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• What the heck is the "Structure and Interpretation of Computer Programs" cover drawing about?

  - by Paul Reiners

  What the heck is the Structure and Interpretation of Computer Programs cover drawing about? I mean I know what "eval", "apply", and '?' all mean, but I'm having a hard time deciphering the rest of the picture. Who the heck is the maiden? Does she work for the wizard? Why the heck is she pointing at the table? Is she pointing at that little bowl-type thing? Or the books? Or the table in general? Is she trying to tell the wizard that he should apply some sort of Lisp wizardry to the table or the items on it? Or is she just telling him something prosaic, such as his food is getting cold? What the heck is the one leg on that table that looks like...a leg...with a foot at the end (as legs tend to have)? How does the table balance on one leg? (Or is that another leg in the shadows?) [Note: I'm waiting for a lengthy build to finish in case you were wondering.]

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• Database solution for 200million writes/day, monthly summarization queries

  - by sb

  Hello. I'm looking for help deciding on which database system to use. (I've been googling and reading for the past few hours; it now seems worthwhile to ask for help from someone with firsthand knowledge.) I need to log around 200 million rows (or more) per 8 hour workday to a database, then perform weekly/monthly/yearly summary queries on that data. The summary queries would be for collecting data for things like billing statements, eg. "How many transactions of type A did each user run this month?" (could be more complex, but that's the general idea). I can spread the database amongst several machines, as necessary, but I don't think I can take old data offline. I'll definitely need to be able to query a month's worth of data, maybe a year. These queries would be for my own use, and wouldn't need to be generated in real-time for an end-user (they could run overnight, if needed). Does anyone have any suggestions as to which databases would be a good fit? P.S. Cassandra looks like it would have no problem handling the writes, but what about the huge monthly table scans? Is anyone familiar with Cassandra/Hadoop MapReduce performance?

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• Django: Storing ordered, arbitrary references

  - by Sarah

  I'm new to Django, and I'm not sure what I want is possible: I have a number of items that I want each AppUser (extended User model) to be able to reference. That is, given an AppUser, I want to be able to extract its list of items in the way that AppUser has chosen to order them. In general, these items would actually be references to something else in the database, and this led me to one possible solution: Store the keys for the given objects in a CommaSeparatedIntegerField in AppUser. This way, a user could have stored {7, 3, 232, 42, 1} in their items field and both the references and their preferred order would be stored. However, this feels hacky. Since most db backends store CommaSeparatedIntegerField as a VARCHAR internally, the user is not only limited by a number of objects, but also the number of digits in their chosen items. Eg. "you may store 10 items if you choose items with itemID < 10, but only 5 items if 10 < itemID < 100". Is there a better way to do this?

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• How To Select First Ancestor That Matches A Selector?

  - by Zach

  General: How can I select the first matching ancestor of an element in jQuery? Example: Take this HTML block <table> <tbody> <tr> <td> <a href="#" class="remove">Remove</a> </td> </tr> <tr> <td> <a href="#" class="remove">Remove</a> </td> </tr> </tbody> </table> I can remove a row in the table by clicking "Remove" using this jQuery code: $('.remove').click(function(){ $(this).parent().parent().hide(); return false; }); This works, but it's pretty fragile. If someone puts the <a> into a <div>, for example, it would break. Is there a selector syntax in jQuery that follows this logic: "Here's an element, now find the closest ancestor that matches some selection criteria and return it" Thanks

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• How do I daemonize an arbitrary script in unix?

  - by dreeves

  I'd like a daemonizer that can turn an arbitrary, generic script or command into a daemon. There are two common cases I'd like to deal with: I have a script that should run forever. If it ever dies (or on reboot), restart it. Don't let there ever be two copies running at once (detect if a copy is already running and don't launch it in that case). I have a simple script or command line command that I'd like to keep executing repeatedly forever (with a short pause between runs). Again, don't allow two copies of the script to ever be running at once. Of course it's trivial to write a "while(true)" loop around the script in case 2 and then apply a solution for case 1, but a more general solution will just solve case 2 directly since that applies to the script in case 1 as well (you may just want a shorter or no pause if the script is not intended to ever die (of course if the script really does never die then the pause doesn't actually matter)). Note that the solution should not involve, say, adding file-locking code or PID recording to the existing scripts. More specifically, I'd like a program "daemonize" that I can run like % daemonize myscript arg1 arg2 or, for example, % daemonize 'echo `date` >> /tmp/times.txt' which would keep a growing list of dates appended to times.txt. (Note that if the argument(s) to daemonize is a script that runs forever as in case 1 above, then daemonize will still do the right thing, restarting it when necessary.) I could then put a command like above in my .login and/or cron it hourly or minutely (depending on how worried I was about it dying unexpectedly). NB: The daemonize script will need to remember the command string it is daemonizing so that if the same command string is daemonized again it does not launch a second copy. Also, the solution should ideally work on both OS X and linux but solutions for one or the other are welcome. (If I'm thinking of this all wrong or there are quick-and-dirty partial solutions, I'd love to hear that too.)

