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• How do i cast A to object to class A when B can typcast to A?

  - by acidzombie24

  Basically i want to do this. ee causes a bad cast exception. NOTE: o can be ANYTHING. It may not be B, it can be C, D, E, F etc. But this should work as long as o is a class that can typecast into A (B is such a class. It uses an implicit operator overload) var b = (B)"sz"; var e = (A)b; object o = b; var ee = (A)o;

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• Compile time string hashing

  - by Caspin

  I have read in few different places that using c++0x's new string literals it might be possible to compute a string's hash at compile time. However, no one seems to be ready to come out and say that it will be possible or how it would be done. Is this possible? What would the operator look like? I'm particularly interested use cases like this. void foo( const std::string& value ) { switch( std::hash(value) ) { case "one"_hash: one(); break; case "two"_hash: two(); break; /*many more cases*/ default: other(); break; } } Note: the compile time hash function doesn't have to look exactly as I've written it. I did my best to guess what the final solution would look like, but meta_hash<"string"_meta>::value could also be a viable solution.

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• Linq to sql translation to sql of custom method

  - by DJPB

  hi there is there a way to translate an expression to sql to use with linq to sql? for example I have a method that compares two values example: MyComparer.Compare(value1, value2, ">") return value1 > value2 MyComparer.Compare(value1, value2, "=") return value1 == value2 MyComparer.Compare(value1, value2, "<=") return value1 <= value2 and i would like a query like var list = from i in dataContext.items where MyComparer.Compare(i.value, someValue, "some operator") select ... this won't work because, obviously, MyComparer doesn't translate to sql maybe this is a twisted question, but how can i translate this method to sql or is this possible? tks

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• Load binary file using fstream

  - by Kirill V. Lyadvinsky

  I'm trying to load binary file using fstream in the following way: #include <iostream #include <fstream #include <iterator #include <vector using namespace std; int main() { basic_fstream<uint32_t file( "somefile.dat", ios::in|ios::binary ); vector<uint32_t buffer; buffer.assign( istream_iterator<uint32_t, uint32_t( file ), istream_iterator<uint32_t, uint32_t() ); cout << buffer.size() << endl; return 0; } But it doesn't work. In Ubuntu it crashed with std::bad_cast exception. In MSVC++ 2008 it just prints 0. I know that I could use file.read to load file, but I want to use iterator and operator>> to load parts of the file. Is that possible? Why the code above doesn't work?

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• Java 'Prototype' pattern - new vs clone vs class.newInstance

  - by Guillaume

  In my project there are some 'Prototype' factories that create instances by cloning a final private instance. The author of those factories says that this pattern provides better performance than calling 'new' operator. Using google to get some clues about that, I've found nothing really relevant about that. Here is a small excerpt found in a javdoc from an unknown project javdoc from an unknown project Sadly, clone() is rather slower than calling new. However it is a lot faster than calling java.lang.Class.newInstance(), and somewhat faster than rolling our own "cloner" method. For me it's looking like an old best practice of the java 1.1 time. Does someone know more about this ? Is this a good practice to use that with 'modern' jvm ?

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• How do I copy object in Qt?

  - by Martin

  I'm using Qt and have some real basic problems. I have created my own widget MyTest that have a variable obj. I need to set this variable obj from an object outside of the widget so that the variable is copied not just a pointer to another object. I get an error message and can't figure out how to do this basic stuff. This is the code I'm using: MyTest.h: class MyTest : public QWidget { Q_OBJECT public: void setObj(QObject &inobj); QObject obj; .... } MyTest.cpp: void MyTest::setObj(QObject &inobj) { obj = inobj; //HERE I get the error message: "illegal access from 'QObject' to protected/private member 'QObject::operator=(const QObject &)'" } main.cpp: int main(int argc, char *argv[]) { QApplication a(argc, argv); QObject *ob = new QObject(); MyTest w; w.setObj(*ob); } Thanks for your help!

