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• SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2

  - by pinaldave

  Social media has created an Always Connected World for us. Recently I enrolled myself to learn new technologies as a student. I had decided to focus on learning and decided not to stay connected on the internet while I am in the learning session. On the second day of the event after the learning was over, I noticed lots of notification from my friend on my various social media handle. He had connected with me on Twitter, Facebook, Google+, LinkedIn, YouTube as well SMS, WhatsApp on the phone, Skype messages and not to forget with a few emails. I right away called him up. The problem was very unique – let us hear the problem in his own words. “Pinal – we are in big trouble we are not able to figure out what is going on. Our product details table is continuously loosing rows. Lots of rows have disappeared since morning and we are unable to find why the rows are getting deleted. We have made sure that there is no DELETE command executed on the table as well. The matter of the fact, we have removed every single place the code which is referencing the table. We have done so many crazy things out of desperation but no luck. The rows are continuously deleted in a random pattern. Do you think we have problems with intrusion or virus?” After describing the problems he had pasted few rants about why I was not available during the day. I think it will be not smart to post those exact words here (due to many reasons). Well, my immediate reaction was to get online with him. His problem was unique to him and his team was all out to fix the issue since morning. As he said he has done quite a lot out in desperation. I started asking questions from audit, policy management and profiling the data. Very soon I realize that I think this problem was not as advanced as it looked. There was no intrusion, SQL Injection or virus issue. Well, long story short first - It was a very simple issue of foreign key created with ON UPDATE CASCADE and ON DELETE CASCADE.  CASCADE allows deletions or updates of key values to cascade through the tables defined to have foreign key relationships that can be traced back to the table on which the modification is performed. ON DELETE CASCADE specifies that if an attempt is made to delete a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are also deleted. ON UPDATE CASCADE specifies that if an attempt is made to update a key value in a row, where the key value is referenced by foreign keys in existing rows in other tables, all of the foreign key values are also updated to the new value specified for the key. (Reference: BOL) In simple words – due to ON DELETE CASCASE whenever is specified when the data from Table A is deleted and if it is referenced in another table using foreign key it will be deleted as well. In my friend’s case, they had two tables, Products and ProductDetails. They had created foreign key referential integrity of the product id between the table. Now the as fall was up they were updating their catalogue. When they were updating the catalogue they were deleting products which are no more available. As the changes were cascading the corresponding rows were also deleted from another table. This is CORRECT. The matter of the fact, there is no error or anything and SQL Server is behaving how it should be behaving. The problem was in the understanding and inappropriate implementations of business logic.  What they needed was Product Master Table, Current Product Catalogue, and Product Order Details History tables. However, they were using only two tables and without proper understanding the relation between them was build using foreign keys. If there were only two table, they should have used soft delete which will not actually delete the record but just hide it from the original product table. This workaround could have got them saved from cascading delete issues. I will be writing a detailed post on the design implications etc in my future post as in above three lines I cannot cover every issue related to designing and it is also not the scope of the blog post. More about designing in future blog posts. Once they learn their mistake, they were happy as there was no intrusion but trust me sometime we are our own enemy and this is a great example of it. In tomorrow’s blog post we will go over their code and workarounds. Feel free to share your opinions, experiences and comments. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Detecting long held keys on keyboard

  - by Robinson Joaquin

  I just want to ask if can I check for "KEY"(keyboard) that is HOLD/PRESSED for a long time, because I am to create a clone of breakout with air hockey for 2 different human players. Here's the list of my concern: Do I need other/ 3rd party library for KEY HOLDS? Is multi-threading needed? I don't know anything about this multi-threading stuff and I don't think about using one(I'm just a NEWBIE). One more thing, what if the two players pressed their respective key at the same time, how can I program to avoid error or worse one player's key is prioritized first before the the key of the other. example: Player 1 = W for UP & S for DOWN Player 2 = O for UP & L for DOWN (example: W & L is pressed at the same time) PS: I use GLUT for the visuals of the game.

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• gpg passcode error

  - by shantanu

  I just created my gpg key using developer.ubuntu.com packaging page's documentation and also upload the public key in key server. When i import the key into launchpad it sent me an encrypted message. Now i give a command to decrypt the message gpg -d launchpad.txt it asked for a passcode. I gave one which i used to create gpg key. but it shows error again again. I repeat the process(gpg creation) again but stuck on .... passcode(decryption). What is the problem?

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• How is intermediate data organized in MapReduce?

