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• Copy constructor bug

  - by user168715

  I'm writing a simple nD-vector class, but am encountering a strange bug. I've stripped out the class to the bare minimum that still reproduces the bug: #include <iostream> using namespace std; template<unsigned int size> class nvector { public: nvector() {data_ = new double[size];} ~nvector() {delete[] data_;} template<unsigned int size2> nvector(const nvector<size2> &other) { data_ = new double[size]; int i=0; for(; i<size && i < size2; i++) data_[i] = other[i]; for(; i<size; i++) data_[i] = 0; } double &operator[](int i) {return data_[i];} const double&operator[](int i) const {return data_[i];} private: const nvector<size> &operator=(const nvector<size> &other); //Intentionally unimplemented for now double *data_; }; int main() { nvector<2> vector2d; vector2d[0] = 1; vector2d[1] = 2; nvector<3> vector3d(vector2d); for(int i=0; i<3; i++) cout << vector3d[i] << " "; cout << endl; //Prints 1 2 0 nvector<3> other3d(vector3d); for(int i=0; i<3; i++) cout << other3d[i] << " "; cout << endl; //Prints 1 2 0 } //Segfault??? On the surface this seems to work fine, and both tests print out the correct values. However, at the end of main the program crashes with a segfault, which I've traced to nvector's destructor. At first I thought the (incorrect) default assignment operator was somehow being called, which is why I added the (currently) unimplemented explicit assignment operator to rule this possibility out. So my copy constructor must be buggy, but I'm having one of those days where I'm staring at extremely simple code and just can't see it. Do you guys have any ideas?

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• factory class, wrong number of arguments being passed to subclass constructor

  - by Hugh Bothwell

  I was looking at Python: Exception in the separated module works wrong which uses a multi-purpose GnuLibError class to 'stand in' for a variety of different errors. Each sub-error has its own ID number and error format string. I figured it would be better written as a hierarchy of Exception classes, and set out to do so: class GNULibError(Exception): sub_exceptions = 0 # patched with dict of subclasses once subclasses are created err_num = 0 err_format = None def __new__(cls, *args): print("new {}".format(cls)) # DEBUG if len(args) and args[0] in GNULibError.sub_exceptions: print(" factory -> {} {}".format(GNULibError.sub_exceptions[args[0]], args[1:])) # DEBUG return super(GNULibError, cls).__new__(GNULibError.sub_exceptions[args[0]], *(args[1:])) else: print(" plain {} {}".format(cls, args)) # DEBUG return super(GNULibError, cls).__new__(cls, *args) def __init__(self, *args): cls = type(self) print("init {} {}".format(cls, args)) # DEBUG self.args = args if cls.err_format is None: self.message = str(args) else: self.message = "[GNU Error {}] ".format(cls.err_num) + cls.err_format.format(*args) def __str__(self): return self.message def __repr__(self): return '{}{}'.format(type(self).__name__, self.args) class GNULibError_Directory(GNULibError): err_num = 1 err_format = "destination directory does not exist: {}" class GNULibError_Config(GNULibError): err_num = 2 err_format = "configure file does not exist: {}" class GNULibError_Module(GNULibError): err_num = 3 err_format = "selected module does not exist: {}" class GNULibError_Cache(GNULibError): err_num = 4 err_format = "{} is expected to contain gl_M4_BASE({})" class GNULibError_Sourcebase(GNULibError): err_num = 5 err_format = "missing sourcebase argument: {}" class GNULibError_Docbase(GNULibError): err_num = 6 err_format = "missing docbase argument: {}" class GNULibError_Testbase(GNULibError): err_num = 7 err_format = "missing testsbase argument: {}" class GNULibError_Libname(GNULibError): err_num = 8 err_format = "missing libname argument: {}" # patch master class with subclass reference # (TO DO: auto-detect all available subclasses instead of hardcoding them) GNULibError.sub_exceptions = { 1: GNULibError_Directory, 2: GNULibError_Config, 3: GNULibError_Module, 4: GNULibError_Cache, 5: GNULibError_Sourcebase, 6: GNULibError_Docbase, 7: GNULibError_Testbase, 8: GNULibError_Libname } This starts out with GNULibError as a factory class - if you call it with an error number belonging to a recognized subclass, it returns an object belonging to that subclass, otherwise it returns itself as a default error type. Based on this code, the following should be exactly equivalent (but aren't): e = GNULibError(3, 'missing.lib') f = GNULibError_Module('missing.lib') print e # -> '[GNU Error 3] selected module does not exist: 3' print f # -> '[GNU Error 3] selected module does not exist: missing.lib' I added some strategic print statements, and the error seems to be in GNULibError.__new__: >>> e = GNULibError(3, 'missing.lib') new <class '__main__.GNULibError'> factory -> <class '__main__.GNULibError_Module'> ('missing.lib',) # good... init <class '__main__.GNULibError_Module'> (3, 'missing.lib') # NO! ^ why? I call the subclass constructor as subclass.__new__(*args[1:]) - this should drop the 3, the subclass type ID - and yet its __init__ is still getting the 3 anyway! How can I trim the argument list that gets passed to subclass.__init__?

