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  • What is the Proper approach for Constructing a PhysicalAddress object from Byte Array

    - by Paul Farry
    I'm trying to understand what the correct approach for a constructor that accepts a Byte Array with regard to how it stores it's data (specifically with PhysicalAddress) I have an array of 6 bytes (theAddress) that is constructed once. I have a source array of 18bytes (theAddresses) that is loaded from a TCP Connection. I then copy the 6bytes from theAddress+offset into theAddress and construct the PhysicalAddress from it. Problem is that the PhysicalAddress just stores the Reference to the array that was passed in. Therefore if you subsequently check the addresses they only ever point to the last address that was copied in. When I took a look inside the PhysicalAddress with reflector it's easy to see what's going on. public PhysicalAddress(byte[] address) { this.changed = true; this.address = address; } Now I know this can be solved by creating theAddress array on each pass, but I wanted to find out what really is the best practice for this. Should the constructor of an object that accepts a byte array create it's own private Variable for holding the data and copy it from the original Should it just hold the reference to what was passed in. Should I just created theAddress on each pass in the loop

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  • C# creating a Class, having objects as member variables? I think the objects are garbage collecte

    - by Bryan
    So I have a class that has the following member variables. I have get and set functions for every piece of data in this class. public class NavigationMesh { public Vector3 node; int weight; bool isWall; bool hasTreasure; public NavigationMesh(int x, int y, int z, bool setWall, bool setTreasure) { //default constructor //Console.WriteLine(x + " " + y + " " + z); node = new Vector3(x, y, z); //Console.WriteLine(node.X + " " + node.Y + " " + node.Z); isWall = setWall; hasTreasure = setTreasure; weight = 1; }// end constructor public float getX() { Console.WriteLine(node.X); return node.X; } public float getY() { Console.WriteLine(node.Y); return node.Y; } public float getZ() { Console.WriteLine(node.Z); return node.Z; } public bool getWall() { return isWall; } public void setWall(bool item) { isWall = item; } public bool getTreasure() { return hasTreasure; } public void setTreasure(bool item) { hasTreasure = item; } public int getWeight() { return weight; } }// end class In another class, I have a 2-Dim array that looks like this NavigationMesh[,] mesh; mesh = new NavigationMesh[502,502]; I use a double for loop to assign this, my problem is I cannot get the data I need out of the Vector3 node object after I create this object in my array with my "getters". I've tried making the Vector3 a static variable, however I think it refers to the last instance of the object. How do I keep all of these object in memory? I think there being garbage collected. Any thoughts?

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  • Using generics in F# to create an EnumArray type

    - by Matthew
    I've created an F# class to represent an array that allocates one element for each value of a specific enum. I'm using an explicit constructor that creates a dictionary from enum values to array indices, and an Item property so that you can write expressions like: let my_array = new EnumArray<EnumType, int> my_array.[EnumType.enum_value] <- 5 However, I'm getting the following obscure compilation error at the line marked with '// FS0670' below. error FS0670: This code is not sufficiently generic. The type variable ^e when ^e : enum<int> and ^e : equality and ^e : (static member op_Explicit : ^e -> int) could not be generalized because it would escape its scope. I'm at a loss - can anyone explain this error? type EnumArray< 'e, 'v when 'e : enum<int> and 'e : equality and ^e : (static member op_Explicit : ^e -> int) > = val enum_to_int : Dictionary<'e, int> val a : 'v array new() as this = { enum_to_int = new Dictionary<'e, int>() a = Array.zeroCreate (Enum.GetValues(typeof<'e>).Length) } then for (e : obj) in Enum.GetValues(typeof<'e>) do this.enum_to_int.Add(e :?> 'e, int(e :?> 'e)) member this.Item with get (idx : 'e) : 'v = this.a.[this.enum_to_int.[idx]] // FS0670 and set (idx : 'e) (c : 'v) = this.a.[this.enum_to_int.[idx]] <- c

