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• How do I get an overview and a methodology for programming in Python

  - by Peter Nielsen

  I've started to learn Python and programming from scratch. I have not programmed before so it's a new experience. I do seem to grasp most of the concepts, from variables to definitions and modules. I still need to learn a lot more about what the different libraries and modules do and also I lack knowledge on OOP and classes in Python. I see people who just program in Python like that's all they have ever done and I am still just coming to grips with it. Is there a way, some tools, a logical methodology that would give me an overview or a good hold of how to handle programming problems ? For instance, I'm trying to create a parser which we need at the office . I also need to create a spider that would collect links from various websites. Is there a formidable way of studying the various modules to see what is needed ? Or is it just nose to the grind stone and understand what the documentation says ? Sorry for the lengthy question..

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• cocoa hello world screensaver

  - by RW

  I have been studying NSView and as such I thought I would give a shot at a screen saver. I have been able to display and image in an NSView but I can't seen to modify this example code to display a simple picture in ScreenSaverView. http://www.mactech.com/articles/mactech/Vol.20/20.06/ScreenSaversInCocoa/ BTW great tutorial that works with Snow Leopard. I would think to simply display an image I would need something that looked like this... What am I doing wrong? // // try_screensaverView.m // try screensaver // #import "try_screensaverView.h" @implementation try_screensaverView - (id)initWithFrame:(NSRect)frame isPreview:(BOOL)isPreview { self = [super initWithFrame:frame isPreview:isPreview]; if (self) { [self setAnimationTimeInterval:1]; //refresh once per sec } return self; } - (void)startAnimation { [super startAnimation]; NSString *path = [[NSBundle mainBundle] pathForResource:@"leaf" ofType:@"JPG" inDirectory:@""]; image = [[NSImage alloc] initWithContentsOfFile:path]; } - (void)stopAnimation { [super stopAnimation]; } - (void)drawRect:(NSRect)rect { [super drawRect:rect]; } - (void)animateOneFrame { ////////////////////////////////////////////////////////// //load image and display This does not scale the image NSRect bounds = [self bounds]; NSSize newSize; newSize.width = bounds.size.width; newSize.height = bounds.size.height; [image setSize:newSize]; NSRect imageRect; imageRect.origin = NSZeroPoint; imageRect.size = [image size]; NSRect drawingRect = imageRect; [image drawInRect:drawingRect fromRect:imageRect operation:NSCompositeSourceOver fraction:1]; } - (BOOL)hasConfigureSheet { return NO; } - (NSWindow*)configureSheet { return nil; } @end

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• Time complexity with bit cost

  - by Keyser

  I think I might have completely misunderstood bit cost analysis. I'm trying to wrap my head around the concept of studying an algorithm's time complexity with respect to bit cost (instead of unit cost) and it seems to be impossible to find anything on the subject. Is this considered to be so trivial that no one ever needs to have it explained to them? Well I do. (Also, there doesn't even seem to be anything on wikipedia which is very unusual). Here's what I have so far: The bit cost of multiplication and division of two numbers with n bits is O(n^2) (in general?) So, for example: int number = 2; for(int i = 0; i < n; i++ ){ number = i*i; } has a time complexity with respect to bit cost of O(n^3), because it does n multiplications (right?) But in a regular scenario we want the time complexity with respect to the input. So, how does that scenario work? The number of bits in i could be considered a constant. Which would make the time complexity the same as with unit cost except with a bigger constant (and both would be linear). Also, I'm guessing addition and subtraction can be done in constant time, O(1). Couldn't find any info on it but it seems reasonable since it's one assembler operation.

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• Creating spotlight in OpenGL scene

