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• C# ArrayList calling on a constructor class

  - by EvanRyan

  I'm aware that an ArrayList is probably not the way to go with this particular situation, but humor me and help me lose this headache. I have a constructor class like follows: class Peoples { public string LastName; public string FirstName; public Peoples(string lastName, string firstName) { LastName = lastName; FirstName = firstName; } } And I'm trying to build an ArrayList to build a collection by calling on this constructor. However, I can't seem to find a way to build the ArrayList properly when I use this constructor. I have figured it out with an Array, but not an ArrayList. I have been messing with this to try to build my ArrayList: ArrayList people = new ArrayList(); people[0] = new Peoples("Bar", "Foo"); people[1] = new Peoples("Quirk", "Baz"); people[2] = new Peopls("Get", "Gad"); My indexing is apparently out of range according to the exception I get.

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• Spring overloaded constructor injection

  - by noob

  This is the code : public class Triangle { private String color; private int height; public Triangle(String color,int height){ this.color = color; this.height = height; } public Triangle(int height ,String color){ this.color = color; this.height = height; } public void draw() { System.out.println("Triangle is drawn , + "color:"+color+" ,height:"+height); } } The Spring config-file is : <bean id="triangle" class="org.tester.Triangle"> <constructor-arg value="20" /> <constructor-arg value="10" /> </bean> Is there any specific rule to determine which constructor will be called by Spring ?

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• c++ Using const in a copy constructor?

  - by Anton

  I have never written copy constructor, so in order to avoid pain i wanted to know if what i have coded is legit. It compiles but i am not sure that it works as a copy constructor should. Also do i have to use const in the copy constructor or i can simply drop it. (What i dont like about const is that the compiler cries if i use some non const functions). //EditNode.h class EditNode { explicit EditNode(QString elementName); EditNode(const EditNode &src); } //EditNodeContainer.h class EditNodeContainer : public EditNode { explicit EditNodeContainer(QString elementName); EditNodeContainer(const EditNodeContainer &src); } //EditNodeContainer.cpp EditNodeContainer::EditNodeContainer(QString elementName):EditNode(elementName) { } //This seems to compile but not sure if it works EditNodeContainer::EditNodeContainer(const EditNodeContainer &src):EditNode(src) { } //the idea whould be to do something like this EditNodeContainer *container1 = new EditNodeContainer("c1"); EditNodeContainer *copyContainer = new EditNodeContainer(container1);

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• Java: design problem with private-final-int-value and empty constructor

  - by HH

  $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; //DUE to new Klowledge: Design Problem //I think having an empty constructor like this // is an design problem, shall I remove it? What do you think? // When to use an empty constructor? InitInt(){} public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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• C++ method chaining including class constructor

  - by jena

  Hello, I'm trying to implement method chaining in C++, which turns out to be quite easy if the constructor call of a class is a separate statement, e.g: Foo foo; foo.bar().baz(); But as soon as the constructor call becomes part of the method chain, the compiler complains about expecting ";" in place of "." immediately after the constructor call: Foo foo().bar().baz(); I'm wondering now if this is actually possible in C++. Here is my test class: class Foo { public: Foo() { } Foo& bar() { return *this; } Foo& baz() { return *this; } }; I also found an example for "fluent interfaces" in C++ (http://en.wikipedia.org/wiki/Fluent_interface#C.2B.2B) which seems to be exactly what I'm searching for. However, I get the same compiler error for that code. Thanks in advance for any hint. Best, Jean

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• Would this constructor be acceptable practice?

  - by Robb

  Let's assume I have a c++ class that have properly implemented a copy constructor and an overloaded = operator. By properly implemented I mean they are working and perform a deep copy: Class1::Class1(const Class1 &class1) { // Perform copy } Class1& Class1::operator=(const Class1 *class1) { // perform copy return *this; } Now lets say I have this constructor as well: Class1::Class1(Class1 *class1) { *this = *class1; } My question is would the above constructor be acceptable practice? This is code that i've inherited and maintaining.

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• Constructor return value

  - by Ivan Gromov

  Could you tell me what is wrong with my class constructor? Code: CVector::CVector (int size_) { if (size_ > 0) { this->size = size_; this->data = new double[size]; for (int i = 0; i < size; i++) { (*this)(i) = i; } } cout << "constructor end" << endl; return; } Usage example: tvector = CVector(6); I get an access violation after "constructor end" output.

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• Why Java cannot find my constructor?

