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• File IO with Streams - Best Memory Buffer Size

  - by AJ

  I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance).

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• What's the state of PHP unit testing frameworks in 2010?

  - by Pekka

  As far as I can see, PHPUnit is the only serious product in the field at the moment. It is widely used, is integrated into Continuous Integration suites like phpUnderControl, and well regarded. The thing is, I don't really like working with PHPUnit. I find it hard to set up (PEAR is the only officially supported installation method, and I hate PEAR), sometimes complicated to work with and, correct me if I'm wrong, lacking executability from a web page context (i.e. no CLI, which would really be nice when developing a web app.) The only competition to I can see is Simpletest, which looks very nice but hasn't seen a new release for almost two years, which tends to rule it out for me - Unit Testing is quite a static field, true, but as I will be deploying those tests alongside web applications, I would like to see active development on the project, at least for security updates and such. There is a SO question that pretty much confirms what I'm saying: Simple test vs PHPunit Seeing that that is almost two years old as well, though, I think it's time to ask again: Does anybody know any other serious feature-complete unit testing frameworks? Am I wrong in my criticism of PHPUnit? Is there still development going on for SimpleTest?

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• Exporting and reformatting data out of MS Excel

  - by Matt H

  I have a huge Excel spreadsheet containing telephone calling rates to a number of different countries. The format of the columns is: Country, RateLocality, Prefixes, Rate, Wholesale e.g. Afganistan, Default, 93;930;931;9321;9322;9323;9324;9325;9326;9327;9328;9329;9331;9332;9333;9334;9335;9336;9337;9338;9339;9341;9342;9343;9344;9345;9346;9347;9348;9349;9351;9352;9353;9354;9355;9356;9357;9358;9359;9361;9362;9363;9364;9365;9366;9367;9368;9369;9371;9372;9373;9374;9376;938;939; $ 1.023, $0.455 These rates change every so often and I need to get them into another system that can import them using CSV. The eventual format is: LD PREPEND CODE ie. 00 or 011,CountryCode,Area Code,Comment,Connect Cost,Included Seconds,Per Minute Cost,Pricelist,Increment So to convert that above line I'd have 00,"Afganistan",93,"Default",1.023,60,1.023,10 00,"Afganistan",931,"Default",1.023,60,1.023,10 ... 00,"Afganistan",939,"Default",1.023,60,1.023,10 Where 00, 60 and 10 are hard coded and merged with the other data from excel. How can I export this data into the required format given that I need to reformat it as it goes. Should I export to XML and use XSLT or some other process to massage the data into CSV? If that is the case, how do I do it simply and quickly.

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• C# comparing two files regex problem.

  - by Mike

  Hi everyone, what I'm trying to do is open a huge list of files (about 40k records, and match them on a line in a file that contains 2 millions records. And if my line from file A matches a line in file B write out that line. File A contains a bunch of files without extensions and file B contains full file paths including extensions. i'm using this but i cant get it to go... string alphaFilePath = (@"C:\Documents and Settings\g\Desktop\Arrp\Find\natst_ready.txt"); List<string> alphaFileContent = new List<string>(); using (FileStream fs = new FileStream(alphaFilePath, FileMode.Open)) using (StreamReader rdr = new StreamReader(fs)) { while (!rdr.EndOfStream) { alphaFileContent.Add(rdr.ReadLine()); } } string betaFilePath = @"C:\Documents and Settings\g\Desktop\Arryup\Find\eble.txt"; StringBuilder sb = new StringBuilder(); using (FileStream fs = new FileStream(betaFilePath, FileMode.Open)) using (StreamReader rdr = new StreamReader(fs)) { while (!rdr.EndOfStream) { string betaFileLine = rdr.ReadLine(); string matchup = Regex.Match(alphaFileContent, @"(\\)(\\)(\\)(\\)(\\)(\\)(\\)(\\)(.*)(\.)").Groups[9].Value; if (alphaFileContent.Equals(matchup)) { File.AppendAllText(@"C:\array_tech.txt", betaFileLine); } } } This doesnt work because the alphafilecontent is a single line only and i'm having a hard time figuring out how to get my regex to work on the file that contains all the file paths (Betafilepath) here is a sample of the beta file path. C:\arres_i\Grn\Ora\SEC\DBZ_EX1\Nes\001\DZO-EX00001.txt Here is the line i'm trying to compare from my alpha DZO-EX00001

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• C# How to create various objects at runtime that can hold strongly typed data?

