copy-constructor

问题 Why doesn't Java support a copy constructor like in C++? 回答1: Java does. They're just not called implicitly like they are in C++ and I suspect that's your real question. Firstly, a copy constructor is nothing more than: public class Blah { private int foo; public Blah() { } // public no-args constructor public Blah(Blah b) { foo = b.foo; } // copy constructor } Now C++ will implicitly call the copy constructor with a statement like this: Blah b2 = b1; Cloning/copying in that instance simply

问题 Sometimes it's necessary to prohibit a copy constructor in a C++ class so that class becomes "non-copyable". Of course, operator= should be prohibited at the same time. So far I've seen two ways to do that. Way 1 is to declare the method private and give it no implementation: class Class { //useful stuff, then private: Class( const Class& ); //not implemented anywhere void operator=( const Class& ); //not implemented anywhere }; Way 2 is to declare the method private and give it "empty"

问题 I have heard that C++ has something called "conversion constructors" or "converting constructors". What are these, and what are they for? I saw it mentioned with regards to this code: class MyClass { public: int a, b; MyClass( int i ) {} } int main() { MyClass M = 1 ; } 回答1: The definition for a converting constructor is different between C++03 and C++11. In both cases it must be a non- explicit constructor (otherwise it wouldn't be involved in implicit conversions), but for C++03 it must

问题 I know that Qobjects are supposed to be identities not values eg you cannot copy them and by default the copy constructor and assignment are disabled as explained in qt documentation. But is it possible to create a new QObject from an existing one using a clone method? Would this be a logic error ? If I say QObject b; QObject a; b.cloneFrom(a); or QObject a = new QOBject(); QObject b = new QOBject(); b->cloneFrom(a); and the clone method copies stuff like members etc would this be wrong? And

问题 I have a rather large and lengthy class where the implicitly generated copy-constructor would almost do exactly the right thing, except for one specific field. Is there a way to write a user-defined copy-constructor that calls the implicit version, and then adds one or two lines at the end? Or do I have to write a lengthy, (and boring, and typo-prone) user-defined copy-constructor that mostly duplicates the implicit one? class MySimpleObject { private: FieldA m_fieldA; FieldB m_fieldB; [...

问题 This question refers only to pre C++11 . Consider the following seemingly broken code: struct X { X(){} // default user-provided constructor private: X(const X&){} }; int main() { X x = X(); } Live on Coliru According to cppreference.com in pre C++11 the default ctor will be called: The effects of value initialization are: 1) if T is a class type with at least one user-provided constructor of any kind, the default constructor is called; ... This seem to imply that the copy ctor doesn't

问题 I made this constructor, and I need to make a deep copy of it. I don't really understand the meaning of a deep copy. I know it makes independent copy of an object that has its own dynamic memory, but I don't understand what the need is for this. I'm also not sure how to actually implement the deep copy. Any suggestions? Here is my constructor that I need to make deep copy of: Could anyone provide some syntax help, like a skeleton? template<class t_type> inline ALIST<t_type>::ALIST() { t_type

问题 I would like to store some std::unique_ptr<my_type> into a std::vector . Since my_type provides a clone() method it's quite straightforward to make deep copies of my_type * . The point is how to extend std::unique_ptr preserving all its functionalities while adding the copy ctor and the assignment operator. Inheritance? Templace specialization? Could you please provide a code snippet? 回答1: The purpose of std::unique_ptr is for it to be unique i.e. it shouldn't be copyable. That's why they

问题 public class SuperCar: Car { public bool SuperWheels { get {return true; } } } public class Car { public bool HasSteeringWheel { get {return true;} } } How can I set the base class for the derived Supercar? For example, I want to simply set SuperCars base class like this: public void SetCar( Car car ) { SuperCar scar = new SuperCar(); car.Base = car; } Basically, if I have Car objects, I do not want to manually iterate through every property of the car in order to setup the SuperCar oject,

问题 I'm having some trouble getting my copy constructor to work in my BigInt class I'm working on. In BigIntVector.cpp in the copy constructor, the lines: for (int i = 0; i < vectorSize; i++) { vectorArray[i] = orig.vectorArray[i]; } causes the exception 0xC0000005: Access violation writing location 0x00000000. Any help figuring out why would be appreciated. Thank you. In BigInt.cpp : // copy constructor BigInt::BigInt(BigInt const& orig) : isPositive(orig.isPositive) , base(orig.base) , skip