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  • Where in memory are stored nullable types?

    - by Ondrej Slinták
    This is maybe a follow up to question about nullable types. Where exactly are nullable value types (int?...) stored in memory? First I thought it's clear enough, as Nullable<T> is struct and those are value types. Then I found Jon Skeet's article "Memory in .NET", which says: Note that a value type variable can never have a value of null - it wouldn't make any sense, as null is a reference type concept, meaning "the value of this reference type variable isn't a reference to any object at all". I am little bit confused after reading this statement. So let's say I have int? a = null;. As int is normally a value type, is it stored somehow inside struct Nullable<T> in stack (I used "normally" because I don't know what happens with value type when it becomes nullable)? Or anything else happens here - perhaps in heap?

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  • Comparing numeric strings

    - by Kiren Siva
    From the question PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons I know PHP interpret strings as numbers whenever it can. "10" < "1a" => 10 less than 1 expecting false "1a" < "2" => 1 less than 2 expecting true "10" > "2" => 10 greater than 2 expecting true But in the case of "10" < "1a" php returns true. I am not understanding the concept please help me to clarify it. Edit: But when I add "10" + "1a" it returns 11 that means php interprets "10" as 10 and "1a" as 1. Is that correct?

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  • what is a performance way to 'tree-walking' through my Entity Framework data

    - by Greg
    Hi, I have a Entity Framework design with a few tables that define a "graph". So there can be a large chain of relationships between objects in the few tables via concept of parent/child relationships. What is a performance way to 'tree-walking' through my Entity Framework data? That is I assume I wouldn't want to load the full set of all NODES and RELATIONSHIPS from the database for the purpose of walking the tree, where the end result may only be identifying leaf nodes? Or would this be OK with the way lazy loading may work at the column/parameter level? Else how could I load just the skeleton of the objects and then when needing to refer to any attributes have them lazy load then?

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  • c# hierarchy collection library? - anyone know of one (e.g. GetDirectChildren, GetAllChildren, GetPa

    - by Greg
    Hi, Does anyone know of a solid C# library / approach to manage a hierarchy/web type collection? This would be a library that would basic consist of the concept of nodes & relationships, for example to model web pages/files linked under a URL, or modeling IT infrastructure. It would have key methods such as: Node.GetDirectParents() Node.GetRootParents() Node.GetDirectChildren() Node.GetAllChildren() So it's smarts would include the ability to "walk the tree" of nodes based on the relationships when someone does ask for "give me all the children under this node" for example. It ideally include a persistence layer, to save/retrieve such data to/from a databases (e.g. with a Nodes and Relationships table). Thanks

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  • Screening (multi)collinearity in a reggresion model

    - by aL3xa
    I hope that this one is not going to be "ask-and-answer" question... here goes: (multi)collinearity refers to extremely high correlations between predictors in the regression model. How to cure them... well, sometimes you don't need to "cure" collinearity, since it doesn't affect regression model itself, but interpretation of an effect of individual predictors. One way to spot collinearity is to put each predictor as a dependent variable, and other predictors as independent variables, determine R2, and if it's larger than .9 (or .95), we can consider predictor redundant. This is one "method"... what about other approaches? Some of them are time consuming, like excluding predictors from model and watching for b-coefficient changes - they should be noticeably different. Of course, we must always bare in mind specific context/goal of analysis... Sometimes, only remedy is to repeat a research, but right now, I'm interested in various ways of screening redundant predictors when (multi)collinearity occurs in a regression model.

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  • Doesn't JavaScript support closures with local variables?

    - by qollin
    I am very puzzled about this code: var closures = []; function create() { for (var i = 0; i < 5; i++) { closures[i] = function() { alert("i = " + i); }; } } function run() { for (var i = 0; i < 5; i++) { closures[i](); } } create(); run(); From my understanding it should print 0,1,2,3,4 (isn't this the concept of closures?). Instead it prints 5,5,5,5,5. I tried Rhino and Firefox. Could someone explain this behavior to me? Thx in advance.

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  • How to render consistence and smooth moving animation on iphone / ipod / iphone simulator.

