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• How to switch users in a smooth way in a Point-Of-Sale system?

  - by Sanoj

  I am designing a Point-Of-Sale system for a small shop. The shop just have one Point-Of-Sale but often they are one to three users (sellers) in the shop. Each user have their own user account in the system so they login and logout very often. How should I design the login/logout system in a good way? For the moment the users don't use passwords, because it takes so long time to type the password each time they login. The Platform is Windows Vista but I would like to support Windows 7 too. We use Active Directory on the Network. The system is developed in Java/Swing for the moment, but I'm thinking about to change to C#.NET/WPF. I am thinking about an SmartCard solution, but I don't know if that fits my situation. It would be more secure (which I like) but I don't know if it will be easy to implement and smooth to use, i.e. can I have the POS-system running in the background or started very quickly when the users switch? Are SmartCard solutions very expensive? (My customers are small shops) Is it preferred to use .NET or Java in a SmartCard solution? What other solutions do I have other than passwords/no passwords/smartcards? How should I design the login/logout system in a good way? Is there any good solution using SmartCards for this purpose? I would like suggested solutions both for C#.NET/WPF and Java/Swing platforms. I would like suggested solutions both for Active Directory solutions and solutions that only use one user profile in Windows. How is this problem solved in similar products? I have only seen password-solutions, but they are clumsy.

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• Finding distance to the closest point in a point cloud on an uniform grid

  - by erik

  I have a 3D grid of size AxBxC with equal distance, d, between the points in the grid. Given a number of points, what is the best way of finding the distance to the closest point for each grid point (Every grid point should contain the distance to the closest point in the point cloud) given the assumptions below? Assume that A, B and C are quite big in relation to d, giving a grid of maybe 500x500x500 and that there will be around 1 million points. Also assume that if the distance to the nearest point exceds a distance of D, we do not care about the nearest point distance, and it can safely be set to some large number (D is maybe 2 to 10 times d) Since there will be a great number of grid points and points to search from, a simple exhaustive: for each grid point: for each point: if distance between points < minDistance: minDistance = distance between points is not a good alternative. I was thinking of doing something along the lines of: create a container of size A*B*C where each element holds a container of points for each point: define indexX = round((point position x - grid min position x)/d) // same for y and z add the point to the correct index of the container for each grid point: search the container of that grid point and find the closest point if no points in container and D > 0.5d: search the 26 container indices nearest to the grid point for a closest point .. continue with next layer until a point is found or the distance to that layer is greater than D Basically: put the points in buckets and do a radial search outwards until a points is found for each grid point. Is this a good way of solving the problem, or are there better/faster ways? A solution which is good for parallelisation is preferred.

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• refactor LINQ TO SQL custom properties that instantiate datacontext

  - by Thiago Silva

  I am working on an existing ASP.NET MVC app that started small and has grown with time to require a good re-architecture and refactoring. One thing that I am struggling with is that we've got partial classes of the L2S entities so we could add some extra properties, but these props create a new data context and query the DB for a subset of data. This would be the equivalent to doing the following in SQL, which is not a very good way to write this query as oppsed to joins: SELECT tbl1.stuff, (SELECT nestedValue FROM tbl2 WHERE tbl2.Foo = tbl1.Bar), tbl1.moreStuff FROM tbl1 so in short here's what we've got in some of our partial entity classes: public partial class Ticket { public StatusUpdate LastStatusUpdate { get { //this static method call returns a new DataContext but needs to be refactored var ctx = OurDataContext.GetContext(); var su = Compiled_Query_GetLastUpdate(ctx, this.TicketId); return su; } } } We've got some functions that create a compiled query, but the issue is that we also have some DataLoadOptions defined in the DataContext, and because we instantiate a new datacontext for getting these nested property, we get an exception "Compiled Queries across DataContexts with different LoadOptions not supported" . The first DataContext is coming from a DataContextFactory that we implemented with the refactorings, but this second one is just hanging off the entity property getter. We're implementing the Repository pattern in the refactoring process, so we must stop doing stuff like the above. Does anyone know of a good way to address this issue?

