787, "august": 9.2111604702328922, "september": 9.7905249446675153, "may": 9.1329712474607962, "january": 10.479614016604238, "june": 9.3710235926961936, "april": 9.5897372624830304, "december": 10.052587677671438, "july": 8.9508877843925561, "november": 10.925339756096172 }, } To deserialize it, I use ActiveRecord's from_json, but instead of a Person::Admin object with all the associations in place, I get this error: >> Person::Admin.new.from_json(json) NameError: uninitialized constant Person::Admin::DudeMonthlyNiceness Am I doing something wrong? Is there a better way to deserialize data? (I can modify the backend easily) UPDATE: the original title was "How to deserialize from json to ActiveRecord objects with associations?" but it ended up being my mistake in specifying associations so I changed the title.

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  • Dictionaries with more than one key per value in Python

    - by nickname
    I am attempting to create a nice interface to access a data set where each value has several possible keys. For example, suppose that I have both a number and a name for each value in the data set. I want to be able to access each value using either the number OR the name. I have considered several possible implementations: Using two separate dictionaries, one for the data values organized by number, and one for the data values organized by name. Simply assigning two keys to the same value in a dictionary. Creating dictionaries mapping each name to the corresponding number, and vice versa Attempting to create a hash function that maps each name to a number, etc. (related to the above) Creating an object to encapsulate all three pieces of data, then using one key to map dictionary keys to the objects and simply searching the dictionary to map the other key to the object. None of these seem ideal. The first seems ugly and unmaintainable. The second also seems fragile. The third/fourth seem plausible, but seem to require either much manual specification or an overly complex implementation. Finally, the fifth loses constant-time performance for one of the lookups. In C/C++, I believe that I would use pointers to reference the same piece of data from different keys. I know that the problem is rather similar to a database lookup problem by a non-key column, however, I would like (if possible), to maintain the approximate O(1) performance of Python dictionaries. What is the most Pythonic way to achieve this data structure?

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  • getting another website data to manipulate it's value in perl

    - by aun ali
    use CGI qw(:standard); use CGI::Carp qw(fatalsToBrowser warningsToBrowser); our @a=param(src="http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update"); print header(),start_html('results.pl'); $a=http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update; '<iframe frameborder="0" scrolling="no" height="95" width="213" allowtransparency="true" marginwidth="0" marginheight="0" src="http://fxrates.forexpros.com/index.php?pairs_ids=1525;&header-text-color=%23FFFFFF&curr-name-color=%230059b0&inner-text-color=%23000000&green-text-color=%232A8215&green-background=%23B7F4C2&red-text-color=%23DC0001&red-background=%23FFE2E2&inner-border-color=%23CBCBCB&border-color=%23cbcbcb&bg1=%23F6F6F6&bg2=%23ffffff&bid=hide&ask=hide&last=hide&high=hide&low=hide&change=hide&change_in_percents=hide&last_update=show"></iframe><br /><div style="width:213"><span style="float:left"><span style="font-size: 11px;color: #333333;text-decoration: none;">The <a href="http://www.forexpros.com/quotes" target="_blank" style="font-size: 11px;color: #06529D; font-weight: bold;" class="underline_link">Forex Quotes</a> are Powered by Forexpros - The Leading Financial Portal.</span></span></div>'; print '<br/>'; print "$a"; print end_html();' getting error: Can't modify constant item in scalar assignment at livedata.pl line 4, near ""http://fxrates.forexpros.com/index.php?pairs_ids=1525=last_update")" syntax error at livedata.pl line 6, near "http:" Execution of livedata.pl aborted due to compilation errors.

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  • Why is passing a string literal into a char* argument only sometimes a compiler error?

    - by Brian Postow
    I'm working in a C, and C++ program. We used to be compiling without the make-strings-writable option. But that was getting a bunch of warnings, so I turned it off. Then I got a whole bunch of errors of the form "Cannot convert const char* to char* in argmuent 3 of function foo". So, I went through and made a whole lot of changes to fix those. However, today, the program CRASHED because the literal "" was getting passed into a function that was expecting a char*, and was setting the 0th character to 0. It wasn't doing anything bad, just trying to edit a constant, and crashing. My question is, why wasn't that a compiler error? In case it matters, this was on a mac compiled with gcc-4.0. EDIT: added code: char * host = FindArgDefault("EMailLinkHost", ""); stripCRLF(linkHost, '\n'); where: char *FindArgDefault(char *argName, char *defVal) {// simplified char * val = defVal; return(val); } and void stripCRLF(char *str, char delim) { char *p, *q; for (p = q = str; *p; ++p) { if (*p == 0xd || *p == 0xa) { if (p[1] == (*p ^ 7)) ++p; if (delim == -1) *p = delim; } *q++ = *p; } *q = 0; // DIES HERE } This compiled and ran until it tried to set *q to 0...

