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  • Reading a binary file in perl: Bad File Descriptor

    - by Magicked
    I'm trying to read a binary file 40 bytes at a time, then check to see if all those bytes are 0x00, and if so ignore them. If not, it will write them back out to another file (basically just cutting out large blocks of null bytes). This may not be the most efficient way to do this, but I'm not worried about that. However, right now I'm getting a "Bad File Descriptor" error and I cannot figure out why. my $comp = "\x00" * 40; my $byte_count = 0; my $infile = "/home/magicked/image1"; my $outfile = "/home/magicked/image1_short"; open IN, "<$infile"; open OUT, ">$outfile"; binmode IN; binmode OUT; my ($buf, $data, $n); while (read (IN, $buf, 40)) { ### Problem is here ### $boo = 1; for ($i = 0; $i < 40; $i++) { if ($comp[$i] != $buf[$i]) { $i = 40; print OUT $buf; $byte_count += 40; } } } die "Problems! $!\n" if $!; close OUT; close IN; I marked with a comment where it is breaking. Thanks for any help!

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  • Combining Data from two MySQL tables.

    - by Nick
    I'm trying to combine data from two tables in MySQL with PHP. I want to select all the data (id, title, post_by, content and created_at) from the "posts" table. Then I would like to select the comment_id COUNT from the "comments" table IF the comment_id equals the posts id. Finally, I would like to echo/print something on this order: <? echo $row->title; ?> Posted by <? echo $row->post_by; ?> on <? echo $row->created_at; ?> CST <? echo $row->content; ?> <? echo $row->comment_id; ?> comments | <a href="comment.php?id=<? echo $row->id; ?>">view/post comments</a> I'm uncertain as to how to "combine" the data from two tables. I have tried numerous things and have spent several evenings and have had no luck. Any help would be greatly appreciated!

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  • How to check if a node's value in one XML is present in another XML with a specific attribute?

    - by Manish
    The question seems to be little confusing. So let me describe my situation through an example: Suppose I have an XML: A.xml <Cakes> <Cake>Egg</Cake> <Cake>Banana</Cake> </Cakes> Another XML: B.xml <Cakes> <Cake show="true">Egg</Cake> <Cake show="true">Strawberry</Cake> <Cake show="false">Banana</Cake> </Cakes> Now I want to show some text say "TRUE" if all the Cake in A.xml have show="true" in B.xml else "FALSE". In the above case, it will print FALSE. I need to develop an XSL for that. I can loop through all the Cake in A.xml and check if that cake has show="true" in B.xml but I don't know how to break in between (and set a variable) if a show="false" is found. Is it possible? Any help/comments appreciated.

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  • Compound Primary Key in Hibernate using Annotations

    - by Rich
    Hi, I have a table which uses two columns to represent its primary key, a transaction id and then the sequence number. I tried what was recommended http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#entity-mapping in section 2.2.3.2.2, but when I used the Hibernate session to commit this Entity object, it leaves out the TXN_ID field in the insert statement and only includes the BA_SEQ field! What's going wrong? Here's the related code excerpt: @Id @Column(name="TXN_ID") private long txn_id; public long getTxnId(){return txn_id;} public void setTxnId(long t){this.txn_id=t;} @Id @Column(name="BA_SEQ") private int seq; public int getSeq(){return seq;} public void setSeq(int s){this.seq=s;} And here are some log statements to show what exactly happens to fail: In createKeepTxnId of DAO base class: about to commit Transaction :: txn_id->90625 seq->0 ...<Snip>... Hibernate: insert into TBL (BA_ACCT_TXN_ID, BA_AUTH_SRVC_TXN_ID, BILL_SRVC_ID, BA_BILL_SRVC_TXN_ID, BA_CAUSE_TXN_ID, BA_CHANNEL, CUSTOMER_ID, BA_MERCHANT_FREETEXT, MERCHANT_ID, MERCHANT_PARENT_ID, MERCHANT_ROOT_ID, BA_MERCHANT_TXN_ID, BA_PRICE, BA_PRICE_CRNCY, BA_PROP_REQS, BA_PROP_VALS, BA_REFERENCE, RESERVED_1, RESERVED_2, RESERVED_3, SRVC_PROD_ID, BA_STATUS, BA_TAX_NAME, BA_TAX_RATE, BA_TIMESTAMP, BA_SEQ) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?) [WARN] util.JDBCExceptionReporter SQL Error: 1400, SQLState: 23000 [ERROR] util.JDBCExceptionReporter ORA-01400: cannot insert NULL into ("SCHEMA"."TBL"."TXN_ID") The important thing to note is I print out the entity object which has a txn_id set, and then the following insert into statement does not include TXN_ID in the listing and thus the NOT NULL table constraint rejects the query.

