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• Is there any way to force my Linux box to always boot up with a self-assigned IP address?

  - by Jeremy Friesner

  This is perhaps an unusual request: I'm trying to get a Debian Linux box to always give itself a self-assigned IP address (i.e. 169.254.x.y) on boot. In particular, I want it to do that even when there is a DHCP server present on the LAN. That is, it should not request an IP address from the DHCP server. From what I can see in the "man interfaces" text, there is an option for "manual", and an option for "dhcp". Manual assignment won't do, since I need multiple boxes to work on the same LAN without requiring any manual configuration... and "dhcp" does what I want, but only if there is no DHCP server on the LAN. (A requirement is that the functionality of these boxes should not be affected by the presence or absence of a DHCP server). Is there a trick that I can use to get this behavior? EDIT: By "no manual configuration", I mean that I should be able to take this box (headless) to any LAN anywhere, plug in the Ethernet cable, and have it do its thing. I shouldn't have to ssh to the box and edit files to get it working each time it is moved to a different LAN.

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• C# : Number Conversion Problem

  - by Sayem Ahmed

  Today I faced a strange problem in C#. I have an ASP.NET page where user can enter certain price, quantity etc. I get the price value, convert it to double, then multiply it with 100 and then typecast it to an integer. When the price is "33.30", after converting it to double it remains 33.3 (obviously...), but after multiplying it with 100, it becomes 3329.9999999999995, and when I cast it to integer by applying simple cast operator "(int) (price * 100) ", it becomes 3329. Right now I have no idea why this is happening. So I thought may be you guys can help :) .

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• DataSet with many OR clauses

  - by Silvan

  Hello :) I've got a little problem with a query which I create in the Visual Studio Designer. I need a query with a lot of 'OR'-clauses for the same column. I found the operator 'IN', but I don't know how to use that in the Visual Studio Designer: Example IN: SELECT EmployeeID, FirstName, LastName, HireDate, City FROM Employees WHERE City IN ('Seattle', 'Tacoma', 'Redmond') I tried to do it in this way: SELECT [MachineryId], [ConstructionSiteId], [DateTime], [Latitude], [Longitude], [HoursCounter] FROM [PositionData] WHERE [MachineryID] IN @MachineryIDs But this doesn't work. Is there another way to handle a lot of OR clauses? Thank you very much for your help.

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• Pointing to vectors

  - by Matt Munson

  #include <iostream> #include <vector> using namespace std; int main () { vector <int> qwerty; qwerty.push_back(5); vector <int>* p = &qwerty; cout << p[0]; //error: no match for 'operator<<' in 'std::cout << * p' } I'm generally unclear on how to use pointers with vectors, so I'm pretty mystified as to why this is not working. To my mind, this should print 5 to screen.

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• Consing lists with user-defined type in Haskell

  - by user1319603

  I have this type I defined myself: data Item = Book String String String Int -- Title, Author, Year, Qty | Movie String String String Int -- Title, Director, Year, Qty | CD String String String Int deriving Show -- Title, Artist, Year, Qty I've created an empty list all_Items = [] With the following function I am trying to insert a new book of type Item (Book) into the all_Items addBook all_Items = do putStrLn "Enter the title of the book" tit <- getLine putStrLn "Enter the author of the book" aut <- getLine putStrLn "Enter the year this book was published" yr <- getLine putStrLn "Enter quantity of copies for this item in the inventory" qty <- getLine Book tit aut yr (read qty::Int):all_Items return(all_Items) I however am receiving this error: Couldn't match expected type `IO a0' with actual type `[a1]' The error points to the line where I am using the consing operator to add the new book to the list. I can gather that it is a type error but I can't figure out what it is that I am doing wrong and how to fix it. Thanks in Advance!

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• rails - Redirecting console output to a file

  - by egarcia

  On a bash console, if I do this: cd mydir ls -l > mydir.txt The operator captures the standard input and redirects it to a file; so I get the listing of files in mydir.txt instead of in the standard output. Is there any way to do something similar on the rails console? I've got a ruby statement that generates lots of prints (~8k lines) and I'd like to be able to see it completely, but the console only "remembers" the last 1024 lines or so. So I thought about redirecting to a file - If anyone knows a better option, I'm all ears.

