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• Writing a VM - well formed bytecode?

  - by David Titarenco

  Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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• How can I get this week's dates in Perl?

  - by ABach

  I have the following loop to calculate the dates of the current week and print them out. It works, but I am swimming in the amount of date/time possibilities in Perl and want to get your opinion on whether there is a better way. Here's the code I've written: #!/usr/bin/env perl use warnings; use strict; use DateTime; # Calculate numeric value of today and the # target day (Monday = 1, Sunday = 7); the # target, in this case, is Monday, since that's # when I want the week to start my $today_dt = DateTime->now; my $today = $today_dt->day_of_week; my $target = 1; # Create DateTime copies to act as the "bookends" # for the date range my ($start, $end) = ($today_dt->clone(), $today_dt->clone()); if ($today == $target) { # If today is the target, "start" is already set; # we simply need to set the end date $end->add( days => 6 ); } else { # Otherwise, we calculate the Monday preceeding today # and the Sunday following today my $delta = ($target - $today + 7) % 7; $start->add( days => $delta - 7 ); $end->add( days => $delta - 1 ); } # I clone the DateTime object again because, for some reason, # I'm wary of using $start directly... my $cur_date = $start->clone(); while ($cur_date <= $end) { my $date_ymd = $cur_date->ymd; print "$date_ymd\n"; $cur_date->add( days => 1 ); } As mentioned, this works, but is it the quickest or most efficient? I'm guessing that quickness and efficiency may not necessarily go together, but your feedback is very appreciated.

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• SQL Databases and table design/organization

  - by John McMullen

  (NOOB disclaimer) I'm working on a system (a type of map), that is accessed mostly via 3 fields: ID (auto incremented), X coordinate, and Y coordinate. As it is right now, i have all data on the map, stored in 1 table. Whenever the map display is loaded it simply queries the database for contents in x and y, and the DB gives the data (other fields in the same entry). If an item on the map is doing something, it has a flag saying its doing something, and then has an ID of the action in another table holding that type of 'actions'. Essentially, for all map data, its stored in 1 table. All actions of a certain type are stored in their own table. I'm a noob, and i'm wondering what the most effective/efficient structure for such a design? (a map that has items, and each item has stats/actions). I'm using PHP atm, using standard SQL queries to get my data. Should i split up the tables so that there are only x number of entries on a table? (coord range limits)? Should it just keep growing and growing? There's a lot of queries to the table... so just tryin to see what is best :/

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• Web development scheme for staging and production servers using Git Push

  - by ServAce85

  I am using git to manage a dynamic website (PHP + MySQL) and I want to send my files from my localhost to my staging and development servers in the most efficient and hassle-free way. I am currently convinced that the best way for me to approach this problem is to use this git branching model to organize my local git repo. From there, I will use the release branches to push to my staging server for testing. Once I am happy that the release code works on the staging server, I can then merge with my master branch and push that to my production server. Pushing to Staging Server: As noted in many introductory git posts, I could run into problems pushing into a non-bare repo, so, as suggested in this response, I plan to push the release branch to a bare repo on the server and have a post-receive hook that clones the bare repo to a non-bare repo that also acts as the web-hosted directory. Pushing to Production Server: Here's my newest source of confusion... In the response that I cited above, it made me curious as to why @Paul states that it's a completely different story when pushing to a live, development server. I guess I don't see the problem. Would it be safe and hassle-free to follow the same steps as above, but for the master branch? Where are the potential pit-falls? Config Files: With respect to configuration files that are unique to each environment (.htaccess, config.php, etc), it seems simplest to .gitignore each of those files in their respective repos on their respective servers. Can you see anything immediately wrong with this? Better solutions? Accessing Data: Finally, as I initially stated, the site uses MySQL databases to store data. How would you suggest I access that data (for testing purposes) from the staging server and localhost? I realize that I may have asked way too many questions for a single post, but since they're all related to the best way to set up this development scheme, I thought it was necessary.