  - by JL

  Is it possible to create objects at runtime without having to have hard coded class definitions, then populate properties with primitives or even strongly typed data types? For example: Lets say I want to an XML config file that could hold configuration values for connecting to various systems in an SOA application. In C# I read in these values, but for each system the properties are different (e.g: SQL might have a connection string, while SharePoint might need a username + password + domain + url, while yet an smtp server would need username + password + port + url) So instead of creating static classes as follows public class SharePointConfiguration or public class SQLConfiguration, then have each class with custom properties (this is cumbersome) Is there not a more preferred way to achieve this, without using 1990's methods, in otherwords it would still be nice to have intellisense and code completion and named properties. Since this collection of properties (object) would be passed within the class and possible to other classes from function to function I am also wondering where this class definition would get defined if its all happening at run time. Any recommendations, and hope the question was clear enough. Would like to use language features, not hacks. Thank you.

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• Efficient Multiplication of Varying-Length #s [Conceptual]

  - by Milan Patel

  Write the pseudocode of an algorithm that takes in two arbitrary length numbers (provided as strings), and computes the product of these numbers. Use an efficient procedure for multiplication of large numbers of arbitrary length. Analyze the efficiency of your algorithm. I decided to take the (semi) easy way out and use the Russian Peasant Algorithm. It works like this: a * b = a/2 * 2b if a is even a * b = (a-1)/2 * 2b + a if a is odd My pseudocode is: rpa(x, y){ if x is 1 return y if x is even return rpa(x/2, 2y) if x is odd return rpa((x-1)/2, 2y) + y } I have 3 questions: Is this efficient for arbitrary length numbers? I implemented it in C and tried varying length numbers. The run-time in was near-instant in all cases so it's hard to tell empirically... Can I apply the Master's Theorem to understand the complexity...? a = # subproblems in recursion = 1 (max 1 recursive call across all states) n / b = size of each subproblem = n / 1 - b = 1 (problem doesn't change size...?) f(n^d) = work done outside recursive calls = 1 - d = 0 (the addition when a is odd) a = 1, b^d = 1, a = b^d - complexity is in n^d*log(n) = log(n) this makes sense logically since we are halving the problem at each step, right? What might my professor mean by providing arbitrary length numbers "as strings". Why do that? Many thanks in advance

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• gcc compilations (sometimes) result in cpu underload

  - by confusedCoder

  I have a larger C++ program which starts out by reading thousands of small text files into memory and storing data in stl containers. This takes about a minute. Periodically, a compilation will exhibit behavior where that initial part of the program will run at about 22-23% CPU load. Once that step is over, it goes back to ~100% CPU. It is more likely to happen with O2 flag turned on but not consistently. It happens even less often with the -p flag which makes it almost impossible to profile. I did capture it once but the gprof output wasn't helpful - everything runs with the same relative speed just at low cpu usage. I am quite certain that this has nothing to do with multiple cores. I do have a quad-core cpu, and most of the code is multi-threaded, but I tested this issue running a single thread. Also, when I run the problematic step in multiple threads, each thread only runs at ~20% CPU. I apologize ahead of time for the vagueness of the question but I have run out of ideas as to how to troubleshoot it further, so any hints might be helpful. UPDATE: Just to make sure it's clear, the problematic part of the code does sometimes (~30-40% of the compilations) run at 100% CPU, so it's hard to buy the (otherwise reasonable) argument that I/O is the bottleneck

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• "Function object is unsubscriptable" in basic integer to string mapping function