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• How to localize an app on Google App Engine?

  - by Petri Pennanen

  What options are there for localizing an app on Google App Engine? How do you do it using Webapp, Django, web2py or [insert framework here]. 1. Readable URLs and entity key names Readable URLs are good for usability and search engine optimization (Stack Overflow is a good example on how to do it). On Google App Engine, key based queries are recommended for performance reasons. It follows that it is good practice to use the entity key name in the URL, so that the entity can be fetched from the datastore as quickly as possible. Currently I use the function below to create key names: import re import unicodedata def urlify(unicode_string): """Translates latin1 unicode strings to url friendly ASCII. Converts accented latin1 characters to their non-accented ASCII counterparts, converts to lowercase, converts spaces to hyphens and removes all characters that are not alphanumeric ASCII. Arguments unicode_string: Unicode encoded string. Returns String consisting of alphanumeric (ASCII) characters and hyphens. """ str = unicodedata.normalize('NFKD', unicode_string).encode('ASCII', 'ignore') str = re.sub('[^\w\s-]', '', str).strip().lower() return re.sub('[-\s]+', '-', str) This works fine for English and Swedish, however it will fail for non-western scripts and remove letters from some western ones (like Norwegian and Danish with their œ and ø). Can anyone suggest a method that works with more languages? 2. Translating templates Does Django internationalization and localization work on Google App Engine? Are there any extra steps that must be performed? Is it possible to use Django i18n and l10n for Django templates while using Webapp? The Jinja2 template language provides integration with Babel. How well does this work, in your experience? What options are avilable for your chosen template language? 3. Translated datastore content When serving content from (or storing it to) the datastore: Is there a better way than getting the *accept_language* parameter from the HTTP request and matching this with a language property that you have set with each entity?

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• In a digital photo, how can I detect if a mountain is obscured by clouds?

  - by Gavin Brock

  The problem I have a collection of digital photos of a mountain in Japan. However the mountain is often obscured by clouds or fog. What techniques can I use to detect that the mountain is visible in the image? I am currently using Perl with the Imager module, but open to alternatives. All the images are taken from the exact same position - these are some samples. My naïve solution I started by taking several horizontal pixel samples of the mountain cone and comparing the brightness values to other samples from the sky. This worked well for differentiating good image 1 and bad image 2. However in the autumn it snowed and the mountain became brighter than the sky, like image 3, and my simple brightness test started to fail. Image 4 is an example of an edge case. I would classify this as a good image since some of the mountain is clearly visible. UPDATE 1 Thank you for the suggestions - I am happy you all vastly over-estimated my competence. Based on the answers, I have started trying the ImageMagick edge-detect transform, which gives me a much simpler image to analyze. convert sample.jpg -edge 1 edge.jpg I assume I should use some kind of masking to get rid of the trees and most of the clouds. Once I have the masked image, what is the best way to compare the similarity to a 'good' image? I guess the "compare" command suited for this job? How do I get a numeric 'similarity' value from this?

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• Opengl-es draw an .obj file, but how?

  - by lacas

  I d like to parse an .obj file. My parser is working good, but my displaying is not good. Obj file is here my code is: public ObjModelParser parse() { long startTime = System.currentTimeMillis(); InputStream fileIn = resources.openRawResource(resourceID); BufferedReader buffer = new BufferedReader(new InputStreamReader(fileIn)); String line=""; Log.e("model loader", "Start parsing object " + resourceID); try { while ((line = buffer.readLine()) != null) { StringTokenizer parts = new StringTokenizer(line, " "); int numTokens = parts.countTokens(); if (numTokens == 0) continue; String part = parts.nextToken(); if (part.equals(VERTEX)) { Log.e("v ", line); vertices.add(Float.parseFloat(parts.nextToken())); vertices.add(Float.parseFloat(parts.nextToken())); vertices.add(Float.parseFloat(parts.nextToken())); .... and my displaying code is: draw that model with TRIANGLE_STRIP and gl.glDrawArrays(rendermode, 0, coords.length/dimension); What is the mistake here? edited: file here to show what is my good coords from my program for a cube, and what is from .obj file, that never show Thanks, Leslie

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• What type of webapp is the sweet spot for Scala's Lift framework?

