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• Handling Exceptions that happen in a asp.net MVC Controller Constructor

  - by Jason

  What's the best way to handle exceptions that happen from within a controller's constructor? All I can think of to do is use Application_OnError() or put a try/catch in my ControllerFactory. Neither of these solutions seem ideal. Application_OnError is to broad - I have some non-mvc content in the site that has its own error handling. Using a try/catch block seems kinda hacky. If I'm serving different content type -html/text/json/rss.... I would like to be able to handle the exception from within the action method instead of having to write all kinds of conditions to determine what kind of error message to serve. Am I missing something here, or has anyone else dealt with this?

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• Template class implicit copy constructor issues

  - by Nate

  Stepping through my program in gdb, line 108 returns right back to the calling function, and doesn't call the copy constructor in class A, like (I thought) it should: template <class S> class A{ //etc... A( const A & old ){ //do stuff... } //etc... }; template <class T> class B{ //etc... A<T> ReturnsAnA(){ A<T> result; // do some stuff with result return result; //line 108 } //etc... }; Any hints? I've banged my head against the wall about this for 4 hours now, and can't seem to come up with what's happening here.

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• Error Instantiating an Inner Class in Parent's Constructor...

  - by stormin986

  In my application's main class (subclass of Application), I have a public inner class that simply contains 3 public string objects. In the parent class I declare an object of that inner class. public class MainApplication extends Application { public class Data { public String x; public String y; public String z; } private Data data; MainApplication() { data = new Data() data.x = "String"; } } After I instantiate the object in the constructor, I get a runtime error when I try to assign any of the inner class object's variables. Any idea what's up here??

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• C++ Constructor Initializer List - using member functions of initialized members

  - by Andy

  I've run into the following a few times with initializer lists and I've never been able to explain it well. Can anyone explain why exactly the following fails (I don't have a compiler to catch typos, so bear with me): class Foo { public: Foo( int i ) : m_i( i ) {} //works with no problem int getInt() {return m_i;} ~Foo {} private: int m_i; }; class Bar { public: Bar() : m_foo( 5 ), //this is ok m_myInt( m_foo.getInt() ) //runtime error, seg 11 {} ~Bar() {} private: Foo m_foo; int m_myInt; }; When trying to call member functions of members initialized higher up the initializer list, I get seg faults. I seem to recall this is a known problem (or perhaps somehow by design) but I've never seen it well described. The attached example is contrived with plain old data types, but substitute the Bar::m_myInt with another object lacking a default (empty) constructor and the issue is more real. Can anyone enlighten me? Thanks!

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• Constructor with non-instance variable assistant?

  - by Robert Fischer

  I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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• C++ catch constructor exception

  - by aaa

  hi. I do not seem to understand how to catch constructor exception. Here is relevant code: struct Thread { rysq::cuda::Fock fock_; template<class iterator> Thread(const rysq::cuda::Centers &centers, const iterator (&blocks)[4]) : fock_() { if (!fock_) throw; } }; Thread *ct; try { ct = new Thread(centers_, blocks); } catch(...) { return false; } // catch never happens, So catch statement do not execute and I get unhandled exception. What did I do wrong? this is straight C++ using g++.

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• Disallow private constructor invocation in friend function

  - by user2907032

  Is there any way to not allow private construction in friend function, In case we do have private constructor with friend function in our class. Only Static method should be responsible for object creation and other than this compiler should flash error message #include <iostream> #include <memory> using namespace std; class a { public: void see () { cout<<"Motimaa"; } static a& getinstance() { static a instance; return instance; } private: a() {}; friend void access(); }; void access () { a obj; obj.see();//still friend function can access } int main() { a::getinstance().see(); access(); return 1; }

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• How do I get the default constructor value in a function

  - by lax

  public class AppXmlLogWritter { public int randomNumber; public string LogDateTime = ""; public AppXmlLogWritter() { Random random = new Random(); randomNumber = random.Next(9999); LogDateTime = DateTime.Now.ToString("yyyyMMdd HHmmss"); } public AppXmlLogWritter(int intLogIDPrefix, string strLogApplication, string strLogFilePath) { LogIDPrefix = intLogIDPrefix; LogApplication = strLogApplication; LogFilePath = strLogFilePath; } public void WriteXmlLog(string LogFlag) { string value=LogDateTime + randomNumber;**//Here i m getting 0 no date time and random number generated** } } AppXmlLogWritter objParameterized = new AppXmlLogWritter(1234, "LogApplication", "LogFilepath"); AppXmlLogWritter objParmeterlessConstr = new AppXmlLogWritter(); objParameterized.WriteXmlLog("0", "LogFlag"); How do I get the default constructor value in this function?