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• SQL queries to determine all values that would satisfy an arbitrary query

  - by jasterm007

  I'm trying to figure out how to efficiently run a set of queries that will provide a new table of all values that would return results for an arbitrary query. Say my table has a schema like: id name age city What is an efficient way to list all values that would return results for an arbitrary query, say "NOT city=X AND age BETWEEN Y and Z"? My naive approach for this would be to use a script and recurse through all possible combinations of {city, age, age} and see which SELECTs return more than 0 results, but that seems incredibly inefficient. I've also tried building large joins on {city, age, age} as well and basically using that table as an argument list to the query, but that quickly becomes an impossibility for queries on many columns. For simple conjunctive equality queries, i.e. "name=X and age=Y", this is much simpler, as I can do something like SELECT name, age, count(*) AS count FROM main GROUP BY name, age HAVING count > 0 But I'm having difficulty coming up with a general approach for anything more complicated than that. Any pointers in the right direction would be most helpful, thanks.

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• Looking for a good C++/.net book

  - by Michael Minerva

  I have recently started to feel that I need to greatly improve my C++ skills especially in the realm of .net. I graduated from a good four year university with a degree in computer science about 9 months ago and I have since been doing full time contract work for a small software company in my local area. Most of my work has been done using Java/lisp/cocoa/XML and before that most of my programming in my senior year was in java/C#. I did a decent amount of C++ in my Sophomore year and in my free time before that but I feel that my general knowledge of C++/.net is very lacking for the opportunities that are now coming my way. Can anyone recommend a good book that could help me get up too speed? I feel I do not need a very basic introduction to C++ but something that covers the fundamentals of .net would be good for me. So basically what I need is a book or books that would be good for a .net novice and a C++ developer who is just beyond novice. Also, a book that would help bein an interview by giving me a conversional understanding of C++ would be great. Thanks a lot!.

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• What's the deal with the hidden Throw when catching a ThreadAbortException?

  - by priehl

  I'm going through a book of general c# development, and I've come to the thread abort section. The book says something along the lines that when you call Thread.Abort() on another thread, that thread will throw a ThreadAbortException, and even if you tried to supress it it would automatically rethrow it, unless you did some bs that's generally frowned upon. Here's the simple example offered. using System; using System.Threading; public class EntryPoint { private static void ThreadFunc() { ulong counter = 0; while (true) { try { Console.WriteLine("{0}", counter++); } catch (ThreadAbortException) { // Attempt to swallow the exception and continue. Console.WriteLine("Abort!"); } } } static void Main() { try { Thread newThread = new Thread(new ThreadStart(EntryPoint.ThreadFunc)); newThread.Start(); Thread.Sleep(2000); // Abort the thread. newThread.Abort(); // Wait for thread to finish. newThread.Join(); } catch (Exception e) { Console.WriteLine(e.ToString()); } } } The book says: When your thread finishes processing the abort exception, the runtime implicitly rethrows it at the end of your exception handler. It’s the same as if you had rethrown the exception yourself. Therefore, any outer exception handlers or finally blocks will still execute normally. In the example, the call to Join won’t be waiting forever as initially expected. So i wrapped a try catch around the Thread.Abort() call and set a break point, expecting it to hit this, considering the text says "any outer exception handlers or finally blocks will still execute normally". BUT IT DOES NOT. I'm racking my brain to figure out why. Anyone have any thoughts on why this isn't the case? Is the book wrong? Thanks in advance.