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  • Can knowing C actually hurt the code you write in higher level languages?

    - by Jurily
    The question seems settled, beaten to death even. Smart people have said smart things on the subject. To be a really good programmer, you need to know C. Or do you? I was enlightened twice this week. The first one made me realize that my assumptions don't go further than my knowledge behind them, and given the complexity of software running on my machine, that's almost non-existent. But what really drove it home was this Slashdot comment: The end result is that I notice the many naive ways in which traditional C "bare metal" programmers assume that higher level languages are implemented. They make bad "optimization" decisions in projects they influence, because they have no idea how a compiler works or how different a good runtime system may be from the naive macro-assembler model they understand. Then it hit me: C is just one more abstraction, like all others. Even the CPU itself is only an abstraction! I've just never seen it break, because I don't have the tools to measure it. I'm confused. Has my mind been mutilated beyond recovery, like Dijkstra said about BASIC? Am I living in a constant state of premature optimization? Is there hope for me, now that I realized I know nothing about anything? Is there anything to know, even? And why is it so fascinating, that everything I've written in the last five years might have been fundamentally wrong? To sum it up: is there any value in knowing more than the API docs tell me? EDIT: Made CW. Of course this also means now you must post examples of the interpreter/runtime optimizing better than we do :)

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  • How does Access 2007's moveNext/moveFirst/, etc., feature work?

    - by Chris M
    I'm not an Access expert, but am an SQL expert. I inherited an Access front-end referencing a SQL 2005 database that worked OK for about 5000 records, but is failing miserably for 800k records... Behind the scenes in the SQL profiler & activity manager I see some kind of Access query like: SELECT "MS1"."id" FROM "dbo"."customer" "MS1" ORDER BY "MS1"."id" The MS prefix doesn't appear in any Access code I can see. I'm suspicious of the built-in Access navigation code: DoCmd.GoToRecord , , acNext The GoToRecord has AcRecord constant, which includes things like acFirst, acLast, acNext, acPrevious and acGoTo. What does it mean in a database context to move to the "next" record? This particular table uses an identity column as the PK, so is it internally grabbing all the IDs and then moving to the one that is the next highest??? If so, how would it work if a table was comprised of three different fields for the PK? Or am I on the wrong track, and something else in Access is calling that statement? Unfortunately I see a ton of prepared statements in the profiler. THanks!

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  • Why do people keep parsing HTML using regex? [closed]

    - by polygenelubricants
    As much as I love regular expressions, it's obvious to me that it's not the best tool for parsing HTML, especially given the numerous good HTML parsers out there. And yet there are numerous questions on stackoverflow that attempts to parse HTML using regex. And people would always point out what a bad idea that is in the comments. And the accepted answer would often have a disclaimer how this isn't really the ideal way of doing things. But based on the constant flow of questions, it still seems that people keep parsing HTML using regex, despite the perceived difficulty in reading and maintaining it (and that's putting correctness aside for now). So my question is: why? Is it because it's easy to learn? Is it because it's faster? Is it because it's the industry standard? Is it because there are already so many reusable regexes to build from? Is it because 100% correctness is never really the objective? (90% good enough?) etc... I'd also like to hear from the downvoters why they did so. Is it because: There's absolutely nothing wrong with using regex to parse HTML and asking "Why?" is just dumb? The premise of the question is flawed because the people who are using regex to parse HTML is such a small minority?

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  • Cannot generate/run migrations on rails 2.3.4

    - by Brian Roisentul
    I used to work with rails 2.3.2 before and then I decided to upgrade to version 2.3.4. Today I tried to generate a migration(I could do this fine with version 2.3.2) and I got the following error message: C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/initializer.rb:812:in `const_missing': uninitialized constant ActiveSupport (NameError) from D:/Proyectos/Cursometro/www/config/environment.rb:33 from C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/initializer.rb:111:in `run' from D:/Proyectos/Cursometro/www/config/environment.rb:15 from D:/Proyectos/Cursometro/www/config/environment.rb:31:in `require' from C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/generate.rb:1 from C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/rails-2.3.4/lib/commands/generate.rb:31:in `require' from C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from script\generate:3 I don't know why this is happening. Everything worked fine in 2.3.2 and now it doesn't.