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• How to make Databinding type safe and support refactoring

  - by Ian Ringrose

  When I wish to bind a control to a property of my object, I have to provide the name of the property as a string. This is not very good because: If the property is removed or renamed, I don’t get a compiler warning. If a rename the property with a refactoring tool, it is likely the data binding will not be updated. I don’t get an error until runtime if the type of the property is wrong, e.g. binding an integer to a date chooser. Is there a design-paten that gets round this, but still has the ease of use of data-binding? (This is a problem in WinForm, Asp.net and WPF and most likely lots of other systems) I have now found "workarounds for nameof() operator in C#: typesafe databinding" that also has a good starting point for a solution.

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• How do I remove a USB drive's write protection?

  - by nate

  I have a SanDisk Cruser Blade USB stick that suddenly seems to be write protected. I tried running DiskPart but after I write the command "attributes disk clear readonly" it displays this: Microsoft DiskPart version 5.1.3565 ADD - Add a mirror to a simple volume. ACTIVE - Marks the current basic partition as an active boot partition. ASSIGN - Assign a drive letter or mount point to the selected volume. BREAK - Break a mirror set. CLEAN - Clear the configuration information, or all information, off the disk. CONVERT - Converts between different disk formats. CREATE - Create a volume or partition. DELETE - Delete an object. DETAIL - Provide details about an object. EXIT - Exit DiskPart EXTEND - Extend a volume. HELP - Prints a list of commands. IMPORT - Imports a disk group. LIST - Prints out a list of objects. INACTIVE - Marks the current basic partition as an inactive partition. ONLINE - Online a disk that is currently marked as offline. REM - Does nothing. Used to comment scripts. REMOVE - Remove a drive letter or mount point assignment. REPAIR - Repair a RAID-5 volume. RESCAN - Rescan the computer looking for disks and volumes. RETAIN - Place a retainer partition under a simple volume. SELECT - Move the focus to an object. It's like when you type help at the DiskPart prompt, so how do I get past this? This problem started when I plugged the stick into a laptop which had viruses, if that's any help.

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• R: ggplot2, how to add a number of layers to a plot at once to reduce code

  - by John

  library(ggplot2) This code produces a nice looking plot: qplot(cty, hwy, data = mpg, colour = displ) + scale_y_log2() + labs(x="x axis") + labs(y="y axis") + opts(title = "my title") But I want to setup variables to try and to reduce code repetition: log_scale <- scale_y_log2() xscale <- labs(x="x axis") yscale <- labs(y="y axis") title <- opts(title = "my title") my_scales <- c(log_scale, xscale, yscale, title) # make a variable to hold the scale info changes above So that I can do this and add a bunch of things at the same time: qplot(cty, hwy, data = mpg, colour = displ) + my_scales # add these to your plot. but I get this error: Error in object$class : $ operator is invalid for atomic vectors I realize that the things going into my_scales need to be layers / different types of objects, but I don't see what they should be.

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• Can Xen be configured to dedicate only one port of a dual-port NIC to a domU?

  - by jamieb

  I'm using CentOS 5.4 on my dom0 with a stock Xen kernel. I'm attempting to use the pciback module to hide some of the Ethernet ports from the host and reserve them for a domU I intend to use for a firewall (process described here). However, when I launch the domU, I get the following error message: Using config file "/etc/xen/firewall". Error: pci: improper device assignment specified: pci: 0000:01:04.0 must be co-assigned to the same guest with 0000:01:06.0, but it is not owned by pciback. lspci gives me the following output: 00:00.0 Host bridge: Intel Corporation 82945G/GZ/P/PL Memory Controller Hub (rev 02) 00:02.0 VGA compatible controller: Intel Corporation 82945G/GZ Integrated Graphics Controller (rev 02) 00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI Controller #1 (rev 01) 00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI Controller #2 (rev 01) 00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI Controller #3 (rev 01) 00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI Controller #4 (rev 01) 00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI Controller (rev 01) 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev e1) 00:1f.0 ISA bridge: Intel Corporation 82801GB/GR (ICH7 Family) LPC Interface Bridge (rev 01) 00:1f.2 IDE interface: Intel Corporation 82801GB/GR/GH (ICH7 Family) SATA IDE Controller (rev 01) 00:1f.3 SMBus: Intel Corporation 82801G (ICH7 Family) SMBus Controller (rev 01) 01:04.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10) 01:06.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10) 01:07.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10) From the sound of the error message, it seems like I also need to dedicate eth0 (PCI ID 01:04.0) to the domU. Am I correct? If not, what am I doing wrong? Thanks!