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  • SQL query error while trying to put a file in the database

    - by DaGhostman Dimitrov
    Hey Guys I have a big problem that I have no Idea why.. I have few forms that upload files to the database, all of them work fine except one.. I use the same query in all(simple insert). I think that it has something to do with the files i am trying to upload but I am not sure. Here is the code: if ($_POST['action'] == 'hndlDocs') { $ref = $_POST['reference']; // Numeric value of $doc = file_get_contents($_FILES['doc']['tmp_name']); $link = mysqli_connect('localhost','XXXXX','XXXXX','documents'); mysqli_query($link,"SET autocommit = 0"); $query = "INSERT INTO documents ({$ref}, '{$doc}', '{$_FILES['doc']['type']}') ;"; mysqli_query($link,$query); if (mysqli_error($link)) { var_dump(mysqli_error($link)); mysqli_rollback($link); } else { print("<script> window.history.back(); </script>"); mysqli_commit($link); } } The database has only these fields: DATABASE documents ( reference INT(5) NOT NULL, //it is unsigned zerofill doc LONGBLOB NOT NULL, //this should contain the binary data mime_type TEXT NOT NULL // the mime type of the file php allows only application/pdf and image/jpeg ); And the error I get is : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '00001, '????' at line 1 I will appreciate every help. Cheers!

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  • EXEC_BAD_ACCESS error comes in my applicatoin in iphone

    - by Jaimin
    when i print dictionary i got this error.. here my dictTf is mutabledictionay.. when i m in home page i selct few fields and click find. so new view comes with the result.. now i go back and again click find without changing anything.. now comes proper.. now at this moment when i go back it shows this in the dictionay and EXEC_BAD_ACCESS eror comes... Printing description of dictTf: The program being debugged was signaled while in a function called from GDB. GDB has restored the context to what it was before the call. To change this behavior use "set unwindonsignal off" Evaluation of the expression containing the function (CFShow) will be abandoned. The program being debugged was signaled while in a function called from GDB. GDB has restored the context to what it was before the call. To change this behavior use "set unwindonsignal off" Evaluation of the expression containing the function (CFShow) will be abandoned. (gdb)

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  • define a closure as method from class

    - by user272839
    Hi, i'm trying to play with php5.3 and closure. I see here (Listing 7. Closure inside an object : http://www.ibm.com/developerworks/opensource/library/os-php-5.3new2/index.html) that it's possible to use $this in the callback function, but it's not. So I try to give $this as use variable : $self = $this; $foo = function() use($self) { //do something with $self } So to use the same example : class Dog { private $_name; protected $_color; public function __construct($name, $color) { $this->_name = $name; $this->_color = $color; } public function greet($greeting) { $self = $this; return function() use ($greeting, $self) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; }; } } $dog = new Dog("Rover","red"); $dog->greet("Hello"); Output: Hello, I am a red dog named Rover. First of all this example does not print the string but return the function, but that's not my problem. Secondly I can't access to private or protected, because the callback function is a global function and not in the context from the Dog object. Tha't my problem. It's the same as : function greet($greeting, $object) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; } And I want : public function greet($greeting) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; } Which is from Dog and not global. I hope that I am clear ...

