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• When is (true == x) === !!x false?

  - by Paul S.

  JavaScript has different equality comparison operators Equal == Strict equal === It also has a logical NOT ! and I've tended to think of using a double logical NOT, !!x, as basically the same as true == x. However I know this is not always the case, e.g. x = [] because [] is truthy for ! but falsy for ==. So, for which xs would (true == x) === !!x give false? Alternatively, what is falsy by == but not !! (or vice versa)?

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• How to find the remainder of large number division in C++?

  - by Beelzeboul

  Hello, I have a question regarding modulus in C++. What I was trying to do was divide a very large number, lets say for example, M % 2, where M = 54,302,495,302,423. However, when I go to compile it says that the number is to 'long' for int. Then when I switch it to a double it repeats the same error message. Is there a way I can do this in which I will get the remainder of this very large number or possibly an even larger number? Thanks for your help, much appreciated.

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• Help with implementing a function to change size of dynamic array

  - by iRobot

  I'm trying to write a function that will change the size of a dynamic array to a new size. In my header file, I have: Image **images; //pointer to a dynamic array of image pointers int maximum; //size I want to do this by allocating a new array and copying the values over without changing their indices. If there are non-null pointers outside the range newmax, then we cant do this. So heres what I have: There are no compilation or runtime errors. However, I find that the new array isnt getting sized right. When I run the following test case: I should get an index out of bounds error, but instead the system lets it slide. Can anyone see the mistake? I've looked for hours but cant find anything.

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• A little javascript help needed here (easy).

  - by Camran

  function addOption(selectbox, val, txt){ ...... } addOption(list, "Cars", "Cars"); I need to add this in front of the text of the function: &nbsp;&nbsp;&nbsp; So that there is space coming in before the option text...Never mind what it is for, it is just confusing... I just don't know how to insert it into the js code. If I do it like this: addOption(list, "Cars", "&nbsp;&nbsp;&nbsp;Cars"); Then the &nbsp;&nbsp;&nbsp; comes into the text, so it gets displayed for the users. However I need it to be interpreted as "space"... If you don't understand let me know... How can I do this? Quotes, double quotes etc? Thanks

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• Can I reproduce Scala's behavior for == ?

  - by JPP

  In Programming in Scala, I can read that the == operator behaves as if it was defined like this: final def == (that: Any): Boolean = if (null eq this) {null eq that} else {this equals that} But there must actually be compiler magic to avoid null pointer exceptions, right? Is there any way for me to replicate this behavior with pure Scala; i.e., have an operator/method return one thing if the receiver is null and another one if it isn't? What I mean is an actual implementation of null eq this. I suppose I can write a "pimp" and then define the method on the wrapper class, but is there a more direct way to do this?

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• c++ - FIFO implementation

  - by Narek

  While implementing a FIFO I have used the following structure: struct Node { T info_; Node* link_; Node(T info, Node* link=0): info_(info), link_(link) {} }; I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it's pointer? Is this a kind of infinite loop? And finally, if this is a bad practice, how I could implement a better FIFO.

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• question abouut string sort

  - by davit-datuashvili

  i have question from programming pearls problem is following show how to use lomuto's partitioning scheme to sort varying length bit strings in time proportional to the sum oof their length and algorithm is following each record in x[0..n-1] has an integer length and pointer to the array bit[0..length-1] code void bsort(l,u,depth){ if (l>=u) return; for (int i=l;i<u;i++) if (x[i].length<depth) swap(i,l++); m=l; if (x[i].bit[depth] ==0) swap(i,m++); bsort(l,m-1,depth+1); bsort(m,u,depth+1); please help me i need following things 1. how this algorith works 2.how implement in java?

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• between syntax, are there any equal function

  - by gcc

  /* char **mainp=malloc(sizeof(char *)*2); mainp[0]=malloc(sizeof(char)*300); mainp[1]=malloc(sizeof(char )*300); */ *I have some input about propositional calculus *After calculating some math funtion-removing paranthesis-changing"&" with ","-replacing "|" with"," I have >> (1) P,-Q,Q,-R is stored in mainp[0] R,A,P,B,F is stored in mainp[1] *My question is: Between comma , I have want to compare two pointer array. If there is any equal two or more functions(Q,-R is function representation) ,function which you will show me how to write must return int. According to example (1),function will return 1 (I expect like that) /*I have som thought://which function should I have use:*/ in for loop if( strspn(mainp[0][i])==1 ) increment d; continue; or in for loop srtcmp(mainp[0][i],mainp[1]);

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• mysql_real_escape_string & slashes (again, oh yes)

  - by Fizzadar

  Righto, firstly magic quotes & runtime are disabled correctly in php.ini, and confirmed by phpinfo(). PHP version: 5.3.4 MySQL version: 5.1.52 I'm only use mysql_real_escape_string on the data, after htmlspecialchars and a trim, that's all the data cleaning on the variable. Yet, when I submit a single quote, the slash remains in the database. When running mysql_query I'm using "' . $var . '", although in the past this hasn't changed anything (could be due to the double quotes?). Any ideas? and please don't tell me about PDO/prepared statements, I'm aware of them and I have my reasons for doing it this way. Thanks!