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• Efficiently sending protocol buffer messages with http on an android platform

  - by Ben Griffiths

  I'm trying to send messages generated by Google Protocol Buffer code via a simple HTTP scheme to a server. What I have currently have implemented is here (forgive the obvious incompletion...): HttpClient client = new DefaultHttpClient(); String url = "http://192.168.1.69:8888/sdroidmarshal"; HttpPost postRequest = new HttpPost(url); String proto = offers.build().toString(); List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1); nameValuePairs.add(new BasicNameValuePair("sdroidmsg", proto)); postRequest.setEntity(new UrlEncodedFormEntity(nameValuePairs)); try { ResponseHandler<String> responseHandler = new BasicResponseHandler(); String responseBody = client.execute(postRequest, responseHandler); } catch (Throwable t) { } I'm not that experienced with communications over the internet and no more so with HTTP - while I do understand the basics... So my question, before I blindly develop the rest of the application around this, is whether or not this is particularly efficient? I ideally would like to keep messages small and I assume toString() adds some unnecessary formatting.

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• Need Help finding an appropriate task asignment algoritm for a collage project involving coordinatin

  - by Trif Mircea

  Hello. I am a long time lurker here and have found over time many answers regarding jquery and web development topics so I decided to ask a question of my own. This time I have to create a c++ project for collage which should help manage the workflow of a company providing all kinds of services through in the field teams. The ideas I have so far are: client-server application; the server is a dispatcher where all the orders from clients get and the clients are mobile devices (PDAs) each team in the field having one a order from a client is a task. Each task is made up of a series of subtasks. You have a database with estimations on how long a task should take to complete you also know what tasks or subtasks each team on the field can perform based on what kind of specialists made up the team (not going to complicate the problem by adding needed materials, it is considered that if a member of a team can perform a subtask he has the stuff needed) Now knowing these factors, what would a good task assignment algorithm be? The criteria is: how many tasks can a team do, how many tasks they have in the queue, it could also be location, how far away are they from the place but I don't think I can implement that.. It needs to be efficient and also to adapt quickly is the human dispatcher manually assigns a task. Any help or leads would be really appreciated. Also I'm not 100% sure in the idea so if you have another way you would go about creating such an application please share, even if it just a quick outline. I have to write a theoretical part too so even if the ideas are far more complex that what i outlined that would be ok ; I'd write those and implement what I can.

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• Real time embeddable http server library required

  - by Howard May

  Having looked at several available http server libraries I have not yet found what I am looking for and am sure I can't be the first to have this set of requirements. I need a library which presents an API which is 'pipelined'. Pipelining is used to describe an HTTP feature where multiple HTTP requests can be sent across a TCP link at a time without waiting for a response. I want a similar feature on the library API where my application can receive all of those request without having to send a response (I will respond but want the ability to process multiple requests at a time to reduce the impact of internal latency). So the web server library will need to support the following flow 1) HTTP Client transmits http request 1 2) HTTP Client transmits http request 2 ... 3) Web Server Library receives request 1 and passes it to My Web Server App 4) My Web Server App receives request 1 and dispatches it to My System 5) Web Server receives request 2 and passes it to My Web Server App 6) My Web Server App receives request 2 and dispatches it to My System 7) My Web Server App receives response to request 1 from My System and passes it to Web Server 8) Web Server transmits HTTP response 1 to HTTP Client 9) My Web Server App receives response to request 2 from My System and passes it to Web Server 10) Web Server transmits HTTP response 2 to HTTP Client Hopefully this illustrates my requirement. There are two key points to recognise. Responses to the Web Server Library are asynchronous and there may be several HTTP requests passed to My Web Server App with responses outstanding. Additional requirements are Embeddable into an existing 'C' application Small footprint; I don't need all the functionality available in Apache etc. Efficient; will need to support thousands of requests a second Allows asynchronous responses to requests; their is a small latency to responses and given the required request throughput a synchronous architecture is not going to work for me. Support persistent TCP connections Support use with Server-Push Comet connections Open Source / GPL support for HTTPS Portable across linux, windows; preferably more. I will be very grateful for any recommendation Best Regards