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• My iPhone app ran fine in simulator but crashed in device (iPod touch 3.1.2) test, I got the followi

  - by Mickey Shine

  I was running myapp on an iPod touch and I noticed it missed some libraries. Is that the reason? [Session started at 2010-03-19 15:57:04 +0800.] GNU gdb 6.3.50-20050815 (Apple version gdb-1128) (Fri Dec 18 10:08:53 UTC 2009) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "--host=i386-apple-darwin --target=arm-apple-darwin".tty /dev/ttys007 Loading program into debugger… Program loaded. target remote-mobile /tmp/.XcodeGDBRemote-237-78 Switching to remote-macosx protocol mem 0x1000 0x3fffffff cache mem 0x40000000 0xffffffff none mem 0x00000000 0x0fff none run Running… [Switching to thread 11779] [Switching to thread 11779] sharedlibrary apply-load-rules all (gdb) continue warning: Unable to read symbols for "/Library/MobileSubstrate/MobileSubstrate.dylib" (file not found). 2010-03-19 15:57:18.892 myapp[2338:207] MS:Notice: Installing: com.yourcompany.myapp [myapp] (478.52) 2010-03-19 15:57:19.145 myapp[2338:207] MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib warning: Unable to read symbols for "/Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib" (file not found). warning: Unable to read symbols for "/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/lib/libsubstrate.dylib" (file not found). MS:Warning: message not found [myappAppDelegate applicationWillResignActive:] MS:Warning: message not found [myappAppDelegate applicationDidBecomeActive:] 2010-03-19 15:57:19.550 myapp[2338:207] in FirstViewController 2010-03-19 15:57:20.344 myapp[2338:207] in load table view 2010-03-19 15:57:20.478 myapp[2338:207] in loading splash view 2010-03-19 15:57:22.793 myapp[2338:207] in set interface Program received signal: “0”. warning: check_safe_call: could not restore current frame

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• What is the best (Windows) program launcher?

  - by AR

  One of the biggest general productivity boosters I've used is a good program launcher. I was a long-time user of SlickRun, and I've tried a few others. My current favorite is Executor - by far the best I've used. Other options: Executor: My current favorite Vista Start Menu: Pretty good, actually, but Executor is similar (binds to Win+Z) and much more flexible. Quicksilver: For Macs only, but it seems to be the gold standard against which most other launchers are measured. Google Desktop: Press Ctrl+Ctrl and it's a quick launcher! AutoHotKey: Much,much more than just a launcher - more than I need, really. SlickRun: simple and unobtrusive Launchy: Seems to be the launcher of choice for many StackOverflow users :) Colibri: "Type Ahead - Information at the tip of your wings". Quite a cool concept. Many, many others. Scott Hanselman outlines some more here. I realize that everyone will have their own preferences, but the question is: is there anything that really stands out in terms of speed, features, and especially productivity increase?

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• Database PK-FK design for future-effective-date entries?

  - by Scott Balmos

  Ultimately I'm going to convert this into a Hibernate/JPA design. But I wanted to start out from purely a database perspective. We have various tables containing data that is future-effective-dated. Take an employee table with the following pseudo-definition: employee id INT AUTO_INCREMENT ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Very simplistic. But let's say Employee A has id = 1, effectiveFrom = 1/1/2011, effectiveTo = 1/1/2099. That employee is going to be changing jobs in the future, which would in theory create a new row, id = 2 with effectiveFrom = 7/1/2011, effectiveTo = 1/1/2099, and id = 1's effectiveTo updated to 6/30/2011. But now, my program would have to go through any table that has a FK relationship to employee every night, and update those FK to reference the newly-effective employee entry. I have seen various postings in both pure SQL and Hibernate forums that I should have a separate employee_versions table, which is where I would have all effective-dated data stored, resulting in the updated pseudo-definition below: employee id INT AUTO_INCREMENT employee_versions id INT AUTO_INCREMENT employee_id INT FK employee.id ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Then to get any actual data, one would have to actually select from employee_versions with the proper employee_id and date range. This feels rather unnatural to have this secondary "versions" table for each versioned entity. Anyone have any opinions, suggestions from your own prior work, etc? Like I said, I'm taking this purely from a general SQL design standpoint first before layering in Hibernate on top. Thanks!

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• Tools for debugging when debugger can't get you there?