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• C# Closing a form during a constructor

  - by pm_2

  Is it possible to close a form while the constructor is executing (or simply to stop it showing at this stage)? I have the following code: public partial class MyForm : Form { public MyForm() { if (MyFunc()) { this.Close(); } } } Which errors in Main(), here: static void Main() { ... // Following line errors Application.Run(new MyForm()); } I’ve tried checking the result of MyForm like this: static void Main() { ... MyForm frm = new MyForm(); if (frm != null) { // Following line errors Application.Run(frm); } } But that doesn’t seem to help. Can anyone tell me a way around this, please? Maybe a way to check the form to see if it still exists?

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• C# Constructor Problem When Using Generics

  - by Jimbo

  Please see an example of my code below: public class ScrollableCheckboxList { public List<ScrollableCheckboxItem> listitems; public void ScrollableCheckboxList<TModel>(IEnumerable<TModel> items, string valueField, string textField, string titleField) where TModel : class { listitems = new List<ScrollableCheckboxItem>(); foreach (TModel item in items) { Type t = typeof(TModel); PropertyInfo[] props = new [] { t.GetProperty(textField), t.GetProperty(valueField), t.GetProperty(titleField) }; listitems.Add(new ScrollableCheckboxItem { text = props[0].GetValue(item, null).ToString(), value = props[1].GetValue(item, null).ToString(), title = props[2].GetValue(item, null).ToString() }); } } } The code produces the following error: 'ScrollableCheckboxList': member names cannot be the same as their enclosing type This clearly means that there is a method in the class that has the same name as the class, but usually insinuates that the method is trying to return something (which is not allowed) In my case, all I have done is declare a constructor - why would this be a problem?

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• Copy Constructor in C++

  - by user265260

  i have this code #include <iostream> using namespace std; class Test{ public: int a; Test(int i=0):a(i){} ~Test(){ cout << a << endl; } Test(const Test &){ cout << "copy" << endl; } void operator=(const Test &){ cout << "=" << endl; } Test operator+(Test& p){ Test res(a+p.a); return res; } }; int main (int argc, char const *argv[]){ Test t1(10), t2(20); Test t3=t1+t2; return 0; } Output: 30 20 10 Why isnt the copy constructor called here?

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• Constructor Definition

  - by mctl87

  Ok so i have a class Vector: #include <cstdlib> class Vec { private: size_t size; int * ptab; public: Vec(size_t n); ~Vec() {delete [] ptab;} size_t size() const {return size;} int & operator[](int n) {return ptab[n];} int operator[](int n) const {return ptab[n];} void operator=(Vec const& v); }; inline Vec::Vec(size_t n) : size(n), ptab(new int[n]) { } and the problem is that in one of my homework exercises i have to extend constructor def, so all elements will be initialized with zeros. I thought i know the basics but cant get through this dynamic array -.- ps. sry for gramma and other mistakes ;)

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• Using a named pipe to simulate a serial port on a VMware virtual machine (linux host and client)

  - by Dave M

  Trying to write a python program to create a simulated data stream and feed it, through a named pipe, to a VMware virtual machine. The host is running Ubuntu 11.10 and VMware player 5.0.0. The Vm is running Ubuntu netbook 10.04. I am able to get the pipe working on the local machine but I am not able to get the pipe to pass data through the virtual serial port to the programs running on the virtual machine. #!/usr/bin/python import os # # Create a named pipe that will be used as the serial port on a VMware virtual machine SerialPipe = '/tmp/gpsd2NMEA' try: os.unlink(SerialPipe) except: pass os.mkfifo(SerialPipe) # # Open the named pipe NMEApipe = os.open(SerialPipe, os.O_RDWR|os.O_NONBLOCK) # # Write a string to the named pipe NMEAtime = "235959" os.write(NMEApipe, str( '%s\n' % NMEAtime )) Test to see if the python program is working on the host machine (displays 235959 if data is passing through the pipe) $ cat /tmp/gpsd2NMEA 235959 Serial port as defined in the VMware .vmx file: serial0.present = "TRUE" serial0.startConnected = "TRUE" serial0.fileType = "pipe" serial0.fileName = "/tmp/gpsd2NMEA" serial0.pipe.endPoint = "client" serial0.autodetect = "FALSE" serial0.tryNoRxLoss = "TRUE" serial0.yieldOnMsrRead = "TRUE" Test to see if the serial port in the VM is receiving data $ cat /dev/ttyS0 or $ minicom -D /dev/ttyS0 or $ stty -F /dev/ttyS0 cs8 -parenb -cstopb 115200 $ echo < /dev/ttyS0 None of these display any data from the python program.

