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• Where do I find a good explanation of Javascript-ese

  - by tzenes

  I realize that title may require explanation. The language I first learned was C, and it shows in all my programs... even those not written in C. For example, when I first learned F# I wrote my F# programs like C programs. It wasn't until someone explained the pipe operator and mapping with anonymous functions that I started to understand the F#-ese, how to write F# like a F# programmer and not a C programmer. Now I've written a little javascript, mostly basic stuff using jquery, but I was hoping there was a good resource where I could learn to write javascript programs like a javascript programmer.

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• generalizing the pumping lemma for UNIX-style regular expressions

  - by Avi

  Most UNIX regular expressions have, besides the usual *,+,? operators a backslash operator where \1,\2,... match whatever's in the last parentheses, so for example L=(a)b\1* matches the (non regular) language a^n b a^n On one hand, this seems to be pretty powerful since you can create (a*)b\1b\1 to match the language a^n b a^n b a^n which can't even be recognized by a stack automaton. On the other hand, I'm pretty sure a^n b^n cannot be expressed this way. Two questions: 1. Is there any literature on this family of languages (UNIX-y regular). In particular, is there a version of the pumping lemma for these? 2. Can someone prove (or perhaps disprove) that a^n b^n cannot be expressed this way? Thanks

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• Help me finish this Python self-challenge.

  - by Hamish Grubijan

  This is not a homework. I saw this article praising Linq library and how great it is for doing combinatorics stuff, and I thought to myself: Python can do it in a more readable fashion. After half hour of dabbing with Python I failed. Please finish where I left off. Also, do it in the most Pythonic and efficient way possible please. from itertools import permutations from operator import mul from functools import reduce glob_lst = [] def divisible(n): return (sum(j*10^i for i,j in enumerate(reversed(glob_lst))) % n == 0) oneToNine = list(range(1, 10)) twoToNine = oneToNine[1:] for perm in permutations(oneToNine, 9): for n in twoToNine: glob_lst = perm[1:n] #print(glob_lst) if not divisible(n): continue else: # Is invoked if the loop succeeds # So, we found the number print(perm) Thanks!

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• Objective-c string appending causes exception

  - by Dave C

  Hello Everyone, The following code is causing me some problems. The third line causes a program crash... it doesn't happen the first time I step through but somehow later on in the program. If I comment out that third line, the program runs smoothly. NSString *myRequestString = @"text"; int i = 1; myRequestString = [myRequestString stringByAppendingString:[NSString stringWithFormat: @"t=%d", i]]; That code causes this exception: * -[CFString release]: message sent to deallocated instance 0xb4c43fe0 On a side note, can anyone tell me how to concatenate strings in objective-c like any other normal language... I can't believe that there is no concatenation operator. Any and all help is greatly appreciated.

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• Command Line PHP with shell_exec works for root but not others

  - by Kristopher Ives

  I have a very simple script that is to test if running a shell_exec (or backtick operator) basically works: #!/usr/bin/php5-cli <?php echo "This is a PHP script\n"; echo `ls -l /home/stoysnet/`; Unless I run this as root, it always gives me: $ ./foo.php This is a PHP script Warning: _shell_exec(): Permission Denied in /home/stoysnet/foo.php on line 5 I've tried running this via PHP in a few different ways, but I always get the same error. However, when I put the script into a subdirectory of /etc/ owned by root:root and executed as root it works. What gives?

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• Working with expression AST:s

  - by Marcus

  Hi, Is there any best practice when working with AST:s? I have a parsed expression AST. ConstantExpression, BinaryExpression etc. I want to populate a GUI-dialog with information from the AST, and it's here where I get kinda confused because my code gets pretty messy. Example: expression = "Var1 > 10 AND Var2 < 20" I want to populate two textboxes with value 10 resp. 20 from the AST. What I'm doing now is a recursive method that checks for correct child expression-types (with .Net Is-operator) and acts accordingly and the code is really "smelly" :) Is there any design pattern, like Visitor or such, that makes this somewhat easier/more readable/maintainable ?

