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  • Can I use the [] operator in C++ to create virtual arrays

    - by Shane MacLaughlin
    I have a large code base, originally C ported to C++ many years ago, that is operating on a number of large arrays of spatial data. These arrays contain structs representing point and triangle entities that represent surface models. I need to refactor the code such that the specific way these entities are stored internally varies for specific scenarios. For example if the points lie on a regular flat grid, I don't need to store the X and Y coordinates, as they can be calculated on the fly, as can the triangles. Similarly, I want to take advantage of out of core tools such as STXXL for storage. The simplest way of doing this is replacing array access with put and get type functions, e.g. point[i].x = XV; becomes Point p = GetPoint(i); p.x = XV; PutPoint(i,p); As you can imagine, this is a very tedious refactor on a large code base, prone to all sorts of errors en route. What I'd like to do is write a class that mimics the array by overloading the [] operator. As the arrays already live on the heap, and move around with reallocs, the code already assumes that references into the array such as point *p = point + i; may not be used. Is this class feasible to write? For example writing the methods below in terms of the [] operator; void MyClass::PutPoint(int Index, Point p) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); StoreGridPoint(xoffs,yoffs,p.z); } else m_PointArray[Index] = p; } } Point MyClass::GetPoint(int Index) { if (m_StorageStrategy == RegularGrid) { int xoffs,yoffs; ComputeGridFromIndex(Index,xoffs,yoffs); return GetGridPoint(xoffs,yoffs); // GetGridPoint returns Point } else return m_PointArray[Index]; } } My concern is that all the array classes I've seen tend to pass by reference, whereas I think I'll have to pass structs by value. I think it should work put other than performance, can anyone see any major pitfalls with this approach. n.b. the reason I have to pass by value is to get point[a].z = point[b].z + point[c].z to work correctly where the underlying storage type varies.

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  • complex arguments for function

    - by myPost1
    My task is to create function funCall taking four arguments : pointer for 2d array of ints that stores pairs of numbers variable int maintaining number of numbers in 2d array pointer for table of pointers to functions int variable storing info about number of pointers to functions I was thinking about something like this : typedef int(*funPtr)(int, int); funPtr arrayOfFuncPtrs[]; void funCall( *int[][]k, int a, *funPtr z, int b); { }

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  • CodeIgniter Form Validation

    - by mmcglynn
    I am trying to set up validation on a simple contact form that is created using the form helper. No validation at all occurs. What is wrong? In the code below, the “good” keyword always shows, regardless of what is entered into the form, and the saved values set via set_value are never shown. Controller // Contact function contact() { $data['pageTitle'] = "Contact"; $data['bodyId'] = "contact"; $this->load->library('form_validation'); $config_rules = array ('email' => 'required','message' => 'required'); $this->form_validation->set_rules($config_rules); if ($this->form_validation->run() == FALSE) { echo "bad"; $data['include'] = "v_contact"; $this->load->view('v_template',$data); } else { echo "good"; $data['include'] = "v_contact"; $this->load->view('v_template',$data); } } View echo validation_errors(); echo form_open('events/contact'); // name echo form_label('Name', 'name'); $data = array ( 'name' => 'name', 'id' => 'name', 'maxlength' => '64', 'size' => '40', 'value' => set_value('name') ); echo form_input($data) . "\n<br />"; // email address echo form_label('Email Address', 'email'); $data = array ( 'name' => 'email', 'id' => 'email', 'maxlength' => '64', 'size' => '40', 'value' => set_value('email') ); echo form_input($data) . "\n<br />"; // message echo form_label('Message', 'message'); $data = array ( 'name' => 'message', 'id' => 'message', 'rows' => '8', 'cols' => '35', 'value' => set_value('message') ); echo form_textarea($data) . "\n<br />"; echo form_submit('mysubmit', 'Send Message'); echo form_close();

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  • java dynamic function calling

    - by dpaksp
    here is that case....i have an String array that contains only method names of yyyyyy.java file in xxxxxx.java file am creaing yyyyyy.java 's instance (say obj) now i have access obj.fuction_name....that function i should get from that String array in loop ...is that possible ... thank u

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  • Thread safety in C# arrays