  - by ajay

  What kind of applications are the sweet spot for Scala's lift web framework. My requirements: Ease of development and maintainability Ready for production purposes. i.e. good active online community, regular patches and updates for security and performance fixes etc. Framework should survive a few years. I don't want to write a app in a framework for which no updates/patches are available after 1 year. Has good UI templating engines Interoperation with Java (Scala satisfies this arleady. Just mentioning here for completeness sake) Good component oriented development. Time required to develop should be proportion to the complexity of web application. Should not be totally configuration based. I hate it when code gets automatically generated for me and does all sorts of magic under the hood. That is a debugging nightmare. Amount of Lift knowledge required to develop a webapp should be proportional to the complexity of the web application. i.e I should't have to spend 10+ hours learning Lift just to develop a simple TODO application. (I have knowledge of Databases, Scala) Does Lift satisfy these requirements?

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• Better ways to implement a modulo operation (algorithm question)

  - by ryxxui

  I've been trying to implement a modular exponentiator recently. I'm writing the code in VHDL, but I'm looking for advice of a more algorithmic nature. The main component of the modular exponentiator is a modular multiplier which I also have to implement myself. I haven't had any problems with the multiplication algorithm- it's just adding and shifting and I've done a good job of figuring out what all of my variables mean so that I can multiply in a pretty reasonable amount of time. The problem that I'm having is with implementing the modulus operation in the multiplier. I know that performing repeated subtractions will work, but it will also be slow. I found out that I could shift the modulus to effectively subtract large multiples of the modulus but I think there might still be better ways to do this. The algorithm that I'm using works something like this (weird pseudocode follows): result,modulus : integer (n bits) (previously defined) shiftcount : integer (initialized to zero) while( (modulus<result) and (modulus(n-1) != 1) ){ modulus = modulus << 1 shiftcount++ } for(i=shiftcount;i>=0;i++){ if(modulus<result){result = result-modulus} if(i!=0){modulus = modulus << 1} } So...is this a good algorithm, or at least a good place to start? Wikipedia doesn't really discuss algorithms for implementing the modulo operation, and whenever I try to search elsewhere I find really interesting but incredibly complicated (and often unrelated) research papers and publications. If there's an obvious way to implement this that I'm not seeing, I'd really appreciate some feedback.

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• Load Ruby on Rails models without loading the entire framework

  - by epochwolf

  I'm looking to create a custom daemon that will run various database tasks such as delaying mailings and user notifications (each notice is a separate row in the notifications table). I don't want to use script/runner or rake to do these tasks because it is possible that some of the tasks only require the create of one or two database rows or thousands of rows depending on the task. I don't want the overhead of launching a ruby process or loading the entire rails framework for each operation. I plan to keep this daemon in memory full time. To create this daemon I would like to use my models from my ruby on rails application. I have a number of rails plugins such as acts_as_tree and AASM that I will need loaded if I where to use the models. Some of the plugins I need to load are custom hacks on ActiveRecord::Base that I've created. (I am willing to accept removing or recoding some of the plugins if they need components from other parts of rails.) My questions are Is this a good idea? And - Is this possible to do in a way that doesn't have me manually including each file in my models and plugins? If not a good idea What is a good alternative? (I am not apposed to doing writing my own SQL queries but I would have to add database constraints and a separate user for the daemon to prevent any stupid accidents. Given my lack of familiarity with configuring a database, I would like to use active record as a crutch.)