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  • PHP class to C# class?

    - by LordSauron
    I work for a company that makes application's in C#. recently we got a customer asking us to look in to rebuilding an application written in PHP. This application receives GPS data from car mounted boxes and processes that into workable information. The manufacturer for the GPS device has a PHP class that parses the received information and extracts coordinates. We were looking in to rewriting the PHP class to a C# class so we can use it and adapt it. And here it comes, on the manufacturers website there is a singel line of text that got my skin krawling: "The encoding format and contents of the transmitted data are subject to constant changes. This is caused by implementations of additional features by new module firmware versions which makes it virtually impossible to document it and for you to properly decode it yourself." So i am now looking for a option to use the "constantly changing" PHP class and access it in C#. Some thing link a shell only exposing some function's i need. Except i have no idea how i can do this. Can any one help me find a solution for this.

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  • C++ variable to const expression

    - by user1344784
    template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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  • How to alter Postgres table data based on its contents?

    - by williamjones
    This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google. I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row. There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these). It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database. First, a quick threshold question of, is this a good idea? Any feedback or anything I missed? Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?

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  • Move SELECT to SQL Server side

    - by noober
    Hello all, I have an SQLCLR trigger. It contains a large and messy SELECT inside, with parts like: (CASE WHEN EXISTS(SELECT * FROM INSERTED I WHERE I.ID = R.ID) THEN '1' ELSE '0' END) AS IsUpdated -- Is selected row just added? as well as JOINs etc. I like to have the result as a single table with all included. Question 1. Can I move this SELECT to SQL Server side? If yes, how to do this? Saying "move", I mean to create a stored procedure or something else that can be executed before reading dataset in while cycle. The 2 following questions make sense only if answer is "yes". Why do I want to move SELECT? First off, I don't like mixing SQL with C# code. At second, I suppose that server-side queries run faster, since the server have more chances to cache them. Question 2. Am I right? Is it some sort of optimizing? Also, the SELECT contains constant strings, but they are localizable. For instance, WHERE R.Status = "Enabled" "Enabled" should be changed for French, German etc. So, I want to write 2 static methods -- OnCreate and OnDestroy -- then mark them as stored procedures. When registering/unregistering my assembly on server side, just call them respectively. In OnCreate format the SELECT string, replacing {0}, {1}... with required values from the assembly resources. Then I can localize resources only, not every script. Question 3. Is it good idea? Is there an existing attribute to mark methods to be executed by SQL Server automatically after (un)registartion an assembly? Regards,

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  • C++ Virtual Methods for Class-Specific Attributes or External Structure

    - by acanaday
    I have a set of classes which are all derived from a common base class. I want to use these classes polymorphically. The interface defines a set of getter methods whose return values are constant across a given derived class, but vary from one derived class to another. e.g.: enum AVal { A_VAL_ONE, A_VAL_TWO, A_VAL_THREE }; enum BVal { B_VAL_ONE, B_VAL_TWO, B_VAL_THREE }; class Base { //... virtual AVal getAVal() const = 0; virtual BVal getBVal() const = 0; //... }; class One : public Base { //... AVal getAVal() const { return A_VAL_ONE }; BVal getBVal() const { return B_VAL_ONE }; //... }; class Two : public Base { //... AVal getAVal() const { return A_VAL_TWO }; BVal getBVal() const { return B_VAL_TWO }; //... }; etc. Is this a common way of doing things? If performance is an important consideration, would I be better off pulling the attributes out into an external structure, e.g.: struct Vals { AVal a_val; VBal b_val; }; storing a Vals* in each instance, and rewriting Base as follows? class Base { //... public: AVal getAVal() const { return _vals->a_val; }; BVal getBVal() const { return _vals->b_val; }; //... private: Vals* _vals; }; Is the extra dereference essentially the same as the vtable lookup? What is the established idiom for this type of situation? Are both of these solutions dumb? Any insights are greatly appreciated

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  • How do I access the names of VB6 modules from code?

