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  • DRYing out implementation of ICloneable in several classes

    - by Sarah Vessels
    I have several different classes that I want to be cloneable: GenericRow, GenericRows, ParticularRow, and ParticularRows. There is the following class hierarchy: GenericRow is the parent of ParticularRow, and GenericRows is the parent of ParticularRows. Each class implements ICloneable because I want to be able to create deep copies of instances of each. I find myself writing the exact same code for Clone() in each class: object ICloneable.Clone() { object clone; using (var stream = new MemoryStream()) { var formatter = new BinaryFormatter(); // Serialize this object formatter.Serialize(stream, this); stream.Position = 0; // Deserialize to another object clone = formatter.Deserialize(stream); } return clone; } I then provide a convenience wrapper method, for example in GenericRows: public GenericRows Clone() { return (GenericRows)((ICloneable)this).Clone(); } I am fine with the convenience wrapper methods looking about the same in each class because it's very little code and it does differ from class to class by return type, cast, etc. However, ICloneable.Clone() is identical in all four classes. Can I abstract this somehow so it is only defined in one place? My concern was that if I made some utility class/object extension method, it would not correctly make a deep copy of the particular instance I want copied. Is this a good idea anyway?

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  • Question regarding ideal database implementation for iPhone app

    - by Jeff
    So I have a question about the ideal setup for an app I am getting ready to build. The app is basically going to be a memorization tool and I already have an sqlite database full of content that I will be using for the app. The user will navigate through the contents of the database(using the uipickerview), and select something for memorization. If that row or cell of data is selected, it is put into a pool or a uitableview that is dedicated to showing which items you have in your "need to memorize" pool. When you go to that tableview, you can select the row, and the actual data would be populated. All information in the tableview would be deletable, in the event that they don't want it there anymore... Thats it. I know that with database interfacing, there are a few different options out there, in this particular setup, is core data the easiest approach? Is there any other way that would be better? I am just kind of looking for a point in the right direction, any help is greatly appreciated!!

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  • GetIDsOfNames implementation

    - by fearlesscoder
    Hi all, I need to implement GetIDsOfNames in my C++ application and I have no idea how to do that. I understand that I should implement GetTypeInfo, GetTypeInfoCount for that. I found a code sample which uses LIBID, but I don't have LIBID, and I don't know where to get one. What I really need is a good explanation of IDispatch interface internals...

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  • C++ Memory Allocation & Linked List Implementation

    - by pws5068
    I'm writing software to simulate the "first-fit" memory allocation schema. Basically, I allocate a large X megabyte chunk of memory and subdivide it into blocks when chunks are requested according to the schema. I'm using a linked list called "node" as a header for each block of memory (so that we can find the next block without tediously looping through every address value. head_ptr = (char*) malloc(total_size + sizeof(node)); if(head_ptr == NULL) return -1; // Malloc Error .. :-( node* head_node = new node; // Build block header head_node->next = NULL; head_node->previous = NULL; // Header points to next block (which doesn't exist yet) memset(head_ptr,head_node, sizeof(node)); ` But this last line returns: error: invalid conversion from 'node*' to 'int' I understand why this is invalid.. but how can I place my node into the pointer location of my newly allocated memory?

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  • Lockless queue implementation ends up having a loop under stress

    - by Fozi
    I have lockless queues written in C in form of a linked list that contains requests from several threads posted to and handled in a single thread. After a few hours of stress I end up having the last request's next pointer pointing to itself, which creates an endless loop and locks up the handling thread. The application runs (and fails) on both Linux and Windows. I'm debugging on Windows, where my COMPARE_EXCHANGE_PTR maps to InterlockedCompareExchangePointer. This is the code that pushes a request to the head of the list, and is called from several threads: void push_request(struct request * volatile * root, struct request * request) { assert(request); do { request->next = *root; } while(COMPARE_EXCHANGE_PTR(root, request, request->next) != request->next); } This is the code that gets a request from the end of the list, and is only called by a single thread that is handling them: struct request * pop_request(struct request * volatile * root) { struct request * volatile * p; struct request * request; do { p = root; while(*p && (*p)->next) p = &(*p)->next; // <- loops here request = *p; } while(COMPARE_EXCHANGE_PTR(p, NULL, request) != request); assert(request->next == NULL); return request; } Note that I'm not using a tail pointer because I wanted to avoid the complication of having to deal with the tail pointer in push_request. However I suspect that the problem might be in the way I find the end of the list. There are several places that push a request into the queue, but they all look generaly like this: // device->requests is defined as struct request * volatile requests; struct request * request = malloc(sizeof(struct request)); if(request) { // fill out request fields push_request(&device->requests, request); sem_post(device->request_sem); } The code that handles the request is doing more than that, but in essence does this in a loop: if(sem_wait_timeout(device->request_sem, timeout) == sem_success) { struct request * request = pop_request(&device->requests); // handle request free(request); } I also just added a function that is checking the list for duplicates before and after each operation, but I'm afraid that this check will change the timing so that I will never encounter the point where it fails. (I'm waiting for it to break as I'm writing this.) When I break the hanging program the handler thread loops in pop_request at the marked position. I have a valid list of one or more requests and the last one's next pointer points to itself. The request queues are usually short, I've never seen more then 10, and only 1 and 3 the two times I could take a look at this failure in the debugger. I thought this through as much as I could and I came to the conclusion that I should never be able to end up with a loop in my list unless I push the same request twice. I'm quite sure that this never happens. I'm also fairly sure (although not completely) that it's not the ABA problem. I know that I might pop more than one request at the same time, but I believe this is irrelevant here, and I've never seen it happening. (I'll fix this as well) I thought long and hard about how I can break my function, but I don't see a way to end up with a loop. So the question is: Can someone see a way how this can break? Can someone prove that this can not? Eventually I will solve this (maybe by using a tail pointer or some other solution - locking would be a problem because the threads that post should not be locked, I do have a RW lock at hand though) but I would like to make sure that changing the list actually solves my problem (as opposed to makes it just less likely because of different timing).