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• TPageControl tab area OnMouseEnter OnMouseLeave events

  - by daemon_x

  Hello, I need to catch the "OnMouseEnter" and "0nMouseLeave" for a certain area of the TPageControl component. With that specific area I mean the whole "tab header" rectangle. The problem is, that the page control doesn't catch the messages (I'm catching internal control messages CM_MOUSEENTER and CM_MOUSELEAVE) in the "empty" space. The aim for me is to draw a small arrow in the right empty side when user hovers in the red framed area (and drawing is just piece of cake) and erase it when leaves this area. And I'm don't care about the overflow of the tabs (which causes to draw scrolling double button) - that will never happen.

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• I am looking for a svn helper program

  - by uzay95

  I didn't remember the name of this program. But i can remember how it works. Program is working on tray. When we double click on it it is showing its main window. :) I could add some criterias to make automatic commit(and maybe update). For ex: if a file changes or if files to be deleted, you can commit. The best part of this program is: "it is FREE" I don't remember exactly but i think it has M name in its name (but i don't remember). I think this program written by an Italian man. And its web site was very simple (and i think its fonts were green)

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• log (1-var) operation in C

  - by heike

  I am trying to code this algorithm. I am stuck in the part of log((1.0-u)/u))/beta; As I understand, I can not get the result of this in C, as it will always return me with negative value log (returning imaginary value). Tried to print the result of log(1-5) for instance, it gives me with Nan. How can I get the result of double x = (alpha - log((1.0-u)/u))/beta then? Would appreciate for any pointers to solve this problem. Thank you

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• Break the limit of threading, segmentation fault

  - by user353573

  use pthread_create to create limited number of threads running concurrently Successfully compile and run However, after adding function pointer array to run the function, Segmentation fault Where is wrong? workserver number: 0 Segmentation fault void* workserver(void arg) { int status; while(true) { printf("workserver number: %d\n", (int)arg); ( job_queue[(int)arg])(); sleep(3); status = pthread_mutex_lock(&data.mutex); if(status != 0) printf("%d lock mutex", status); data.value = 1; status = pthread_cond_signal(&data.cond); if(status != 0) printf("%d signal condition", status); status = pthread_mutex_unlock(&data.mutex); if(status != 0) printf("%d unlock mutex", status); } }

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• Method to register method to be called when event is raised

  - by zaidwaqi

  I have a Panel which contains 20 PictureBox controls. If a user clicks on any of the controls, I want a method within the Panel to be called. How do I do this? public class MyPanel : Panel { public MyPanel() { for(int i = 0; i < 20; i++) { Controls.Add(new PictureBox()); } } // DOESN'T WORK. // function to register functions to be called if the pictureboxes are clicked. public void RegisterFunction( <function pointer> func ) { foreach ( Control c in Controls ) { c.Click += new EventHandler( func ); } } } How do I implement RegisterFunction()? Also, if there are cool C# features that can make the code more elegant, please share.

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• strategy to allocate/free lots of small objects

  - by aaa

  hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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• RSpec "undefined local variable or method `user'"

  - by Justin

  I have the following test written in RSpec: describe '#create' do ... it 'redirects users to profile page' do response.should redirect_to user_path(user) end ... ... And the following in my UsersController: def create @user = User.new(params[:user]) if @user.save redirect_to user_path(@user) end end Does anyone know why this is returning the following error: NameError: undefined local variable or method 'user' I also tried changing this to be root_url in both cases instead of user_path(user) and it gave a different error saying: Expected response to be a <:redirect>, but was <200> Does anyone know what the issue might be? I have double-checked my code and have seen similar questions posted online, but haven't been able to find a solution. Thanks in advance for any help!

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• bash screen title usage (screen -t "something")

  - by atrioom

  I was working with screen lately and wanted to use the -t option for it. What's the point of the-t option if the title of the screen does not show anywhere like when using -list or within the screen when it's attached? There is a command CTRL-A double-quote(") to see all active screens, and then it shows the title, but that does not really do the job, because I have to have the screen attached already. I want to read out the title BEFORE attaching any screens, to attach the right one in the first place. Is there a method to use -t in a convenient way? Edit: There is one method: "ctrl-a "" and then "ctrl-a {numberofscreen}". I guess that's the best way to use the screen titles?

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• Are unspecified and undefined behavior required to be consistent between compiles?