    - by shakthi
    I am trying render a simple animation(object movement animations) on iphone. I used opengl for object rendering. Movements appears to be smooth on the simulator. But if I used same code in the ipod, object movement is slower. In the iphone it is still slower. I googled a bit and found 'frame rate independent rendering method', which taught me the concept of 'time interval' and object movement based on it. However result is very unpleasant. There is a lot of jerk in the animation even when fps remains above 20. Following code fragment is used for calculation of time interval between successive frames and I am using that to move my animation. NSTimeInterval GetTimeIntervals(NSTimeInterval * inLastElapsedTime ) { NSTimeInterval intervalTime = 0; NSTimeInterval currentTime = [NSDate timeIntervalSinceReferenceDate]; if(*inLastElapsedTime != 0 ) { intervalTime = currentTime - *inLastElapsedTime; } *inLastElapsedTime = currentTime; return intervalTime; }

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  • Connecting Ingres from C

    - by avesus
    I need to connect to an Ingres supplied demodb through OpenAPI, both Ingres and C application running on windows. What i have done: Created a "node" in the Ingres Network Utility named "usernode". created user accounts in the Ingres installation (named "user" password "user") and in the Windows user management (the same creds.) Granted necessary privileges to the user in the database. In C code i have called IIapi_connect() function with an IIAPI_CONNPARM structure. Used members: co_target = "usernode::demodb", co_username = "user", co_password = "user" But IIapi_connect() call returns an error: "User provided a vnode as part of the database name (vnode::dbname), but connection information for that vnode is missing. Enter connection information for the vnode using NETUTIL." Anybody knows something that is a weird concept "node"? What are the minimum steps (in the database administration and the function parameters passing) necessary for the successful connect?

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  • Maximum Possible File Name Length in Windows Kernel

    - by Lambert
    I was wondering, what is the longest possible name length allowed by the Windows kernel? E.g.: I know the kernel uses UNICODE_STRING structures to hold all object paths, and since the byte length of a wide-character string is stored inside a USHORT, that allows for a maximum path length of 2^15 - 1 characters. Is there a similar, hard restriction on a file name (rather than path)? (I don't care if NTFS or FAT32 imposes a particular restriction; I'm looking for the longest possible theoretically allowed name in the kernel, assuming no additional file system or shell restrictions.) (Edit: For those wondering why this even matters, consider that normally, traversing a directory is achieved by FindFirstFile/FindNextFile calls, one call per file. Given the function named NtQueryDirectoryFile, which is the underlying system call and which returns multiple file names per call, it's actually possible to take advantage of this maximum-length restriction on the path to make an extremely-fast directory traverser that uses solely the stack as a buffer. Now I'm trying to extend that concept, and I need to know the maximum size of a file name.)

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  • iOS: is it allowed to paint outside the bounds

    - by Tbee
    If clipToBounds = YES then you can draw all you want, but you only can paint inside the bounds. If it is set to NO then painting outside the bounds is possible, but is it allowed? The reason that I'm asking is because iOS uses the concept where the environment takes care of making sure the correct parts of the screen are (re)painted (e.g. setNeedsDisplay). If I draw outside my bounds, will it goof up? I have tried it, and it seems to work, but?

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  • Images or files in GNU Smalltalk?

    - by Marc
    Hi, I'm new to Smalltalk. I think I understand the basics of the language and now want to start with GNU Smalltalk (as it's free and has bindings for GTK). As I'm coming from the PHP and Java-Corner, I'm not familiar with the concept of the Smalltalk images. And I even read now, that you don't need to use images in GNU Smalltalk. Now I'm confused ;-) So is it possible to work with files and to include the classes I need with the PackageLoader class? I would be happy when I could use my favourite texteditor (vim) for coding instead of an IDE, too ;-) Please enlight me :-)

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  • What is the "task" in twitter Storm parallelism

    - by John Wang
    I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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  • How to extend a website?

    - by eltados
    This is quite a concept idea. I would like to create a website that can be extend by different programmer a bit "a la facebook" Let's me explain i want to develop a very simple core application that for example would store images and i want to develop or allow external developer to develop web app that would be able to act on the image i can take this example of an OS that would store files and you can "install" different program for example to view the files or edit. How can i reproduce the model in the Web / cloud plateform using API ? I hope this question make sense to any body. Thank you by advance

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  • Android Database

    - by Max
    I'm trying to build a simple app to get to grips with android as I'm new. I have programmed for years in PHP and MySQL so it's not completely unfamiliar to me, but one concept is at the moment confusing to me. If I wanted to create this app with 100's of questions how would I create the database like this. What I mean is at the moment my app runs and creates the database. Would I need to do this everytime the app runs as i'm guessing if it was a lot bigger it would mean a slow load evert time. Or is there a way to create the database once and then when the app runs there is no need to populate it. Max