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• Output of gcc -fdump-tree-original

  - by Job

  If I dump the code generated by GCC for a virtual destructor (with -fdump-tree-original), I get something like this: ;; Function virtual Foo::~Foo() (null) ;; enabled by -tree-original { <<cleanup_point <<< Unknown tree: expr_stmt (void) (((struct Foo *) this)->_vptr.Foo = &_ZTV3Foo + 8) >>> >>; } <D.20148>:; if ((bool) (__in_chrg & 1)) { <<cleanup_point <<< Unknown tree: expr_stmt operator delete ((void *) this) >>> >>; } My question is: where is the code after "<D.20148>:;" located? It is outside of the destructor so when is this code executed?

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• How to dynamically compose a bitmask?

  - by mystify

  Lets say I have to provide an value as bitmask. NSUInteger options = kFoo | kBar | kFooBar; and lets say that bitmask is really huge and may have 100 options. But which options I have, depends on a lot of situations. How could I dynamically compose such a bitmask? Is this valid? NSUInteger options; if (foo) { options = options | kFoo; } if (bar) { options = options | kBar; } if (fooBar) { options = options | kFooBar; } (despite the fact that this would probably crash when doing that | bitmask operator thing to "nothing".

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• What is Perl's equivalent to awk's /text/,/END/ ?

  - by kSiR

  I am looking to replace a nasty shell script that uses awk to trim down some HTML. The problem is I cannot find anything in Perl that does the aforementioned function awk '/<TABLE\ WIDTH\=\"100\%\" BORDER\=1\ CELLSPACING\=0><TR\ class\=\"tabhead\"><TH>State<\/TH>/,/END/' How can I do this in Perl? the expected output would be <TABLE WIDTH="100%" BORDER=1 CELLSPACING=0><TR class="tabhead"><TH>State</TH> The Perl flipflop operator gives me WAY more. (Everything between the asterisks is junk) *<h2>Browse Monitors (1 out of 497)</h2><br><font size="-1" style="font-weight:normal"> Use the <A HREF=/SiteScope/cgi/go.exe/SiteScope?page=monitorSummary&account=login15 >Monitor Description Report</a> to view current monitor configuration settings.</font>*<TABLE WIDTH="100%" BORDER=1 CELLSPACING=0><TR class="tabhead"><TH>State</TH>

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• QObject cloning

  - by Olorin

  I know that Qobjects are supposed to be identities not values eg you cannot copy them and by default the copy constructor and asignment are disabled as explained in qt documentation. But is it possible to create a new Qobject from an existing one using a clone method? Would this be a logic error ? If i say QObject b; QObject a; b.cloneFrom(a); or QObject a = new QBject(); QObject b = new QBject(); b->cloneFrom(a); and the clone method copyes stuff like members etc would this be wrong? And if this is ok can i write my own copy constructor and asignment operator that does just that? Note: i actually want to try this with classes that inherit qobject.

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• .NET Type Conversion Issue: Simple but difficult

  - by jaderanderson

  Well, the question is kinda simple. I have a object defined as: public class FullListObject : System.Collections.ArrayList, IPagedCollection And when i try to: IPagedCollection pagedCollection = (IPagedCollection)value; It don't work... value is a FullListObject... this is my new code trying to get around a issue with the "is" operator. When the system tests (value is IPagedCollection) it never gets true for FullListObject. How to cast the object to another object with a interface type?

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• Newbie Python programmer tangling with Lists.