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  • Scope of the c++ using directive

    - by ThomasMcLeod
    From section 7.3.4.2 of the c++11 standard: A using-directive specifies that the names in the nominated namespace can be used in the scope in which the using-directive appears after the using-directive. During unqualified name lookup (3.4.1), the names appear as if they were declared in the nearest enclosing namespace which contains both the using-directive and the nominated namespace. [ Note: In this context, “contains” means “contains directly or indirectly”. —end note ] What do the second and third sentences mean exactly? Please give example. Here is the code I am attempting to understand: namespace A { int i = 7; } namespace B { using namespace A; int i = i + 11; } int main(int argc, char * argv[]) { std::cout << A::i << " " << B::i << std::endl; return 0; } It print "7 7" and not "7 18" as I would expect. Sorry for the typo, the program actually prints "7 11".

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  • Why does the output look like this?

    - by cjk
    I have a c program below, I would like to send out a 32 bit message in a particular order Eg.0x00000001. #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <stdint.h> struct test { uint16_t a; uint16_t b; }; int main(int argc, char const *argv[]) { char buf[4]; struct test* ptr=(struct test*)buf; ptr->a=0x0000; ptr->b=0x0001; printf("%x %x\n",buf[0],buf[1]); //output is 0 0 printf("%x %x\n",buf[2],buf[3]); //output is 1 0 return 0; } Then I test it by print out the values in char array. I got output in the above comments. Shouldn't the output be 0 0 and 0 1? since but[3] is the last byte? Is there anything I missed? Thanks!

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  • How to parse time stamps with Unicode characters in Java or Perl?

    - by ram
    I'm trying to make my code as generic as possible. I'm trying to parse install time of a product installation. I will have two files in the product, one that has time stamp I need to parse and other file tells the language of the installation. This is how I'm parsing the timestamp public class ts { public static void main (String[] args){ String installTime = "2009/11/26 \u4e0b\u5348 04:40:54"; //This timestamp I got from the first file. Those unicode charecters are some Chinese charecters...AM/PM I guess //Locale = new Locale();//don't set the language yet SimpleDateFormat df = (SimpleDateFormat)DateFormat.getDateTimeInstance(DateFormat.DEFAULT,DateFormat.DEFAULT); Date instTime = null; try { instTime = df.parse(installTime); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println(instTime.toString()); } } The output I get is Parsing Failed java.text.ParseException: Unparseable date: "2009/11/26 \u4e0b\u5348 04:40:54" at java.text.DateFormat.parse(Unknown Source) at ts.main(ts.java:39) Exception in thread "main" java.lang.NullPointerException at ts.main(ts.java:45) It throws exception and at the end when I print it, it shows some proper date... wrong though. I would really appreciate if you could clarify me on these doubts How to parse timestamps that have unicode characters if this is not the proper way? If parsing is failed, how could instTime able to hold some date, wrong though? I know its some chinese,Korean time stamps so I set the locale to zh and ko as follows.. even then same error comes again Locale = new Locale("ko"); Locale = new Locale("ja"); Locale = new Locale("zh"); How can I do the same thing in Perl? I can't use Date::Manip package; Is there any other way?

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  • Options for displaying OG groups a node is published for on node page?

    - by Erik Töyrä
    What I want I have several OG groups in which content can be published. I would like to display which OG groups a node has been published for when viewing the node page. Like in "This page is published for: Department A, Department B." The code snipped below shows the data I have in the $node object in node.tpl.php. This data is generated by the OG module. Extracted data from $node ... [og_groups] => Array ( [993] => 993 [2078] => 2078 ) [og_groups_both] => Array ( [993] => Department A [2078] => Department B ) ... I know I could loop through the og_groups_both array in node.tpl.php and generate the output from there, but it feels like a quite dirty solution. The ideal solution would be to have a $og_groups variable in node.tpl.php, similiar to how $submitted is used in node.tpl.php (see below). Example of how $submitted is used <?php if ($submitted): ?> <div class="submitted"><?php print $submitted; ?></div> <?php endif; ?> Should I use hook_load() in a custom module to insert the new variable $og_groups in $node? What options do I have and which solution would you recommend?