  - by Victor Oliveira

  Im studying OpenGL and trying to create a spot light at my application. The code that Im using for my #vertex-shader is below: #:vertex-shader #{ #version 150 core in vec3 in_pos; in vec2 in_tc; out vec2 tc; glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 20.0f); GLfloat spot_direction[] = { -1.0, -1.0, 0.0 }; glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spot_direction); glEnable(GL_LIGHT0); void main() { vec4 pos= vec4(vec3(1.0)*in_pos - vec3(1.0), 1.0); pos.z=0.0; gl_Position = pos; tc = in_tc; } } The thing is, everytime Im trying to run the code an Error that says: Type: other, Source: api, ID: 131169, Severity: low Message: Framebuffer detailed info: The driver allocated storage for renderbuffer 1. len = 157, written = 0 failed to compile vertex shader of deferred: directional info log for shader deferred: directional vertex info log for shader deferred: directional: ERROR: Unbound variable: when Specifications: Renderer: GeForce GTX 580/PCIe/SSE2 Version: 3.3.0 NVIDIA 319.17 GLSL: 3.30 NVIDIA via Cg compiler Status: Using GLEW 1.9.0 1024 x 768 OS: Linux debian I guess to create this spotlight is pretty much simple, but since Im really new to OpenGL I dont have a clue how to do it until now, even reading sources like: http://www.glprogramming.com/red/chapter05.html#name3 Read also in some place that light spots can get really hard to understand, but I cant avoid this step right now since Im following my lecture schedule. Could anybody help me?

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• How can we change views in a UISplitViewController other than using the popover and selecting?

  - by wolverine

  I have done a sample app with UISplitViewController studying the example they have provided. I have created three detailviews and have configured them to change by the default means. Either using the left/master view in landscape AND using the popover in the portrait orientation. Now I am trying to move to another view(previous/next) from the currentView by using left/right swipe in each view. For that, what I did was just created a function in the RootViewController. I copy-pasted the same code as that of the tablerow selection used by the popover from the RootViewController. I am calling this function from my current view's controller and is passing the respective index of the view(to be displayed next) from the current view. Function is being called but nothing is happening. Plz help me OR is anyother way to do it other than this complex step? I am giving the function that I used to change the view. - (void) rearrangeViews:(int)viewRow { UIViewController <SubstitutableDetailViewController> *detailViewController = nil; if (viewRow == 0) { DetailViewController *newDetailViewController = [[DetailViewController alloc] initWithNibName:@"DetailView" bundle:nil]; detailViewController = newDetailViewController; } if (viewRow == 1) { SecondDetailViewController *newDetailViewController = [[SecondDetailViewController alloc] initWithNibName:@"SecondDetailView" bundle:nil]; detailViewController = newDetailViewController; } if (viewRow == 2) { ThirdDetailViewController *newDetailViewController = [[ThirdDetailViewController alloc] initWithNibName:@"ThirdDetailView" bundle:nil]; detailViewController = newDetailViewController; } // Update the split view controller's view controllers array. NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController, detailViewController, nil]; splitViewController.viewControllers = viewControllers; [viewControllers release]; if (rootPopoverButtonItem != nil) { [detailViewController showRootPopoverButtonItem:self.rootPopoverButtonItem]; } [detailViewController release]; }

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• Using game of life or other virtual environment for artificial (intelligence) life simulation? [clos

  - by Berlin Brown

  One of my interests in AI focuses not so much on data but more on biologic computing. This includes neural networks, mapping the brain, cellular-automata, virtual life and environments. Described below is an exciting project that includes develop a virtual environment for bots to evolve in. "Polyworld is a cross-platform (Linux, Mac OS X) program written by Larry Yaeger to evolve Artificial Intelligence through natural selection and evolutionary algorithms." http://en.wikipedia.org/wiki/Polyworld " Polyworld is a promising project for studying virtual life but it still is far from creating an "intelligent autonomous" agent. Here is my question, in theory, what parameters would you use create an AI environment? Possibly a brain environment? Possibly multiple self contained life organisms that have their own "brain" or life structures. I would like a create a spin on the game of life simulation. What if you have a 64x64 game of life grid. But instead of one grid, you might have N number of grids. The N number of grids are your "life force" If all of the game of life entities die in a particular grid then that entire grid dies. A group of "grids" makes up a life form. I don't have an immediate goal. First, I want to simulate an environment and visualize what is going on in the environment with OpenGL and see if there are any interesting properties to the environment. I then want to add "scarce resources" and see if the AI environment can manage resources adequately.

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• How can I create a new Person object correctly in Javascript?

