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  • Interview Question in C#

    - by amutha
    A Technical Lead asked me that ,he created a class,he declared object and initialized it.But some circumstance we may get "null reference" exception.He explained there are 1000 reasons for that and asked me to tell a single reason.I am unable to figure it out. What the reason(s) ,we may get such exception?

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  • Redis, it's memory limit and persistance question?

    - by Kirzilla
    Hello, I'm rather new to Redis and before using it I'd like to learn some important (as for me) details on it. So.... Redis is using RAM and HDD for storing data. RAM is used as fast read/write storage, HDD is used to make this data persistant. When Redis is started it loads all data from HDD to RAM or it loads only often queried data to the RAM? What if I have 500Mb Redis storage on HDD, but I have only 100Mb or RAM for Redis. Where can I read about it? Thank you PS: Sorry for my English

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  • Mercurial hg add question

    - by rahulchandran
    I typed in hg add and I am brand new to mercurial and the result of this was a bunch of dll's exe's pdb's etc all got added Nothing's been committed yet and I basically want to undo the add. the documentation for hg forget is not very clear not sure if that is want I want How do I undo the add before the next commit I do have some real files that need adding so after I can undo the add I will use add with the exclude flag Thanks

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  • notification scheduling question

    - by sims
    Hi Stackers! I'm building an app that needs to send out notifications to users depending on user definable "notifications". So the notifications are not per event. They are arbitrary. A cron job should query the database and send out emails when it finds an event with matching criterion. The is a scheduling app. So naturally, one of the criterion is time. I think I've figured it out, but I'm sure there are better ideas out there as it seems to be a fairly common thing to do. I think I'll limit the users ability to "minutes before hand" to get notified as opposed to seconds or hours. So I have an eventA and notificationA. notificationA should be triggered if an event is due within 45 minutes. So eventA starts at 17:30. The user should be notified at 16:45. But the cron job might not run exactly at 00 seconds. So when the difference is not 45 minutes and 0 seconds it is, say, 45 minutes and 5 seconds. Notification time is past. Email doesn't get sent. User misses event. Shugar. We should also take into account that the cron job might take a long time to run. So maybe we should only trigger it every 5 minutes. So we need a bigger interval maybe. So then my guess would be to say that: if ((eventDueTime - now notificationTimeValue - interval) && (eventDueTime - now < notificationTimeValue + interval)) sendTheFrikinNotificationAlready(); It seems kind of risky if the there are thousands of notifications to send out. I guess I could make a thread for each notification and then a thread for each event that matches the criterion. That might help. Does that make sense? Any other ideas? Thanks!

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  • NIS password mapping question

    - by papoyan
    I have NIS server with user "techsupport", which has uid/gid = 517 I've configured NIS and NFS on that server, as well as NFS/NIS client on the remote web server. Now I need to techsupport user to be able to login to web server using techsupport username, but HAVE root privileges. I need this, so I can easily track, which support agent doing what on the web server. Everything works fine, when from NIS server, I ssh to the web server with tech support user nisserver# ssh [email protected] I can authenticate against the NIS server just fine, and my home directory that is on NIS server, get's mounted on web server just fine. The Only two problems I have are : my GID on web server is webserver# id uid=517(techsupport) gid=517(client_jonny) groups=517(client_jonny) (as you can see, that it picked up gid of a client that exists on the web server, since it's same number) I need to make sure, that my "techsupport" user has ROOT privileges. How can I achieve this? I remember that I've seen identical results elsewhere, but LDAP was used, is there a way to achieve this with NIS/NFS setup? Thank you in advance,

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  • newbie question: how to show a drop down menu with this function

    - by Mellon
    My model object (e.g. MyObject) has one property (e.g. color), the "color" property holds a string value which comes from a list of string (e.g. colors=['red','yellow', 'black']). now, I have one instance of myObject get from database and show on the view page in a row, I need to show the 'color' property of myObject in a drop down menu with the current value as the default selected. How to implement this in Rails 3 in my view page. (Later, when user select from the dropdown menu, the object will be updated in DB based on user's selection) Please explain with instance "myObject" and list "colors=[...]"