  - by Roman

  Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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• C# - default parameter values from previous parameter

  - by Sagar R. Kothari

  namespace HelloConsole { public class BOX { double height, length, breadth; public BOX() { } // here, I wish to pass 'h' to remaining parameters if not passed // FOLLOWING Gives compilation error. public BOX (double h, double l = h, double b = h) { Console.WriteLine ("Constructor with default parameters"); height = h; length = l; breadth = b; } } } // // BOX a = new BOX(); // default constructor. all okay here. // BOX b = new BOX(10,20,30); // all parameter passed. all okay here. // BOX c = new BOX(10); // Here, I want = length=10, breadth=10,height=10; // BOX d = new BOX(10,20); // Here, I want = length=10, breadth=20,height=10; Question is : 'To achieve above, Is 'constructor overloading' (as follows) is the only option? public BOX(double h) { height = length = breadth = h; } public BOX(double h, double l) { height = breadth = h; length = l; }

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• variadic constructors

  - by FredOverflow

  Are variadic constructors supposed to hide the implicitly generated ones, i.e. the default constructor and the copy constructor? struct Foo { template<typename... Args> Foo(Args&&... x) { std::cout << "inside the variadic constructor\n"; } }; int main() { Foo a; Foo b(a); } Somehow I was expecting this to print nothing after reading this answer, but it prints inside the variadic constructor twice on g++ 4.5.0 :( Is this behavior correct?

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• Accessing the Private Constructor

  - by harigm

  I am java developer, went for an interview. I have been asked a question about the Private constructor 1) Can I access a Private Constructor of a Class and Instantiate the class. I was thinking and gave the answer directly--- "NO" But its wrong, can any one help Why NO? and How we can achieve this

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• Call a constructor from variable arguments with PHP

  - by zneak

  Hello guys, I have a function that takes variadic arguments, that I obtain from func_get_args(). This function needs to call a constructor with those arguments. However, I don't know how to do it. With call_user_func, you can call functions with an array of arguments, but how would you call a constructor from it? I can't just pass the array of arguments to it; it must believe I've called it "normally". Thank you!

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• Calling assignment operator in copy constructor

  - by stas

  Are there some drawbacks of such implementation of copy-constructor? Foo::Foo(const Foo& i_foo) { *this = i_foo; } As I remember, it was recommend in some book to call copy constructor from assignment operator and use well-known swap trick, but I don't remember, why...

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• behaviour of the implicit copy constructor / assignment operator

  - by Tobias Langner

  Hello, I have a question regarding the C++ Standard. Suppose you have a base class with user defined copy constructor and assignment operator. The derived class uses the implicit one generated by the compiler. Does copying / assignment of the derived class call the user defined copy constructor / assignment operator? Or do you need to implement user defined versions that call the base class? Thank you for your help.

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• Perl - Calling subclass constructor from superclass (OO)

  - by Emmel

  This may turn out to be an embarrassingly stupid question, but better than potentially creating embarrassingly stupid code. :-) This is an OO design question, really. Let's say I have an object class 'Foos' that represents a set of dynamic configuration elements, which are obtained by querying a command on disk, 'mycrazyfoos -getconfig'. Let's say that there are two categories of behavior that I want 'Foos' objects to have: Existing ones: one is, query ones that exist in the command output I just mentioned (/usr/bin/mycrazyfoos -getconfig`. Make modifications to existing ones via shelling out commands. Create new ones that don't exist; new 'crazyfoos', using a complex set of /usr/bin/mycrazyfoos commands and parameters. Here I'm not really just querying, but actually running a bunch of system() commands. Affecting changes. Here's my class structure: Foos.pm package Foos, which has a new($hashref-{name = 'myfooname',) constructor that takes a 'crazyfoo NAME' and then queries the existence of that NAME to see if it already exists (by shelling out and running the mycrazyfoos command above). If that crazyfoo already exists, return a Foos::Existing object. Any changes to this object requires shelling out, running commands and getting confirmation that everything ran okay. If this is the way to go, then the new() constructor needs to have a test to see which subclass constructor to use (if that even makes sense in this context). Here are the subclasses: Foos/Existing.pm As mentioned above, this is for when a Foos object already exists. Foos/Pending.pm This is an object that will be created if, in the above, the 'crazyfoo NAME' doesn't actually exist. In this case, the new() constructor above will be checked for additional parameters, and it will go ahead and, when called using -create() shell out using system() and create a new object... possibly returning an 'Existing' one... OR As I type this out, I am realizing it is perhaps it's better to have a single: (an alternative arrangement) Foos class, that has a -new() that takes just a name -create() that takes additional creation parameters -delete(), -change() and other params that affect ones that exist; that will have to just be checked dynamically. So here we are, two main directions to go with this. I'm curious which would be the more intelligent way to go.