  - by Pedro Cattori

  From what I understand, each mapper outputs an intermediate file. The intermediate data (data contained in each intermediate file) is then sorted by key. Then, a reducer is assigned a key by the master. The reducer reads from the intermediate file containing the key and then calls reduce using the data it has read. But in detail, how is the intermediate data organized? Can a data corresponding to a key be held in multiple intermediate files? What happens when there is too much data corresponding to one key to be held by a single file? In short, how do intermediate partitions differ from intermediate files and how are these differences dealt with in the implementation?

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• Mulitple movements with keyboard in C++

  - by DDukesterman

  Im trying to get my movement of a ball to just move in a fluid like motion. How can I have it that when I press the up key, down key, left key, or right key, it doesnt move up one unit, stop, then keep moving. Also, how can i have it move in two directions at the same time wthout stopping another direction when letting off a key? Thanks if(GetAsyncKeyState(VK_UP)) { if(g_nGameState == SETTINGUPSHOT_GAMESTATE || g_nGameState == INITIAL_GAMESTATE) { g_cObjectWorld.AdjustCueBallY(MOVEDELTA); g_cObjectWorld.ResetImpulseVector(); } } if(GetAsyncKeyState(VK_DOWN)) { if(g_nGameState == SETTINGUPSHOT_GAMESTATE || g_nGameState == INITIAL_GAMESTATE) { g_cObjectWorld.AdjustCueBallY(-MOVEDELTA); g_cObjectWorld.ResetImpulseVector(); } } if(GetAsyncKeyState(VK_LEFT)) { if(g_nGameState == SETTINGUPSHOT_GAMESTATE || g_nGameState == INITIAL_GAMESTATE) { g_cObjectWorld.AdjustCueBallX(-MOVEDELTA); g_cObjectWorld.ResetImpulseVector(); } } if(GetAsyncKeyState(VK_RIGHT)) { if(g_nGameState == SETTINGUPSHOT_GAMESTATE || g_nGameState == INITIAL_GAMESTATE) { g_cObjectWorld.AdjustCueBallX(MOVEDELTA); g_cObjectWorld.ResetImpulseVector(); } }

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• Simple calculator app crashes when a third number key is punched.

  - by Justin

  Hi , I am a newbie to the iphone app world. So I thought I try my luck with a calculator app. Unfortunately I am running into an issue where if I press a third key in the calculator the app crashes. Sometimes I get this error EXC_BAD_ACCESS. Here is a code in my CalculatorViewController.m file. #import "CalculatorViewController.h" @implementation CalculatorViewController @synthesize screenText; - (IBAction)buttonPressed:(id)sender { NSString *title = [sender titleForState:UIControlStateNormal]; [self collect:title]; } - (void)collect:(NSString *)digitz { NSString * newText = nil; if ([digitz isEqualToString:@"+"]) { [self add:result]; big_digit = nil; } else if ([digitz isEqualToString:@"+"]) { [self sub:result]; } else if ([digitz isEqualToString:@"x"]) { [self multiply:result]; } else if ([digitz isEqualToString:@"="]) { [self equate:result]; } else { if (big_digit != nil && [big_digit isEqualToString:@"0"] == FALSE) big_digit = [big_digit stringByAppendingFormat:@"%@",digitz]; else big_digit = (NSMutableString *) digitz; result = (int) big_digit; newText = [[NSString alloc] initWithFormat: @"%@",big_digit]; } screenText.text = newText; [newText release]; } - (void)add:(int)res { NSString * newText = nil; ans = ans + res; newText = [[NSString alloc] initWithFormat: @"%@",ans]; screenText.text = newText; [newText release]; } Can anyone spot an obvious issue here. Here is the respective header file too. #import <UIKit/UIKit.h> @interface CalculatorViewController : UIViewController { UILabel *screenText; int number; int result; int ans; //NSString *big_digit; NSMutableString * big_digit ; } @property (nonatomic, retain) IBOutlet UILabel *screenText; - (IBAction)buttonPressed:(id)sender; - (void)collect:(NSString *)digitz; - (void)add:(int)num; - (void)sub:(int)num; - (void)multiply:(int)num; - (void)equate:(int)num; @end

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• What is causing this SQL 2005 Primary Key Deadlock between two real-time bulk upserts?