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• Considerations when architecting an extensible application using MEF

  - by Dan Bryant

  I've begun experimenting with dependency injection (in particular, MEF) for one of my projects, which has a number of different extensibility points. I'm starting to get a feel for what I can do with MEF, but I'd like to hear from others who have more experience with the technology. A few specific cases: My main use case at the moment is exposing various singleton-like services that my extensions make use of. My Framework assembly exposes service interfaces and my Engine assembly contains concrete implementations. This works well, but I may not want to allow all of my extensions to have access to all of my services. Is there a good way within MEF to limit which particular imports I allow a newly instantiated extension to resolve? This particular application has extension objects that I repeatedly instantiate. I can import multiple types of Controllers and Machines, which are instantiated in different combinations for a Project. I couldn't find a good way to do this with MEF, so I'm doing my own type discovery and instantiation. Is there a good way to do this within MEF or other DI frameworks? I welcome input on any other things to watch out for or surprising capabilities you've discovered that have changed the way you architect.

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• Why can't I create a database in an empty ASP MVC 2 project using Project->Add->New Item->SQL Server

  - by Dr Dork

  I'm diving head first into ASP MVC and am playing around with creating and manipulating a database. I did a search and found this tutorial for creating a database, however when I follow it, I get this error when trying to add a new database to my fresh, empty ASP MVC 2 project... A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) The only requirement the tutorial mentioned was SQL Server Express, but when I went to download it, it said it was already installed. I'm assuming it was part of the VS 2010 RC I installed and am running. So I don't know what else I need if I am missing something. This is all new to me, so I'm sure I'm missing something obvious here and after I'm done posting this question, I plan to do some more research into the topic of databases and how they work with ASP MVC. In the meantime, I was you could help me answer a couple high level questions... What am I missing/forgetting to do that is causing this error? Any suggestions for good resources/tutorials that focus on using databases with ASP MVC? I've done a lot of database programming in the past, so I'm familiar with the concepts of relational databases and the SQL language. I wish I could find a good resource for learning how to work with them in an ASP dev environment, as well as a good breakdown of all the related technologies used for working with them (i.e. LINQ to SQL). Thanks so much in advance for all your help! I'm going to start researching these questions right now.

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• Is there a way to avoid spaghetti code over the years?

  - by Yoni Roit

  I've had several programming jobs. Each one with 20-50 developers, project going on for 3-5 years. Every time it's the same. Some programmers are bright, some are average. Everyone has their CS degree, everyone read design patterns. Intentions are good, people are trying hard to write good code but still after a couple of years the code turns into spaghetti. Changes in module A suddenly break module B. There are always these parts of code that no one can understand except for the person who wrote it. Changing infrastructure is impossible and backwards compatibility issues prevent good features to get in. Half of the time you just want to rewrite everything from scratch. And people more experienced than me treat this as normal. Is it? Does it have to be? What can I do to avoid this or should I accept it as a fact of life? Edit: Guys, I am impressed with the amount and quality of responses here. This site and its community rock!

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• Should I learn VB.NET or C#?

  - by Ravi

  Background I have decided to do my graduation project (yet to start) in .NET. Regarding it, I am bit confused about: what language should I learn: VB.NET or C#? What I have learnt from those who know it that both VB.NET and C# have: The same concepts VB.NET is simpler as it is more like English statements but also C# is simple too if you already know C (Which I do know) Question So considering some factors, e.g. career point of view, newness, challenging and beneficial, etc., what language should I choose? Please help me out. And clearly do justify your answer (whatever reason you have.) References (Extra) A little information about what project I am doing: It is a database file system. Technologies I'll be using are SQL Server, WPF, etc. I just love the concept of Database file system.So those who want to know more about Database file system, here are the links DBFS (This one is really good.Serves as primary reference for me) Towards A Single Folder Filesystem stackoverflow-What is a database file system? UPDATE1 : After some really good explained answers (actually all are good at their place), I have finally decided to go with C# for myself. Thank you all. Still, you are requested to put your opinion (Once it is reopened,of course) UPDATE2 : Question reopened and made community wiki.Thank you all.

