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  • Can a stack have an exception safe method for returning and removing the top element with move seman

    - by Motti
    In an answer to a question about std::stack::pop() I claimed that the reason pop does not return the value is for exception safety reason (what happens if the copy constructor throws). @Konrad commented that now with move semantics this is no longer relevant. Is this true? AFAIK, move constructors can throw, but perhaps with noexcept it can still be achieved. For bonus points what thread safety guarantees can this operation supply?

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • Reading Data from DDFS ValueError: No JSON object could be decoded

    - by secumind
    I'm running dozens of map reduce jobs for a number of different purposes using disco. My data has grown enormous and I thought I would try using DDFS for a change rather than standard txt files. I've followed the DISCO map/reduce example Counting Words as a map/reduce job, without to much difficulty and with the help of others, Reading JSON specific data into DISCO I've gotten past one of my latest problems. I'm trying to read data in/out of ddfs to better chunk and distribute it but am having a bit of trouble. Here's an example file: file.txt {"favorited": false, "in_reply_to_user_id": null, "contributors": null, "truncated": false, "text": "I'll call him back tomorrow I guess", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": null, "coordinates": null, "in_reply_to_user_id_str": null, "entities": {"user_mentions": [], "hashtags": [], "urls": []}, "in_reply_to_status_id": null, "id_str": "168931016843603968", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/305726905/FASHION-3.png", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1818996723/image_normal.jpg", "profile_sidebar_fill_color": "292727", "is_translator": false, "id": 113532729, "profile_text_color": "000000", "followers_count": 78, "protected": false, "location": "With My Niggas In Paris!", "default_profile_image": false, "listed_count": 0, "utc_offset": -21600, "statuses_count": 6733, "description": "Made in CHINA., Educated && Making My Own $$. Fear GOD && Put Him 1st. #TeamFollowBack #TeamiPhone\n", "friends_count": 74, "profile_link_color": "b03f3f", "profile_image_url": "http://a2.twimg.com/profile_images/1818996723/image_normal.jpg", "notifications": null, "show_all_inline_media": false, "geo_enabled": true, "profile_background_color": "1f9199", "id_str": "113532729", "profile_background_image_url": "http://a3.twimg.com/profile_background_images/305726905/FASHION-3.png", "name": "Bee'Jay", "lang": "en", "profile_background_tile": true, "favourites_count": 19, "screen_name": "OohMyBEEsNice", "url": "http://www.bitchimpaid.org", "created_at": "Fri Feb 12 03:32:54 +0000 2010", "contributors_enabled": false, "time_zone": "Central Time (US & Canada)", "profile_sidebar_border_color": "000000", "default_profile": false, "following": null}, "in_reply_to_screen_name": null, "retweet_count": 0, "geo": null, "id": 168931016843603968, "source": "<a href=\"http://twitter.com/#!/download/iphone\" rel=\"nofollow\">Twitter for iPhone</a>"} {"favorited": false, "in_reply_to_user_id": 50940453, "contributors": null, "truncated": false, "text": "@LegaMrvica @MimozaBand makasi om artis :D kadoo kadoo", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": "168653037894770688", "coordinates": null, "in_reply_to_user_id_str": "50940453", "entities": {"user_mentions": [{"indices": [0, 11], "screen_name": "LegaMrvica", "id": 50940453, "name": "Lega_thePianis", "id_str": "50940453"}, {"indices": [12, 23], "screen_name": "MimozaBand", "id": 375128905, "name": "Mimoza", "id_str": "375128905"}], "hashtags": [], "urls": []}, "in_reply_to_status_id": 168653037894770688, "id_str": "168931016868761600", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/347686061/Galungan_dan_Kuningan.jpg", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1803845596/Picture_20124_normal.jpg", "profile_sidebar_fill_color": "DDFFCC", "is_translator": false, "id": 48293450, "profile_text_color": "333333", "followers_count": 182, "protected": false, "location": "\u00dcT: -6.906799,107.622383", "default_profile_image": false, "listed_count": 0, "utc_offset": -28800, "statuses_count": 3052, "description": "Fashion design maranatha '11 // traditional dancer (bali) at sanggar tampak siring & Natya Nataraja", "friends_count": 206, "profile_link_color": "0084B4", "profile_image_url": "http://a3.twimg.com/profile_images/1803845596/Picture_20124_normal.jpg", "notifications": null, "show_all_inline_media": false, "geo_enabled": true, "profile_background_color": "9AE4E8", "id_str": "48293450", "profile_background_image_url": "http://a0.twimg.com/profile_background_images/347686061/Galungan_dan_Kuningan.jpg", "name": "nana afiff", "lang": "en", "profile_background_tile": true, "favourites_count": 2, "screen_name": "hasnfebria", "url": null, "created_at": "Thu Jun 18 08:50:29 +0000 2009", "contributors_enabled": false, "time_zone": "Pacific Time (US & Canada)", "profile_sidebar_border_color": "BDDCAD", "default_profile": false, "following": null}, "in_reply_to_screen_name": "LegaMrvica", "retweet_count": 0, "geo": null, "id": 168931016868761600, "source": "<a href=\"http://blackberry.com/twitter\" rel=\"nofollow\">Twitter for BlackBerry\u00ae</a>"} {"favorited": false, "in_reply_to_user_id": 27260086, "contributors": null, "truncated": false, "text": "@justinbieber u were born to be somebody, and u're super important in beliebers' life. thanks for all biebs. I love u. follow me? 84", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": null, "coordinates": null, "in_reply_to_user_id_str": "27260086", "entities": {"user_mentions": [{"indices": [0, 