    - by Betamoo
    Does having 2 different threads : one reading from a C# array (e.g from first location), and another one writing to the same C# array but to a different location(e.g to the last location) is thread safe or not? (And I mean here without locking reading nor writing)

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  • Request for member Name in something not a structure or Union

    - by Ashutosh
    Hey Folks, I am trying to Call the webservices in my app and while checking it in console it's showing the number of objects. (as i am using the Mutable array) and then while trying to display the name of the objects (here it's location) it's giving me an error in this line for (SDZArrayOfLocationWithLatestGrades* location in a) { NSLog(@" - %@", location.Name); // error here and a is the mutable array } PLease help me with this and Happy New Year to All!!!!!! Thanks,

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  • Why doesn't Java allow for the creaton of generic arrays?

    - by byte
    There are plenty of questions on stackoverflow from people who have attempted to create an array of generics like so: ArrayList<Foo>[] poo = new ArrayList<Foo>[5]; And the answer of course is that the Java specification doesn't allow you to declare an array of generics. My question however is why ? What is the technical reason underlying this restriction in the java language or java vm? It's a technical curiosity I've always wondered about.

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  • php mysql_query return empty value

    - by proyb2
    I create a directory listing and came across this issue. what value does mysql_query($query1) return if there is no value My script received this message from $result, would it be alright to pass array(0)? Warning: mysql_fetch_array($result) expects parameter 1 to be resource, array given in

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  • PHP object exchange between servers

    - by bensiu
    I got script what read from database and manipulate it so on the end I got $result array... on one server is it possible to serialize this object and pass it to other script so this $result array could be available for other script on second server... I got on first server: return serialize ( $results ); and on second: $data = unserialize ( file_get_contents ( 'http://www.......com/reader.php' ) ); ...but there is no communication between .... What I am doing wrong ? Bensiu

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  • 2d convolution using python and numpy

    - by mikip
    Hi I am trying to perform a 2d convolution in python using numpy I have a 2d array as follows with kernel H_r for the rows and H_c for the columns data = np.zeros((nr, nc), dtype=np.float32) #fill array with some data here then convolve for r in range(nr): data[r,:] = np.convolve(data[r,:], H_r, 'same') for c in range(nc): data[:,c] = np.convolve(data[:,c], H_c, 'same') It does not produce the output that I was expecting, does this code look OK Thanks

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  • How to use length indicator in a C++ program

    - by cj
    I want to make a program in C++ that reads a file where each field will have a number before it that indicates how long it is. The problem is I read every record in object of a class; how do I make the attributes of the class dynamic? For example if the field is "john" it will read it in a 4 char array. I don't want to make an array of 1000 elements as minimum memory usage is very important.

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  • Extend multiple classes at once

    - by Starkers
    I want to share a method amongst all Ruby's data object classes. That is to say the following classes: Hash String Number Array Firstly, any classes I've missed out? Secondly, how can I share my_method amongst all classes at once? class Hash def my_method "hi" end end class String def my_method "hi" end end class Number def my_method "hi" end end class Array def my_method "hi" end end

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  • Wrong data retrieved from database