  - by skimania

  Here's the scenario: I've got a table called MarketDataCurrent (MDC) that has live updating stock prices. I've got one process called 'LiveFeed' which reads prices streaming from the wire, queues up inserts, and uses a 'bulk upload to temp table then insert/update to MDC table.' (BulkUpsert) I've got another process which then reads this data, computes other data, and then saves the results back into the same table, using a similar BulkUpsert stored proc. Thirdly, there are a multitude of users running a C# Gui polling the MDC table and reading updates from it. Now, during the day when the data is changing rapidly, things run pretty smoothly, but then, after market hours, we've recently started seeing an increasing number of Deadlock exceptions coming out of the database, nowadays we see 10-20 a day. The imporant thing to note here is that these happen when the values are NOT changing. Here's all the relevant info: Table Def: CREATE TABLE [dbo].[MarketDataCurrent]( [MDID] [int] NOT NULL, [LastUpdate] [datetime] NOT NULL, [Value] [float] NOT NULL, [Source] [varchar](20) NULL, CONSTRAINT [PK_MarketDataCurrent] PRIMARY KEY CLUSTERED ( [MDID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] - stackoverflow wont let me post images until my reputation goes up to 10, so i'll add them as soon as you bump me up, hopefully as a result of this question. ![alt text][1] [1]: http://farm5.static.flickr.com/4049/4690759452_6b94ff7b34.jpg I've got a Sql Profiler Trace Running, catching the deadlocks, and here's what all the graphs look like. stackoverflow wont let me post images until my reputation goes up to 10, so i'll add them as soon as you bump me up, hopefully as a result of this question. ![alt text][2] [2]: http://farm5.static.flickr.com/4035/4690125231_78d84c9e15_b.jpg Process 258 is called the following 'BulkUpsert' stored proc, repeatedly, while 73 is calling the next one: ALTER proc [dbo].[MarketDataCurrent_BulkUpload] @updateTime datetime, @source varchar(10) as begin transaction update c with (rowlock) set LastUpdate = getdate(), Value = t.Value, Source = @source from MarketDataCurrent c INNER JOIN #MDTUP t ON c.MDID = t.mdid where c.lastUpdate < @updateTime and c.mdid not in (select mdid from MarketData where LiveFeedTicker is not null and PriceSource like 'LiveFeed.%') and c.value <> t.value insert into MarketDataCurrent with (rowlock) select MDID, getdate(), Value, @source from #MDTUP where mdid not in (select mdid from MarketDataCurrent with (nolock)) and mdid not in (select mdid from MarketData where LiveFeedTicker is not null and PriceSource like 'LiveFeed.%') commit And the other one: ALTER PROCEDURE [dbo].[MarketDataCurrent_LiveFeedUpload] AS begin transaction -- Update existing mdid UPDATE c WITH (ROWLOCK) SET LastUpdate = t.LastUpdate, Value = t.Value, Source = t.Source FROM MarketDataCurrent c INNER JOIN #TEMPTABLE2 t ON c.MDID = t.mdid; -- Insert new MDID INSERT INTO MarketDataCurrent with (ROWLOCK) SELECT * FROM #TEMPTABLE2 WHERE MDID NOT IN (SELECT MDID FROM MarketDataCurrent with (NOLOCK)) -- Clean up the temp table DELETE #TEMPTABLE2 commit To clarify, those Temp Tables are being created by the C# code on the same connection and are populated using the C# SqlBulkCopy class. To me it looks like it's deadlocking on the PK of the table, so I tried removing that PK and switching to a Unique Constraint instead but that increased the number of deadlocks 10-fold. I'm totally lost as to what to do about this situation and am open to just about any suggestion. HELP!!

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• Linq query with aggregate function OrderBy

  - by Billy Logan

  Hello everyone, I have the following LinqToEntities query, but am unsure of where or how to add the orderby clause: var results = from d in db.TBLDESIGNER join s in db.TBLDESIGN on d.ID equals s.TBLDESIGNER.ID where s.COMPLETED && d.ACTIVE let value = new { s, d} let key = new { d.ID, d.FIRST_NAME, d.LAST_NAME } group value by key into g orderby g.Key.FIRST_NAME ascending, g.Key.LAST_NAME ascending select new { ID = g.Key.ID, FirstName = g.Key.FIRST_NAME, LastName = g.Key.LAST_NAME, Count = g.Count() }; This should be sorted by First_Name ascending and then Last_Name ascending. I have tried adding ordering but It has had no effect on the result set. Could someone please provide an example of where the orderby would go assuming the query above. Thanks, Billy

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• jquery xml select

  - by Geln

  hi, How to select items whose sub-tag key's text starts with '001'? <root> <item> <key>001001</key> <text>thanks</text> </item> <item> <key>001002</key> <text>very</text> </item> <item> <key>002001</key> <text>much</text> </item> </root> $(xml).find("item>[filter string]").each(function() { alert(this); });

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• Why am I getting unexpected output trying to write a hash structure to a file?