  - by IanWhalen

  I'm trying to write a function to return the word string of any number less than 1000. Everytime I run my code at the interactive prompt it appears to work without issue but when I try to import wordify and run it with a test number higher than 20 it fails as "TypeError: 'function' object is unsubscriptable". Based on the error message, it seems the issue is when it tries to index numString (for example trying to extract the number 4 out of the test case of n = 24) and the compiler thinks numString is a function instead of a string. since the first line of the function is me defining numString as a string of the variable n, I'm not really sure why that is. Any help in getting around this error, or even just help in explaining why I'm seeing it, would be awesome. def wordify(n): # Convert n to a string to parse out ones, tens and hundreds later. numString = str(n) # N less than 20 is hard-coded. if n < 21: return numToWordMap(n) # N between 21 and 99 parses ones and tens then concatenates. elif n < 100: onesNum = numString[-1] ones = numToWordMap(int(onesNum)) tensNum = numString[-2] tens = numToWordMap(int(tensNum)*10) return tens+ones else: # TODO pass def numToWordMap(num): mapping = { 0:"", 1:"one", 2:"two", 3:"three", 4:"four", 5:"five", 6:"six", 7:"seven", 8:"eight", 9:"nine", 10:"ten", 11:"eleven", 12:"twelve", 13:"thirteen", 14:"fourteen", 15:"fifteen", 16:"sixteen", 17:"seventeen", 18:"eighteen", 19:"nineteen", 20:"twenty", 30:"thirty", 40:"fourty", 50:"fifty", 60:"sixty", 70:"seventy", 80:"eighty", 90:"ninety", 100:"onehundred", 200:"twohundred", 300:"threehundred", 400:"fourhundred", 500:"fivehundred", 600:"sixhundred", 700:"sevenhundred", 800:"eighthundred", 900:"ninehundred", } return mapping[num] if __name__ == '__main__': pass

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• iOS 7: Best way to implement an textview that presents previous input but is easy to clear

  - by Frank R.

  I'm porting a Mac app to the iPhone and I've run into an unexpected problem. On the Mac there's a text field that is automatically pre-selected (= first responder) when a dialog shows up. The text field shows the text you entered in the field the last time and the text is pre-selected so that if you just start typing it gets cleared away. If you want to edit the existing text instead you just hit the forwards or backwards arrow. On the iPhone this behavior seems very hard to implement. The text view shows up with the old text and I can even get it to pre-select but whatever I do the result is not quite right. When I use [aTextView setMarkedText: myText selectedRange: newRange]; the text does show up as marked and if I just start typing the old text goes away. However there's no equivalent to the cursor keys on iOS, so I cannot NOT erase the text.. which is hardly the point. What kind of iOS idiom would be appropriate for giving the option to either edit or overwrite existing text? Best regards, Frank

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• How to catch exceptions from processes in C#

  - by kitofr

  I all... I have an acceptance runner program here that looks something like this: public Result Run(CommandParser parser) { var result = new Result(); var watch = new Stopwatch(); watch.Start(); try { _testConsole.Start(); parser.ForEachInput(input => { _testConsole.StandardInput.WriteLine(input); return _testConsole.TotalProcessorTime.TotalSeconds < parser.TimeLimit; }); if (TimeLimitExceeded(parser.TimeLimit)) { watch.Stop(); _testConsole.Kill(); ReportThatTestTimedOut(result); } else { result.Status = GetProgramOutput() == parser.Expected ? ResultStatus.Passed : ResultStatus.Failed; watch.Stop(); } } catch (Exception) { result.Status = ResultStatus.Exception; } result.Elapsed = watch.Elapsed; return result; } the _testConsole is an Process adapter that wraps a regular .net process into something more workable. I do however have a hard time to catch any exceptions from the started process (i.e. the catch statement is pointless here) I'm using something like: _process = new Process { StartInfo = { FileName = pathToProcess, UseShellExecute = false, CreateNoWindow = true, RedirectStandardInput = true, RedirectStandardOutput = true, RedirectStandardError = true, Arguments = arguments } }; to set up the process. Any ideas?

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• Convenient way to do "wrong way rebase" in git?