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  • What's the recommended implementation for hashing OLE Variants?

    - by Barry Kelly
    OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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  • internal implementation of database Queries

    - by harigm
    In my experience I have used many queries like select, order by, where clause etc.. in mysql, sql-server, oracle etc For a moment i have thought, 1)how is this internally written to implement the above queries 2) which language do they use? 3) is that programming language? if yes which language? 4)what kind of environment required to implement this kind of complex database

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  • Good book(s) for MMORPG design & implementation?

    - by mawg
    I am a long time professional C/C++ programmer (mostly embedded systems) and a hobbyist windows & php hacker. Can anyone recommend a book(s) specifically aimed at designing and (hopefully) implementing an MMORPG? I don't need general how to design or how to code books. Maybe a really good generic games book, but I am not interested in 1st person shooters, I want to know what it takes to implement an MMORPG. Good books, maybe also good URLs. Thanks just searching eBay and Amazon threw up a whole slew of books. Amazon's customer reviews give me an idea of how good they are, and the overview tells me what areas they cover

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  • Is there a faster TList implementation ?

    - by dmauric.mp
    My application makes heavy use of TList, so I was wondering if there are any alternative implementations that are faster or optimized for particular use case. I know of RtlVCLOptimize.pas 2.77, which has optimized implementations of several TList methods. But I'd like to know if there is anything else out there. I also don't require it to be a TList descendant, I just need the TList functionality regardless of how it's implemented. It's entirely possible, given the rather basic functionality TList provides, that there is not much room for improvement, but would still like to verify that, hence this question.

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  • MySQL Hashing Function Implementation

    - by Jonas Stevens
    I know that php has md5(), sha1(), and the hash() functions, but I want to create a hash using the MySQL PASSWORD() function. So far, the only way I can think of is to just query the server, but I want a function (preferably in php or Perl) that will do the same thing without querying MySQL at all. For example: MySQL hash - 464bb2cb3cf18b66 MySQL5 hash - *01D01F5CA7CA8BA771E03F4AC55EC73C11EFA229 Thanks!

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  • Drag and drop an image from desktop to a web text editor (implementation in javascript)

    - by fatmatto
    I tried to write reasonably short title but i failed i guess.. Hi everybody here's what i'm trying to do: I want to implement a web text editor able to recognize when the user drag a image file over it's editing surface and it automa(gically) starts the upload and insert the image near the cursor position. In other words i don't want the user to do the usual "insert-image-browse-ok". Atm i am not very good at javascript ... i know JQuery but i have not a clear idea about how to implement this... i don't know if there's an event handler able to help me in this situation... if not then there should be i think or web apps would miss some kind of interactivity. I've heard miracles about HTML5 could it help me? I've seen such things in Google Wave but that surface doesn't seem to be a form field... google lab's black magic i guess.... Thank you in advance.

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  • Is this implementation truely tail-recursive?