  - by Harm De Weirdt

  I have a hash in which I store the products a customer buys (%orders). It uses the product code as key and has a reference to an array with the other info as value. At the end of the program, I have to rewrite the inventory to the updated version (i.e. subtract the quantity of the bought items) This is how I do rewrite the inventory: sub rewriteInventory{ open(FILE,'>inv.txt'); foreach $key(%inventory){ print FILE "$key\|$inventory{$key}[0]\|$inventory{$key}[1]\|$inventory{$key}[2]\n" } close(FILE); } where $inventory{$key}[x] is 0 → Title, 1 → price, 2 → quantity. The problem here is that when I look at inv.txt afterwards, I see things like this: CD-911|Lady Gaga - The Fame|15.99|21 ARRAY(0x145030c)||| BOOK-1453|The Da Vinci Code - Dan Brown|14.75|12 ARRAY(0x145bee4)||| Where do these ARRAY(0x145030c)||| entries come from? Or more important, how do I get rid of them?

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• What's a reliable and practical way to protect software with a user license ?

  - by Frank

  I know software companies use licenses to protect their softwares, but I also know there are keygen programs to bypass them. I'm a Java developer, if I put my program online for sale, what's a reliable and practical way to protect it ? How about something like this, would it work ? <1> I use ProGuard to protect the source code. <2> Sign the executable Jar file. <3> Since my Java program only need to work on PC [I need to use JDIC in it], I wrap the final executable Jar into an .exe file which makes it harder to decompile. <4> When a user first downloads and runs my app, it checks for a Pass file on his PC. <5> If the Pass file doesn't exist, run the app in demo mode, exits in 5 minutes. <6> When demo exits a panel opens with a "Buy Now" button. This demo mode repeats forever unless step <7> happens. <7> If user clicks the "Buy Now" button, he fills out a detailed form [name, phone, email ...], presses a "Verify Info" button to save the form to a Pass file, leaving license Key # field empty in this newly generated Pass file. <8> Pressing "Verify Info" button will take him to a html form pre-filled with his info to verify what he is buying, also hidden in the form's input filed is a license Key number. He can now press a "Pay Now" button to goto Paypal to finish the process. <9> The hidden license Key # will be passed to Paypal as product Id info and emailed to me. <10> After I got the payment and Paypal email, I'll add the license Key # to a valid license Key list, and put it on my site, only I know the url. The list is updated hourly. <11> Few hours later when the user runs the app again, it can find the Pass file on his PC, but the license Key # value is empty, so it goes to the valid list url to see if its license Key # is on the list, if so, write the license Key # into the Pass file, and the next time it starts again, it will find the valid license Key # and start in purchased mode without exiting in 5 minutes. <12> If it can't find its license Key # on the list from my url, run in demo mode. <13> In order to prevent a user from copying and using another paid user's valid Pass file, the license Key # is unique to each PC [I'm trying to find how], so a valid Pass file only works on one PC. Only after a user has paid will Paypal email me the valid license Key # with his payment. <14> The Id checking goes like this : Use the CPU ID : "CPU_01-02-ABC" for example, encrypt it to the result ID : "XeR5TY67rgf", and compare it to the list on my url, if "XeR5TY67rgf" is not on my valid user list, run in demo mode. If it exists write "XeR5TY67rgf" into the Pass File license field. In order to get a unique license Key, can I use his PC's CPU Id ? Or something unique and useful [ relatively less likely to change ]. If so let's say this CPU ID is "CPU_01-02-ABC", I can encrypt it to something like "XeR5TY67rgf", and pass it to Paypal as product Id in the hidden html form field, then I'll get it from Paypal's email notification, and add it to the valid license Key # list on the url. So, even if a hacker knows it uses CPU Id, he can't write it into the Pass file field, because only encrypted Ids are valid Ids. And only my program knows how to generate the encrypted Ids. And even if another hacker knows the encrypted Id is hidden in the html form input field, as long as it's not on my url list, it's still invalid. Can anyone find any flaw in the above system ? Is it practical ? And most importantly how do I get hold of this unique ID that can represent a user's PC ? Frank

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• Can't access dojo object property using string variable

  - by Kareem

  I am retrieving a json associative array using a dojo xhrGet request. The data comes back just fine, however I need the app to be able to display the keys and their properties (or values) without knowing the keys beforehand. So, I do the following: function getData() { dojo.xhrGet( { url: "ytd_process.php", handleAs: "json", load: function(response) { for (var key in response) { dojo.byId("boxes").innerHTML+="<div id=\"box\">"+key+":"+response.key+"</div>"; } console.dir(response); // Dump it to the console } }); }; The keys are retrieved and displayed on the page, but the response.key returns undefined. I know the syntax is correct because if I replace .key with an actual key value it will display correctly. It appears it doesn't like a string as the key. Any help or advice would be greatly appreciated. Thank you.