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• Unity The parameter host could not be resolved when attempting to call constructor

  - by Terrance

  When I attempt to instantiate my instance of the base class I get the error: a ResolutionFailedException with roughly the following error "The parameter host could not be resolved when attempting to call constructor" I'm currently not using an Interface for the base type and my instance of the class is inheriting the base type class. I'm new to Unity and DI so I'm thinking its something I forgot possibly. ExeConfigurationFileMap map = new ExeConfigurationFileMap(); map.ExeConfigFilename = "Unity.Config"; Configuration config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None); UnityConfigurationSection section = (UnityConfigurationSection)config.GetSection("unity"); IUnityContainer container = new UnityContainer(); section.Containers.Default.Configure(container); //Throws exception here on this BaseCalculatorServer server = container.Resolve<BaseCalculatorServer>(); and the Unity.Config file <container> <types> <type name ="CalculatorServer" type="Calculator.Logic.BaseCalculatorServer, Calculator.Logic" mapTo="Calculator.Logic.CalculateApi, Calculator.Logic"/> </types> </container> </containers> The Base class using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.Serialization; using System.ServiceModel; using System.ServiceModel.Transactions; using Microsoft.Practices.Unity; using Calculator.Logic; namespace Calculator.Logic { public class BaseCalculatorServer : IDisposable { public BaseCalculatorServer(){} public CalculateDelegate Calculate { get; set; } public CalculationHistoryDelegate CalculationHistory { get; set; } /// <summary> /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources. /// </summary> public void Dispose() { this.Dispose(); } } } The Implementation using System; using System.Collections.Generic; using System.Linq; using System.Text; using Calculator.Logic; using System.ServiceModel; using System.ServiceModel.Configuration; using Microsoft.Practices.Unity; namespace Calculator.Logic { public class CalculateApi:BaseCalculatorServer { public CalculateApi(ServiceHost host) { host.Open(); Console.WriteLine("Press Enter To Exit"); Console.ReadLine(); host.Close(); } public CalculateDelegate Calculate { get; set; } public CalculationHistoryDelegate CalculationHistory { get; set; } } } Yes both base class and implementation are in the same Namespace and thats something design wise that will change once I get this working. Oh and a more detailed error Resolution of the dependency failed, type = "Calculator.Logic.BaseCalculatorServer", name = "". Exception message is: The current build operation (build key Build Key[Calculator.Logic.BaseCalculatorServer, null]) failed: The value for the property "Calculate" could not be resolved. (Strategy type BuildPlanStrategy, index 3)

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• Strange intermittent SQL connection error, fixes on reboot, comes back after 3-5 days (ASP.NET)