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  • Simple App Engine Sessions Implementation

    - by raz0r
    Here is a very basic class for handling sessions on App Engine: """Lightweight implementation of cookie-based sessions for Google App Engine. Classes: Session """ import os import random import Cookie from google.appengine.api import memcache _COOKIE_NAME = 'app-sid' _COOKIE_PATH = '/' _SESSION_EXPIRE_TIME = 180 * 60 class Session(object): """Cookie-based session implementation using Memcached.""" def __init__(self): self.sid = None self.key = None self.session = None cookie_str = os.environ.get('HTTP_COOKIE', '') self.cookie = Cookie.SimpleCookie() self.cookie.load(cookie_str) if self.cookie.get(_COOKIE_NAME): self.sid = self.cookie[_COOKIE_NAME].value self.key = 'session-' + self.sid self.session = memcache.get(self.key) if self.session: self._update_memcache() else: self.sid = str(random.random())[5:] + str(random.random())[5:] self.key = 'session-' + self.sid self.session = dict() memcache.add(self.key, self.session, _SESSION_EXPIRE_TIME) self.cookie[_COOKIE_NAME] = self.sid self.cookie[_COOKIE_NAME]['path'] = _COOKIE_PATH print self.cookie def __len__(self): return len(self.session) def __getitem__(self, key): if key in self.session: return self.session[key] raise KeyError(str(key)) def __setitem__(self, key, value): self.session[key] = value self._update_memcache() def __delitem__(self, key): if key in self.session: del self.session[key] self._update_memcache() return None raise KeyError(str(key)) def __contains__(self, item): try: i = self.__getitem__(item) except KeyError: return False return True def _update_memcache(self): memcache.replace(self.key, self.session, _SESSION_EXPIRE_TIME) I would like some advices on how to improve the code for better security. Note: In the production version it will also save a copy of the session in the datastore. Note': I know there are much more complete implementations available online though I would like to learn more about this subject so please don't answer the question with "use that" or "use the other" library.

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  • Crosstab with multiple items

    - by Michael Wexler
    In SPSS, it is (relatively) easy to create a cross tab with multiple variables using the factors as the table heading. So, something like the following (made up data, etc.). Q1, Q2, and Q3 each have either a 1, a 2, or a 3 for each person. 1 (very Often) 2 (Rarely) 3 (Never) Q1. Likes it 12 15 13 Q2. Recommends it 22 11 10 Q3. Used it 22 12 9 In SPSS, one can even request row, column, or total percentages. I've tried table(), ftable(), xtab(), CrossTable() from gmodels, and CrossTable() from descr, and none of these can handle (afaik) multiple variables; they mostly seem to handle 1 variable crossed with another variable, and the 3rd creates layers. Is there a package with some good cross tabbing/table examples that I could use to figure this out? I'm sure I'm missing something simple, so I appreciate you pointing out what I missed. Perhaps I have to generate each row as a separate list and then make a dataframe and print the dataframe?

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  • How can I define an empty array in a Perl construtor?

    - by Laimoncijus
    I am just beginner with Perl, so if it sounds stupid - sorry for that :) My problem is - I am trying to write a class, which has an empty array, defined in constructor of a class. So I am doing this like this: package MyClass; use strict; sub new { my ($C) = @_; my $self = { items => () }; bless $self, ref $C || $C; } sub get { return $_[0]->{items}; } 1; Later I am testing my class with simple script: use strict; use Data::Dumper; use MyClass; my $o = MyClass->new(); my @items = $o->get(); print "length = ", scalar(@items), "\n", Dumper(@items); And while running the script I get following: $ perl my_test.pl length = 1 $VAR1 = undef; Why am I doing wrong what causes that I get my items array filled with undef? Maybe someone could show me example how the class would need to be defined so I would not get any default values in my array?