  - by TimDog

  I'm still struggling with this concept. I have two different Person objects, very simply: ;Person1 = (function() { function P (fname, lname) { P.FirstName = fname; P.LastName = lname; return P; } P.FirstName = ''; P.LastName = ''; var prName = 'private'; P.showPrivate = function() { alert(prName); }; return P; })(); ;Person2 = (function() { var prName = 'private'; this.FirstName = ''; this.LastName = ''; this.showPrivate = function() { alert(prName); }; return function(fname, lname) { this.FirstName = fname; this.LastName = lname; } })(); And let's say I invoke them like this: var s = new Array(); //Person1 s.push(new Person1("sal", "smith")); s.push(new Person1("bill", "wonk")); alert(s[0].FirstName); alert(s[1].FirstName); s[1].showPrivate(); //Person2 s.push(new Person2("sal", "smith")); s.push(new Person2("bill", "wonk")); alert(s[2].FirstName); alert(s[3].FirstName); s[3].showPrivate(); The Person1 set alerts "bill" twice, then alerts "private" once -- so it recognizes the showPrivate function, but the local FirstName variable gets overwritten. The second Person2 set alerts "sal", then "bill", but it fails when the showPrivate function is called. The new keyword here works as I'd expect, but showPrivate (which I thought was a publicly exposed function within the closure) is apparently not public. I want to get my object to have distinct copies of all local variables and also expose public methods -- I've been studying closures quite a bit, but I'm still confused on this one. Thanks for your help.

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• Automated testing for Facebook SDK wrapper

  - by Andree

  Hi there! In my Facebook application, I have one Facebook wrapper class to encapsulates some call to Facebook API. I want to to write a unit test for this wrapper class, but since it depends on a so called "access token", which we should get from Facebook dynamically, I'm not sure if it's possible to write one. But apparently the Facebook SDK itself has a PHPUnit test class. After studying the test code for a while, I know that involves a creation of dummy cookie-based session key. private static $VALID_EXPIRED_SESSION = array( 'access_token' => '254752073152|2.I_eTFkcTKSzX5no3jI4r1Q__.3600.1273359600-1677846385|uI7GwrmBUed8seZZ05JbdzGFUpk.', 'expires' => '1273359600', 'secret' => '0d9F7pxWjM_QakY_51VZqw__', 'session_key' => '2.I_eTFkcTKSzX5no3jI4r1Q__.3600.1273359600-1677846385', 'sig' => '9f6ae89510b30dddb3f864f3caf32fb3', 'uid' => '1677846385' ); . . . $cookieName = 'fbs_' . self::APP_ID; $session = self::$VALID_EXPIRED_SESSION; $_COOKIE[$cookieName] = '"' . http_build_query($session) . '"'; What I don't understand is, how do I get the "access_token", "sig", "session_key" etc? As far as I'm concerned, it should be dynamically exchanged from Facebook and involves user action (logging in).

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• What are the worst examples of moral failure in the history of software engineering?

  - by Amanda S

  Many computer science curricula include a class or at least a lecture on disasters caused by software bugs, such as the Therac-25 incidents or Ariane 5 Flight 501. Indeed, Wikipedia has a list of software bugs with serious consequences, and a question on StackOverflow addresses some of them too. We study the failures of the past so that we don't repeat them, and I believe that rather than ignoring them or excusing them, it's important to look at these failures squarely and remind ourselves exactly how the mistakes made by people in our profession cost real money and real lives. By studying failures caused by uncaught bugs and bad process, we learn certain lessons about rigorous testing and accountability, and we make sure that our innocent mistakes are caught before they cause major problems. There are kinds of less innocent failure in software engineering, however, and I think it's just as important to study the serious consequences caused by programmers motivated by malice, greed, or just plain amorality. Thus we can learn about the ethical questions that arise in our profession, and how to respond when we are faced with them ourselves. Unfortunately, it's much harder to find lists of these failures--the only one I can come up with is that apocryphal "DOS ain't done 'til Lotus won't run" story. What are the worst examples of moral failure in the history of software engineering?

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• Core principles, rules, and habits for CS students

  - by Asad Butt

  No doubt there is a lot to read on blogs, in books, and on Stack Overflow, but can we identify some guidelines for CS students to use while studying? For me these are: Finish your course books early and read 4-5 times more material relative to your course work. Programming is the one of the fastest evolving professions. Follow the blogs on a daily basis for the latest updates, news, and technologies. Instead of relying on assignments and exams, do at least one extra, non-graded, small to medium-sized project for every programming course. Fight hard for internships or work placements even if they are unpaid, since 3 months of work 1 year at college. Practice everything, every possible and impossible way. Try doing every bit of your assignments project yourself; i.e. fight for every inch. Rely on documentation as the first source for help and samples, Google, and online forums as the last source. Participate often in online communities and forums to learn the best possible approach for every solution to your problem. (After doing your bit.) Make testing one of your habits as it is getting more important everyday in programming. Make writing one of your habits. Write something productive once or twice a week and publish it.