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• Bash and regex problem : check for tokens entered into a Coke vending machine

  - by Michael Mao

  Hi all: Here is a "challenge question" I've got from Linux system programming lecture. Any of the following strings will give you a Coke if you kick: L = { aaaa, aab, aba, baa, bb, aaaa"a", aaaa"b", aab"a", … ab"b"a, ba"b"a, ab"bbbbbb"a, ... } The letters shown in wrapped double quotes indicate coins that would have fallen through (but those strings are still part of the language in this example). Exercise (a bit hard) show this is the language of a regular expression And this is what I've got so far : #!/usr/bin/bash echo "A bottle of Coke costs you 40 cents" echo -e "Please enter tokens (a = 10 cents, b = 20 cents) in a sequence like 'abba' :\c" read tokens #if [ $tokens = aaaa ]||[ $tokens = aab ]||[ $tokens = bb ] #then # echo "Good! now a coke is yours!" #else echo "Thanks for your money, byebye!" if [[ $token =~ 'aaaa|aab|bb' ]] then echo "Good! now a coke is yours!" else echo "Thanks for your money, byebye!" fi Sadly it doesn't work... always outputs "Thanks for your money, byebye!" I believe something is wrong with syntax... We didn't provided with any good reference book and the only instruction from the professor was to consult "anything you find useful online" and "research the problem yourself" :( I know how could I do it in any programming language such as Java, but get it done with bash script + regex seems not "a bit hard" but in fact "too hard" for anyone with little knowledge on something advanced as "lookahead"(is this the terminology ?) I don't know if there is a way to express the following concept in the language of regex: Valid entry would consist of exactly one of the three components : aaaa, aab and bb, regardless of order, followed by an arbitrary sequence of a or b's So this is what is should be like : (a{4}Ua{2}bUb{2})(aUb)* where the content in first braces is order irrelevant. Thanks a lot in advance for any hints and/or tips :)

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• compareTo and nested Enums

  - by echox

  Hi, in "A Programmers Guide to Java SCJP Certification" I found an example which I can't follow. This the given enum: enum Scale3 { GOOD(Grade.C), BETTER(Grade.B), BEST(Grade.A); enum Grade {A, B, C} private Grade grade; Scale3(Grade grade) { this.grade = grade; } public Grade getGrade() { return grade; } } This is the given expression: Scale3.GOOD.getGrade().compareTo(Scale3.Grade.A) > 0; I don't understand why this expression will be true? The return value will be 2. compareTo() will return a value 0 if the given object is "less" than the object. Scale3.Grade.A is the "biggest" element of Grades, its ordinal number is 0. Scale3.GOOD is the "biggest" element of Scale3, its ordinal number is also 0. The constructor of Scale3 is called with Scale3.Grade.C, which ordinal number is 2. So the given expression is equal to the following code: Scale3.Grade.C.compareTo(Scale3.Grade.A) > 0; A is "bigger" than C, so shouldn't be the result < 0?

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• Why does the same Getopt::Long code work differently in different programs?

  - by ennuikiller

  The following code works in one script yet in another only works if a specify the -- end of options flag before specifying an option: my $opt; GetOptions( 'help|h' => sub { usage("you want help?? hahaha, hopefully you're not serious!!"); }, 'file|f=s' => \$opt->{FILE}, 'report|r' => \$opt->{REPORT}, ) or usage("Bad Options"); In other words, the same code words in good.pl and bad.pl like so: good.pl -f bad.pl -- -f If I try bad.pl -f I get unknown option:f. Anyone have any clue as to what can cause this behavior? Thanks in advance! I've solved this..... and btw it's a VERY clear question (so why the downvotes)? I'll state it again: What would cause the identical GetOptions block to work in these 2 ways: "good.pl -f" "bad.pl -- -f" see how clear? Maybe you guys should think about it as if it were a TEST!