13], "screen_name": "justinbieber", "id": 27260086, "name": "Justin Bieber", "id_str": "27260086"}], "hashtags": [], "urls": []}, "in_reply_to_status_id": null, "id_str": "168931016856178688", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/416005864/Captura.JPG", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1808883280/Captura6_normal.JPG", "profile_sidebar_fill_color": "f5e7f3", "is_translator": false, "id": 406750700, "profile_text_color": "333333", "followers_count": 1122, "protected": false, "location": "Adentro de una supra.", "default_profile_image": false, "listed_count": 0, "utc_offset": -14400, "statuses_count": 20966, "description": "Mi \u00eddolo es @justinbieber , si te gusta \u00a1genial!, si no, solo respetalo. El cambi\u00f3 mi vida completamente y mi sue\u00f1o es conocerlo #TrueBelieber . ", "friends_count": 1015, "profile_link_color": "9404b8", "profile_image_url": "http://a1.twimg.com/profile_images/1808883280/Captura6_normal.JPG", "notifications": null, "show_all_inline_media": false, "geo_enabled": false, "profile_background_color": "f9fcfa", "id_str": "406750700", "profile_background_image_url": "http://a3.twimg.com/profile_background_images/416005864/Captura.JPG", "name": "neversaynever,right?", "lang": "es", "profile_background_tile": false, "favourites_count": 22, "screen_name": "True_Belieebers", "url": "http://www.wehavebieber-fever.tumblr.com", "created_at": "Mon Nov 07 04:17:40 +0000 2011", "contributors_enabled": false, "time_zone": "Santiago", "profile_sidebar_border_color": "C0DEED", "default_profile": false, "following": null}, "in_reply_to_screen_name": "justinbieber", "retweet_count": 0, "geo": null, "id": 168931016856178688, "source": "<a href=\"http://yfrog.com\" rel=\"nofollow\">Yfrog</a>"} I load it into DDFS with: # ddfs chunk data:test1 ./file.txt created: disco://localhost/ddfs/vol0/blob/44/file_txt-0$549-db27b-125e1 I test that the file is indeed loaded into ddfs with: # ddfs xcat data:test1 {"favorited": false, "in_reply_to_user_id": null, "contributors": null, "truncated": false, "text": "I'll call him back tomorrow I guess", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": null, "coordinates": null, "in_reply_to_user_id_str": null, "entities": {"user_mentions": [], "hashtags": [], "urls": []}, "in_reply_to_status_id": null, "id_str": "168931016843603968", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/305726905/FASHION-3.png", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1818996723/image_normal.jpg", "profile_sidebar_fill_color": "292727", "is_translator": false, "id": 113532729, "profile_text_color": "000000", "followers_count": 78, "protected": false, "location": "With My Niggas In Paris!", "default_profile_image": false, "listed_count": 0, "utc_offset": -21600, "statuses_count": 6733, "description": "Made in CHINA., Educated && Making My Own $$. Fear GOD && Put Him 1st. #TeamFollowBack #TeamiPhone\n", "friends_count": 74, "profile_link_color": "b03f3f", "profile_image_url": "http://a2.twimg.com/profile_images/1818996723/image_normal.jpg", "notifications": null, "show_all_inline_media": false, "geo_enabled": true, "profile_background_color": "1f9199", "id_str": "113532729", "profile_background_image_url": "http://a3.twimg.com/profile_background_images/305726905/FASHION-3.png", "name": "Bee'Jay", "lang": "en", "profile_background_tile": true, "favourites_count": 19, "screen_name": "OohMyBEEsNice", "url": "http://www.bitchimpaid.org", "created_at": "Fri Feb 12 03:32:54 +0000 2010", "contributors_enabled": false, "time_zone": "Central Time (US & Canada)", "profile_sidebar_border_color": "000000", "default_profile": false, "following": null}, "in_reply_to_screen_name": null, "retweet_count": 0, "geo": null, "id": 168931016843603968, "source": "<a href=\"http://twitter.com/#!/download/iphone\" rel=\"nofollow\">Twitter for iPhone</a>"} {"favorited": false, "in_reply_to_user_id": 50940453, "contributors": null, "truncated": false, "text": "@LegaMrvica @MimozaBand makasi om artis :D kadoo kadoo", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": "168653037894770688", "coordinates": null, "in_reply_to_user_id_str": "50940453", "entities": {"user_mentions": [{"indices": [0, 11], "screen_name": "LegaMrvica", "id": 50940453, "name": "Lega_thePianis", "id_str": "50940453"}, {"indices": [12, 23], "screen_name": "MimozaBand", "id": 375128905, "name": "Mimoza", "id_str": "375128905"}], "hashtags": [], "urls": []}, "in_reply_to_status_id": 168653037894770688, "id_str": "168931016868761600", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/347686061/Galungan_dan_Kuningan.jpg", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1803845596/Picture_20124_normal.jpg", "profile_sidebar_fill_color": "DDFFCC", "is_translator": false, "id": 48293450, "profile_text_color": "333333", "followers_count": 182, "protected": false, "location": "\u00dcT: -6.906799,107.622383", "default_profile_image": false, "listed_count": 0, "utc_offset": -28800, "statuses_count": 3052, "description": "Fashion design maranatha '11 // traditional dancer (bali) at sanggar tampak siring & Natya Nataraja", "friends_count": 206, "profile_link_color": "0084B4", "profile_image_url": "http://a3.twimg.com/profile_images/1803845596/Picture_20124_normal.jpg", "notifications": null, "show_all_inline_media": false, "geo_enabled": true, "profile_background_color": "9AE4E8", "id_str": "48293450", "profile_background_image_url": "http://a0.twimg.com/profile_background_images/347686061/Galungan_dan_Kuningan.jpg", "name": "nana afiff", "lang": "en", "profile_background_tile": true, "favourites_count": 2, "screen_name": "hasnfebria", "url": null, "created_at": "Thu Jun 18 08:50:29 +0000 