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  • JAVA MySql multiple word search

    - by user1703849
    i have a database in MySql that has a name column in it which contains several words(description). I am connected to database with java through eclipse. I have a search, that returns results if only name field contains one word. id: name: info: type: 1 balloon big red balloon big 2 house expensive beautiful luxury 3 chicken wings deep fried wings tasty these are just random words but as an example my search can only see ex. balloon and then show info, but if i type chicken wings, it does nothing. so it possible somehow to search from columns with multiple words? this is my search code below import java.io.*; import java.sql.*; import java.util.*; class Search { public static void main(String[] args) { Scanner inp``ut = new Scanner(System.in); try { Connection con = DriverManager.getConnection( "jdbc:mysql://example/mydb", "user", "password"); Statement stmt = (Statement) con.createStatement(); System.out.print("enter search: "); String name = input.next(); String SQL = "SELECT * FROM menu where name LIKE '" + name + "'"; ResultSet rs = stmt.executeQuery(SQL); while (rs.next()) { System.out.println("Name: " +rs.getString("name")); System.out.println("Description: " + rs.getString("info") ); System.out.println("Price: " + rs.getString("Price")); } } catch (Exception e) { System.out.println("ERROR: " + e.getMessage()); } } }

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  • Problem with checkboxes, sql select statements & php

    - by smokey20
    I am trying to display some rows from a database table based on choices submitted by the user. Here is my form code <form action="choice.php" method="POST" > <input type="checkbox" name="variable[]" value="Apple">Apple <input type="checkbox" name="variable[]" value="Banana">Banana <input type="checkbox" name="variable[]" value="Orange">Orange <input type="checkbox" name="variable[]" value="Melon">Melon <input type="checkbox" name="variable[]" value="Blackberry">Blackberry From what I understand I am placing the values of these into an array called variable. Two of my columns are called receipe name and ingredients(each field under ingredients can store a number of fruits). What I would like to do is, if a number of checkboxes are selected then the receipe name/s is displayed. Here is my php code. <?php // Make a MySQL Connection mysql_connect("localhost", "*****", "*****") or die(mysql_error()); mysql_select_db("****") or die(mysql_error()); $variable=$_POST['variable']; foreach ($variable as $variablename) { echo "$variablename is checked"; } $query = "SELECT receipename FROM fruit WHERE $variable like ingredients"; $row = mysql_fetch_assoc($result); foreach ($_POST['variabble'] as $ingredients) echo $row[$ingredients] . '<br/>'; ?> I am very new to php and just wish to display the data, I do not need to perform any actions on it. I have tried many select statements but I cannot get any results to display. My db connection is fine and it does print out what variables are checked. Many thanks in advance.

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  • BeautifulSoup: just get inside of a tag, no matter how many enclosing tags there are

    - by AP257
    I'm trying to scrape all the inner html from the <p> elements in a web page using BeautifulSoup. There are internal tags, but I don't care, I just want to get the internal text. For example, for: <p>Red</p> <p><i>Blue</i></p> <p>Yellow</p> <p>Light <b>green</b></p> How can I extract: Red Blue Yellow Light green Neither .string nor .contents[0] does what I need. Nor does .extract(), because I don't want to have to specify the internal tags in advance - I want to deal with any that may occur. Is there a 'just get the visible HTML' type of method in BeautifulSoup? ----UPDATE------ On advice, trying: p_tags = page.findAll('p',text=True) for i, p_tag in enumerate(p_tags): print str(p_tag) But that doesn't help - it just prints out: Red <i>Blue</i> Yellow Light <b>green</b>

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  • In what order should the Python concepts be explained to absolute beginners?