    - by Mark Bertenshaw
    Hi All - It is unlikely that there is an answer for this one, but I'm asking anyway. I am currently maintaining some code, which is likely to be refactored soon. Before that happens, I want to make the standard error handling code, which is injected by an Add-In, more efficient and take up less space. One thing that annoys me is that every module has a constant called m_ksModuleName that is used to construct a big string, which is then rethrown from the error handler so we can trace the error stack. This is all template code, i.e. repetivitve, but I could easily strip it down to a procedure call. Now, I have fixed the code so that you can pass the Me reference to the procedure - but you can't do that for the BAS modules. Nor can you access the project name (the part which would be passed as part of a ProgramID, for instance) - although you get given it when you raise an error yourself. All these strings are contained in the EXE, DLL or OCX - believe me, I've used a debugger to find them. But how can I access these in code? -- Mark Bertenshaw

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  • Efficient mapping of game entity positions in Java

    - by byte
    In Java (Swing), say I've got a 2D game where I have various types of entities on the screen, such as a player, bad guys, powerups, etc. When the player moves across the screen, in order to do efficient checking of what is in the immediate vicinity of the player, I would think I'd want indexed access to the things that are near the character based on their position. For example, if player 'P' steps onto element 'E' in the following example... | | | | | | | | | |P| | | | |E| | | | | | | | | ... would be to do something like: if(player.getPosition().x == entity.getPosition().x && entity.getPosition.y == thing.getPosition().y) { //do something } And thats fine, but that implies that the entities hold their positions, and therefor if I had MANY entities on the screen I would have to loop through all possible entities available and check each ones position against the player position. This seems really inefficient especially if you start getting tons of entities. So, I would suspect I'd want some sort of map like Map<Point, Entity> map = new HashMap<Point, Entity>(); And store my point information there, so that I could access these entities in constant time. The only problem with that approach is that, if I want to move an entity to a different point on the screen, I'd have to search through the values of the HashMap for the entity I want to move (inefficient since I dont know its Point position ahead of time), and then once I've found it remove it from the HashMap, and re-insert it with the new position information. Any suggestions or advice on what sort of data structure / storage format I ought to be using here in order to have efficient access to Entities based on their position, as well as Position's based on the Entity?

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  • Time taken for memcpy decreases after certain point

    - by tss
    I ve a code which increases the size of the memory(identified by a pointer) exponentially. Instead of realloc, I use malloc followed by memcpy.. Something like this.. int size=5,newsize; int *c = malloc(size*sizeof(int)); int *temp; while(1) { newsize=2*size; //begin time temp=malloc(newsize*sizeof(int)); memcpy(temp,c,size*sizeof(int)); //end time //print time in mili seconds c=temp; size=newsize; } Thus the number of bytes getting copied is increasing exponentially. The time required for this task also increases almost linearly with the increase in size. However after certain point, the time taken abruptly reduces to a very small value and then remains constant. I recorded time for similar code, copyin data(Of my own type) 5 -> 10 - 2 ms 10 -> 20 - 2 ms . . 2560 -> 5120 - 5 ms . . 20480 -> 40960 - 30 ms 40960 -> 91920 - 58 ms 367680 -> 735360 - 2 ms 735360 -> 1470720 - 2 ms 1470720 -> 2941440 - 2 ms What is the reason for this drop in time ? Does a more optimal memcpy method get called when the size is large ?

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  • Time complexity of a powerset generating function

    - by Lirik
    I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string): public static HashSet<string> GeneratePowerSet(string input) { HashSet<string> powerSet = new HashSet<string>(); if (string.IsNullOrEmpty(input)) return powerSet; int powSetSize = (int)Math.Pow(2.0, (double)input.Length); // Start at 1 to skip the empty string case for (int i = 1; i < powSetSize; i++) { string str = Convert.ToString(i, 2); string pset = str; for (int k = str.Length; k < input.Length; k++) { pset = "0" + pset; } string set = string.Empty; for (int j = 0; j < pset.Length; j++) { if (pset[j] == '1') { set = string.Concat(set, input[j].ToString()); } } powerSet.Add(set); } return powerSet; } So my attempt is this: let the size of the input string be n in the outer for loop, must iterate 2^n times (because the set size is 2^n). in the inner for loop, we must iterate 2*n times (at worst). 1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct? And n*(2^n) is worse than n^2. if n = 4 then (4*(2^4)) = 64 (4^2) = 16 if n = 100 then (10*(2^10)) = 10240 (10^2) = 100 2. Is there a faster way to generate a power set, or is this about optimal?