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• Error while excuting a simple boost thread program

  - by Eternal Learner

  Hi All, Could you tell mw what is the problem with the below boost::thread program #include<iostream> #include<boost/thread/thread.hpp> boost::mutex mutex; class A { public: A() : a(0) {} void operator()() { boost::mutex::scoped_lock lock(mutex); } private: int a; }; int main() { boost::thread thr1(A()); boost::thread thr2(A()); thr1.join(); thr2.join(); } I get the error message: error: request for member 'join' in 'thr1', which is of non-class type 'boost::thread()(A ()())' BoostThread2.cpp:30: error: request for member 'join' in 'thr2', which is of non-class type 'boost::thread ()(A ()())'

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• Vanishing Windows Desktop Shortcut Keys

  - by Henry Keiter

  The Situation Like you, I have many applications that I like to open. I've set up keyboard shortcuts for the most common, by placing a link on the desktop and setting its Shortcut Key property: This is all fine and dandy, most of the time. When I want to bring up the GIMP, I press Ctrl+Alt+G and the GIMP launches. Lovely. The Problem Sometimes--perhaps once a month per desktop shortcut--the shortcut key assignment simply vanishes. I press Ctrl+Alt+G and nothing happens, so I go check the shortcut and see that lo and behold: nothing is there. This happens regularly to all my shortcuts (not all at once). It doesn't matter what keys I assign, and there doesn't seem to be any correlation with particular applications being open or anything of that sort. This has happened on every Windows XP machine I've ever used with any regularity. Obviously what makes this issue particularly obnoxious is that it's not easily reproducible. I have searched long and hard for a solution for (or at least acknowledgement of) this problem, to no avail, so hopefully you guys know something that I don't. I did find this question, where the answers are all basically "use a third-party app", but as far as I could tell that was a slightly different issue, related to Explorer being busy. If the solution for this turns out to be the same, fine, but I'd prefer a native fix if at all possible. Note: I've tagged this with Windows in general because I seem to remember it happening on Windows 7 as well as XP, but I rarely notice it because I use the start-menu search in preference to desktop shortcuts.

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• varchar comparison in SQL Server

  - by Ram

  I am looking for some SQL varchar comparison function like C# string.compare (we can ignore case for now, should return zero when the character expression are same and a non zero expression when they are different) Basically I have some alphanumeric column in one table which needs to be verified in another table. I cannot do select A.col1 - B.col1 from (query) as "-" operator cannot be applied on character expressions I cannot cast my expression as int (and then do a difference/subtraction) as it fails select cast ('ASXT000R' as int) Conversion failed when converting varchar 'ASXT000R' to int Soundex would not do it as soundex is same for 2 similar strings Difference would not do it as select difference('abc','ABC') = 4 (as per msdn, difference is the difference in the soundex of 2 character expressions and difference =4 implies least different) Is there any other way of doing it ?

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• LINQ Quicksort is Unstable Except When Cascading

  - by Mystagogue

  On page 64 of "LINQ To Objects Using C# 4.0" (Tony Magennis) he states that LINQ's quicksort ordering algorithm is unstable... ...although this is simply solved by cascading the result into a ThenBy or ThenByDescending operator. Huh? Why would cascading an unstable sortation into another sortation fix the result? In fact, I'd say that isn't possible. The original order, once passed through an unstable sort, is simply lost. What am I missing here?

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• Dynamically allocated structure and casting.

  - by Simone Margaritelli

  Let's say I have a first structure like this: typedef struct { int ivalue; char cvalue; } Foo; And a second one: typedef struct { int ivalue; char cvalue; unsigned char some_data_block[0xFF]; } Bar; Now let's say I do the following: Foo *pfoo; Bar *pbar; pbar = new Bar; pfoo = (Foo *)pbar; delete pfoo; Now, when I call the delete operator, how much memory does it free? sizeof(int) + sizeof(char) Or sizeof(int) + sizeof(char) + sizeof(char) * 0xFF ? And if it's the first case due to the casting, is there any way to prevent this memory leak from happening? Note: please don't answer "use C++ polymorphism" or similar, I am using this method for a reason.

