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  • Why does accessing a member of a malloced array of structs seg fault?

    - by WSkinner
    I am working through Learn C The Hard Way and am stumped on something. I've written a simplified version of the problem I am running into to make it easier to get down to it. Here is the code: #include <stdlib.h> #define GROUP_SIZE 10 #define DATA_SIZE 64 struct Dummy { char *name; }; struct Group { struct Dummy **dummies; }; int main() { struct Group *group1 = malloc(sizeof(struct Group)); group1->dummies = malloc(sizeof(struct Dummy) * GROUP_SIZE); struct Dummy *dummy1 = group1->dummies[3]; // Why does this seg fault? dummy1->name = (char *) malloc(DATA_SIZE); return 0; } when I try to set the name pointer on one of my dummies I get a seg fault. Using valgrind it tells me this is uninitialized space. Why is this?

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  • How can I tell if a byte array has already been compressed?

    - by MikeG
    Hi, Can I rely on the first few bytes of data compressed using the System.IO.Compression.DeflateStream in .NET always being the same? These bytes seem to always be the 1st bytes: 237, 189, 7, 96, 28, 73, 150, 37, 38, 47 , ... I'm assuming this is some kind of header, I'd like to assume that this header is fixed and isn't going to change. Has anyone got any extra info about this? Background info (The reason I want to know this info is...) I have a load of data in a database table that could do with being made smaller. I've decided I'm going to start compressing the data and not going to bother compressing the existing data. When the data gets into my .NET code the data is a String. I'd like to be able to look at the 1st few bytes of the string and see if it has been compressed, if it has then I need to de-compress it. I was originally thinking I could convert the string to bytes and just try de-compressing the data. Then if an exception happens, I could just assume it wasn't compressed. But I think checking the header bytes would give me much better performance. Many thanks, Mike G

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  • How to search on a array and display the items on tableview using a searchbar?

    - by skiria
    Hi, I would like to search on a arrays hierachy and display the results on a tableview. The tableview is empty when we run the app and the, when we search it, the data is written. What's the best way to do this? I read tutorials wich explains how it search on a tableview, but i want to search in all of arrays hierachy. I have 3 classes class video //iVars to allocate the video metadata NSInteger videoID; NSString *nameVideo; NSString *nameCategory; NSString *nameTopic; NSString *user; NSString *date; NSString *description; NSString *urlThumbnail; NSString *urlVideo; class Topic NSInteger TopicId; NSString nameTopic; NSMutableArray videos; class Category NSInteger CategoryId; NSString nameCategory NSMutableArray topics AppDelegate NSMutableArray categories

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  • How do I use an index in an array reference as a method reference in Perl?

    - by Robert P
    Similar to this question about iterating over subroutine references, and as a result of answering this question about a OO dispatch table, I was wondering how to call a method reference inside a reference, without removing it first, or if it was even possible. For example: package Class::Foo; use 5.012; #Yay autostrict! use warnings; # a basic constructor for illustration purposes.... sub new { my $class = shift; return bless {}, $class; } # some subroutines for flavor... sub sub1 { say 'in sub 1' } sub sub2 { say 'in sub 2' } sub sub3 { say 'in sub 3' } # and a way to dynamically load the tests we're running... sub sublist { my $self = shift; return [ $self->can('sub1'); $self->can('sub3'}; $self->can('sub2'); ]; } package main; my $instance = Class::Foo->new(a => 1, b => 2, c => 3); my $tests = $instance->sublist(); my $index = int(rand($#{$tests})); # <-- HERE So, at HERE, we could do: my $ref = $tests->{$index}; $instance->$ref(); but how would we do this, without removing the reference first?

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  • If free() knows the length of my array, why can't I ask for it in my own code?