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• Have any software engineers gotten math degrees later in their careers?

  - by vin

  I have a bachelors in computer science and worked the last 12 years as a software engineer. I'm bored with doing general development work, so I want to specialize. I'm thinking about getting a master's degree in math so I can build math models and write algorithms to implement them. I'm unsure what type of work I'd do (financial, gaming, graphics, science, research, etc) but I'm open minded. I would need to refresh my undergrad math skills (which are old and faded), but I loved algebra and calculus. I've been working with couple statisticians so I've been finding myself more interested in statistics. Since I'm a parent supporting a household, I would have to continue working while studying. Have any software engineers taken this route? (Specifically, going from BS in comp sci to MS in math.) If so, what advice do you have for coursework, financing, and getting a job that combines programming with advanced math? How abundant are these kinds of jobs? I'm not sure where one starts. Also, how do you hop from a BS to an MS in a different subject?

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• Are programming languages and methods inefficient? (assembler and C knowledge needed)

  - by b-gen-jack-o-neill

  Hi, for a long time, I am thinking and studying output of C language compiler in assembler form, as well as CPU architecture. I know this may be silly to you, but it seems to me that something is very ineffective. Please, don´t be angry if I am wrong, and there is some reason I do not see for all these principles. I will be very glad if you tell me why is it designed this way. I actually truly believe I am wrong, I know the genius minds of people which get PCs together knew a reason to do so. What exactly, do you ask? I´ll tell you right away, I use C as a example: 1: Stack local scope memory allocation: So, typical local memory allocation uses stack. Just copy esp to ebp and than allocate all the memory via ebp. OK, I would understand this if you explicitly need allocate RAM by default stack values, but if I do understand it correctly, modern OS use paging as a translation layer between application and physical RAM, when address you desire is further translated before reaching actual RAM byte. So why don´t just say 0x00000000 is int a,0x00000004 is int b and so? And access them just by mov 0x00000000,#10? Because you wont actually access memory blocks 0x00000000 and 0x00000004 but those your OS set the paging tables to. Actually, since memory allocation by ebp and esp use indirect addressing, "my" way would be even faster. 2: Variable allocation duplicity: When you run application, Loader load its code into RAM. When you create variable, or string, compiler generates code that pushes these values on the top o stack when created in main. So there is actual instruction for do so, and that actual number in memory. So, there are 2 entries of the same value in RAM. One in form of instruction, second in form of actual bytes in the RAM. But why? Why not to just when declaring variable count at which memory block it would be, than when used, just insert this memory location?

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• entity framework vNext wish list

  - by Fred Yang

  I have been intensively studying and use ef4 in my project. I do feel the improvement that it has over version 1. But I found that I have something I cannot get around easily. Here is a list I want it to be better in ef vNext. the model designer should allow multiple view of the same model, so that I don't need cram all my entity into a single view. respect user's manual edit of edmx. Currently, the some database view object simply can not be imported to the model because the designer "smartly" think that the view does not have a primary key, so that I have to manually edit the edmx to correct designer's behavior. But in the next "update from database" task, designer will revert my customization. For now, I simply fallback to manually edit the edmx file at all, or I have to use compare tool to keep the new update, and rollback and put the new update into my old edmx file manually. Designer should be improved to allow default behavior and user's manual control. I want control not to let the designer refresh the change of imported object. support user defined table function. linq is about Composability, stored proc dos not support composability. I wish I could use user defined table function which support this. What are you wishes for EF vNext?

