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  • Why does concatenating a boolean value return an integer?

    - by joshhunt
    In python, you can concatenate boolean values, and it would return an integer. Example: >>> True True >>> True + True 2 >>> True + False 1 >>> True + True + True 3 >>> True + True + False 2 >>> False + False 0 Why? Why does this make sense? I understand that True is often represented as 1, whereas False is represented as 0, but that still does not explain how adding two values together of the same type returns a completely different type.

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  • Do you have to create a View Controller to move between views?

    - by Frames84
    I want a single startup view with a button and a welcome screen. When the button is pressed I then want to navigate to a second view which contains a table view and toolbar. I've tried creating a ViewController but my button is shown on all views. I just want a single view, then when it's pressed i go to the next view and the 'real' app starts. Can someone please try and explain the best architecture to do this? (like in chapter 6 of beginning iPhone 3 Development by Dave Mark and Jeff LaMarche ) Thanks

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  • typedef declaration syntax

    - by mt_serg
    Some days ago I looked at boost sources and found interesting typedef. There is a code from "boost\detail\none_t.hpp": namespace boost { namespace detail { struct none_helper{}; typedef int none_helper::*none_t ; } // namespace detail } // namespace boost I didn't see syntax like that earlier and can't explain the sense of that. This typedef introduces name "none_t" as pointer to int in boost::detail namespace. What the syntax is? And what difference between "typedef int none_helper::*none_t" and for example "typedef int *none_t" ?

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  • Objective C for Windows

    - by Luther Baker
    What would be the best way to write Objective-C on the Windows platform? Cygwin and gcc? Is there a way I can somehow integrate this into Visual Studio? Along those lines - are there any suggestions as to how to link in and use the Windows SDK for something like this. Its a different beast but I know I can write assembly and link in the Windows DLLs giving me accessibility to those calls but I don't know how to do this without googling and getting piecemeal directions. Is anyone aware of a good online or book resource to do or explain these kinds of things?

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  • Custom components vs default components in GUI Design. Which is more practical? (.NET)

    - by AlexRednic
    Ok, so is it better to create my own components (Either inherit them from existing ones or creating them from scratch) or to use the ones that come by default? I'm asking this under the umbrella of scalability, overhead and other factors that my contribute on each of the choices. UPDATE: Sorry if I'm to vague. I don't really know how to explain myself better. Isn't it a good idea to inherit each default component? For example what if I'm to design a rather large application and for example i need to change the display format on a DateTimePicker. Wouldn't it better to think ahead and inherit it and use the inherited component instead of the defaults? But, wouldn't it add a lot of overhead in small applications?

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  • Different behaviour of browsers while caching the same file.

    - by Amrita
    I am trying to implement mod_disk_caching. i wrote a php code as shown in the example of the tutorial i was following. i fired the following in the terminal a2enmod cache a2enmod disk_cache /etc/init.d/apache2 force-reload then in the php code "; ? now i tried running it using firefox. In the first execution i got the following timestamp. 1308643975 here, when i press refresh, the timestamp changes (as the file is reloaded from the server) and remains the same when i click the link again (as the file is retrieved from the cache). Now i am trying the same with IExplorer. As per my understanding, the timestamp should be the same as the subsequent request for the file will be retrieved only from the cache. But i got a different timestamp. Can anyone explain me the reason for this? Why is it giving separate timestamps when the browsers are different? Thanks and Regards, AMJ

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  • Result of Long Positive Integers & Search and element in array..

    - by AGeek
    Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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  • Deriving PathInfo class in web routes?

    - by drozzy
    I am reading the web-routes tutorial in Happstack, and I have no idea what this is doing: $(derivePathInfo ''Sitemap) class PathInfo a where toPathSegments :: a -> [String] fromPathSegments :: URLParser a The doc simply says: we use template-haskell to derive an instance of PathInfo for the Sitemap type. but where does it "store" it? I thought haskell had no state, and is PathInfo our own thing, or is it part of happstack? If someone could explain this, for dummies? Thanks.

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  • How do I use a UIView subclass as a container?

    - by dxq
    I'm trying to subclass UIView to create a custom view that is essentially a container. The subclass contains a UILabel and a UIImageView- I can't make either of them show up. Here's an example of what I've been trying: In my main view controller: - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) { ViewClass *myView = [[ViewClass alloc] initWithFrame:CGRectMake(100, 100, 150, 150)]; [view addSubview:myView]; } return self; } In my UIView subclass: - (id)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { UILabel *word = [[[UILabel alloc] initWithFrame:[self bounds]] autorelease]; word.text = @"WHY ISN'T THIS SHOWING UP!?"; [self addSubview:word]; } return self; } Can anyone explain what I'm doing wrong? I'm way out of practice with UIKit and Obj-C, and I figure I'm probably missing something obvious.