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• CA2000 passing object reference to base constructor in C#

  - by Timothy

  I receive a warning when I run some code through Visual Studio's Code Analysis utility which I'm not sure how to resolve. Perhaps someone here has come across a similar issue, resolved it, and is willing to share their insight. I'm programming a custom-painted cell used in a DataGridView control. The code resembles: public class DataGridViewMyCustomColumn : DataGridViewColumn { public DataGridViewMyCustomColumn() : base(new DataGridViewMyCustomCell()) { } It generates the following warning: CA2000 : Microsoft.Reliability : In method 'DataGridViewMyCustomColumn.DataGridViewMyCustomColumn()' call System.IDisposable.Dispose on object 'new DataGridViewMyCustomCell()' before all references to it are out of scope. I understand it is warning me DataGridViewMyCustomCell (or a class that it inherits from) implements the IDisposable interface and the Dispose() method should be called to clean up any resources claimed by DataGridViewMyCustomCell when it is no longer. The examples I've seen on the internet suggest a using block to scope the lifetime of the object and have the system automatically dispose it, but base isn't recognized when moved into the body of the constructor so I can't write a using block around it... which I'm not sure I'd want to do anyway, since wouldn't that instruct the run time to free the object which could still be used later inside the base class? My question then, is the code okay as is? Or, how could it be refactored to resolve the warning? I don't want to suppress the warning unless it is truly appropriate to do so.

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• Temporary non-const istream reference in constructor (C++)

  - by Christopher Bruns

  It seems that a constructor that takes a non-const reference to an istream cannot be constructed with a temporary value in C++. #include <iostream> #include <sstream> using namespace std; class Bar { public: explicit Bar(std::istream& is) {} }; int main() { istringstream stream1("bar1"); Bar bar1(stream1); // OK on all platforms // compile error on linux, Mac gcc; OK on Windows MSVC Bar bar2(istringstream("bar2")); return 0; } This compiles fine with MSVC, but not with gcc. Using gcc I get a compile error: g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:18: error: no matching function for call to ‘Bar::Bar(std::istringstream)’ test.cpp:9: note: candidates are: Bar::Bar(std::istream&) test.cpp:7: note: Bar::Bar(const Bar&) Is there something philosophically wrong with the second way (bar2) of constructing a Bar object? It looks nicer to me, and does not require that stream1 variable that is only needed for a moment.

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• Enums, Constructor overloads with similar conversions.

  - by David Thornley

  Why does VisualC++ (2008) get confused 'C2666: 2 overloads have similar conversions' when I specify an enum as the second parameter, but not when I define a bool type? Shouldn't type matching already rule out the second constructor because it is of a 'basic_string' type? #include <string> using namespace std; enum EMyEnum { mbOne, mbTwo }; class test { public: #if 1 // 0 = COMPILE_OK, 1 = COMPILE_FAIL test(basic_string<char> myString, EMyEnum myBool2) { } test(bool myBool, bool myBool2) { } #else test(basic_string<char> myString, bool myBool2) { } test(bool myBool, bool myBool2) { } #endif }; void testme() { test("test", mbOne); } I can work around this by specifying a reference 'ie. basic_string &myString' but not if it is 'const basic_string &myString'. Also calling explicitly via "test((basic_string)"test", mbOne);" also works. I suspect this has something to do with every expression/type being resolved to a bool via an inherent '!=0'. Curious for comments all the same :)

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• Ruby - calling constructor without arguments & removal of new line characters