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  • Python form POST using urllib2 (also question on saving/using cookies)

    - by morpheous
    I am trying to write a function to post form data and save returned cookie info in a file so that the next time the page is visited, the cookie information is sent to the server (i.e. normal browser behavior). I wrote this relatively easily in C++ using curlib, but have spent almost an entire day trying to write this in Python, using urllib2 - and still no success. This is what I have so far: import urllib, urllib2 import logging # the path and filename to save your cookies in COOKIEFILE = 'cookies.lwp' cj = None ClientCookie = None cookielib = None logger = logging.getLogger(__name__) # Let's see if cookielib is available try: import cookielib except ImportError: logger.debug('importing cookielib failed. Trying ClientCookie') try: import ClientCookie except ImportError: logger.debug('ClientCookie isn\'t available either') urlopen = urllib2.urlopen Request = urllib2.Request else: logger.debug('imported ClientCookie succesfully') urlopen = ClientCookie.urlopen Request = ClientCookie.Request cj = ClientCookie.LWPCookieJar() else: logger.debug('Successfully imported cookielib') urlopen = urllib2.urlopen Request = urllib2.Request # This is a subclass of FileCookieJar # that has useful load and save methods cj = cookielib.LWPCookieJar() login_params = {'name': 'anon', 'password': 'pass' } def login(theurl, login_params): init_cookies(); data = urllib.urlencode(login_params) txheaders = {'User-agent' : 'Mozilla/4.0 (compatible; MSIE 5.5; Windows NT)'} try: # create a request object req = Request(theurl, data, txheaders) # and open it to return a handle on the url handle = urlopen(req) except IOError, e: log.debug('Failed to open "%s".' % theurl) if hasattr(e, 'code'): log.debug('Failed with error code - %s.' % e.code) elif hasattr(e, 'reason'): log.debug("The error object has the following 'reason' attribute :"+e.reason) sys.exit() else: if cj is None: log.debug('We don\'t have a cookie library available - sorry.') else: print 'These are the cookies we have received so far :' for index, cookie in enumerate(cj): print index, ' : ', cookie # save the cookies again cj.save(COOKIEFILE) #return the data return handle.read() # FIXME: I need to fix this so that it takes into account any cookie data we may have stored def get_page(*args, **query): if len(args) != 1: raise ValueError( "post_page() takes exactly 1 argument (%d given)" % len(args) ) url = args[0] query = urllib.urlencode(list(query.iteritems())) if not url.endswith('/') and query: url += '/' if query: url += "?" + query resource = urllib.urlopen(url) logger.debug('GET url "%s" => "%s", code %d' % (url, resource.url, resource.code)) return resource.read() When I attempt to log in, I pass the correct username and pwd,. yet the login fails, and no cookie data is saved. My two questions are: can anyone see whats wrong with the login() function, and how may I fix it? how may I modify the get_page() function to make use of any cookie info I have saved ?

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  • Objective-C Array/List Question

    - by Dave C
    What is the best practice, even in general programming, when you have an undefined, possibly infinite, amount of items that you need in an array but don't have defined bounds. Can you define an endless array in objective c that you can keep pushing items onto, like other lanaguages have a list item. Thanks for any help.

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  • C# LINQ question, Why need new here?

    - by 5YrsLaterDBA
    Why we need the new in the select statement on one of them? var runs = from sampleDataTable in db.SampleData from sampleInfoTable in db.SampleInfo where sampleDataTable.SampleInfo.SampleInfoId == sampleInfoTable.SampleInfoId select new {sampleDataTable.Timestamp, sampleDataTable.SampleDataId, sampleInfoTable.Lane} ; and var runs2 = from sampleDataTable in db.SampleData from sampleInfoTable in db.SampleInfo where sampleDataTable.SampleInfo.SampleInfoId == sampleInfoTable.SampleInfoId && sampleDataTable.Timestamp == timestamp select sampleInfoTable.Lane;