    - by CFP
    Hello everyone! I've come up with the following code to compute in a tail-recursive way the result of an expression such as 3 4 * 1 + cos 8 * (aka 8*cos(1+(3*4))) The code is in OCaml. I'm using a list refto emulate a stack. type token = Num of float | Fun of (float->float) | Op of (float->float->float);; let pop l = let top = (List.hd !l) in l := List.tl (!l); top;; let push x l = l := (x::!l);; let empty l = (l = []);; let pile = ref [];; let eval data = let stack = ref data in let rec _eval cont = match (pop stack) with | Num(n) -> cont n; | Fun(f) -> _eval (fun x -> cont (f x)); | Op(op) -> _eval (fun x -> cont (op x (_eval (fun y->y)))); in _eval (fun x->x) ;; eval [Fun(fun x -> x**2.); Op(fun x y -> x+.y); Num(1.); Num(3.)];; I've used continuations to ensure tail-recursion, but since my stack implements some sort of a tree, and therefore provides quite a bad interface to what should be handled as a disjoint union type, the call to my function to evaluate the left branch with an identity continuation somehow irks a little. Yet it's working perfectly, but I have the feeling than in calling the _eval (fun y->y) bit, there must be something wrong happening, since it doesn't seem that this call can replace the previous one in the stack structure... Am I misunderstanding something here? I mean, I understand that with only the first call to _eval there wouldn't be any problem optimizing the calls, but here it seems to me that evaluation the _eval (fun y->y) will require to be stacked up, and therefore will fill the stack, possibly leading to an overflow... Thanks!

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  • Pointer-based binary heap implementation

    - by Derek Chiang
    Is it even possible to implement a binary heap using pointers rather than an array? I have searched around the internet (including SO) and no answer can be found. The main problem here is that, how do you keep track of the last pointer? When you insert X into the heap, you place X at the last pointer and then bubble it up. Now, where does the last pointer point to? And also, what happens when you want to remove the root? You exchange the root with the last element, and then bubble the new root down. Now, how do you know what's the new "last element" that you need when you remove root again?

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  • Best pageable table implementation in GWT

    - by Steve Buikhuizen
    I need to add a paging, sortable table to my GWT application. I see lots of these out there so I'm looking for your experience to save me time by choosing the best one. So far I'm looking at... http://code.google.com/p/gwt-advanced-table/ http://code.google.com/p/google-web-toolkit-incubator/wiki/PagingScrollTableOld I like the second one best. Any stories to tell?

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  • Cross-Browser jQuery text-zoom implementation

    - by JMC Creative
    I've got some code to increase/decrease font size. This is giving me a headache because each browser seems to implement the $.css('font-size') differently (see jquery bug). The part that's really killing me, though, is that Firefox is scaling up okay, but when I use the scale down function below, it scales up. Webkit & IE are both working as expected. Any ideas on that? I put this in a fiddle here: http://jsfiddle.net/srQ3P/1/ where you can see it working as expected, and you can see it broken in firefox at the project page: http://cumberlandme.info/residents MAJOR EDIT Sorry, the issue is not the code, it's firefox buggy behavior. After I zoom in or out with the browser controls (ctrl + plus or ctrol + minus) the js goes haywire. This doesn't happen in other browsers. This is the real issue. Any advice on that

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  • Interface that Entails the Implementation of Indexer

    - by Ngu Soon Hui
    I am looking for a framework-defined interface that declares indexer. In other words, I am looking for something like this: public interface IYourList<T> { T this[int index] { get; set; } } I just wonder whether .Net framework contains such interface? If yes, what is it called? You might ask why I can't just create the interface myself. Well, I could have. But if .Net framework already has that why should I reinvent the wheel?

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  • Which Queue implementation to use in Java?

    - by devoured elysium
    I need to use a FIFO structure in my application. It needs to have at most 5 elements. I'd like to have something easy to use (I don't care for concurrency) that implements the Collection interface. I've tried the LinkedList, that seems to come from Queue, but it doesn't seem to allow me to set it's maximum capacity. It feels as if I just want at max 5 elements but try to add 20, it will just keep increasing in size to fit it. I'd like something that'd work the following way: XQueue<Integer> queue = new XQueue<Integer>(5); //where 5 is the maximum number of elements I want in my queue. for (int i = 0; i < 10; ++i) { queue.offer(i); } for (int i = 0; i < 5; ++i) { System.out.println(queue.poll()); } That'd print: 5 6 7 8 9 Thanks

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  • Implementation of APIs on diferent platforms

    - by b-gen-jack-o-neill
    OK, this is basicly just about any non-default OS API running on all different OS. But for my example let´s consider platform Windows, API SDL (Simple DirectMedia Layer). Actually this question came to my mind when I was reading about SDL. Originally, I thought that on Windows (and basicly any other OS) you must use OS API to make certain actions, like wrtiting to screen, creating window and so on, becouse that API knows what kernel calls and system subroutines calls it has to do. But when I read about SDL, I surprised me, becouse, you cannot make computer to do anything more than OS can, since you cannot acess HW directly, only thru OS API, from Console allocation to DirectX. So, my question actually is, how does this not-default-OS APIs work? Do they use (wrap) original system API (like MFC wraps win32 api)? Or, do they actually have direct acess to Windows kernel? Or is there any third, way in between? Thanks.