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  • segmentation fault

    - by gcc
    int num_arrays; char *p[20]; char tempc; int i=0; do { p[i]=malloc(sizeof(int)); scanf("%s",p[i]); tempc=p[i]; ++i; }while(tempc=='x'); num_arrays=atoi(p[0]); When i write num_arrays=atoi(..),gcc give me segmentation fault or memory stack is exceeded, I don't understand why it behaves like that can anyone explain, why?

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  • How to execute a large PHP Script ?

    - by atif089
    Well basically I may want to execute a script that may take as much as 1 hours as well. What I really want to do is Send SMS to my users using a third party API. So its basically like I supply my script with an array of phone numbers and fire the method to send SMS. However assuming it take 5 seconds to send 1 SMS and I want to send 1000 SMS which is roughly 1 - 2 hours. I can use set_time_limit() because I am on shared host. One way to do this is store numbers in a session and execute each SMS and use javascript to refresh that page until end. This way I need to keep my browser open and the execution will stop if my Internet Connection is disconnected. So, Is there any better way to do this ? Hope I am clear enough to explain what I want? I want to execute a large script that may take hours to execute without getting timeout.

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  • How to find scrollable elements in DOM using XPath?

    - by ak.
    Basically I need to find all elements on the page that have a scrollbar (vertical or horizontal) How to tell if an element has a scrollbar and can actually be scrolled? I found this code snippet on jsperf. Is it possible to capture the logic behind the code into and XPath expression? Or are there any other ways to check for scrollbars? Added: Just to explain what I'm trying to do: I'm developing extension for Firefox. Basically it introduces Vim-style mouseless shortcuts (I know there is Vimperator and Pentadactyl...). One of the features I'd like to implement is to allow the use to select the container that's scrolled with j/k keys. That's why I need to discover all scrollable elements on any given random page.

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  • Choosing the right and learning assembler for compiler-writing

    - by X A
    I'm writing a compiler and I have gone through all the steps (tokenizing, parsing, syntax tree structures, etc.) that they show you in all the compiler books. (Please don't comment with the link to the "Resources for writing a compiler" question!). I have chosen to use NASM together with alink as my backend. Now my problem is: I just can't find any good resources for learning NASM and assembly in general. The wikibook (german) on x86 assembly is horrible. They don't even explain the code they write there, I currently can't even get simple things like adding 1 to 2 and outputting the result working. Where can I learn NASM x86 assembly?

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  • Replacing TCP/IP pipe with WCF

    - by msarchet
    So currently my company is using a TCP/IP connection to talk between server and client programs, right now we are building this connection using System.RunTime.Remoting, which is clunky and not that reliable. It was built about 5 years ago and the model keeps getting reused and it's starting to propagate some issues, ports used, refused connections, etc. I'm trying to find some resources on how to change this over to WCF but I'm not really sure what I am looking for or what I should be searching. If you want some more information on what were actually doing with it I can go into some detail, but I'll need to pull up the code and make sure I explain it completely. thanks!

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  • NetNamedPipe: varying response time when communication is idling

    - by Sven Künzler
    I have two WCF apps communicating one-way over named pipes. All is nice, except for one thing: Normally, the request/response cycle takes zero (marginal) time. However, if there was a time span of, say, half a minute without any communication, the request/response increases up to ~300-500ms. I looked around the net and I got the idea of using a heart beat/ping mechanism to keep the communication channel busy. Using trial and error I found that when doing a request each 10 seconds, the response times stay low. Starting at around 15s intervals, the "hiccup" response times begin to appear. Now I'm wondering where this phenomenon is originating from. I tried setting alle conceivable timeouts on both sides to 1 minute, but that did not help. Can anybody explain what's going on there?

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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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  • C++ - Resources in static library question

    - by HardCoder1986
    Hello! This isn't a duplicate of http://stackoverflow.com/questions/531502/vc-resources-in-a-static-library because it didn't help :) I have a static library with TWO .rc files in it's project. When I build my project using the Debug configuration, I retrieve the following error (MSVS2008): fatal error LNK1241: resource file res_yyy.res already specified Note, that this happens only in Debug and Release library builds without any troubles. The command line for Resources page in project configuration looks the same for every build: /fo"...(Path here)/Debug/project_name.res" /fo"...(Path here)/Release/project_name.res" and I can't understand what's the trouble. Any ideas? UPDATE I don't know why this happens, but when I turn "Use Link-Time Code Generation" option on the problem goes away. Could somebody explain why does this happen? I feel like MS-compiler is doing something really strange here. Thanks.

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  • How to increase query speed without using full-text search?

    - by andre matos
    This is my simple query; By searching selectnothing I'm sure I'll have no hits. SELECT nome_t FROM myTable WHERE nome_t ILIKE '%selectnothing%'; This is the EXPLAIN ANALYZE VERBOSE Seq Scan on myTable (cost=0.00..15259.04 rows=37 width=29) (actual time=2153.061..2153.061 rows=0 loops=1) Output: nome_t Filter: (nome_t ~~* '%selectnothing%'::text) Total runtime: 2153.116 ms myTable has around 350k rows and the table definition is something like: CREATE TABLE myTable ( nome_t text NOT NULL, ) I have an index on nome_t as stated below: CREATE INDEX idx_m_nome_t ON myTable USING btree (nome_t); Although this is clearly a good candidate for Fulltext search I would like to rule that option out for now. This query is meant to be run from a web application and currently it's taking around 2 seconds which is obviously too much; Is there anything I can do, like using other index methods, to improve the speed of this query?