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• PHP / MYSQL: Sanitizing user input - is this a bad idea?

  - by Greg

  I have one "go" script that fetches any other script requested and this is what I wrote to sanitize user input: foreach ($_REQUEST as $key => $value){ if (get_magic_quotes_gpc()) $_REQUEST[$key] = mysql_real_escape_string(stripslashes($value)); else $_REQUEST[$key] = mysql_real_escape_string($value); } I haven't seen anyone else use this approach. Is there any reason not to? EDIT - amended for to work for arrays: function mysql_escape($thing) { if (is_array($thing)) { $escaped = array(); foreach ($thing as $key => $value) { $escaped[$key] = mysql_escape($value); } return $escaped; } // else if (get_magic_quotes_gpc()) $thing = stripslashes($thing); return mysql_real_escape_string($thing); } foreach ($_REQUEST as $key => $value){ $_REQUEST[$key] = mysql_escape($value); }

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• How do I set a variable inside a bash for loop?

  - by Isaac Moore

  I need to set a variable inside of a bash for loop, which for some reason, is not working for me. Here is an excerpt of my script: function unlockBoxAll { appdir=$(grep -i "CutTheRope.app" /tmp/App_list.tmp) for lvl in {0..24} key="UNLOCKED_$box_$lvl" plutil -key "$key" -value "1" "$appdir/../Library/Preferences/com.chillingo.cuttherope.plist" 2>&1> /dev/null successCheck=$(plutil -key "$key" "$appdir/../Library/Preferences/com.chillingo.cuttherope.plist") if [ "$successCheck" -eq "1" ]; then echo "Success! " else echo "Failed: Key is $successCheck " fi done } As you can see, I try to write to a variable inside the loop with: key="UNLOCKED_$box_$lvl" But when I do that, I get this: /usr/bin/cutTheRope.sh: line 23: syntax error near unexpected token `key="UNLOCKED_$box_$lvl"' /usr/bin/cutTheRope.sh: line 23: `key="UNLOCKED_$box_$lvl"' What am I not doing right? Is there another way to do this? Please help, thanks.

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• Chrome SSL Security Issue under Windows systems?

  - by fraido

  The Fortify.net website allows you to check what SSL Encryption key is used by your browser. I gave it a try with the browsers I've on my machine and these are the results Fedora 9 Firefox 3.0.8 = AES cipher, 256-bit key Chrome 4.0.249.30 = AES cipher, 256-bit key Windows XP SP3 IE 6.0.2x = RC4 cipher, 128-bit key Firefox = AES cipher, 256-bit key Chrome 4.1.249.1042 (42199) = RC4 cipher, 128-bit key .... WHAT!!?!! Chrome is using RC4 128-bit (as IE6 does) that is well known as been very weak! Chrome under Unix works fine... I'm wondering how is this possible? Do you have this issue or is there a way to change the default key to be AES 256bit? I'm using Chrome as the main browser under Windows and I'm really considering to switch back to Firefox

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• javascript object access performance

  - by youdontmeanmuch

  In Javascript, when your getting a property of an object, is there a performance penalty to getting the whole object vs only getting a property of that object? Also Keep in mind I'm not talking about DOM access these are pure simple Javascript objects. For example: Is there some kind of performance difference between the following code: Assumed to be faster but not sure: var length = some.object[key].length; if(length === condition){ // Do something that doesnt need anything inside of some.object[key] } else{ var object = some.object[key]; // Do something that requires stuff inside of some.object[key] } I think this would be slower but not sure if it matters. var object = some.object[key]; if(object.length === condition){ // Do something that doesnt need anything inside of some.object[key] } else{ // Do something that requires stuff inside of some.object[key] }

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• How to hide keys in application?

  - by WilliamKF

  I have a C++ client/server application where the client and server are my executable. Each time a connection is made between the client and server, I generate a new encryption key for that session and I wish to transmit this session key and encrypt this session key using a static key that is built into both the client and server. However, running strings on my executable reveals the static key. How can I hide the embedded static key in my client and server application so that they are not easily extracted and thus allowing someone to decode my session key.

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• Database design for a Fantasy league

  - by Samidh T

  Here's the basic schema for my database Table user{ userid numeber primary key, count number } Table player{ pid number primary key, } Table user-player{ userid number primary key foreign key(user), pid number primary key foreign key(player) } Table temp{ pid number primary key, points number } Here's what I intend to do... After every match the temp table is updated which holds the id of players that played the last match and the points they earned. Next run a procedure that will match the pid from temp table with every uid of user-player table having the same pid. add the points from temp table to the count of user table for every matching uid. empty temp table. My questions is considering 200 players and 10000 users,Will this method be efficient? I am going to be using mysql for this.