    - by holyredbeard
    So, I want to retrieve the order of the elements of a list. The order is set before by the user, and are stored in the table below. Because I also want to retrieve name and description of the list elements I need to combine two tables (see below). However, what is actually retrieved is an array containing 16 elements (should be four because it only exists four elements as for now). The array is too long to post here, but I put it in a phpFiddle to be found here if you're interested. Well, I have really tried to find what's wrong (probably something easy as always), but with no luck. Thanks a lot for your time and help! listModel.php: public function GetOrderedElements($userId, $listId) { // $userId = 46 // $listId = 1 $query = "SELECT le.listElemId, le.listElemName, le.listElemDesc, lo.listElemOrderPlace FROM listElement AS le INNER JOIN listElemOrder AS lo ON le.listId = lo.listId WHERE lo.userId = ? AND lo.listId = ? ORDER BY listElemId"; $stmt = $this->m_db->Prepare($query); $stmt->bind_param("ii", $userId, $listId); $listElements = $this->m_db->GetOrderedElements($stmt); return $listElements; } database.php: public function GetOrderedElements(\mysqli_stmt $stmt) { if ($stmt === FALSE) { throw new \Exception($this->mysqli->error); } if ($stmt->execute() == FALSE) { throw new \Exception($this->mysqli->error); } if ($stmt->bind_result($listElemId, $listElemName, $listElemDesc, $listElemOrderPlace) == FALSE) { throw new \Exception($this->mysqli->error); } $listElements = array(); while ($stmt->fetch()) { $listElements[] = array('listElemId' => $listElemId, 'listElemName' => $listElemName, 'listElemDesc' => $listElemDesc, 'listElemOrderPlace' => $listElemOrderPlace); } var_dump($listElements); $stmt->Close(); return $listElements; } from the database: listElemOrder: listElemOrderId | listId | listElemId | userId | listElemOrderPlace 1 1 1 46 1 2 1 2 46 4 3 1 3 46 2 4 1 4 46 3 listElement: listElemId | listElemName | listId | listElemDesc | listElemOrderPlace 1 Elem A 1 Derp NULL 2 Elem B 1 Herp NULL 3 Elem C 1 Lorum NULL 4 Elem D 1 Ipsum NULL Note: 'listElemOrderPlace' in the table listElement is the final order of the elements (all users average), not to be mixed with the one with the same name in the other table, that's only a specific user's order of the list elements (which is the interesting one in this case).

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  • Need Help Loading and Manipulating Bitmap Data

    - by Dave
    Using VB6, I need to load a bitmap image and subsequently manipulate some of its data - specifically, I want to rotate a section within the image, and in the end keep the image intact with the rotated section. How do I (1) find out where an image gets loaded into memory (a physical address), and (2) in what format is it stored, a 1-D array, 2-D array, or what? Maybe you can even suggest a better way to do this. Thanks.

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  • NSMutableDictionary confused over how to use keys with certain code ?

    - by Jules
    I'm getting data from a database and I need to add the string field value and the record id. However, I need this to work with some existing code... I'm replacing this (see code below) and getting data from my database. NSDictionary *dict = [[NSDictionary alloc] initWithContentsOfFile:path]; self.allCategories = dict; [dict release]; But needs to work with these key and value search functions. - (void)resetSearch { NSMutableDictionary *allCategoriesCopy = [self.allCategories mutableDeepCopy]; self.Categories = allCategoriesCopy; [allCategoriesCopy release]; NSMutableArray *keyArray = [[NSMutableArray alloc] init]; [keyArray addObject:UITableViewIndexSearch]; [keyArray addObjectsFromArray:[[self.allCategories allKeys] sortedArrayUsingSelector:@selector(compare:)]]; self.keys = keyArray; [keyArray release]; } . - (void)handleSearchForTerm:(NSString *)searchTerm { NSMutableArray *sectionsToRemove = [[NSMutableArray alloc] init]; [self resetSearch]; for (NSString *key in self.keys) { NSMutableArray *array = [Categories valueForKey:key]; NSMutableArray *toRemove = [[NSMutableArray alloc] init]; for (NSString *name in array) { if ([name rangeOfString:searchTerm options:NSCaseInsensitiveSearch].location == NSNotFound) [toRemove addObject:name]; } if ([array count] == [toRemove count]) [sectionsToRemove addObject:key]; [array removeObjectsInArray:toRemove]; [toRemove release]; } [self.keys removeObjectsInArray:sectionsToRemove]; [sectionsToRemove release]; [table reloadData]; } Keep getting an error from this code... NSDictionary *arrayTmp= [[NSDictionary alloc] init]; ... loop records int cid = sqlite3_column_int(statementTMP, 0); NSString *category = [[NSString alloc] initWithUTF8String:(char *)sqlite3_column_text(statementTMP, 1)]; [arrayTmp setObject:category forKey:[NSString stringWithFormat:@"%i", cid]]; Error caused by line above * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString count]: unrecognized selector sent to instance 0x4d4c500' * Call stack at first throw * ... end loop self.allCategories = arrayTmp; [arrayTmp release];

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  • a problem with char** in c

    - by sagi
    hello i have an char** arr which is an array of strings and i want to erase the 2 last cell of the array or maybe to create a new char** but without those last 2 cells thank you very much.

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