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• Converting an AnsiString to a Unicode String

  - by jrodenhi

  I'm converting a D2006 program to D2010. I have a value stored in a single byte per character string in my database and I need to load it into a control that has a LoadFromStream, so my plan was to write the string to a stream and use that with LoadFromStream. But it did not work. In studying the problem, I see an issue that tells me that I don't really understand how conversion from AnsiString to Unicode string works. Here is some code I am puzzling over: oStringStream := TStringStream.Create(sBuffer); sUnicodeStream := oPayGrid.sStream; //explicit conversion to unicode string iSize1 := StringElementSize(oPaygrid.sStream); iSize2 := StringElementSize(sUnicodeStream); oStringStream.WriteString(sUnicodeStream); When I get to the last line, iSize1 does equal 1 and iSize2 does equal 2, so that part is what I understood from my reading. But, on the last line, after I write the string to the stream, and look at the Bytes Property of the string, it shows this (the string starts as '16,159'): (49 {$31}, 54 {$36}, 44 {$2C}, 49 {$31}, 53 {$35}, 57 {$39} ... I was expecting that it might look something like (49 {$31}, 00 {$00}, 54 {$36}, 00 {$00}, 44 {$2C}, 00 {$00}, 49 {$31}, 00 {$00}, 53 {$35}, 00 {$00}, 57 {$39}, 00 {$00} ... I'm not getting the right results out of the LoadFromStream because it is reading from the stream two bytes at a time, but the data it is receiving is not arranged that way. What is it that I should do to give the LoadFromStream a well formed stream of data based on a unicode string? Thank you for your help.

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• Setting up a domain using WAMP and NameCheap's DNS service

  - by Mike Jones

  So, I've been working on this for far longer than I should be and I'm quite thoroughly perplexed and lost. I apologize if this turns out to be a facile question, but I'm entirely befuddled and very much in need of some guidance. Earlier today I registered a cheap .info domain on NameCheap just to play around with as I learn webdev. I have WAMP installed on my computer and I've been testing my projects through localhost. I thought it would be a good idea to have a domain at my disposal in order to understand how it works and better test my work. NameCheap has a complimentary DNS service (not that I entirely understand what DNS is, although I tried), so I'm using that. I direct both the "@" and "www" host names to my IP address, as shown in the below tutorial: https://www.namecheap.com/support/knowledgebase/article.aspx/319/78/how-can-i-setup-an-a-address-record-for-my-domain However, now when I go to the URL of the domain I bought, it confronts me with a login box that seems to be coming from my wifi network. How do I set this up so that it hosts the information in my WAMP server? Thanks in advance for any help, I really appreciate it. And, as a side-note, what should read (print or online) to better understand the structure of the internet? I've been studying HTML/CSS/Javascript, but I'm not sure where to look for pragmatic and comprehensive information on how the internet works and how to utilize it as a website administrator. Thanks so much.

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• What category of combinatorial problems appear on the logic games section of the LSAT?

  - by Merjit

  There's a category of logic problem on the LSAT that goes like this: Seven consecutive time slots for a broadcast, numbered in chronological order I through 7, will be filled by six song tapes-G, H, L, O, P, S-and exactly one news tape. Each tape is to be assigned to a different time slot, and no tape is longer than any other tape. The broadcast is subject to the following restrictions: L must be played immediately before O. The news tape must be played at some time after L. There must be exactly two time slots between G and P, regardless of whether G comes before P or whether G comes after P. I'm interested in generating a list of permutations that satisfy the conditions as a way of studying for the test and as a programming challenge. However, I'm not sure what class of permutation problem this is. I've generalized the type problem as follows: Given an n-length array A: How many ways can a set of n unique items be arranged within A? Eg. How many ways are there to rearrange ABCDEFG? If the length of the set of unique items is less than the length of A, how many ways can the set be arranged within A if items in the set may occur more than once? Eg. ABCDEF = AABCDEF; ABBCDEF, etc. How many ways can a set of unique items be arranged within A if the items of the set are subject to "blocking conditions"? My thought is to encode the restrictions and then use something like Python's itertools to generate the permutations. Thoughts and suggestions are welcome.

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• Boost Binary Endian parser not working?