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  • Differences between matrix implementation in C

    - by tempy
    I created two 2D arrays (matrix) in C in two different ways. I don't understand the difference between the way they're represented in the memory, and the reason why I can't refer to them in the same way: scanf("%d", &intMatrix1[i][j]); //can't refer as &intMatrix1[(i * lines)+j]) scanf("%d", &intMatrix2[(i * lines)+j]); //can't refer as &intMatrix2[i][j]) What is the difference between the ways these two arrays are implemented and why do I have to refer to them differently? How do I refer to an element in each of the arrays in the same way (?????? in my printMatrix function)? int main() { int **intMatrix1; int *intMatrix2; int i, j, lines, columns; lines = 3; columns = 2; /************************* intMatrix1 ****************************/ intMatrix1 = (int **)malloc(lines * sizeof(int *)); for (i = 0; i < lines; ++i) intMatrix1[i] = (int *)malloc(columns * sizeof(int)); for (i = 0; i < lines; ++i) { for (j = 0; j < columns; ++j) { printf("Type a number for intMatrix1[%d][%d]\t", i, j); scanf("%d", &intMatrix1[i][j]); } } /************************* intMatrix2 ****************************/ intMatrix2 = (int *)malloc(lines * columns * sizeof(int)); for (i = 0; i < lines; ++i) { for (j = 0; j < columns; ++j) { printf("Type a number for intMatrix2[%d][%d]\t", i, j); scanf("%d", &intMatrix2[(i * lines)+j]); } } /************** printing intMatrix1 & intMatrix2 ****************/ printf("intMatrix1:\n\n"); printMatrix(*intMatrix1, lines, columns); printf("intMatrix2:\n\n"); printMatrix(intMatrix2, lines, columns); } /************************* printMatrix ****************************/ void printMatrix(int *ptArray, int h, int w) { int i, j; printf("Printing matrix...\n\n\n"); for (i = 0; i < h; ++i) for (j = 0; j < w; ++j) printf("array[%d][%d] ==============> %d\n, i, j, ??????); }

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  • C++ option/long option implementation

    - by K Hein
    I am working on a parser for meta programming language using C++ on Linux platform. Right now, I need to implement option/long option for the parser to provide some additional features. Basically, if the user pass in some additional option, the parser needs to store statistics while parsing the text files. I can think of two ways to implement it. One way is to user global to store options entered by users. Another way is to create a singleton class to store options. So I would like to know if there is any other way to implement it. What is the best/most recommended way of implementing it? Thanks in advance. Regards, K.Hein

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  • Ajax with Jsf 1.1 implementation

    - by Rohan Ved
    I am using JSF1.1 in that, have this code_ <%@ taglib uri="http://java.sun.com/jsf/html" prefix="h"%> <%@ taglib uri="http://java.sun.com/jsf/core" prefix="f"%> <%@ taglib uri="http://www.azureworlds.org" prefix="azure"%> <%@ taglib uri="http://myfaces.apache.org/tomahawk" prefix="x"%> <%@ taglib uri="http://www.asifqamar.com/jsf/asif" prefix="a"%> ... <x:selectOneMenu value="#{hotelBean.state}"> <f:selectItem itemLabel="Select One" itemValue="" /> <f:selectItem value="#{hotelBean.mapStates }" /> <x:ajax update="city" listener="#{hotelBean.handleCityChange}" /> </x:selectOneMenu> <h:outputText value="City* " /> <x:selectOneMenu id="city" value="#{hotelBean.city}"> <f:selectItem itemLabel="Select One" itemValue="" /> <f:selectItem value="#{hotelBean.mapCities }" /> </x:selectOneMenu> line x:ajax update="city" listener="#{hotelBean.handleCityChange}" is not working , i searched but got JSF1.1 not support for Ajax. then what can i do for this? and i have less knowledge of JS. Thanx

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  • AutoComplete implementation - Interview Question

    - by user181218
    Hi, Say you have a DB table with two cols: SearchPhrase(String) | Popularity(Int). You need to initialize a DS so that you could use it to implement an autocomplete feature (like google suggest) comfortably. The requirement: Once the data from the db is processed into the data structure, when you type a letter you get the 10 most popular searchphrases from the db starting with that letter,then when you type the next one you get the 10 .... with these two letters and so on. The question only concerns planning the ds and pseudocoding Insert,Search etc. Note: YOU CANNOT USE TRIE DS. Any ideas?

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