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  • mdadm raid5 recover double disk failure - with a twist (drive order)

    - by Peter Bos
    Let me acknowledge first off that I have made mistakes, and that I have a backup for most but not all of the data on this RAID. I still have hope of recovering the rest of the data. I don't have the kind of money to take the drives to a recovery expert company. Mistake #0, not having a 100% backup. I know. I have a mdadm RAID5 system of 4x3TB. Drives /dev/sd[b-e], all with one partition /dev/sd[b-e]1. I'm aware that RAID5 on very large drives is risky, yet I did it anyway. Recent events The RAID become degraded after a two drive failure. One drive [/dev/sdc] is really gone, the other [/dev/sde] came back up after a power cycle, but was not automatically re-added to the RAID. So I was left with a 4 device RAID with only 2 active drives [/dev/sdb and /dev/sdd]. Mistake #1, not using dd copies of the drives for restoring the RAID. I did not have the drives or the time. Mistake #2, not making a backup of the superblock and mdadm -E of the remaining drives. Recovery attempt I reassembled the RAID in degraded mode with mdadm --assemble --force /dev/md0, using /dev/sd[bde]1. I could then access my data. I replaced /dev/sdc with a spare; empty; identical drive. I removed the old /dev/sdc1 from the RAID mdadm --fail /dev/md0 /dev/sdc1 Mistake #3, not doing this before replacing the drive I then partitioned the new /dev/sdc and added it to the RAID. mdadm --add /dev/md0 /dev/sdc1 It then began to restore the RAID. ETA 300 mins. I followed the process via /proc/mdstat to 2% and then went to do other stuff. Checking the result Several hours (but less then 300 mins) later, I checked the process. It had stopped due to a read error on /dev/sde1. Here is where the trouble really starts I then removed /dev/sde1 from the RAID and re-added it. I can't remember why I did this; it was late. mdadm --manage /dev/md0 --remove /dev/sde1 mdadm --manage /dev/md0 --add /dev/sde1 However, /dev/sde1 was now marked as spare. So I decided to recreate the whole array using --assume-clean using what I thought was the right order, and with /dev/sdc1 missing. mdadm --create /dev/md0 --assume-clean -l5 -n4 /dev/sdb1 missing /dev/sdd1 /dev/sde1 That worked, but the filesystem was not recognized while trying to mount. (It should have been EXT4). Device order I then checked a recent backup I had of /proc/mdstat, and I found the drive order. md0 : active raid5 sdb1[0] sde1[4] sdd1[2] sdc1[1] 8790402048 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU] I then remembered this RAID had suffered a drive loss about a year ago, and recovered from it by replacing the faulty drive with a spare one. That may have scrambled the device order a bit...so there was no drive [3] but only [0],[1],[2], and [4]. I tried to find the drive order with the Permute_array script: https://raid.wiki.kernel.org/index.php/Permute_array.pl but that did not find the right order. Questions I now have two main questions: I screwed up all the superblocks on the drives, but only gave: mdadm --create --assume-clean commands (so I should not have overwritten the data itself on /dev/sd[bde]1. Am I right that in theory the RAID can be restored [assuming for a moment that /dev/sde1 is ok] if I just find the right device order? Is it important that /dev/sde1 be given the device number [4] in the RAID? When I create it with mdadm --create /dev/md0 --assume-clean -l5 -n4 \ /dev/sdb1 missing /dev/sdd1 /dev/sde1 it is assigned the number [3]. I wonder if that is relevant to the calculation of the parity blocks. If it turns out to be important, how can I recreate the array with /dev/sdb1[0] missing[1] /dev/sdd1[2] /dev/sde1[4]? If I could get that to work I could start it in degraded mode and add the new drive /dev/sdc1 and let it resync again. It's OK if you would like to point out to me that this may not have been the best course of action, but you'll find that I realized this. It would be great if anyone has any suggestions.

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  • Objective-C respondsToSelector question.