  - by Hai

  I am studying how to use boost spirit Qi binary endian parser. I write a small test parser program according to here and basics examples, but it doesn't work proper. It gave me the msg:"Error:no match". Here is my code. #include "boost/spirit/include/qi.hpp" #include "boost/spirit/include/phoenix_core.hpp" #include "boost/spirit/include/phoenix_operator.hpp" #include "boost/spirit/include/qi_binary.hpp" // parsing binary data in various endianness template '<'typename P, typename T void binary_parser( char const* input, P const& endian_word_type, T& voxel, bool full_match = true) { using boost::spirit::qi::parse; char const* f(input); char const* l(f + strlen(f)); bool result1 = parse(f,l,endian_word_type,voxel); bool result2 =((!full_match) || (f ==l)); if ( result1 && result2) { //doing nothing, parsing data is pass to voxel alreay } else { std::cerr << "Error: not match!!" << std::endl; exit(1); } } typedef boost::uint16_t bs_int16; typedef boost::uint32_t bs_int32; int main ( int argc, char *argv[] ) { namespace qi = boost::spirit::qi; namespace ascii = boost::spirit::ascii; using qi::big_word; using qi::big_dword; boost::uint32_t ui; float uf; binary_parser("\x01\x02\x03\x04",big_word,ui); assert(ui=0x01020304); binary_parser("\x01\x02\x03\x04",big_word,uf); assert(uf=0x01020304); return 0; }' I almost copy the example, but why this binary parser doesn't work. I use Mac OS 10.5.8 and gcc 4.01 compiler.

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• What noncluster index would be better to create on SQL Server?

  - by Junior Mayhé

  Here I am studying nonclustered indexes on SQL Server Management Studio. I've created a table with more than 1 million records. This table has a primary key. SELECT CustomerName FROM Customers Which leads the execution plan to show me: I/O cost = 3.45646 Operator cost = 4.57715 For the first attempt to improve performance, I've created a nonclustered index for this table: CREATE NONCLUSTERED INDEX [IX_CustomerID_CustomerName] ON [dbo].[Customers] ( [CustomerId] ASC, [CustomerName] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this first try, I've executed the select statement and the execution plan shows me: I/O cost = 2.79942 Operator cost = 3.92001 Now the second try, I've deleted this nonclustered index in order to create a new one. CREATE NONCLUSTERED INDEX [IX_CategoryName] ON [dbo].[Categories] ( [CategoryId] ASC ) INCLUDE ( [CategoryName]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this second try, I've executed the select statement and the execution plan shows me the same result: I/O cost = 2.79942 Operator cost = 3.92001 Am I doing something wrong or this is expected? Shall I use the first nonclustered index with two fields, or the second nonclustered with one field (CategoryID) including the second field (CategoryName)?

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• text-transform cannot change/be overwritten? (css)

  - by Radek

  I am studying css and I do not understand why some OTHER text and line 2 has red underline effect on them. I thought I either changed it for class others or reset it to none for class line2 I tried `text-decoration:none' for both .line2 and .others and the text was still red underlined. <html> <head> <style type="text/css"> .line {color:red; text-transform:uppercase; text-decoration:underline;} .line2 {color:blue; text-transform:none;} .others {color:black; text-transform:lowercase; text-decoration:blink; font-weight:bold;} </style> </head> <body> <div class='line'> line 1 <div class='others'><BR>some OTHER text<BR></DIV> <div class='line2'> <BR>line 2 </div> </div> </body> </html>

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• pointer in c and the c program

  - by sandy101

  Hello, I am studying the pointer and i come to this program .... #include <stdio.h> void swap(int *,int *); int main() { int a=10; int b=20; swap(&a,&b); printf("the value is %d and %d",a,b); return 0; } void swap(int *a,int*b) { int t; t=*a; *a=*b; *b=t; printf("%d and%d\n",*a,*b); } can any one tell me why this main function return the value reversed . The thing i understood till now is that the function call in c does not affect the main function and it's values . I also want to know how much the space a pointer variable occupied like integer have occupied the 2 bytes and the various application use and advantages of the pointer .... plz.... anyone help

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• How to learn a C++ GUI library effectively?

  - by Chan

  Hello everyone, I have many options for GUI in my head while searching in stackoverflow, but these are what I chose among others: Qt gtkmm GTK+ I used GTK+ couple years ago, and I felt so painful when using C API without string object and containers. I prefer C++ style, I then switched to C++ gtkmm, but the documentation was bad at that time. I found no help when encountering an issue. Now I want to give a hard try for Qt4, but I really want to know how to learn a GUI librarie effectively. With core C++, I usually pick up a problem and try to solve it in different ways using that particular technique, functionality. On the other hand, after skimming through the documentation from Qt site, I don't think this way of studying is applicable, since the GUI classes and APIs are so much bigger. Plus I'm still in school, so I won't have much time to play all the day long with it. How do you guys learn GUI before? Can anyone share some experiences how they learn thing, that would be an invaluable input for me! Best regards, Chan Nguyen

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• Is going for a BCS the right move for me?