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  • Module not found

    - by TMP
    Hi There! I've been working on this one quite a bit and haven't gotten any closer to a solution. I juut dug up my old copy of the WindowsHookLib again - It's available with source at http://www.codeproject.com/KB/DLL/WindowsHookLib.aspx. This library allows Global Windows Mouse/Keyboard/Clipboard Hooks, which is very useful. I'm trying to use the Mouse Hook in here to Capture Mouse-Motion (I could use a Timer that always polls Cursor.Position, but I plan on using more features of WindowsHookLib later). Code as follows: MouseHook mh = new MouseHook(); mh.InstallHook(); mh.MouseMove += new EventHandler<WindowsHookLib.MouseEventArgs>(mh_MouseMove); But on the call to InstallHook(), I get an Exception: "The specified Module could not be found". Strange. Searching, I found that someone thought this occurs because a DLL is not in a place included in the Windows PATH variable, and because placing it in system32 didn't help I went the whole hog and translated the thing to C# for inclusion directly in my project (I was curious how it works). However the error was obstinately persistent, so I dug a bit on this, and found the Code in the Library that is responsible: In InstallHook(), we have IntPtr hinstDLL = Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]); this._hMouseHook = UnsafeNativeMethods.SetWindowsHookEx(14, this._mouseProc, hinstDLL, 0); if (this._hMouseHook == IntPtr.Zero) { throw new MouseHookException(new Win32Exception(Marshal.GetLastWin32Error()).Message); } And this (after modification and recompile) tells me that what I'm really getting is a Windows error "ERROR_MOD_NOT_FOUND"! Now, Here I'm stumped. Didn't I just compile the Hook Library directly into my project? (UnsafeMethods.SetWindowsHookEx is just a DllImported Method from user32) Any Answers, or Prods in the right direction, or any hints, pointers or similar are very much appreciated!

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  • C++ destructos causing crash's

    - by larsonator
    ok, so i got a some what intricate program that simulates the uni systems of students, units, and students enrolling in units. Students are stored in a binary search tree, Units are stored in a standard list. Student has a list of Unit Pointers, to store which units he/she is enrolled in Unit has a list of Student pointers, to store students which are enrolled in that unit. The unit collections (storing units in a list) as made as a static variable where the main function is, as is the Binary search tree of students. when its finaly time to close the program, i call the destructors of each. but at some stage, during the destructors on the unit side, Unhandled exception at 0x002e4200 in ClassAllocation.exe: 0xC0000005: Access violation reading location 0x00000000. UnitCollection destructor: UnitCol::~UnitCol() { list<Unit>::iterator itr; for(itr = UnitCollection.begin(); itr != UnitCollection.end();) { UnitCollection.pop_front(); itr = UnitCollection.begin(); } } Unit Destructor Unit::~Unit() { } now i got the same sorta problem on the student side of things BST destructors void StudentCol::Destructor(const BTreeNode * r) { if(r!= 0) { Destructor(r->getLChild()); Destructor(r->getRChild()); delete r; } } StudentCol::~StudentCol() { Destructor(root); } Student Destructor Student::~Student() { } so yeah any help would be greatly appreciated

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  • Changing a url depending on what link chosen (HTML) no asp.

    - by Ozaki
    TLDR I need to change a javascript variable on the same page after clicking a link (can be from a different page) so that the getjson request pulls different data without having to duplicate on html pages. I am using some getJSON requests with Jquery, to make calls to populate my pages. I want to be able to (in plain HTML / javascript) when the user clicks say "link 1" or "link 2" to open the same page (say page.html) but change the get request url to "link 1" or "link 2". Page.html var url = ??; $.getJSON(url, function(data){} link 1 var url = host/link1 <a href="page.html">link1</a> link2 var url = host/link2 <a href="page.html">link2</a> So I call the same page but am able to populate it with different content. Purposely staying away from asp. Was thinking maybe of inserting the content into a div after page load so the url can be set or something along those lines. Any ideas how I might go about this?

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  • Passing PHP variables trough functions?