    - by Chris Cooper
    I know that it's a common convention to pass the length of dynamically allocated arrays to functions that manipulate them: void initializeAndFree(int* anArray, int length); int main(){ int arrayLength = 0; scanf("%d", &arrayLength); int* myArray = (int*)malloc(sizeof(int)*arrayLength); initializeAndFree(myArray, arrayLength); } void initializeAndFree(int* anArray, int length){ int i = 0; for (i = 0; i < length; i++) { anArray[i] = 0; } free(anArray); } but if there's no way for me to get the length of the allocated memory from a pointer, how does free() "automagically" know what to deallocate? Why can't I get in on the magic, as a C programmer? Where does free() get its free (har-har) knowledge from?

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  • Database Structure for CakePHP Models

    - by Michael T. Smith
    We're building a data tracking web app using CakePHP, and I'm having some issues getting the database structure right. We have Companies that haveMany Sites. Sites haveMany DataSamples. Tags haveAndBelongToMany Sites. That is all set up fine. The problem is "ranking" the sites within tags. We need to store it in the database as an archive. I created a Rank model that is setup like this: rank ( id (int), sample_id (int), tag_id (int), site_id (int), rank (int), total_rows) ) So, the question is, how do I create the associations for tag, site and sample to rank? I originally set them as haveMany. But the returned structures don't get me where I'd like to be. It looks like: [Site] => Array ( [Sample] = Array(), [Tag] = Array() ) When I'm really looking for: [Site] => Array ( [Tag] = Array ( [Sample] => Array ( [Rank] => Array ( ...data... ) ) ) ) I think that I may not be structuring the database properly; so if I need to update please let me know. Otherwise, how do I write a find query that gets me where I need to be? Thanks! Thoughts? Need more details? Just ask!

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  • While loop in foreach loop not looping correctly

    - by tominated
    I'm trying to make a very basic php ORM as for a school project. I have got almost everything working, but I'm trying to map results to an array. Here's a snippet of code to hopefully assist my explanation. $results = array(); foreach($this->columns as $column){ $current = array(); while($row = mysql_fetch_array($this->results)){ $current[] = $row[$column]; print_r($current); echo '<br><br>'; } $results[$column] = $current; } print_r($results); return mysql_fetch_array($this->results); This works, but the while loop only works on the first column. The print_r($results); shows the following: Array ( [testID] => Array ( [0] => 1 [1] => 2 ) [testName] => Array ( ) [testData] => Array ( ) ) Can anybody shed some light? Thanks in advance!

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  • How to construct query to update nested array document in mongo?

    - by GowtGM
    I am having following document in mongo, { "_id" : ObjectId("506e9e54a4e8f51423679428"), "description" : "ffffffffffffffff", "menus" : [ { "_id" : ObjectId("506e9e5aa4e8f51423679429"), "description" : "ffffffffffffffffffff", "items" : [ { "name" : "xcvxc", "description" : "vxvxcvxc", "text" : "vxcvxcvx", "menuKey" : "0", "onSelect" : "1", "_id" : ObjectId("506e9f07a4e8f5142367942f") } , { "name" : "abcd", "description" : "qqq", "text" : "qqq", "menuKey" : "0", "onSelect" : "3", "_id" : ObjectId("507e9f07a4e8f5142367942f") } ] }, { "_id" : ObjectId("506e9e5aa4e8f51423679429"), "description" : "rrrrr", "items" : [ { "name" : "xcc", "description" : "vx", "text" : "vxc", "menuKey" : "0", "onSelect" : "2", "_id" : ObjectId("506e9f07a4e8f5142367942f") } ] } ] } Now , i want to update the following document : { "name" : "abcd", "description" : "qqq", "text" : "qqq", "menuKey" : "0", "onSelect" : "3", "_id" : ObjectId("507e9f07a4e8f5142367942f") } I am having main documnet id: "_id" : ObjectId("506e9e54a4e8f51423679428") and menus id "_id" : ObjectId("506e9e54a4e8f51423679428") as well as items id "_id" : ObjectId("507e9f07a4e8f5142367942f") which is to be updated. I have tried using the following query: db.collection.update({ "_id" : { "$oid" : "506e9e54a4e8f51423679428"} , "menus._id" : { "$oid" : "506e9e5aa4e8f51423679429"}},{ "$set" : { "menus.$.items" : { "_id" : { "$oid" : "506e9f07a4e8f5142367942f"}} , "menus.$.items.$.name" : "xcvxc66666", ...}},false,false); but its not working...