  - by Sergio Tapia

  Here's what I've got so far: # A. match_ends # Given a list of strings, return the count of the number of # strings where the string length is 2 or more and the first # and last chars of the string are the same. # Note: python does not have a ++ operator, but += works. def match_ends(words): counter = 0 for word in words: if len(word) >= 2 and word[0] == word[-1]: counter += counter return counter # +++your code here+++ return I'm following the Google Python Class, so this isn't homework, but me just learning and improving myself; so please no negative comments about 'not doing my homework'. :P What do you guys think I'm doing wrong here? Here's the result: match_ends X got: 0 expected: 3 X got: 0 expected: 2 X got: 0 expected: 1 I'm really loving Python, so I just know that I'll get better at it. :)

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• Legal uses of setjmp and GCC

  - by Chris Lutz

  Using GCC (4.0 for me), is this legal: if(__builtin_expect(setjmp(buf) != 0, 1)) { // handle error } else { // do action } I found a discussion saying it caused a problem for GCC back in 2003, but I would imagine that they would have fixed it by now. The C standard says that it's illegal to use setjmp unless it's one of four conditions, the relevant one being this: one operand of a relational or equality operator with the other operand an integer constant expression, with the resulting expression being the entire controlling expression of a selection or iteration statement; But if this is a GCC extension, can I guarantee that it will work under for GCC, since it's already nonstandard functionality? I tested it and it seemed to work, though I don't know how much testing I'd have to do to actually break it. (I'm hiding the call to __builtin_expect behind a macro, which is defined as a no-op for non-GCC, so it would be perfectly legal for other compilers.)

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• Most mind-blowing C++ hack you've ever seen?

  - by sblom

  In the same spirit as the "Hidden features of X?" series, what are the most mind-blowingly well-executed "I didn't even think the language could do that!" hacks that you've ever seen in C++. For example, my recent favorite is an implementation of the "operator" --> for pre-C++0x lambdas. Another fantastic example is Multi-dimensional analog literals. (Note: this is a community wiki question to avoid the appearance of reputation-whoring.)

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• Linq to SQL problem

  - by Ronnie Overby

  I have a local collection of recordId's (integers). I need to retrieve records that have every one of their child records' ids in that local collection. Here is my query: public List<int> OwnerIds { get; private set; } ... filteredPatches = from p in filteredPatches where OwnerIds.All(o => p.PatchesOwners.Select(x => x.OwnerId).Contains(o)) select p; I am getting this error: Local sequence cannot be used in Linq to SQL implementation of query operators except the Contains() operator. I get that .All() isn't supported by Linq to SQL, but is there a way to do what I am trying to do?

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• How do I obtain a new stateful session bean in a servlet thread?

  - by FarmBoy

  I'm experimenting with EJB3 I would like to inject a stateful session bean into a servlet, so that each user that hits the servlet would obtain a new bean. Obviously, I can't let the bean be an instance variable for the servlet, as that will be shared. And apparantly injecting local variables isn't allowed. I can use the new operator to create a bean, but that doesn't seem the right approach. Is there a right way to do this? It seems like what I'm trying to do is fairly straightforward, after all, we would want each new customer to find an empty shopping cart.

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• Which is faster in Python: x**.5 or math.sqrt(x)?

  - by Casey

  I've been wondering this for some time. As the title say, which is faster, the actual function or simply raising to the half power? UPDATE This is not a matter of premature optimization. This is simply a question of how the underlying code actually works. What is the theory of how Python code works? I sent Guido van Rossum an email cause I really wanted to know the differences in these methods. My email: There are at least 3 ways to do a square root in Python: math.sqrt, the '**' operator and pow(x,.5). I'm just curious as to the differences in the implementation of each of these. When it comes to efficiency which is better? His response: pow and ** are equivalent; math.sqrt doesn't work for complex numbers, and links to the C sqrt() function. As to which one is faster, I have no idea...

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• grails gsp test evaluates to false, but block is still rendered. Why?

  - by ?????

  I'm baffled with Grails test operator. This expression: <g:if test="${!(preferences.displayOption.equals('ANA') || preferences.displayOption.equals('FLOP'))} "> ${!(preferences.displayOption.equals('ANA') || preferences.displayOption.equals('FLOP'))} </g:if> prints false How can that be? I'm printing the exact same condition I'm testing for! even though I'm certain the test condition evaluates to 'false' because it prints false in the very next line, the statements inside the g:if are being rendered. Anu ideas as to what's going on.

