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  • Why does C++ allow variable length arrays that aren't dynamically allocated?

    - by Maulrus
    I'm relatively new to C++, and from the beginning it's been drilled into me that you can't do something like int x; cin >> x; int array[x]; Instead, you must use dynamic memory. However, I recently discovered that the above will compile (though I get a -pedantic warning saying it's forbidden by ISO C++). I know that it's obviously a bad idea to do it if it's not allowed by the standard, but I previously didn't even know this was possible. My question is, why does g++ allow variable length arrays that aren't dynamically allocated if it's not allowed by the standard? Also, if it's possible for the compiler to do it, why isn't it in the standard?

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  • How to merge arrays with same key and different value in PHP?

    - by Martin
    Hi guys, I have arrays similarly to these: 0 => Array ( [0] => Finance / Shopping / Food, [1] => 47 ) 1 => Array ( [0] => Finance / Shopping / Food, [1] => 25 ) 2 => Array ( [0] => Finance / Shopping / Electronic, [1] => 190 ) I need to create one array with [0] as a key and [1] as value. The tricky part is that if the [0] is same it add [1] to existing value. So the result I want is: array ([Finance / Shopping / Food]=> 72, [Finance / Shopping / Electronic] => 190); thanks

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  • Using temporary arrays to cut down on code - inefficient?

    - by tommaisey
    I'm new to c++ (and SO) so sorry if this is obvious. I've started using temporary arrays in my code to cut down on repetition and to make it easier to do the same thing to multiple objects. So instead of: MyObject obj1, obj2, obj3, obj4; obj1.doSomming(arg); obj2.doSomming(arg); obj3.doSomming(arg); obj4.doSomming(arg); I'm doing: MyObject obj1, obj2, obj3, obj4; MyObject* objs[] = {&obj1, &obj2, &obj3, &obj4}; for (int i = 0; i !=4; ++i) objs[i]->doSomming(arg); Is this detrimental to performance? Like, does it cause unnecessary memory allocation? Is it good practice? Thanks.

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  • PowerShell One-Liners: Collections, Hashtables, Arrays and Strings

    The way to learn PowerShell is to browse and nibble, rather than to sit down to a formal five-course meal. In his continuing series on PowerShell one-liners, Michael Sorens provides Fast Food for busy professionals who want results quickly and aren't too faddy. Part 3 has as its tasty confections - Collections, Hashtables, arrays and strings. "A real time saver" Andy Doyle, Head of IT ServicesAndy and his team saved time by automating backup and restores with SQL Backup Pro. Find out how much time you could save. Download a free trial now.

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  • Adding multiple byte arrays in c# [migrated]

    - by James P. Wright
    I'm working on a legacy system that uses byte arrays for permission levels. Example: 00 00 00 00 00 00 00 01 means they have "Full Control" 00 00 00 00 00 00 00 02 means they have "Add Control" 00 00 00 00 00 00 00 04 means they have "Delete Control" So, if a User has "00 00 00 00 00 00 00 07" that means they have all 3 (as far as it has been explained to me). Now, my question is that I need to know how to get to "0x07" when creating/checking records. I don't know the syntax for actually combining 0x01, 0x02 and 0x04 so that I come out with 0x07.

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  • arrays format (Javascript)

    - by João Melo
    i have a list of users, with minions, something like this: User52: minion10 minion12 User32: minion13 minion11 i've been keeping in an array where the "location" is the id, like this: Users: [52]User minions: [10]minion [12]minion [32]User minions: [13]minion [11]minion so i can access them easily like this: user[UserID].minions[MinionID] (ex: user[32].minions[11]) but when i print it or send it by json i get something like this: {,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,minion,,,,,,,,,,,,,,minion} but should i keep using like this or should i change to something like this: User = function(){ this.minions = ...; this.getMinion = function(value){ for(var m in this.minions){ if(this.minions[m].id == value){ return this.minions[m]; break; } } } } and get it like this: user.getMinion(MinionID); Question: i get better performance using a "short" array but using loops every time i need a minion, or using "long" arrays, but no need for loop and getting values directly from the id "name"?

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  • IE Problem: Jagged Scrolling and Dragging Inside Large Viewport

    - by br4inwash3r
    My site is a single page website with a very large "canvas" size. and to navigate around the site i'm using jquery scrollTo and jquery Dragscrollable plugin. in IE 7 & 8 the scrolling/dragging movement is very jagged. at first i thought it was my script or some other plugin that's causing this. but after i stripped down everything it's still the same. i've tried a few tips i've found around here. but none is really working for me. i know i should be asking this question to the plugin developers. i did.. i just thought maybe you guys have some other solution for this issue. here's the URL to the demo site: http://satuhati.com/bare/template/ really appreciate any help u can give :) thx..