  - by Ryan

  For some reason every 3-5 days our web app loses the ability to open a connection to the db with the following error, the strange thing is that all we have to do is reboot the container (it is a VPS) and it is restored to normal functionality. Then a few days later or so it happens again. Has anyone ever had such a problem? I have noticed a lot of ANONYMOUS LOGONs in the security log in the middle of the night from our AD server which is strange, and also some from an IP in Amsterdam. I am not sure how to tell what exactly they mean or if it is related or not. Server Error in '/ntsb' Application. A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) Source Error: Line 11: Line 12: Line 13: dbConnection.Open() Line 14: Line 15: Source File: C:\Inetpub\wwwroot\includes\connection.ascx Line: 13 Stack Trace: [SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)] System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +248 System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) +245 System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, SqlConnection owningObject) +475 System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, Int64 timerExpire, SqlConnection owningObject) +260 System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String host, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, Int64 timerStart) +2445449 System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance) +2445144 System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance) +354 System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection) +703 System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnection owningConnection, DbConnectionPool pool, DbConnectionOptions options) +54 System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject) +2414696 System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject) +92 System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject) +1657 System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) +84 System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) +1645687 System.Data.SqlClient.SqlConnection.Open() +258 ASP.includes_connection_ascx.getConnection() in C:\Inetpub\wwwroot\includes\connection.ascx:13 ASP.default_aspx.Page_Load(Object sender, EventArgs e) in C:\Inetpub\wwwroot\Default.aspx:16 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +25 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +42 System.Web.UI.Control.OnLoad(EventArgs e) +132 System.Web.UI.Control.LoadRecursive() +66 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2428 Version Information: Microsoft .NET Framework Version:2.0.50727.3053; ASP.NET Version:2.0.50727.3053

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• How can I pipe two Perl CORE::system commands in a cross-platform way?

  - by Pedro Silva

  I'm writing a System::Wrapper module to abstract away from CORE::system and the qx operator. I have a serial method that attempts to connect command1's output to command2's input. I've made some progress using named pipes, but POSIX::mkfifo is not cross-platform. Here's part of what I have so far (the run method at the bottom basically calls system): package main; my $obj1 = System::Wrapper->new( interpreter => 'perl', arguments => [-pe => q{''}], input => ['input.txt'], description => 'Concatenate input.txt to STDOUT', ); my $obj2 = System::Wrapper->new( interpreter => 'perl', arguments => [-pe => q{'$_ = reverse $_}'}], description => 'Reverse lines of input input', output => { '>' => 'output' }, ); $obj1->serial( $obj2 ); package System::Wrapper; #... sub serial { my ($self, @commands) = @_; eval { require POSIX; POSIX->import(); require threads; }; my $tmp_dir = File::Spec->tmpdir(); my $last = $self; my @threads; push @commands, $self; for my $command (@commands) { croak sprintf "%s::serial: type of args to serial must be '%s', not '%s'", ref $self, ref $self, ref $command || $command unless ref $command eq ref $self; my $named_pipe = File::Spec->catfile( $tmp_dir, int \$command ); POSIX::mkfifo( $named_pipe, 0777 ) or croak sprintf "%s::serial: couldn't create named pipe %s: %s", ref $self, $named_pipe, $!; $last->output( { '>' => $named_pipe } ); $command->input( $named_pipe ); push @threads, threads->new( sub{ $last->run } ); $last = $command; } $_->join for @threads; } #... My specific questions: Is there an alternative to POSIX::mkfifo that is cross-platform? Win32 named pipes don't work, as you can't open those as regular files, neither do sockets, for the same reasons. 2. The above doesn't quite work; the two threads get spawned correctly, but nothing flows across the pipe. I suppose that might have something to do with pipe deadlocking or output buffering. What throws me off is that when I run those two commands in the actual shell, everything works as expected. Point 2 is solved; a -p fifo file test was not testing the correct file.

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• C++ templated factory constructor/de-serialization