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• RRAS with DHCP when the IP pool is on a different subnet

  - by John B

  I run a small business network and the last couple of days I have been setting up some equipment to add VPN capabilities to our network. I've got the following set up: Windows 2008 R2 with RRAS - 172.22.200.50 Cisco RV082 router - 172.22.100.1 / 172.22.200.1 The Cisco router only support DHCP on a single class C network; 172.22.100.0/24. On the Cisco router I have set up an additional subnet; 172.22.200.0/24. The DHCP range is 172.22.100.200-254 When a PPTP connection comes in to the router, it is forwarded to my RRAS at 172.22.200.50. If I configure RRAS to assign IPs from a static pool on the 172.22.200.0/24 subnet everything works fine except the DNS suffix / search domain. However, if I set RRAS to use DHCP I am no longer able to contact any devices on the network. The IP I receive is on a different subnet (172.22.100.0/24). Is it possible to still use DHCP as the method of ip assignment in RRAS, even when the IP adresses assigned are in a different subnet? If yes, what piece of configuration am I missing to fix the VPN connection issues mentioned in the paragraph above. The reason I want RRAS with DHCP to work is because from what I have understood, this is the "only" way to hand out a DNS suffix to VPN clients. Any help on this matter is greatly appreciated!

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• n++ vs n=n+1. Which one is faster

  - by piemesons

  Somebody asked me Is n++ faster than n=n+1? My answer:-- ++ is a unary operator in C which(n++) takes only one machine instruction to execute while n=n+1 takes more than one machine instructions to execute. Anyone correct me if I am wrong, but in Assembler it take something like this: n++: inc n n = n + 1; mov ax n add ax 1 mov n ax its not exactli this, but it's near it.but in most cases a good compiler will change n = n + 1 to ++n.So A good compiler will generate same code for both and hence the same time to execute.

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• Ruby RegEx not matching valid expression

  - by Matthew Carriere

  I have the following expression: ^\w(\s(+|-|\/|*)\s\w)*$ This simply looks to match a mathematical expression, where a user is prompted for terms separated by basic operators (ex: price + tax) The user may enter more than just 2 terms and one operator (ex: price + tax + moretax) I tested this expression in Rubular http://rubular.com/ With the terms: a + a (MATCH) a + a + a (MATCH) a + a + a + a a a + a a Everything works, but when I use it in Ruby it does not work! expression =~ /^\w(\s(+|-|\/|*)\s\w)*$/ I started picking the expression apart and noticed that if I remove the start of line caret it finds matches but isn't correct. a + a (MATCH) a a (MATCH) <-- this is not correct Why is this expression not working in Ruby code? (I am using Ruby 1.8.7 p174)

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• How does this C# asp.net random password code work?

  - by quakkels

  Hello all, I'm new to .NET and C# and I'm trying to figure out how this code works: public static string CreateRandomPassword(int PasswordLength) { String _allowedChars = "abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWXYZ23456789"; Byte[] randomBytes = new Byte[PasswordLength]; RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetBytes(randomBytes); char[] chars = new char[PasswordLength]; int allowedCharCount = _allowedChars.Length; for(int i = 0;i<PasswordLength;i++) { /// /// I don't understand how this line works: /// chars[i] = _allowedChars[(int)randomBytes[i] % allowedCharCount]; } return new string(chars); } I think I've got a pretty good handle on most of this. I haven't been able to understand the following line: chars[i] = _allowedChars[(int)randomBytes[i] % allowedCharCount]; I understand that the code generates random binary numbers and uses those random numbers in the for loop to select a character from the _allowedChars string. What I don't get is why this code uses the modulous operator (%) to get the _allowedChars index value. Thanks for any help

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• Is Unix not a PC Operating System?