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  • Avoiding jagged text when pasting into vi?

    - by overtherainbow
    Hello Although I have no problem using SecureCRT (5.1.2 build 274) to work from Windows and connect to PC's running Linux, I have a problem when connecting to an embedded Asterisk appliance that provides"vi" through BusyBox 1.4.1 (2008-03-10). The issue I'm having, is that when I paste code into vi, the text appears jagged like this: <?php try { $dbh = new PDO("sqlite:./db.sqlite"); $dbh->exec("CREATE TABLE IF NOT EXISTS customer (id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR(255))"); Does someone what the problem is? Is there a way to reconfigure either BusyBox or SecureCRT so that I can paste successfully? Thank you.

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  • C# Making private instance variable accesable (jagged array)

    - by Chris
    Hello, In a attempt to put some more oop in a program i am looking to make a private instance variable in one class (object) accesable to a class. private byte [][] J; All those code refers to this jagged array with this. Now in the other class i putted all the for loops along with the consolewritlines to display the wanted results. Basicly it says "the name J does not exist in the current context" But how exactly do i make this J accesable? I have tried with get and set but i keep getting 'cannot convert to byte to byte[][]' Also what kind of cyntax would i need with get and set? Something along like this? Or would i need several more steps? : public Byte JArray get { return J; } //can converrt to byte here set { J = value; } //cannnot convert to byte here Kind regards

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  • Why does reusing arrays increase performance so significantly in c#?

    - by Willem
    In my code, I perform a large number of tasks, each requiring a large array of memory to temporarily store data. I have about 500 tasks. At the beginning of each task, I allocate memory for an array : double[] tempDoubleArray = new double[M]; M is a large number depending on the precise task, typically around 2000000. Now, I do some complex calculations to fill the array, and in the end I use the array to determine the result of this task. After that, the tempDoubleArray goes out of scope. Profiling reveals that the calls to construct the arrays are time consuming. So, I decide to try and reuse the array, by making it static and reusing it. It requires some additional juggling to figure out the minimum size of the array, requiring an extra pass through all tasks, but it works. Now, the program is much faster (from 80 sec to 22 sec for execution of all tasks). double[] tempDoubleArray = staticDoubleArray; However, I'm a bit in the dark of why precisely this works so well. Id say that in the original code, when the tempDoubleArray goes out of scope, it can be collected, so allocating a new array should not be that hard right? I ask this because understanding why it works might help me figuring out other ways to achieve the same effect, and because I would like to know in what cases allocation gives performance issues.

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  • Good C++ array class for dealing with large arrays of data in a fast and memory efficient way?

    - by Shane MacLaughlin
    Following on from a previous question relating to heap usage restrictions, I'm looking for a good standard C++ class for dealing with big arrays of data in a way that is both memory efficient and speed efficient. I had been allocating the array using a single malloc/HealAlloc but after multiple trys using various calls, keep falling foul of heap fragmentation. So the conclusion I've come to, other than porting to 64 bit, is to use a mechanism that allows me to have a large array spanning multiple smaller memory fragments. I don't want an alloc per element as that is very memory inefficient, so the plan is to write a class that overrides the [] operator and select an appropriate element based on the index. Is there already a decent class out there to do this, or am I better off rolling my own? From my understanding, and some googling, a 32 bit Windows process should theoretically be able address up to 2GB. Now assuming I've 2GB installed, and various other processes and services are hogging about 400MB, how much usable memory do you think my program can reasonably expect to get from the heap? I'm currently using various flavours of Visual C++.

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  • Vertex data split into separate buffers or one one structure?

    - by kiba2
    Is it better to have all vertex data in one structure like this: class MyVertex { int x,y,z; int u,v; int normalx, normaly, normalz; } Or to have each component (location, normal, texture coordinates) in separate arrays/buffers? To me it always seemed logical to keep the data grouped together in one structure because they'd always be the same for each instance of a shared vertex and that seems to be true for things like character models (ex: the normal should be an average of adjacent normals for smooth lighting). One instance where this doesn't seem to work is other kinds of meshes like say a cube where the texture coordinates for each may be the same but that causes them to be different where the vertices are shared. Does everybody normally keep them separate? Won't this make them less space efficient if there needs to be an instance of texture coordinates and normals for each triangle vertex (They won't be indexed)? Can OpenGL even handle this mixing of indexed (for location) vs non-indexed buffers in the same VBO?