2009", "contributors_enabled": false, "time_zone": "Pacific Time (US & Canada)", "profile_sidebar_border_color": "BDDCAD", "default_profile": false, "following": null}, "in_reply_to_screen_name": "LegaMrvica", "retweet_count": 0, "geo": null, "id": 168931016868761600, "source": "<a href=\"http://blackberry.com/twitter\" rel=\"nofollow\">Twitter for BlackBerry\u00ae</a>"} {"favorited": false, "in_reply_to_user_id": 27260086, "contributors": null, "truncated": false, "text": "@justinbieber u were born to be somebody, and u're super important in beliebers' life. thanks for all biebs. I love u. follow me? 84", "created_at": "Mon Feb 13 05:34:27 +0000 2012", "retweeted": false, "in_reply_to_status_id_str": null, "coordinates": null, "in_reply_to_user_id_str": "27260086", "entities": {"user_mentions": [{"indices": [0, 13], "screen_name": "justinbieber", "id": 27260086, "name": "Justin Bieber", "id_str": "27260086"}], "hashtags": [], "urls": []}, "in_reply_to_status_id": null, "id_str": "168931016856178688", "place": null, "user": {"follow_request_sent": null, "profile_use_background_image": true, "profile_background_image_url_https": "https://si0.twimg.com/profile_background_images/416005864/Captura.JPG", "verified": false, "profile_image_url_https": "https://si0.twimg.com/profile_images/1808883280/Captura6_normal.JPG", "profile_sidebar_fill_color": "f5e7f3", "is_translator": false, "id": 406750700, "profile_text_color": "333333", "followers_count": 1122, "protected": false, "location": "Adentro de una supra.", "default_profile_image": false, "listed_count": 0, "utc_offset": -14400, "statuses_count": 20966, "description": "Mi \u00eddolo es @justinbieber , si te gusta \u00a1genial!, si no, solo respetalo. El cambi\u00f3 mi vida completamente y mi sue\u00f1o es conocerlo #TrueBelieber . ", "friends_count": 1015, "profile_link_color": "9404b8", "profile_image_url": "http://a1.twimg.com/profile_images/1808883280/Captura6_normal.JPG", "notifications": null, "show_all_inline_media": false, "geo_enabled": false, "profile_background_color": "f9fcfa", "id_str": "406750700", "profile_background_image_url": "http://a3.twimg.com/profile_background_images/416005864/Captura.JPG", "name": "neversaynever,right?", "lang": "es", "profile_background_tile": false, "favourites_count": 22, "screen_name": "True_Belieebers", "url": "http://www.wehavebieber-fever.tumblr.com", "created_at": "Mon Nov 07 04:17:40 +0000 2011", "contributors_enabled": false, "time_zone": "Santiago", "profile_sidebar_border_color": "C0DEED", "default_profile": false, "following": null}, "in_reply_to_screen_name": "justinbieber", "retweet_count": 0, "geo": null, "id": 168931016856178688, "source": "<a href=\"http://yfrog.com\" rel=\"nofollow\">Yfrog</a> At this point everything is great, I load up the script that resulted from a previous Stack Post: from disco.core import Job, result_iterator import gzip def map(line, params): import unicodedata import json r = json.loads(line).get('text') s = unicodedata.normalize('NFD', r).encode('ascii', 'ignore') for word in s.split(): yield word, 1 def reduce(iter, params): from disco.util import kvgroup for word, counts in kvgroup(sorted(iter)): yield word, sum(counts) if __name__ == '__main__': job = Job().run(input=["tag://data:test1"], map=map, reduce=reduce) for word, count in result_iterator(job.wait(show=True)): print word, count NOTE: That this script runs file if the input=["file.txt"], however when I run it with "tag://data:test1" I get the following error: # DISCO_EVENTS=1 python count_normal_words.py Job@549:db30e:25bd8: Status: [map] 0 waiting, 1 running, 0 done, 0 failed 2012/11/25 21:43:26 master New job initialized! 2012/11/25 21:43:26 master Starting job 2012/11/25 21:43:26 master Starting map phase 2012/11/25 21:43:26 master map:0 assigned to solice 2012/11/25 21:43:26 master ERROR: Job failed: Worker at 'solice' died: Traceback (most recent call last): File "/home/DISCO/data/solice/01/Job@549:db30e:25bd8/usr/local/lib/python2.7/site-packages/disco/worker/__init__.py", line 329, in main job.worker.start(task, job, **jobargs) File "/home/DISCO/data/solice/01/Job@549:db30e:25bd8/usr/local/lib/python2.7/site-packages/disco/worker/__init__.py", line 290, in start self.run(task, job, **jobargs) File "/home/DISCO/data/solice/01/Job@549:db30e:25bd8/usr/local/lib/python2.7/site-packages/disco/worker/classic/worker.py", line 286, in run getattr(self, task.mode)(task, params) File "/home/DISCO/data/solice/01/Job@549:db30e:25bd8/usr/local/lib/python2.7/site-packages/disco/worker/classic/worker.py", line 299, in map for key, val in self['map'](entry, params): File "count_normal_words.py", line 12, in map File "/usr/lib64/python2.7/json/__init__.py", line 326, in loads return _default_decoder.decode(s) File "/usr/lib64/python2.7/json/decoder.py", line 366, in decode obj, end = self.raw_decode(s, idx=_w(s, 0).end()) File "/usr/lib64/python2.7/json/decoder.py", line 384, in raw_decode raise ValueError("No JSON object could be decoded") ValueError: No JSON object could be decoded 2012/11/25 21:43:26 master WARN: Job killed Status: [map] 1 waiting, 0 running, 0 done, 1 failed Traceback (most recent call last): File "count_normal_words.py", line 28, in <module> for word, count in result_iterator(job.wait(show=True)): File "/usr/local/lib/python2.7/site-packages/disco/core.py", line 348, in wait timeout, poll_interval * 1000) File "/usr/local/lib/python2.7/site-packages/disco/core.py", line 309, in check_results raise JobError(Job(name=jobname, master=self), "Status %s" % status) disco.error.JobError: Job Job@549:db30e:25bd8 failed: Status dead The Error states: ValueError: No JSON object could be decoded. Again, this works fine using the text file as input but now DDFS. Any ideas, I'm open to suggestions?