  - by Kaz

  I want to pull in newer commits from master into topic, but not in such a way that topic changes are replayed over top of master, but rather vice versa. I want the new changes from master to be played on top of topic, and the result to be installed as the new topic head. I can get exactly the right object if I rebase master to topic, the only problem being that the object is installed as the new head of master rather than topic. Is there some nice way to do this without manually shuffling around temporary head pointers? Edit: Here is how it can be achieved using a temporary branch head, but it's clumsy: git checkout master git checkout -b temp # temp points to master git rebase topic # topic is brought into temp, temp changes played on top Now we have the object we want, and it's pointed at by temp. git checkout topic git reset --hard temp Now topic has it; and all that is left is to tidy up by deleting temp: git branch -d temp Another way is to to do away with temp and just rebase master, and then reset topic to master. Finally, reset master back to what it was by pulling its old head from the reflog, or a cut-and-paste buffer.

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• Embedded scripting engine in .Net app

  - by Nate

  I am looking to replace an old control being used for scripting an application. The control used to be called SAX Basic, but is now called WinWrap. It provides us with two primary functions. 1) It's a scripting engine (VB) 2) It has a GUI for developing and debugging scripts that get run in the hosting application. The first feature it provides is actually pretty easy to replace. There are so many great methods of running just about any kind of code at runtime that it's almost a non-issue. Just about any language targeting the .Net runtime will work for us. We've looked at running C#, PowerShell, VB.Net, IronPython, etc. I've also taken a brief look at Lua and F#, but honestly the language isn't the biggest barrier here. Now, for the hard part that seems to keep getting me stuck. We want a code editor, and debugger. Something simple, not unlike PowerShell's ISE would be fine. Just as long as a file could be created, saved, debugged and executed. I'm currently looking into Visual Studio 2010 Shell (Isolated) and I'm also looking at the feasibility of embedding PowerShell ISE in my application. Are there any other editor's I could embed/use in my application? Purchasing a product is not out of the question. It comes down to a combination of ease of use, how well it meets our needs, and how simple deployment and licensing is for developers. Thanks for the pointers

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• Map Literals to Object Properties/Values

  - by vijay

  For eg, my input XML is look like this. <root> <myelemt> <input type="variable"> <variable>STARTDATE</variable> <variable>CUSTOMERNAME</variable> </input> </myelemt> </root> it is deserialized and loaded into the object MyXmlElemtObj in my code i have written like this, if(MyXmlElemtObj.input.variable.ToUpper() == "STARTDATE") ProcessObjectB(ObjectA.OrderDate); if(MyXmlElemtObj.input.variable.ToUpper() == "CUSTOMERNAME") ProcessObjectB(ObjectC.UserName); Here I am mapping those input literals to some objects value. The one thing that scares me is seeing some ** hard-coded literals** all over my code. Instead i would like to write something like ProcessObjectB(Common.GetMappedvalue(MyXmlElemtObj.input.variable)); Is there a way to isolate this mapping thing to common class, where i will predefine which literal is mapped to which values. The problem is the values are of objects created at the run time. If my question is making sense then So how do i achieve this? I think i have given all the necessary details. if anything is missing please metnion. Thx Much.

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• Java constructor using generic types

  - by Beer Me

  I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method breweryMethod() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // breweryMethod() is an instance method // of Brewery, of which <T> is a subclass (right?) c.breweryMethod(); // "The method breweryMethod() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void brewerySubClassMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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• Xcode 4: nib files not loading when run, can't find UI elements

  - by Jordan

  So, I just downloaded Xcode 4 and installed it. I was actually quite looking forward to the single window and integrated IB... - However, when I open and run one of my projects, the nib files that the project uses don't seem to load. Instead I'm left looking at a blank white screen (iPhone). This project ran well and fine on Xcode 3.2. So I thought... this can't be that hard to fix. So I opened up a nib file, thinking that maybe editing or creating a new one from scratch could point me in the right direction. But I can't find the old resources panel from interface builder anywhere. How am I meant to create a new view or add buttons? I know I'm probably just missing something obvious :s Did anyone else have the same nib file problems - is there a fix (or something stupidly simple that I'm forgetting about)? - EDIT: Ok. If I background and un-background the app, the view loads fine. But this happens every time I build, on both iPhone and iOS simulator, i.e. the app doesn't work properly until it's been backgrounded. All the code for loading the view follows from - (void)applicationDidFinishLaunching:(UIApplication *)application. Now I am really confused. - Thanks :)

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• How to make div follow scrolling smoothly with jQuery?