  - by brian1001

  I have a fairly complex (approx 200,000 lines of C++ code) application that has decided to crash, although it crashes a little differently on a couple of different systems. The trick is that it doesn't crash or trap out in debugger. It only crashes when the application .EXE is run independently (either the debug EXE or the release EXE - both behave the same way). When it crashes in the debug EXE, and I get it to start debugging, the call stack is buried down into the windows/MFC part of things, and isn't reflecting any of my code. Perhaps I'm seeing a stack corruption of some sort, but I'm just not sure at the moment. My question is more general - it's about tools and techniques. I'm an old programmer (C and assembly language days), and a relative newcomer (couple/few years) to C++ and Visual Studio (2003 for this projecT). Are there tricks or techniques anyone's had success with in tracking down crashing issues when you cannot make the software crash in a debugger session? Stuff like permission issues, for example? The only thing I've thought of is to start plugging in debug/status messages to a logfile, but that's a long, hard way to go. Been there, done that. Any better suggestions? Am I missing some tools that would help? Is VS 2008 better for this kind of thing? Thanks for any guidance. Some very smart people here (you know who you are!). cheers.

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• Learning Java and logic using debugger. Did I cheat?

  - by centr0

  After a break from coding in general, my way of thinking logically faded (as if it was there to begin with...). I'm no master programmer. Intermediate at best. I decided to see if i can write an algorithm to print out the fibonacci sequence in Java. I got really frustrated because it was something so simple, and used the debugger to see what was going on with my variables. solved it in less than a minute with the help of the debugger. Is this cheating? When I read code either from a book or someone else's, I now find that it takes me a little more time to understand. If the alghorithm is complex (to me) i end up writing notes as to whats going on in the loop. A primitive debugger if you will. When you other programmers read code, do you also need to write things down as to whats the code doing? Or are you a genius and and just retain it?

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• Worpress WorkFlow Modfications

  - by blgnklc

  Hi All WordPress Lovers, I would like to ask a help about Zensor which is a plugin that you publish a post then a moderator approves the post to be published on the wordpress blog site. When a post is awating for approval, each awaiting post is appearing "waiting moderation". But, I dont want any link appears before moderator approval. Actually I found the joing sentence below; 1- Must be added to the end of JOIN part of any query: LEFT JOIN wp_zensor ON ID = wp_zensor.post_id 2- Must be added to the end of WHERE condition : AND wp_zensor.moderation_status = 'approved' Could you please show me; where should I add these modification on the category link presentation below: <h2>Politics</h2> <?php $recent = new WP_Query("cat=31&showposts=1"); while($recent->have_posts()) : $recent->the_post();?> <b><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></b> <?php the_content_limit(140, "devami &raquo;"); ?> <div class="hppostmeta"> <p><?php the_time('j F Y, H:i'); ?> | <?php the_author_posts_link(); ?></p> </div> <?php endwhile; ?> Or any general solutions will be welcomed. Thanks. BK

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• Java Equivalent of C++ .dll?

  - by Matt D

  So, I've been programming for a while now, but since I haven't worked on many larger, modular projects, I haven't come across this issue before. I know what a .dll is in C++, and how they are used. But every time I've seen similar things in Java, they've always been packaged with source code. For instance, what would I do if I wanted to give a Java library to someone else, but not expose the source code? Instead of the source, I would just give a library as well as a Javadoc, or something along those lines, with the public methods/functions, to another programmer who could then implement them in their own Java code. For instance, if I wanted to create a SAX parser that could be "borrowed" by another programmer, but (for some reason--can't think of one in this specific example lol) I don't want to expose my source. Maybe there's a login involved that I don't want exploited--I don't know. But what would be the Java way of doing this? With C++, .dll files make it much easier, but I have never run into a Java equivalent so far. (I'm pretty new to Java, and a pretty new "real-world" programmer, in general as well)

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• Problem with Java FX Look and Feel

  - by drachenfels

  Hi, I was looking at some of the examples from the Deitel and Deitel's book for Programming in Java, and one of the first examples is a very simple Swing display. Hence this snippet of code : import javax.swing.*; public class cdea { public static void main(String args[]){ JOptionPane.showMessageDialog(null,"\"Welcome to Java Programming!\""); System.exit(0); //end method main } } I read some stuff regarding how one can get native UI look and feel by using UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName()); to the program. However, when I just add this to my main method, it gives me a host of errors. Specifically : Multiple markers at this line - Unhandled exception type IllegalAccessException - Unhandled exception type InstantiationException - Unhandled exception type ClassNotFoundException - Unhandled exception type UnsupportedLookAndFeelException However when I use it as part of a try/catch exception loop (is that what it is called?) as detailed on http://stackoverflow.com/questions/1590863/getting-java-applications-to-look-native-on-windows-how , I get the program running properly. Could anyone tell me in simple language why this is so? As in, why can't I directly get the System look and feel; why do I have to use it with exception handling? I'm new to Java, and OOP in general, so I'm sorry if I'm being too simplistic.