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  • (solved) jQuery click and drag/scroll window: jagged movement

    - by Josh
    Edit: derp, using pageX/Y instead of clientX/Y -- apparently scrollBy expects input with that offset rather than the other. Jaggy movement gone. I am getting jagged movement when doing small scroll increments using the following bindings. Can anyone point me in the right direction for how to smooth this out? FYI, its intermittent. It seems like, if I click and hold for a second, then drag at a decent speed there are no problems. Edit: What the hell? I get this output on debug... obvious jog backwards and forwards. This will happen in succession and seems to have no correlation with the mouse, other than the mouse is moving. x 398 : 403 y 374 : 377 x 403 : 399 y 377 : 374 x 399 : 404 y 374 : 377 Josh sococo.client.panMap = function(e){ e.preventDefault(); var movex = sococo.client.currX - e.pageX ; var movey = sococo.client.currY - e.pageY; console.log( sococo.client.currX +" : " + e.pageX ); window.scrollBy(movex,movey); sococo.client.currY = e.pageY; sococo.client.currX = e.pageX; } $(document).mousedown( function(e){ e.preventDefault(); sococo.client.currX = e.pageX; sococo.client.currY = e.pageY; $(document).bind( "mousemove", sococo.client.panMap ); }); $(document).mouseup( function(e){ e.preventDefault(); $(document).unbind( "mousemove", sococo.client.panMap ); });

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  • Is there a way to find how how "deep" a PHP array is?

    - by Thomas Owens
    A PHP array can have arrays for its elements. And those arrays can have arrays and so on and so forth. Is there a way to find out the maximum nesting that exists in a PHP array? An example would be a function that returns 1 if the initial array does not have arrays as elements, 2 if at least one element is an array, and so on.

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  • Using LINQ to Obtain Max of Columns for Two Dimensional Arrays

    - by Ngu Soon Hui
    Is there anyway to use LINQ to obtain the maximum of each columns for two dimensional arrays? Assume that I have the following: var arrays = new double[5,100](); I want to get the maximum of arrays[0,:], arrays[1,:] .... arrays[4,:]. How to use LINQ to do it? I could have use such method public double GetMax(double[,] arr, int rowIndex) { var colCount = arr.GetLength(1); double max = 0.0; for(int i=0; i<colCount; i++) { max=Math.Max(Math.Abs(arr[rowIndex, i]), max); } return max; } But I would prefer a more succinct ways of doing things.

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  • Java Array Comparison

    - by BlairHippo
    Working within Java, let's say I have two objects that, thanks to obj.getClass().isArray(), I know are both arrays. Let's further say that I want to compare those two arrays to each other -- possibly by using Arrays.equals. Is there a graceful way to do this without resorting to a big exhaustive if/else tree to figure out which flavor of Arrays.equals needs to be used? I'm looking for something that's less of an eyesore than this: if (obj1 instanceof byte[] && obj2 instanceof byte[]) { return Arrays.equals((byte[])obj1, (byte[])obj2); } else if (obj1 instanceof boolean[] && obj2 instanceof boolean[]) { ...

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  • Is there a more efficient AS3 way to compare 2 arrays for adds, removes & updates?

    - by WillyCornbread
    Hi all - I'm wondering if there is a better way to approach this than my current solution... I have a list of items, I then retrieve another list of items. I need to compare the two lists and come up with a list of items that are existing (for update), a list that are not existing in the new list (for removal) and a list of items that are not existing in the old list (for adding). Here is what I'm doing now - basically creating a lookup object for testing if an item exists. Thanks for any tips. for each (itm in _oldItems) { _oldLookup[itm.itemNumber] = itm; } // Loop through items and check if they already exist in the 'old' list for each (itm in _items) { // If an item exists in the old list - push it for update if (_oldLookup[itm.itemNumber]) { _itemsToUpdate.push(itm); } else // otherwise push it into the items to add { _itemsToAdd.push(itm); } // remove it from the lookup list - this will leave only // items for removal remaining in the lookup delete _oldLookup[itm.itemNumber]; } // The items remaining in the lookup object have neither been added or updated - // so they must be for removal - add to list for removal for each (itm in _oldLookup) { _itemsToRemove.push(itm); }

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  • How do I sum up weighted arrays in PHP?

    - by christian studer
    Hod do I multiply the values of a multi-dimensional array with weigths and sum up the results into a new array in PHP or in general? The boring way looks like this: $weights = array(0.25, 0.4, 0.2, 0.15); $values = array ( array(5,10,15), array(20,25,30), array(35,40,45), array(50,55,60) ); $result = array(); for($i = 0; $i < count($values[0]); ++$i) { $result[$i] = 0; foreach($weights as $index => $thisWeight) $result[$i] += $thisWeight * $values[$index][$i]; } Is there a more elegant solution?