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• Require a default constructor in java?

  - by jdc0589

  Is there any way to require that a class have a default (no parameter) constructor, aside from using a reflection check like the following? (the following would work, but it's hacky and reflection is slow) boolean valid = false; for(Constructor<?> c : TParse.class.getConstructors()) { if(c.getParameterTypes().length == 0) { valid = true; break; } } if(!valid) throw new MissingDefaultConstructorException(...);

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• Calling methods in super class constructor of subclass constructor?

  - by deamon

  Calling methods in super class constructor of subclass constructor? Passing configuration to the __init__ method which calls register implicitely: class Base: def __init__(self, *verbs=("get", "post")): self._register(verbs) def _register(self, *verbs): pass class Sub(Base): def __init__(self): super().__init__("get", "post", "put") Or calling register explicitely in the subclass' __init__ method: class Base: def __init__(self): self._register("get", "post") def _register(self, *verbs): pass class Sub(Base): def __init__(self): _register("get", "post", "put") What is better or more pythonic? Or is it only a matter of taste?

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• constructor in objective c

  - by zp26

  HI, I have create my iPhone apps but i have a problem. I have a classViewController where i have implemented my program. I must alloc 3 NSMutableArray but i don't want do it in a grapich methods. There isn't a constructor like java for my class? Thanks so much and sorry for my english XP // I want put it in a method like constructor java arrayPosizioni = [[NSMutableArray alloc]init]; nomePosizioneCorrente = [NSString stringWithFormat:@"noPosition"];

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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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• Calling MethodBase's Invoke on a constructor (reflection)

  - by Alix

  Hi everyone. First of all, sorry if this has been asked before. I've done a pretty comprehensive search and found nothing quite like it, but I may have missed something. And now to the question: I'm trying to invoke a constructor through reflection, with no luck. Basically, I have an object that I want to clone, so I look up the copy constructor for its type and then want to invoke it. Here's what I have: public Object clone(Object toClone) { MethodBase copyConstructor = type.GetConstructor( new Type[] { toClone.GetType() }); return method.Invoke(toClone, new object[] { toClone }); //<-- doesn't work } I call the above method like so: List list = new List(new int[] { 0, 1, 2 }); List clone = (List) clone(list); Now, notice the invoke method I'm using is MethodBase's invoke. ConstructorInfo provides an invoke method that does work if invoked like this: return ((ConstructorInfo) method).Invoke(new object[] { toClone }); However, I want to use MethodBase's method, because in reality instead of looking up the copy constructor every time I will store it in a dictionary, and the dictionary contains both methods and constructors, so it's a Dictionary<MethodBase>, not Dictionary<ConstructorInfo>. I could of course cast to ConstructorInfo as I do above, but I'd rather avoid the casting and use the MethodBase method directly. I just can't figure out the right parameters. Any help? Thanks so much.

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• Strange constructor

  - by Bilthon

  Well, I'm gonna be pretty straightforward here, I just have a piece of code in c++ which I'm not sure I really understand and need some help with. Ok, to simplify lets just say I have a class that is defined like this: (the real class is a little bit more complicated, but this is what matters) class myClass : public Runnable { Semaphore *m_pMySemaphore; __Queue<Requests> *m_pQueue; Request m_Request; VetorSlotBuffer *m_vetorSlotBuffer; } Up to here nothing is wrong, myClass is just a regular class which has 3 members that actually are pointers to other classes and an object of the class Request, the implementation of those classes not being important for my point here. Then when this person implemented the constructor for myClass he or she did this: myClass::myClass() : m_pMySemaphore(0), m_pQueue(0), m_vetorSlotBuffer(0) { } It's pretty evident that those three variables are treated like that by the constructor because they are pointers, am I right? but what kind of syntax is that? am I setting the pointers to null by doing that? I've seen a little bit of c++ already but never found something like that. And secondly, what's the deal with the ":" after the constructor declaration? that I've seen but never took the time to investigate. Is this like an inner class or something? Thank you very much in advance. Nelson R. Perez

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• Object does not exist after constructor?

  - by openbas

  Hello, I have a constructor that looks like this (in c++): Interpreter::Interpreter() { tempDat == new DataObject(); tempDat->clear(); } the constructor of dataObject does absolutely nothing, and clear does this: bool DataObject::clear() { //clear the object if (current_max_id > 0) { indexTypeLookup.clear(); intData.clear(); doubleData.clear(); current_max_id = 0; } } Those members are defined as follows: std::map<int, int> indexTypeLookup; std::map<int, int> intData; std::map<int, double> doubleData; Now the strange thing is that I'm getting a segfault on tempDat-clear(); gdb says tempDat is null. How is that possible? The constructor of tempDat cannot fail, it looks like this: DataObject::DataObject() : current_max_id(0) { } I know there are probably better way's of making such a data structure, but I really like to know where this segfault problem is coming from..