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• iPhone settings not honoured

  - by winsmith

  My iPhone app has the following problem: Freshly installed, when I read out my "Play Sound" preference with the following code: defaults = [NSUserDefaults standardUserDefaults]; NSLog(@"Play Sounds? %d", [defaults boolForKey:@"play_sounds_preference"]); The setting always reads out as false, even though the default setting is set to true. Any ideas? Here is my Root.plist: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>StringsTable</key> <string>Root</string> <key>PreferenceSpecifiers</key> <array> <dict> <key>Type</key> <string>PSGroupSpecifier</string> <key>Title</key> <string>General Settings</string> </dict> <dict> <key>Type</key> <string>PSToggleSwitchSpecifier</string> <key>Title</key> <string>Sounds</string> <key>Key</key> <string>play_sounds_preference</string> <key>DefaultValue</key> <true/> </dict> </array> </dict> </plist> When the user opens the Settings.app and navigates to my app's name, THEN the setting reads out as true, even if the user doesn't change anything.

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• Solving problems with near infinite potential solutions

  - by Zonda333

  Today I read the following problem: Use the digits 2, 0, 1, 1 and the operations +, -, x, ÷, sqrt, ^ , !, (), combinations, and permutations to write equations for the counting numbers 1 through 100. All four digits must be used in each expression. Only the digits 2, 0, 1, 1 may be used, and each must be used exactly once. Decimals may be used, as in .1, .02, etc. Digits may be combined; numbers such as 20 or 101 may be used. Example: 60 = 10*(2+1)!, 54 = ¹¹C2 - 0! Though I was able to quickly find around 50 solutions quite easily in my head, I thought programming it would be a far superior solution. However, I then realized I had no clue how to go about solving a problem like this. I am not asking for complete code for me to copy and paste, but for ideas about how I would solve this problems, and others like it that have nearly infinite potential solutions. As I will be writing it in python, where I have the most experience, I would prefer if the answers were more python based, but general ideas are great too.

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• Practice of checking 'trueness' or 'equality' of conditional statements - does it really make sense?

  - by senthilkumar1033

  I remember many years back, when I was in school, one of my computer science teachers taught us that it was better to check for 'trueness' or 'equality' of a condition and not the negative stuff like 'inequality'. Let me elaborate - If a piece of conditional code can be written by checking whether an expression is true or false, we should check the 'trueness'. Example: Finding out whether a number is odd - it can be done in two ways: if ( num % 2 != 0 ) { // Number is odd } or if ( num % 2 == 1 ) { // Number is odd } When I was beginning to code, I knew that num % 2 == 0 implies the number is even, so I just put a ! there to check if it is odd. But he was like 'Don't check NOT conditions. Have the practice of checking the 'trueness' or 'equality' of conditions whenever possible.' And he recommended that I use the second piece of code. I am not for or against either but I just wanted to know - what difference does it make? Please don't reply 'Technically the output will be the same' - we ALL know that. Is it a general programming practice or is it his own programming practice that he is preaching to others?

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• Exception thrown when creating database

  - by Bob

  For some reason, I can't get embedded firebird sql to work on Windows using C#/.NET. Here's my code: string BuildConnectionString() { FbConnectionStringBuilder builder = new FbConnectionStringBuilder(); builder.DataSource = "localhost"; builder.UserID = "SYSDBA"; builder.Password = "masterkey"; builder.Database = "database.fdb"; builder.ServerType = FbServerType.Embedded; return builder.ConnectionString; } private void OnConnectClicked(object sender, EventArgs e) { string cString = BuildConnectionString(); FbConnection.CreateDatabase( cString ); FbConnection connection = new FbConnection( cString ); connection.Open(); //CreateTable(); //FillListView(); connection.Close(); } When I call FbConnection.CreateDatabase, I get the following exception: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B) I'm very new to SQL and Firebird in general, so I'm not sure how to resolve this issue. Anyone?