  - by KRao

  Hi, I was looking at the boost serialization library, and the intrusive way to provide support for serialization is to define a member function with signature (simplifying): class ToBeSerialized { public: //Define this to support serialization //Notice not virtual function! template<class Archive> void serialize(Archive & ar) {.....} }; Moreover, one way to support serilization of derived class trough base pointers is to use a macro of the type: //No mention to the base class(es) from which Derived_class inherits BOOST_CLASS_EXPORT_GUID(Derived_class, "derived_class") where Derived_class is some class which is inheriting from a base class, say Base_class. Thanks to this macro, it is possible to serialize classes of type Derived_class through pointers to Base_class correctly. The question is: I am used in C++ to write abstract factories implemented through a map from std::string to (pointer to) functions which return objects of the desired type (and eveything is fine thanks to covariant types). Hover I fail to see how I could use the above non-virtual serialize template member function to properly de-serialize (i.e. construct) an object without knowing its type (but assuming that the type information has been stored by the serializer, say in a string). What I would like to do (keeping the same nomenclature as above) is something like the following: XmlArchive xmlArchive; //A type or archive xmlArchive.open("C:/ser.txt"); //Contains type information for the serialized class Base_class* basePtr = Factory<Base_class>::create("derived_class",xmlArchive); with the function on the righ-hand side creating an object on the heap of type Derived_class (via default constructor, this is the part I know how to solve) and calling the serialize function of xmlArchive (here I am stuck!), i.e. do something like: Base_class* Factory<Base_class>::create("derived_class",xmlArchive) { Base_class* basePtr = new Base_class; //OK, doable, usual map string to pointer to function static_cast<Derived_class*>( basePtr )->serialize( xmlArchive ); //De-serialization, how????? return basePtr; } I am sure this can be done (boost serialize does it but its code is impenetrable! :P), but I fail to figure out how. The key problem is that the serialize function is a template function. So I cannot have a pointer to a generic templated function. As the point in writing the templated serialize function is to make the code generic (i.e. not having to re-write the serialize function for different Archivers), it does not make sense then to have to register all the derived classes for all possible archive types, like: MY_CLASS_REGISTER(Derived_class, XmlArchive); MY_CLASS_REGISTER(Derived_class, TxtArchive); ... In fact in my code I relies on overloading to get the correct behaviour: void serialize( XmlArchive& archive, Derived_class& derived ); void serialize( TxtArchive& archive, Derived_class& derived ); ... The key point to keep in mind is that the archive type is always known, i.e. I am never using runtime polymorphism for the archive class...(again I am using overloading on the archive type). Any suggestion to help me out? Thank you very much in advance! Cheers

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• Difficulty creating classes and arrays of those classes C#

  - by Lucifer Fayte

  I'm trying to implement a Discrete Fourier Transformation algorithm for a project I'm doing in school. But creating a class is seeming to be difficult(which it shouldn't be). I'm using Visual Studio 2012. Basically I need a class called Complex to store the two values I get from a DFT; The real portion and the imaginary portion. This is what I have so far for that: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace SoundEditor_V3 { public class Complex { public double real; public double im; public Complex() { real = 0; im = 0; } } } The problem is that it doesn't recognize the constructor as a constructor, now I'm just learning C#, but I looked it up online and this is how it's supposed to look apparently. It recognizes my constructor as a method. Why is that? Am I creating the class wrong? It's doing the same thing for my Fourier class as well. So each time I try to create a Fourier object and then use it's method...there is no such thing. example, I do this: Fourier fou = new Fourier(); fou.DFT(s, N, amp, 0); and it tells me fou is a 'field' but is used like a 'type' why is it saying that? Here is the code for my Fourier class as well: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace SoundEditor_V3 { public class Fourier { //FOURIER //N = number of samples //s is the array of samples(data) //amp is the array where the complex result will be written to //start is the where in the array to start public void DFT(byte[] s, int N, ref Complex[] amp, int start) { Complex tem = new Complex(); int f; int t; for (f = 0; f < N; f++) { tem.real = 0; tem.im = 0; for (t = 0; t < N; t++) { tem.real += s[t + start] * Math.Cos(2 * Math.PI * t * f / N); tem.im -= s[t + start] * Math.Sin(2 * Math.PI * t * f / N); } amp[f].real = tem.real; amp[f].im = tem.im; } } //INVERSE FOURIER public void IDFT(Complex[] A, ref int[] s) { int N = A.Length; int t, f; double result; for (t = 0; t < N; t++) { result = 0; for (f = 0; f < N; f++) { result += A[f].real * Math.Cos(2 * Math.PI * t * f / N) - A[f].im * Math.Sin(2 * Math.PI * t * f / N); } s[t] = (int)Math.Round(result); } } } } I'm very much stuck at the moment, any and all help would be appreciated. Thank you.

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• Requring static class setter to be called before constructor, bad design?

  - by roverred

  I have a class, say Foo, and every instance of Foo will need and contain the same List object, myList. Since every class instance will share the same List Object, I thought it would be good to make myList static and use a static function to set myList before the constructor is called. I was wondering if this was bad, because this requires the setter to be called before the constructor? If the person doesn't, the program will crash. Alternative way would be passing myList every time.