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  • Convert object to DateRange

    - by user655832
    I'm querying an underlying PostgreSQL database using Pandas 0.8. Pandas is returning the DataFrame properly but the underlying timestamp column in my database is being returned as a generic "object" type in Pandas. As I would eventually like to seasonal normalization of my data I am curious as to how to convert this generic "object" column to something that is appropriate for analysis. Here is my current code to retrieve the data: # get records from db example import pandas.io.sql as psql import psycopg2 # define query to get all subs created this year QRY = """ select i i, i * random() f, case when random() > 0.5 then true else false end t, (current_date - (i*random())::int)::timestamp with time zone tsz from generate_series(1,1000) as s(i) order by 4 ; """ CONN_STRING = "host='localhost' port=5432 dbname='postgres' user='postgres'" # connect to db conn = psycopg2.connect(CONN_STRING) # get some data set index on relid column df = psql.frame_query(QRY, con=conn) print "Row count retrieved: %i" % (len(df),) Thanks for any help you can render. M

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  • Using Property Builtin with GAE Datastore's Model

    - by ejel
    I want to make attributes of GAE Model properties. The reason is for cases like to turn the value into uppercase before storing it. For a plain Python class, I would do something like: Foo(db.Model): def get_attr(self): return self.something def set_attr(self, value): self.something = value.upper() if value != None else None attr = property(get_attr, set_attr) However, GAE Datastore have their own concept of Property class, I looked into the documentation and it seems that I could override get_value_for_datastore(model_instance) to achieve my goal. Nevertheless, I don't know what model_instance is and how to extract the corresponding field from it. Is overriding GAE Property classes the right way to provides getter/setter-like functionality? If so, how to do it? Added: One potential issue of overriding get_value_for_datastore that I think of is it might not get called before the object was put into datastore. Hence getting the attribute before storing the object would yield an incorrect value.

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  • Java resource management: please help to understand Findbugs results.

    - by java.is.for.desktop
    Hello, everyone! Findbugs bugs me about a method which opens two Closeable instances, but I can't understand why. Source public static void sourceXmlToBeautifiedXml(File input, File output) throws TransformerException, IOException, JAXBException { FileReader fileReader = new FileReader(input); FileWriter fileWriter = new FileWriter(output); try { // may throw something sourceXmlToBeautifiedXml(fileReader, fileWriter); } finally { try { fileReader.close(); } finally { fileWriter.close(); } } } Findbugs analysis Findbugs tells me Method [...] may fail to clean up java.io.Reader [...] and points to the line with FileReader fileReader = ... Question Who is wrong: me or Findbugs?

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  • Creating an Excel Template for different data size

    - by dassouki
    I created an excel template for a file i've done for a routine work calculation. The file takes data from the data logger and does some analysis on it and outputs one number regardless of the input size. The problem I'm having is i have to modify the sheet to suit the number of rows, as everyday the data logger outputs a different number of rows. there are about 15 sheets in the workbook and it's annoying to have to change everyone of them everyday. What i'd like to do input the data logger csv, and boom the result gets outputted. Is there a way through vba or not to ahieve

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  • Why to store username and password in Keychain in iPhone app

    - by Suriya
    I have worked with NSUserDefault but this keychain concept is totally new for me. I have tried looking for similar Questions but couldn't find the exact reason to do so. What I have done: I already know how to store data in NSUserDefault. and also the reason why do we need to store it. Regarding Keychain I just know that storing in keychain stores the data with some extra security by encoding the original text while NSUserDefault stores the data as plain text. Is this the only reason for storing the data in keychain?

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  • Leak caused by fread

    - by Jack
    I'm profiling code of a game I wrote and I'm wondering how it is possible that the following snippet causes an heap increase of 4kb (I'm profiling with Heapshot Analysis of Xcode) every time it is executed: u8 WorldManager::versionOfMap(FILE *file) { char magic[4]; u8 version; fread(magic, 4, 1, file); <-- this is the line fread(&version,1,1,file); fseek(file, 0, SEEK_SET); return version; } According to the profiler the highlighted line allocates 4.00Kb of memory with a malloc every time the function is called, memory which is never released. This thing seems to happen with other calls to fread around the code, but this was the most eclatant one. Is there anything trivial I'm missing? Is it something internal I shouldn't care about? Just as a note: I'm profiling it on an iPhone and it's compiled as release (-O2).