  - by Michel Carroll

  I'm at a fork in the road. I need somebody to give me some advice from their personal journey in IT. At the moment, I have a college diploma (2 years) in Computer Programmer, and about 2 years of professional experience in the field of software. I'm currently freelancing my programming skills to the public, and am enjoying a nice income, and the rewards of flexibly working on a variety of projects with different cool people. I'm young (21 years old), passionate about software, technology, the internet, and also business. I know if I ever want to dwell deeper into the software industry, I might have a hard time doing so without a Bachelors in Computer Science. On one side, I think I'm better off getting my BCS while I'm still young and malleable. Also, the thought of learning even more stuff in my field is really exciting to me. On the flip side, it means another 3-4 years of studying, and jeopardizing my chances of going on vacation and accumulating wealth for a long time. Considering that I'm already pretty successful with my college diploma, do you think it's a good idea for me to go get my BCS? Will it open up many more doors in the future?

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• Inheritance and type parameters of Traversable

  - by Jesper

  I'm studying the source code of the Scala 2.8 collection classes. I have questions about the hierarchy of scala.collection.Traversable. Look at the following declarations: package scala.collection trait Traversable[+A] extends TraversableLike[A, Traversable[A]] with GenericTraversableTemplate[A, Traversable] trait TraversableLike[+A, +Repr] extends HasNewBuilder[A, Repr] with TraversableOnce[A] package scala.collection.generic trait HasNewBuilder[+A, +Repr] trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] Question: Why does Traversable extend GenericTraversableTemplate with type parameters [A, Traversable] - why not [A, Traversable[A]]? I tried some experimenting with a small program with the same structure and got a strange error message when I tried to change it to Traversable[A]: error: Traversable[A] takes no type parameters, expected: one I guess that the use of the @uncheckedVariance annotation in GenericTraversableTemplate also has to do with this? (That seems like a kind of potentially unsafe hack to force things to work...). Question: When you look at the hierarchy, you see that Traversable inherits HasNewBuilder twice (once via TraversableLike and once via GenericTraversableTemplate), but with slightly different type parameters. How does this work exactly? Why don't the different type parameters cause an error?

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• Symfony generating database from model

  - by Sergej Jevsejev

  Hello, I am having troubles generating a simple database form model. I am using: Doctrine on Symfony 1.4.4 MySQL Workbench 5.2.16 with Doctrine Export 0.4.2dev So my ERL Model is: http://img708.imageshack.us/img708/1716/tmg.png Genereted YAML file: --- detect_relations: true options: collate: utf8_unicode_ci charset: utf8 type: InnoDB Course: columns: id: type: integer(4) primary: true notnull: true autoincrement: true name: type: string(255) notnull: true keywords: type: string(255) notnull: true summary: type: clob(65535) notnull: true Lecture: columns: id: type: integer(4) primary: true notnull: true autoincrement: true course_id: type: integer(4) primary: true notnull: true name: type: string(255) notnull: true description: type: string(255) notnull: true url: type: string(255) relations: Course: class: Course local: course_id foreign: id foreignAlias: Lectures foreignType: many owningSide: true User: columns: id: type: integer(4) primary: true unique: true notnull: true autoincrement: true firstName: type: string(255) notnull: true lastName: type: string(255) notnull: true email: type: string(255) unique: true notnull: true designation: type: string(1024) personalHeadline: type: string(1024) shortBio: type: clob(65535) UserCourse: tableName: user_has_course columns: user_id: type: integer(4) primary: true notnull: true course_id: type: integer(4) primary: true notnull: true relations: User: class: User local: user_id foreign: id foreignAlias: UserCourses foreignType: many owningSide: true Course: class: Course local: course_id foreign: id foreignAlias: UserCourses foreignType: many owningSide: true And no matter what I try this error occurs after: symfony doctrine:build --all --no-confirmation SQLSTATE[42000]: Syntax error or access violation: 1072 Key column 'user_userid' doesn't exist in table. Failing Query: "ALTER TABLE user_has_course ADD CONSTRAINT user_has_course_user_userid_user_id FOREIGN KEY (user_userid) REFERENCES user(id)". Failing Query: ALTER TABLE user_has_course ADD CONSTRAINT user_has_cou rse_user_userid_user_id FOREIGN KEY (user_userid) REFERENCES user(id) Currently I am studying Symfony, and stuck with this error. Please help.

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