    - by Mateus Nunes
    I'm facing some troubles to pass php variables value trough functions,every time i try to use a variable inside one of my functions its value becomes nil,let me be more specific.I have the following code in my php file: $myvar = $Session['username']; function updateuserinformation(){ if(trim($_FILES["fileUpload"]["tmp_name"]) != ""){ $images = $_FILES["fileUpload"]["tmp_name"]; $new_images = "thumbnails_".$_FILES["fileUpload"]["name"]; copy($_FILES["fileUpload"]["tmp_name"],"Photos/".$_FILES["fileUpload"]["name"]); $width=200; //*** Fix Width & Heigh (Autu caculate) ***// $size=GetimageSize($images); $height=round($width*$size[1]/$size[0]); $images_orig = ImageCreateFromJPEG($images); $photoX = ImagesX($images_orig); $photoY = ImagesY($images_orig); $images_fin = ImageCreateTrueColor($width, $height); ImageCopyResampled($images_fin, $images_orig, 0, 0, 0, 0, $width+1, $height+1, $photoX, $photoY); ImageJPEG($images_fin,"Photos/".$new_images); ImageDestroy($images_orig); ImageDestroy($images_fin); print $data["foo"]; echo"$myvar"; mysql_query("UPDATE users SET userpictureaddress = 'http://www.litsdevelopment.com/litsapplication/userimages/MATEUS' WHERE username = 'Mateus' "); } } I trying to use the $myvar value in my function but every time i run the code it just doesn't work,i've already tried global,globals,arrays and session for nothing worked.Of corse i'm making a little mistake in some part of it,but anyone know what is the correct way to do this?

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  • Use queried json data in a function

    - by SztupY
    I have a code similar to this: $.ajax({ success: function(data) { text = ''; for (var i = 0; i< data.length; i++) { text = text + '<a href="#" id="Data_'+ i +'">' + data[i].Name + "</a><br />"; } $("#SomeId").html(text); for (var i = 0; i< data.length; i++) { $("#Data_"+i).click(function() { alert(data[i]); RunFunction(data[i]); return false; }); } } }); This gets an array of some data in json format, then iterates through this array generating a link for each entry. Now I want to add a function for each link that will run a function that does something with this data. The problem is that the data seems to be unavailable after the ajax success function is called (although I thought that they behave like closures). What is the best way to use the queried json data later on? (I think setting it as a global variable would do the job, but I want to avoid that, mainly because this ajax request might be called multiple times) Thanks.

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  • What is a NULL value

    - by Adi
    I am wondering , what exactly is stored in the memory when we say a particular variable pointer to be NULL. suppose I have a structure, say typdef struct MEM_LIST MEM_INSTANCE; struct MEM_LIST { char *start_addr; int size; MEM_INSTANCE *next; }; MEM_INSTANCE *front; front = (MEM_INSTANCE*)malloc(sizeof(MEM_INSTANCE*)); -1) If I make front=NULL. What will be the value which actually gets stored in the different fields of the front, say front-size ,front-start_addr. Is it 0 or something else. I have limited knowledge in this NULL thing. -2) If I do a free(front); It frees the memory which is pointed out by front. So what exactly free means here, does it make it NULL or make it all 0. -3) What can be a good strategy to deal with initialization of pointers and freeing them . Thanks in advance

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  • Execute process conditionally in Windows PowerShell (e.g. the && and || operators in Bash)

    - by Dustin
    I'm wondering if anybody knows of a way to conditionally execute a program depending on the exit success/failure of the previous program. Is there any way for me to execute a program2 immediately after program1 if program1 exits successfully without testing the LASTEXITCODE variable? I tried the -band and -and operators to no avail, though I had a feeling they wouldn't work anyway, and the best substitute is a combination of a semicolon and an if statement. I mean, when it comes to building a package somewhat automatically from source on Linux, the && operator can't be beaten: # Configure a package, compile it and install it ./configure && make && sudo make install PowerShell would require me to do the following, assuming I could actually use the same build system in PowerShell: # Configure a package, compile it and install it .\configure ; if ($LASTEXITCODE -eq 0) { make ; if ($LASTEXITCODE -eq 0) { sudo make install } } Sure, I could use multiple lines, save it in a file and execute the script, but the idea is for it to be concise (save keystrokes). Perhaps it's just a difference between PowerShell and Bash (and even the built-in Windows command prompt which supports the && operator) I'll need to adjust to, but if there's a cleaner way to do it, I'd love to know.

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  • pthreads: reader/writer locks, upgrading read lock to write lock

    - by ScaryAardvark
    I'm using read/write locks on Linux and I've found that trying to upgrade a read locked object to a write lock deadlocks. i.e. // acquire the read lock in thread 1. pthread_rwlock_rdlock( &lock ); // make a decision to upgrade the lock in threads 1. pthread_rwlock_wrlock( &lock ); // this deadlocks as already hold read lock. I've read the man page and it's quite specific. The calling thread may deadlock if at the time the call is made it holds the read-write lock (whether a read or write lock). What is the best way to upgrade a read lock to a write lock in these circumstances.. I don't want to introduce a race on the variable I'm protecting. Presumably I can create another mutex to encompass the releasing of the read lock and the acquiring of the write lock but then I don't really see the use of read/write locks. I might as well simply use a normal mutex. Thx