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  • C++ Constructor With Parameters Won't Initialize, Errors C2059 and C2228

    - by Some Girl
    I'm a C# programmer trying to muddle through C++ to create a Windows Forms Application. I have a Windows Form that makes use of a user-created class. Basically I'm trying to use a constructor that takes parameters, but my form won't let me initialize the object with parameter. Here's the code, hopefully somebody can explain the problem to me because I'm completely baffled... Here's my header file: BankAcct.h public ref class BankAcct { private: int money; public: BankAcct(); BankAcct(int); void Deposit(int); void GetBalance(int&); }; And my definition file: BankAcct.cpp #include "StdAfx.h" #include "BankAcct.h" BankAcct::BankAcct() { money = 0; } BankAcct::BankAcct(int startAmt) { money = startAmt; } void BankAcct::Deposit(int depAmt) { money += depAmt; } void BankAcct::GetBalance(int& balance) { balance = money; } And finally my main form. Won't copy the whole thing, of course, but I'm trying to declare the new bank account object, and start it with a balance of say $50. private: BankAcct myAccount(50); //does not work! WHY?? //private: //BankAcct myAccount; //works then in the form constructor my code is this: public: frmBank(void) { InitializeComponent(); int bal; myAccount.GetBalance(bal); lblBankBalance->Text += Convert::ToString(bal); } I've included the BankAcct.h file at the top of my frmBank.h, what else am I doing wrong here? It works great if I use the default constructor (the one that starts the bank balance at zero). I get the following error messages: error C2059: syntax error: 'constant' and error C2228: left of '.GetBalance' must have class/struct/union Thank you for any and all help on this one!!

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  • Can this line of code really throw an IndexOutOfRange exception?

    - by Jonathan M
    I am getting an IndexOutOfRange exception on the following line of code: var searchLastCriteria = (SearchCriteria)Session.GetSafely(WebConstants.KeyNames.SEARCH_LAST_CRITERIA); I'll explain the above here: SearchCriteria is an Enum with only two values Session is the HttpSessionState GetSafely is an extension method that looks like this: public static object GetSafely(this HttpSessionState source, string key) { try { return source[key]; } catch (Exception exc) { log.Info(exc); return null; } } WebConstants.KeyNames.SEARCH_LAST_CRITERIA is simply a constant I've tried everything to replicate this error, but I cannot reproduce it. I am beginning to think the stack trace is wrong. I thought perhaps the exception was actually coming from the GetSafely call, but it is swallowing the exceptions, so that can't be the case, and even if it was, it should show up in the stack trace. Is there anything in the line of code above that could possible throw an IndexOutOfRange exception? I know the line will throw an NullReferenceException if GetSafely returns null, and it will also throw an InvalidCastException if it returns anything that cannot be cast to SearchCriteria, but an IndexOutOfRange exception? I'm scratching my head here. Here is the stack trace: $LOG--> 2010-06-11 07:01:33,814 [ERROR] SERVERA (14) Web.Global - Index was outside the bounds of the array. System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.IndexOutOfRangeException: Index was outside the bounds of the array. at IterateSearchResult(Boolean next) in C:\Projects\Web\UserControls\AccountHeader.ascx.cs:line 242 at nextAccountLink_Click(Object sender, EventArgs e) in C:\Projects\Web\UserControls\AccountHeader.ascx.cs:line 232

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  • How to accommodate for the different screen resolution of iPhone 4?

    - by mystify
    This is a programming question! Read on before you vote to close! According to Apple, iPhone 4 has a new screen resolution: 3.5-inch (diagonal) widescreen Multi-Touch display 960-by-640-pixel resolution at 326 ppi This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most -if not all- developers do is: They designed everything in such a way, that a touchable area is -for example- 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom. Edit: It seems Apple has integrated an switch that allows to tell if an app is highRes or not. Nice. When we develop high-resolution apps, probably they won't work on older devices. And if they did, they would suffer a lot from 4-times the size of any image, having to scale them down in memory. This is community wiki. Just add anything that you think is relevant to this huge problem (constant screen res was one of the main reasons why I didn't go for Android!!).

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