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• C programming: hashtable insertion/search

  - by Ricardo Campos

  Hello i have a problem with my hash table its implemented like this: #define HT_SIZE 10 typedef struct _list_t_ { char key[20]; char string[20]; char prevValue[20]; struct _list_t_ *next; } list_t; typedef struct _hash_table_t_ { int size; /* the size of the table */ list_t ***table; /* first */ sem_t lock; } hash_table_t; I have a Linked list with 3 pointers because i want a hash table with several partitions (shards), here is my initialization of my Hash table: hash_table_t *create_hash_table(int NUM_SERVER_THREADS, int num_shards){ hash_table_t *new_table; int j,i; if (HT_SIZE<1) return NULL; /* invalid size for table */ /* Attempt to allocate memory for the hashtable structure */ new_table = (hash_table_t*)malloc(sizeof(hash_table_t)*HT_SIZE); /* Attempt to allocate memory for the table itself */ new_table->table = (list_t ***)calloc(1,sizeof(list_t **)); /* Initialize the elements of the table */ for(j=0; j<num_shards; j++){ new_table->table[j] = (list_t **)calloc(1,sizeof(list_t *)); for(i=0; i<HT_SIZE; i++){ new_table->table[j][i] = (list_t *)calloc(1,sizeof(list_t )); } } /* Set the table's size */ new_table->size = HT_SIZE; sem_init(&new_table->lock, 0, 1); return new_table; } Here is my search function to search in the hash table list_t *lookup_string(hash_table_t *hashtable, char *key, int shardId){ list_t *list ; int hashval = hash(key); /* Go to the correct list based on the hash value and see if key is * in the list. If it is, return return a pointer to the list element. * If it isn't, the item isn't in the table, so return NULL. */ sem_wait(&hashtable->lock); for(list = hashtable->table[shardId][hashval]; list != NULL; list =list->next) { if (strcmp(key, list->key) == 0){ sem_post(&hashtable->lock); return list; } } sem_post(&hashtable->lock); return NULL; } And my insert function: char *add_string(hash_table_t *hashtable, char *str,char *key, int shardId){ list_t *new_list; list_t *current_list; unsigned int hashval = hash(key); /*printf("|%d|%d|%s|\n",hashval,shardId,key);*/ /* Lock for concurrency */ sem_wait(&hashtable->lock); /* Attempt to allocate memory for list */ new_list = (list_t*)malloc(sizeof(list_t)); /* Does item already exist? */ sem_post(&hashtable->lock); current_list = lookup_string(hashtable, key,shardId); sem_wait(&hashtable->lock); /* item already exists, don't insert it again. */ if (current_list != NULL){ strcpy(new_list->prevValue,current_list->string); strcpy(new_list->string,str); strcpy(new_list->key,key); new_list->next = hashtable->table[shardId][hashval]; hashtable->table[shardId][hashval] = new_list; sem_post(&hashtable->lock); return new_list->prevValue; } /* Insert into list */ strcpy(new_list->string,str); strcpy(new_list->key,key); new_list->next = hashtable->table[shardId][hashval]; hashtable->table[shardId][hashval] = new_list; /* Unlock */ sem_post(&hashtable->lock); return new_list->prevValue; } My main class runs some of tests by executing the insertion / reading / delete from the elements of the hash table the problem is when i have more than 4 partitions/shards the tests stop at the first reading element saying it returned the wrong value NULL on the search function, when its less than 4 it runs perfectly well and passes all the tests. You can see my main.c in here if you want to give a look: http://hostcode.sourceforge.net/view/1105 My complete Hash table code: http://hostcode.sourceforge.net/view/1103 And other functions where hash table code is executed: .c file http://hostcode.sourceforge.net/view/1104 .h file http://hostcode.sourceforge.net/view/1106 Thank for you time, i appreciate any help you can give to me this is a college important project that I'm trying to solve and I'm stuck here for 2 days.