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  • SqlBulkCopy slow as molasses

    - by Chris
    I'm looking for the fastest way to load bulk data via c#. I have this script that does the job but slow. I read testimonies that SqlBulkCopy is the fastest. 1000 records 2.5 seconds. files contain anywhere near 5000 records to 250k What are some of the things that can slow it down? Table Def: CREATE TABLE [dbo].[tempDispositions]( [QuotaGroup] [varchar](100) NULL, [Country] [varchar](50) NULL, [ServiceGroup] [varchar](50) NULL, [Language] [varchar](50) NULL, [ContactChannel] [varchar](10) NULL, [TrackingID] [varchar](20) NULL, [CaseClosedDate] [varchar](25) NULL, [MSFTRep] [varchar](50) NULL, [CustEmail] [varchar](100) NULL, [CustPhone] [varchar](100) NULL, [CustomerName] [nvarchar](100) NULL, [ProductFamily] [varchar](35) NULL, [ProductSubType] [varchar](255) NULL, [CandidateReceivedDate] [varchar](25) NULL, [SurveyMode] [varchar](1) NULL, [SurveyWaveStartDate] [varchar](25) NULL, [SurveyInvitationDate] [varchar](25) NULL, [SurveyReminderDate] [varchar](25) NULL, [SurveyCompleteDate] [varchar](25) NULL, [OptOutDate] [varchar](25) NULL, [SurveyWaveEndDate] [varchar](25) NULL, [DispositionCode] [varchar](5) NULL, [SurveyName] [varchar](20) NULL, [SurveyVendor] [varchar](20) NULL, [BusinessUnitName] [varchar](25) NULL, [UploadId] [int] NULL, [LineNumber] [int] NULL, [BusinessUnitSubgroup] [varchar](25) NULL, [FileDate] [datetime] NULL ) ON [PRIMARY] and here's the code private void BulkLoadContent(DataTable dt) { OnMessage("Bulk loading records to temp table"); OnSubMessage("Bulk Load Started"); using (SqlBulkCopy bcp = new SqlBulkCopy(conn)) { bcp.DestinationTableName = "dbo.tempDispositions"; bcp.BulkCopyTimeout = 0; foreach (DataColumn dc in dt.Columns) { bcp.ColumnMappings.Add(dc.ColumnName, dc.ColumnName); } bcp.NotifyAfter = 2000; bcp.SqlRowsCopied += new SqlRowsCopiedEventHandler(bcp_SqlRowsCopied); bcp.WriteToServer(dt); bcp.Close(); } }