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• Problem draw line by Quartz 2D with alpha property < 1.0 on iPhone

  - by The Khanh

  Hello Everybody ! This code i use to draw in my app. So i have problem, if i draw with alpha property = 1. It is very good but if i change alpha property = 0.2 then my paint is not good. How do i make for better with alpha property = 0.2. http://www.flickr.com/photos/9601621@N05/page1/ Draw with alpha = 1: It is good Draw with alpha = 0.2: It is bad - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { if ([self.view superview] && (headerView.frame.origin.y == -30)) { mouseSwiped = YES; UITouch *touch = [touches anyObject]; CGPoint currentPoint = [touch locationInView:self.view]; currentPoint.y -= 20; UIGraphicsBeginImageContext(self.view.frame.size); CGContextRef context = UIGraphicsGetCurrentContext(); [drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; CGContextSetLineCap(context, kCGLineCapRound); CGContextSetLineWidth(context, currentBrushProperty.brushSize); CGContextSetRGBStrokeColor(context, [self red], [self green], [self blue], currentBrushProperty.brushTransparency); CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0); CGContextBeginPath(context); CGContextMoveToPoint(context, lastPoint.x, lastPoint.y); CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y); CGContextStrokePath(context); drawImage.image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); lastPoint = currentPoint; }} Help me, please.

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• Considerations when architecting an application using Dependency Injection

  - by Dan Bryant

  I've begun experimenting with dependency injection (in particular, MEF) for one of my projects, which has a number of different extensibility points. I'm starting to get a feel for what I can do with MEF, but I'd like to hear from others who have more experience with the technology. A few specific cases: My main use case at the moment is exposing various singleton-like services that my extensions make use of. My Framework assembly exposes service interfaces and my Engine assembly contains concrete implementations. This works well, but I may not want to allow all of my extensions to have access to all of my services. Is there a good way within MEF to limit which particular imports I allow a newly instantiated extension to resolve? This particular application has extension objects that I repeatedly instantiate. I can import multiple types of Controllers and Machines, which are instantiated in different combinations for a Project. I couldn't find a good way to do this with MEF, so I'm doing my own type discovery and instantiation. Is there a good way to do this within MEF or other DI frameworks? I welcome input on any other things to watch out for or surprising capabilities you've discovered that have changed the way you architect.

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• Why do I get "Error 6060" when I try to use DBD::Advantage with a 64-bit perl on Linux?

  - by WarheadsSE

  I realize that I am attempting to go beyond the "supported" behavior of the manf's released drivers for Perl, after all they have only released it in package with x86 .so's. However, since I cannot use their package with x64 Perl on a RHEL 5.4 x86_64 box, and maintaining a seperate install of x86 Perl just for this one package, I have made an attempt to get this puppy working thanks to released 64-bit .so's that accompany other driver packages for Advantage. What I have done to this point: download beta 10 DBI drivers, in 32 download beta 10 PHP extension (it contains 32 and x86_64) copy the required DLLs into the ads-lib location (eg /usr/local/ads/lib64) compile the Perl DBI driver with the path to the lib64's .so's Good compilation, good install, good use. The problem is that I always get : failed: [iAnywhere Solutions][Advantage SQL][ASA] Error 6060: Advantage Database Server not available on specified server. axServerConnect (SQL-HY000)(DBD: db_login/SQLConnect err=-1) Does anyone have any ideas? EDIT: fixed package name in post title EDIT: Updated title. It appears that it's not just the x64 perl, but the RHEL 5.4 underneath that may be interfering. As commented below, I managed to shoe-horn a x86 perl onto the system, and compile the DBD::Advantage 9.99, and later replacing that with 9.10, and none of these x86 would connect either. Neither library (9.99 or 9.10) in either bit-edness will connect from this x86_64 server to the windows server's UNC path. I have successfully mounted this share without problems, but still I cannot seem to connect to the 9.1. I have tried: \hostname\PATH \FQDN\PATH \IP\PATH and all of these variations with the port (default) 6262 included. My windows machine connects fine, with both 9.1 and 9.99 from strawberry perl.