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• visual studio intellisense error

  - by rakkarage

  template <typename T> class Test { friend Test<T> & operator * (T lhs, const Test<T> & rhs) { Test<T> r(rhs); // return r *= lhs; } } 4 IntelliSense: identifier "T" is undefined why is T defined on line 3 but not line 4? i mean i guess its not a real error just an intellisense error... it works anyway but is there something wrong? can i fix it? or remove the red squiggles somehow? thanks i am using visual studio 2010... i wonder if this happens in other versions as well?

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• different explanation

  - by Delirium tremens

  The following code echoes 5, not 10: $global_obj = null; class my_class { var $value; function my_class() { global $global_obj; $global_obj = &$this; } } $a = new my_class; $a->my_value = 5; $global_obj->my_value = 10; echo $a->my_value; "Upon first examination, it would seem that the constructor of my_class stores a reference to itself inside the $global_obj variable. Therefore, one would expect that, when we later change the value of $global_obj-my_value to 10, the corresponding value in $a would change as well. Unfortunately, the new operator does not return a reference, but a copy of the newly created object." Please, give me a different explanation.

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• C++ Urban Myths

  - by Neil Butterworth

  I'm starting to write an article on what I'm calling "C++ Urban Myths" - that is, ideas and conceptions about C++ that are common but have no actual roots in reality. Some that I've come up with so far are: TR1 is part of standard C++ TR1 (technical Report #1) proposed a whole bunch of changes to C++. Unfortunately, it was never accepted. It is faster to use iterators to access a vector than operator[] Or vice versa. All tests I've carried out indicate the two are nearly identical in performance. The C++ Standard contains something called the STL It doesn't - neither "STL" nor "Standard Template Library" appear in the Standard. I'm wondering if the SO C++ community can come up with any better ones? Ideally, they should be expressible in a single sentence, and not involve any code. Edit: I guess I didn't make it clear enough that I was interested in myths believed by C++ developers, not misconceptions held by non-C++users. Oh well...

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• How does Hibernate detect dirty state of an entity object?

  - by ???'Lenik

  Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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• SQL vs MySQL: Rules about aggregate operations and GROUP BY

  - by Phazyck

  In this book I'm currently reading while following a course on databases, the following example of an illegal query using an aggregate operator is given: Find the name and age of the oldest sailor. Consider the following attempt to answer this query: SELECT S.name, S.age FROM Sailors.S The intent is for this query to return not only the maximum age but also the name of the sailors having that age. However, this query is illegal in SQL--if the SELECT clause uses an aggregate operation, then it must use only aggregate operations unless the query contains a GROUP BY clause! Some time later while doing an exercise using MySQL, I faced a similar problem, and made a mistake similar to the one mentioned. However, MySQL didn't complain and just spit out some tables which later turned out not be what I needed. Is the query above really illegal in SQL, but legal in MySQL, and if so, why is that? In what situation would one need to make such a query?

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• functor returning 0

  - by Jon

  I've recently started teaching myself the standard template library. I was curious as to why the GetTotal() method in this class is returning 0? ... class Count { public: Count() : total(0){} void operator() (int val){ total += val;} int GetTotal() { return total;} private: int total; }; void main() { set<int> s; Count c; for(int i = 0; i < 10; i++) s.inset(i); for_each(s.begin(), s.end(), c); cout << c.GetTotal() << endl; }

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• error: typedef name may not be a nested-name-specifier

  - by Autopulated

  I am trying to do something along the lines of this answer, and struggling: $ gcc --version gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu4) file.cpp:7: error: template argument 1 is invalid file.cpp:7: error: typedef name may not be a nested-name-specifier And the offending part of the file: template <class R, class C, class T0=void, class T1=void, class T2=void> struct MemberWrap; template <class R, class C, class T0> struct MemberWrap<R, C, T0>{ typedef R (C::*member_t)(T0); typedef typename boost::add_reference<typename T0>::type> TC0; // <---- offending line MemberWrap(member_t f) : m_wrapped(f){ } R operator()(C* p, TC0 p0){ GILRelease guard; return (p->*(this->m_wrapped))(p0); } member_t m_wrapped; };

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• What is Ruby's double-colon (::) all about?

