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• Explanation needed for sum of prime below n numbers

  - by Bala Krishnan

  Today I solved a problem given in Project Euler its problem no 10 and it took 7 hrs for my python program to show the result. But in that forum itself a person named lassevk posted solution for this and it took only 4 sec. And its not possible for me to post this question in that forum because its not discussion forum. So, think about this if you want to mark this question as non-constructive. marked = [0] * 2000000 value = 3 s = 2 while value < 2000000: if marked[value] == 0: s += value i = value while i < 2000000: marked[i] = 1 i += value value += 2 print s If any one understand this code please explain it simple as possible. Link to the Problem 10 question.

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• Should I make sure arguments aren't null before using them in a function.

  - by Nathan W

  The title may not really explain what I'm really trying to get at, couldn't really think of a way to describe what I mean. I was wondering if it is good practice to check the arguments that a function accepts for nulls or empty before using them. I have this function which just wraps some hash creation like so. Public Shared Function GenerateHash(ByVal FilePath As IO.FileInfo) As String If (FilePath Is Nothing) Then Throw New ArgumentNullException("FilePath") End If Dim _sha As New Security.Cryptography.MD5CryptoServiceProvider Dim _Hash = Convert.ToBase64String(_sha.ComputeHash(New IO.FileStream(FilePath.FullName, IO.FileMode.Open, IO.FileAccess.Read))) Return _Hash End Function As you can see I just takes a IO.Fileinfo as an argument, at the start of the function I am checking to make sure that it is not nothing. I'm wondering is this good practice or should I just let it get to the actual hasher and then throw the exception because it is null.? Thanks.

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• does adding static library need xcode project of static library for linking?

  - by mirdad

  I have seen some static library projects in iOS.I see two different types of linking static library. 1)adding .a static library to new xcode project and its header files only. 2)adding .a static library to new xcode project and adding the xcode project through which static library has created. when I remove the the xcode project through which static library has created from the 2nd project, it gives error.I tried first approach for 2nd one.But it is not working. Can you please explain why it is differed? Will it be differed by the xcode versions we use? is The second approach for old xcode versions?

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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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• SQL statement HAVING MAX(some+thing)=some+thing

  - by Andreas

  I'm having trouble with Microsoft Access 2003, it's complaining about this statement: select cardnr from change where year(date)<2009 group by cardnr having max(time+date) = (time+date) and cardto='VIP' What I want to do is, for every distinct cardnr in the table change, to find the row with the latest (time+date) that is before year 2009, and then just select the rows with cardto='VIP'. This validator says it's OK, Access says it's not OK. This is the message I get: "you tried to execute a query that does not include the specified expression 'max(time+date)=time+date and cardto='VIP' and cardnr=' as part of an aggregate function." Could someone please explain what I'm doing wrong and the right way to do it? Thanks

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• Lucene .NET IndexWriter lock

  - by Pini Salim

  My question related to the next code snippet: static void Main(string[] args) { Lucene.Net.Store.Directory d = FSDirectory.Open(new DirectoryInfo(/*my index path*/)); IndexWriter writer = new IndexWriter(d, new WhitespaceAnalyzer()); //Exiting without closing the indexd writer... } In this test, I opened an IndexWriter without closing it - so even after the test exits, the write.lock file still exists in the index directory, so I expected that the next time I open an instance of IndexWriter to that index, a LockObatinFailedException will be thrown. Can someone please explain to me why am I wrong? I mean, does the meaning of the write.lock file is to protect creation of two IndexWriters in the same process only? that doesnt seems the right answer to me...

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• Purpose of Instance Methods vs. Class Methods in Objective-C

  - by qegal

  I have checked out all these questions... Difference Class and Instance Methods Difference between class methods and instance methods? Objective-C: Class vs Instance Methods? ...and all they explain is how instance methods are used on instances of a class and class methods are used with the class name, when a message is sent to a class object. This is helpful, but I'm curious to know why one would use a class method vs. an instance method. I'm fairly new to iOS application development, and usually use class methods, and I feel like I'm doing something wrong. Thanks in advanced!

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• Analyzing Python Code: Modulus Operator

  - by Bhubhu Hbuhdbus

  I was looking at some code in Python (I know nothing about Python) and I came across this portion: def do_req(body): global host, req data = "" s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, 80)) s.sendall(req % (len(body), body)) tmpdata = s.recv(8192) while len(tmpdata) > 0: data += tmpdata tmpdata = s.recv(8192) s.close() return data This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes. My question is what is happening at the "s.sendall()" part? Obviously the entire body cannot be sent at once and I'm guessing it is reduced by way of the modulus operator. I don't know how it works in Python, though. Can anyone explain? Thanks.

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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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• 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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• 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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• The pros and cons of use JSON for WCF service

  - by brz dot net

  What are the pros and cons of the following 2 cases: Case I: Traditional way: Add service reference in project. Create object and Get data from service on server side and bind to asp.net grid. Case II: Update Service for JSON behavior. Add service reference in project. Call service from javascript to get data. Bind data to jquery grid. Which one is the best approach and why?(Not developer point of view) If there is another approach which is more optimized, please explain it.

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• What do you do when you feel you need a variadic list comprehension?

  - by cspyr0

  I would like to make a method where I could give it a list of lengths and it would return all combinations of cartesian coordinates up to those lengths. Easier to explain with an example: cart [2,5] Prelude> [ [0,0],[0,1],[0,2],[0,3],[0,4],[1,0],[1,1],[1,2],[1,3],[1,4] ] cart [2,2,2] Prelude> [ [0,0,0],[0,0,1],[0,1,0],[0,1,1],[1,0,0],[1,0,1],[1,1,0],[1,1,1] ] A simple list comprehension won't work because I don't know how long the lists are going to be. While I love Haskell's simplicity for many problems, this is one that I could write procedurally (in C or something) in 5 minutes whereas Haskell gives me an aneurysm! A solution to this specific problem would help me out a lot; I'd also love to hear about your thought processes when tackling stuff like this.

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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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• 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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• A simple group-by (no count) in Django

  - by Daniel Quinn

  If this were raw-SQL, it'd be a no-brainer, but in Django, this is proving to be quite difficult to find. What I want is this really: SELECT user_id FROM django_comments WHERE content_type_id = ? AND object_pk = ? GROUP BY user_id It's those last two lines that're the problem. I'd like to do this the "Django-way" but the only thing I've found is mention of aggregates and annotations, which I don't think solve this issue... do they? If someone could explain this to me, I'd really appreciate it.

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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 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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• 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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• PropelBundle database:create for postgres

  - by Karol85

  I've installed propel bundle for symfony2. my database configuration is: propel: dbal: driver: pgsql user: postgres password: postgres dsn: pgsql:host=localhost;port=5432;dbname=test_database options: {} attributes: {} When i wan to create this database from console (console propel: database:create) i have got strange error : Unable to open PDO connection [wrapped: SQLSTATE[08006] [7] FATAL: database "pgsql" does not exist. i created pgsql database on my localhost and everything was good. Database "test_database" was succesfull created. Can somebody explain me why i got this previous error? On mysql i've created database without any problems.

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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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• 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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• 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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• 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 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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