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• Properties vs. Fields: Need help grasping the uses of Properties over Fields.

  - by pghtech

  First off, I have read through a list of postings on this topic and I don't feel I have grasped properties because of what I had come to understand about encapsulation and field modifiers (private, public..ect). One of the main aspects of C# that I have come to learn is the importance of data protection within your code by the use of encapsulation. I 'thought' I understood that to be because of the ability of the use of the modifiers (private, public, internal, protected). However, after learning about properties I am sort of torn in understanding not only properties uses, but the overall importance/ability of data protection (what I understood as encapsulation) within C#. To be more specific, everything I have read when I got to properties in C# is that you should try to use them in place of fields when you can because of: 1) they allow you to change the data type when you can't when directly accessing the field directly. 2) they add a level of protection to data access However, from what I 'thought' I had come to know about the use of field modifiers did #2, it seemed to me that properties just generated additional code unless you had some reason to change the type (#1) - because you are (more or less) creating hidden methods to access fields as opposed to directly. Then there is the whole modifiers being able to be added to Properties which further complicates my understanding for the need of properties to access data. I have read a number of chapters from different writers on "properties" and none have really explained a good understanding of properties vs. fields vs. encapsulation (and good programming methods). Can someone explain: 1) why I would want to use properties instead of fields (especially when it appears I am just adding additional code 2) any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code? 3) Any general rules of thumb when it comes to good programming methods in relation to when to use what? Thanks and sorry for the long post - I didn't want to just ask a question that has been asked 100x without explaining why I am asking it again.

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• Speed vs security vs compatibility over methods to do string concatenation in Python

  - by Cawas

  Similar questions have been brought (good speed comparison there) on this same subject. Hopefully this question is different and updated to Python 2.6 and 3.0. So far I believe the faster and most compatible method (among different Python versions) is the plain simple + sign: text = "whatever" + " you " + SAY But I keep hearing and reading it's not secure and / or advisable. I'm not even sure how many methods are there to manipulate strings! I could count only about 4: There's interpolation and all its sub-options such as % and format and then there's the simple ones, join and +. Finally, the new approach to string formatting, which is with format, is certainly not good for backwards compatibility at same time making % not good for forward compatibility. But should it be used for every string manipulation, including every concatenation, whenever we restrict ourselves to 3.x only? Well, maybe this is more of a wiki than a question, but I do wish to have an answer on which is the proper usage of each string manipulation method. And which one could be generally used with each focus in mind (best all around for compatibility, for speed and for security). Thanks.

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• Concurrency and Coordination Runtime (CCR) Learning Resources

  - by Harry

  I have recently been learning the in's and out's of the Concurrency and Coordination Runtime (CCR). Finding good learning resources for this relatively new technology has been quite difficult. (A quick google search brings up "Creedence Clearwater Revival" as the top result!) Some of the resources I have found: Free e-book chapter from WROX on the Robotics Developer Studio Good Article/post on InfoQ Robotic's Member blog Very active MSDN CCR Forum - Got plenty of help from here! Great MSDN Magazine by Jeffrey Richter Official CCR User Guide - Didn't find this very helpful Great blogging series on CCR iodyner CCR Related Blog - Update: Moved to here Eight or so Videos on Channel9.msdn.com CCR Patterns page on MS Robotics Studio - I haven't read this yet 4 x CCR Questions on Stackoverflow - Most of the questions have been Mine! LOL CCR and DSS toolkit has now been released to MSDN Members Do you have any good learning resources for the CCR? I really hope that Microsoft will publish more material, so far it has been too Robotics specific. I believe that MS needs to acknowledge that most people are using the CCR in issolation from the DSS and Robotics Studio. Update The Mix 2010 conference had a presentation by Myspace about how they have used the CCR framework in their middle tier. They also open sourced the code base. MySpace DataRelay Mix Video Presentation