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• Recursion in prepared statements

  - by Rob

  I've been using PDO and preparing all my statements primarily for security reasons. However, I have a part of my code that does execute the same statement many times with different parameters, and I thought this would be where the prepared statements really shine. But they actually break the code... The basic logic of the code is this. function someFunction($something) { global $pdo; $array = array(); static $handle = null; if (!$handle) { $handle = $pdo->prepare("A STATEMENT WITH :a_param"); } $handle->bindValue(":a_param", $something); if ($handle->execute()) { while ($row = $handle->fetch()) { $array[] = someFunction($row['blah']); } } return $array; } It looked fine to me, but it was missing out a lot of rows. Eventually I realised that the statement handle was being changed (executed with different param), which means the call to fetch in the while loop will only ever work once, then the function calls itself again, and the result set is changed. So I am wondering what's the best way of using PDO prepared statements in a recursive way. One way could be to use fetchAll(), but it says in the manual that has a substantial overhead. The whole point of this is to make it more efficient. The other thing I could do is not reuse a static handle, and instead make a new one every time. I believe that since the query string is the same, internally the MySQL driver will be using a prepared statement anyway, so there is just the small overhead of creating a new handle on each recursive call. Personally I think that defeats the point. Or is there some way of rewriting this?

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• Is there any benefit to my rather quirky character sizing convention?

  - by Paul Alan Taylor

  I love things that are a power of 2. I celebrated my 32nd birthday knowing it was the last time in 32 years I'd be able to claim that my age was a power of 2. I'm obsessed. It's like being some Z-list Batman villain, except without the colourful adventures and a face full of batarangs. I ensure that all my enum values are powers of 2, if only for future bitwise operations, and I'm reasonably assured that there is some purpose (even if latent) for doing it. Where I'm less sure, is in how I define the lengths of database fields. Again, I can't help it. Everything ends up being a power of 2. CREATE TABLE Person ( PersonID int IDENTITY PRIMARY KEY ,Firstname varchar(64) ,Surname varchar(128) ) Can any SQL super-boffins who know about the internals of how stuff is stored and retrieved tell me whether there is any benefit to my inexplicable obsession? Is it more efficient to size character fields this way? Can anyone pop in with an "actually, what you're doing works because ....."? I suspect I'm just getting crazier in my older age, but it'd be nice to know that there is some method to my madness.

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• SQL Server 2008 - Keyword search using table Join

  - by Aaron Wagner

  Ok, I created a Stored Procedure that, among other things, is searching 5 columns for a particular keyword. To accomplish this, I have the keywords parameter being split out by a function and returned as a table. Then I do a Left Join on that table, using a LIKE constraint. So, I had this working beautifully, and then all of the sudden it stops working. Now it is returning every row, instead of just the rows it needs. The other caveat, is that if the keyword parameter is empty, it should ignore it. Given what's below, is there A) a glaring mistake, or B) a more efficient way to approach this? Here is what I have currently: ALTER PROCEDURE [dbo].[usp_getOppsPaged] @startRowIndex int, @maximumRows int, @city varchar(100) = NULL, @state char(2) = NULL, @zip varchar(10) = NULL, @classification varchar(15) = NULL, @startDateMin date = NULL, @startDateMax date = NULL, @endDateMin date = NULL, @endDateMax date = NULL, @keywords varchar(400) = NULL AS BEGIN SET NOCOUNT ON; ;WITH Results_CTE AS ( SELECT opportunities.*, organizations.*, departments.dept_name, departments.dept_address, departments.dept_building_name, departments.dept_suite_num, departments.dept_city, departments.dept_state, departments.dept_zip, departments.dept_international_address, departments.dept_phone, departments.dept_website, departments.dept_gen_list, ROW_NUMBER() OVER (ORDER BY opp_id) AS RowNum FROM opportunities JOIN departments ON opportunities.dept_id = departments.dept_id JOIN organizations ON departments.org_id=organizations.org_id LEFT JOIN Split(',',@keywords) AS kw ON (title LIKE '%'+kw.s+'%' OR [description] LIKE '%'+kw.s+'%' OR tasks LIKE '%'+kw.s+'%' OR requirements LIKE '%'+kw.s+'%' OR comments LIKE '%'+kw.s+'%') WHERE ( (@city IS NOT NULL AND (city LIKE '%'+@city+'%' OR dept_city LIKE '%'+@city+'%' OR org_city LIKE '%'+@city+'%')) OR (@state IS NOT NULL AND ([state] = @state OR dept_state = @state OR org_state = @state)) OR (@zip IS NOT NULL AND (zip = @zip OR dept_zip = @zip OR org_zip = @zip)) OR (@classification IS NOT NULL AND (classification LIKE '%'+@classification+'%')) OR ((@startDateMin IS NOT NULL AND @startDateMax IS NOT NULL) AND ([start_date] BETWEEN @startDateMin AND @startDateMax)) OR ((@endDateMin IS NOT NULL AND @endDateMax IS NOT NULL) AND ([end_date] BETWEEN @endDateMin AND @endDateMax)) OR ( (@city IS NULL AND @state IS NULL AND @zip IS NULL AND @classification IS NULL AND @startDateMin IS NULL AND @startDateMax IS NULL AND @endDateMin IS NULL AND @endDateMin IS NULL) ) ) ) SELECT * FROM Results_CTE WHERE RowNum >= @startRowIndex AND RowNum < @startRowIndex + @maximumRows; END