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  • Java try finally variations

    - by Petr Gladkikh
    This question nags me for a while but I did not found complete answer to it yet (e.g. this one is for C# http://stackoverflow.com/questions/463029/initializing-disposable-resources-outside-or-inside-try-finally). Consider two following Java code fragments: Closeable in = new FileInputStream("data.txt"); try { doSomething(in); } finally { in.close(); } and second variation Closeable in = null; try { in = new FileInputStream("data.txt"); doSomething(in); } finally { if (null != in) in.close(); } The part that worries me is that the thread might be somewhat interrupted between the moment resource is acquired (e.g. file is opened) but resulting value is not assigned to respective local variable. Is there any other scenarios the thread might be interrupted in the point above other than: InterruptedException (e.g. via Thread#interrupt()) or OutOfMemoryError exception is thrown JVM exits (e.g. via kill, System.exit()) Hardware fail (or bug in JVM for complete list :) I have read that second approach is somewhat more "idiomatic" but IMO in the scenario above there's no difference and in all other scenarios they are equal. So the question: What are the differences between the two? Which should I prefer if I do concerned about freeing resources (especially in heavily multi-threading applications)? Why? I would appreciate if anyone points me to parts of Java/JVM specs that support the answers.

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  • c++ multithread

    - by chnet
    I use C++ to implement a thread class. My code shows in the following. I have a problem about how to access thread data. In the class Thread, I create a thread use pthread_create() function. then it calls EntryPoint() function to start thread created. In the Run function, I want to access the mask variable, it always shows segment fault. So, my question is whether the new created thread copy the data in original class? How to access the thread own data? class Thread { public: int mask; pthread_t thread; Thread( int ); void start(); static void * EntryPoint (void *); void Run(); }; Thread::Thread( int a) { mask =a; } void Thread::Run() { cout<<"thread begin to run" <<endl; cout << mask <<endl; // it always show segmentfault here } void * Thread::EntryPoint(void * pthis) { cout << "entry" <<endl; Thread *pt = (Thread *) pthis; pt->Run(); } void Thread::start() { pthread_create(&thread, NULL, EntryPoint, (void *)ThreadId ); pthread_join(thread, NULL); } int main() { int input_array[8]={3,1,2,5,6,8,7,4}; Thread t1(1); t1.start(); }

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  • Set "Start With" value for Oracle sequence dynamically

    - by Allan
    I'm trying to create a release script that can be deployed on multiple databases, but where the data can be merged back together at a later date. The obvious way to handle this is to set the sequence numbers for production data sufficiently high in subsequent deployments to prevent collisions. The problem is in coming up with a release script that will accept the environment number and set the "Start With" value of the sequences appropriately. Ideally, I'd like to use something like this: ACCEPT EnvironNum PROMPT 'Enter the Environment Number: ' --[more scripting] CREATE SEQUENCE seq1 START WITH &EnvironNum*100000; --[more scripting] This doesn't work because you can't evaluate a numeric expression in DDL. Another option is to create the sequences using dynamic SQL via PL/SQL. ACCEPT EnvironNum PROMPT 'Enter the Environment Number: ' --[more scripting] EXEC execute immediate 'CREATE SEQUENCE seq1 START WITH ' || &EnvironNum*100000; --[more scripting] However, I'd prefer to avoid this solution as I generally try to avoid issuing DDL in PL/SQL. Finally, the third option I've come up with is simply to accept the Start With value as a substitution variable, instead of the environment number. Does anyone have a better thought on how to go about this?

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  • FF extension: saving a value in preferences and retrieving in the js file

    - by encryptor
    I am making an extension which should take a link as the user input only once. Then the entire extension keeps using that link on various functions in the JS file. When the user changes it, the value accessed by the js file also changes accordingly. I am using the following but it does not work for me var pref_manager = Components.classes["@mozilla.org/preferencesservice;1"].getService(Components.interfaces.nsIPrefService) function setInstance(){ if (pref_manager.prefHasUserValue("myvar")) { instance = pref_manager.getString("myvar"); alert(instance); } if(instance == null){ instance = prompt("Please enter webcenter host and port"); // Setting the value pref_manager.setString("myvar", instance); } } instance is the global variable in which i take the user input. The alert (instance) does not show up, which means there is some problem by the way i am saving the pref or extracting it. Can someone please help me with this. I have never worked with preferences before. so even if there are minor problems i might not be able to figure out.