    - by Holli
    From what I have learned so far: In Objective-C you can send any message to any object. If the object does implement the right method it will be executed otherwise nothing will happen. This is because before the message is send Objective-C will perform respondsToSelector. I hope I am right so far. I did a little program for testing where an action is invoked every time a slider is moved. Also for testing I set the sender to NSButton but in fact it is an NSSlider. Now I asked the object if it will respond to setAlternateTitle. While a NSButton will do and NSSlider will not. If I run the code and do respondsToSelector myself it will tell me the object will not respond to that selector. If I test something else like intValue, it will respond. So my code is fine so far. - (IBAction)sliderDidMove:(id)sender { NSButton *slider = sender; BOOL responds = [slider respondsToSelector:@selector(setAlternateTitle)]; if(responds == YES) { NSLog(@"YES"); } else { NSLog(@"NO"); } [slider setAlternateTitle:@"Hello World"]; } But when I actually send the setAlternateTitle message the program will crash and I am not exactly sure why. Shouldn't it do a respondsToSelector before sending the message?

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  • question about InnoDB deadlock in MySQL?

    - by WilliamLou
    I found this kind of interesting problem in MySQL InnoDB engine, could anyone explain why the engine always claim it's a deadlock. First, I created a table with a single row, single column: CREATE TABLE `SeqNum` (`current_seq_num` bigint(30) NOT NULL default '0', PRIMARY KEY (`current_seq_num`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | Now, I have two MySQL connector threads, In thread1: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; Query OK, 1 row affected (0.00 sec) Now, in thread2, I did the exactly same: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; before the default innodb_lock_wait_timeout, the thread2 just wait for thread1 to release its exclusive lock on the table, and it's normal. However, in thread1, if I input the following update query: mysql> update SeqNum set `current_seq_num` = 8; ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction Now, thread2 get the select query finished because thread1 quits. In addition, in thread1, if I input the update query with a where clause, it can be executed very well: mysql> update SeqNum set `current_seq_num` = 8 where `current_seq_num` =5 Query OK, 1 row affected (0.00 sec) Could anyone explain this?

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  • Question How to integrate SQL Server Express with VS C# Express

    - by paul
    I have just installed VS C# Express 2008 which includes SQL Server Express 2008. It all went ok and I can see VS C# and SQL Server in the list of installed products. When I start VS C# it looks fine but in the DB Explorer / Data Conection context menu the option 'Create new SQL Server Database' is disabled. I have uninstalled all VS products and reinstalled but the problem remains. Do I need to do anything else? Can anyone help? Thanks

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  • Apostrophe turning to question mark when using php handler in .htaccess

    - by Tony Deefer
    I have a .htm page on a site, that for reasons I won't go into cannot be renamed .php I have added some php code to the top of the page, (sets a cookie and redirects to another page) and added the following to .htaccess to parse the .htm file as php AddHandler application/x-httpd-php5 .html .htm As soon as this is added to .htaccess all apostrophe's change into questions marks. Using charset UTF-8 Can anyone offer a solution that does not involve renaming the file .php? Many thanks

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  • vim: wrap question

    - by remio
    I would like to wrap the text 5 characters before the end of window (without breacking the line). I don't know how to do this without putting an EOL character in the text (wrapmargin/textwidth).

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  • Regex question: Why isn't this matching?

    - by AllenG
    I have the following regex: (?<=\.\d+?)0+(?=\D|$) I'm running it against a string which contains the following: SVC~NU^0270~313.3~329.18~~10~~6.00: When it runs, it matches the 6.00 (correctly) which my logic then trims by one zero to turn into 6.0. The regex then runs again (or should) but fails to pick up the 6.0. I'm by no means an expert on Regex, but my understanding of my expression is that it's looking for a decimal with 1 or more optional (so, really zero or more) digits prior to one or more zeros which are then followed by any non-digit character or the line break. Assuming that interpretation is correct, I can't see why it wouldn't match on the second pass. For that matter, I'm not sure why my Regex.Replace isn't matching the full 6.00 on the first pass and removing both of the trailing zeros... Any suggestions?