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• one table is shared between several websites

  - by sami

  I have a static table that's shared by several websites. By static, I mean that the data is read but never updated by the websites. Currently, all websites are served from the same server but that may change. I want to minimize the need for creating/maintaining this table for each of the websites, so I thought about turning it to an xml file that's stored in a shared library that all websites have access to. The problem is I use an ORM and use forign key constraints to ensure integrity of the ids used from that table, so by removing that table out of the MySQL database into an XML file, will this affect the integrity of the ids coming from that table? My table looks like this <table name="entry"> <column name="id" type="INTEGER" primaryKey="true" autoIncrement="true" /> <column name="title" type="VARCHAR" size="500" required="true" /> </table> and I use it as a foreign key in other tables <table name="refer"> <column name="id" type="INTEGER" primaryKey="true" autoIncrement="true" /> <column name="linkto" type="INTEGER"/> <foreign-key foreignTable="entry"> <reference local="linkto" foreign="id" /> </foreign-key> </table> So I'm wondering if I remove that table out of the database, is there a way to retain that referential integrity? And of course are these any other efficient ways to do the same thing? I just don't want to have to repeat that table for several websites.

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• how to synchronize database table and directory with php

  - by twmulloy

  hello, I have a directory with files and a database table with what should be the same files. I would like to be able to synchronize the database table with the directory. What would be the most efficient way to do this? or would I realistically only be able to do this in a brute manner? Here's my approach: 1. retrieve all of the files in the directory as array 2. retrieve all of the filenames in the database table as array 3. loop through the file values in the directory array and use in_array() on the database table array to verify the filename is in that array, and if not then start building an array to insert the missing filenames. run db query to add each missing file row to database table 4. loop through directory array and use in_array() on the directory array and anything not found in the directory array will just be deleted from the table. Is there a better way to go about this? or something better for this in php than in_array()?

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• design an extendable database model

  - by wishi_

  Hi! Currently I'm doing a project whose specifications are unclear - well who doesn't. I wonder what's the best development strategy to design a DB, that's going to be extended sooner or later with additional tables and relations. I want to include "changeability". My main concern is that I want to apply design patterns (it's a university project) and I want to separate the constant factors from those, that change by choosing appropriate design patterns - in my case MVC and a set of sub-patterns at model level. When it comes to the DB however, I may have to resdesign my model in my MVC approach, because my domain model at a later stage my require a different set of classes representing the DB tables. I use Hibernate as an abstraction layer between DB and application. Would you start with a very minimal DB, just a few tables and relations? And what if I want an efficient DB, too? I wonder what strategies are applied in the real world. Stakeholder analysis for example isn't a sufficient planing solution when it comes to changing requirements. I think - at a DB level - my design pattern ends. So there's breach whose impact I'd like to minimize with a smart strategy.