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  • How do I mock a method with an open array parameter in PascalMock?

    - by Oliver Giesen
    I'm currently in the process of getting started with unit testing and mocking for good and I stumbled over the following method that I can't seem to fabricate a working mock implementation for: function GetInstance(const AIID: TGUID; out AInstance; const AArgs: array of const; const AContextID: TImplContextID = CID_DEFAULT): Boolean; (TImplContextID is just an alias for Integer) I thought it would have to look something like this: function TImplementationProviderMock.GetInstance( const AIID: TGUID; out AInstance; const AArgs: array of const; const AContextID: TImplContextID): Boolean; begin Result := AddCall('GetInstance') .WithParams([@AIID, AContextID]) .ReturnsOutParams([AInstance]) .ReturnValue; end; But the compiler complains about the .ReturnsOutParams([AInstance]) saying "Bad argument type in variable type array constructor.". Also I haven't found a way to specify the open array parameter AArgs at all. Also, is using the @-notation for the TGUID-typed parameter the right way to go? Is it possible to mock this method with the current version of PascalMock at all? Update: I now realize I got the purpose of ReturnsOutParams completely wrong: It's intended to be used for populating the values to be returned when defining the expectations rather than for mocking the call itself. I now think the correct syntax for mocking the out parameter would probably have to look more like this: function TImplementationProviderMock.GetInstance( const AIID: TGUID; out AInstance; const AArgs: array of const; const AContextID: TImplContextID): Boolean; var lCall: TMockMethod; begin lCall := AddCall('GetInstance').WithParams([@AIID, AContextID]); Pointer(AInstance) := lCall.OutParams[0]; Result := lCall.ReturnValue; end; The questions that remain are how to mock the open array parameter AArgs and whether passing the TGUID argument (i.e. a value type) by address will work out...

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  • Generic dataset handling library

    - by Pep.
    Hello, I want to build a generic Perl module for handling and analysing biomedical character separated datasets and which can, most certain, be used on any kind of datasets that contain a mixture of categorical (A,B,C,..) and continuous (1.2,3,881..) and identifier (XXX1,XXX2...). The plan is to have people initialize the module and then use some arguments to point to the data file(s), the place were the analysis reports should be placed and the structure of the data. By structure of data I mean which variable is in which place and its name/type. And this is where I need some enlightenment. I am baffled how to do this in a clean way. Obviously, having people create a simple schema file, be it XML or some other format would be the cleanest but maybe not all people enjoy doing something like this. The solutions I can think of are: Create a configuration file in XML or similar and with a prespecified format. Pass the information during initialization of the module. Use the first row of the data as headers and try to guess types (ouch) Surely there must be a "canonical" way of doing this that is also usable and efficient. Thanks p.

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  • memcache is not storing data accross requests

    - by morpheous
    I am new to using memcache, so I may be doing something wrong. I have written a wrapper class around memcache. The wrapper class has only static methods, so is a quasi singleton. The class looks something like this: class myCache { private static $memcache = null; private static $initialized = false; public static function init() { if (self::$initialized) return; self::$memcache = new Memcache(); if (self::configure()) //connects to daemon { self::store('foo', 'bar'); } else throw ConnectionError('I barfed'); } public static function store($key, $data, $flag=MEMCACHE_COMPRESSED, $timeout=86400) { if (self::$memcache->get($key)!== false) return self::$memcache->replace($key, $data, $flag, $timeout); return self::$memcache->set($key, $data, $flag, $timeout); } public static function fetch($key) { return self::$memcache->get($key); } } //in my index.php file, I use the class like this require_once('myCache.php'); myCache::init(); echo 'Stored value is: '. myCache::fetch('foo'); The problem is that the myCache::init() method is being executed in full everytime a page is requested. I then remembered that static variables do not maintain state accross page requests. So I decided instead, to store the flag that indicates whether the server contains the start up data (for our purposes, the variable 'foo', with value 'bar') in memcache itself. Once the status flag is stored in memcache itself, It solves the problem of the initialisation data being loaded for every page request (which quite frankly, defeats the purpose of memcache). However, having solved that problem, when I come to fetch the data in memcache, it is empty. I dont understand whats going on. Can anyone clarify how I can store my data once and retrieve it accross page requests? BTW, (just to clarify), the get/set is working correctly, and if I allow memcache to load the initialisation data for each page request, (which is silly), then the data is available in memcache.