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  • .NET and C# Exceptions. What is it reasonable to catch.

    - by djna
    Disclaimer, I'm from a Java background. I don't do much C#. There's a great deal of transfer between the two worlds, but of course there are differences and one is in the way Exceptions tend to be thought about. I recently answered a C# question suggesting that under some circstances it's reasonable to do this: try { some work } catch (Exeption e) { commonExceptionHandler(); } (The reasons why are immaterial). I got a response that I don't quite understand: until .NET 4.0, it's very bad to catch Exception. It means you catch various low-level fatal errors and so disguise bugs. It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed, so even if the callExceptionReporter fuunction tries to log and quit, it may not even get to that point (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database). May I'm more confused than I realise, but I don't agree with some of that. Please would other folks comment. I understand that there are many low level Exceptions we don't want to swallow. My commonExceptionHandler() function could reasonably rethrow those. This seems consistent with this answer to a related question. Which does say "Depending on your context it can be acceptable to use catch(...), providing the exception is re-thrown." So I conclude using catch (Exception ) is not always evil, silently swallowing certain exceptions is. The phrase "Until .NET 4 it is very bad to Catch Exception" What changes in .NET 4? IS this a reference to AggregateException, which may give us some new things to do with exceptions we catch, but I don't think changes the fundamental "don't swallow" rule. The next phrase really bothers be. Can this be right? It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database) My understanding is that if some low level code had lowLevelMethod() { try { lowestLevelMethod(); } finally { some really important stuff } } and in my code I call lowLevel(); try { lowLevel() } catch (Exception e) { exception handling and maybe rethrowing } Whether or not I catch Exception this has no effect whatever on the excution of the finally block. By the time we leave lowLevelMethod() the finally has already run. If the finally is going to do any of the bad things, such as corrupt my disk, then it will do so. My catching the Exception made no difference. If It reaches my Exception block I need to do the right thing, but I can't be the cause of dmis-executing finallys

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  • How do you access the Source Error, Source File and Line Number of an exception to use in a custom e

    - by Iain Fraser
    Basically I want to take the following: And make it match the styling of the rest of the application. I am creating a custom error page in my C# based project and I want it to be able to show the same information that is displayed in the ASP.NET default error page. From fiddling with reflector I can see that this is generated through HttpException.GetHtmlErrorMessage() but when I try to use this in my exception it returns null.

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  • JavaScript: why `null == 0` is false?

    - by lemonedo
    I had to write a routine that increments the value of a variable by 1 if it is a number, or assigns 0 to the variable if it is not a number. The variable can be incremented by the expression, or be assigned null. No other write access to the variable is allowed. So, the variable can be in three states: it is 0, a positive integer, or null. My first implementation was: v >= 0 ? v += 1 : v = 0 (Yes, I admit that v === null ? v = 0 : v += 1 is the exact solution, but I wanted to be concise then.) It failed since null >= 0 is true. I was confused, since if a value is not a number, an numeric expression involving it must be false always. Then I found that null is like 0, since null + 1 == 1, 1 / null == Infinity, Math.pow(2.718281828, null) == 1, ... Strangely enough, however, null == 0 is evaluated to false. I guess null is the only value that makes the following expression false: (v == 0) === (v >= 0 && v <= 0) So why null is so special in JavaScript?

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  • I've caught an exception!! Now what?

    - by Jonesy
    Hi folks, I've started using try catch blocks (bit late i know!) but now im not sure what to do with the exception once i've caught it. What do people usually do here? -- Jonesy Try connection.Open() Dim sqlCmd As New SqlCommand("do some SQL", connection) Dim sqlDa As New SqlDataAdapter(sqlCmd) sqlDa.Fill(dt) Catch ex As SQLException ' ahhhh what to do now!!!? Finally connection.Close() End Try

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  • Is it possible to control Visual Studio exception handling from the debugged code itself?