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• Determining polygon intersection and containment

  - by Victor Liu

  I have a set of simple (no holes, no self-intersections) polygons, and I need to check that they don't intersect each other (one can be entirely contained in another; that is okay). I can check this by simply checking the per-vertex inside-ness of one polygon versus other polygons. I also need to determine the containment tree, which is the set of relationships that say which polygon contains any given polygon. Since no polygon can intersect any other, then any contained polygon has a unique container; the "next-bigger" one. In other words, if A contains B contains C, then A is the parent of B, and B is the parent of C, and we don't consider A the parent of C. The question: How do I efficiently determine the containment relationships and check the non-intersection criterion? I ask this as one question because maybe a combined algorithm is more efficient than solving each problem separately. The algorithm should take as input a list of polygons, given by a list of their vertices. It should produce a boolean B indicating if none of the polygons intersect any other polygon, and also if B = true, a list of pairs (P, C) where polygon P is the parent of child C. This is not homework. This is for a hobby project I am working on.

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• help me reason about F# threads

  - by Kevin Cantu

  In goofing around with some F# (via MonoDevelop), I have written a routine which lists files in a directory with one thread: let rec loop (path:string) = Array.append ( path |> Directory.GetFiles ) ( path |> Directory.GetDirectories |> Array.map loop |> Array.concat ) And then an asynchronous version of it: let rec loopPar (path:string) = Array.append ( path |> Directory.GetFiles ) ( let paths = path |> Directory.GetDirectories if paths <> [||] then [| for p in paths -> async { return (loopPar p) } |] |> Async.Parallel |> Async.RunSynchronously |> Array.concat else [||] ) On small directories, the asynchronous version works fine. On bigger directories (e.g. many thousands of directories and files), the asynchronous version seems to hang. What am I missing? I know that creating thousands of threads is never going to be the most efficient solution -- I only have 8 CPUs -- but I am baffled that for larger directories the asynchronous function just doesn't respond (even after a half hour). It doesn't visibly fail, though, which baffles me. Is there a thread pool which is exhausted? How do these threads actually work?

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• Two radically different queries against 4 mil records execute in the same time - one uses brute force.

  - by IanC

  I'm using SQL Server 2008. I have a table with over 3 million records, which is related to another table with a million records. I have spent a few days experimenting with different ways of querying these tables. I have it down to two radically different queries, both of which take 6s to execute on my laptop. The first query uses a brute force method of evaluating possibly likely matches, and removes incorrect matches via aggregate summation calculations. The second gets all possibly likely matches, then removes incorrect matches via an EXCEPT query that uses two dedicated indexes to find the low and high mismatches. Logically, one would expect the brute force to be slow and the indexes one to be fast. Not so. And I have experimented heavily with indexes until I got the best speed. Further, the brute force query doesn't require as many indexes, which means that technically it would yield better overall system performance. Below are the two execution plans. If you can't see them, please let me know and I'll re-post then in landscape orientation / mail them to you. Brute-force query: Index-based exception query: My question is, based on the execution plans, which one look more efficient? I realize that thing may change as my data grows.

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• Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

  - by mihi

  Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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• IPad SQLite Push and Pull Data from external MS SQL Server DB

  - by MattyD

  This carries on from my previous post (http://stackoverflow.com/questions/4182664/ipad-app-pull-and-push-relational-data). My plan is that when the ipad application starts I am going to pull data (config data i.e. Departments, Types etc etc relational data that is used across the system) from a webhosted MS SQL Server DB via a webservice and populate it into an SQL Lite DB on the IPad. Then when I load a listing I will pull the data over the line again via a webservice and populate it into the SQL Lite db on the ipad (than just run select commands to populate the listing). My questions are: 1. What is the most efficient way to transfer data across the line via the web? Everyone seems to do it a different way. My idea is that I will have a webService for each type of data pull (e.g. RetrieveContactListing) that will query the db and than convert that data into "something" to send across the line. My question really is what is the "something" that it should be converting into? 2. Everyone talks about odata services. Is this suited for applications where complex read and writes are needed? Ive created a simple iphone app before that talked to an sql server db (i just sent my own structured xml across the line) but now with this app the data calls are going to be a lot larger so efficiency is key.

