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• Why can't we just use a hash of passphrase as the encryption key (and IV) with symmetric encryption algorithms?

  - by TX_

  Inspired by my previous question, now I have a very interesting idea: Do you really ever need to use Rfc2898DeriveBytes or similar classes to "securely derive" the encryption key and initialization vector from the passphrase string, or will just a simple hash of that string work equally well as a key/IV, when encrypting the data with symmetric algorithm (e.g. AES, DES, etc.)? I see tons of AES encryption code snippets, where Rfc2898DeriveBytes class is used to derive the encryption key and initialization vector (IV) from the password string. It is assumed that one should use a random salt and a shitload of iterations to derive secure enough key/IV for the encryption. While deriving bytes from password string using this method is quite useful in some scenarios, I think that's not applicable when encrypting data with symmetric algorithms! Here is why: using salt makes sense when there is a possibility to build precalculated rainbow tables, and when attacker gets his hands on hash he looks up the original password as a result. But... with symmetric data encryption, I think this is not required, as the hash of password string, or the encryption key, is never stored anywhere. So, if we just get the SHA1 hash of password, and use it as the encryption key/IV, isn't that going to be equally secure? What is the purpose of using Rfc2898DeriveBytes class to generate key/IV from password string (which is a very very performance-intensive operation), when we could just use a SHA1 (or any other) hash of that password? Hash would result in random bit distribution in a key (as opposed to using string bytes directly). And attacker would have to brute-force the whole range of key (e.g. if key length is 256bit he would have to try 2^256 combinations) anyway. So either I'm wrong in a dangerous way, or all those samples of AES encryption (including many upvoted answers here at SO), etc. that use Rfc2898DeriveBytes method to generate encryption key and IV are just wrong.

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• C++: Copy contructor: Use Getters or access member vars directly?

  - by cbrulak

  Have a simple container class: public Container { public: Container() {} Container(const Container& cont) //option 1 { SetMyString(cont.GetMyString()); } //OR Container(const Container& cont) //option 2 { m_str1 = cont.m_str1; } public string GetMyString() { return m_str1;} public void SetMyString(string str) { m_str1 = str;} private: string m_str1; } So, would you recommend this method or accessing the member variables directly? In the example, all code is inline, but in our real code there is no inline code. Update (29 Sept 09): Some of these answers are well written however they seem to get missing the point of this question: this is simple contrived example to discuss using getters/setters vs variables initializer lists or private validator functions are not really part of this question. I'm wondering if either design will make the code easier to maintain and expand. Some ppl are focusing on the string in this example however it is just an example, imagine it is a different object instead. I'm not concerned about performance. we're not programming on the PDP-11

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• Best way to update/insert into a table based on a remote table.

  - by martilyo

  I have two very large enterprise tables in an Oracle 10g database. One table keeps the historical information of the other table. The problem is, I'm getting to the point where the records are just too many that my insert update is taking too long and my session is getting killed by the governor. Here's a pseudocode of my update process: sqlsel := 'SELECT col1, col2, col3, sysdate FROM table2@remote_location dpi WHERE (col1, col2, col3) IN ( SELECT col1, col2, col3 FROM table2@remote_location MINUS SELECT DISTINCT col1, col2, col3 FROM table1 mpc WHERE facility = '''||load_facility||''' )'; EXECUTE IMMEDIATE sqlsel BULK COLLECT INTO table1; I've tried the MERGE statement: MERGE INTO table1 t1 USING ( SELECT col1, col2, col3 FROM table2@remote_location ) t2 ON ( t1.col1 = t2.col1 AND t1.col2 = t2.col2 AND t1.col3 = t2.col3 ) WHEN NOT MATCHED THEN INSERT (t1.col1, t1.col2, t1.col3, t1.update_dttm ) VALUES (t2.col1, t2.col2, t2.col3, sysdate ) But there seems to be a confirmed bug on versions prior to Oracle 10.2.0.4 on the merge statement when doing a merge using a remote database. The chance of getting an enterprise upgrade is slim so is there a way to further optimize my first query or write it in another way to have it run best performance wise? Thanks.

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• UDP security and identifying incoming data.