    - by mark
    Dear ladies and sirs. I am wondering if it is possible to control the Visual Studio exception handling options from the code itself. For instance, I would like to turn off stopping on FCE for a certain piece of code, that generates many FCE, however, I would like it to be active for all the other code. Is it possible to do it from code? Something like this: visualStudio.DoNotStopOnFCE() try { // some code generating many FCE } catch {} visualStudio.StopOnFCE() Thanks.

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  • Where to define exception classes, inside classes or on a higher level?

    - by rve
    Should exception classes be part of the class which may throw them or should they exist on a higher level? For example : class Test { public: class FooException: public ExceptionBase { }; void functionThrowingFooException(); }; or class FooException: public ExceptionBase { }; class Test { public: void functionThrowingFooException(); }; (functionThrowingFooException() is the only function to ever throw a FooException)

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  • SDL_BlitSurface segmentation fault (surfaces aren't null)

    - by Trollkemada
    My app is crashing on SDL_BlitSurface() and i can't figure out why. I think it has something to do with my static object. If you read the code you'll why I think so. This happens when the limits of the map are reached, i.e. (iwidth || jheight). This is the code: Map.cpp (this render) Tile const * Map::getTyle(int i, int j) const { if (i >= 0 && j >= 0 && i < width && j < height) { return data[i][j]; } else { return &Tile::ERROR_TYLE; // This makes SDL_BlitSurface (called later) crash //return new Tile(TileType::ERROR); // This works with not problem (but is memory leak, of course) } } void Map::render(int x, int y, int width, int height) const { //DEBUG("(Rendering...) x: "<<x<<", y: "<<y<<", width: "<<width<<", height: "<<height); int firstI = x / TileType::PIXEL_PER_TILE; int firstJ = y / TileType::PIXEL_PER_TILE; int lastI = (x+width) / TileType::PIXEL_PER_TILE; int lastJ = (y+height) / TileType::PIXEL_PER_TILE; // The previous integer division rounds down when dealing with positive values, but it rounds up // negative values. This is a fix for that (We need those values always rounded down) if (firstI < 0) { firstI--; } if (firstJ < 0) { firstJ--; } const int firstX = x; const int firstY = y; SDL_Rect srcRect; SDL_Rect dstRect; for (int i=firstI; i <= lastI; i++) { for (int j=firstJ; j <= lastJ; j++) { if (i*TileType::PIXEL_PER_TILE < x) { srcRect.x = x % TileType::PIXEL_PER_TILE; srcRect.w = TileType::PIXEL_PER_TILE - (x % TileType::PIXEL_PER_TILE); dstRect.x = i*TileType::PIXEL_PER_TILE + (x % TileType::PIXEL_PER_TILE) - firstX; } else if (i*TileType::PIXEL_PER_TILE >= x + width) { srcRect.x = 0; srcRect.w = x % TileType::PIXEL_PER_TILE; dstRect.x = i*TileType::PIXEL_PER_TILE - firstX; } else { srcRect.x = 0; srcRect.w = TileType::PIXEL_PER_TILE; dstRect.x = i*TileType::PIXEL_PER_TILE - firstX; } if (j*TileType::PIXEL_PER_TILE < y) { srcRect.y = 0; srcRect.h = TileType::PIXEL_PER_TILE - (y % TileType::PIXEL_PER_TILE); dstRect.y = j*TileType::PIXEL_PER_TILE + (y % TileType::PIXEL_PER_TILE) - firstY; } else if (j*TileType::PIXEL_PER_TILE >= y + height) { srcRect.y = y % TileType::PIXEL_PER_TILE; srcRect.h = y % TileType::PIXEL_PER_TILE; dstRect.y = j*TileType::PIXEL_PER_TILE - firstY; } else { srcRect.y = 0; srcRect.h = TileType::PIXEL_PER_TILE; dstRect.y = j*TileType::PIXEL_PER_TILE - firstY; } SDL::YtoSDL(dstRect.y, srcRect.h); SDL_BlitSurface(getTyle(i,j)->getType()->getSurface(), &srcRect, SDL::getScreen(), &dstRect); // <-- Crash HERE /*DEBUG("i = "<<i<<", j = "<<j); DEBUG("srcRect.x = "<<srcRect.x<<", srcRect.y = "<<srcRect.y<<", srcRect.w = "<<srcRect.w<<", srcRect.h = "<<srcRect.h); DEBUG("dstRect.x = "<<dstRect.x<<", dstRect.y = "<<dstRect.y);*/ } } } Tile.h #ifndef TILE_H #define TILE_H #include "TileType.h" class Tile { private: TileType const * type; public: static const Tile ERROR_TYLE; Tile(TileType const * t); ~Tile(); TileType const * getType() const; }; #endif Tile.cpp #include "Tile.h" const Tile Tile::ERROR_TYLE(TileType::ERROR); Tile::Tile(TileType const * t) : type(t) {} Tile::~Tile() {} TileType const * Tile::getType() const { return type; } TileType.h #ifndef TILETYPE_H #define TILETYPE_H #include "SDL.h" #include "DEBUG.h" class TileType { protected: TileType(); ~TileType(); public: static const int PIXEL_PER_TILE = 30; static const TileType * ERROR; static const TileType * AIR; static const TileType * SOLID; virtual SDL_Surface * getSurface() const = 0; virtual bool isSolid(int x, int y) const = 0; }; #endif ErrorTyle.h #ifndef ERRORTILE_H #define ERRORTILE_H #include "TileType.h" class ErrorTile : public TileType { friend class TileType; private: ErrorTile(); mutable SDL_Surface * surface; static const char * FILE_PATH; public: SDL_Surface * getSurface() const; bool isSolid(int x, int y) const ; }; #endif ErrorTyle.cpp (The surface can't be loaded when building the object, because it is a static object and SDL_Init() needs to be called first) #include "ErrorTile.h" const char * ErrorTile::FILE_PATH = ("C:\\error.bmp"); ErrorTile::ErrorTile() : TileType(), surface(NULL) {} SDL_Surface * ErrorTile::getSurface() const { if (surface == NULL) { if (SDL::isOn()) { surface = SDL::loadAndOptimice(ErrorTile::FILE_PATH); if (surface->w != TileType::PIXEL_PER_TILE || surface->h != TileType::PIXEL_PER_TILE) { WARNING("Bad tile surface size"); } } else { ERROR("Trying to load a surface, but SDL is not on"); } } if (surface == NULL) { // This if doesn't get called, so surface != NULL ERROR("WTF? Can't load surface :\\"); } return surface; } bool ErrorTile::isSolid(int x, int y) const { return true; }