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• C question: Padding bits in unsigned integers and bitwise operations (C89)

  - by Anonymous Question Guy

  I have a lot of code that performs bitwise operations on unsigned integers. I wrote my code with the assumption that those operations were on integers of fixed width without any padding bits. For example an array of 32 bit unsigned integers of which all 32 bits available for each integer. I'm looking to make my code more portable and I'm focused on making sure I'm C89 compliant (in this case). One of the issues that I've come across is possible padded integers. Take this extreme example, taken from the GMP manual: However on Cray vector systems it may be noted that short and int are always stored in 8 bytes (and with sizeof indicating that) but use only 32 or 46 bits. The nails feature can account for this, by passing for instance 8*sizeof(int)-INT_BIT. I've also read about this type of padding in other places. I actually read of a post on SO last night (forgive me, I don't have the link and I'm going to cite something similar from memory) where if you have, say, a double with 60 usable bits the other 4 could be used for padding and those padding bits could serve some internal purpose so they cannot be modified. So let's say for example my code is compiled on a platform where an unsigned int type is sized at 4 bytes, each byte being 8 bits, however the most significant 2 bits are padding bits. Would UINT_MAX in that case be 0x3FFFFFFF (1073741823) ? #include <stdio.h> #include <stdlib.h> /* padding bits represented by underscores */ int main( int argc, char **argv ) { unsigned int a = 0x2AAAAAAA; /* __101010101010101010101010101010 */ unsigned int b = 0x15555555; /* __010101010101010101010101010101 */ unsigned int c = a ^ b; /* ?? __111111111111111111111111111111 */ unsigned int d = c << 5; /* ?? __111111111111111111111111100000 */ unsigned int e = d >> 5; /* ?? __000001111111111111111111111111 */ printf( "a: %X\nb: %X\nc: %X\nd: %X\ne: %X\n", a, b, c, d, e ); return 0; } is it safe to XOR two integers with padding bits? wouldn't I XOR whatever the padding bits are? I can't find this behavior covered in C89. furthermore is the c var guaranteed to be 0x3FFFFFFF or if for example the two padding bits were both on in a or b would c be 0xFFFFFFFF ? same question with d and e. am i manipulating the padding bits by shifting? I would expect to see this below, assuming 32 bits with the 2 most significant bits used for padding, but I want to know if something like this is guaranteed: a: 2AAAAAAA b: 15555555 c: 3FFFFFFF d: 3FFFFFE0 e: 01FFFFFF Also are padding bits always the most significant bits or could they be the least significant bits? Thanks guys EDIT 12/19/2010 5PM EST: Christoph has answered my question. Thanks! I had also asked (above) whether padding bits are always the most significant bits. This is cited in the rationale for the C99 standard, and the answer is no. I am playing it safe and assuming the same for C89. Here is specifically what the C99 rationale says for §6.2.6.2 (Representation of Integer Types): Padding bits are user-accessible in an unsigned integer type. For example, suppose a machine uses a pair of 16-bit shorts (each with its own sign bit) to make up a 32-bit int and the sign bit of the lower short is ignored when used in this 32-bit int. Then, as a 32-bit signed int, there is a padding bit (in the middle of the 32 bits) that is ignored in determining the value of the 32-bit signed int. But, if this 32-bit item is treated as a 32-bit unsigned int, then that padding bit is visible to the user’s program. The C committee was told that there is a machine that works this way, and that is one reason that padding bits were added to C99. Footnotes 44 and 45 mention that parity bits might be padding bits. The committee does not know of any machines with user-accessible parity bits within an integer. Therefore, the committee is not aware of any machines that treat parity bits as padding bits. EDIT 12/28/2010 3PM EST: I found an interesting discussion on comp.lang.c from a few months ago. Bitwise Operator Effects on Padding Bits (VelocityReviews reader) Bitwise Operator Effects on Padding Bits (Google Groups alternate link) One point made by Dietmar which I found interesting: Let's note that padding bits are not necessary for the existence of trap representations; combinations of value bits which do not represent a value of the object type would also do.