  - by Corelgott

  I am doing my Bachelor at a university. In a written assignment the professor posted the task: "Name 3 PC-Operating Systems". Well, I went on an included a variety of OS (Linux, Windows, OSx) including Unix & Solaris. Today I recieved a mail from my prof saying: Unix is not a PC-Operating System. Many Unix-variants are not PC-hardware compatible (like AIX & HP-UX. About Solaris: there was one PC-compatible version...) I am kind of suprised: Even if may Unix-variants are Power-PC and different bit-order – Those don't stop being PCs now, right? The question was given in a written assigment! It was not a question that came up during lecture! Due to the original task being in German, I'll include it just to make sure nobody suspects an error in the translation. Frage: Nennen Sie 3 PC-Betriebssysteme. Antwort: Unix ist kein PC-Betriebssystem, viele Unix-Varianten sind nicht auf PC-Hardware lauffähig (AIX, HP-UX). Von Solaris gab es mal eine PC-Variante.

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• Creating a Rails query from a hash of user input

  - by Jamie

  I'm attempting to create a fairly complex search engine for a project using a variable number of search criteria. The user input is sorted into an array of hashes. The hashes contain the following information: { :column => "", :value => "", :operator => "", # Such as: =, !=, <, >, etc. :and_or => "", # Two possible values: "and" and "or" } How can I loop through this array and use the information in these hashes to make an ActiveRecord WHERE query?

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• Help using Horner's rule and Hash Functions in JAVA?

  - by Matt

  I am trying to use Horner's rule to convert words to integers. I understand how it works and how if the word is long, it may cause an overflow. My ultimate goal is to use the converted integer in a hash function h(x)=x mod tableSize. My book suggests, because of the overflow, you could "apply the mod operator after computing each parenthesized expression in Horner's rule." I don't exactly understand what they mean by this. Say the expression looks like this: ((14*32+15)*32+20)*32+5 Do I take the mod tableSize after each parenthesized expression and add them together? What would it look like with this hash function and this example of Horner's rule?

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• Implement functionality in PHP?

  - by Rachel

  How can we Implement Bisect Python functionality in PHP Implement function bisect_left($arr, $item); as a pure-PHP routine to do a binary-bisection search for the position at which to insert $item into $list, maintaining the sort order therein. Assumptions: Assume that $arr is already sorted by whatever comparisons would be yielded by the stock PHP < operator, and that it's indexed on ints. The function should return an int, representing the index within the array at which $item would be inserted to maintain the order of the array. The returned index should be below any elements in $arr equal to $item, i.e., the insertion index should be "to the left" of anything equal to $item. Search routine should not be linear! That is, it should honor the name, and should attempt to find it by iteratively bisecting the list and comparing only around the midpoint.

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• Optimal method to create a large string containing several variables?

  - by Runcible

  I want to create a string that contains many variables: std::string name1 = "Frank"; std::string name2 = "Joe"; std::string name3 = "Nancy"; std::string name4 = "Sherlock"; std::string sentence; sentence = name1 + " and " + name2 + " sat down with " + name3; sentence += " to play cards, while " + name4 + " played the violin."; This should produce a sentence that reads Frank and Joe sat down with Nancy to play cards, while Sherlock played the violin. My question is: What is the optimal way to accomplish this? I am concerned that constantly using the + operator is ineffecient. Is there a better way?

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• How to model a social news feed on Google App Engine

  - by PEZ

  We want to implement a "News feed" where a user can see messages broadcasted by her friends, sorted with newest message first. But the feed should reflect changes in her friends list. (If she adds new friends, messages from those should be included in the feed, and if she removes friends their messages should not be included.) If we use the pubsub-test example and attach a recipient list to each message this means a lot of manipulation of the message recipients lists when users connect and disconnect friends. We first modeled publish-subscribe "fan out" using conventional RDBMS thinking. It seemed to work at first, but then, since the IN operator works the way it does, we quickly realized we couldn't continue on that path. We found Brett Slatkin's presentation from last years Google I/O and we have now watched it a few times but it isn't clear to us how to do it with "dynamic" recipient lists. What we need are some hints on how to "think" when modeling this.

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