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  • functions in F# .. why is it not compiling

    - by Tanmoy
    Hi, I have written two versions of code. The first one works as expected and print "Hi". the second one gives me error that "block following this let is unfinished" 1st version #light let samplefn() = let z = 2 let z = z * 2 printfn "hi" samplefn() 2nd version #light let samplefn() = let z = 2 let z = z * 2 samplefn() Only difference is the printfn is absent in the second version. I am using Visual Studio 2010 as my IDE. I am very new to F# but this error seems very strange to me. I guess I am missing some very important concept. Please explain. Edit: Also if I do it outside the function I get error even with the first version of code. #light let z = 2 let z = z * 2 printfn "Error: Duplicate definition of value z"

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  • How to implement "drag n drop" user interface on website?

    - by Nikkeloodeni
    Hello, I was wondering what would be the best way to implement some kind of "drag n drop" user interface? What i mean is that there would be one main page and every link click (eg. other sections like about, gallery, contact form) would open a new drag n drop element on top of that main page. Something like windows desktop where you can move your application windows around the screen. Would it be best to call different functions with AJAX when a link is clicked? Like "gallery" link would call gallery-function and retrieve dynamically generated contents of that "window" with AJAX call and then just load that stuff on some div? Or would some other type of approach suit better for this? I hope I was able to explain this clearly enough. I'm looking for a proper "design pattern" to implement this. All suggestions are wellcome! :)

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  • Employer wants direct, no-hack, ie6 support for CSS. Should I talk him out of it?

    - by DavidR
    I'm currently employed by a website Designer, he gets the clients and sends me a mockup in a fireworks file, and I send him the html/css/js. The problem is that he wants direct ie6 compatibility for every site I build. That is, no conditional ie6 hack, no separate style sheets. A lot of my html has suffered because of it. I just started writing html with him last summer, he took me in as an intern and taught me everything about it. Since then I built 4 web pages, but I haven't yet made anything I'm really proud of. Should I be trying harder to create stellar code beside my limitations or should I set him down and explain that his demands are killing the code for modern browsers?

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  • Space requirements of a merge-sort

    - by Arkaitz Jimenez
    I'm trying to understand the space requirements for a Mergesort, O(n). I see that time requirements are basically, amount of levels(logn) * merge(n) so that makes (n log n). Now, we are still allocating n per level, in 2 different arrays, left and right. I do understand that the key here is that when the recursive functions return the space gets deallocated, but I'm not seeing it too obvious. Besides, all the info I find, just states space required is O(n) but don't explain it. Any hint? function merge_sort(m) if length(m) = 1 return m var list left, right, result var integer middle = length(m) / 2 for each x in m up to middle add x to left for each x in m after middle add x to right left = merge_sort(left) right = merge_sort(right) result = merge(left, right) return result

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  • After a period of time, nslookup still works, but pinging, and an auto-refeshed website, fails.

    - by Mark Hurd
    Contrary to this question this is for a dotted name (gw.localnet.au), and it doesn't happen straight away. Only after some period of time (quite a long time, possibly days). In fact this is for my ADSL router and its internal IP address which I have named within the router itself and in my Windows Server 2003 Domain Controller DNS Service. Specifically, localnet.au is a Active-Directory-backed primary domain. In fact, an ipconfig /flushdns may fix the problem, but only after a while (about the time it took me to type in this question :-) ). That doesn't explain the root cause though...

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  • How does this iterative Tower of Hanoi work? C

    - by Nitesh Panchal
    Hello, while surfing google, i found this interesting solution to Tower Of Hanoi which doesn't even use stack. Can anybody explain me in brief, what is it actually doing? And this solution really acceptable? #include <stdio.h> #include <stdlib.h> int main() { int n, x; printf( "How many disks? " ); scanf( "%d", &n ); printf("\n"); for (x=1; x < (1 << n); x++) printf( "move from tower %i to tower %i.\n", (x&x-1)%3, ((x|x-1)+1)%3 ); return 0; }

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  • Neural Network Basics

    - by Stat Onetwothree
    I'm a computer science student and for this years project, I need to create and apply a Genetic Algorithm to something. I think Neural Networks would be a good thing to apply it to, but I'm having trouble understanding them. I fully understand the concepts but none of the websites out there really explain the following which is blocking my understanding: How the decision is made for how many nodes there are. What the nodes actually represent and do. What part the weights and bias actually play in classification. Could someone please shed some light on this for me? Also, I'd really appreciate it if you have any similar ideas for what I could apply a GA to. Thanks very much! :)

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