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• Hash default value not being used

  - by ba

  Today I tried the following snippets of code and I don't understand why I get different results between them. As far as I can understand they are the same. One uses the default value off Hash and the other snippet creates an empty array for the key before it'll be accessed. Anyone who understands what's going on? :) # Hash default if the key doesn't have a value set is an empty Array a = Hash.new([]) a[:key] << 2 # => [2] p a # => {} nil p a[:key] # => [2] # Explicitly add an array for all nodes before creating b = Hash.new b[:key] ||= [] b[:key] << 2 # => [2] p b # => {:key=>[2]}

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• Send Ctrl+Up to a window

  - by dutt

  I'm trying to send messages to a window that says Ctrl and Up-arrow has been pressed. I've got the basics down, I can send presses of the space key that registeres fine. But I can't seem to get the ctrl+up working. chosen code snippets: [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)] static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam); Now this works fine for sending Space: public static void SendKeyPress(IntPtr handle, VKeys key) { SendMessage(handle, (int) WMessages.WM_KEYDOWN, (int) key, 0); SendMessage(handle, (int)WMessages.WM_KEYUP, (int)key, 0); } But this doesn't work for sending Ctrl+Up: public static void SendKeyPress(IntPtr handle, VKeys key, bool control) { SendMessage(handle, (int) WMessages.WM_KEYDOWN, (int) key, 0); SendMessage(handle, (int) WMessages.WM_KEYDOWN, (int)VKeys.VK_CONTROL, 0); SendMessage(handle, (int)WMessages.WM_KEYUP, (int)key, 0); SendMessage(handle, (int)WMessages.WM_KEYUP, (int)VKeys.VK_CONTROL, 0); } What am I missing?

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• Converting keys of an array/object-tree to lowercase

  - by tstenner

  Im currently optimizing a PHP application and found one function being called around 10-20k times, so I'd thought I'd start optimization there. function keysToLower($obj) { if(!is_object($obj) && !is_array($obj)) return $obj; foreach($obj as $key=>$element) { $element=keysToLower($element); if(is_object($obj)) { $obj->{strtolower($key)}=$element; if(!ctype_lower($key)) unset($obj->{$key}); } else if(is_array($obj) && ctype_upper($key)) { $obj[strtolower($key)]=$element; unset($obj[$key]); } } return $obj; } Most of the time is spent in recursive calls (which are quite slow in PHP), but I don't see any way to convert it to a loop. What would you do?

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• Pygame single push event

  - by Miller92Time

  in Pygame i am trying to translate an image by 10% in each direction using each arrow key. right now the code i am using moves the image as long as the key is pushed down, what I want is for it to move only once regardless if the key is still pushed down or not. if event.type == KEYDOWN: if (event.key == K_RIGHT): DISPLAYSURF.fill((255,255,255)) #Clears the screen translation_x(100) draw(1) if (event.key == K_LEFT): DISPLAYSURF.fill((255,255,255)) #Clears the screen translation_x(-100) draw(2) if (event.key == K_UP): DISPLAYSURF.fill((255,255,255)) #Clears the screen translation_y(100) draw(3) if (event.key == K_DOWN): DISPLAYSURF.fill((255,255,255)) #Clears the screen translation_y(-100) draw(4) is there a simpler way of implementing this besides using time.sleep

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• How to write a list to a text file in the correct format

  - by lia1000

  I've got this piece of code that I want to write the output to a text file but with the correct format i.e. no brackets, single quotes so it appears as a formatted list. This is the code: file = open("env5.txt", "w"); for key in os.environ.keys(): env = os.environ[key]; key1 = key; list = str([key, env]).replace("'","").replace('[]', ''); list2 = list[1:-1]; print(list2); file.writelines(list2); file.close(); This is the original code: for key in os.environ.keys(): print(key, os.environ[key]); Many thanks

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• C#/.NET Little Wonders: Using &lsquo;default&rsquo; to Get Default Values