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• bind9 dlz/mysql at ubuntu segfault libmysqlclient.so

  - by Theos

  I have a big problem. I installed the bind9 nameserver to three different computer. two Ubuntu 10.04.4 LTS, and one Ubuntu 11.10 I compiled it 9.7.0, 9.7.3, 9.9.0 with this method: ./configure --prefix=/usr --sysconfdir=/etc/bind --localstatedir=/var \ --mandir=/usr/share/man --infodir=/usr/share/info \ --enable-threads --enable-largefile --with-libtool --enable-shared --enable-static \ --with-openssl=/usr --with-gssapi=/usr --with-gnu-ld \ --with-dlz-mysql=yes --with-dlz-bdb=no \ --with-dlz-filesystem=yes --with-geoip=/usr make make install After the set up for dlz/mysql, the BIND server is working perfetctly until 5-30 minute long. Ahter i got segfault. I resolve temporaly the problem with a simple process watchdog, and if the named is stopped, the watchdog is restart it, but this is not a good idea in long therm. My log output is: messages: Apr 13 19:33:51 dnsvm kernel: [ 8.088696] eth0: link up Apr 13 19:33:58 WATCHDOG: named not running. Restarting Apr 13 19:35:08 dnsvm kernel: [ 87.082572] named[1027]: segfault at 88 ip b71c4291 sp b5adfe30 error 4 in libmysqlclient.so.16.0.0[b714e000+1aa000] Apr 13 19:35:08 WATCHDOG: named not running. Restarting Apr 13 19:35:08 dnsvm kernel: [ 87.457510] named[1423]: segfault at 68 ip b71d6122 sp b52f0a40 error 4 in libmysqlclient.so.16.0.0[b7160000+1aa000] Apr 13 19:35:09 WATCHDOG: named not running. Restarting Apr 13 19:41:56 dnsvm kernel: [ 494.838206] named[1448]: segfault at 88 ip b731c291 sp b5436e30 error 4 in libmysqlclient.so.16.0.0[b72a6000+1aa000] Apr 13 19:41:57 WATCHDOG: named not running. Restarting Apr 13 19:57:26 dnsvm kernel: [ 1424.023409] named[2976]: segfault at 88 ip b72d1291 sp b6beee30 error 4 in libmysqlclient.so.16.0.0[b725b000+1aa000] Apr 13 19:57:26 WATCHDOG: named not running. Restarting Apr 13 20:11:56 dnsvm kernel: [ 2294.324663] named[6441]: segfault at 88 ip b7357291 sp b6473e30 error 4 in libmysqlclient.so.16.0.0[b72e1000+1aa000] Apr 13 20:11:57 WATCHDOG: named not running. Restarting syslog: http://pastebin.com/hjUyt8gN the first server is a native, normal x64 server (u1004lts), the second is virtualised server (u11.10) the third is also virtualised (10.04lts) This servers is only for dns providing with mysql server db. But the problem is be with all server, and all bind version. named.conf: http://pastebin.com/zwm1yP7V Can anybody help me, or any good idea?

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• Using named_scopes on the join model of a has_many :through

  - by uberllama

  Hi folks. I've been beating my head against the wall on something that on the surface should be very simple. Lets say I have the following simplified models: user.rb has_many :memberships has_many :groups, :through => :memberships membership.rb belongs_to :group belongs_to :user STATUS_CODES = {:admin => 1, :member => 2, :invited => 3} named_scope :active, :conditions => {:status => [[STATUS_CODES[:admin], STATUS_CODES[:member]]} group.rb has_many :memberships has_many :users, :through => :memberships Simple, right? So what I want to do is get a collection of all the groups a user is active in, using the existing named scope on the join model. Something along the lines of User.find(1).groups.active. Obviously this doesn't work. But as it stands, I need to do something like User.find(1).membrships.active.all(:include => :group) which returns a collection of memberships plus groups. I don't want that. I know I can add another has_many on the User model with conditions that duplicate the :active named_scope on the Membership model, but that's gross. has_many :active_groups, :through => :memberships, :source => :group, :conditions => ... So my question: is there a way of using intermediary named scopes when traversing directly between models? Many thanks.