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• C++ - passing references to boost::shared_ptr

  - by abigagli

  If I have a function that needs to work with a shared_ptr, wouldn't it be more efficient to pass it a reference to it (so to avoid copying the shared_ptr object)? What are the possible bad side effects? I envision two possible cases: 1) inside the function a copy is made of the argument, like in ClassA::take_copy_of_sp(boost::shared_ptr<foo> &sp) { ... m_sp_member=sp; //This will copy the object, incrementing refcount ... } 2) inside the function the argument is only used, like in Class::only_work_with_sp(boost::shared_ptr<foo> &sp) //Again, no copy here { ... sp->do_something(); ... } I can't see in both cases a good reason to pass the boost::shared_ptr by value instead of by reference. Passing by value would only "temporarily" increment the reference count due to the copying, and then decrement it when exiting the function scope. Am I overlooking something? Andrea. EDIT: Just to clarify, after reading several answers : I perfectly agree on the premature-optimization concerns, and I alwasy try to first-profile-then-work-on-the-hotspots. My question was more from a purely technical code-point-of-view, if you know what I mean.

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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• C#. How to pass message from unsafe callback to managed code?

  - by maxima120

  Is there a simple example of how to pass messages from unsafe callback to managed code? I have a proprietary dll which receives some messages packed in structs and all is coming to a callback function. The example of usage is as follows but it calls unsafe code too. I want to pass the messages into my application which is all managed code. *P.S. I have no experience in interop or unsafe code. I used to develop in C++ 8 yrs ago but remember very little from that nightmarish times :) P.P.S. The application is loaded as hell, the original devs claim it processes 2mil messages per sec.. I need a most efficient solution.* static unsafe int OnCoreCallback(IntPtr pSys, IntPtr pMsg) { // Alias structure pointers to the pointers passed in. CoreSystem* pCoreSys = (CoreSystem*)pSys; CoreMessage* pCoreMsg = (CoreMessage*)pMsg; // message handler function. if (pCoreMsg->MessageType == Core.MSG_STATUS) OnCoreStatus(pCoreSys, pCoreMsg); // Continue running return (int)Core.CALLBACKRETURN_CONTINUE; } Thank you.

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• How do I detect proximity of the mouse pointer to a line in Flex?

  - by Hanno Fietz

  I'm working on a charting UI in Flex. One of the features I want to implement is "snapping" of the mousepointer to the data points in the diagram. I. e., if the user hovers the mouse pointer over a line diagram and gets close to the data point, I want the pointer to move to the exact coordinates and show a marker, like this: Currently, the lines are drawn on a Shape, using the Graphics API. The Shape is a child DisplayObject of a custom UIComponent subclass with the exact same dimensions. This means, I already get mouseOver events on the parent of the diagram's canvas. Now I need a way to detect if the pointer is close to one of the data points. I. e. I need an answer to the question "Which data points lie within a radius of x pixels from my current position and which of them is closest?" upon each move of the mouse. I can think of the following possibilities: draw the lines not as simple lines in the graphics API, but as more advanced objects that can have their own mouseOver events. However, I want the snapping to trigger before the mouse is actually over the line. check the original data for possible candidates upon each mouse movement. Using binary search, I might be able to reduce the number of items I have to compare sufficently. prepare some kind of new data structure from the raw data that makes the above search more efficient. I don't know how that would look like. I'm guessing this is a pretty standard problem for a number of applications, but probably the actual code usually is inside of some framework. Is there anything I can read about this topic?