  - by Charles

  I have been creating an application using UDP for transmitting and receiving information. The problem I am running into is security. Right now I am using the IP/socketid in determining what data belongs to whom. However, I have been reading about how people could simply spoof their IP, then just send data as a specific IP. So this seems to be the wrong way to do it (insecure). So how else am I suppose to identify what data belongs to what users? For instance you have 10 users connected, all have specific data. The server would need to match the user data to this data we received. The only way I can see to do this is to use some sort of client/server key system and encrypt the data. I am curious as to how other applications (or games, since that's what this application is) make sure their data is genuine. Also there is the fact that encryption takes much longer to process than unencrypted. Although I am not sure by how much it will affect performance. Any information would be appreciated. Thanks.

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• How much does an InnoDB table benefit from having fixed-length rows?

  - by Philip Eve

  I know that dependent on the database storage engine in use, a performance benefit can be found if all of the rows in the table can be guaranteed to be the same length (by avoiding nullable columns and not using any VARCHAR, TEXT or BLOB columns). I'm not clear on how far this applies to InnoDB, with its funny table arrangements. Let's give an example: I have the following table CREATE TABLE `PlayerGameRcd` ( `User` SMALLINT UNSIGNED NOT NULL, `Game` MEDIUMINT UNSIGNED NOT NULL, `GameResult` ENUM('Quit', 'Kicked by Vote', 'Kicked by Admin', 'Kicked by System', 'Finished 5th', 'Finished 4th', 'Finished 3rd', 'Finished 2nd', 'Finished 1st', 'Game Aborted', 'Playing', 'Hide' ) NOT NULL DEFAULT 'Playing', `Inherited` TINYINT NOT NULL, `GameCounts` TINYINT NOT NULL, `Colour` TINYINT UNSIGNED NOT NULL, `Score` SMALLINT UNSIGNED NOT NULL DEFAULT 0, `NumLongTurns` TINYINT UNSIGNED NOT NULL DEFAULT 0, `Notes` MEDIUMTEXT, `CurrentOccupant` TINYINT UNSIGNED NOT NULL DEFAULT 0, PRIMARY KEY (`Game`, `User`), UNIQUE KEY `PGR_multi_uk` (`Game`, `CurrentOccupant`, `Colour`), INDEX `Stats_ind_PGR` (`GameCounts`, `GameResult`, `Score`, `User`), INDEX `GameList_ind_PGR` (`User`, `CurrentOccupant`, `Game`, `Colour`), CONSTRAINT `Constr_PlayerGameRcd_User_fk` FOREIGN KEY `User_fk` (`User`) REFERENCES `User` (`UserID`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `Constr_PlayerGameRcd_Game_fk` FOREIGN KEY `Game_fk` (`Game`) REFERENCES `Game` (`GameID`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=INNODB CHARACTER SET utf8 COLLATE utf8_general_ci The only column that is nullable is Notes, which is MEDIUMTEXT. This table presently has 33097 rows (which I appreciate is small as yet). Of these rows, only 61 have values in Notes. How much of an improvement might I see from, say, adding a new table to store the Notes column in and performing LEFT JOINs when necessary?

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• What collection object is appropriate for fixed ordering of values?

  - by makerofthings7

  Scenario: I am tracking several performance counters and have a CounterDescription[] correlate to DataSnapshot[]... where CounterDescription[n] describes the data loaded within DataSnapshot[n]. I want to expose an easy to use API within C# that will allow for the easy and efficient expansion of the arrays. For example CounterDescription[0] = Humidity; DataSnapshot[0] = .9; CounterDescription[1] = Temp; DataSnapshot[1] = 63; My upload object is defined like this: Note how my intent is to correlate many Datasnapshots with a dattime reference, and using the offset of the data to refer to its meaning. This was determined to be the most efficient way to store the data on the back-end, and has now reflected itself into the following structure: public class myDataObject { [DataMember] public SortedDictionary<DateTime, float[]> Pages { get; set; } /// <summary> /// An array that identifies what each position in the array is supposed to be /// </summary> [DataMember] public CounterDescription[] Counters { get; set; } } I will need to expand each of these arrays (float[] and CounterDescription[] ), but whatever data already exists must stay in that relative offset. Which .NET objects support this? I think Array[] , LinkedList<t>, and List<t> Are able to keep the data fixed in the right locations. What do you think?