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• Why `A & a = a` is valid?

  - by psaghelyi

  #include <iostream> #include <assert.h> using namespace std; struct Base { Base() : m_member1(1) {} Base(const Base & other) { assert(this != &other); // this should trigger m_member1 = other.m_member1; } int m_member1; }; struct Derived { Derived(Base & base) : m_base(m_base) {} // m_base(base) Base & m_base; }; void main() { Base base; Derived derived(base); cout << derived.m_base.m_member1 << endl; // crashes here } The above example is a synthesized version of a mistyped constructor. I used reference at the class member Derived::m_base because I wanted to make sure that the member will be initialized as the constructor had called. One problem is that nor GCC nor MSVC gives me a warning at m_base(m_base). But the more serious for me is that the assert finds everything fine and the application crashes later (sometimes far away from the mistake). Question: Is there any way to indicate such mistakes?

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• Rails named_scope across multiple tables

  - by wakiki

  I'm trying to tidy up my code by using named_scopes in Rails 2.3.x but where I'm struggling with the has_many :through associations. I'm wondering if I'm putting the scopes in the wrong place... Here's some pseudo code below. The problem is that the :accepted named scope is replicated twice... I could of course call :accepted something different but these are the statuses on the table and it seems wrong to call them something different. Can anyone shed light on whether I'm doing the following correctly or not? I know Rails 3 is out but it's still in beta and it's a big project I'm doing so I can't use it in production yet. class Person < ActiveRecord::Base has_many :connections has_many :contacts, :through => :connections named_scope :accepted, :conditions => ["connections.status = ?", Connection::ACCEPTED] # the :accepted named_scope is duplicated named_scope :accepted, :conditions => ["memberships.status = ?", Membership::ACCEPTED] end class Group < ActiveRecord::Base has_many :memberships has_many :members, :through => :memberships end class Connection < ActiveRecord::Base belongs_to :person belongs_to :contact, :class_name => "Person", :foreign_key => "contact_id" end class Membership < ActiveRecord::Base belongs_to :person belongs_to :group end I'm trying to run something like person.contacts.accepted and group.members.accepted which are two different things. Shouldn't the named_scopes be in the Membership and Connection classes? One solution is to just call the two different named scope something different in the Person class or even to create separate associations (ie. has_many :accepted_members and has_many :accepted_contacts) but it seems hackish and in reality I have many more than just accepted (ie. banned members, ignored connections, pending, requested etc etc)

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• get and set for class in model - MVC 2 asp.net

  - by bergin

  Hi there, I want to improve the program so it has a proper constructor but also works with the models environment of MVC. I currently have: public void recordDocument(int order_id, string filename, string physical_path, string slug, int bytes) { ArchiveDocument doc = new ArchiveDocument(); doc.order_id = order_id; doc.filename = filename; doc.physical_path = physical_path; doc.slug = slug; doc.bytes = bytes; db.ArchiveDocuments.InsertOnSubmit(doc); } This obviously should be a constructor and should change to the leaner: public void recordDocument(ArchiveDocument doc) { db.ArchiveDocuments.InsertOnSubmit(doc); } with a get & set somewhere else - not sure of the syntax - do I create a partial class? so: creating in the somewhere repository - ArchiveDocument doc = new ArchiveDocument(order_id, idTaggedFilename, physical_path, slug, bytes); and then: namespace ordering.Models { public partial class ArchiveDocument { int order_id, string filename, string physical_path, string slug, int bytes; public archiveDocument(int order_id, string filename, string physical_path, string slug, int bytes){ this.order_id = order_id; etc } } How should I alter the code?