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• C++ Constructor With Parameters Won't Initialize, Errors C2059 and C2228

  - by Some Girl

  I'm a C# programmer trying to muddle through C++ to create a Windows Forms Application. I have a Windows Form that makes use of a user-created class. Basically I'm trying to use a constructor that takes parameters, but my form won't let me initialize the object with parameter. Here's the code, hopefully somebody can explain the problem to me because I'm completely baffled... Here's my header file: BankAcct.h public ref class BankAcct { private: int money; public: BankAcct(); BankAcct(int); void Deposit(int); void GetBalance(int&); }; And my definition file: BankAcct.cpp #include "StdAfx.h" #include "BankAcct.h" BankAcct::BankAcct() { money = 0; } BankAcct::BankAcct(int startAmt) { money = startAmt; } void BankAcct::Deposit(int depAmt) { money += depAmt; } void BankAcct::GetBalance(int& balance) { balance = money; } And finally my main form. Won't copy the whole thing, of course, but I'm trying to declare the new bank account object, and start it with a balance of say $50. private: BankAcct myAccount(50); //does not work! WHY?? //private: //BankAcct myAccount; //works then in the form constructor my code is this: public: frmBank(void) { InitializeComponent(); int bal; myAccount.GetBalance(bal); lblBankBalance->Text += Convert::ToString(bal); } I've included the BankAcct.h file at the top of my frmBank.h, what else am I doing wrong here? It works great if I use the default constructor (the one that starts the bank balance at zero). I get the following error messages: error C2059: syntax error: 'constant' and error C2228: left of '.GetBalance' must have class/struct/union Thank you for any and all help on this one!!

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• c++ STL vector is not acccepting the copy constructor

  - by prabhakaran

  I wrote a code ( c++,visual studio 2010) which is having a vector, even I though copy const is declared, but is still showing that copy const is not declared Here the code #include<iostream> #include<vector> using namespace std; class A { public: A(){cout << "Default A is acting" << endl ;} A(A &a){cout << "Copy Constructor of A is acting" << endl ;} }; int main() { A a; A b=a; vector<A> nothing; nothing.push_back(a); int n; cin >> n; } The error I got is Error 1 error C2558: class 'A' : no copy constructor available or copy constructor is declared 'explicit' c:\program files\microsoft visual studio 10.0\vc\include\xmemory 48 1 delete Anybody please help me

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• Constructor ambiguous quesiton

  - by Crystal

  I'm trying to create a simple date class, but I get an error on my main file that says, "call of overloaded Date() is ambiguous." I'm not sure why since I thought as long as I had different parameters for my constructor, I was ok. Here is my code: header file: #ifndef DATE_H #define DATE_H using std::string; class Date { public: static const int monthsPerYear = 12; // num of months in a yr Date(int = 1, int = 1, int = 1900); // default constructor Date(); // uses system time to create object void print() const; // print date in month/day/year format ~Date(); // provided to confirm destruction order string getMonth(int month) const; // gets month in text format private: int month; // 1 - 12 int day; // 1 - 31 int year; // any year int checkDay(int) const; }; #endif .cpp file #include <iostream> #include <iomanip> #include <string> #include <ctime> #include "Date.h" using namespace std; Date::Date() { time_t seconds = time(NULL); struct tm* t = localtime(&seconds); month = t->tm_mon; day = t->tm_mday; year = t->tm_year; } Date::Date(int mn, int dy, int yr) { if (mn > 0 && mn <= monthsPerYear) month = mn; else { month = 1; // invalid month set to 1 cout << "Invalid month (" << mn << ") set to 1.\n"; } year = yr; // could validate yr day = checkDay(dy); // validate the day // output Date object to show when its constructor is called cout << "Date object constructor for date "; print(); cout << endl; } void Date::print() const { string str; cout << month << '/' << day << '/' << year << '\n'; // new code for HW2 cout << setfill('0') << setw(3) << day; // prints in ddd cout << " " << year << '\n'; // yyyy format str = getMonth(month); // prints in month (full word), day, year cout << str << " " << day << ", " << year << '\n'; } and my main.cpp #include <iostream> #include "Date.h" using std::cout; int main() { Date date1(4, 30, 1980); date1.print(); cout << '\n'; Date date2; date2.print(); }

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