    - by Tomaž Pisanski
    I am teaching Python to undergraduate math majors. I am interested in the optimal order in which students should be introduced to various Python concepts. In my view, at each stage the students should be able to solve a non-trivial programming problem using only the tools available at that time. Each new tool should enable a simpler solution to a familiar problem. A selection of numerous concepts available in Python is essential in order to keep students focused. They should also motivated and should appreciate each newly mastered tool without too much memorization. Here are some specific questions: For instance, my predecessor introduced lists before strings. I think the opposite is a better solution. Should function definitions be introduced at the very beginning or after mastering basic structured programming ideas, such as decisions (if) and loops (while)? Should sets be introduced before dictionaries? Is it better to introduce reading and writing files early in the course or should one use input and print for most of the course? Any suggestions with explanations are most welcome.

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  • Regular Expression with Names and Emails

    - by Nina
    I am having a problem with regular expressions at the moment. What I'm trying to do is that for each line through the iteration, it checks for this type of pattern: Lastname, Firstname If it finds the name, then it will take the first letter of the first name, and the first six letters of the lastname and form it as an email. I have the following: $checklast = "[A-z],"; $checkfirst = "[A-z]"; if (ereg($checklast, $parts[1])||ereg($checkfirst, $parts[2])){ $first = preg_replace($checkfirst, $checkfirst{1,1}, $parts[2]); print "<a href='mailto:[email protected];'> $parts[$i] </a>"; } This one obviously broke the code. But I was initially attempting to find only the first letter of the firstname and then after that the first six letters of the lastname followed by the @email.com This didn't work out too well. I'm not sure what to do at this point. Any help is much appreciated.

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  • How to compare two file structures in PHP?

    - by OM The Eternity
    I have a function which gives me the complete file structure upto n-level, function getDirectory($path = '.', $ignore = '') { $dirTree = array (); $dirTreeTemp = array (); $ignore[] = '.'; $ignore[] = '..'; $dh = @opendir($path); while (false !== ($file = readdir($dh))) { if (!in_array($file, $ignore)) { if (!is_dir("$path/$file")) { //display of file and directory name with their modification time $stat = stat("$path/$file"); $statdir = stat("$path"); $dirTree["$path"][] = $file. " === ". date('Y-m-d H:i:s', $stat['mtime']) . " Directory == ".$path."===". date('Y-m-d H:i:s', $statdir['mtime']) ; } else { $dirTreeTemp = getDirectory("$path/$file", $ignore); if (is_array($dirTreeTemp))$dirTree = array_merge($dirTree, $dirTreeTemp); } } } closedir($dh); return $dirTree; } $ignore = array('.htaccess', 'error_log', 'cgi-bin', 'php.ini', '.ftpquota'); //function call $dirTree = getDirectory('.', $ignore); //file structure array print print_r($dirTree); Now here my requirement is , I have two sites The Development/Test Site- where i do testing of all the changes The Production Site- where I finally post all the changes as per test in development site Now, for example, I have tested an image upload in the Development/test site, and i found it appropriate to publish on Production site then i will completely transfer the Development/Test DB detail to Production DB, but now I want to compare the files structure as well to transfer the corresponding image file to Production folder. There could be the situation when I update the image by editing the image and upload it with same name, now in this case the image file would be already present there, which will restrict the use of "file_exist" logic, so for these type of situations....HOW CAN I COMPARE THE TWO FILE STRUCTURE TO GET THE SYNCHRONIZATION DONE AS PER REQUIREMENT??