  - by Meltemi

  I'd probably be able to answer this for myself if "::" wasn't so hard to Google. Didn't see anything on SO so thought I'd try my luck. What is this double-colon :: all about? I see it everywhere in Rails: class User < ActiveRecord::Base or… ActionController::Routing::Routes.draw do |map| I found a definition from this guy: The :: is a unary operator that allows: constants, instance methods and class methods defined within a class or module, to be accessed from anywhere outside the class or module. but that just leads to more questions. What good is scope (private, protected) if you can just use :: to expose anything?

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• If-statement with logical OR

  - by exiter2000

  public class Test{ public static void main(String args[]){ int a = 0; int b = 1; int c = 10; if ( a == 0 || b++ == c ){ a = b + c; }else{ b = a + c; } System.out.println("a: " + a + ",b: " + b + ",c: " + c); } } Ok, this is Java code and the output is a: 11,b: 1,c: 10 And I believe the C acts same as Java in this case That is because second condition(b++ == c) would never executed if the first condition is true in 'OR' operator. There is a "NAME" for this. I just don't remember what it is. Does anyone know what this is called?? Thanks in advance

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• CompareValidator works in listview's editItemTemplate but not in insertitemtemplate

  - by Sam

  Hi, I have a validation problem I have a listview, in the edit item template I have two composite controls with a textbox inside I put a comparevalidator on it <asp:CompareValidator ID="myCompareValidator" runat="server" ControlToValidate="mycompositecontrol1" ControlToCompare="mycompositecontrol2" Operator="GreaterThanEqual" Type="Date" Display="Dynamic" ErrorMessage="there is an error !" Text="!" ValidationGroup="myValidationGroup" /> It works great ! so I do exactly the same operation in the InserItemTemplate (It's a copy/paste) but this time, it doesn't work, I have no error message in my validationsummary and near my control to validate! If you know that problem, help me please thanks in advance

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• LINQ-to-SQL: Searching against a CSV

  - by Peter Bridger

  I'm using LINQtoSQL and I want to return a list of matching records for a CSV contains a list of IDs to match. The following code is my starting point, having turned a CSV string in a string array, then into a generic list (which I thought LINQ would like) - but it doesn't: Error Error 22 Operator '==' cannot be applied to operands of type 'int' and 'System.Collections.Generic.List<int>' C:\Documents and Settings\....\Search.cs 41 42 C:\...\ Code DataContext db = new DataContext(); List<int> geographyList = new List<int>( Convert.ToInt32(geography.Split(',')) ); var geographyMatches = from cg in db.ContactGeographies where cg.GeographyId == geographyList select new { cg.ContactId }; Where do I go from here?

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• HASHREF in Perl

  - by Uri

  I'm trying to decrypt a Perl code which I'm not familiar with, somehow related to HashRef. I'm using Amazon::S3, but my question is a general Perl question. See the code below: use Amazon::S3; my $s3 = Amazon::S3-new( ... ); my $response = $s3-buckets; Documentation (here) sais, about s3-buckets: Returns undef on error, else HASHREF of results The following line is working for me, but I don't understand why: for $b in ( @ { $response-{buckets} } ) { print "bucket: " . $b-bucket . "\n"; } I'm buzzled by each operator on the first line. What type exactly are $response, $respone-{bucket}. Looks like the expression within the 'for' is an array, but I don't understand this syntax: @{ ... }?

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• Prolog for beginners about logic and syntax

  - by lnotik

  Hello everybody. I have this question : I need to create a paradict "rightGuesses" which will get 3 arguments , each one of them is a list of letters : 1) The list of guessed letters 2) The word i have to guess 3) The letters that where guessed so far . for example : rightGuesses([n,o,p,q], [p,r,o,l,o,g], Ans). will give us Ans = [p, -, o, -, o, -]. i made: rightGuesses([],T2,[ANS]) rightGuesses([A|T1],T2,[ANS]):- (member(A,T2))=\=true , rightGuesses(T1,T2,[ _ |'-']). rightGuesses([A|T1],T2,[ANS]):- member(A,T2), rightGuesses(T1,T2,[ _ |A]). but i get : ERROR: c:/users/leonid/desktop/file3.pl:5:0: Syntax error: Operator expected Warning: c:/users/leonid/desktop/file3.pl:6: when i trying to compile it what is my problem , and is there is a better way to do it ? thanks in advance.