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  • PHP Arrays: Loop trough array with a lot of conditional statements. Help / Best practices

    - by Jonathan
    Hi, I have a problem I don't know how to get it to work the best way. I need to loop trough an array like the one below. I need to check if the [country] index is equal to a Spanish speaking country (lot of countries) and then get those [title] indexes of the correspondent country and check for duplicates. The original array: Array ( [0] => Array ( [title] => Jeux de pouvoir [country] => France ) [1] => Array ( [title] => Los secretos del poder [country] => Argentina ) [2] => Array ( [title] => Los secretos del poder [country] => Mexico ) [3] => Array ( [title] => El poder secreto [country] => Uruguay ) ) To help you understand, the final result I need to get looks something like this: Array ( [0] => Array ( [title] => Los secretos del poder [country] => Argetnina, Mexico ) [1] => Array ( [title] => El poder secreto [country] => Uruguay ) )

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  • How can one put together multiple arrays into one string?

    - by Noor
    I'm having a hard time describing what I'm looking for. If we pretend that we're pulling an array (I've used the .split to get user input data) where each line represents a link. How can I then add an anchor tagg to that link that I'm pulling? I need to be able to put < a href=" + thearray + "anything< /a. The reason for this is that I'm dynamically creating a list. I think that if I create two variables, one with this part < a href=" one with the closing and then call some sort of function that puts those two and the pulled array in between them until the list is complete. Does this make any sense?

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  • Array inside of Arrays; Java (Help with Lab Assignment)

    - by Adam
    We are working on a lab assignment for my CS&E class and I think I can ask this question without going into detail of the entire lab requirements, but is it possible for an array to be inside of an array? For example, would this work: int [] arrayOne = new int[3]; arrayOne[0] = Start of an array If this is possible how do you go about doing it?

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  • C++: is it safe to work with std::vectors as if they were arrays?

    - by peoro
    I need to have a fixed-size array of elements and to call on them functions that require to know about how they're placed in memory, in particular: functions like glVertexPointer, that needs to know where the vertices are, how distant they are one from the other and so on. In my case vertices would be members of the elements to store. to get the index of an element within this array, I'd prefer to avoid having an index field within my elements, but would rather play with pointers arithmetic (ie: index of Element *x will be x - & array[0]) -- btw, this sounds dirty to me: is it good practice or should I do something else? Is it safe to use std::vector for this? Something makes me think that an std::array would be more appropriate but: Constructor and destructor for my structure will be rarely called: I don't mind about such overhead. I'm going to set the std::vector capacity to size I need (the size that would use for an std::array, thus won't take any overhead due to sporadic reallocation. I don't mind a little space overhead for std::vector's internal structure. I could use the ability to resize the vector (or better: to have a size chosen during setup), and I think there's no way to do this with std::array, since its size is a template parameter (that's too bad: I could do that even with an old C-like array, just dynamically allocating it on the heap). If std::vector is fine for my purpose I'd like to know into details if it will have some runtime overhead with respect to std::array (or to a plain C array): I know that it'll call the default constructor for any element once I increase its size (but I guess this won't cost anything if my data has got an empty default constructor?), same for destructor. Anything else?

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  • Why getting active record error when trying to work on arrays?

    - by keruilin
    I have the following association in my User model: has_and_belongs_to_many :friends, :class_name => 'User', :foreign_key => 'friend_id' I have the following uniqueness constraint in my user_users table: UNIQUE KEY `no_duplicate_friends` (`user_id`,`friend_id`) In my code, I am retrieving a user's friends -- friends = user.friends. friends is an array. I have a scenario where I want add the user with all those friends to the friends array. Ex: friends << user_with_all_those_homies However, I get the following error: ActiveRecord::StatementInvalid: Mysql::Error: Duplicate entry '18-18' for key 'no_duplicate_friends': INSERT INTO `users_users` (`friend_id`, `user_id`) VALUES (18, 18) What gives?

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  • Best way for saving infinit playlists (arrays) into db? (php mySql)

    - by Ole Jak
    So client gives me a string like "1,23,23,abc,ggg,544,tf4," from user 12 . There can be infinit number of elements with no spaces just value,value,... structure. I have users table (with users uId(key), names etc). I have streams table with ( sId(key), externalID, etc values). User sends me externalId's. And I need to hawe externalId's in play list (not my sId's). I need some way to store such array into my DB and be able to get it from DB. I need to be able to do 2 things return such string back to user be able to get na array from it like {1; 23; 23; abc; ggg; 544; tf4;} So what is best method (best here means shourt(small amount of) code) to store such data into db to retrivew stored tata in bouth ways shown

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