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  • Better Java method Syntax? Return early or late? [closed]

    - by Gandalf
    Duplicate: Should a function have only one return statement? and Single return or multiple return statements? Often times you might have a method that checks numerous conditions and returns a status (lets say boolean for now). Is it better to define a flag, set it during the method, and return it at the end : boolean validate(DomainObject o) { boolean valid = false; if (o.property == x) { valid = true; } else if (o.property2 == y) { valid = true; } ... return valid; } or is it better/more correct to simply return once you know the method's outcome? boolean validate(DomainObject o) { if (o.property == x) { return true; } else if (o.property2 == y) { return true; } ... return false; } Now obviously there could be try/catch blocks and all other kinds of conditions, but I think the concept is clear. Opinions?

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  • how to solve nested list programs [closed]

    - by riya
    write a function to get most popular car that accepts a car detail as input and returns the most popular car name along with its average rating .Each element of car details list is a sublist that provides the below information about a car (a)name of a car(b)car price (c) list of ratings obtained by car from various agencies.Incase two cars have the same average rating then the car with the lesser price qualifies as most popular car? here's my solution-: (define-struct cardetails ("name" price list of '(ratings)) (define car1 (make-cardetails "toyota" 123 '( 1 2 3))) (define car2 (make-cardetails "santro" 321 '( 2 2 3))) (define car3 (make-cardetails "toyota" 100 '( 1 2 3))) (define cardetailslist(list(car1) (car2)(car 3))) (let loop ((count 0)) (let (len (length cardetailslist)) (if(< count len) (string-ref (string-ref n)0) now please tell me how to find maximum average and display car name.it's not a homework question tomorrow is my test and we have not been taught this concept in class although it is very important from test point of view

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  • R: including model specifications in xtable(anova(...))

    - by HamiltonUlmer
    Hello R comrades: I have a bunch of loglinear models, which, for our purposes will just be glm() objects called mx, my, mz. I want to get a nicely-formatted xtable of the analysis of deviance, so naturally I would want to perform xtable(anova(mx, my, mz, test = "Chisq")). The vanilla output of xtable, however, doesn't include the model specifications. I'd like to include those for all the ANOVA tests I'm running, so if there is not a param I'm missing that does this I'll probably just have to hack up my own solution. But looking over the help page, there doesn't seem to be an easy way to include the model specifications. Any thoughts? Alternatives? If it helps this was done in 2.9.1 with xtable 1.5-5.

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  • Processing an n-ary ANTLR AST one child at a time

    - by Chris Lieb
    I currently have a compiler that uses an AST where all children of a code block are on the same level (ie, block.children == {stm1, stm2, stm3, etc...}). I am trying to do liveness analysis on this tree, which means that I need to take the value returned from the processing of stm1 and then pass it to stm2, then take the value returned by stm2 and pass it to stm3, and so on. I do not see a way of executing the child rules in this fashion when the AST is structured this way. Is there a way to allow me to chain the execution of the child grammar items with my given AST, or am I going to have to go through the painful process of refactoring the parser to generate a nested structure and updating the rest of the compiler to work with the new AST? Example ANTLR grammar fragment: block : ^(BLOCK statement*) ; statement : // stuff ; What I hope I don't have to go to: block : ^(BLOCK statementList) ; statementList : ^(StmLst statement statement+) | ^(StmLst statement) ; statement : // stuff ;

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  • Screen capture during testing

    - by Edwward
    This is an application for reviewing performance tests. Simple in concept, tricky to describe. Picture: 1) Recording interactions with a WPF program so the inputs can be played back. 2) Playing the inputs back while doing a continuous screen capture. 3) Capturing wall time as well as continuous CPU percentages during playback. 4) Repeating steps (2) and (3) lots of times. 5) Writing the relevant stuff out to files/db. 6) Reading it and putting it all in a fancy UI for easy review/analysis. The killer for me is (2). I could use some guidance on a good, possibly commercial, screen capture SDK. I would also welcome the news that my whole problem already has a solution. And of course any thoughts on the overall idea would also be great. Thanks. Ed

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