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• Java: using generic wildcards with subclassing

  - by gibberish

  Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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• C++: Construction and initialization order guarantees

  - by Helltone

  Hi, I have some doubts about construction and initialization order guarantees in C++. For instance, the following code has four classes X, Y, Z and W. The main function instantiates an object of class X. X contains an object of class Y, and derives from class Z, so both constructors will be called. Additionally, the const char* parameter passed to X's constructor will be implicitly converted to W, so W's constructor must also be called. What are the guarantees the C++ standard gives on the order of the calls to the copy constructors? Or, equivalently, this program is allowed to print? #include <iostream> class Z { public: Z() { std::cout << "Z" << std::endl; } }; class Y { public: Y() { std::cout << "Y" << std::endl; } }; class W { public: W(const char*) { std::cout << "W" << std::endl; } }; class X : public Z { public: X(const W&) { std::cout << "X" << std::endl; } private: Y y; }; int main(int, char*[]) { X x("x"); return 0; }

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• Complicated .NET factory design

  - by Tom W

  Hello SO; I'm planning to ask a fairly elaborate question that is also something of a musing here, so bear with me... I'm trying to design a factory implementation for a simulation application. The simulation will consist of different sorts of entities i.e. it is not a homogenous simulation in any respect. As a result, there will be numerous very different concrete implementations and only the very general properties will be abstracted at the top level. What I'd like to be able to do is create new simulation entities by calling a method on the model with a series of named arguments representing the parameters of the entity, and have the model infer what type of object is being described by the inbound parameters (from the names of the parameters and potentially the sequence they occur in) and call a factory method on the appropriate derived class. For example, if I pass the model a pair of parameters (Param1=5000, Param2="Bacon") I would like it to infer that the names Param1 and Param2 'belong' to the class "Blob1" and call a shared function "getBlob1" with named parameters Param1:=5000, Param2:="Bacon" whereas if I pass the model (Param1=5000, Param3=50) it would call a similar factory method for Blob2; because Param1 and Param3 in that order 'belong' to Blob2. I foresee several issues to resolve: Whether or not I can reflect on the available types with string parameter names and how to do this if it's possible Whether or not there's a neat way of doing the appropriate constructor inference from the combinatoric properties of the argument list or whether I'm going to have to bodge something to do it 'by hand'. If possible I'd like the model class to be able to accept parameters as parameters rather than as some collection of keys and values, which would require the model to expose a large number of parametrised methods at runtime without me having to code them explicitly - presumably one for every factory method available in the relevant namespace. What I'm really asking is how you'd go about implementing such a system, rather than whether or not it's fundamentally possible. I don't have the foresight or experience with .NET reflection to be able to figure out a way by myself. Hopefully this will prove an informative discussion.

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• Why would one want to use the public constructors on Boolean and similar immutable classes?

  - by Robert J. Walker

  (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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• Master/Slave DNS setup vs. rsync'ed DNS servers

  - by Jakobud

  We currently have primary and secondary DNS servers on our corporate network. They are setup in a master/slave type setup, where the slave gets its DNS information from the master. I'm trying to figure out what the real advantage is for the master/slave setup instead of just setting up an automated rsync between the two to keep the DNS settings matched. Can anyone shed some light on this? Or is it just a preferential thing? If that is the case, it seems like the rsync setup would be much easier to setup, maintain and understand.

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• Should I use /etc/bind/zones/ or /var/cache/bind/?

  - by nbolton

  Each tutorial seems to have a different opinion on this. For my ISC BIND zones, should I use /etc/bind/zones/ or /var/cache/bind/? In the last install, I used /var/cache/bind/ but only because I was guided to do so; however I just spotted a pid file in there for this new Debian install, so I figured that using the "working directory" to store zone files probably wasn't the best idea. It seems that many admins use this so they don't have to type the full path when declaring a new zone. For example: file "/etc/bind/zones/db.foobar.com"; Instead of: file "db.foobar.com"; Is obviously easier to type, but is it good or bad practice? Some may also suggest setting the working directory to /etc/bind/zones: options { // directory "/var/cache/bind"; directory "/etc/bind/zones"; } ... but something tells me this isn't good practice, since the pid file would be created there I assume (unless it's just in /var/cache/bind by coincidence). I took a look at the manpage but it didn't seem to say what the directory option was for, any ideas exactly what it was design for?

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• DNS and mod_rewrite not-collaborating

  - by ???? ?????????