  - by Martti Laine

  Hello I'm creating a blog layout, which has an sidebar. In sidebar there are sections/boxes, but the last one of these boxes should follow scrolling when none of the other boxes are visible. So, when user scrolls down, he sees a normal sidebar, but when user has went down enough, sidebar ends but the last box starts to follow on the top of the screen. I have seen this a lot on different kind of sites. So hard to explain with my english. I already made it to follow screen smoothly with animate() but couldn't get it like this. Hope you understood. I already tried in Google for almost an hour but couldn't figure out any keywords (due to my bad english). EDIT: My code at the moment: $(window).scroll(function(){ $.each($('.follow-scroll'),function(){ var eloffset = $(this).offset(); var windowpos = $(window).scrollTop(); if(windowpos<eloffset.top) { var finaldestination = 0; } else { var finaldestination = windowpos; } $(this).stop().animate({'top':finaldestination},200); }); });

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• What tools do you have at your disposal as a manager to promote a way of thinking

  - by John Leidegren

  This question goes beoynd just programming, but I'd like to get some input on this, if that's okay with the community. Preferably from people that do a lot of coding themselves but also manage other people coding. My problem is this. We have all these ideas that we know is good for the overall strategy of the company and the problem is not figuring out what to do, it's to come about this change. Just telling someone to do things differently isn't enough and it's hard to promote a mind set that is shared within all of the company, (this will take time). If I could jump forward I'd like it if we could create a very nurturing company culture that promotes these ideals cross all areas but I'm not sure what tools to use. And by tools I mean anything I'm legally permitted to do. e.g. we could talk about, we could arrange traning sessions, we could spend more time in meeting (talk about it more), we could spend more time designing, we could spend more time pair-programming, we could add/remove incentive or we could encurage more play. Ultimately if we did all of these things what will be the recurring theme that ties this together. I'd like to be able to answer the question -- why should we do things like this? -- and come up with an answer that explains how important it is to think about our ideals from begining to end. I've puposly avoided to talk about or specifics of the situtation becuase I believe that it narrows things down too much. But I guess, by know you either know how to answer this question or you're as confused as I am ;) I'd love to hear from people who had to bring about a change in order to go from chaos to order, or fix something in the organization which wasn't working. And I'd like to hear it from the perspective of the developer and designer. -- or -- You could simply weigh in on what are the most important qualities in an organization encurage or stimulate rigid fun development cycle from start to finish?

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• Building a survey to put in a WordPress website using Python/Django

  - by chiurox

  So I've been given a task to build a survey to get data regarding time slot preferences of prospective students for a particular course. I know there are really quick solutions to this like Google Forms, SurveyMonkey, but since it's not unusually hard, I want to implement the survey myself in a totally new language as an opportunity to get started with it and also be able to customize and provide dynamic info to the users who are voting. Although I have done some stuff in PHP, C++, javascript, etc, I'm pretty new to Python+Django framework but it's something I've been meaning to get into since a long time ago. Initially, what I want is to make a grid with the days of the week as columns and time-durations as rows. In each cell I want to provide users a way to choose how strong (high/medium/low) their preference for this particular day+time is. I also want to show how many "votes" have already been cast for this particular preference because this will influence a lot in their decisions and as a result make this process easier when we are going to define the classes. I'll probably store the data in MySQL. Could anyone point me to some really good Python+Django tutorials for my particular purpose? Does anyone think I'm wasting my time with this trivial task by choosing new tools and that I should just use something I already know (like PHP) or a free service or plugin for Wordpress? Thanks!

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• How to model in J2EE / JEE?