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  • Public-facing SharePoint 2007 portal - authentication question

    - by jdcorr
    I am involved in developing a portal with a public-facing side. For this i created a web application with windows authentication for intranet zone and after that, I created an extension for an internet zone with fba. In the internet extension we have the following requirement: - able to acess to sharepoint backoffice using fba. - have a authentication mecanism for portal visitors, where they can authenticate and acess to a page where they can subscribe the newsletter and define some site appearance (this users can't acess to sharepoint backoffice). My idea is use the aspnet membership provider to authenticate both users and create diferente roles for them. Anyone suggests another approach? Is there any way to ensure that visitors (2 case) do not enter the backoffice portal? Thanks

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  • An important question on iPhone file writing

    - by Kyle
    I use the NSHomeDirectory() function to get the app's home folder, and write to the Documents directory within that. I'm curious, though, what happens when the user downloads an update for the app in the appstore? Will it all be deleted? When I delete the app on the device, then reinstall it, its wiped out. So, I'm curious to know what will happen with an update. I can't find this in the documentation at all. Thanks alot for reading. I really tried to find this asked somewhere else first, but couldn't. Hopefully this page will be informative to guys like me who are confused on the subject.

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  • Core Location question....

    - by Moshe
    This tutorial on mobileorchard.com uses 2 classes (or 2 sets of .h and .m) to implement core location. Can I just use everything there in my existing class? How would I do that? Also, is the - (id) init { self = [super init]; if (self != nil) { self.locationManager = [[[CLLocationManager alloc] init] autorelease]; self.locationManager.delegate = self; // send loc updates to myself } return self; } method the same as the usual initWithNib? I;m trying to quickly implement something based on location information. As much help describing the above linked tutorial would be helpful. Thanks. No - really, Thank You.

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  • Simple css question - sticky footers, etc.

    - by Elliot
    So I used the example for sticky footers from: http://ryanfait.com/sticky-footer/ It worked great, except for one thing - when content in my main div gets too long, it overlaps the footer, rather than pushing it down the page. Any suggestions? Thanks! Elliot

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  • NHibernate criteria query question

    - by Chris
    I have 3 related objects (Entry, GamePlay, Prize) and I'm trying to find the best way to query them for what I need using NHibernate. When a request comes in, I need to query the Entries table for a matching entry and, if found, get a) the latest game play along with the first game play that has a prize attached. Prize is a child of GamePlay and each Entry object has a GamePlays property (IList). Currently, I'm working on a method that pulls the matching Entry and eagerly loads all game plays and associated prizes, but it seems wasteful to load all game plays just to find the latest one and any that contain a prize. Right now, my query looks like this: var entry = session.CreateCriteria<Entry>() .Add(Restrictions.Eq("Phone", phone)) .AddOrder(Order.Desc("Created")) .SetFetchMode("GamePlays", FetchMode.Join) .SetMaxResults(1).UniqueResult<Entry>(); Two problems with this: It loads all game plays up front. With 365 days of data, this could easily balloon to 300k of data per query. It doesn't eagerly load the Prize child property for each game. Therefore, my code that loops through the GamePlays list looking for a non-null Prize must make a call to load each Prize property I check. I'm not an nhibernate expert, but I know there has to be a better way to do this. Ideally, I'd like to do the following (pseudocode): entry = findEntry(phoneNumber) lastPlay = getLatestGamePlay(Entry) firstWinningPlay = getFirstWinningGamePlay(Entry) The end result of course is that I have the entry details, the latest game play, and the first winning game play. The catch is that I want to do this in as few database calls as possible, otherwise I'd just execute 3 separate queries. The object definitions look like: public class Entry { public Guid Id {get;set;} public string Phone {get;set;} public IList<GamePlay> GamePlays {get;set;} // ... other properties } public class GamePlay { public Guid Id {get;set;} public Entry Entry {get;set;} public Prize Prize {get;set;} // ... other properties } public class Prize { public Guid Id {get;set;} // ... other properties } The proper NHibernate mappings are in place, so I just need help figuring out how to set up the criteria query (not looking for HQL, don't use it).

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