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• In Ruby are there any related applications of the syntax: class << self ... end

  - by pez_dispenser

  class << self attr_accessor :n, :totalX, :totalY end The syntax above is used for defining class instance variables. But when I think about what syntax implies, it doesn't make any sense to me, so I'm wondering if this type of syntax is used for any other types of definitions. My point of confusion here is this: class << self The append operator normally means "add what's on the right to the object on the left". But in the context of this block, how does that add up to "put the contents of this block into the definition of the class instance rather than the instance"? For the same reason I'm confused as to why in one context class << self can define class instance variables while in another it seems to create class variables such as here: class Point # Instance methods go here class << self # Class methods go here end end

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• Compare two String with MySQL

  - by Scorpi0

  Hi, I wan't to compare two strings in a SQL request so I can retrieve the best match, the aim is to propose to an operator the best zip code possible. For example, in France, we have Integer Zip code, so I made an easy request : SELECT * FROM myTable ORDER BY abs(zip_code - 75000) This request returns first the data closest of Paris. Unfortunatelly, United Kingdom have zip code like AB421RS, so my request can't do it. I see in SQL Server a function 'Difference' : http://www.java2s.com/Code/SQLServer/String-Functions/DIFFERENCEworkoutwhenonestringsoundssimilartoanotherstring.htm But I use MySQL.. Is there anyone who have a good idea to do the trick in one simple request ? PS : the Levenshtein Distance will not do it, as I really wan't to compare string like if they were number. ABCDEF have to be closer to AWXYZ than to ZBCDEF.

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• LINQ Searching Only Allowing Equivalency

  - by Mad Halfling

  Hi folks, I'm trying to filter a set of records based on a sub-object's criteria. This compiles ok recordList = recordList.Where(r => r.Areas.Where(a => a.Area == "Z").Count() > 0); but this doesn't recordList = recordList.Where(r => r.Areas.Where(a => a.Area <= "Z").Count() > 0); giving these errors Cannot convert lambda expression to type 'string' because it is not a delegate type Delegate 'System.Func' does not take '1' arguments Operator '<=' cannot be applied to operands of type 'string' and 'string' != works ok, by any sort of less than or greater than operation fails.

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• Memory leak in Qt signal and slots

  - by Ajay

  Hello, I am running valgrind on my Qt code,and even on successful exit of the application, get the following report from valgrind 8,832 bytes in 92 blocks are still reachable in loss record 12 of 12 at 0x4025390: operator new(unsigned int) (vg_replace_malloc.c:214) ==3339== by 0x4B75F05: QMutex::QMutex(QMutex::RecursionMode) (qmutex.cpp:123) ==3339== by 0x4B77602: QMutexPool::get(void const*) (qmutexpool.cpp:137) ==3339== by 0x4CA0EC2: signalSlotLock(QObject const*) (qobject.cpp:112) ==3339== by 0x4CA3939: QMetaObjectPrivate::connect(QObject const*, int, QObject const*, int, int, int*) (qobject.cpp:2900) ==3339== by 0x4CA5C00: QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) (qobject.cpp:2599) I disconnect all signal connections and also delete the objects. The above mentioned leak increases if i increase the amount of signal and slot connections? Can anybody help with this?

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• What does this xkcd code do?

  - by cobbal

  On the xkcd site today, the following appeared as a joke in a <script language="scheme"> tag so what does the following code do / represent? (define (eval exp env) (cond ((self-evaluating? exp) exp) ((variable? exp) (lookup-variable-value exp env)) ((quoted? exp) (text-of-quotation exp)) ((assignment? exp) (eval-assignment exp env)) ((definition? exp) (eval-definition exp env)) ((if? exp) (eval-if exp env)) ((lambda? exp) (make-procedure (lambda-parameters exp) (lambda-body exp) env)) ((begin? exp) (eval-sequence (begin-actions exp) env)) ((cond? exp) (eval (cond->if exp) env)) ((application? exp) (apply (eval (operator exp) env) (list-of-values (operands exp) env))) (else (error "Common Lisp or Netscape Navigator 4.0+ Required" exp))))

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• Using local classes with STL algorithms

  - by David Rodríguez - dribeas

  I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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