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  • Quickest way to compare a bunch of array or list of values.

    - by zapping
    Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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  • How is this Perl code selecting two different elements from an array?

    - by Mike
    I have inherited some code from a guy whose favorite past time was to shorten every line to its absolute minimum (and sometimes only to make it look cool). His code is hard to understand but I managed to understand (and rewrite) most of it. Now I have stumbled on a piece of code which, no matter how hard I try, I cannot understand. my @heads = grep {s/\.txt$//} OSA::Fast::IO::Ls->ls($SysKey,'fo','osr/tiparlo',qr{^\d+\.txt$}) || (); my @selected_heads = (); for my $i (0..1) { $selected_heads[$i] = int rand scalar @heads; for my $j (0..@heads-1) { last if (!grep $j eq $_, @selected_heads[0..$i-1]); $selected_heads[$i] = ($selected_heads[$i] + 1) % @heads; #WTF? } my $head_nr = sprintf "%04d", $i; OSA::Fast::IO::Cp->cp($SysKey,'',"osr/tiparlo/$heads[$selected_heads[$i]].txt","$recdir/heads/$head_nr.txt"); OSA::Fast::IO::Cp->cp($SysKey,'',"osr/tiparlo/$heads[$selected_heads[$i]].cache","$recdir/heads/$head_nr.cache"); } From what I can understand, this is supposed to be some kind of randomizer, but I never saw a more complex way to achieve randomness. Or are my assumptions wrong? At least, that's what this code is supposed to do. Select 2 random files and copy them. === NOTES === The OSA Framework is a Framework of our own. They are named after their UNIX counterparts and do some basic testing so that the application does not need to bother with that.

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  • How to tell where I am in an array with pointer arythmetic?

    - by klez
    In C, I have declared a memory area like this: int cells = 512; int* memory = (int*) malloc ((sizeof (int)) * cells); And I place myself more or less in the middle int* current_cell = memory + ((cells / 2) * sizeof (int)); My question is, while I increment *current_cell, how do I know if I reached the end of the allocated memory area?

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  • Why new String(bytes, enc).getBytes(enc) does not return the original byte array?

    - by Bozho
    I made the following "simulation": byte[] b = new byte[256]; for (int i = 0; i < 256; i ++) { b[i] = (byte) (i - 128); } byte[] transformed = new String(b, "cp1251").getBytes("cp1251"); for (int i = 0; i < b.length; i ++) { if (b[i] != transformed[i]) { System.out.println("Wrong : " + i); } } For cp1251 this outputs only one wrong byte - at position 23. For KOI8-R - all fine. For cp1252 - 4 or 5 differences. What is the reason for this and how can this be overcome? I know it is wrong to represent byte arrays as strings in whatever encoding, but it is a requirement of the protocol of a payment provider, so I don't have a choice. Update: representing it in ISO-8859-1 works, and I'll use it for the byte[] part, and cp1251 for the textual part, so the question remains only out of curiousity

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  • What is the ISO C++ way to directly define a conversion function to reference to array?

    - by ben
    According to the standard, a conversion function has a function-id operator conversion-type-id, which would look like, say, operator char(&)[4] I believe. But I cannot figure out where to put the function parameter list. gcc does not accept either of operator char(&())[4] or operator char(&)[4]() or anything I can think of. Now, gcc seems to accept (&operator char ())[4] but clang does not, and I am inclined to not either, since it does not seem to fit the grammar as I understand it. I do not want to use a typedef because I want to avoid polluting the namespace with it.