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• How to efficiently implement a strategy pattern with spring ?

  - by Anth0

  I have a web application developped in J2EE 1.5 with Spring framework. Application contains "dashboards" which are simple pages where a bunch of information are regrouped and where user can modify some status. Managers want me to add a logging system in database for three of theses dashboards. Each dashboard has different information but the log should be traced by date and user's login. What I'd like to do is to implement the Strategy pattern kind of like this : interface DashboardLog { void createLog(String login, Date now); } // Implementation for one dashboard class PrintDashboardLog implements DashboardLog { Integer docId; String status; void createLog(String login, Date now){ // Some code } } class DashboardsManager { DashboardLog logger; String login; Date now; void createLog(){ logger.log(login,now); } } class UpdateDocAction{ DashboardsManager dbManager; void updateSomeField(){ // Some action // Now it's time to log dbManagers.setLogger = new PrintDashboardLog(docId, status); dbManagers.createLog(); } } Is it "correct" (good practice, performance, ...) to do it this way ? Is there a better way ? Note :I did not write basic stuff like constructors and getter/setter.

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• Setting pixel values in Nvidia NPP ImageCPU objects?

  - by solvingPuzzles

  In the Nvidia Performance Primitives (NPP) image processing examples in the CUDA SDK distribution, images are typically stored on the CPU as ImageCPU objects, and images are stored on the GPU as ImageNPP objects. boxFilterNPP.cpp is an example from the CUDA SDK that uses these ImageCPU and ImageNPP objects. When using a filter (convolution) function like nppiFilter, it makes sense to define a filter as an ImageCPU object. However, I see no clear way setting the values of an ImageCPU object. npp::ImageCPU_32f_C1 hostKernel(3,3); //allocate space for 3x3 convolution kernel //want to set hostKernel to [-1 0 1; -1 0 1; -1 0 1] hostKernel[0][0] = -1; //this doesn't compile hostKernel(0,0) = -1; //this doesn't compile hostKernel.at(0,0) = -1; //this doesn't compile How can I manually put values into an ImageCPU object? Notes: I didn't actually use nppiFilter in the code snippet; I'm just mentioning nppiFilter as a motivating example for writing values into an ImageCPU object. The boxFilterNPP.cpp example doesn't involve writing directly to an ImageCPU object, because nppiFilterBox is a special case of nppiFilter that uses a built-in gaussian smoothing filter (probably something like [1 1 1; 1 1 1; 1 1 1]).

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• How to give new life into a five years old, simple but reliable PHP form?

  - by Sam

  Hi all. I have a script in php 5.2. I want to use a simple form. I found something a programmer made for me about 5 years ago. When I use it, PHP outputs an error now unless I set register_long_arrays = On, then it works fine. On the PHP website, however, it says: Warning This feature has been DEPRECATED as of PHP 5.3.0. Relying on this feature is highly discouraged. It's recommended to turn them off, for performance reasons. Instead, use the superglobal arrays, like $_GET. Should I listen to PHP's warning, or just enable the option and keep using my old form happily? If the former, then how/where do I change this simple form, so it does not rely on the deprecated setting? Your answer is much appreciated. form.htm <html><body> <form method="POST" action="form_sent.php"> ... </form> </body></html> form_sent.php <html><body> <?php $email = $HTTP_POST_VARS[email]; $mailto = "[email protected]"; $mailsubj = "A Form was Sent from Website!"; $mailhead = "From: $email\n"; reset ($HTTP_POST_VARS); $mailbody = "Values submitted from web site form:\n"; while (list($key, $val) = each ($HTTP_POST_VARS)){$mailbody .= "$key : $val\n";} if (!eregi("\n",$HTTP_POST_VARS[email])) { mail($mailto, $mailsubj, $mailbody, $mailhead); } ?> <b>Form Sent. Thank you.</b> </body></html>

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• How to control the "flow" of an ASP.NET MVC (3.0) web app that relies on Facebook membership, with Facebook C# SDK?