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  • Python - Things one MUST avoid

    - by Anurag Uniyal
    Today I was bitten again by "Mutable default arguments" after many years. I usually don't use mutable default arguments unless needed but I think with time I forgot about that, and today in the application I added tocElements=[] in a pdf generation function's argument list and now 'Table of Content' gets longer and longer after each invocation of "generate pdf" :) My question is what other things should I add to my list of things to MUST avoid? 1 Mutable default arguments 2 import modules always same way e.g. 'from y import x' and 'import x' are totally different things actually they are treated as different modules see http://stackoverflow.com/questions/1459236/module-reimported-if-imported-from-different-path 3 Do not use range in place of lists because range() will become an iterator anyway, so things like this will fail, so wrap it by list myIndexList = [0,1,3] isListSorted = myIndexList == range(3) # will fail in 3.0 isListSorted = myIndexList == list(range(3)) # will not same thing can be mistakenly done with xrange e.g myIndexList == xrange(3). 4 Catching multiple exceptions try: raise KeyError("hmm bug") except KeyError,TypeError: print TypeError It prints "hmm bug", though it is not a bug, it looks like we are catching exceptions of type KeyError,TypeError but instead we are catching KeyError only as variable TypeError, instead use try: raise KeyError("hmm bug") except (KeyError,TypeError): print TypeError

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  • Validating Time & Date To Be At Least A Certain Amount Of Time In The Future

    - by MJH
    I've built a reservation form for a taxi company which works fine, but I'm having an issue with users making reservations that are due too soon in the future. Since the entire form is kind of long, I first want to make sure the user is not trying to make a reservation for less than an hour ahead of time, without them having to fill out the whole form. This is what I have come up with so far, but it's just not working: <?php //Set local time zone. date_default_timezone_set('America/New_York'); //Get current date and time. $current_time = date('Y-m-d H:i:s'); //Set reservation time variable $res_datetime = $_POST['res_datetime']; //Set event time. $event_time = strtotime($res_datetime); ?> <!doctype html> <html> <head> <meta charset="utf-8"> <title>Check Date and Time</title> </head> <?php //Check to be sure reservation time is at least one hour in the future. if (($current_time - $event_time) <= (3600)) { echo "You must make a reservation at least one hour ahead of time."; } ?> <form name="datetime" action="" method="post"> <input name="res_datetime" type="datetime-local" id="res_datetime"> <input type="submit"> </form> <body> </body> </html> How can I create a validation check to make sure the date and time of the reservation is at least one hour ahead of time?

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  • Is it possible for a function called from within an object to have access to that object's scope?

    - by Elliot Bonneville
    I can't think of a way to explain what I'm after more than I've done in the title, so I'll repeat it. Is it possible for an anonymous function called from within an object to have access to that object's scope? The following code block should explain what I'm trying to do better than I can: function myObj(testFunc) { this.testFunc = testFunc; this.Foo = function Foo(test) { this.test = test; this.saySomething = function(text) { alert(text); }; }; var Foo = this.Foo; this.testFunc.apply(this); } var test = new myObj(function() { var test = new Foo(); test.saySomething("Hello world"); }); When I run this, I get an error: "Foo is not defined." How do I ensure that Foo will be defined when I call the anonymous function? Here's a jsFiddle for further experimentation. Edit: I am aware of the fact that adding the line var Foo = this.Foo; to the anonymous function I pass in to my instance of myObj will make this work. However, I'd like to avoid having to expose the variable inside the anonymous function--do I have any other options?.