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• Deserialize xml which uses attribute name/value pairs

  - by Bodyloss

  My application receives a constant stream of xml files which are more or less a direct copy of the database record <record type="update"> <field name="id">987654321</field> <field name="user_id">4321</field> <field name="updated">2011-11-24 13:43:23</field> </record> And I need to deserialize this into a class which provides nullable property's for all columns class Record { public long? Id { get; set; } public long? UserId { get; set; } public DateTime? Updated { get; set; } } I just cant seem to work out a method of doing this without having to parse the xml file manually and switch on the field's name attribute to store the values. Is their a way this can be achieved quickly using an XmlSerializer? And if not is their a more efficient way of parsing it manually? Regards and thanks My main problem is that the attribute name needs to have its value set to a property name and its value as the contents of a <field>..</field> element

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• Is There a Better Way to Feed Different Parameters into Functions with If-Statements?

  - by FlowofSoul

  I've been teaching myself Python for a little while now, and I've never programmed before. I just wrote a basic backup program that writes out the progress of each individual file while it is copying. I wrote a function that determines buffer size so that smaller files are copied with a smaller buffer, and bigger files are copied with a bigger buffer. The way I have the code set up now doesn't seem very efficient, as there is an if loop that then leads to another if loops, creating four options, and they all just call the same function with different parameters. import os import sys def smartcopy(filestocopy, dest_path, show_progress = False): """Determines what buffer size to use with copy() Setting show_progress to True calls back display_progress()""" #filestocopy is a list of dictionaries for the files needed to be copied #dictionaries are used as the fullpath, st_mtime, and size are needed if len(filestocopy.keys()) == 0: return None #Determines average file size for which buffer to use average_size = 0 for key in filestocopy.keys(): average_size += int(filestocopy[key]['size']) average_size = average_size/len(filestocopy.keys()) #Smaller buffer for smaller files if average_size < 1024*10000: #Buffer sizes determined by informal tests on my laptop if show_progress: for key in filestocopy.keys(): #dest_path+key is the destination path, as the key is the relative path #and the dest_path is the top level folder copy(filestocopy[key]['fullpath'], dest_path+key, callback = lambda pos, total: display_progress(pos, total, key)) else: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, callback = None) #Bigger buffer for bigger files else: if show_progress: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, 1024*2600, callback = lambda pos, total: display_progress(pos, total, key)) else: for key in filestocopy.keys(): copy(filestocopy[key]['fullpath'], dest_path+key, 1024*2600) def display_progress(pos, total, filename): percent = round(float(pos)/float(total)*100,2) if percent <= 100: sys.stdout.write(filename + ' - ' + str(percent)+'% \r') else: percent = 100 sys.stdout.write(filename + ' - Completed \n') Is there a better way to accomplish what I'm doing? Sorry if the code is commented poorly or hard to follow. I didn't want to ask someone to read through all 120 lines of my poorly written code, so I just isolated the two functions. Thanks for any help.

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• How do people handle foreign keys on clients when synchronizing to master db

  - by excsm

  Hi, I'm writing an application with offline support. i.e. browser/mobile clients sync commands to the master db every so often. I'm using uuid's on both client and server-side. When synching up to the server, the servre will return a map of local uuids (luid) to server uuids (suid). Upon receiving this map, clients updated their records suid attributes with the appropriate values. However, say a client record, e.g. a todo, has an attribute 'list_id' which holds the foreign key to the todos' list record. I use luids in foreign_keys on clients. However, when that attribute is sent over to the server, it would dirty the server db with luids rather than the suid the server is using. My current solution, is for the master server to keep a record of the mappings of luids to suids (per client id) and for each foreign key in a command, look up the suid for that particular client and use the suid instead. I'm wondering wether others have come across thus problem and if so how they have solved it? Is there a more efficient, simpler way? I took a look at this question "Synchronizing one or more databases with a master database - Foreign keys (5)" and someone seemed to suggest my current solution as one option, composite keys using suids and autoincrementing sequences and another option using -ve ids for client ids and then updating all negative ids with the suids. Both of these other options seem like a lot more work. Thanks, Saimon

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