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• Access to SQL Server 2005 from a non-domain machine using Windows authentication

  - by user304582

  Hi, I have a Windows domain within which a machine is running SQL Server 2005 and which is configured to support only Windows authentication. I would like to run a C# client application on a machine on the same network, but which is NOT on the domain, and access a database on the SQL Server 2005 instance. I thought that it would be a simple matter of doing something like this: string connectionString = "Data Source=server;Initial Catalog=database;User Id=domain\user;Password=password"; SqlConnection connection = new SqlConnection(connectionString); connection.Open(); However, this fails: the client-side error is: System.Data.SqlClient.SqlException: Login failed for user 'domain\user' and the server-side error is: Error 18456, Severity 14, State 5 I have tried various things including setting integrated security to true and false, and \ instead of \ in the User Id, but without success. In general, I know that it possible to connect to the SQL Server 2005 instance from a non-domain machine (for example, I am working with a Linux-based application which happily does this), but I don't seem to be able to work out how to do it from a Windows machine. Help would be appreciated! Thanks, Martin

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• How to track a projects extraneous quirks

  - by Steerpike

  Hello, It's possible that the answer to this question may just be standard bug tracking software like jira or fogbugz, but I'm kind of hoping someone out there knows a better system for what I'm describing. My most current project is requiring a lot of setup quirkiness to get into a position where I can actually start a coding section. For example: A series of convoluted internal company commands before I can insitgate an SSH. Making sure any third party classes that make external calls have internal company proxy options setup - while also making sure these setting wont be set up when installed on a production environment Making sure the proxy is set before trying to install pear packages. Other similar things, mostly involving internal IT security and getting it to work with modules and packages. Individually none of these things is a huge deal, and I've written extensive notes to myself regarding exact commands and aditions I've made, but they're currently in a general text document and it's going to be hard to remember exactly where what I need is far down the line. We also have several new staff starting soon and I' rather give them an easier time of setting up their programming environments. Like I said, they aren't 'programming quirks' exactly, but just the constant fiddling that comes about before programming starts in earnest. Any thoughts on the best way to documents these things for my own and future generations sanity?

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• Is Maven really flexible?

  - by Dima

  I understand how Maven works with .java files in src/java/main. But may it be used for a more general case? Let us put it more abstract: Suppose I already have some a.exe that read some (not necessarily only .java) sources from directories A1, A2, A3 and puts some files (maybe some are generated .java) to directories B1, B2. I also have some b.exe that currently reads files from B1, B2, B3 and generates something else. Some more similar steps. (A real life problem stands behind). I would like to right POM.xml file so that maven will do this work. Is that possible? I assume that a.exe and b.exe should be warped as maven plugings. Next, in Maven docs I see : <build> <sourceDirectory>${basedir}/src/main/java</sourceDirectory> <scriptSourceDirectory>${basedir}/src/main/scripts</scriptSourceDirectory> <testSourceDirectory>${basedir}/src/test/java</testSourceDirectory> <outputDirectory>${basedir}/target/classes</outputDirectory> <testOutputDirectory>${basedir}/target/test-classes</testOutputDirectory> ... </build> What bothers me is that "sourceDirectory" looks by itself as a hard coded name. Will Maven accept A1 and A2 tags instead?

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• How can I compare the performance of log() and fp division in C++?

  - by Ventzi Zhechev

  Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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• How costly performance-wise are these actions in iPhone objective-C?

  - by Alex Gosselin

  This is really a few questions in one, I'm wondering what the performance cost is for these things, as I haven't really been following a best practice of any sort for these. The answers may also be useful to other readers, if somebody knows these. (1) If I need the core data managed object context, is it bad to use #import "myAppDelegate.h" //farther down in the code: NSManagedObjectContext *context = [(myAppDelegate.h*)[[UIApplication sharedApplication] delegate] managedObjectContext]; as opposed to leaving the warning you get if you don't cast the delegate? (2) What is the cheapest way to hard-code a string? I have been using return @"myString"; on occasion in some functions where I need to pass it to a variety of places, is it better to do it this way: static NSString *str = @"myString"; return str; (3) How costly is it to subclass an object i wrote vs. making a new one, in general? (4) When I am using core data and navigating through a hierarchy of some sort, is it necessary to turn things back into faults somehow after I read some info from them? or is this done automatically? Thanks for any help.

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