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Today’s little wonder is another of those small items that can help a lot in certain situations, especially when writing generics.  In particular, it is useful in determining what the default value of a given type would be. The Problem: what’s the default value for a generic type? There comes a time when you’re writing generic code where you may want to set an item of a given generic type.  Seems simple enough, right?  We’ll let’s see! Let’s say we want to query a Dictionary<TKey, TValue> for a given key and get back the value, but if the key doesn’t exist, we’d like a default value instead of throwing an exception. So, for example, we might have a the following dictionary defined: 1: var lookup = new Dictionary<int, string> 2: { 3: { 1, "Apple" }, 4: { 2, "Orange" }, 5: { 3, "Banana" }, 6: { 4, "Pear" }, 7: { 9, "Peach" } 8: }; And using those definitions, perhaps we want to do something like this: 1: // assume a default 2: string value = "Unknown"; 3:  4: // if the item exists in dictionary, get its value 5: if (lookup.ContainsKey(5)) 6: { 7: value = lookup[5]; 8: } But that’s inefficient, because then we’re double-hashing (once for ContainsKey() and once for the indexer).  Well, to avoid the double-hashing, we could use TryGetValue() instead: 1: string value; 2:  3: // if key exists, value will be put in value, if not default it 4: if (!lookup.TryGetValue(5, out value)) 5: { 6: value = "Unknown"; 7: } But the “flow” of using of TryGetValue() can get clunky at times when you just want to assign either the value or a default to a variable.  Essentially it’s 3-ish lines (depending on formatting) for 1 assignment.  So perhaps instead we’d like to write an extension method to support a cleaner interface that will return a default if the item isn’t found: 1: public static class DictionaryExtensions 2: { 3: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 4: TKey key, TValue defaultIfNotFound) 5: { 6: TValue value; 7:  8: // value will be the result or the default for TValue 9: if (!dict.TryGetValue(key, out value)) 10: { 11: value = defaultIfNotFound; 12: } 13:  14: return value; 15: } 16: } 17:  So this creates an extension method on Dictionary<TKey, TValue> that will attempt to get a value using the given key, and will return the defaultIfNotFound as a stand-in if the key does not exist. This code compiles, fine, but what if we would like to go one step further and allow them to specify a default if not found, or accept the default for the type?  Obviously, we could overload the method to take the default or not, but that would be duplicated code and a bit heavy for just specifying a default.  It seems reasonable that we could set the not found value to be either the default for the type, or the specified value. So what if we defaulted the type to null? 1: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 2: TKey key, TValue defaultIfNotFound = null) // ... No, this won’t work, because only reference types (and Nullable<T> wrapped types due to syntactical sugar) can be assigned to null.  So what about a calling parameterless constructor? 1: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 2: TKey key, TValue defaultIfNotFound = new TValue()) // ... No, this won’t work either for several reasons.  First, we’d expect a reference type to return null, not an “empty” instance.  Secondly, not all reference types have a parameter-less constructor (string for example does not).  And finally, a constructor cannot be determined at compile-time, while default values can. The Solution: default(T) – returns the default value for type T Many of us know the default keyword for its uses in switch statements as the default case.  But it has another use as well: it can return us the default value for a given type.  And since it generates the same defaults that default field initialization uses, it can be determined at compile-time as well. For example: 1: var x = default(int); // x is 0 2:  3: var y = default(bool); // y is false 4:  5: var z = default(string); // z is null 6:  7: var t = default(TimeSpan); // t is a TimeSpan with Ticks == 0 8:  9: var n = default(int?); // n is a Nullable<int> with HasValue == false Notice that for numeric types the default is 0, and for reference types the default is null.  In addition, for struct types, the value is a default-constructed struct – which simply means a struct where every field has their default value (hence 0 Ticks for TimeSpan, etc.). So using this, we could modify our code to this: 1: public static class DictionaryExtensions 2: { 3: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 4: TKey key, TValue defaultIfNotFound = default(TValue)) 5: { 6: TValue value; 7:  8: // value will be the result or the default for TValue 9: if (!dict.TryGetValue(key, out value)) 10: { 11: value = defaultIfNotFound; 12: } 13:  14: return value; 15: } 16: } Now, if defaultIfNotFound is unspecified, it will use default(TValue) which will be the default value for whatever value type the dictionary holds.  So let’s consider how we could use this: 1: lookup.GetValueOrDefault(1); // returns “Apple” 2:  3: lookup.GetValueOrDefault(5); // returns null 4:  5: lookup.GetValueOrDefault(5, “Unknown”); // returns “Unknown” 6:  Again, do not confuse a parameter-less constructor with the default value for a type.  Remember that the default value for any type is the compile-time default for any instance of that type (0 for numeric, false for bool, null for reference types, and struct will all default fields for struct).  Consider the difference: 1: // both zero 2: int i1 = default(int); 3: int i2 = new int(); 4:  5: // both “zeroed” structs 6: var dt1 = default(DateTime); 7: var dt2 = new DateTime(); 8:  9: // sb1 is null, sb2 is an “empty” string builder 10: var sb1 = default(StringBuilder()); 11: var sb2 = new StringBuilder(); So in the above code, notice that the value types all resolve the same whether using default or parameter-less construction.  This is because a value type is never null (even Nullable<T> wrapped types are never “null” in a reference sense), they will just by default contain fields with all default values. However, for reference types, the default is null and not a constructed instance.  Also it should be noted that not all classes have parameter-less constructors (string, for instance, doesn’t have one – and doesn’t need one). Summary Whenever you need to get the default value for a type, especially a generic type, consider using the default keyword.  This handy word will give you the default value for the given type at compile-time, which can then be used for initialization, optional parameters, etc. Technorati Tags: C#,CSharp,.NET,Little Wonders,default

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