  - by sharptooth

  Let's pretend my program contains a specific construct the C++ Standard states to be unspecified behavior. This basically means the implementation has to do something reasonable but is allowed not to document it. But is the implementation required to produce the same behavior every time it compiles a specific construct with unspecified behavior or is it allowed to produce different behavior in different compiles? What about undefined behavior? Let's pretend my program contains a construct that is UB according to the Standard. The implementation is allowed to exhibit any behavior. But can this behavior differ between compiles of the same program on the same compiler with same settings in the same environment? In other words, if I dereference a null pointer on line 78 in file X.cpp and the implementation formats the drive in such case does it mean that it will do the same after the program is recompiled?

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• Can a thread call wait() on two locks at once in Java (6)

  - by Dr. Monkey

  I've just been messing around with threads in Java to get my head around them (it seems like the best way to do so) and now understand what's going on with synchronize, wait() and notify(). I'm curious about whether there's a way to wait() on two resources at once. I think the following won't quite do what I'm thinking of: synchronized(token1) { synchronized(token2) { token1.wait(); token2.wait(); //won't run until token1 is returned System.out.println("I got both tokens back"); } } In this (very contrived) case token2 will be held until token1 is returned, then token1 will be held until token2 is returned. The goal is to release both token1 and token2, then resume when both are available (note that moving the token1.wait() outside the inner synchronized loop is not what I'm getting at). A loop checking whether both are available might be more appropriate to achieve this behaviour (would this be getting near the idea of double-check locking?), but would use up extra resources - I'm not after a definitive solution since this is just to satisfy my curiosity.

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• Doubling a number - shift left vs. multiplication

  - by ToxicAvenger

  What are the differences between int size = (int)((length * 200L) / 100L); // (1) and int size = length << 1; // (2) (length is int in both cases) I assume both code snippets want to double the length parameter. I'd be tempted to use (2) ... so are there any advantages for using (1)? I looked at the edge cases when overflow occurs, and both versions seem to have the same behavior. Please tell me what am I missing.

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• referencing struct fields in c with square brackets and an index instead of . and ->?

  - by lsiebert

  Assuming I have a structure such as: typedef struct { char * string1; char * string2; } TWO_WORDS; such that all the fields are of the same type, and my main has TWO_WORDS tw; can I reference string1 with tw[0] and string2 with two[1]? If so: is this part of the c standard? do i have to cast the struct to an array first? what about fields which are different sizes in memory what about fields which are different types but the same size? can you do pointer arithmetic within a structure? -

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• MySQL query with JOINS and GROUP BY

  - by user1854049

  I'm building a MySQL query but I can't seem to get it right. I have four tables: - customers - orders - sales_rates - purchase_rates There is a 1:n relation 'customernr' between customers and orders. There is a 1:n relation 'ordernr' between orders and sales_rates. There is a 1:n relation 'ordernr' between orders and purchase_rates. What I would like to do is produce an output of all customers with their total purchase and sales amounts. So far I have the following query. SELECT c.customernr, c.customer_name, SUM(sr.sales_price) AS sales_price, SUM(pr.purchase_price) AS purchase_price FROM orders o, customers c, sales_rates sr, purchase_rates pr WHERE o.customernr = c.customernr AND o.ordernr = sr.ordernr AND o.ordernr = pr.ordernr GROUP BY k.bedrijfsnaam The result of the sales_price and purchase_price is far too high. I seem to be getting double counts. What am I doing wrong? Is it possible to perform this in a single query? Thank for your response!

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• Abstract class and operator!= in c++

  - by Alessandro Teruzzi

  Hi All, I have problem implementing the operator!= in a set class deriving from an abstact one. The code looks like this: class Abstract { public: //to make the syntax easier let's use a raw pointer virtual bool operator!=(const Abstract* other) = 0; }; class Implementation { SomeObject impl_; //that already implement the operator!= public: bool operator!=(const Abstract* other) { return dynamic_cast<Implementation*>(other)->impl_ != this->impl_; } }; This code works but it has the drawback to use dynamic_cast and I need to handle error in casting operation. This is a generic problem that occur when a function of a concrete class it is trying to using some internal information (not available at the abstract class level) to perform a task. Is there any better way to solve this kind of problem? Cheers

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• How to do hex8 encoding in c?

  - by Tech163

  I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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• How do you get good line spacing with lpr?

  - by dan

  I'm using lpr with the following flags: lpr -o cpi=12 -o lpi=8 -o page-left=36 -o page-top=36 -o page-bottom=36 But the lines appear too close together. But if I decrease lpi to 6 or something, the font just gets taller. What I really want is control over the amount of space between the lines. My makeshift solution is to insert blank lines in the document using sed G, but ideally I would like to achieve 1.5 line spacing instead of full double-spaced. Is this possible?

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