  - by Harry

  Let's say, I have decided to go with J(2)EE stack for my enterprise application. Now, for domain modelling (or: for designing the M of MVC), which APIs can I safely assume and use, and which I should stay away from... say, via a layer of abstraction? For example, Should I go ahead and litter my Model with calls to Hibernate/JPA API? Or, should I build an abstraction... a persistence layer of my own to avoid hard-coding against these two specific persistence APIs? Why I ask this: Few years ago, there was this Kodo API which got superseded by Hibernate. If one had designed a persistence layer and coded the rest of the model against this layer (instead of littering the Model with calls to specific vendor API), it would have allowed one to (relatively) easily switch from Kodo to Hibernate to xyz. Is it recommended to make aggressive use of the *QL provided by your persistence vendor in your domain model? I'm not aware of any real-world issues (like performance, scalability, portability, etc) arising out of a heavy use of an HQL-like language. Why I ask this: I would like to avoid, as much as possible, writing custom code when the same could be accomplished via query language that is more portable than SQL. Sorry, but I'm a complete newbie to this area. Where could I find more info on this topic? Many thanks in advance. /HS

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• Apache friendly urls

  - by HaukurHaf

  Hi everyone. I've got a small CMS system written in PHP and running on Apache. The format of the URLs this CMS system uses/generates is: /display.php?PageID=xxx where xxx is just some integer number. As you can see, those URLs are not very friendly, neither for users nor search engines. I believe that using mod_rewrite (or something like that) and .htaccess files I should be able to configure Apache for URL-rewriting. I have searched for information about this before but I did not find any easy method to do this, it always involved messing with regular expressions, which I'm not very familiar with. Since the website in question is really simple and small, just 5-10 different pages, I would really like to be able to just hard-code the configuration, without any special rules or regexps. I'd just like to map a friendly URL to an actual URL, perhaps like this: /about = /display.php?PageID=44 /products = /display.php?PageID=34 etc. Is it possible to configure the mod_rewrite plugin in a basic way like this? Could someone explain the easiest method to do this? Explain it to me as if I was a child :-) Thanks in advance!

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• Read in double type from txt file - C++

  - by Greenhouse Gases

  Hi there I'm in the midst of a university project and have decided to implement a method that can accept information from a text file (in this instance called "locations.txt"). input from the text file will look like this: London 345 456 Madrid 234 345 Beinjing 345 456 Frankfurt 456 567 The function looks like this currently (and you will notice I am missing the While condition to finish adding input when reaches end of text in locations.txt, i tried using eof but this didnt work?!). Also get function expects a char and so cant accept input thats a double which is what the latitude and longitude are defined as... void populateList(){ ifstream inputFile; inputFile.open ("locations.txt"); temp = new locationNode; // declare the space for a pointer item and assign a temporary pointer to it while(HASNT REACHED END OF TEXT FILE!!) { inputFile.getline(temp-nodeCityName, MAX_LENGTH); // inputFile.get(temp-nodeLati, MAX_LENGTH); // inputFile.get(temp-nodeLongi, MAX_LENGTH); temp-Next = NULL; //set to NULL as when one is added it is currently the last in the list and so can not point to the next if(start_ptr == NULL){ // if list is currently empty, start_ptr will point to this node start_ptr = temp; } else { temp2 = start_ptr; // We know this is not NULL - list not empty! while (temp2-Next != NULL) { temp2 = temp2-Next; // Move to next link in chain until reach end of list } temp2->Next = temp; } } inputFile.close(); } Any help you can provide would be most useful. If I need to provide anymore detail I will do, I'm in a bustling canteen atm and concentrating is hard!!

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• Reverse-projection 2D points into 3D

  - by ehsan baghaki

  Suppose we have a 3d Space with a plane on it with an arbitary equation : ax+by+cz+d=0 now suppose that we pick 3 random points on that plane: (x0,y0,z0) (x1,y1,z1) (x1,y1,z1) now i have a different point of view(camera) for this plane. i mean i have a different camera that will look at this plane from a different point of view. From that camera point of view these points have different locations. for example (x0,y0,z0) will be (x0',y0') and (x1,y1,z1) will be (x1',y1') and (x2,y2,z2) will be (x2',y2') from the new camera point of view. So here is my a little hard question! I want to pick a point for example (X,Y) from the new camera point of view and tell where it will be on that plane. All i know is that 3 points and their locations on 3d space and their projection locations on the new camera view. Do you know the coefficients of the plane-equation and the camera positions (along with the projection), or do you only have the six points? - Nils i know the location of first 3 points. therefore we can calculate the coefficients of the plane. so we know exactly where the plane is from (0,0,0) point of view. and then we have the camera that can only see the points! So the only thing that camera sees is 3 points and also it knows their locations in 3d space (and for sure their locations on 2d camera view plane). and after all i want to look at camera view, pick a point (for example (x1,y1)) and tell where is that point on that plane. (for sure this (X,Y,Z) point should fit on the plane equation). Also i know nothing about the camera location.