  - by Chad

  I want to totally remove the standard ASP.NET membership system and use Facebook only for my web app's membership. Note, this is not a Facebook canvas app question. Typically, in an ASP.NET app you have some key properties & methods to control the "flow" of an app. Notably: Request.IsAuthenticated, [Authorize] (in MVC apps), Membership.GetUser() and Roles.IsUserInRole(), among others. It looks like [FacebookAuthorize] is equivalent to [Authorize]. Also, there's some standard work I do across all controllers in my site. So I built a BaseController that overrides OnActionExecuting(FilterContext). Typically, I populate ViewData with the user's profile within this action. Would performance suffer if I made a call to fbApp.Get("me") in this action? I use the Facebook Javascript SDK to do registration, which is nice and easy. But that's all client-side, and I'm having a hard time wrapping my mind around when to use client-side facebook calls versus server-side. There will be a point when I need to grab the user's facebook uid and store it in a "profile" table along with a few other bits of data. That would probably be best handled on the return url from the registration plugin... correct? On a side note, what data is returned from fbApp.Get("me")?

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• R optimization: How can I avoid a for loop in this situation?

  - by chrisamiller

  I'm trying to do a simple genomic track intersection in R, and running into major performance problems, probably related to my use of for loops. In this situation, I have pre-defined windows at intervals of 100bp and I'm trying to calculate how much of each window is covered by the annotations in mylist. Graphically, it looks something like this: 0 100 200 300 400 500 600 windows: |-----|-----|-----|-----|-----|-----| mylist: |-| |-----------| So I wrote some code to do just that, but it's fairly slow and has become a bottleneck in my code: ##window for each 100-bp segment windows <- numeric(6) ##second track mylist = vector("list") mylist[[1]] = c(1,20) mylist[[2]] = c(120,320) ##do the intersection for(i in 1:length(mylist)){ st <- floor(mylist[[i]][1]/100)+1 sp <- floor(mylist[[i]][2]/100)+1 for(j in st:sp){ b <- max((j-1)*100, mylist[[i]][1]) e <- min(j*100, mylist[[i]][2]) windows[j] <- windows[j] + e - b + 1 } } print(windows) [1] 20 81 101 21 0 0 Naturally, this is being used on data sets that are much larger than the example I provide here. Through some profiling, I can see that the bottleneck is in the for loops, but my clumsy attempt to vectorize it using *apply functions resulted in code that runs an order of magnitude more slowly. I suppose I could write something in C, but I'd like to avoid that if possible. Can anyone suggest another approach that will speed this calculation up?

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• Better language or checking tool?

  - by rwallace

  This is primarily aimed at programmers who use unmanaged languages like C and C++ in preference to managed languages, forgoing some forms of error checking to obtain benefits like the ability to work in extremely resource constrained systems or the last increment of performance, though I would also be interested in answers from those who use managed languages. Which of the following would be of most value? A language that would optionally compile to CLR byte code or to machine code via C, and would provide things like optional array bounds checking, more support for memory management in environments where you can't use garbage collection, and faster compile times than typical C++ projects. (Think e.g. Ada or Eiffel with Python syntax.) A tool that would take existing C code and perform static analysis to look for things like potential null pointer dereferences and array overflows. (Think e.g. an open source equivalent to Coverity.) Something else I haven't thought of. Or put another way, when you're using C family languages, is the top of your wish list more expressiveness, better error checking or something else? The reason I'm asking is that I have a design and prototype parser for #1, and an outline design for #2, and I'm wondering which would be the better use of resources to work on after my current project is up and running; but I think the answers may be useful for other tools programmers also. (As usual with questions of this nature, if the answer you would give is already there, please upvote it.)

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• Obfuscator for .NET assembly (Maybe just a C++ obfuscator?)

  - by Pirate for Profit

  The software company I work for is using a ton of open source LGPL/BSD/MIT C++ code that we have written wrappers around to port "helper classes" into a .NET assembly, via C++/CLI. These libraries have wrapped old cryptic APIs into easy-to-use ones based on common sense, and will be very helpful for a lot of different tasks will be included in many future client's applications, and we might even license it to other software companies in the same field. So naturally we are tasked with looking into solutions for securing the code from prying eyes. What we're trying to do is stop the casual observer from seeing what's going on. Now I have hacked some crazy shit in EverQuest and other video games in my day so I know with enough tireless effort anything can be done. But we don't want to make it easy for whomever. To the point, besides the Visual Studio compiler's optimizations, is there's a C++ obfuscator or .NET assembly obfuscator (after it's been built o.O) or something that would scramble everything up, re-arrange data structures, string constants, etc. idk? And if such a thing exists, we'd be curious to know how that would impact performance, as some sections of code are time critical (funny saying that using a managed M$ framework).