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  • How to index a table with a Type 2 slowly changing dimension for optimal performance

    - by The Lazy DBA
    Suppose you have a table with a Type 2 slowly-changing dimension. Let's express this table as follows, with the following columns: * [Key] * [Value1] * ... * [ValueN] * [StartDate] * [ExpiryDate] In this example, let's suppose that [StartDate] is effectively the date in which the values for a given [Key] become known to the system. So our primary key would be composed of both [StartDate] and [Key]. When a new set of values arrives for a given [Key], we assign [ExpiryDate] to some pre-defined high surrogate value such as '12/31/9999'. We then set the existing "most recent" records for that [Key] to have an [ExpiryDate] that is equal to the [StartDate] of the new value. A simple update based on a join. So if we always wanted to get the most recent records for a given [Key], we know we could create a clustered index that is: * [ExpiryDate] ASC * [Key] ASC Although the keyspace may be very wide (say, a million keys), we can minimize the number of pages between reads by initially ordering them by [ExpiryDate]. And since we know the most recent record for a given key will always have an [ExpiryDate] of '12/31/9999', we can use that to our advantage. However... what if we want to get a point-in-time snapshot of all [Key]s at a given time? Theoretically, the entirety of the keyspace isn't all being updated at the same time. Therefore for a given point-in-time, the window between [StartDate] and [ExpiryDate] is variable, so ordering by either [StartDate] or [ExpiryDate] would never yield a result in which all the records you're looking for are contiguous. Granted, you can immediately throw out all records in which the [StartDate] is greater than your defined point-in-time. In essence, in a typical RDBMS, what indexing strategy affords the best way to minimize the number of reads to retrieve the values for all keys for a given point-in-time? I realize I can at least maximize IO by partitioning the table by [Key], however this certainly isn't ideal. Alternatively, is there a different type of slowly-changing-dimension that solves this problem in a more performant manner?

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  • Read Java in as Hex

    - by James
    Hi, I have tried to solve this but I keep coming up with stuff that is no help I'm sure this is easy (when you know how of course ;) ) What I would like to do is read in a file using a byte stream like below: while((read = in.read()) != -1){ //code removed to save space Integer.toHexString(read); System.out.println(read); } When it prints out the Hex to the screen it will print out numbers fine e.g 31 13 12 0 but when it comes to a hex code that should be 01 31 it will print 0 131. I want to read it in to a variable like you would see in a hex editor i.e 00 11 21 31 no single numbers as i need to scan the whole file and look for patterns which I know how to do I'm just stuck on this :/ so in short i need a variabe to contain the two hex characters i.e int temp = 01 not int temp = 0 , I hope this all makes sense, I'm a little confused as it's 3am! If anyone knows how to do this I would be most greatful, p.s thanks for the help in advance this site has saved me loads of research and have learnt a lot! Many thanks.

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  • In Python, how can I find the index of the first item in a list that is NOT some value?

    - by Ryan B. Lynch
    Python's list type has an index(x) method. It takes a single parameter x, and returns the (integer) index of the first item in the list that has the value x. Basically, I need to invert the index(x) method. I need to get the index of the first value in a list that does NOT have the value x. I would probably be able to even just use a function that returns the index of the first item with a value != None. I can think of a 'for' loop implementation with an incrementing counter variable, but I feel like I'm missing something. Is there an existing method, or a one-line Python construction that can handle this? In my program, the situation comes up when I'm handling lists returned from complex regex matches. All but one item in each list have a value of None. If I just needed the matched string, I could use a list comprehension like '[x for x in [my_list] if x is not None]', but I need the index in order to figure out which capture group in my regex actually caused the match.

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  • How is a referencing environment generally implemented for closures?

    - by Alexandr Kurilin
    Let's say I have a statically/lexically scoped language with deep binding and I create a closure. The closure will consist of the statements I want executed plus the so called referencing environment, or, to quote this post, the collection of variables which can be used. What does this referencing environment actually look like implementation-wise? I was recently reading about ObjectiveC's implementation of blocks, and the author suggests that behind the scenes you get a copy of all of the variables on the stack and also of all the references to heap objects. The explanation claims that you get a "snapshot" of the referencing environment at the point in time of the closure's creation. Is that more or less what happens, or did I misread that? Is anything done to "freeze" a separate copy of the heap objects, or is it safe to assume that if they get modified between closure creation and the closure executing, the closure will no longer be operating on the original version of the object? If indeed there's copying being made, are there memory usage considerations in situations where one might want to create plenty of closures and store them somewhere? I think that misunderstanding of some of these concepts might lead to tricky issues like the ones Eric Lippert mentions in this blog post. It's interesting because you'd think that it wouldn't make sense to keep a reference to a value type that might be gone by the time the closure is called, but I'm guessing that in C# the compiler will figure out that the variable is needed later and put it into the heap instead. It seems that in most memory-managed languages everything is a reference and thus ObjectiveC is a somewhat unique situation with having to deal with copying what's on the stack.

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