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  • It&rsquo;s ok to throw System.Exception&hellip;

    - by Chris Skardon
    No. No it’s not. It’s not just me saying that, it’s the Microsoft guidelines: http://msdn.microsoft.com/en-us/library/ms229007.aspx  Do not throw System.Exception or System.SystemException. Also – as important: Do not catch System.Exception or System.SystemException in framework code, unless you intend to re-throw.. Throwing: Always, always try to pick the most specific exception type you can, if the parameter you have received in your method is null, throw an ArgumentNullException, value received greater than expected? ArgumentOutOfRangeException. For example: public void ArgChecker(int theInt, string theString) { if (theInt < 0) throw new ArgumentOutOfRangeException("theInt", theInt, "theInt needs to be greater than zero."); if (theString == null) throw new ArgumentNullException("theString"); if (theString.Length == 0) throw new ArgumentException("theString needs to have content.", "theString"); } Why do we want to do this? It’s a lot of extra code when compared with a simple: public void ArgChecker(int theInt, string theString) { if (theInt < 0 || string.IsNullOrWhiteSpace(theString)) throw new Exception("The parameters were invalid."); } It all comes down to a couple of things; the catching of the exceptions, and the information you are passing back to the calling code. Catching: Ok, so let’s go with introduction level Exception handling, taught by many-a-university: You do all your work in a try clause, and catch anything wrong in the catch clause. So this tends to give us code like this: try { /* All the shizzle */ } catch { /* Deal with errors */ } But of course, we can improve on that by catching the exception so we can report on it: try { } catch(Exception ex) { /* Log that 'ex' occurred? */ } Now we’re at the point where people tend to go: Brilliant, I’ve got exception handling nailed, what next??? and code gets littered with the catch(Exception ex) nastiness. Why is it nasty? Let’s imagine for a moment our code is throwing an ArgumentNullException which we’re catching in the catch block and logging. Ok, the log entry has been made, so we can debug the code right? We’ve got all the info… What about an OutOfMemoryException – what can we do with that? That’s right, not a lot, chances are you can’t even log it (you are out of memory after all), but you’ve caught it – and as such - have hidden it. So, as part of this, there are two things you can do one, is the rethrow method: try { /* code */ } catch (Exception ex) { //Log throw; } Note, it’s not catch (Exception ex) { throw ex; } as that will wipe all your important stack trace information. This does get your exception to continue, and is the only reason you would catch Exception (anywhere other than a global catch-all) in your code. The other preferred method is to catch the exceptions you can deal with. It may not matter that the string I’m passing in is null, and I can cope with it like this: try{ DoSomething(myString); } catch(ArgumentNullException){} And that’s fine, it means that any exceptions I can’t deal with (OutOfMemory for example) will be propagated out to other code that can deal with it. Of course, this is horribly messy, no one wants try / catch blocks everywhere and that’s why Microsoft added the ‘Try’ methods to the framework, and it’s a strategy we should continue. If I try: int i = (int) "one"; I will get an InvalidCastException which means I need the try / catch block, but I could mitigate this using the ‘TryParse’ method: int i; if(!Int32.TryParse("one", out i)) return; Similarly, in the ‘DoSomething’ example, it might be beneficial to have a ‘TryDoSomething’ that returns a boolean value indicating the success of continuing. Obviously this isn’t practical in every case, so use the ol’ common sense approach. Onwards Yer thanks Chris, I’m looking forward to writing tonnes of new code. Fear not, that is where helpers come into it… (but that’s the next post)