  - by Raj

  I am a newbie at Ruby, I have written down a sample program. I dont understand the following: Why constructor without any arguments are not called in Ruby? How do we access the class variable outside the class' definition? Why does it always append newline characters at the end of the string? How do we strip it? Code: class Employee attr_reader :empid attr_writer :empid attr_writer :name def name return @name.upcase end attr_accessor :salary @@employeeCount = 0 def initiaze() @@employeeCount += 1 puts ("Initialize called!") end def getCount return @@employeeCount end end anEmp = Employee.new print ("Enter new employee name: ") anEmp.name = gets() print ("Enter #{anEmp.name}'s employee ID: ") anEmp.empid = gets() print ("Enter salary for #{anEmp.name}: ") anEmp.salary = gets() theEmpName = anEmp.name.split.join("\n") theEmpID = anEmp.empid.split.join("\n") theEmpSalary = anEmp.salary.split.join("\n") anEmp = Employee.new() anEmp = Employee.new() theCount = anEmp.getCount puts ("New employee #{theEmpName} with employee ID #{theEmpID} has been enrolled, welcome to hell! You have been paid as low as $ #{theEmpSalary}") puts ("Total number of employees created = #{theCount}") Output: Enter new employee name: Lionel Messi Enter LIONEL MESSI 's employee ID: 10 Enter salary for LIONEL MESSI : 10000000 New employee LIONEL MESSI with employee ID 10 has been enrolled, welcome to hell! You have been paid as low as $ 10000000 Total number of employees created = 0 Thanks

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• stealing inside the move constructor

  - by FredOverflow

  During the implementation of the move constructor of a toy class, I noticed a pattern: array2D(array2D&& that) { data_ = that.data_; that.data_ = 0; height_ = that.height_; that.height_ = 0; width_ = that.width_; that.width_ = 0; size_ = that.size_; that.size_ = 0; } The pattern obviously being: member = that.member; that.member = 0; So I wrote a preprocessor macro to make stealing less verbose and error-prone: #define STEAL(member) member = that.member; that.member = 0; Now the implementation looks as following: array2D(array2D&& that) { STEAL(data_); STEAL(height_); STEAL(width_); STEAL(size_); } Are there any downsides to this? Is there a cleaner solution that does not require the preprocessor?

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• Inheritance and choose constructor from base class

  - by myle

  My question is rather simple, but I am stuck. How can I choose the desired constructor from base class? // node.h #ifndef NODE_H #define NODE_H #include <vector> // definition of an exception-class class WrongBoundsException { }; class Node { public: ... Node(double, double, std::vector<double>&) throw (WrongBoundsException); ... }; #endif // InternalNode.h #ifndef INTERNALNODE_H #define INTERNALNODE_H #include <vector> #include "Node.h" class InternalNode : public Node { public: // the position of the leftmost child (child left) int left_child; // the position of the parent int parent; InternalNode(double, double, std::vector<double>&, int parent, int left_child) throw (WrongBoundsException); private: int abcd; }; #endif // InternalNode.cpp #include "InternalNode.h" #define UNDEFINED_CHILD -1 #define ROOT -1 // Here is the problem InternalNode::InternalNode(double a, double b, std::vector<double> &v, int par, int lc) throw (WrongBoundsException) : Node(a, b, v), parent(par), left_child(lc) { std::cout << par << std::endl; } I get: $ g++ InternalNode.cpp InternalNode.cpp:16: error: declaration of ‘InternalNode::InternalNode(double, double, std::vector &, int, int) throw (WrongBoundsException)’ throws different exceptions InternalNode.h:17: error: from previous declaration ‘InternalNode::InternalNode(double, double, std::vector &, int, int)’ UPDATE 0: Fixed missing : UPDATE 1: Fixed throw exception

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• Copy constructor demo (crashing...)

  - by AKN

  Here is the program... class CopyCon { public: char *name; CopyCon() { name = new char; } CopyCon(const CopyCon &objCopyCon) { name = new char; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete name; name = NULL; } } }; int main() { CopyCon objCopyCon1; objCopyCon1.name = "Hai"; CopyCon objCopyCon2(objCopyCon1); objCopyCon1.name = "Hello"; cout<<objCopyCon2.name<<endl; return 0; } Once the code execution completes, when the destructor called, it crashes on 'delete' saying... Debug Error! Program: ... HEAP CORRUPTION DETECTED: after Normal block (#124) at 0x00366990. CRT detected that the application wrote to memory after end of heap buffer. (Press Retry to debug the application) Don't we have to clear the heap memory in destructor. What's wrong with this program? Pls someone help! Copy constructor works perfectly as intended. But still... !?