  Hello, I have added a CNAME record to my DNS on my CentOS server to redirect subdomain.mydomain.com to another server. I also use mod_rewrite to rewrite mydomain.com to www.mydomain.com: RewriteEngine on RewriteCond %{HTTP_HOST} ^mydomain\.com$ [NC] RewriteRule ^(.*)$ http://www.mydomain.com/$1 [L,R=301] this is placed into .htaccess in the root public html directory Now, the problem is that whenever I lookup subdomain.mydomain.com it redirects me to www.mydomain.com I tried adding another RewriteCond: RewriteEngine on RewriteCond %{HTTP_HOST} ^mydomain\.com$ [NC] RewriteCond %{HTTP_HOST} !^subdomain\.mydomain\.com$ [NC] RewriteRule ^(.*)$ http://www.mydomain.com/$1 [L,R=301] But it didn't help... Anyone has some ideas?

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• BIND split-view DNS config problem

  - by organicveggie

  We have two DNS servers: one external server controlled by our ISP and one internal server controlled by us. I'd like internal requests for foo.example.com to map to 192.168.100.5 and external requests continue to map to 1.2.3.4, so I'm trying to configure a view in bind. Unfortunately, bind fails when I attempt to reload the configuration. I'm sure I'm missing something simple, but I can't figure out what it is. options { directory "/var/cache/bind"; forwarders { 8.8.8.8; 8.8.4.4; }; auth-nxdomain no; # conform to RFC1035 listen-on-v6 { any; }; }; zone "." { type hint; file "/etc/bind/db.root"; }; zone "localhost" { type master; file "/etc/bind/db.local"; }; zone "127.in-addr.arpa" { type master; file "/etc/bind/db.127"; }; zone "0.in-addr.arpa" { type master; file "/etc/bind/db.0"; }; zone "255.in-addr.arpa" { type master; file "/etc/bind/db.255"; }; view "internal" { zone "example.com" { type master; notify no; file "/etc/bind/db.example.com"; }; }; zone "example.corp" { type master; file "/etc/bind/db.example.corp"; }; zone "100.168.192.in-addr.arpa" { type master; notify no; file "/etc/bind/db.192"; }; I have excluded the entries in the view for allow-recursion and recursion in an attempt to simplify the configuration. If I remove the view and just load the example.com zone directly, it works fine. Any advice on what I might be missing?

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• An SQLite/STDIN Conundrum, Specific to AIX

  - by mikfreedman

  Hi there! I'm been playing around with SQlite at work, specifically with trying to get the sqlite3 command line tool to accept stdin instead of a file. Sounds easy enough, on linux you can execute a command like: echo 'test' | sqlite3 test.db '.import /dev/stdin test' unfortunately - our machines at work run AIX (5 & 6) and as far as I can tell, there is no equivalent to the virtual file /dev/stdin. I managed to hack together an equivalent command that works on AIX using a temporary file. echo 'test' | cat - > /tmp/blah ; sqlite3 test.db '.import /dev/stdin test' ; rm /tmp/blah Now, does it need to use STDIN? isn't this temporary file thing enough? Probably, but I was hoping someone with better unix-fu had a more elegant solution. note: the data I would like to import is only provided via STDOUT, so that's what the echo 'test' command is all about

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• error: no matching function for call to ‘BSTreeNode<int, int>::BSTreeNode(int, int, NULL, NULL)’ - what's wrong?

  - by Alexander Suraphel

  error: no matching function for call to ‘BSTreeNode::BSTreeNode(int, int, NULL, NULL)’ candidates are: BSTreeNode::BSTreeNode(KF, DT&, BSTreeNode*, BSTreeNode*) [with KF = int, DT = int] here is how I used it: BSTreeNode<int, int> newNode(5,9, NULL, NULL) ; I defined it as follows: BSTreeNode(KF sKey, DT &data, BSTreeNode *lt, BSTreeNode *rt):key(sKey),dataItem(data), left(lt), right(rt){} what's wrong with using my constructor this way? i've been pulling out my hair all night please help me ASAP!!

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• Boost singleton and restricted

  - by Ockonal

  Hello, I'm using boost singleton from thread/detail. There is in manual, that constructor should have signlature: boost::restricted. But I can't find any reference for this type in boost library. Why do I need in this and where I can find it?

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• Any Name Entity Recognition - web services available

  - by Gublooo

  Hello I wanted to know if there are any paid or free named entity recognition web services available. Basically I'm looking for something - where if I pass a text like: "John had french fries at Burger King" It should be identify - something along the lines: Person: John Organization: Burger King I've heard of Annie from GATE - but I dont think it has a web service available. Thanks

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