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  • Go and a bad prime number algorithm

    - by anonymous
    I wrote this prime number sieving algorithm and it doesn't run properly. I can't find the error in the algorithm itself. Could someone help me? This is what it's supposed to print: [2 3 5 7 11 13 17 19 23 29] Versus what it actually prints: [3 5 7 11 13 17 19 23 25 29] . package main import "fmt" func main() { var primes = sieve(makeNumbers(29)) fmt.Printf("%d\n", primes); } func makeNumbers(n int) []int { var numbers = make([]int, n - 1) for i := 0; i < len(numbers); i++ { numbers[i] = i + 2 } return numbers } func sieve(numbers []int) []int { var numCopy = numbers var max = numbers[len(numbers)-1] var sievedNumbers = make([]int, 0) for i := 0; numCopy[i]*numCopy[i] <= max; i++ { for j := i; j < len(numCopy); j++ { if numCopy[j] % numCopy[i] != 0 || j == i { sievedNumbers = append(sievedNumbers, numCopy[j]) } } numCopy = sievedNumbers sievedNumbers = make([]int, 0) } return numCopy }

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  • How to keep track of call statistics? C++

    - by tf.rz
    I'm working on a project that delivers statistics to the user. I created a class called Dog, And it has several functions. Speak, woof, run, fetch, etc. I want to have a function that spits out how many times each function has been called. I'm also interested in the constructor calls and destructor calls as well. I have a header file which defines all the functions, then a separate .cc file that implements them. My question is, is there a way to keep track of how many times each function is called? I have a function called print that will fetch the "statistics" and then output them to standard output. I was considering using static integers as part of the class itself, declaring several integers to keep track of those things. I know the compiler will create a copy of the integer and initialize it to a minimum value, and then I'll increment the integers in the .cc functions. I also thought about having static integers as a global variable in the .cc. Which way is easier? Or is there a better way to do this? Any help is greatly appreciated!

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  • Java abstract visitor - guarantueed to succeed? If so, why?

    - by disown
    I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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  • How to map (large) integer on (small in size( alphanumeric string with PHP? (Cantor?)

    - by Glooh
    Dear all, I can't figure out how to optimally do the following in PHP: In a database, I have messages with a unique ID, like 19041985. Now, I want to refer to these messages in a short-url service but not using generated hashes but by simply 'calculate' the original ID. In other words, for example: http://short.url/sYsn7 should let me calculate the message ID the visitor would like to request. To make it more obvious, I wrote the following in PHP to generate these 'alphanumeric ID versions' and of course, the other way around will let me calculate the original message ID. The question is: Is this the optimal way of doing this? I hardly think so, but can't think of anything else. $alphanumString = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_'; for($i=0;$i < strlen($alphanumString);$i++) { $alphanumArray[$i] = substr($alphanumString,$i,1); } $id = 19041985; $out = ''; for($i=0;$i < strlen($id);$i++) { if(isset($alphanumString["".substr($id,$i,2).""]) && strlen($alphanumString["".substr($id,$i,2).""]) 0) { $out.=$alphanumString["".substr($id,$i,2).""]; } else { $out.=$alphanumString["".substr($id,$i,1).""]; $out.=$alphanumString["".substr($id,($i+1),1).""]; } $i++; } print $out;

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  • Python list should be empty on class instance initialisation, but it's not. Why?

    - by canavanin
    Hi everyone! I would like to create instances of a class containing a list that's empty by default; instead of later setting this list to the final full list I would like to successively add items to it. Here's a piece of sample code illustrating this: #!/usr/bin/python class test: def __init__(self, lst=[], intg=0): self.lista = lst self.integer = intg name_dict = {} counter = 0 for name in ('Anne', 'Leo', 'Suzy'): counter += 1 name_dict[name] = test() name_dict[name].integer += 1 name_dict[name].lista.append(counter) print name, name_dict[name].integer, name_dict[name].lista When I ran the above program I expected to get Anne 1 [1] Leo 1 [2] Suzy 1 [3] as I assumed lista to always be initialised to an empty list. What I got instead was this: Anne 1 [1] Leo 1 [1, 2] Suzy 1 [1, 2, 3] If I replace self.lista = lst by self.lista = [] it works fine, just like when I add the line name_dict[name].lista = [] to the for loop. Why is it that the contents of the previous objects' lists are retained, yet their values of integer aren't? I am rather new to Python, so it would be great if someone could point out to me where my thoughts/assumptions have gone astray. Thanks a lot in advance for your replies.

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