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• C++ Initialize array in constructor EXC_BAD_ACCESS

  - by user890395

  I'm creating a simple constructor and initializing an array: // Construtor Cinema::Cinema(){ // Initalize reservations for(int i = 0; i < 18; i++){ for(int j = 0; j < 12; j++){ setReservation(i, j, 0); } } // Set default name setMovieName("N/A"); // Set default price setPrice(8); } The setReservation function: void Cinema::setReservation(int row, int column, int reservation){ this->reservations[row][column] = reservation; } The setMovieName function: void Cinema::setMovieName(std::string movieName){ this->movieName = movieName; } For some odd reason when I run the program, the setMovieName function gives the following error: "Program Received Signal: EXC_BAD_ACCESS" If I take out the for-loop that initializes the array of reservations, the problem goes away and the movie name is set without any problems. Any idea what I'm doing wrong? This is the Cinema.h file: #ifndef Cinema_h #define Cinema_h class Cinema{ private: int reservations[17][11]; std::string movieName; float price; public: // Construtor Cinema(); // getters/setters int getReservation(int row, int column); int getNumReservations(); std::string getMovieName(); float getPrice(); void setReservation(int row, int column, int reservation); void setMovieName(std::string movieName); void setPrice(float price); }; #endif

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• Should a C++ constructor do real work?

  - by Wade Williams

  I'm strugging with some advice I have in the back of my mind but for which I can't remember the reasoning. I seem to remember at some point reading some advice (can't remember the source) that C++ constructors should not do real work. Rather, they should initialize variables only. The advice when on to explain that real work should be done in some sort of init() method, to be called separately after the instance was created. The situation is I have a class that represents a hardware device. It makes logical sense to me for the constructor to call the routines that query the device in order to build up the instance variables that describe the device. In other words, once new instantiates the object, the developer receives an object which is ready to be used, no separate call to object-init() required. Is there a good reason why constructors shouldn't do real work? Obviously it could slow allocation time, but that wouldn't be any different if calling a separate method immediately after allocation. Just trying to figure out what gotchas I not currently considering that might have lead to such advice.

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• Is it bad practise to initialise fields outside of an explicit constructor

  - by MrTortoise

  So its monday and we are arguing about coding practises. The examples here are a litttle too simple, but the real deal has several constructors. In order to initialise the simple values (eg dates to their min value) I have moved the code out of the constructors and into the field definitions. public class ConstructorExample { string _string = "John"; } public class ConstructorExample2 { string _string; public ConstructorExample2() { _string = "John"; } } How should it be done by the book. I tend to be very case by case and so am maybe a little lax abotu this kind of thing. However i feel that accams razor tells me to move the initialisation out of multiple constructors. Of course I could always move this shared initialisation into a private method. The question is essentially ... is initialising fields where they are defined as opposed to the constructor bad in any way? The argument I am facing is one of error handling, but i do not feel it is relevant as there are no possible exceptions that won't be picked up at compile time.

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• calling constructor of the class in the destructor of the same class

  - by dicaprio

  Experts !! I know this question is one of the lousy one , but still I dared to open my mind , hoping I would learn from all. I was trying some examples as part of my routine and did this horrible thing, I called the constructor of the class from destructor of the same class. I don't really know if this is ever required in real programming , I cant think of any real time scenarios where we really need to call functions/CTOR in our destructor. Usually , destructor is meant for cleaning up. If my understanding is correct, why the compiler doesn't complain ? Is this because it is valid for some good reasons ? If so what are they ? I tried on Sun Forte, g++ and VC++ compiler and none of them complain about it. using namespace std; class test{ public: test(){ cout<<"CTOR"<<endl; } ~test() {cout<<"DTOR"<<endl; test(); }};

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• MySQL on Windows - how do I set the wait_timeout for connections using named pipes?

  - by gustafc

  I use a MySQL database running on a Windows box, and for performance reasons I'm connecting to it using named pipes. The (Java) application using the database (through Hibernate) can let the connection lie idle for quite a long time, which causes the connection to fail with the following message: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 33 558 297 milliseconds ago. The last packet sent successfully to the server was 33 558 297 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem. autoReconnect unfortunately has no effect (and neither does autoReconnectForPools), but the wait_timeout docs state that wait_timeout only applies "to TCP/IP and Unix socket file connections, not to connections made via named pipes, or shared memory". How can I change the wait_timeout for named pipes?

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