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  • ZendX Jquery Decorator

    - by iJD
    How use partial decorator in Jquery Element I use this code for Form Element: $title = new Zend_Form_Element_Text('title'); $title->setRequired(true) ->setAttrib('class', 'inputbox') ->setLabel('Title'); $title->viewScript = 'RegElement.phtml'; $title->setDecorators( array( array('ViewScript', array('class' => 'RegElement')) ) ); But when i use Jquery Element i dont know how implement it: $datePicker = new ZendX_JQuery_Form_Element_DatePicker( "datePicker1", array("label" => "Date:") ); $datePicker->viewScript = 'RegElement.phtml'; $datePicker->setDecorators( array( array('ViewScript', array('class' => 'RegElement')) ) ); //views/scripts/RegElement.phtml <li class="row <?php echo $this->class ?>"> <div class="cont-error"> <?php echo $this->formErrors($this->element->getMessages()); ?> </div> <div class="rowfields"> <?php echo $this->formLabel($this->element->getName(), $this->element->getLabel()) ?> <?php echo $this->{$this->element->helper}( $this->element->getName(), $this->element->getValue(), $this->element->getAttribs() ) ?> </div> <div class="hint"><?php echo $this->element->getDescription() ?></div> </li> And display this error: Warning: Exception caught by form: Cannot render jQuery form element without at least one decorator implementing the 'ZendX_JQuery_Form_Decorator_UiWidgetElementMarker' interface. I need display datePicker with same format. but idk how implement this interface. thx for your help.

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  • Cakephp, Route old google search results to new home page

    - by ion
    Hi there, I have created a new website for a company and I would like all the previous search engine results to be redirected. Since there were quite a few pages and most of them where using an id I would like to use something generic instead of re-routing all the old pages. My first thought was to do that: Router::connect('/*', array('controller' => 'pages', 'action' => 'display', 'home')); And put that at the very end of the routes.php file [since it is prioritized] so that all requests not validating with previous route actions would return true with this one and redirect to homepage. However this does not work. I'm pasting my routes.php file [since it is small] hoping that someone could give me a hint: Router::connect('/', array('controller' => 'pages', 'action' => 'display', 'home')); Router::connect('/company/*', array('controller' => 'articles', 'action' => 'view')); Router::connect('/contact/*', array('controller' => 'contacts', 'action' => 'view')); Router::connect('/lang/*', array('controller' => 'p28n', 'action' => 'change')); Router::connect('/eng/*', array('controller' => 'p28n', 'action' => 'shuntRequest', 'lang' => 'eng')); Router::connect('/gre/*', array('controller' => 'p28n', 'action' => 'shuntRequest', 'lang' => 'gre')); Router::parseExtensions('xml');

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  • What's an easy way of storing an array of numbers in Javascript that I can add/remove from?

    - by SLC
    In C# I would create a List then I could add and remove numbers very easily. Does identical functionality exist in Javascript, or do I have to write my own methods to search and remove items using a loop? var NumberList = []; NumberList.Add(17); NumberList.Add(25); NumberList.Remove(17); etc. I know I can use .push to add a number, so I guess it's really how to remove an individual number without using a loop that I'm looking for. edit: of course, if there's no other way then I'll use a loop!:)

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  • how to put a value to an array when a checkbox is checked? c#?

    - by Jan Darren Noroña
    I am making a random character generator, i have 2 forms, form1 and form2, on my form2 i have the checkboxes there, so if the user checked checkbox1, on my form1 it will only display 1 character, now if the user check all 5 checkboxes, my form1 will generate 5 characters. i have a button on form1 that will trigger an event on generating random characters. characters: '+','-','*','/','%' how will my code be? I am using WINDOWS FORMS APPLICATION. pics here: form1: http://i49.tinypic.com/30bzos8.png form2: http://i50.tinypic.com/k00ndt.png char[] select = new char[] { '+' , '-' , '*' , '/', '%' }; var rand = new Random(); char num = select[rand.Next(5)];

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