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• Array of Arrays - writing to File problem

  - by iFloh

  Hi, and again my array of arrays ... I try to improve my app performance by buffering arrays on file for later reuse. I have an NSMutableArray that contains about 30 NSMutableArrays with NSNumber, NSDate and NSString Objects. I try to write the file using this call: bool result = [myArray writeToFile:[fileMethods getFullPath:[NSString stringWithFormat:@"iEts%@.arr", [aDate shortDateString]]] atomically:NO]; = result = FALSE. The Path method is: + (NSString *) getFullPath:(NSString *)forFileName { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:forFileName]; } and the aDate call returns a shortDateString with ddMMyy. The NSLog NSLog(@"%@", [fileMethods getFullPath:[NSString stringWithFormat:@"iEts%@.arr", [aDate shortDateString]]]); on the path generation returns: /Users/me/Library/Application Support/iPhone Simulator/User/Applications/86729620-EC1D-4C10-A799-0C638BB27933/Documents/iEts010510.arr FURTHER: It must have something to do with the Array of Arrays, since I also write 3 further simple arrays (containing NSStrings) that all succeed. The Array of Arrays gets generated using the addObject method Any ideas what could cause the trouble?

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• WCF with MANY database connections

  - by Jorge Dominguez

  I'm working in the development of an ERP type .Net WinForms application consuming a WCF service. It's to be used by many small companies (in the range of 100-200). Database is SQL Server 2008 and the service will be hosted as a Windows service. Even thought there will be a single DB Server, our customer insists in having separate databases for each company. That is because of stability/support concerns (like DB being damaged or took offline for some reason thus affecting all clients). Concerns coming from previous experiences (not necessarily with same platform). With a single database, connections to the DB would be opened at service start up and pooling used, but, I'm not sure how connections could be managed in a multiple DB scenario: Could a connection to the corresponding DB be opened and closed for each service request? would performance be acceptable? If a connection is opened and maintained for each company accessing the system, what's the practical limit of opened connections (to different databases)? It would be very interesting to hear your opinions and suggestions for this situation. Tanks

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• Tracking a fragment of a file in two places with git

  - by mabraham

  Hi, I have code such as void myfunc() { introduction(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } which I wish to duplicate into two versions, viz: void myfuncA() { introduction(); minorchangeA(); while(condition()) { complex(); loop(); interior(); code(); } cleanup(); } void myfuncB() { introduction(); minorchangeB(); while(condition()) { complex(); modifiedB(); loop(); interior(); code(); } cleanup(); extracleanupB(); } git claims to track content rather than files, so do I need to tell it that there are chunks here that are common to both myfuncA and myfuncB so that when merging with upstream changes to myfunc that those changes should propagate to both myfuncA and myfuncB? If so, how? The code could be written so that myfuncAB did the correct thing at each point by testing for condition A or B, but that could seriously hinder readability or performance.

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• Using an embedded DB (SQLite / SQL Compact) for Message Passing within an app?

  - by wk1989

  Hello, Just out of curiosity, for applications that have a fairly complicated module tree, would something like sqlite/sql compact edition work well for message passing? So if I have modules containing data such as: \SubsystemA\SubSubSysB\ModuleB\ModuleDataC, \SubSystemB\SubSubSystemC\ModuleA\ModuleDataX Using traditional message passing/routing, you have to go through intermediate modules in order to pass a message to ModuleB to request say ModuleDataC. Instead of doing that, if we we simply store "\SubsystemA\SubSubSysB\ModuleB\ModuleDataC" in a sqlite database, getting that data is as simple as a sql query and needs no routing and passing stuff around. Has anyone done this before? Even if you haven't, do you foresee any issues & performance impact? The only concern I have right now would be the passing of custom types, e.g. if ModuleDataC is a custom data structure or a pointer, I'll need some way of storing the data structure into the DB or storing the pointer into the DB. Thanks, JW EDIT One usage case I haven't thought about is when you want to send a message from ModuleA to ModuleB to get ModuleB to do something rather than just getting/setting data. Is it possible to do this using an embedded DB? I believe callback from the DB would be needed, how feasible is this?