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• Multiplying complex with constant in C++

  - by Atilla Filiz

  The following code fails to compile #include <iostream> #include <cmath> #include <complex> using namespace std; int main(void) { const double b=3; complex <double> i(0, 1), comp; comp = b*i; comp=3*i; return 0; } with error: no match for ‘operator*’ in ‘3 * i’ What is wrong here, why cannot I multiply with immediate constants?

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• Is this a correct implementation of singleton C++?

  - by Kamal

  class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); // Not Implemented A& operator=(A const& copy); // Not Implemented static A* pA; }; A* A::pA = NULL;

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• How do I handle editing of custom types in a C# datagridview?

  - by Ian Hopkinson

  I have a datagridview in which one column contains a custom class, which I have set using: dgvPeriods.Columns[1].ValueType = typeof(ExDateTime); It is rigged up to display correctly by handling the CellFormatting event, but I'm unsure what event to handle for cell editing. In the absence of doing anything I get a FormatException as the datagridview tries to convert String to ExDateTime as I try to move focus out of the edited cell. I tried adding type conversion to my ExDateTime custom class: public static implicit operator ExDateTime(string b) { return new ExDateTime(b); } But this this didn't work. I also tried handling the DataError event, but this seems to fire too late. The datagridview is not databound.

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• Is there an existing algorithm for this notation translation/conversion?

  - by John

  A system has a notation that would require writing an expression like (A+B)*C as #MUL(#ADD(A,B),C). Is there already an algorithm to do this kind of notation conversion so users can enter in a more conventional way? In other words an algorithm to convert from infix - my notation. First issue is I don't know an exact name for my notation... it's similar to reverse-polish but not quite. Every operator is encoded as a function taking arguments.

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• logfile deleted on Oracle database how to re-create it?

  - by Daniel

  for my database assignment we were looking into 'database corruption' and I was asked to delete the second redo log file which I have done with the command: rm log02a.rdo this was in the $HOME/ORADATA/u03 directory. Now I started up my database using startup pfile=$PFILE nomount then I mounted it using the command alter database mount; now when I try to open it alter database open; it gives me the error: ORA-03113: end-of-file on communication channel Process ID: 22125 Session ID: 25 Serial number: 1 I am assuming this is because the second redo log file is missing. There is still log01a.rdo, but not the one I have deleted. How can I go about recovering this now so that I can open my database again? I have looked into the database created scripts, and it specified the log02a.rdo file to be size 10M and part of group 2. If I do select group#, member from v$logfile; I get: 1 /oradata/student_db/user06/ORADATA/u03/log01a.rdo 2 /oradata/student_db/user06/ORADATA/u03/log02a.rdo 3 /oradata/student_db/user06/ORADATA/u03/log03a.rdo 4 /oradata/student_db/user06/ORADATA/u03/log04a.rdo So it is part of group 2. If I try to add the log02a.rdo file again "already part of the database". If I drop group 2 and then add it again with these commands: ALTER DATABASE ADD LOGFILE GROUP 2 ('$HOME/ORADATA/u03/log02a.rdo') SIZE 10M; Nothing. Supposedly alters the database, but it still won't start up. Any ideas what I can do to re-create this and be able to open my database again?

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• CUDA & VS2010 problem

  - by Kristian D'Amato

  I have scoured the internets looking for an answer to this one, but couldn't find any. I've installed the CUDA 3.2 SDK (and, just now, CUDA 4.0 RC) and everything seems to work fine after long hours of fooling around with include directories, NSight, and all the rest. Well, except this one thing: it keeps highlighting the <<< >>> operator as a mistake. Only on VS2010--not on VS2008. On VS2010 I also get several warnings of the following sort: C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\xdebug(109): warning C4251: 'std::_String_val<_Ty,_Alloc>::_Alval' : class 'std::_DebugHeapAllocator<_Ty>' needs to have dll-interface to be used by clients of class 'std::_String_val<_Ty,_Alloc>' Anyone know how this can be fixed?

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