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• cant get ifstream to work in XCode

  - by segfault

  No matter what I try, I cant get the following code to work correctly. ifstream inFile; inFile.open("sampleplanet"); cout << (inFile.good()); //prints a 1 int levelLW = 0; int numLevels = 0; inFile >> levelLW >> numLevels; cout << (inFile.good()); //prints a 0 at the first cout << (inFile.good());, it prints a 1 and at the second a 0. Which tells me that the file is opening correctly, but inFile is failing as soon as read in from it. The file has more then enough lines/characters, so there is no way I have tried to read past the end of the file by that point. File contents: 8 2 #level 2 XXXXXXXX X......X X..X..XX X.X....X X..XX..X XXXX...X X...T..X XXX..XXX #level 1 XXXXXXXX X......X X..X.XXX X.X..X.X X..XX..X X......X X^....SX XXX.^XXX

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• How to sort objects in a many-to-many relationship in ruby on rails?

  - by Kenji Kina

  I've been trying to deal with this problem for a couple of hours now and haven't been able to come up with a clean solution. It seems I'm not too good with rails... Anyway, I have the following: In code: class Article < ActiveRecord::Base has_many :line_aspects, :dependent => :destroy has_many :aspects, :through => :line_aspects #plus a name field end class LineAspect < ActiveRecord::Base belongs_to :article belongs_to :aspect end class Aspect < ActiveRecord::Base belongs_to :data_type has_many :line_aspects has_many :articles, :through => :line_aspects end Now, what I would like to do, is to sort these in two steps. First list of Articles by their Articles.name, and then inside sort them by Aspect.name (note, not the middleman). For instance, alphabetically (sorry if the notation is not correct): [{ article => 'Apple', line_aspects => [ {:value => 'red'}, #corresponding to the Attribute with :name => 'color' {:value => 'small'} #corresponding to the Attribute with :name => 'shape' ] },{ article => 'Watermelon', line_aspects => [ {:value => 'green'}, #corresponding to the Attribute with :name => 'color' {:value => 'big'} #corresponding to the Attribute with :name => 'shape' ] }] Again, note that these are ordered by the aspect name (color before shape) instead of the specific values of each line (red before green). (NOTE: My intention is to displaye these in a table in the view) I have not found a good way to do this in rails yet (without resorting to N queries). Can anyone tell me a good way to do it?

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• ruby comma operator and step question

  - by ryan_m

  so, i'm trying to learn ruby by doing some project euler questions, and i've run into a couple things i can't explain, and the comma ?operator? is in the middle of both. i haven't been able to find good documentation for this, maybe i'm just not using the google as I should, but good ruby documentation seems a little sparse . . . 1: how do you describe how this is working? the first snippet is the ruby code i don't understand, the second is the code i wrote that does the same thing only after painstakingly tracing the first: #what is this doing? cur, nxt = nxt, cur + nxt #this, apparently, but how to describe the above? nxt = cur + nxt cur = nxt - cur 2: in the following example, how do you describe what the line with 'step' is doing? from what i can gather, the step command works like (range).step(step_size), but this seems to be doing (starting_point).step(ending_point, step_size). Am i right with this assumption? where do i find good doc of this? #/usr/share/doc/ruby1.9.1-examples/examples/sieve.rb # sieve of Eratosthenes max = Integer(ARGV.shift || 100) sieve = [] for i in 2 .. max sieve[i] = i end for i in 2 .. Math.sqrt(max) next unless sieve[i] (i*i).step(max, i) do |j| sieve[j] = nil end end puts sieve.compact.join(", ")

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