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• Datastructure choices for highspeed and memory efficient detection of duplicate of strings

  - by Jonathan Holland

  I have a interesting problem that could be solved in a number of ways: I have a function that takes in a string. If this function has never seen this string before, it needs to perform some processing. If the function has seen the string before, it needs to skip processing. After a specified amount of time, the function should accept duplicate strings. This function may be called thousands of time per second, and the string data may be very large. This is a highly abstracted explanation of the real application, just trying to get down to the core concept for the purpose of the question. The function will need to store state in order to detect duplicates. It also will need to store an associated timestamp in order to expire duplicates. It does NOT need to store the strings, a unique hash of the string would be fine, providing there is no false positives due to collisions (Use a perfect hash?), and the hash function was performant enough. The naive implementation would be simply (in C#): Dictionary<String,DateTime> though in the interest of lowering memory footprint and potentially increasing performance I'm evaluating a custom data structures to handle this instead of a basic hashtable. So, given these constraints, what would you use? EDIT, some additional information that might change proposed implementations: 99% of the strings will not be duplicates. Almost all of the duplicates will arrive back to back, or nearly sequentially. In the real world, the function will be called from multiple worker threads, so state management will need to be synchronized.

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• C++ design question, container of instances and pointers

  - by Tom

  Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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• C++ design question, container of instances and pointers

  - by Tom

  Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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• C++ design question, container of instances and pointers

  - by Tom

  Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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• Why would one want to use the public constructors on Boolean and similar immutable classes?

  - by Robert J. Walker

  (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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• Do I need a spatial index in my database?

  - by Sanoj

  I am designing an application that needs to save geometric shapes in a database. I haven't choosen the database management system yet. In my application, all database queries will have an bounding box as input, and as output I want all shapes within that database. I know that databases with a spatial index is used for this kind of application. But in my application there will not be any queries of type "give me objects nearby x/y" or other more complex queries that are useful in a GIS application. I am planning of having a database without a spatial index and have queries looking like: SELECT * FROM shapes WHERE x < max_x AND x > min_x AND y < max_y AND y > min_y And have an index on the columns x (double) and y (double). As long I can see, I don't really need a database with an spatial index, howsoever my application is close to that kind of applications. And even if I would like to have nearby queries, then I could create a big enough bounding box around that point. Or will this lead to poor performance? Do I really need a spatial database? And when is a spatial index needed?

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• C++ Array vs vector

  - by blue_river

  when using C++ vector, time spent is 718 milliseconds, while when I use Array, time is almost 0 milliseconds. Why so much performance difference? int _tmain(int argc, _TCHAR* argv[]) { const int size = 10000; clock_t start, end; start = clock(); vector<int> v(size*size); for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { v[i*size+j] = 1; } } end = clock(); cout<< (end - start) <<" milliseconds."<<endl; // 718 milliseconds int f = 0; start = clock(); int arr[size*size]; for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { arr[i*size+j] = 1; } } end = clock(); cout<< ( end - start) <<" milliseconds."<<endl; // 0 milliseconds return 0; }

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• Getting the Item Count of a large sharepoint list in fastest way

  - by sooraj

  I am trying to get the count of the items in a sharepoint document library programatically. The scale I am working with is 30-70000 items. We have usercontrol in a smartpart to display the count . Ours is a TEAM site. This is the code to get the total count SPList VoulnterrList = web.Lists[ListTitle]; SPQuery query = new SPQuery(); query.ViewAttributes = "Scope=\"Recursive\""; string queries = "<Where><Eq><FieldRef Name='ApprovalStatus' /><Value Type='Choice'>Pending</Value></Eq></Where>"; query.Query = queries; SPListItemCollection lstitemcollAssoID = VoulnterrList.GetItems(query); lblCount.Text = "Total Proofs: " + VoulnterrList.Items.Count.ToString() + " Pending Proofs: " + lstitemcollAssoID.Count.ToString(); The problem is this has serious performance issue it takes 75 to 80 sec to load the page. if we comment this page load will decrees to 4 sec. Any better approch for this problem Ours is sharepoint 2007

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