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• At what point is it worth using a database?

  - by radix07

  I have a question relating to databases and at what point is worth diving into one. I am primarily an embedded engineer, but I am writing an application using QT to interface with our controller. We are at an odd point where we have enough data that it would be feasible to implement a database (around 700+ items and growing) to manage everything, but I am not sure it is worth the time right now to deal with. I have no problems implementing the GUI with files generated from excel and parsed in, but it gets tedious and hard to track even with VBA scripts. I have been playing around with converting our data into something more manageable for the application side with Microsoft Access and that seems to be working well. If that works out I am only a step (or several) away from using an SQL database and using the QT library to access and modify it. I don't have much experience managing data at this level and am curious what may be the best way to approach this. So what are some of the real benefits of using a database if any in this case? I realize much of this can be very application specific, but some general ideas and suggestions on how to straddle the embedded/application programming line would be helpful. Thanks

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• cellForRowAtIndexPath not called for all sections

  - by Wynn

  I have a UITableView that has five sections. Just as the title describes cellForRowAtIndexPath is only being called for the first four. All connections have been made concerning the datasource and delegate. Also, my numberOfSectionsInTableView clearly returns 5. Printing out the number of sections from within cellForRowAtIndexPath shows the correct number, thus confirming that cellForRowAtIndexPath is simply not being called for all sections. What on earth is going on? I looked pretty hard for an answer to this question but could't find one. If this has already been answered please forgive me and point me in the correct direction. My cellForRowAtIndexPath: - (UITableViewCell *)tableView:(UITableView *)theTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [theTableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; } switch (indexPath.section) { case 0: cell.textLabel.text = ticket.description; break; case 1: cell.textLabel.text = ticket.ticketStatus; break; case 2: cell.textLabel.text = ticket.priority; break; case 3: cell.textLabel.text = ticket.customerOfficePhone; break; case 4: { //This never ever gets executed Comment *comment = [ticket.comments objectAtIndex:indexPath.row]; cell.textLabel.text = comment.commentContent; break; } } return cell; } My numberOfSectionsInTableView: - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 5; } My numberOfRowsInSection: - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { NSInteger numberOfRows; if (section == 4) { numberOfRows = [ticket.comments count]; } else { numberOfRows = 1; } return numberOfRows; } Any suggestions are appreciated. Thanks in advance.

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• google app engine atomic section???

  - by bokertov

  hi, Say you retrieve a set of records from the datastore (something like: select * from MyClass where reserved='false'). how do i ensure that another user doesn't set the reserved is still false? I've looked in the Transaction documentation and got shocked from google's solution which is to catch the exception and retry in a loop. Any solution that I'm missing - it's hard to believe that there's no way to have an atomic operation in this environment. (btw - i could use 'syncronize' inside the servlet but i think it's not valid as there's no way to ensure that there's only one instance of the servlet object, isn't it? same applies to static variable solution) Any idea on how to solve??? (here's the google solution: http://code.google.com/appengine/docs/java/datastore/transactions.html#Entity_Groups look at: Key k = KeyFactory.createKey("Employee", "k12345"); Employee e = pm.getObjectById(Employee.class, k); e.counter += 1; pm.makePersistent(e); This requires a transaction because the value may be updated by another user after this code fetches the object, but before it saves the modified object. Without a transaction, the user's request will use the value of counter prior to the other user's update, and the save will overwrite the new value. With a transaction, the application is told about the other user's update. If the entity is updated during the transaction, then the transaction fails with an exception. The application can repeat the transaction to use the new data. THANKS!

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