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  • Throwing a C++ exception after an inline-asm jump

    - by SoapBox
    I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call. But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work. How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally? The code: #include <iostream> #include <stdexcept> using namespace std; void thrower() { cout << "Inside thrower" << endl; throw runtime_error("some exception"); } int main() { cout << "Top of main" << endl; try { asm volatile ( "jmp *%0" // same thing happens with a call instead of a jmp : : "r"((long)thrower) : ); } catch (exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The expected output: Top of main Inside thrower Caught : some exception Bottom of main The actual output: Top of main Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): some exception Aborted

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  • Catching specific vs. generic exceptions in c#

    - by Scott Vercuski
    This question comes from a code analysis run against an object I've created. The analysis says that I should catch a more specific exception type than just the basic Exception. Do you find yourself using just catching the generic Exception or attempting to catch a specific Exception and defaulting to a generic Exception using multiple catch blocks? One of the code chunks in question is below: internal static bool ClearFlags(string connectionString, Guid ID) { bool returnValue = false; SqlConnection dbEngine = new SqlConnection(connectionString); SqlCommand dbCmd = new SqlCommand("ClearFlags", dbEngine); SqlDataAdapter dataAdapter = new SqlDataAdapter(dbCmd); dbCmd.CommandType = CommandType.StoredProcedure; try { dbCmd.Parameters.AddWithValue("@ID", ID.ToString()); dbEngine.Open(); dbCmd.ExecuteNonQuery(); dbEngine.Close(); returnValue = true; } catch (Exception ex) { ErrorHandler(ex); } return returnValue; } Thank you for your advice EDIT: Here is the warning from the code analysis Warning 351 CA1031 : Microsoft.Design : Modify 'ClearFlags(string, Guid)' to catch a more specific exception than 'Exception' or rethrow the exception

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  • unknown exception error in php

    - by fayer
    i wanna catch all exceptions thrown in a script and then check if they have a error code 23000. if they don't i want to rethrow the exception. here is my code: function myException($exception) { /*** If it is a Doctrine Connection Mysql Duplication Exception ***/ if(get_class($exception) === 'Doctrine_Connection_Mysql_Exception' && $exception->getCode() === 23000) { echo "Duplicate entry"; } else { throw $exception; } } set_exception_handler('myException'); $contact = new Contact(); $contact->email = 'peter'; $contact->save(); but i get this error message and i dont know what it means: Fatal error: Exception thrown without a stack frame in Unknown on line 0 i want to be able to rethrow the original error message if it has not the error code 23000. even when i deleted the check errorcode i still get the same message: function myException($exception) { throw $exception; } set_exception_handler('myException'); $contact = new Contact(); $contact->email = 'peter'; $contact->save(); how could i solve this? thanks

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  • Webcast: Best Practices for Speeding Virtual Infrastructure Deployment with Oracle VM

    - by Honglin Su
    We announced Oracle VM Blade Cluster Reference Configuration last month, see the blog. The new Oracle VM blade cluster reference configuration can help reduce the time to deploy virtual infrastructure by up to 98 percent when compared to multi-vendor configurations. Customers and partners have shown lots of interests. Join Oracle's experts to learn the best practices for speeding virtual infrastructure deployment with Oracle VM, register the webcast (1/25/2011) here.   Virtualization has already been widely accepted as a means to increase IT flexibility and help IT services align better with changing business needs. The flexibility of a virtualized IT infrastructure enables new applications to be rapidly deployed, capacity to be easily scaled, and IT resources to be quickly redirected. The net result is that IT can bring greater value to the business, making virtualization an obvious win from a business perspective. However, building a virtualized infrastructure typically requires assembling and integrating multiple components (e.g. servers, storage, network, virtualization, and operating systems). This infrastructure must be deployed and tested before applications can even be installed. It can take weeks or months to plan, architect, configure, troubleshoot, and deploy a virtualized infrastructure. The process is not only time-consuming, but also error-prone, making it hard to achieve a timely and profitable return on investment.  Oracle is the only vendor that can offer a fully integrated virtualization infrastructure with all of the necessary hardware and software components. The Oracle VM blade cluster reference configuration is a single-vendor solution that addresses every layer of the virtualization stack with Oracle hardware and software components, see the figure below. It enables quick and easy deployment of the virtualized infrastructure using components that have been tested together and are all supported together by Oracle. To learn more about Oracle's virtualization offerings, visit http://oracle.com/virtualization.

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